Monday, January 17, 2011

Awesome Websites You Have to Check Out





People in school

  • http://www.sparknotes.com/
  • http://www.cliffsnotes.com/
  • http://www.chegg.com/
  • http://www.salaryexpert.com
  • http://www.mathway.com/
  • http://www.collegeboard.com/
  • http://www.wolframalpha.com/
  • http://mathworld.wolfram.com/
  • http://www.cramster.com/
  • http://www.khanacademy.org/
  • http://academicearth.org/


Other (movies, music, wallpapers, helpful things, other blogs, etc)

  • http://www.ovguide.com/
  • http://interfacelift.com
  • http://www.cracked.com/
  • http://thechive.com/
  • http://www.genaw.com/lowcarb/recipes.html
  • http://www.mailinator.com/index.jsp
  • http://www.zappos.com/
  • http://www.retailmenot.com/
  • http://www.snagajob.com/
  • http://bhuvans.wordpress.com/2006/08/19/50-common-interview-qa/
  • http://www.politifact.com/truth-o-meter/promises/
  • http://www.techradar.com/news/internet/95-websites-you-should-totally-bookmark-today-639721
  • http://www.prankdial.com/
  • http://www.howstuffworks.com/
  • http://www.rotteneggs.com//
  • http://theoatmeal.com/
  • http://4walled.org/search.php?content=&board=&rez=&sfw=&random=Random
  • http://nik.bot.nu/browse.fu?srt=7
  • http://wallbase.net/random
  • http://stronglifts.com/
  • http://ironaddicts.com/forums/index.php?
  • http://www.lamebook.com/
  • http://atdhe.net/
  • http://www.printfriendly.com/
  • http://www.cutmypic.com/
  • http://www.dealextreme.com/
  • http://www.stilltasty.com/
  • http://www.historicaerials.com/default.aspx
  • http://www.bugmenot.com/
  • http://www.monoprice.com/home/index.asp

Movado Bold






There are certain brands that are synonymous with class – Rolls Royce, Verace, etc. In the watch world there are a lot of them. While cost has always gone hand-in-hand with prestige, Movado is attempting to bend that rule. The Movado Bold collection offers timepieces with a bit of sophistication at prices that won’t significantly dent your bank account.

The Bold collection removes some of the stuffiness and business-y feel of standard Movado’s and makes them a bit more casual (though still appropriate for office and formal wear). Most of the watches in the collection come with shots of color on a primarily black backdrop, though there are a few available for those who want to steer closer to the traditional Movado look. Plus, you can buy them online.

Sunday, January 16, 2011





How Headaches Work

It often begins so innocently -- just a vague sensation of slight pressure around your temples. But soon it intensifies. Before long, it feels as if your head is being squeezed like a stress ball. The pain makes it difficult to focus and starts to affect your mood as well. Only after several hours (and a few pills) does the headache finally subside.

The scenario just described is all too common for the many people who deal with tension headaches. And those who only get this type of headache are the lucky ones. Imagine, for example, the experience of a migraine headache. Strange distortions to your vision might come first as a warning sign, and then the full attack commences. Once the throbbing head pain and nausea are in full swing, resting in a dark room is all you'll feel like doing.

The pain of cluster headaches is even more intense, commonly described as the feeling of a hot poker being stuck into the brain through one's eye socket. Cluster headaches get their name because they come in repeated bursts, with each burst being so excruciating that unlucky victims can often do nothing but pace around in agony.

As opposed to primary headaches, such as the types of headache described above, secondary headaches arise from an underlying injury or illness. For example, a blow to the head can cause internal bleeding that increases pressure within the brain, creating an intense headache. Because secondary headaches can indicate a serious underlying problem, they should never be ignored

So how do you know when it's time to see the doctor about a headache, and what are the different types of headaches it might be? Also, why do headaches hurt in the first place, and how can they be treated?

Let's start on the next page by taking a closer look some of the major headache types.


---------------


The experience of a tension headache, described on the previous page, will be suffered by an estimated 90 percent of Americans during their lifetime. These headaches often feel like pressure is being applied uniformly around the head, or as if the head is being steadily squeezed in a vise. Lasting anywhere from 4 to 72 hours, tension headaches are the most common, but fortunately the least severe, of all headaches types.

Tension headaches can be further classified as episodic or chronic. Episodic tension headaches come and go sporadically, often during times of temporary fatigue, stress or anxiety. Over-the-counter medications and rest are generally effective at relieving episodic tension headaches.

Chronic tension headaches occur regularly, sometimes every day, for weeks to months at a time. Often, it's not simply stress or fatigue that causes chronic tension headaches, but physical or psychological problems. For example, a contributing factor could be constantly strained or stretched muscles, resulting from poor posture, eyestrain or a misaligned bite. Arthritis, joint disorders and depression are other common causes of chronic tension headaches. Untold numbers of people shrug off the pain of chronic headaches when a simple trip to the doctor could reveal the problem behind all the pain.

Around 30 million Americans experience the more intense migraine headaches, which can last for days and be painful to the point of preventing the victim from functioning. Migraine headaches have many unique symptoms that set them apart from tension headaches. For example, migraines are often described as a throbbing pain that begins on one side of the head and then spreads out. Migraines can also come with an increased sensitivity to light and worsen with physical exertion. As a result, migraine sufferers often choose to lie down in the dark in an attempt to reduce their pain.

Another characteristic of a migraine is that it's often accompanied by gastrointestinal disturbances, including abdominal pains. This symptom results from stimulation of the sympathetic nervous system, which is normally activated in response to stress or pain. The digestive system disturbances caused by migraines slow the uptake of ingested medications and reduces their effectiveness.

Migraines are also unique because they're often preceded by warning signs, which might include fatigue, depression, euphoria or even cravings for certain types of foods. For about 20 percent of migraine victims, the onset of an attack is signaled by an aura, which can manifest as an abnormal disturbance to any one of the five senses. Visual auras are by far the most common, and often take the form of wavy lines or flashing lights. (For the full story on migraines, check out How Migraines Work.)

One of the most intense types of headaches is a cluster headache. The pain is usually localized to one side of the head, generally behind one­ eye, which often becomes bloodshot as it tears up and swells. Sometimes the drooping of one eyelid or a reddening eye can indicate the onset of an attack.

Cluster headaches get their name because they can come in repeated bursts, with each burst lasting 15 minutes to three hours. These bursts of pain can appear and disappear, all without warning, in a cycle that continues for days, weeks or months. Sometimes the headaches then stop abruptly for many months, only to start up again during the same season of the following year. Thankfully, only about one in a thousand people has to deal with the experience of cluster headaches.

Tension, migraine and cluster headaches are the three most common types of primary headaches, but countless others exist as well. In total, more than 150 types of headache are categorized by the International Headache Society. Here are a few examples:

* Exertion or exercise headaches typically appear during or after physical activity, and are linked to the widening of blood vessels required to deliver increased amounts of oxygen to the muscles.
* Mixed headaches come with symptoms of both tension and migraine headaches. To treat mixed headaches, a combination of tension and migraine treatments must be carefully balanced.
* Ice cream headaches, also called "brain freeze," occurs when cold foods pressing on the roof of your mouth trigger overlying nerves to quickly widen blood vessels and increase blood flow -- possibly in an attempt to warm up the head as a response to the cold.
* Migraine equivalents are perceived as pain coming from somewhere besides the head. The most common type is an abdominal migraine, which can result in abdominal pain and vomiting, but no head pain.
* Hemiplegic migraine is a rare type of migraine that can cause temporary motor paralysis and sensory deficits on one side of the body, followed by a very severe headache.
* Chronic daily headache (CDH) sufferers experience headaches more than 15 days per month. There are several different types of CDH, including chronic migraines, chronic tension headaches and chronic cluster headaches.

Secondary headaches, in contrast to primary headaches, arise from an underlying injury or illness. They're uncommon but often very serious. There are many possible causes of secondary headaches, including brain tumors, strokes and infections. A sinus infection is one example of a common cause for a secondary headache. In this case, swelling, increased pressure and inflammation in the sinus cavity causes severe, localized pain. Migraines are commonly misdiagnosed as sinus headaches due to similar symptoms. Secondary headaches can indicate the presence of a serious issue that requires immediate medical treatment.

If you experience headaches that are severe, recurring or accompanied by unusual symptoms, it's smart to consult your primary care physician. He or she might ask a series of questions about risk factors and family history, perform a physical exam and run relevant diagnostic tests. Based on the findings of the examination, the physician may recommend lifestyle changes, prescribe drugs or refer you to a headache specialist. Unfortunately, distinguishing between different types of headaches isn't always easy. For example, there aren't even definitive tests able to confirm or rule out the presence of many headache types.

OK, so we've briefly covered some of the major types of headaches, but what causes them? And why are they so painful?




Neither your brain tissue nor the bones of your skull contain pain-sensitive nerve endings, so what is the source of painful headaches? The answer has to do with the parts of your head that do have nerve endings. For example, the network of blood vessels that supply the base and surface of your brain are wrapped with sensitive nerve fibers able to fire off pain signals with a hair trigger. Pain-sensitive nerves can also be found in the scalp and in the muscles of your head, among other places.

Stress, muscular tension, inflammation and the constriction or dilation of blood vessels can all trigger the pain-sensitive endings of these nerves to transmit signals that activate the pain centers in your brain. Tension headaches, for example, can be caused by the chronic stretching of muscles that become tensed with stress or prolonged strain. One source of prolonged muscle tension is eyestrain -- a common cause of headache.

As with so many brain-related issues, doctors and scientists haven't fully uncovered all of the precise mechanisms and underlying causes of each type of headache. However, the experts have uncovered and explored many of the typical pathways involved in certain types of headaches. For example, migraine headaches are linked to changes in the flow of blood through vessels in the brain. As part of the migraine process, certain patterns of brain activity are believed to trigger the constriction of blood vessels, reducing the brain's oxygen supply. As part of a chain reaction, the blood vessels then dilate (widen) in response, and certain chemicals known to cause inflammation are released. The nerves coiled around the blood vessels then shoot off throbbing pain signals that pulse along with the blood flow. Some experts have suggested that in people prone to migraines, these blood vessels are overly reactive to certain conditions.

While the precise biological mechanisms that cause headaches aren't fully understood, many common triggers, or factors that can lead to headaches, are associated with different headache types. For example, stress is the most commonly identified trigger for migraine headaches. Changes in hormone levels within the body are another known trigger, which is why three times more women than men experience migraines.

Experts know even less about the root cause of cluster headaches. Much of what is known about cluster headaches has to do with the common triggers. For example, alcohol (especially red wine) and cigarette smoke are two common factors that contribute to cluster headaches in an unknown way.

­­Because cluster headaches often occur around the same time each day, or during the same season each year, experts do know that cluster headaches are somehow related to the body's natural sleep/wake cycle and with seasonal changes. There's evidence that the hypothalamus, a part of your brain that acts as an internal biological clock of sorts, is involved in the onset of cluster headaches. Unlike tension headaches and migraines, cluster headaches are more common in men. The reason for this is unknown, but could be partially due to a higher link between males and certain risk factors, such as alcohol, smoking and physical exertion.

So we've taken a look at what causes the pain of headaches. Now how do you get rid of it?­

So what kinds of drugs are helpful for treating headaches, and how do they work? First off, there are two major approaches for treating a headache with drugs. Acute, or abortive, treatments are designed to treat a headache once it begins. However, when a person suffers from frequent headaches that don't respond well to acute treatments, it's worthwhile to consider a regular dosage schedule with preventative drugs, which can help keep headaches from occurring in the first place.

Acute drugs, designed to stop headaches, should be the first treatment approach. For milder headaches, or headaches in their early stages, over-the-counter analgesic drugs are often effective for this purpose. Common examples include acetaminophen (Tylenol) and nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin and ibuprofen. Over-the-counter analgesics work by acting on pain centers in the brain or by reducing inflammation around pain-sensitive nerves.

Some common analgesic drugs contain caffeine, which can help to treat headaches by speeding the uptake of medications into the bloodstream. Because caffeine is a stimulant that can alter blood flow within the brain, shifting caffeine levels can also be the cause of headaches. For example, if you try to quit a caffeine addiction cold turkey, you'll be taking away a brain-altering drug that your body was used to having around. Removing it can shift the balance of other chemicals in your brain and lead to withdrawal symptoms -- including major headaches.

Other acute treatments are designed to act directly on parts of the pathways known to be involved in headaches. For example, drugs classified as triptans or ergotamines are used to combat migraines by constricting dilated blood vessels and adjusting the balance of certain chemicals in the brain. To speed delivery into the blood stream, acute treatments are often given as nasal sprays or are sometimes injectable. In the case of migraines, these non-oral delivery methods are important, since the digestive disturbances associated with migraines can interfere with the uptake of ingested drugs. Quick delivery is also important for cluster headaches, which can come on quickly without warning.

Acute treatments for cluster headaches can be similar to the treatments for migraines, although sometimes pure oxygen breathed through a mask or numbing nasal sprays, such as lidocaine, can offer relief. When normal acute drug treatments aren't enough to relieve the pain of a severe headache, a doctor might prescribe stronger narcotic drugs. However, because these types of drugs are habit-forming, health professionals avoid prescribing them when possible.

Patients who experience headaches on a frequent basis sometimes benefit from preventative drug treatments, designed to reduce the chance that a headache will ever start. For example, four drugs approved by the FDA for migraine prevention have been in widespread use for many years. When conventional preventative drug treatments are ineffective for reducing headache frequency, certain antidepressant drugs might be prescribed as an alternative. These are thought to work by affecting the balance of serotonin, a chemical in the brain often involved in the development of headaches due to its effects on blood vessels. Preventative treatments are seldom perfect, though, so it's important to have acute treatments ready as a backup.

Are drugs the only way to treat headaches?

One of the most straightforward ways of preventing headaches is to avoid the triggers that cause them. Because stress is one of the most commonly reported triggers for migraine headaches, a good first line of defense for migraine sufferers is to reduce it by managing their daily schedules. Physical and mental stress can result from changing up your normal routine, so one way to lower stress levels is to keep your daily schedule of sleeping, exercising or eating meals constant.

­Other triggers might not be so easy to pick out. Certain foods and drinks, weather patterns and hormonal changes are just a few of the physical and environmental factors that can contribute to certain types of headaches. Because it can be difficult to identify the specific culprit in any one case, some sufferers find it worthwhile to keep a detailed log, called a headache diary. In this log, a person carefully records details about each headache he or she experiences and lists all notable conditions and factors surrounding it. By comparing the common factors that recur around most headaches, major triggers can often be identified and then avoided in the future.

Another way to lower stress levels and combat headaches is relaxation training. Here, the patient learns specific techniques that can be used to relax his or her body and mind. The next step from there might be biofeedback treatments, in which specialized equipment allows the patient to learn how to enhance his or her control over certain bodily responses related to stress. For example, the equipment might monitor heart rate, body temperature or tension in certain muscles, allowing the patient to learn what patterns of thoughts or activities can affect and control these responses. Once the patient learns how to attain better control of these stress-related responses, the equipment is no longer needed.

Other less conventional treatments might include herbal therapies or acupressure or acupuncture treatments. An individual seeking these types of alternative therapies should be sure to rely on a specialist with the proper training and credentials.


As doctors, scientists and engineers continue to learn about the brain and nervous system, more effective methods of combating headache will be developed. For example, specialized drug treatments might one day be custom designed to best treat each individual patient, based upon his or her specific condition and bodily makeup. As another example, a technique called deep brain stimulation is already used to treat certain brain disorders by stimulating specific areas of the brain with tiny pulses of electricity. In exploratory experiments, deep brain stimulation has been used to effectively control headaches that were otherwise untreatable.

How MRI Works

Dr. Raymond Damadian, a physician and scientist, toiled for years trying to produce a machine that could noninvasively scan the body with the use of magnets. Along with some graduate students, he constructed a superconducting magnet and fashioned a coil of antenna wires. Since no one wanted to be the first one in this contraption, Damadian volunteered to be the first patient.

When he climbed in, however, nothing happened. Damadian was looking at years wasted on a failed invention, but one of his colleagues bravely suggested that he might be too big for the machine. A svelte graduate student volunteered to give it a try, and on July 3, 1977, the first MRI exam was performed on a human being. It took almost five hours to produce one image, and that original machine, named the "Indomitable," is now owned by the Smithsonian Institution.

In just a few decades, the use of magnetic resonance imaging (MRI) scanners has grown tremendously. Doctors may order MRI scans to help diagnose multiple sclerosis, brain tumors, torn ligaments, tendonitis, cancer and strokes, to name just a few. An MRI scan is the best way to see inside the human body without cutting it open.


That may be little comfort to you when you're getting ready for an MRI exam. You're stripped of your jewelry and credit cards and asked detailed questions about all the metallic instruments you might have inside of you. You're put on a tiny slab and pushed into a hole that hardly seems large enough for a person. You're subjected to loud noises, and you have to lie perfectly still, or they're going to do this to you all over again. And with each minute, you can't help but wonder what's happening to your body while it's in this machine. Could it really be that this ordeal is truly better than another imaging technique, such as an X-ray or a CAT scan? What has Raymond Damadian wrought?

Let the magnets of this mighty machine draw you to the next page, and we'll take a look at what's going on inside.


MRI scanners vary in size and shape, and some newer models have a greater degree of openness around the sides. Still, the basic design is the same, and the patient is pushed into a tube that's only about 24 inches (60 centimeters) in diameter [source: Hornak]. But what's in there?

The biggest and most important component of an MRI system is the magnet. There is a horizontal tube -- the same one the patient enters -- running through the magnet from front to back. This tube is known as the bore. But this isn't just any magnet -- we're dealing with an incredibly strong system here, one capable of producing a large, stable magnetic field.

The strength of a magnet in an MRI system is rated using a unit of measure known as a tesla. Another unit of measure commonly used with magnets is the gauss (1 tesla = 10,000 gauss). The magnets in use today in MRI systems create a magnetic field of 0.5-tesla to 2.0-tesla, or 5,000 to 20,000 gauss. When you realize that the Earth's magnetic field measures 0.5 gauss, you can see how powerful these magnets are.

Most MRI systems use a superconducting magnet, which consists of many coils or windings of wire through which a current of electricity is passed, creating a magnetic field of up to 2.0 tesla. Maintaining such a large magnetic field requires a good deal of energy, which is accomplished by superconductivity, or reducing the resistance in the wires to almost zero. To do this, the wires are continually bathed in liquid helium at 452.4 degrees below zero Fahrenheit (269.1 below zero degrees Celsius) [source: Coyne]. This cold is insulated by a vacuum. While superconductive magnets are expensive, the strong magnetic field allows for the highest-quality imaging, and superconductivity keeps the system economical to operate.


Two other magnets are used in MRI systems to a much lesser extent. Resistive magnets are structurally like superconducting magnets, but they lack the liquid helium. This difference means they require a huge amount of electricity, making it prohibitively expensive to operate above a 0.3 tesla level. Permanent magnets have a constant magnetic field, but they're so heavy that it would be difficult to construct one that could sustain a large magnetic field.

There are also three gradient magnets inside the MRI machine. These magnets are much lower strength compared to the main magnetic field; they may range in strength from 180 gauss to 270 gauss. While the main magnet creates an intense, stable magnetic field around the patient, the gradient magnets create a variable field, which allows different parts of the body to be scanned.

Another part of the MRI system is a set of coils that transmit radiofrequency waves into the patient's body. There are different coils for different parts of the body: knees, shoulders, wrists, heads, necks and so on. These coils usually conform to the contour of the body part being imaged, or at least reside very close to it during the exam. Other parts of the machine include a very powerful computer system and a patient table, which slides the patient into the bore. Whether the patient goes in head or feet first is determined by what part of the body needs examining. Once the body part to be scanned is in the exact center, or isocenter, of the magnetic field, the scan can begin.

What goes on during a scan?

When patients slide into an MRI machine, they take with them the billions of atoms that make up the human body. For the purposes of an MRI scan, we're only concerned with the hydrogen atom, which is abundant since the body is mostly made up of water and fat. These atoms are randomly spinning, or precessing, on their axis, like a child's top. All of the atoms are going in various directions, but when placed in a magnetic field, the atoms line up in the direction of the field.

These hydrogen atoms have a strong magnetic moment, which means that in a magnetic field, they line up in the direction of the field. Since the magnetic field runs straight down the center of the machine, the hydrogen protons line up so that they're pointing to either the patient's feet or the head. About half go each way, so that the vast majority of the protons cancel each other out -- that is, for each atom lined up toward the feet, one is lined up toward the head. Only a couple of protons out of every million aren't canceled out. This doesn't sound like much, but the sheer number of hydrogen atoms in the body is enough to create extremely detailed images. It's these unmatched atoms that we're concerned with now.

Next, the MRI machine applies a radio frequency (RF) pulse that is specific only to hydrogen. The system directs the pulse toward the area of the body we want to examine. When the pulse is applied, the unmatched protons absorb the energy and spin again in a different direction. This is the "resonance" part of MRI. The RF pulse forces them to spin at a particular frequency, in a particular direction. The specific frequency of resonance is called the Larmour frequency and is calculated based on the particular tissue being imaged and the strength of the main magnetic field.

At approximately the same time, the three gradient magnets jump into the act. They are arranged in such a manner inside the main magnet that when they're turned on and off rapidly in a specific manner, they alter the main magnetic field on a local level. What this means is that we can pick exactly which area we want a picture of; this area is referred to as the "slice." Think of a loaf of bread with slices as thin as a few millimeters -- the slices in MRI are that precise. Slices can be taken of any part of the body in any direction, giving doctors a huge advantage over any other imaging modality. That also means that you don't have to move for the machine to get an image from a different direction -- the machine can manipulate everything with the gradient magnets.

But the machine makes a tremendous amount of noise during a scan, which sounds like a continual rapid hammering. That's due to the rising electrical current in the wires of the gradient magnets being opposed by the main magnetic field. The stronger the main field, the louder the gradient noise. In most MRI centers, you can bring a music player to drown out the racket, and patients are given earplugs.

When the RF pulse is turned off, the hydrogen protons slowly return to their natural alignment within the magnetic field and release the energy absorbed from the RF pulses. When they do this, they give off a signal that the coils pick up and send to the computer system. But how is this signal converted into a picture that means anything?

The MRI scanner can pick out a very small point inside the patient's body and ask it, essentially, "What type of tissue are you?" The system goes through the patient's body point by point, building up a map of tissue types. It then integrates all of this information to create 2-D images or 3-D models with a mathematical formula known as the Fourier transform. The computer receives the signal from the spinning protons as mathematical data; the data is converted into a picture. That’s the "imaging" part of MRI.

The MRI system uses injectable contrast, or dyes, to alter the local magnetic field in the tissue being examined. Normal and abnormal tissue respond differently to this slight alteration, giving us differing signals. These signals are transferred to the images; an MRI system can display more 250 shades of gray to depict the varying tissue [source: Coyne]. The images allow doctors to visualize different types of tissue abnormalities better than they could without the contrast. We know that when we do "A," normal tissue will look like "B" -- if it doesn't, there might be an abnormality.

An X-ray is very effective for showing doctors a broken bone, but if they want a look at a patient's soft tissue, including organs, ligaments and the circulatory system, then they'll likely want an MRI. And, as we mentioned on the last page, another major advantage of MRI is its ability to image in any plane. Computer tomography (CT), for example, is limited to one plane, the axial plane (in the loaf-of-bread analogy, the axial plane would be how a loaf of bread is normally sliced). An MRI system can create axial images as well as sagitall (slicing the bread side-to-side lengthwise) and coronal (think of the layers in a layer cake) images, or any degree in between, without the patient ever moving.

But for these high-quality images, the patient can't move very much at all. MRI scans require patients to hold still for 20 to 90 minutes or more. Even very slight movement of the part being scanned can cause distorted images that will have to be repeated. And there's a high cost to this kind of quality; MRI systems are very expensive to purchase, and therefore the exams are also very expensive.

But are there any other costs? What about the patient's safety?

Maybe you're concerned about the long-term impact of having all your atoms mixed about, but once you're out of the magnetic field, your body and its chemistry return to normal. There are no known biological hazards to humans from being exposed to magnetic fields of the strength used in medical imaging today. The fact that MRI systems don’t use ionizing radiation, as other imaging devices do, is a comfort to many patients, as is the fact that MRI contrast materials have a very low incidence of side effects. Most facilities prefer not to image pregnant women, due to limited research of the biological effects of magnetic fields on a developing fetus. The decision of whether or not to scan a pregnant patient is made on a case-by-case basis with consultation between the MRI radiologist and the patient's obstetrician.

However, the MRI suite can be a very dangerous place if strict precautions are not observed. Credit cards or anything else with magnetic encoding will be erased. Metal objects can become dangerous projectiles if they are taken into the scan room. For example, paperclips, pens, keys, scissors, jewelry, stethoscopes and any other small objects can be pulled out of pockets and off the body without warning, at which point they fly toward the opening of the magnet at very high speeds.

Big objects pose a risk, too -- mop buckets, vacuum cleaners, IV poles, patient stretchers, heart monitors and countless other objects have all been pulled into the magnetic fields of the MRI. In 2001, a young boy undergoing a scan was killed when an oxygen tank was pulled into the magnetic bore [source: McNeil]. Once, a pistol flew out of a policeman's holster, the force causing the gun to fire. No one was injured.

To ensure safety, patients and support staff should be thoroughly screened for metal objects prior to entering the scan room. Often, however, patients have implants inside them that make it very dangerous for them to be in the presence of a strong magnetic field. These include:

* Metallic fragments in the eye, which are very dangerous as moving these fragments could cause eye damage or blindness
* Pacemakers, which may malfunction during a scan or even near the machine
* Aneurysm clips in the brain, which could tear the very artery they were placed on to repair if the magnet moves them
* Dental implants, if magnetic

Most modern surgical implants, including staples, artificial joints and stents are made of non-magnetic materials, and even if they're not, they may be approved for scanning. But let your doctor know, as some orthopedic hardware in the area of a scan can cause distortions in the image.

How Paintball Works

The most basic piece of paintball equipment is the paintball itself. Just as in tennis or soccer, the ball is the central element of a paintball game. But unlike these older games, paintball has dozens, often hundreds, of "balls" in play at any one time. As the name implies, these balls are actually tiny containers of paint.

Paintballs have an incredibly simple construction. They're actually a lot like gel-cap pills, or bath-oil beads. They consist of a glob of colored liquid encased in a gelatin capsule. The "paint," which comes in many colors, is non-toxic, biodegradable and water soluble (so it will wash off skin and clothing).

Basically, a paintball is like a small water balloon, weighing only a few grams and measuring only 0.68 inches (1.7 cm) in diameter. The capsule holds up if you handle it or drop it from a short distance. When you shoot a paintball from a gun, however, it bursts on impact and leaves a 6-inch (13-cm) splatter of paint.

The job of the paintball gun, sometimes called a marker, is to get the paintball moving at a high rate of speed. In the basic gun, the propulsion system is compressed gas. This gas, which can be compressed carbon dioxide (CO2), nitrogen (N2) or ordinary air, is stored in small cartridges or larger tanks that can be attached to the gun. The gun is also attached to a hopper, which holds the paintballs.



Different guns have different firing systems, but the basic idea in all of them is the same. The gun is cocked in some way so that a paintball can fall out of the hopper and enter the gun's barrel. Then a small burst of compressed gas is released into the barrel, just behind the paintball. The compressed gas pushes the paintball from behind with much greater force than the air on the other side of the paintball, so the paintball is propelled forward.

In order to make the game safe, the power of paintball guns is strictly regulated. Guns in play are adjusted so that the top speed of the fired paintball is 300 feet (91 m) per second. A paintball moving at this speed is unlikely to cause serious injury if it hits your skin, though it will sting and may leave a bruise. Also, since wind resistance starts slowing the paintball down as soon as it leaves the gun, it has a reduced impact when fired from a greater distance. Speeding paintballs can cause serious injury to the eyes or ears, so paintball players always wear head protection.

The relatively slow projectile speed significantly limits the range of paintball fire: The paintball will fall to the ground in a much shorter distance than a faster projectile, such as a bullet. For this reason, firing a paintball gun is a sort of hybrid between firing a gun and throwing a ball. To hit somebody at a distance, the shooter has to tilt the gun up a little bit, so the paintball flies up in the air in an arc, like a football, and comes down on the target.

There are a variety of gun designs on the market, each with a slightly different system, but they are all based on the same principles. In the next section, we'll find out how guns generally work by examining the specific mechanism in a basic "pump" gun, a design that dominated paintball in the game's early days.


In the middle of the gun, there is a long valve tube. This runs from the barrel, where the paintballs are loaded, to a chamber at the back of the gun, where the gas cartridge is connected. Along this path, the tube passes through the bolt, a spring, the hammer and, at the gas-intake end of the gun, the valve seat. At the barrel end of the gun, the tube is always open. But the openings at the other end, which are positioned along the sides of the tube, are blocked off by the surrounding valve seat. The tube is held in position by a cup seal, pushed against the tube by a small spring and the pressure of the gas in the chamber. When the gun isn't cocked, the bolt extends into the barrel, blocking the entryway for the paintballs. To cock the gun, the shooter pulls the bolt backward, pushing against the spring so that the bolt butts up against the hammer. This motion does two things:

* As the bolt slides back, the ammunition intake opens, and a paintball can fall into the barrel.

* On the bottom of the hammer, there is a small spring-loaded latch called a sear. The sear, which pivots on a tiny pin, catches hold of the bolt when the bolt is pushed against the hammer. In this way, the sear binds the bolt and hammer together so they move as one unit.



After pulling the bolt back, the shooter pushes it (along with the hammer) forward. To fire the gun, the shooter pulls the trigger. The trigger pushes up against the back end of the sear, so the front end moves down. This releases the hammer from the bolt, and the spring rapidly propels the hammer backward. As the hammer moves backward, it pushes on a raised lip around the valve tube. This propels the valve tube backward with a burst of force that is greater than the forward force exerted by the rear spring and gas pressure. The valve tube is pushed back for an instant until the spring pushes it back into place. In this instant, the side openings on the tube are exposed, and the pressurized gas can flow through to the barrel. This burst of gas is strong enough to propel the paintball forward at a good rate of speed.


In autococker paintball guns, an adjustable valve automatically diverts compressed gas to the front of the gun after it is fired. This gas serves to push the bolt back again, so the gun recocks. This way, the shooter doesn't have to recock the gun with every shot. Automatic guns use the compressed air, or in some cases an electric motor, to continually recock and fire the gun as long as the trigger is held down. To find out more about these sorts of guns, check out WARPIG.com.

As paintball has evolved, the equipment has become more and more sophisticated. In the next section, we'll look at the history of paintball to find out when and why the game was invented. We'll also look at how the game is played and at other uses of paintball equipment.

Originally, paintball guns weren't intended for sport. The first guns were developed in the 1970s for use in forestry and agriculture. Foresters used the guns to mark certain trees (for research, planning trails). The guns were also used by farmers to mark cattle.

At some point, it occurred to a few foresters or farmers to shoot the guns at each other, and the game of paintball was born. But things didn't really get going until 1981, when a group of 12 weekend warriors got ahold of some forester guns and used them to play a grown-up version of "capture the flag."

In this game, which is still the predominant paintball activity, two teams try to find and steal the other's flag while protecting their own flag from capture. Players are "out" of the game when they get hit with a paintball, and the referee decrees that they are down. Referees are also there to make sure nobody makes physical contact with another player: This is one of the most important rules. A paintball game typically lasts from 15 to 40 minutes, but players may play for six hours or more at a stretch. You can hold a paintball game with only a few people on each team, or with hundreds of people on each team. To find out about other variations on the game of paintball, check out DirectPaintball.com.

The original 12 paintball enthusiasts had a lot to do with launching the sport. Soon after their first game, they bought up hundreds of tree-marking guns from the manufacturer (a company called Nelson) and began selling them to the general public. The idea caught on pretty quickly, and in 1982, the first paintball field opened in Rochester, New York. There are now paintball fields, as well as indoor paintball arenas, all over the world.

One of the most important developments in the history of paintball has been safety equipment. When a paintball hits you on the body, you feel a brief sting. But a paintball round in the eye could actually "knock your eye out." In the early days, many players wore no eye protection at all, and others wore only basic safety goggles. These days, paintball players usually wear full face masks and helmets. This protects them from damage to the eyes, ears, nose and mouth. Just as in football and hockey, safety equipment is absolutely necessary in paintball.










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