Wednesday, 11 April 2007

Brain death is defined as a complete and irreversible cessation of brain activity. Absence of apparent brain function is not enough. Evidence of irreversibility is also required. Brain-death may be confused with a persistent vegetative state.

Traditionally, death has been defined as the cessation of all body functions, including respiration and heartbeat. Since it became possible to revive some people after a period without respiration, heartbeat, or other visible signs of life, as well as to maintain respiration and blood flow artificially using life support treatments, an alternative definition for death was needed. In recent decades, the concept of "brain death" has emerged. By brain-death criteria, a person can be pronounced legally dead even if the heart continues to beat due to life support measures. The first nation in the world to adopt the brain death as the definition of legal death was Finland in 1971. In the United States, Kansas had made a similar law at an even earlier date.

A brain-dead individual has no electrical activity and no clinical evidence of brain function on physical examination (no response to pain, absent cranial nerve reflexes (pupillary response (fixed pupils), oculocephalic reflex, corneal reflexes), absent response to the caloric reflex test and no spontaneous respirations). It is important to distinguish between brain death and states that mimic brain death (eg. barbiturate intoxication, alcohol intoxication, sedative overdose, hypothermia, hypoglycemia, coma or chronic vegetative states). Some comatose patients can recover, and some patients with severe irreversible neurologic dysfunction will nonetheless retain some lower brain functions such as spontaneous respiration, loss of both cortex and brainstem function. Thus anencephaly, in which there is no higher brain present, is generally not considered brain death, although it is certainly an irreversible condition in which it may be appropriate to withdraw life support.

Note that brain electrical activity can stop completely, or apparently completely (a "flat EEG") for some time in deep anaesthesia or during cardiac arrest before being restored. Brain death refers only to the permanent cessation of electrical activity. Numerous people who have experienced such "flat line" experiences have reported near-death experiences, the nature of which is controversial.

It is presumed that a permanent cessation of electrical activity indicates the end of consciousness. Those who view the neo-cortex of the brain as solely responsible for consciousness, however, argue that only electrical activity there should be considered when defining death. In many cases, especially when elevated intracranial pressure prevents blood flow into the brain, the entire brain is nonfunctional; however, some injuries may affect only the neo-cortex.

The diagnosis of brain death needs to be rigorous to ascertain whether the condition is irreversible. Legal criteria vary from place to place, but generally require neurologic exams by two independent physicians. The exams must show complete absence of brain function, and may include two isoelectric (flat-line) EEGs 24 hours apart. The proposed Uniform Determination Of Death Act in the United States attempts to standardize criteria. The patient should have a normal temperature and be free of drugs that can suppress brain activity if the diagnosis is to be made on EEG criteria. Alternatively, a radionuclide cerebral blood flow scan that shows complete absence of intracranial blood flow can be used to confirm the diagnosis without performing EEGs.

Most organ donation for organ transplantation is done in the setting of brain death. In some nations (for instance, Belgium, Brazil, Poland, Portugal and France) everyone is automatically an organ donor, although some jurisdictions (such as Singapore) allow opting out from the system. Elsewhere consent from family members or next-of-kin is required for organ donation. The non-living donor is kept on ventilator support until the organs have been surgically removed. If a brain-dead individual is not an organ donor, ventilator and drug support is discontinued and cardiac death is allowed to occur.


What is fire?

A. Fire is heat and light from rapid combination of oxygen and other materials. The flame, which gives the light, is composed of glowing particles of burning material and luminous gases. For fire to exist, a combustible substance must be present, the temperature must be high enough to cause combustion, and enough oxygen must be present to sustain rapid combustion.

Is fire matter?
A. Matter is anything that has mass and occupies space. The flame itself is a mixture of gases (vaporized fuel, oxygen, carbon dioxide, carbon monoxide, water vapor, and many other things) and so is matter. The light produced by the flame is energy, not matter. The heat produced is also energy, not matter.

Q. What is the State of Matter of Fire or Flame? Is it a Liquid, Solid, or Gas?

A. The ancient Greeks and alchemists thought that fire was an element. They also considered earth, air, and water to be elements. However, the modern definition of an element defines it by the number of protons a pure substance possesses. Fire is made up of many different substances, so it is not an element.
For the most part, fire is a mixture of hot gases. Flames are the result of a chemical reaction, primarily between oxygen in air and a fuel, such as wood or propane. In addition to other products, the reaction produces carbon dioxide, steam, light, and heat. If the flame is hot enough, the gases are ionized and become yet another state of matter: plasma.

Fire is burning, which is combustion, and combustion is a type of oxidation reaction. Oxidation means combined chemically with oxygen . Oxidation is an exothermic reaction, meaning it gives releases heat energy.
The chemical equations for the oxidation of carbon and hydrogen are:
C+O2 -->CO2 (This reaction occurs when there is enough oxygen for the formation of carbon dioxide.)
2C+O2--> (This reaction occurs when there is only enough oxygen for the formation of carbon monoxide.)
2H2 +O2--> 2H2O
These reactions release the energy you feel as heat and light.

Fire is a rapid oxidation process that creates light, heat, and smoke, and varies in intensity. It is commonly used to describe either a fuel in a state of combustion (e.g., a campfire, or a lit fireplace or stove) or a violent, destructive and uncontrolled burning (e.g., in buildings or a wildfire). The discovery of making fire is considered one of the most important evolutions of humankind, for it allowed higher hominids to ward off wild animals, cook food, and provide warmth as well as a source of light in darkness.

Fire can be considered to be a low temperature partial plasma. Plasma; an ionized gas, usually considered to be a distinct state of matter.
A flame is an exothermic, self-sustaining, oxidizing chemical reaction producing energy and glowing hot flame, of which a very small portion is plasma. It consists of reacting gases and solids emitting visible and infrared light, the frequency spectrum of which is dependent on the chemical composition of the burning elements and intermediate reaction products.
In many cases such as burning organic matter like wood or incomplete combustion of gas, incandescent solid particles, soot produces the familiar red-orange 'fire' color light. This light has a continuous spectrum. Complete combustion of gas has a dim blue color due to the emission of single wavelength radiations from various electron transitions in the excited molecules formed in the flame. Usually oxygen is involved, but hydrogen burning in chlorine produces a flame as well, producing the toxic acid hydrogen chloride (HCl). Other possible combinations producing flames, amongst many more, are fluorine and hydrogen, or hydrazine and nitrogen tetroxide. Recent discoveries by the National Aeronautics and Space Administration (NASA) of the United States also has found that gravity plays a role. Modifying the gravity causes different flame types.
The glow of a flame is somewhat complex. Black-body radiation is emitted from soot, gas, and fuel particles, though the soot particles are too small to behave like perfect blackbodies. There is also photon emission by de-excited atoms and molecules in the gases. Much of the radiation is emitted in the visible and infrared bands. The color depends on temperature for the black-body radiation, and chemical makeup for the emission spectra. The dominant color in a flame changes with temperature. The photo of the forest fire is an excellent example of this variation. Near the ground, where most burning is occurring, it is white, the hottest color possible for organic material in general, or yellow. Above the yellow region, the color changes to orange, which is somewhat cooler, then red, which is cooler still. Above the red region, combustion no longer occurs, and the uncombusted carbon particles are visible as black smoke. To eliminate a flame in combustion vehicles there are different steps that are taken. This depends largely on whether the fuel is oil, wood, or high energy (such as fuel for jet engines).
The common distribution of a flame under normal gravity conditions depends on convection, as soot tends to rise to the top of a general flame, such as in a candle in normal gravity conditions, making it yellow. In microgravity or zero gravity, such as an environment in outer space, convection no longer occurs, and the flame becomes spherical, with a tendency to become more blue and more efficient (although they will go out if not moved steadily as the CO2 from combustion does not disperse in microgravity, and tends to smother the flame). There are several possible explanations for this difference, of which the most likely is that the temperature is evenly distributed enough that soot is not formed and complete combustion occurs. Experiments by NASA in microgravity reveal that diffusion flames in microgravity allow more soot to be completely oxidized after they are produced than diffusion flames on Earth, because of a series of mechanisms that behaved differently in microgravity when compared to normal gravity conditions.These discoveries have potential applications in applied science and industry, especially concerning fuel efficiency.

Typical temperatures of fires and flames
• Oxyhydrogen Flame (2000 °C or above)(3645 °F)
• Bunsen Burner Flame (min. to max. setting) (1300 to 1600 °C)(2372-2912 °F)

• Blowtorch Flame (1800 °C)(2370 °F)
• Candle Flame (760 °C)(1400 °F)
• Smouldering cigarette:
o Temperature without drawing: Side of the lit portion; 400 °C (or 750 °F);
Middle of the lit portion: 585 °C (or 1110 °F)
o Temperature during drawing: Middle of the lit portion: 700 °C (or 1290 °F)
• Always hotter in the middle.
Illinois Institute of Technology 3300 South Federal Street, Chicago, Dr. Anne Marie Helmenstine.