Clay Shields, assistant professor of computer science at Georgetown University, explains:
The short answer is: for many reasons. Computers crash because of errors in the operating system (OS) software or the machine’s hardware. Software glitches are probably more common, but those in hardware can be devastating.
The OS does more than allow the user to operate the computer. It provides an interface between applications and the hardware and directs the sharing of system resources among different programs. Any of these tasks can go awry. Perhaps the most common problem occurs when, because of a programming flaw, the OS tries to access an incorrect memory address. In some versions of Microsoft Windows, users might see a general protection fault (GPF) error message; the solution is to restart the program or reboot the computer. Other programming mistakes can drive the OS into an infinite loop, in which it executes the same instructions over and over. The computer appears to lock up and must be reset. Another way things can go amiss: when a programming bug allows information to be written into a memory buffer that is too small to accept it. The information “overflows” out of the buffer and overwrites data in memory, corrupting the OS.
Application programs can also cause difficulties. Newer operating systems (such as Windows NT and Macintosh OS X) have built-in safeguards, but application bugs can affect older ones. Software drivers, which are added to the OS to run devices such as printers, may stir up trouble. That’s why most modern operating systems have a special boot mode that lets users load drivers one at a time, so they can determine which is to blame.
Hardware components must also function correctly for a computer to work. As these components age, their performance degrades. Because the resulting defects are often transient, they are hard to diagnose. For example, a computer’s power supply normally converts alternating current to direct current. If it starts to fail and generates a noisy signal, the computer can crash.
The random-access memory (RAM) can err intermittently, particularly if it gets overheated, and that can corrupt the values the RAM stores at unpredictable times and cause crashes. Excessive heat can crash the central processing unit (CPU). Fans, which blow cooling air into the computer’s case, may fail, making components susceptible to overheating. And they push dirt and dust inside, which can lead to intermittent short circuits; compressed air or a vacuum cleaner easily gets rid of such dirt. Still other hardware problems, including a failed video or network card, are trickier to identify, requiring software tests or the sequential replacement of components.
Errors on a computer’s hard drive are the most intractable. Hard disks store information in units called sectors. If sectors go bad, the data stored on them go, too. If these sectors hold system information, the computer can seize up. Bad sectors also can result from an earlier crash. The system information becomes
corrupted, making the computer unstable; ultimately the OS must be reinstalled. Last and worst, a computer can fail completely and permanently if the machine gets jarred and the head that reads information makes contact with the disk surface.
Saturday, March 13, 2010
Why do hangovers occur?
Sant P. Singh, a professor and chief of endocrinology, diabetes and metabolism at Chicago Medical School, offers this answer:
Several factors appear to be involved in getting a hangover—the unpleasant consequence visited on 75 percent ofthose who drink alcohol to intoxication. The effects includeheadache, nausea, vomiting, thirst, dryness of the mouth,tremors, dizziness, fatigue and muscle cramps. Often there is an accompanying slump in cognitive and visual-spatial skills.
A hangover has been suggested to be an early stage of alcohol withdrawal. Mild shakiness and sweats can occur; some people may even hallucinate. Acetaldehyde, a toxic breakdown product of alcohol metabolism, plays a role in producing symptoms. Chemicals known as congeners that are formed during alcohol processing and maturation also increase the likelihood and severity of a hangover; as a rule of thumb, the darker the liquor, the more congeners it contains. The toxins in congeners are distributed throughout the body as the liver breaks down the alcohol. Last, hangovers cause changes in the blood levels of various hormones, which are responsible for some symptoms. For example, alcohol inhibits antidiuretic hormone, which leads to excessive urination and dehydration. Blood aldosterone and renin levels also increase with a hangover—but unlike antidiuretic hormone, they do not correlate well with symptomatic severity, so their role is less clear.
Individuals are more prone to develop a hangover if they drink alcohol rapidly, mix different types of drinks, and do not dilute the absorption of liquor by eating food or drinking nonalcoholic beverages. Sugar and fluids can help overcome the ensuing hypoglycemia and dehydration, and antacids can reduce nausea. To reduce headache, anti-inflammatory drugs should be used cautiously: aspirin may irritate the stomach, and the toxic effects of acetaminophen on the liver can be amplified by alcohol. Other drugs have been used to treat hangovers, but most have questionable value.
Several factors appear to be involved in getting a hangover—the unpleasant consequence visited on 75 percent ofthose who drink alcohol to intoxication. The effects includeheadache, nausea, vomiting, thirst, dryness of the mouth,tremors, dizziness, fatigue and muscle cramps. Often there is an accompanying slump in cognitive and visual-spatial skills.
A hangover has been suggested to be an early stage of alcohol withdrawal. Mild shakiness and sweats can occur; some people may even hallucinate. Acetaldehyde, a toxic breakdown product of alcohol metabolism, plays a role in producing symptoms. Chemicals known as congeners that are formed during alcohol processing and maturation also increase the likelihood and severity of a hangover; as a rule of thumb, the darker the liquor, the more congeners it contains. The toxins in congeners are distributed throughout the body as the liver breaks down the alcohol. Last, hangovers cause changes in the blood levels of various hormones, which are responsible for some symptoms. For example, alcohol inhibits antidiuretic hormone, which leads to excessive urination and dehydration. Blood aldosterone and renin levels also increase with a hangover—but unlike antidiuretic hormone, they do not correlate well with symptomatic severity, so their role is less clear.
Individuals are more prone to develop a hangover if they drink alcohol rapidly, mix different types of drinks, and do not dilute the absorption of liquor by eating food or drinking nonalcoholic beverages. Sugar and fluids can help overcome the ensuing hypoglycemia and dehydration, and antacids can reduce nausea. To reduce headache, anti-inflammatory drugs should be used cautiously: aspirin may irritate the stomach, and the toxic effects of acetaminophen on the liver can be amplified by alcohol. Other drugs have been used to treat hangovers, but most have questionable value.
Friday, February 26, 2010
Compass in your eye
PEOPLE CAN see the Earth's magnetic field, albeit unconsciously.
The effect is too small to be noticeable, but other animals may use
their eyes in this way to get their bearings, says a report in New
Scientist.
The Earth's magnetic field lines vary depending where you are. They
always run south to north, but are horizontal only at the equator,
dipping in at a steeper angle the greater the latitude.
Birds and some other migrating animals seem to use these angles to
help them navigate, and one theory is that they do so using lightsensitive
cells.
German researchers investigated whether people's eyes are sensitive
to these field lines .
They measured the lowest level of light that people could detect in a
small spot straight ahead of them. They had people face south, west
and south south-west, and used a magnetic coil to create a horizontal
north-facing field.
They then repeated the experiment with the Earth's natural magnetic
field, which in Germany is angled 70 degrees downwards towards
the north.
When the field lines coincided with the direction of the spot, which
only occurred when people faced south in a horizontal field, the
threshold of brightness at which their eyes first detected a very dim
light went up.
The effect was small but significant, say the researchers. Although
we are not conscious of it, the same probably happens when
photoreceptors in the eye are aligned with the Earth's magnetic field.
American researchers studying newts say the light compass in them
probably use specialized photoreceptors to detect the magnetic field
lines.
Magnetic fields interact with spinning electrons, and could
theoretically influence photoreceptor chemicals at the quantum level,
altering their efficiency.
The effect is too small to be noticeable, but other animals may use
their eyes in this way to get their bearings, says a report in New
Scientist.
The Earth's magnetic field lines vary depending where you are. They
always run south to north, but are horizontal only at the equator,
dipping in at a steeper angle the greater the latitude.
Birds and some other migrating animals seem to use these angles to
help them navigate, and one theory is that they do so using lightsensitive
cells.
German researchers investigated whether people's eyes are sensitive
to these field lines .
They measured the lowest level of light that people could detect in a
small spot straight ahead of them. They had people face south, west
and south south-west, and used a magnetic coil to create a horizontal
north-facing field.
They then repeated the experiment with the Earth's natural magnetic
field, which in Germany is angled 70 degrees downwards towards
the north.
When the field lines coincided with the direction of the spot, which
only occurred when people faced south in a horizontal field, the
threshold of brightness at which their eyes first detected a very dim
light went up.
The effect was small but significant, say the researchers. Although
we are not conscious of it, the same probably happens when
photoreceptors in the eye are aligned with the Earth's magnetic field.
American researchers studying newts say the light compass in them
probably use specialized photoreceptors to detect the magnetic field
lines.
Magnetic fields interact with spinning electrons, and could
theoretically influence photoreceptor chemicals at the quantum level,
altering their efficiency.
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