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Tuesday, December 1, 2009
Saturday, November 14, 2009
What Your Eyes Say About Your Health
What Your Eyes Say About Your Health
The importance of a regular eye examination, often, is underrated. Having annual eye examination should be as routine as having a dental check-up every six months. Regular eye examinations are crucial to maintaining a healthy vision and can often detect major medical problems in the early stages of development, such as diabetes and high blood pressure, reports Sade Oguntola.
It was rather fascinating for Mr. Fatia Adeleye, a school teacher, to learn that eye examination can help to identify and recognise minor problems before they become threatening and serious. It was at an awareness meeting organised by his kinsmen as part of the town’s anniversary ceremony that he got the enlightenment.
“I knew getting your eyes checked was important, but I didn’t know it could shed light on so many other health concerns,” he said, adding, “If only, I had had that knowledge much earlier, may be I would have been able to take earlier steps to prevent my mother from dying blind.”
The eye is the window of the body through which it feels its way and enjoys the beauty of the world. When you look at someone’s face, you can even predict the person’s mood, all because the eyes are the windows of the body. This is what psychologists, swindlers and even some native herbalists use. The moment someone comes in, they look at the person’s face to know whether the person has a problem burdening him/her.
The eye, though small, comprises many parts; cornea, iris, pupil, retina, nerves and some other parts. Studying the different features of the eyes like iris, cornea, the shape of the pupil, the optic nerve head, conjunctiva, anterior chamber, the light reflex, amongst others, can go a long way to ascertaining the health status of the body and even predict diseases affecting it.
Health, also, can be observed through the eyes. Doctors often judge a person by the condition of his eyes. Eye examination, besides helping to seek to correct defects in one’s eyesight, is crucial to maintaining healthy vision, and detects major medical problems such as diabetes and high blood pressure in the early stages of development.
Dr. Gboyega Ajayi, an ophthalmologist at Ojolowo Eye Clinic, Veterinary, Mokola, Ibadan, declared that many people were not paying enough attention to their eye health, even though such simple steps such as a yearly eye examination, could detect the presence of many diseases in the body.
He declared that the eyes could reveal a lot, considering the fact that it is the only organ through which blood vessels can be examined directly to know the status of the cardiovascular and the neurological system. Every tissue and fluid type in the eye is a representative of every tissue and every fluid type in the rest of the body.
He emphasised that eye examinations were “even more important for people who are already using corrective lenses;” who might “assume they just need a different lense prescription, when they really have a more serious problem. With eye diseases and disorders, as with most health issues, early detection and treatment are often the keys to avoiding permanent problems.
Some of the existing health problems or an impending one that an eye examination can give, and their possible signs, include the following:
Anaemia: A pale eye indicates insufficient blood. Insufficient blood could be due to many reasons like blood disorder, bleeding, malaria, sign of pregnancy, cancers etc.
Jaundice: When the eyeballs are yellowish, it could mean either jaundice or liver diseases or other problems related to the blood like hepatitis.
Hypertension: If you look through the pupil (with an ophthalmoscope) into the interior part of the eye, you can detect a patient that is hypertensive, and guess the severity of the hypertension. Those suffering from blood shot eyes may be experiencing high blood pressure.
Diabetes: An insight into the eye can also detect diabetes and even the duration of the diabetes. The length of time the persons had suffered from this disease can be actualised. Diabetes affects the blood circulation in your retina (the back of your eye), which causes changes in the blood vessels. The changes occur slowly over many years, therefore, you probably won’t be aware of any difference until the problem becomes acute and your vision is affected.
Sickle cell disease: Though yellowness of the eyeball is common with all sickle cell patients, the study of the internal parts of the eye can still go on further to give the exact type, whether HSS or HSC very specifically.
Cancers: Even though the study of the features of the eye may not be able to categorically state where cancer is actually is in the body, however you can still detect them. These include cancer and tumour of the brain.
Nervous diseases: From the conjuctivita signs, nervous diseases like paralysis and trauma can be picked .
Muscle diseases: Muscle diseases like Myaesthenia gravis sometimes starts with the eyes, and the patients might have double vision and drooping of the eye which could indicate paralysis of some nerves. Also, continuous drooping of the eyelid could signify an auto-immune disorder, particularly thyroid diseases.
Glaucoma: When the eye experiences high blood pressure, it is referred to as glaucoma. It affects the whole body, and when such is left unattended to, can cause blindness. Those that are most at risk of glaucoma are diabetics, senior citizens, Afro-Americans, and those who are short-sighted in addition to people with family history of glaucoma.
River blindness: When eye lesions are noticed during eye examination, especially in people living near fast-flowing streams or rivers, river blindness remains one of the causes to be suspected.
HIV: Mere looking into the eye ball, a precise diagnosis of HIV virus is possible.
Pregnancy: While it is not specific for pregnancy, one can use it, in conjunction with other tests, to confirm pregnancy.
Drug abuse: Even medication used in excess like chloroquine can be diagnosed looking into the eye. Cases of drug addiction, and the type of drug addicted to, can easily be known even this way.
Syphilis: Syphilis is one of the sexually transmitted diseases, predictable through the study of the eye. There would be lesions on the iris.
Cataracts: A cataract is a clouding of the normally clear lens inside the eye. It can be compared to a window that is frosted or “fogged” with steam. The presence and extent of a cataract can be detected during a thorough eye examination. Most cataracts associated with aging, progress gradually over a period of years. However, other cataracts, especially in younger people and people with diabetes, may progress rapidly over a few months and cause a more dramatic worsening of vision.
How can I prevent problems with my eyes from developing?
• Keeping your blood sugar levels well controlled reduces your risk of developing eye diseases or delays the onset.
• Control your weight, your cholesterol levels and your blood pressure through diet and exercise.
• Have a regular appointment with your ophthalmologist at least once a year. It is much easier to stop eye disease from developing into something serious if it is treated in the early stages.
The importance of a regular eye examination, often, is underrated. Having annual eye examination should be as routine as having a dental check-up every six months. Regular eye examinations are crucial to maintaining a healthy vision and can often detect major medical problems in the early stages of development, such as diabetes and high blood pressure, reports Sade Oguntola.
It was rather fascinating for Mr. Fatia Adeleye, a school teacher, to learn that eye examination can help to identify and recognise minor problems before they become threatening and serious. It was at an awareness meeting organised by his kinsmen as part of the town’s anniversary ceremony that he got the enlightenment.
“I knew getting your eyes checked was important, but I didn’t know it could shed light on so many other health concerns,” he said, adding, “If only, I had had that knowledge much earlier, may be I would have been able to take earlier steps to prevent my mother from dying blind.”
The eye is the window of the body through which it feels its way and enjoys the beauty of the world. When you look at someone’s face, you can even predict the person’s mood, all because the eyes are the windows of the body. This is what psychologists, swindlers and even some native herbalists use. The moment someone comes in, they look at the person’s face to know whether the person has a problem burdening him/her.
The eye, though small, comprises many parts; cornea, iris, pupil, retina, nerves and some other parts. Studying the different features of the eyes like iris, cornea, the shape of the pupil, the optic nerve head, conjunctiva, anterior chamber, the light reflex, amongst others, can go a long way to ascertaining the health status of the body and even predict diseases affecting it.
Health, also, can be observed through the eyes. Doctors often judge a person by the condition of his eyes. Eye examination, besides helping to seek to correct defects in one’s eyesight, is crucial to maintaining healthy vision, and detects major medical problems such as diabetes and high blood pressure in the early stages of development.
Dr. Gboyega Ajayi, an ophthalmologist at Ojolowo Eye Clinic, Veterinary, Mokola, Ibadan, declared that many people were not paying enough attention to their eye health, even though such simple steps such as a yearly eye examination, could detect the presence of many diseases in the body.
He declared that the eyes could reveal a lot, considering the fact that it is the only organ through which blood vessels can be examined directly to know the status of the cardiovascular and the neurological system. Every tissue and fluid type in the eye is a representative of every tissue and every fluid type in the rest of the body.
He emphasised that eye examinations were “even more important for people who are already using corrective lenses;” who might “assume they just need a different lense prescription, when they really have a more serious problem. With eye diseases and disorders, as with most health issues, early detection and treatment are often the keys to avoiding permanent problems.
Some of the existing health problems or an impending one that an eye examination can give, and their possible signs, include the following:
Anaemia: A pale eye indicates insufficient blood. Insufficient blood could be due to many reasons like blood disorder, bleeding, malaria, sign of pregnancy, cancers etc.
Jaundice: When the eyeballs are yellowish, it could mean either jaundice or liver diseases or other problems related to the blood like hepatitis.
Hypertension: If you look through the pupil (with an ophthalmoscope) into the interior part of the eye, you can detect a patient that is hypertensive, and guess the severity of the hypertension. Those suffering from blood shot eyes may be experiencing high blood pressure.
Diabetes: An insight into the eye can also detect diabetes and even the duration of the diabetes. The length of time the persons had suffered from this disease can be actualised. Diabetes affects the blood circulation in your retina (the back of your eye), which causes changes in the blood vessels. The changes occur slowly over many years, therefore, you probably won’t be aware of any difference until the problem becomes acute and your vision is affected.
Sickle cell disease: Though yellowness of the eyeball is common with all sickle cell patients, the study of the internal parts of the eye can still go on further to give the exact type, whether HSS or HSC very specifically.
Cancers: Even though the study of the features of the eye may not be able to categorically state where cancer is actually is in the body, however you can still detect them. These include cancer and tumour of the brain.
Nervous diseases: From the conjuctivita signs, nervous diseases like paralysis and trauma can be picked .
Muscle diseases: Muscle diseases like Myaesthenia gravis sometimes starts with the eyes, and the patients might have double vision and drooping of the eye which could indicate paralysis of some nerves. Also, continuous drooping of the eyelid could signify an auto-immune disorder, particularly thyroid diseases.
Glaucoma: When the eye experiences high blood pressure, it is referred to as glaucoma. It affects the whole body, and when such is left unattended to, can cause blindness. Those that are most at risk of glaucoma are diabetics, senior citizens, Afro-Americans, and those who are short-sighted in addition to people with family history of glaucoma.
River blindness: When eye lesions are noticed during eye examination, especially in people living near fast-flowing streams or rivers, river blindness remains one of the causes to be suspected.
HIV: Mere looking into the eye ball, a precise diagnosis of HIV virus is possible.
Pregnancy: While it is not specific for pregnancy, one can use it, in conjunction with other tests, to confirm pregnancy.
Drug abuse: Even medication used in excess like chloroquine can be diagnosed looking into the eye. Cases of drug addiction, and the type of drug addicted to, can easily be known even this way.
Syphilis: Syphilis is one of the sexually transmitted diseases, predictable through the study of the eye. There would be lesions on the iris.
Cataracts: A cataract is a clouding of the normally clear lens inside the eye. It can be compared to a window that is frosted or “fogged” with steam. The presence and extent of a cataract can be detected during a thorough eye examination. Most cataracts associated with aging, progress gradually over a period of years. However, other cataracts, especially in younger people and people with diabetes, may progress rapidly over a few months and cause a more dramatic worsening of vision.
How can I prevent problems with my eyes from developing?
• Keeping your blood sugar levels well controlled reduces your risk of developing eye diseases or delays the onset.
• Control your weight, your cholesterol levels and your blood pressure through diet and exercise.
• Have a regular appointment with your ophthalmologist at least once a year. It is much easier to stop eye disease from developing into something serious if it is treated in the early stages.
Wednesday, November 4, 2009
Problems Of Leadership In Nigeria
Problems Of Leadership In Nigeria
There is no gainsaying the fact that the once promising Nigerian nation is lost deep in the wilderness of underdevelopment and insecurity, due to the effects of corruption and tribal scheming. The situation has become so bad that it would take only a very courageous leadership to get Nigeria out of the woods.
Unfortunately, every administration, since 1960, has come and acted in manners that suggest the nation would require up to a century to have its problems fixed. It has now become a tradition for Nigerian leaders and their aides, both at the state and national levels, to either hide or deny their failures by casting stones at their predecessors.
For half a century, Nigerian leaders have fooled the masses. By all standards, leadership is not supposed to be a tea party like many have taken it to be. Leadership is strictly an instrument for development, unity, peace, and security. Society is usually exposed to varying degrees of threats, whenever leadership fails.
It is often said that bad workmen quarrel with their tools. The same thing applies to leadership. Bad leaders are fond of blaming others for their failures. One prominent characteristic of bad leaders is the readiness to invest in the recruitment of orators and propaganda wizards to help deceive and pin down the patience of hapless citizens.
The blame culture our leaders indulge in has helped to expose one painful fact most public office holders do not understand the true meaning of leadership. Some, therefore, see leadership as opportunities to advance tribal or religious agenda. Others simply see leadership as platforms to amass wealth. Except our leaders begin to appreciate what leadership truly is, Nigeria might continue to suffer underdevelopment, unemployment, poverty, crime and insecurity.
It will be an understatement to declare that Nigeria has lacked purposeful leadership for the most part of its 49 years, as an independent nation. Nigeria would, therefore, need a legion of leaders that are prepared to invest honesty, faithfulness and patriotism. Without this, the nation might not experience growth and peace. There is no doubt that Nigeria has, one time or the other, been blessed with honest leaders. The problem has been that these honest leaders mostly surround themselves with dishonest people in the form of advisers, ministers, and confidants. It is natural for honest leaders, that accept support from dishonest people, to become dishonourable within a very short period of time.
The success stories of Nigerians in the diaspora show that there are enough honest Nigerians who can work with our leaders to fix the myriad of problems that have continued to bedevil this nation. Unfortunately, the nation’s faulty electoral system makes it quite impossible for most leaders to assemble a credible team to work with.
This has forced our leaders to have hoards of mainly dishonest people around them. It is sad to note that even the few honest ones that find their way into government are usually recommended by dishonest kingmakers. This is mostly responsible for the several cases of honest Nigerians who danced naked in the market square shortly after joining government.
For a country with a faulty electoral system, Nigerians do not need a prophet to confirm that the art of king-making in Nigeria is dirty and stinks to the high heavens. There are no internal democracies. Not only are candidates forced on party members, elections are openly rigged by political kingmakers for a price: key to the treasury. This would best explain why, despite all the noise about ICPC, EFCC, and CCB, corruption has continued to grow in the country. It is now fashionable for government to decide who is to be investigated, arraigned in court, bailed, or even convicted.
This has indeed rubbished the much dramatised Rule of Law and war against graft of the present administration. The earlier our leaders stopped deceiving the citizens, the better for the future of this country. Nigeria does not need more than four years to get back on its feet.
Nigeria would reach the sky in a span of four years if the amount of zeal deployed to tackle militancy in the Niger Delta region is directed at corrupt and super tribal zealots in government. No doubt, Nigerian officials are reputed to be among the best fiscal policy formulators and budget planners in the world. The irony, however, is that Nigeria is occupying the bottom rung of the ladder in terms of budget implementation.
This is a clear case of poor leadership. Nigeria would have been among the first 20 most industrialised countries in the world, if her leaders had implemented annual budgets to the tone of 85% at the state and national levels in the last ten years. Nigeria only requires stable power supply, efficient transportation system, access to long term credit facilities, transparency and accountability in government business to enable the private sector drive the nation’s economy up the ladder. All of these would not cost the nation a fortune.
It only requires the right leadership. Perhaps, one should add here that our leaders do not lack the capacities to fix these issues. The snag is that our leaders have been swallowed by their own greed and other human weaknesses.
Just like in the case of the Niger Delta, where those that were benefiting from the activities of militants never wanted peace in the region, there are several thousands of Nigerians who are benefiting from the nation’s poor leadership culture. Some of these persons believe they would lose substantial stake, if there is steady electricity in Nigeria. Is it not a shame that despite the abundance of natural gas in the Niger Delta region, constant power supply has been a mirage in Nigeria? The petroleum sector is no better.
As the sixth largest producer of crude, Nigeria still imports more than 50 percent of petroleum products to service local markets. This status quo is maintained just to make sure some persons have the opportunity to make huge profits through the importation of petroleum products. For how long would our leaders continue to fool the citizenry? To make matters worse, government has been making much noise about the planned withdrawal of petroleum subsidy.
For a nation suffering from poor leadership culture, there is no doubt that subsidy is the only benefit the masses are sure of. Ordinarily, Nigerians will surely resist attempts by government to further impoverish them with the planned increase in the prices of petroleum products by 1st November, 2009.
Furthermore, there are many Nigerians that think an efficient transportation system in the country would impact negatively on their businesses. This is the reason why our federal roads are deliberately allowed to turn into ponds and death traps, despite the existence of FERMA. It is also for the same reason that the rail system has gone comatose over the decades.
More than that, a handful of Nigerians benefit substantially when government businesses are done in secrecy. It has, therefore, been difficult for the nation to reap the benefits of transparency and accountability. All of these persons enumerated above are members of the platoon of kingmakers. They work hand in glove with our leaders to destroy the country. Somehow, the masses have always tended to undermine them because of the subtle manner they operate. They are mostly faceless, but quite a formidable force.
They are very wealthy and influential and too ready to contribute resources to install and manipulate political leaders to their advantage.
One ready question that has always hung on the lips of many Nigerian leaders is: “Is it morally right to bite the fingers that fed me?” This is the problem with leadership in Nigeria. The foundation of many Nigerian leaders can be traced to the heart of dishonest kingmakers. It would be difficult for Nigeria to enjoy quality leadership, as long as the masses are prevented from choosing their leaders. This is the strong reason why the electoral laws should be reformed to make votes count. Electoral fraud is indeed one very big brush that our leaders have used to paint Nigeria black in the eyes of the international community.
Though Nigeria is believed to be giant of Africa, the international community see the true giant in Ghana and South Africa. This fact should help grow patriotism in our leaders.
Yar’Adua had once flaunted his patriotism, when he openly confessed that the 2007 presidential election that brought him to office was flawed. He followed this confession with a firm promise to overhaul the nation’s faulty electoral laws. This honest disposition earned the former governor of Katsina state so much respect among the Nigerian masses and civil society organisations. But with the election season just a few months away, they are beginning to feel betrayed.
Some have gone to the extent of cursing the day they accepted to forgive the ruling party of all her electoral sins before, during, and after the 2007 presidential election. Many Nigerians have begun to argue that the president’s blatant refusal to cede the power to appoint the chairman of INEC is as good as not having any electoral reforms at all. The president’s unwavering resolve to keep the all important right to appoint the electoral commission’s boss has left wide gaps for fertile suspicions among watchers of Nigerian politics. Civil society organisations and opposition politicians have already cried fowl against the continuous delay of the long planned review of the nation’s constitution which was stalled owing to very trivial issues.
Even the claim by the deputy senate president, Ike Ekweremadu, that a whole of N500m was inadequate to enable the National Assembly review the nation’s constitution has been quickly interpreted to be part of a grand plan to scuttle the much anticipated electoral reform process ahead of the next general elections. Whichever way one wants to look at the unfolding drama, the truth still stands out: our leaders are suffering from severe agoraphobia.
It is pertinent to note at this point that Nigeria does not need just honest leaders. There is also an important need for honest followers as well. Honest followers would not ridicule leaders that are unable to own fleet of cars and mansions after leaving office. Many public office holders indulge in corruption because of undue pressure from family members, friends, and political associates. This should, however, not be an excuse for public office holders to steal government money while in office. They should rather put the interest of the nation first and grow the courage to resist extreme demands from whatever quarters.
This is the right time for Nigerian leaders to face the realism of fact. This is even more urgent because the patience of the Nigerian masses has run out. It was mainly for the fear of military intervention and possible disintegration that Nigerian masses ignored the charade that was the 2007 presidential elections. But unfortunately, Nigerians have been gravely hurt by the slow pace of development and high incidents of corruption in the polity.
What is government expecting from the masses that are witnesses to the fact that most public office holders clearly live above their incomes, while they wallow in abject poverty? Nigeria has become a time bomb. It would, therefore, be catastrophic if President Yar’Adua continues to take the patience of Nigerians for granted. For now, the endurance limit of Nigerians has become even shallower than the lower course of the River Niger.
Government’s propaganda can no longer navigate the heart of suffering Nigerian masses. To successfully dredge same, the president should ensure that the electoral system is reformed in line with popular opinion, before the next general elections. This would enable the electorates to take charge of the driving seats and disengage all the unpatriotic kingmakers and apostles of corruption that have held this country back for nearly half a century.
There is no gainsaying the fact that the once promising Nigerian nation is lost deep in the wilderness of underdevelopment and insecurity, due to the effects of corruption and tribal scheming. The situation has become so bad that it would take only a very courageous leadership to get Nigeria out of the woods.
Unfortunately, every administration, since 1960, has come and acted in manners that suggest the nation would require up to a century to have its problems fixed. It has now become a tradition for Nigerian leaders and their aides, both at the state and national levels, to either hide or deny their failures by casting stones at their predecessors.
For half a century, Nigerian leaders have fooled the masses. By all standards, leadership is not supposed to be a tea party like many have taken it to be. Leadership is strictly an instrument for development, unity, peace, and security. Society is usually exposed to varying degrees of threats, whenever leadership fails.
It is often said that bad workmen quarrel with their tools. The same thing applies to leadership. Bad leaders are fond of blaming others for their failures. One prominent characteristic of bad leaders is the readiness to invest in the recruitment of orators and propaganda wizards to help deceive and pin down the patience of hapless citizens.
The blame culture our leaders indulge in has helped to expose one painful fact most public office holders do not understand the true meaning of leadership. Some, therefore, see leadership as opportunities to advance tribal or religious agenda. Others simply see leadership as platforms to amass wealth. Except our leaders begin to appreciate what leadership truly is, Nigeria might continue to suffer underdevelopment, unemployment, poverty, crime and insecurity.
It will be an understatement to declare that Nigeria has lacked purposeful leadership for the most part of its 49 years, as an independent nation. Nigeria would, therefore, need a legion of leaders that are prepared to invest honesty, faithfulness and patriotism. Without this, the nation might not experience growth and peace. There is no doubt that Nigeria has, one time or the other, been blessed with honest leaders. The problem has been that these honest leaders mostly surround themselves with dishonest people in the form of advisers, ministers, and confidants. It is natural for honest leaders, that accept support from dishonest people, to become dishonourable within a very short period of time.
The success stories of Nigerians in the diaspora show that there are enough honest Nigerians who can work with our leaders to fix the myriad of problems that have continued to bedevil this nation. Unfortunately, the nation’s faulty electoral system makes it quite impossible for most leaders to assemble a credible team to work with.
This has forced our leaders to have hoards of mainly dishonest people around them. It is sad to note that even the few honest ones that find their way into government are usually recommended by dishonest kingmakers. This is mostly responsible for the several cases of honest Nigerians who danced naked in the market square shortly after joining government.
For a country with a faulty electoral system, Nigerians do not need a prophet to confirm that the art of king-making in Nigeria is dirty and stinks to the high heavens. There are no internal democracies. Not only are candidates forced on party members, elections are openly rigged by political kingmakers for a price: key to the treasury. This would best explain why, despite all the noise about ICPC, EFCC, and CCB, corruption has continued to grow in the country. It is now fashionable for government to decide who is to be investigated, arraigned in court, bailed, or even convicted.
This has indeed rubbished the much dramatised Rule of Law and war against graft of the present administration. The earlier our leaders stopped deceiving the citizens, the better for the future of this country. Nigeria does not need more than four years to get back on its feet.
Nigeria would reach the sky in a span of four years if the amount of zeal deployed to tackle militancy in the Niger Delta region is directed at corrupt and super tribal zealots in government. No doubt, Nigerian officials are reputed to be among the best fiscal policy formulators and budget planners in the world. The irony, however, is that Nigeria is occupying the bottom rung of the ladder in terms of budget implementation.
This is a clear case of poor leadership. Nigeria would have been among the first 20 most industrialised countries in the world, if her leaders had implemented annual budgets to the tone of 85% at the state and national levels in the last ten years. Nigeria only requires stable power supply, efficient transportation system, access to long term credit facilities, transparency and accountability in government business to enable the private sector drive the nation’s economy up the ladder. All of these would not cost the nation a fortune.
It only requires the right leadership. Perhaps, one should add here that our leaders do not lack the capacities to fix these issues. The snag is that our leaders have been swallowed by their own greed and other human weaknesses.
Just like in the case of the Niger Delta, where those that were benefiting from the activities of militants never wanted peace in the region, there are several thousands of Nigerians who are benefiting from the nation’s poor leadership culture. Some of these persons believe they would lose substantial stake, if there is steady electricity in Nigeria. Is it not a shame that despite the abundance of natural gas in the Niger Delta region, constant power supply has been a mirage in Nigeria? The petroleum sector is no better.
As the sixth largest producer of crude, Nigeria still imports more than 50 percent of petroleum products to service local markets. This status quo is maintained just to make sure some persons have the opportunity to make huge profits through the importation of petroleum products. For how long would our leaders continue to fool the citizenry? To make matters worse, government has been making much noise about the planned withdrawal of petroleum subsidy.
For a nation suffering from poor leadership culture, there is no doubt that subsidy is the only benefit the masses are sure of. Ordinarily, Nigerians will surely resist attempts by government to further impoverish them with the planned increase in the prices of petroleum products by 1st November, 2009.
Furthermore, there are many Nigerians that think an efficient transportation system in the country would impact negatively on their businesses. This is the reason why our federal roads are deliberately allowed to turn into ponds and death traps, despite the existence of FERMA. It is also for the same reason that the rail system has gone comatose over the decades.
More than that, a handful of Nigerians benefit substantially when government businesses are done in secrecy. It has, therefore, been difficult for the nation to reap the benefits of transparency and accountability. All of these persons enumerated above are members of the platoon of kingmakers. They work hand in glove with our leaders to destroy the country. Somehow, the masses have always tended to undermine them because of the subtle manner they operate. They are mostly faceless, but quite a formidable force.
They are very wealthy and influential and too ready to contribute resources to install and manipulate political leaders to their advantage.
One ready question that has always hung on the lips of many Nigerian leaders is: “Is it morally right to bite the fingers that fed me?” This is the problem with leadership in Nigeria. The foundation of many Nigerian leaders can be traced to the heart of dishonest kingmakers. It would be difficult for Nigeria to enjoy quality leadership, as long as the masses are prevented from choosing their leaders. This is the strong reason why the electoral laws should be reformed to make votes count. Electoral fraud is indeed one very big brush that our leaders have used to paint Nigeria black in the eyes of the international community.
Though Nigeria is believed to be giant of Africa, the international community see the true giant in Ghana and South Africa. This fact should help grow patriotism in our leaders.
Yar’Adua had once flaunted his patriotism, when he openly confessed that the 2007 presidential election that brought him to office was flawed. He followed this confession with a firm promise to overhaul the nation’s faulty electoral laws. This honest disposition earned the former governor of Katsina state so much respect among the Nigerian masses and civil society organisations. But with the election season just a few months away, they are beginning to feel betrayed.
Some have gone to the extent of cursing the day they accepted to forgive the ruling party of all her electoral sins before, during, and after the 2007 presidential election. Many Nigerians have begun to argue that the president’s blatant refusal to cede the power to appoint the chairman of INEC is as good as not having any electoral reforms at all. The president’s unwavering resolve to keep the all important right to appoint the electoral commission’s boss has left wide gaps for fertile suspicions among watchers of Nigerian politics. Civil society organisations and opposition politicians have already cried fowl against the continuous delay of the long planned review of the nation’s constitution which was stalled owing to very trivial issues.
Even the claim by the deputy senate president, Ike Ekweremadu, that a whole of N500m was inadequate to enable the National Assembly review the nation’s constitution has been quickly interpreted to be part of a grand plan to scuttle the much anticipated electoral reform process ahead of the next general elections. Whichever way one wants to look at the unfolding drama, the truth still stands out: our leaders are suffering from severe agoraphobia.
It is pertinent to note at this point that Nigeria does not need just honest leaders. There is also an important need for honest followers as well. Honest followers would not ridicule leaders that are unable to own fleet of cars and mansions after leaving office. Many public office holders indulge in corruption because of undue pressure from family members, friends, and political associates. This should, however, not be an excuse for public office holders to steal government money while in office. They should rather put the interest of the nation first and grow the courage to resist extreme demands from whatever quarters.
This is the right time for Nigerian leaders to face the realism of fact. This is even more urgent because the patience of the Nigerian masses has run out. It was mainly for the fear of military intervention and possible disintegration that Nigerian masses ignored the charade that was the 2007 presidential elections. But unfortunately, Nigerians have been gravely hurt by the slow pace of development and high incidents of corruption in the polity.
What is government expecting from the masses that are witnesses to the fact that most public office holders clearly live above their incomes, while they wallow in abject poverty? Nigeria has become a time bomb. It would, therefore, be catastrophic if President Yar’Adua continues to take the patience of Nigerians for granted. For now, the endurance limit of Nigerians has become even shallower than the lower course of the River Niger.
Government’s propaganda can no longer navigate the heart of suffering Nigerian masses. To successfully dredge same, the president should ensure that the electoral system is reformed in line with popular opinion, before the next general elections. This would enable the electorates to take charge of the driving seats and disengage all the unpatriotic kingmakers and apostles of corruption that have held this country back for nearly half a century.
Monday, October 26, 2009
Eye and foot problems in Diabetic related diseases
Eye And Foot Problems In Diabetic related diseases
The term diabetes mellitus refers to a group of medical disorders of varying causes which are usually accompanied by long standing elevations of blood glucose levels over and above what is generally acceptable as normal.
Blood glucose elevation in this situation being a direct consequence of inadequate production of insulin by the body part called the pancreas. Insulin can best be described as a body chemical medically referred to as “hormone.” It is usually released by the pancreas in response to meal or glucose-containing drink.
Diabetes and the Eye
Eye problems which can affect people with diabetes more commonly include cataract (clouding of the lens of the eye), glaucoma (increase of fluid pressure inside the eye, leading to optic nerve damage and loss of vision), diabetic retinopathy (the most common diabetic eye disease) and some less dangerous others.
These eye complications are commonly seen in those with a longer duration of diabetes, those with poorly controlled or uncontrolled diabetes, and those with other organ problems.
These eye problems are often unknown to the sufferer at the early stages when their treatments are better assured, unless they undergo regular eye examinations by an eye doctor.
Eye examinations should be done every six months or yearly. Treatments depend on the advice of the eye care specialist in conjunction with other diabetic care specialists. Cataracts are usually curable with operation; glaucoma is better treated early with drugs, laser and/or operation, while diabetic retinopathy requires laser therapy.
What are the risk factors for diabetic retinopathy?
The longer a person has diabetes, the greater the chance of developing diabetic retinopathy. Almost 80 per cent of people, who have diabetes for 15 years or more, have some damage done on the blood vessels in their retina.
What can be done to prevent diabetic retinopathy?
There is no treatment that can prevent diabetic retinopathy altogether. Persons with any form of diabetes may develop diabetic retinopathy. It has, however, been proven that a good control of diabetes can delay and slow down the rate of progress of diabetic retinopathy and its complications.
Besides good control of blood glucose, one must exercise regularly, keep the blood pressure under control, avoid smoking, and avoid excessive weight.
How do I know if I have diabetic retinopathy?
You might not know that you are having diabetic retinopathy, as there are no symptoms in the early stages of the disease. Therefore, it is essential to have a periodic evaluation of your eye by an eye doctor to detect the condition early.
Early diagnosis and timely treatment are very essential in preventing the complications of this disease and thus, maintaining vision.
How frequently should I get my eye examined?
Because a person with diabetes can have retinopathy and not know it, a regular check-up with an eye care professional is essential. If one has diabetes, it is advised to get a bi-annual or yearly examination with the eye doctor.
The pupils may be dilated with eye drops, so that the eye doctor may have a good look at the back of the eye. Once there is diabetic retinopathy, then the eye doctor will advise if there will be a need for some investigations, treatment or just a follow-up. In these cases, the frequency of follow-up visits is decided on the basis of the severity of the disease.
Treatment for diabetic retinopathy
Specific treatment will be determined by the doctor(s) based on: age, overall health condition, and medical history, extent of the disease involvement, individual tolerance for specific medications, procedures, or therapies, expectations for the course of the disease, personal opinion or preference.
Diabetic retinopathy is often treated with laser surgery to shrink the abnormal blood vessels or to seal the leaking ones.
What are the other possible eye conditions in diabetes?
Glaucoma
People with diabetes are 40 per cent more likely to suffer from glaucoma than people without diabetes. The longer someone has had diabetes, the more common glaucoma is. Risk also increases with age. Glaucoma occurs when pressure builds up in the eye.
In most cases, the pressure causes drainage of the aqueous humour to slow down so that it builds up in the front chamber of the eye. The pressure pinches the blood vessels that carry blood to the retina and optic nerve.
Vision is gradually lost because the retina and nerves are damaged. There are several treatments for glaucoma. Some use drugs to reduce pressure in the eye, while others involve surgery.
Cataracts
Many people without diabetes get cataracts, but people with diabetes are 60 per cent more likely to develop this eye condition. People with diabetes also tend to develop cataracts at a younger age and have them progress faster.
With cataracts, the clear eye lens becomes cloudy, blocking light. To help deal with mild cataracts, one may need to wear sunglasses.
For cataracts that interfere greatly with vision, doctors usually remove the lens of the eye. Sometimes, the patient gets a new transplanted lens. In people with diabetes, retinopathy can get worse after removal of the lens and glaucoma may start to develop.
Foot problems in diabetes
People with diabetes can develop different types of foot problems. Even what appears to be a minor problem can get worse and lead to serious complications.
Foot ulcerations are a common cause for hospital admissions among persons with diabetes, resulting in prolonged hospital stay, loss of the limb (amputation) and even death.
Many of these serious foot problems can, however, be prevented through proper foot care, early identification of foot problems and prompt treatment by a skilled health care provider.
The term diabetes mellitus refers to a group of medical disorders of varying causes which are usually accompanied by long standing elevations of blood glucose levels over and above what is generally acceptable as normal.
Blood glucose elevation in this situation being a direct consequence of inadequate production of insulin by the body part called the pancreas. Insulin can best be described as a body chemical medically referred to as “hormone.” It is usually released by the pancreas in response to meal or glucose-containing drink.
Diabetes and the Eye
Eye problems which can affect people with diabetes more commonly include cataract (clouding of the lens of the eye), glaucoma (increase of fluid pressure inside the eye, leading to optic nerve damage and loss of vision), diabetic retinopathy (the most common diabetic eye disease) and some less dangerous others.
These eye complications are commonly seen in those with a longer duration of diabetes, those with poorly controlled or uncontrolled diabetes, and those with other organ problems.
These eye problems are often unknown to the sufferer at the early stages when their treatments are better assured, unless they undergo regular eye examinations by an eye doctor.
Eye examinations should be done every six months or yearly. Treatments depend on the advice of the eye care specialist in conjunction with other diabetic care specialists. Cataracts are usually curable with operation; glaucoma is better treated early with drugs, laser and/or operation, while diabetic retinopathy requires laser therapy.
What are the risk factors for diabetic retinopathy?
The longer a person has diabetes, the greater the chance of developing diabetic retinopathy. Almost 80 per cent of people, who have diabetes for 15 years or more, have some damage done on the blood vessels in their retina.
What can be done to prevent diabetic retinopathy?
There is no treatment that can prevent diabetic retinopathy altogether. Persons with any form of diabetes may develop diabetic retinopathy. It has, however, been proven that a good control of diabetes can delay and slow down the rate of progress of diabetic retinopathy and its complications.
Besides good control of blood glucose, one must exercise regularly, keep the blood pressure under control, avoid smoking, and avoid excessive weight.
How do I know if I have diabetic retinopathy?
You might not know that you are having diabetic retinopathy, as there are no symptoms in the early stages of the disease. Therefore, it is essential to have a periodic evaluation of your eye by an eye doctor to detect the condition early.
Early diagnosis and timely treatment are very essential in preventing the complications of this disease and thus, maintaining vision.
How frequently should I get my eye examined?
Because a person with diabetes can have retinopathy and not know it, a regular check-up with an eye care professional is essential. If one has diabetes, it is advised to get a bi-annual or yearly examination with the eye doctor.
The pupils may be dilated with eye drops, so that the eye doctor may have a good look at the back of the eye. Once there is diabetic retinopathy, then the eye doctor will advise if there will be a need for some investigations, treatment or just a follow-up. In these cases, the frequency of follow-up visits is decided on the basis of the severity of the disease.
Treatment for diabetic retinopathy
Specific treatment will be determined by the doctor(s) based on: age, overall health condition, and medical history, extent of the disease involvement, individual tolerance for specific medications, procedures, or therapies, expectations for the course of the disease, personal opinion or preference.
Diabetic retinopathy is often treated with laser surgery to shrink the abnormal blood vessels or to seal the leaking ones.
What are the other possible eye conditions in diabetes?
Glaucoma
People with diabetes are 40 per cent more likely to suffer from glaucoma than people without diabetes. The longer someone has had diabetes, the more common glaucoma is. Risk also increases with age. Glaucoma occurs when pressure builds up in the eye.
In most cases, the pressure causes drainage of the aqueous humour to slow down so that it builds up in the front chamber of the eye. The pressure pinches the blood vessels that carry blood to the retina and optic nerve.
Vision is gradually lost because the retina and nerves are damaged. There are several treatments for glaucoma. Some use drugs to reduce pressure in the eye, while others involve surgery.
Cataracts
Many people without diabetes get cataracts, but people with diabetes are 60 per cent more likely to develop this eye condition. People with diabetes also tend to develop cataracts at a younger age and have them progress faster.
With cataracts, the clear eye lens becomes cloudy, blocking light. To help deal with mild cataracts, one may need to wear sunglasses.
For cataracts that interfere greatly with vision, doctors usually remove the lens of the eye. Sometimes, the patient gets a new transplanted lens. In people with diabetes, retinopathy can get worse after removal of the lens and glaucoma may start to develop.
Foot problems in diabetes
People with diabetes can develop different types of foot problems. Even what appears to be a minor problem can get worse and lead to serious complications.
Foot ulcerations are a common cause for hospital admissions among persons with diabetes, resulting in prolonged hospital stay, loss of the limb (amputation) and even death.
Many of these serious foot problems can, however, be prevented through proper foot care, early identification of foot problems and prompt treatment by a skilled health care provider.
Wednesday, October 21, 2009
CAPACITORS
Capacitors
Modern capacitors, by a cm rule.
Type Passive
Invented Ewald Georg von Kleist (October 1745)
Electronic symbol
A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force between the plates. The effect is greatest between wide, flat, parallel, narrowly separated conductors.
An ideal capacitor is characterized by a single constant value, capacitance, which is measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them. In practice, the dielectric between the plates passes a small amount of leakage current. The conductors and leads introduce an equivalent series resistance and the dielectric has an electric field strength limit resulting in a breakdown voltage.
Capacitors are widely used in electronic circuits to block the flow of direct current while allowing alternating current to pass, to filter out interference, to smooth the output of power supplies, and for many other purposes. They are used in resonant circuits in radio frequency equipment to select particular frequencies from a signal with many frequencies.
[edit] History
Battery of four Leyden jars in Museum Boerhave, Leiden.In October 1745, Ewald Georg von Kleist of Pomerania in Germany found that charge could be stored by connecting a high voltage electrostatic generator by a wire to a volume of water in a hand-held glass jar.[1] Von Kleist's hand and the water acted as conductors and the jar as a dielectric (although details of the mechanism were incorrectly identified at the time). Von Kleist found that after removing the generator, touching the wire resulted in a painful spark. In a letter describing the experiment, he said "I would not take a second shock for the kingdom of France."[2] The following year, the Dutch physicist Pieter van Musschenbroek invented a similar capacitor, which was named the Leyden jar, after the University of Leyden where he worked.[3] Daniel Gralath was the first to combine several jars in parallel into a "battery" to increase the charge storage capacity.[citation needed]
Benjamin Franklin investigated the Leyden jar and proved that the charge was stored on the glass, not in the water as others had assumed.[citation needed] He also created the term "battery",[4][5] (as in a battery of cannon), subsequently applied to clusters of electrochemical cells.[6] Leyden jars were later to be made by coating the inside and outside of jars with metal foil, leaving a space at the mouth to prevent arcing between the foils.[citation needed] The earliest unit of capacitance was the 'jar', equivalent to about 1 nanofarad.[citation needed]
Leyden jars or more powerful devices employing flat glass plates alternating with foil conductors were used exclusively up until about 1900, when the invention of wireless (radio) created a demand for standard capacitors, and the steady move to higher frequencies required capacitors with lower inductance. A more compact construction began to be used of a flexible dielectric sheet such as oiled paper sandwiched between sheets of metal foil, rolled or folded into a small package.
Early capacitors were also known as condensers, a term that is still occasionally used today. The term was first used for this purpose by Alessandro Volta in 1782, with reference to the device's ability to store a higher density of electric charge than a normal isolated conductor.[citation needed]
[edit] Theory of operation
Main article: Capacitance
Charge separation in a parallel-plate capacitor causes an internal electric field. A dielectric (orange) reduces the field and increases the capacitance.
A simple demonstration of a parallel-plate capacitorA capacitor consists of two conductors separated by a non-conductive region.[7] The non-conductive substance is called the dielectric medium, although this may also mean a vacuum or a semiconductor depletion region chemically identical to the conductors. A capacitor is assumed to be self-contained and isolated, with no net electric charge and no influence from an external electric field. The conductors thus contain equal and opposite charges on their facing surfaces,[8] and the dielectric contains an electric field. The capacitor is a reasonably general model for electric fields within electric circuits.
An ideal capacitor is wholly characterized by a constant capacitance 'C', defined as the ratio of charge ±'Q' on each conductor to the voltage 'V' between them
Sometimes charge buildup affects the mechanics of the capacitor, causing the capacitance to vary. In this case, capacitance is defined in terms of incremental changes:
In SI units, a capacitance of one farad means that one coulomb of charge on each conductor causes a voltage of one volt across the device.[9]
[edit] Energy storage
Work must be done by an external influence to move charge between the conductors in a capacitor. When the external influence is removed, the charge separation persists and energy is stored in the electric field. If charge is later allowed to return to its equilibrium position, the energy is released. The work done in establishing the electric field, and hence the amount of energy stored, is given by:[10]
[edit] Current-voltage relation
The current i (t ) through a component in an electric circuit is defined as the rate of change of the charge q (t ) that has passed through it. Physical charges cannot pass through the dielectric layer of a capacitor, but rather build up in equal and opposite quantities on the electrodes: as each electron accumulates on the negative plate, one leaves the positive plate. Thus the accumulated charge on the electrodes is equal to the integral of the current, as well as being proportional to the voltage (as discussed above). As with any antiderivative, a constant of integration is added to represent the initial voltage v (t0). This is the integral form of the capacitor equation,[11]
.
Taking the derivative of this, and multiplying by C, yields the derivative form,[12]
.
The dual of the capacitor is the inductor, which stores energy in the magnetic field rather than the electric field. Its current-voltage relation is obtained by exchanging current and voltage in the capacitor equations and replacing C with the inductance L.
[edit] DC circuits
A simple resistor-capacitor circuit demonstrates charging of a capacitor.A series circuit containing only a resistor, a capacitor, a switch and a constant DC source of voltage V0 is known as a charging circuit.[13] If the capacitor is initially uncharged while the switch is open, and the switch is closed at t = 0, it follows from Kirchhoff voltage.
As the capacitor reaches equilibrium with the source voltage, the voltage across the resistor and the current through the entire circuit decay exponentially. The case of discharging a charged capacitor likewise demonstrates exponential decay, but with the initial capacitor voltage replacing V0 and the final voltage being zero.
[edit] AC circuits
See also: reactance (electronics) and electrical impedance#Deriving the device specific impedances
Impedance, the vector sum of reactance and resistance, describes the phase difference and the ratio of amplitudes between sinusoidally varying voltage and sinusoidally varying current at a given frequency. Fourier analysis allows any signal to be constructed from a spectrum of frequencies, whence the circuit's reaction to the various frequencies may be found. The reactance and impedance of a capacitor are respectively
where j is the imaginary unit and ω is the angular velocity of the sinusoidal signal. The - j phase indicates that the AC voltage V = Z I lags the AC current by 90°: the positive current phase corresponds to increasing voltage as the capacitor charges; zero current corresponds to instantaneous constant voltage, etc.
Note that impedance decreases with increasing capacitance and increasing frequency. This implies that a higher-frequency signal or a larger capacitor results in a lower voltage amplitude per current amplitude—an AC "short circuit" or AC coupling. Conversely, for very low frequencies, the reactance will be high, so that a capacitor is nearly an open circuit in AC analysis—those frequencies have been "filtered out".
Capacitors are different from resistors and inductors in that the impedance is inversely proportional to the defining characteristic, i.e. capacitance.
[edit] Parallel plate model
Dielectric is placed between two conducting plates, each of area A and with a separation of d.The simplest capacitor consists of two parallel conductive plates separated by a dielectric with permittivity ε (such as air). The model may also be used to make qualitative predictions for other device geometries. The plates are considered to extend uniformly over an area A and a charge density ±ρ = ±Q/A exists on their surface. Assuming that the width of the plates is much greater than their separation d, the electric field near the centre of the device will be uniform with the magnitude E = ρ/ε. The voltage is defined as the line integral of the electric field between the plates
Solving this for C = Q/V reveals that capacitance increases with area and decreases with separation
.
The capacitance is therefore greatest in devices made from materials with a high permittivity.
[edit] Networks
See also: Series and parallel circuits
For capacitors in parallel
Several capacitors in parallel.Capacitors in a parallel configuration each have the same applied voltage. Their capacitances add up. Charge is apportioned among them by size. Using the schematic diagram to visualize parallel plates, it is apparent that each capacitor contributes to the total surface area.
For capacitors in series
Several capacitors in series.Connected in series, the schematic diagram reveals that the separation distance, not the plate area, adds up. The capacitors each store instantaneous charge build-up equal to that of every other capacitor in the series. The total voltage difference from end to end is apportioned to each capacitor according to the inverse of its capacitance. The entire series acts as a capacitor smaller than any of its components.
Capacitors are combined in series to achieve a higher working voltage, for example for smoothing a high voltage power supply. The voltage ratings, which are based on plate separation, add up. In such an application, several series connections may in turn be connected in parallel, forming a matrix. The goal is to maximize the energy storage utility of each capacitor without overloading it.
Series connection is also used to adapt electrolytic capacitors for AC use.
[edit] Non-ideal behaviour
Capacitors deviate from the ideal capacitor equation in a number of ways. Some of these, such as leakage current and parasitic effects are linear, or can be assumed to be linear, and can be dealt with by adding virtual components to the equivalent circuit of the capacitor. The usual methods of network analysis can then be applied. In other cases, such as with breakdown voltage, the effect is non-linear and normal (i.e., linear) network analysis cannot be used, the effect must be dealt with separately. There is yet another group, which may be linear but invalidate the assumption in the analysis that capacitance is a constant. Such an example is temperature dependence.
[edit] Breakdown voltage
Main article: Breakdown voltage
Above a particular electric field, known as the dielectric strength Eds, the dielectric in a capacitor becomes conductive. The voltage at which this occurs is called the breakdown voltage of the device, and is given by the product of the dielectric strength and the separation between the conductors,[14]
Vbd = Edsd
The maximum energy that can be stored safely in a capacitor is limited by the breakdown voltage. Due to the scaling of capacitance and breakdown voltage with dielectric thickness, all capacitors made with a particular dielectric have approximately equal maximum energy density, to the extent that the dielectric dominates their volume.[15]
For air dielectric capacitors the breakdown field strength is of the order 107 V/m and will be much less when other materials are used for the dielectric. The absolute breakdown voltage of most capacitors is nowhere near such a high number because of the very small distance between the plates. Typical ratings for capacitors used for general electronics applications range from a few volts to 100V or so. For high voltage applications physically much larger capacitors have to be used. In this field, there are a number of factors that can dramatically reduce the breakdown voltage below that to be expected by considering the breakdown field strength of the dielectric alone. For one thing, the geometry of the capacitor conductive parts (plates and connecting wires) is important. In particular, sharp edges or points hugely increase the electric field strength at that point and can lead to a local breakdown. Once this starts to happen, the breakdown will quickly "track" through the dielectric till it reaches the opposite plate and cause a short circuit.[16]
The usual breakdown route is that the field strength becomes large enough to pull electrons in the dielectric from their atoms thus causing conduction. Other scenarios are possible, such as impurities in the dielectric, and, if the dielectric is of a crystalline nature, imperfections in the crystal structure can result in an avalanche breakdown as seen in semi-conductor devices. Breakdown voltage is also affected by pressure, humidity and temperature.[17]
[edit] Equivalent circuit
Two equivalent circuits of a real capacitorAn ideal capacitor only stores and releases electrical energy, without dissipating any. In reality, all capacitors have imperfections within the capacitor's material that create resistance. This is specified as the equivalent series resistance or ESR of a component. This adds a real component to the impedance:
As frequency approaches infinity, the capacitive impedance (or reactance) approaches zero and the ESR becomes significant. As the reactance becomes negligible, power dissipation approaches PRMS. = VRMS.² /RESR.
Similarly to ESR, the capacitor's leads add equivalent series inductance or ESL to the component. This is usually significant only at relatively high frequencies. As inductive reactance is positive and increases with frequency, above a certain frequency capacitance will be canceled by inductance. High frequency engineering involves accounting for the inductance of all connections and components.
If the conductors are separated by a material with a small conductivity rather than a perfect dielectric, then a small leakage current flows directly between them. The capacitor therefore has a finite parallel resistance,[9] and slowly discharges over time (time may vary greatly depending on the capacitor material and quality).
[edit] Ripple current
Ripple current is the AC component of an applied source (often a switched-mode power supply) whose frequency may be constant or varying. Certain types of capacitors, such as electrolytic tantalum capacitors, usually have a rating for maximum ripple current (both in frequency and magnitude). This ripple current can cause damaging heat to be generated within the capacitor due to the current flow across resistive imperfections in the materials used within the capacitor, more commonly referred to as equivalent series resistance (ESR). For example electrolytic tantalum capacitors are limited by ripple current and generally have the highest ESR ratings in the capacitor family, while ceramic capacitors generally have no ripple current limitation and have some of the lowest ESR ratings.
[edit] Instability of capacitance
The capacitance of certain capacitors decreases as the component ages. In ceramic capacitors, this is caused by degradation of the dielectric. The type of dielectric and the ambient operating and storage temperatures are the most significant aging factors, while the operating voltage has a smaller effect. The aging process may be reversed by heating the component above the Curie point. Aging is fastest near the beginning of life of the component, and the device stabilizes over time.[18] Electrolytic capacitors age as the electrolyte evaporates. In contrast with ceramic capacitors, this occurs towards the end of life of the component.
Temperature dependence of capacitance is usually expressed in parts per million (ppm) per °C. It can usually be taken as a broadly linear function but can be noticeably non-linear at the temperature extremes. The temperature coefficient can be either positive or negative, sometimes even amongst different samples of the same type. In other words, the spread in the range of temperature coefficients can encompass zero. See the data sheet in the leakage current section above for an example.
Capacitors, especially older components, can absorb sound waves resulting in a microphonic effect. Vibration moves the plates, causing the capacitance to vary, in turn inducing AC current. Some dielectrics also generate piezoelectricity. The resulting interference is especially problematic in audio applications, potentially causing feedback or unintended recording. In the reverse microphonic effect, the varying electric field between the capacitor plates exerts a physical force, moving them as a speaker. This can generate audible sound, but drains energy and stresses the dielectric and the electrolyte, if any.
[edit] Capacitor types
Main article: Types of capacitor
Practical capacitors are available commercially in many different forms. The type of internal dielectric, the structure of the plates and the device packaging all strongly affect the characteristics of the capacitor, and its applications.
Modern capacitors, by a cm rule.
Type Passive
Invented Ewald Georg von Kleist (October 1745)
Electronic symbol
A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force between the plates. The effect is greatest between wide, flat, parallel, narrowly separated conductors.
An ideal capacitor is characterized by a single constant value, capacitance, which is measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them. In practice, the dielectric between the plates passes a small amount of leakage current. The conductors and leads introduce an equivalent series resistance and the dielectric has an electric field strength limit resulting in a breakdown voltage.
Capacitors are widely used in electronic circuits to block the flow of direct current while allowing alternating current to pass, to filter out interference, to smooth the output of power supplies, and for many other purposes. They are used in resonant circuits in radio frequency equipment to select particular frequencies from a signal with many frequencies.
[edit] History
Battery of four Leyden jars in Museum Boerhave, Leiden.In October 1745, Ewald Georg von Kleist of Pomerania in Germany found that charge could be stored by connecting a high voltage electrostatic generator by a wire to a volume of water in a hand-held glass jar.[1] Von Kleist's hand and the water acted as conductors and the jar as a dielectric (although details of the mechanism were incorrectly identified at the time). Von Kleist found that after removing the generator, touching the wire resulted in a painful spark. In a letter describing the experiment, he said "I would not take a second shock for the kingdom of France."[2] The following year, the Dutch physicist Pieter van Musschenbroek invented a similar capacitor, which was named the Leyden jar, after the University of Leyden where he worked.[3] Daniel Gralath was the first to combine several jars in parallel into a "battery" to increase the charge storage capacity.[citation needed]
Benjamin Franklin investigated the Leyden jar and proved that the charge was stored on the glass, not in the water as others had assumed.[citation needed] He also created the term "battery",[4][5] (as in a battery of cannon), subsequently applied to clusters of electrochemical cells.[6] Leyden jars were later to be made by coating the inside and outside of jars with metal foil, leaving a space at the mouth to prevent arcing between the foils.[citation needed] The earliest unit of capacitance was the 'jar', equivalent to about 1 nanofarad.[citation needed]
Leyden jars or more powerful devices employing flat glass plates alternating with foil conductors were used exclusively up until about 1900, when the invention of wireless (radio) created a demand for standard capacitors, and the steady move to higher frequencies required capacitors with lower inductance. A more compact construction began to be used of a flexible dielectric sheet such as oiled paper sandwiched between sheets of metal foil, rolled or folded into a small package.
Early capacitors were also known as condensers, a term that is still occasionally used today. The term was first used for this purpose by Alessandro Volta in 1782, with reference to the device's ability to store a higher density of electric charge than a normal isolated conductor.[citation needed]
[edit] Theory of operation
Main article: Capacitance
Charge separation in a parallel-plate capacitor causes an internal electric field. A dielectric (orange) reduces the field and increases the capacitance.
A simple demonstration of a parallel-plate capacitorA capacitor consists of two conductors separated by a non-conductive region.[7] The non-conductive substance is called the dielectric medium, although this may also mean a vacuum or a semiconductor depletion region chemically identical to the conductors. A capacitor is assumed to be self-contained and isolated, with no net electric charge and no influence from an external electric field. The conductors thus contain equal and opposite charges on their facing surfaces,[8] and the dielectric contains an electric field. The capacitor is a reasonably general model for electric fields within electric circuits.
An ideal capacitor is wholly characterized by a constant capacitance 'C', defined as the ratio of charge ±'Q' on each conductor to the voltage 'V' between them
Sometimes charge buildup affects the mechanics of the capacitor, causing the capacitance to vary. In this case, capacitance is defined in terms of incremental changes:
In SI units, a capacitance of one farad means that one coulomb of charge on each conductor causes a voltage of one volt across the device.[9]
[edit] Energy storage
Work must be done by an external influence to move charge between the conductors in a capacitor. When the external influence is removed, the charge separation persists and energy is stored in the electric field. If charge is later allowed to return to its equilibrium position, the energy is released. The work done in establishing the electric field, and hence the amount of energy stored, is given by:[10]
[edit] Current-voltage relation
The current i (t ) through a component in an electric circuit is defined as the rate of change of the charge q (t ) that has passed through it. Physical charges cannot pass through the dielectric layer of a capacitor, but rather build up in equal and opposite quantities on the electrodes: as each electron accumulates on the negative plate, one leaves the positive plate. Thus the accumulated charge on the electrodes is equal to the integral of the current, as well as being proportional to the voltage (as discussed above). As with any antiderivative, a constant of integration is added to represent the initial voltage v (t0). This is the integral form of the capacitor equation,[11]
.
Taking the derivative of this, and multiplying by C, yields the derivative form,[12]
.
The dual of the capacitor is the inductor, which stores energy in the magnetic field rather than the electric field. Its current-voltage relation is obtained by exchanging current and voltage in the capacitor equations and replacing C with the inductance L.
[edit] DC circuits
A simple resistor-capacitor circuit demonstrates charging of a capacitor.A series circuit containing only a resistor, a capacitor, a switch and a constant DC source of voltage V0 is known as a charging circuit.[13] If the capacitor is initially uncharged while the switch is open, and the switch is closed at t = 0, it follows from Kirchhoff voltage.
As the capacitor reaches equilibrium with the source voltage, the voltage across the resistor and the current through the entire circuit decay exponentially. The case of discharging a charged capacitor likewise demonstrates exponential decay, but with the initial capacitor voltage replacing V0 and the final voltage being zero.
[edit] AC circuits
See also: reactance (electronics) and electrical impedance#Deriving the device specific impedances
Impedance, the vector sum of reactance and resistance, describes the phase difference and the ratio of amplitudes between sinusoidally varying voltage and sinusoidally varying current at a given frequency. Fourier analysis allows any signal to be constructed from a spectrum of frequencies, whence the circuit's reaction to the various frequencies may be found. The reactance and impedance of a capacitor are respectively
where j is the imaginary unit and ω is the angular velocity of the sinusoidal signal. The - j phase indicates that the AC voltage V = Z I lags the AC current by 90°: the positive current phase corresponds to increasing voltage as the capacitor charges; zero current corresponds to instantaneous constant voltage, etc.
Note that impedance decreases with increasing capacitance and increasing frequency. This implies that a higher-frequency signal or a larger capacitor results in a lower voltage amplitude per current amplitude—an AC "short circuit" or AC coupling. Conversely, for very low frequencies, the reactance will be high, so that a capacitor is nearly an open circuit in AC analysis—those frequencies have been "filtered out".
Capacitors are different from resistors and inductors in that the impedance is inversely proportional to the defining characteristic, i.e. capacitance.
[edit] Parallel plate model
Dielectric is placed between two conducting plates, each of area A and with a separation of d.The simplest capacitor consists of two parallel conductive plates separated by a dielectric with permittivity ε (such as air). The model may also be used to make qualitative predictions for other device geometries. The plates are considered to extend uniformly over an area A and a charge density ±ρ = ±Q/A exists on their surface. Assuming that the width of the plates is much greater than their separation d, the electric field near the centre of the device will be uniform with the magnitude E = ρ/ε. The voltage is defined as the line integral of the electric field between the plates
Solving this for C = Q/V reveals that capacitance increases with area and decreases with separation
.
The capacitance is therefore greatest in devices made from materials with a high permittivity.
[edit] Networks
See also: Series and parallel circuits
For capacitors in parallel
Several capacitors in parallel.Capacitors in a parallel configuration each have the same applied voltage. Their capacitances add up. Charge is apportioned among them by size. Using the schematic diagram to visualize parallel plates, it is apparent that each capacitor contributes to the total surface area.
For capacitors in series
Several capacitors in series.Connected in series, the schematic diagram reveals that the separation distance, not the plate area, adds up. The capacitors each store instantaneous charge build-up equal to that of every other capacitor in the series. The total voltage difference from end to end is apportioned to each capacitor according to the inverse of its capacitance. The entire series acts as a capacitor smaller than any of its components.
Capacitors are combined in series to achieve a higher working voltage, for example for smoothing a high voltage power supply. The voltage ratings, which are based on plate separation, add up. In such an application, several series connections may in turn be connected in parallel, forming a matrix. The goal is to maximize the energy storage utility of each capacitor without overloading it.
Series connection is also used to adapt electrolytic capacitors for AC use.
[edit] Non-ideal behaviour
Capacitors deviate from the ideal capacitor equation in a number of ways. Some of these, such as leakage current and parasitic effects are linear, or can be assumed to be linear, and can be dealt with by adding virtual components to the equivalent circuit of the capacitor. The usual methods of network analysis can then be applied. In other cases, such as with breakdown voltage, the effect is non-linear and normal (i.e., linear) network analysis cannot be used, the effect must be dealt with separately. There is yet another group, which may be linear but invalidate the assumption in the analysis that capacitance is a constant. Such an example is temperature dependence.
[edit] Breakdown voltage
Main article: Breakdown voltage
Above a particular electric field, known as the dielectric strength Eds, the dielectric in a capacitor becomes conductive. The voltage at which this occurs is called the breakdown voltage of the device, and is given by the product of the dielectric strength and the separation between the conductors,[14]
Vbd = Edsd
The maximum energy that can be stored safely in a capacitor is limited by the breakdown voltage. Due to the scaling of capacitance and breakdown voltage with dielectric thickness, all capacitors made with a particular dielectric have approximately equal maximum energy density, to the extent that the dielectric dominates their volume.[15]
For air dielectric capacitors the breakdown field strength is of the order 107 V/m and will be much less when other materials are used for the dielectric. The absolute breakdown voltage of most capacitors is nowhere near such a high number because of the very small distance between the plates. Typical ratings for capacitors used for general electronics applications range from a few volts to 100V or so. For high voltage applications physically much larger capacitors have to be used. In this field, there are a number of factors that can dramatically reduce the breakdown voltage below that to be expected by considering the breakdown field strength of the dielectric alone. For one thing, the geometry of the capacitor conductive parts (plates and connecting wires) is important. In particular, sharp edges or points hugely increase the electric field strength at that point and can lead to a local breakdown. Once this starts to happen, the breakdown will quickly "track" through the dielectric till it reaches the opposite plate and cause a short circuit.[16]
The usual breakdown route is that the field strength becomes large enough to pull electrons in the dielectric from their atoms thus causing conduction. Other scenarios are possible, such as impurities in the dielectric, and, if the dielectric is of a crystalline nature, imperfections in the crystal structure can result in an avalanche breakdown as seen in semi-conductor devices. Breakdown voltage is also affected by pressure, humidity and temperature.[17]
[edit] Equivalent circuit
Two equivalent circuits of a real capacitorAn ideal capacitor only stores and releases electrical energy, without dissipating any. In reality, all capacitors have imperfections within the capacitor's material that create resistance. This is specified as the equivalent series resistance or ESR of a component. This adds a real component to the impedance:
As frequency approaches infinity, the capacitive impedance (or reactance) approaches zero and the ESR becomes significant. As the reactance becomes negligible, power dissipation approaches PRMS. = VRMS.² /RESR.
Similarly to ESR, the capacitor's leads add equivalent series inductance or ESL to the component. This is usually significant only at relatively high frequencies. As inductive reactance is positive and increases with frequency, above a certain frequency capacitance will be canceled by inductance. High frequency engineering involves accounting for the inductance of all connections and components.
If the conductors are separated by a material with a small conductivity rather than a perfect dielectric, then a small leakage current flows directly between them. The capacitor therefore has a finite parallel resistance,[9] and slowly discharges over time (time may vary greatly depending on the capacitor material and quality).
[edit] Ripple current
Ripple current is the AC component of an applied source (often a switched-mode power supply) whose frequency may be constant or varying. Certain types of capacitors, such as electrolytic tantalum capacitors, usually have a rating for maximum ripple current (both in frequency and magnitude). This ripple current can cause damaging heat to be generated within the capacitor due to the current flow across resistive imperfections in the materials used within the capacitor, more commonly referred to as equivalent series resistance (ESR). For example electrolytic tantalum capacitors are limited by ripple current and generally have the highest ESR ratings in the capacitor family, while ceramic capacitors generally have no ripple current limitation and have some of the lowest ESR ratings.
[edit] Instability of capacitance
The capacitance of certain capacitors decreases as the component ages. In ceramic capacitors, this is caused by degradation of the dielectric. The type of dielectric and the ambient operating and storage temperatures are the most significant aging factors, while the operating voltage has a smaller effect. The aging process may be reversed by heating the component above the Curie point. Aging is fastest near the beginning of life of the component, and the device stabilizes over time.[18] Electrolytic capacitors age as the electrolyte evaporates. In contrast with ceramic capacitors, this occurs towards the end of life of the component.
Temperature dependence of capacitance is usually expressed in parts per million (ppm) per °C. It can usually be taken as a broadly linear function but can be noticeably non-linear at the temperature extremes. The temperature coefficient can be either positive or negative, sometimes even amongst different samples of the same type. In other words, the spread in the range of temperature coefficients can encompass zero. See the data sheet in the leakage current section above for an example.
Capacitors, especially older components, can absorb sound waves resulting in a microphonic effect. Vibration moves the plates, causing the capacitance to vary, in turn inducing AC current. Some dielectrics also generate piezoelectricity. The resulting interference is especially problematic in audio applications, potentially causing feedback or unintended recording. In the reverse microphonic effect, the varying electric field between the capacitor plates exerts a physical force, moving them as a speaker. This can generate audible sound, but drains energy and stresses the dielectric and the electrolyte, if any.
[edit] Capacitor types
Main article: Types of capacitor
Practical capacitors are available commercially in many different forms. The type of internal dielectric, the structure of the plates and the device packaging all strongly affect the characteristics of the capacitor, and its applications.
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