entropy

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The tendency of a system that is left to itself to descend into chaos
A measure of the amount of information and noise present in a signal
For parents, the concept of entropy is easy to understand, because children inevitably increase entropy, while parents struggle to reduce it Entropy is a measure of disorganization, which children create when they spread their Happy Meal toys across a room (and perhaps the best measure of economic progress is whether we give our children these opportunities to create entropy) In the context of IFE, the entropy of deuterium and tritium are much lower for D-T ice than D-T gas at the same temperature The practical result is that D-T gas, when compressed to a high pressure, reaches much higher temperatures than D-T ice, potentially a temperature high enough to initiate a fusion burn Unfortunately, it takes a lot more energy to compress D-T gas to this temperature--thus the desire in IFE to start with most of the D-T fuel as easily-compressed D-T ice
A certain property of a body, expressed as a measurable quantity, such that when there is no communication of heat the quantity remains constant, but when heat enters or leaves the body the quantity increases or diminishes
(communication theory) a numerical measure of the uncertainty of an outcome; "the signal contained thousands of bits of information"
Entropy is a state of disorder, confusion, and disorganization. a lack of order in a system, including the idea that the lack of order increases over a period of time (entropie, from trepein ). Measure of a system's energy that is unavailable for work, or of the degree of a system's disorder. When heat is added to a system held at constant temperature, the change in entropy is related to the change in energy, the pressure, the temperature, and the change in volume. Its magnitude varies from zero to the total amount of energy in a system. The concept, first proposed in 1850 by the German physicist Rudolf Clausius (1822-1888), is sometimes presented as the second law of thermodynamics, which states that entropy increases during irreversible processes such as spontaneous mixing of hot and cold gases, uncontrolled expansion of a gas into a vacuum, and combustion of fuel. In popular, nontechnical use, entropy is regarded as a measure of the chaos or randomness of a system
1 A measure of the dispersal or degradation of energy 2 A measure of the disorder or randomness in a closed system For example, the entropy of an unburned piece of wood and its surroundings is lower than the entropy of the ashes, burnt remains, and warmed surroundings due to burning the that piece of wood
The entropy is regarded as measured from some standard temperature and pressure
In macroscropic thermodynamic, entropy is simply defined as a state variable whose changes in value are defined by the Second Law and whose absolute value for some matierals can be fixed according to the Third Law However, statistical mechanics provides more insight into the nature of entropy It is a measure of the "disorder" of a system, by which is meant the number of available configurations or microscopic states that are consistent with a given macroscopic or average state This relation, S = k ln , is inscribed on Boltzmann's tombstone
the measure of randomness or disorder of a system; in chemical reactions and molecular processes, spontaneous progress is always made in a direction which will increase the total state of disorder; as an analogy, throwing a bundle of confetti in the air will result in many isolated pieces scattered all over the ground, not the single bundle from which the pieces originated
is a measure of the unavailability of energy in a substance
a measure of the degree of disorder or randomness in a system
A measure of the disorder of a system
Entropy is the measure of the disorder or randomness of energy and matter in a system
The production of heat in every energy change The gradual "winding down" of the universe The amount of disorder and randomness in a system
The randomness, or disorder in a system
The entropy of a system is defined in terms of the number the number of states accessible to it by the relation It provides a logarithmic measure of the degree of randomness of a system
(thermodynamics) a thermodynamic quantity representing the amount of energy in a system that is no longer available for doing mechanical work; "entropy increases as matter and energy in the universe degrade to an ultimate state of inert uniformity"
A measure of the disorder in a system
The degree of randomness or disorder in a system
The degree of randomness of or disorder of a system
If a small amount, h, of heat enters the body when its temperature is t in the thermodynamic scale the entropy of the body is increased by h &?; t
A thermodynamic state or property that measures the degree of disorder or randomness of a system
1 A measure of the extent to which the energy of a system is unavailable A mathematically defined thermodynamic function of state, the increase in which gives a measure of the energy of a system which has ceased to be available for work during a certain process: ds = (du + pdv)/T >= dq/T where s is specific entropy; u is specific internal energy; p is pressure; v is specific volume; T is Kelvin temperature; and q is heat per unit mass For reversible processes, ds = dq/T In terms of potential temperature , ds = cp (d/)where cp is the specific heat at constant pressure See third law of thermodynamics
For our purposes, the entropy measure gives us the average amount of information in bits in some attribute of an instance The rationale for this is as follows: -log2(p) is the amount of information in bits associated with an event of probability p - for example, with an event of probability ½, like flipping a fair coin, log2((p) is -log2(½) = 1, so there is one bit of information This should coincide with our intuition of what a bit means (if we have one) If there is a range of possible outcomes with associated probabilities, then to work out the average number of bits, we need to multiply the number of bits for each outcome (-log2(p) by the probability p and sum over all the outcomes This is where the formula comes from Entropy is used in the ID3 decision tree induction algorithm
The tendency of systems to lose energy and order and to settle to more homogenous (similar) states Often referred to as 'Heat Death' or the 2nd Law of Thermodynamics
Sometimes called the thermodynamic function
Measure of the disorder of a system
A measure of the disorder in a system; thermodynamic systems tend to react in ways that increase their entropy
A measure of the unavailability of energy in a substance
the disorder of a system, said always to increase with time by the second law of thermodynamics
thermodynamics, countable
A measure of the amount of disorder in a system
a measurement of the disorder or randomness of a system Entropy is symbolized by S and entropy change by DS The entropy of a pure crystalline substance is 0 at absolute zero, and increases as the temperature increases The second law of thermodynamics states that "every system left to itself will change to a position of maximum entropy"
{i} measure of the level of disorder in a system; amount of unavailable energy in a system (Thermodynamics)
(1) The internal energy of a system that cannot be converted to mechanical work (2) The property that describes the disorder of a system
arrow of time
Shannon entropy
information entropy
algorithmic entropy
Kolmogorov complexity
entropic
Of, pertaining to, or as a consequence of entropy
information entropy
A measure of the uncertainty associated with a random variable ; a measure of the average information content one is missing when one does not know the value of the random variable ; usually in units such as bits

A passphrase is similar to a password, except it can be a phrase with a series of words, punctuation, numbers, whitespace, or any string of characters you want. Good passphrases are 10-30 characters long, are not simple sentences or otherwise easily guessable (English prose has only 1-2 bits of entropy per character, and provides very bad passphrases), and contain a mix of upper and lowercase letters, numbers, and non-alphanumeric characters. — BSD General Commands Manual : ssh-keygen(1), October 2, 2010.

conformational entropy
entropy calculated from the probability that a state could be reached by chance alone
entropy