Computed tomography (CT)

2008-04-20T04:07:00.000-07:00

Computed tomography (CT) is a medical imaging method employing tomography. Digital geometry processing is used to generate a three-dimensional image of the inside of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation. The word "tomography" is derived from the Greek tomos (slice) and graphein (to write).

Computed tomography was originally known as the "EMI scan" as it was developed at a research branch of EMI, a company best known today for its music and recording business. It was later known as computed axial tomography (CAT or CT scan) and body section roentgenography.

CT produces a volume of data which can be manipulated, through a process known as windowing, in order to demonstrate various structures based on their ability to block the X-ray beam. Although historically (see below) the images generated were in the axial or transverse plane (orthogonal to the long axis of the body), modern scanners allow this volume of data to be reformatted in various planes or even as volumetric (3D) representations of structures.

Although most common in healthcare, CT is also used in other fields, for example nondestructive materials testing. Another example is the DigiMorph project at the University of Texas at Austin which uses a CT scanner to study biological and paleontological specimens.

Fire

2008-02-20T03:11:00.001-08:00

Fire is the heat and light energy released during a chemical reaction, in particular a combustion reaction. Depending on the substances alight, and any impurities within, the color of the flame and the fire intensity might vary.

Flaming fires

Flaming fires involve the chemical oxidation of a fuel (combustion or release of energy) with associated flame, heat, and light. The flame itself occurs within a region of gas where intense exothermic reactions are taking place. An exothermic reaction is a chemical reaction whereby heat and energy are released as a substance changes to a more stable chemical form (in the case of fire, usually generating carbon dioxide and water). As chemical reactions occur within the fuel being burned, light and heat are released. Depending upon the specific chemical and physical change taking place within the fuel, the flame may or may not emit light in the visible spectrum. For example, burning alcohol or burning hydrogen is usually invisible to the naked eye although the heat given off is tremendous.

The visible flame has little mass, and it is comprised of luminous gases which emit energy (photons) as part of the oxidation process. The color of the flame is dependent upon the energy level of the photons emitted. Lower energy levels produce colors toward the red end of the light spectrum while higher energy levels produce colors toward the blue end of the spectrum. The hottest flames are white in appearance. The color of a fire may also be affected by chemical elements in the flame, such as barium giving a green flame color. The flame color depends also on the unoxidized carbon particles. In some cases there is a partial fuel oxidation due to oxygen lack in the central part of the flame, where combustion reactions take place. In such cases the unoxidized hot carbon particles emit radiation in the light spectrum, resulting in a yellow/red flame, such that of a common house fireplace.