Enthalpy is the heat energy exchange that takes place during chemical reactions. It has the symbol H and is measured in kJ/mol, or kilojoules per mole. The energy exchanged with the surrounding environment at constant pressure is called the enthalpy change of a reaction. When the reaction is giving off heat, it is said to be exothermic. In this situation, the enthalpy change is negative, since the reaction is going from high energy to low energy due to the loss of heat energy to its surroundings. If energy flows from the surrounding environment into a system, or heat is being taken in, it is said to be endothermic. In this instance, the enthalpy change is positive as the system is gaining energy in the form of heat.For an exothermic reaction, the energy of the reactants of the reaction would be higher than the energy of the products resulting. The opposite is true for endothermic reactions. Two ways of measuring a change in enthalpy are a simple calorimeter or a simple flame calorimeter. A simple calorimeter is made up of a container of water, with heat transferred into the water. The change in temperature of the water that is recorded will be due to the energy exchange of the reaction. When a simple calorimeter is used, the reaction takes place within the water in the calorimeter itself.
A bacterial artificial chromosome (BAC) is one of a class of tools, called vectors, that microbiologists use to insert genes into a bacterium — usually e coli. Inserting genes alters the properties of the bacterium in a process called transformation. A scientist can alter a strain of bacteria using a BAC, then compare the altered bacteria to an unaltered strain to discover what role the inserted genes play in cell biology. The bacterial artificial chromosome is one of a number of plasmid-based vectors. Plasmids are free-floating rings of DNA that many bacteria contain in addition to their chromosomal DNA. Plasmids like the bacterial artificial chromosome are inserted into bacteria using a process called electroporation. Electroporation involves disturbing the cell membrane with an electric shock, which creates temporary openings through which molecules may be inserted. F-factor plasmids are used naturally by bacteria to transfer DNA from one cell to another during periods of environmental stress, in order to increase genetic variability and the likelihood of survival.
There are three types of fingerprint patterns within what is known as the Henry Classification System, a method of differentiating fingerprint types that has endured for more than 100 years. Although every human fingerprint is unique, the Henry system breaks down the varieties into three types — the arch, the loop and the whorl.
The arch fingerprint type has a pattern of ridges that curve upward, forming what resembles a stacked row of arches. In the plain arch, the lines usually flow consistently from one side of the fingertip to the other. This is widely considered the easiest type of print to identify.
The loop fingerprint has ridges that curl around the fingertip. The ridges point in one direction before rising and flowing in the opposite direction. Like the arch type, the loop is divided into two categories. The radial loop’s ridges move in a downward slope from the direction of the pinky toward the thumb. The ulnar loop’s ridges move downward in the opposite direction toward the pinky, the digit found on the same side as the forearm’s long ulna bone.
One of the most varied, complex fingerprint patterns is the whorl, which is broken down into four sub-categories. Whorl ridges form frequently closed, rounded shapes that expand outward from the delta, the point at which the ridges converge or form a different pattern.
The most important factor determining the damage of an asteroid impact is the energy it releases upon impact. This is calculated by multiplying half the asteroid's mass by the square of its velocity. The typical range of asteroid velocities is quite limited — most measured values are between 12 and 20 km/sec (7.5 - 12.4 mi/sec). Comets are much faster, ranging between 50 and 70 km/sec (31 - 43.5 mi/sec). Other factors influencing the environmental effects of an asteroid impact include its size (obviously), angle of impact (the most probable is 45 degrees), and impact surface (water, silicate rock, or crystalline rock). Asteroids about a meter in diameter are thought to enter the Earth's atmosphere about once every month, leaving 100 ft (30 m) craters in their wake. The largest asteroid impact in the last 4 billion years is thought to be the asteroid which created the Vredefort crater in South Africa, with a diameter of about 20 km (12 mi).
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Food is spoilt when certain microorganisms begin to reproduce on and digest its surface, releasing harmful toxins as byproducts of their metabolic processes. Sometimes the microorganisms themselves — mostly bacteria and fungus — present a risk to humans, as ingesting them is an invitation to reproduce within the host’s body. Therefore, to preserve food, one must ensure that it is difficult or impossible for microorganisms to reproduce or survive in it.
High-salt and high-sugar mixtures preserve food because they are absorbent relative to the internal fluid of microorganisms, causing them to shrivel up and eventually die. When a layer of a high-salt or high-sugar substance is used to preserve food, the food is protected from microbial invasions.
The gyroscope was named by Leon Foucault, a French physicist, in an attempt to demonstrate the earth's rotation. A freely rotating disk, called a rotor, was mounted on a spinning axis in the center of a larger, stable wheel. As the earth spun on its axis, the stable wheel rotated with it, but the rotor did not move. The movement of the mounted wheel followed the rotation of the earth, rotating around the center disk and demonstrating the earth's spin.
In addition to the rotor, modern gyroscopes typically have two additional rings, called gimbals, in the center of a larger stable ring. The rotor spins on an axle connected to the smaller, inner gimbal. This gimbal rotates on a horizontal axis created by its connection to the larger, outer gimbal. The larger gimbal rotates vertically and spins on an axis connected to the stable outside ring
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An electromagnetic relay is a type of electrical switch controlled by an electromagnet. The electromagnetic relay is used in a variety of applications, including alarms and sensors, signal switching, and the detection and control of faults on electrical distribution lines. The core of the electromagnetic relay, naturally, is an electromagnet, formed by winding a coil around an iron core. When the coil is energized by passing current through it, the core in turn becomes magnetized, attracting a pivoting iron armature. The electromagnetic relay usually makes use of a diode to restrict the flow of the charge, with the cathode connected at the most positive end of the coil. The electromagnetic relay is capable of controlling an output of higher power than the input, and it is often used as a buffer to isolate circuits of varying energy potentials as a result.
A car engine is also known as an internal combustion engine, and is designed to use small, controlled explosions to create the power necessary to move the vehicle. This type of engine is used in lawnmowers, motorcycles and other motorized devices. All car engines are designed to use a four stroke combustion cycle. The four strokes are the intake, compression, combustion and exhaust. These strokes are repeated in quick succession to generate power. All parts of the combustion cycle take place within an enclosed car engine.
A small, controlled explosion forces the piston, or "arms," of the engine to move. When the energy from the explosion is almost worn out, another explosion occurs, forcing the pistons to move again. This recurring cycle generates the power needed
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Nanotechnology is a branch of science that deals with particles 1-100 nanometers in size. Experts believe possible dangers of nanotechnology lie in how these tiny particles might interact with the environment, and more importantly, with the human body. Complicating the dangers of nanotechnology, size and shape of nanoparticles affect the level of toxicity, preempting the ease of uniform categories even when considering a single element. In general, experts report smaller particles are more bioactive and toxic. Their ability to interact with other living systems increases because they can easily cross the skin, lung, and in some cases the blood/brain barriers. Once inside the body, there may be further biochemical reactions like the creation of free radicals that damage cells.
Nanotechnology should not be confused with molecular nanotechnology (MNT) a still theoretical science dedicated to manufacturing products from the atom up through use of nanoscale machines.
Thunder is caused by lightning, which is essentially a stream of electrons flowing between or within clouds, or between a cloud and the ground. The air surrounding the electron stream is heated to as hot as 50,000 degrees Farhenheit, which is three times hotter than the surface of the sun. As the superheated air cools it produces a resonating tube of partial vacuum surrounding the lightning's path. The nearby air rapidly expands and contracts. This causes the column to vibrate like a tubular drum head and produces a tremendous crack. As the vibrations gradually die out, the sound echoes and reverberates, generating the rumbling we call thunder.The speed of sound is even more insignificant when compared to the speed of light. The light from the flash reaches us in a fraction of a second, whereas the sound lags along like a snail following an interplanetary rocket.
The audiovisual spectacle of thunder and lightning is a combination of the dynamics of the vibration of air molecules and their disturbance by electrical forces. It is an awesome show--and one that reminds all of us of the powers of nature and our own insignificance in relation to them.
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