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Topic: Reversible process

Related Topics

Thermodynamic reversibility

Quasistatic process

Isothermal process

Adiabatic process

Entropy

Isobaric process

Carnot cycle

Isentropic process

Heat engine

Carnot heat engine

Thermodynamics

Ideal gas law

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	A Process
		Processes may be totally reversible, allowing the process to move backwards from the final state to the initial state.
		Reversible processes are such that no information is unrecoverable (lost) during the operation of this process; thus, given the output, one can still move back to the input.
		Processes consistent with assumptions defined by mathematicians may be defined as mathematical functions, such as those obtained by pressing mathematical operator keys on a calculator.
	ils.unc.edu /~losee/b5/node4.html (1953 words)

	Reversible process (thermodynamics) - Wikipedia, the free encyclopedia
		A process that is not reversible is termed irreversible.
		A reversible process changes the state of a system in such a way that the net change in the combined entropy of the system and its surroundings is zero.
		Reversible processes define the boundaries of how efficient heat engines can be in thermodynamics and engineering: a reversible process is one where no heat is lost from the system as "waste", and the machine is thus as efficient as it can possibly be (see Carnot cycle).
	en.wikipedia.org /wiki/Reversible_process_(thermodynamics) (567 words)

	Reversible Process -- from Eric Weisstein's World of Physics
		A reversible process is one in which the timescale is assumed to be so slow that every intermediate state deviates only infinitesimally from equilibrium.
		A good approximation to a reversible process would be realized by removing the sand one grain at a time and carefully recording the thermodynamic variables (temperature and pressure in this case) after each grain of sand is removed.
		This would be a reversible expansion and one could individually return the grains of sand one at a time and reproduce each intermediate state exactly, thus reversing the transformation.
	scienceworld.wolfram.com /physics/ReversibleProcess.html (168 words)

	Reversibility - Wikipedia, the free encyclopedia
		A reversible process in thermodynamics, a process or cycle such that the net change at each stage in the combined entropy of the system and its surroundings is zero.
		A reversible reaction in chemistry, for which the position of the chemical equilibrium is very sensitive to the imposed physical conditions; so the reaction can be made to run either forwards or in reverse by changing those conditions.
		Irreversibility - in thermodynamics, processes that are not reversible are termed irreversible.
	en.wikipedia.org /wiki/Reversible_process (244 words)

	Reversible processes (via CobWeb/3.1 planetlab1.netlab.uky.edu) (Site not responding. Last check: 2007-11-04)
		This is the hallmark of a reversible process: an infinitesimal change in the external conditions reverses the direction of the change.
		A finite reversible process passes through an infinite set of such states, and so can be drawn as a solid line on the plot.
		During an irreversible process the system is not in an equilibrium state, and so cannot be represented on the plot; an irreversible process is often drawn as a straight dotted line joining the initial and final equilibrium states.
	theory.ph.man.ac.uk.cob-web.org:8888 /~judith/stat_therm/node23.html (260 words)

	physics - Reversible process (via CobWeb/3.1 planetlab2.isi.jhu.edu) (Site not responding. Last check: 2007-11-04)
		In thermodynamics, a reversible process (or reversible cycle if the process is cyclic) is a process that can be "reversed" by means of infinitesimal changes in some property of the system (Sears and Salinger, 1986).
		Alternatively, a reversible process changes the state of a system in such a way that the net change in the combined entropy of the system and its surroundings (if any) is zero.
		Reversible processes define the boundaries of how efficient heat engines can be in thermodynamics and engineering: a reversible process is one where no heat is lost from the system as "waste" (or "disorder"), and the machine is thus as efficient as it can possibly be (see Carnot cycle).
	www.physicsdaily.com.cob-web.org:8888 /physics/Reversible_process (194 words)

	UNIFIED ENGINEERING September 1996 (Site not responding. Last check: 2007-11-04)
		The process is not reversible; That is there is no way to undo the change and leave no mark on the rest of the universe.
		If we carefully extract the maximum possible work from the system with a piston, then it is conceivable to think that we could reverse the process and put that work back into the system and everything (the system and the surroundings) would be back to the initial state.
		For reversible processes (the most efficient processes possible), the net change in entropy in the universe (system + surroundings) is zero.
	web.mit.edu /16.unified/www/FALL/thermodynamics/chapter_7.htm (1289 words)

	Reversible Process Thermodynamic - Engineers Edge (Site not responding. Last check: 2007-11-04)
		A reversible process for a system is defined as a process that, once having taken place, can be reversed, and in so doing leaves no change in either the system or surroundings.
		In reality, there are no truly reversible processes; however, for analysis purposes, one uses reversible to make the analysis simpler, and to determine maximum theoretical efficiencies.
		Therefore, the reversible process is an appropriate starting point on which to base engineering study and calculation.
	www.engineersedge.com /thermodynamics/reversible_process.htm (243 words)

	Thermodynamics Definitions and Terminology - Engineers Edge (Site not responding. Last check: 2007-11-04)
		Heat Regeneration - A process during which heat is transferred to a thermal energy storage device (regenerator) during one part of the cycle and is transferred back to the working fluid during another part of the cycle.
		In a reversible process, the ratio of the heat associated with the high temperature to the heat associated with the low temperature is equal to the ratio of the high temperature over the low temperature.
		Reversible Process - A process in which the system can be returned to its initial state without leaving any trace on the surroundings.
	www.engineersedge.com /thermodynamics.htm (2559 words)

	Reversible computing - Wikipedia, the free encyclopedia (via CobWeb/3.1 planetlab2.isi.jhu.edu) (Site not responding. Last check: 2007-11-04)
		The term reversible computing refers to any computational process that is (at least to some close approximation) reversible, i.e., time-invertible, meaning that a time-reversed version of the process could exist within the same general dynamical framework as the original process.
		For example, within the context of deterministic dynamical frameworks, a necessary condition for reversibility is that the transition function mapping states to their successors at a given later time should be one-to-one.
		A discrete, deterministic computational process is said to be logically reversible if the transition function that maps old computational states to new ones is a one-to-one function.
	en.wikipedia.org.cob-web.org:8888 /wiki/Reversible_computing (792 words)

	JCE 1997 (74) 286 [Mar] An Exceptional Theoretical Process Belandria replies
		Another common comment considers that the process of Figure 1 is not allowed by thermodynamics because it is impossible that the isothermal compression process with internal entropy coupling requires less work than a conventional reversible isothermal compression for the same initial and final state.
		During the process heat is released to tank B, where the temperature varies from 373 to 1500 K and both tanks are covered externally by an adiabatic wall.
		The internal entropy coupling process allows the existence of a path with a final pressure greater than the value expected from simple mechanical arguments, and the system does more work than a reversible process between the same states.
	jchemed.chem.wisc.edu /Journal/Issues/1997/mar/abs286_2.html (4624 words)

	BIOPHYSICS 354
		The process must (in principle) be able to perform useful work on the surroundings, if a suitable coupling process is available.
		From this it is obvious that if a process occurs in which the system is returned to its initial state, the values for changes in the variables of state are zero (the cyclic integral for dG, dA, dH, etc. is 0).
		In principle, we can imagine a process in which each work term is performed separately (through a separate change in state of the system), while all other variables are held constant.
	www.life.uiuc.edu /crofts/bioph354/thermo_lesson.html (1043 words)

	Thermodynamics Entropy
		To determine the change in entropy the process is replaced by a reversible process which has the same initial and final conditions i.e.
		In this case although the process is adiabetic because it is not reversible it is not isentropic.
		An adiabetic process is one which is insulated against heat transfer and an isentropic process is one with a constant entropy.
	www.roymech.co.uk /Related/Thermos/Thermos_Entropy.html (820 words)

	Energy of Seawater Desalination (Site not responding. Last check: 2007-11-04)
		The same energy is invested in any reversible desalination process, and it is independent of the detailed technology employed, exact mechanism, or number of process stages.
		Osmosis is, in principle, a reversible process, though, its application deviates from reversibility.
		The process is reversible since the direction of the partition movement, and therefore, also of the water flow through the membrane, can be reversed at any given moment.
	urila.tripod.com /desalination.htm (730 words)

	Change in entropy in irreversible and reversible process
		It is stated that the change in entropy of an isolated system during an irreversible process is > 0; while for a reversible process, it is = 0.
		In the famous "quasi-static" isothermal process, total entropy of the system (the gas) is unchanged when the system returns to the original state.
		Again, not in the real world: the grains of sand would have to be stored at the height at which they are put on/taken off, otherwise outside work would be necessary; furthermore, perfect frictionless machines would be required to move the grains from their storage potisions to the piston.
	www.physicsforums.com /showthread.php?p=822991 (929 words)

	Entropy (Site not responding. Last check: 2007-11-04)
		The point to note is that for a reversible process, for each step taken, the system is in equilibrium, and that a small step in one direction, say causing compression, can be exactly reversed by a small step in the opposite direction, causing expansion.
		No process in nature is fully reversible, and for a process to be considered as reversible, we need to ignore all effects such as friction, imperfect insulation and so on which would cause irreversiblity.
		Idealization of a thermodyamic process as being reversible is analogous to Newton's idealization in stating his first law, since complications which come from friction and other irreversible effects are inessential in understanding the underlying principles of thermodyamics.
	srikant.org /core/node9.html (4602 words)

	Cancer cells suppress large regions of DNA by a reversible process that can be tackled
		DNA methylation is one of the main epigenetic processes.
		Chemical processes such as methylation can cause epigenetic changes where small molecules are reversibly attached onto a gene.
		Methylation is a reversible process and as such is a good target for molecular-based cancer therapies.
	www.eurekalert.org /pub_releases/2006-04/ra-ccs_1042006.php (565 words)

	Thermodynamic Process
		reversed, and in so doing leaves no change in either the system or surroundings.
		Therefore, the reversible process is an appropriate starting point on which to base engineering
		Although the reversible process can be approximated, it can never be matched by real processes.
	www.tpub.com /content/doe/h1012v1/css/h1012v1_54.htm (374 words)

	CHEM 331
		In an adiabatic process, no heat is gained or lost by the system.
		Note that the final temperature is much higher than for the reversible case, even though both compressions were carried out adiabatically to the same final volume.
		Reversible, adiabatic compression of a van der Waals gas.
	classweb.gmu.edu /sdavis/chem331/adiabatic.htm (2360 words)

	HW #7
		1-2 Heat is transferred to the steam in a reversible manner while the temperature is held constant until the steam exists as a saturated vapor.
		2-3 The steam expands in an adiabatic, reversible process until the pressure is 15 kPa.
		Helium gas is compressed from 90 kPa and 30°C to 450 kPa in a reversible, adiabatic process.
	courses.washington.edu /cheme260/Homework/hw7.htm (678 words)

	Early stages of p53-induced apoptosis are reversible
		In addition, these reversible apoptotic cells are not selected as the result of the development of apoptosis resistance or inactivation of p53 (Figure 3).
		As a possible mechanism for this reversibility, we have previously shown that DNA repair activity is increased early in p53-induced apoptosis.
		As p53 is a mediator of both processes, it may be required for the reversal of all types of apoptosis induction.
	www.nature.com /cdd/journal/v8/n2/full/4400786a.html (6814 words)

	Immunity by ubiquitylation: a reversible process of modification : Nature Reviews Immunology (Site not responding. Last check: 2007-11-04)
		Immunity by ubiquitylation: a reversible process of modification
		The process of protein ubiquitylation — which is catalysed by coordinated enzymatic reactions that are mediated by enzymes known as E1, E2 and E3 — has an important role in the modulation of immune responses.
		Importantly, protein ubiquitylation is a reversible process, and removal of ubiquitin molecules is mediated by de-ubiquitylating enzymes: for example, A20, which has been implicated in the regulation of immune responses.
	www.nature.com /doifinder/10.1038/nri1731 (234 words)

	The Second Law of Thermodynamics, Evolution, and Probability (via CobWeb/3.1 planetlab1.netlab.uky.edu) (Site not responding. Last check: 2007-11-04)
		The restoration process, if it were to take place in actuality, would have to be accompanied by at least a small amount of irreversibility, and hence an additional increase in the entropy of the surroundings beyond the entropy increase from the system's original irreversible change.
		Remember, reversible processes are postulated to simplify the calculation of the entropy change in a system; it is not necessary that they be capable of being achieved experimentally.
		The concept of reversibility is merely a means to an end: the calculation of entropy change accompanying an irreversible process.
	www.talkorigins.org.cob-web.org:8888 /faqs/thermo/probability.html (4599 words)

	What is entropy?
		For example, the reversible expansion of a gas can be achieved by reducing the external pressure in a series of infinitessimal steps; reversing any step will restore the system and the surroundings to their previous state.
		As the number of steps increases, the processes become less irreversible; that is, the difference between the work done in expansion and that required to re-compress the gas diminishes.
		It can be shown that as a process such as the expansion of a gas is carried out in successively longer series of smaller steps, the absolute value of q approaches a minimum, and that of w approaches a maximum that is characteristic of the particular process.
	www.chem1.com /acad/webtext/thermeq/TE2.html (2667 words)

	Reversible Process For Forming Supramolecular Polymers Could Be The Basis Of Fibers, Molecular Transport Mechanisms
		Reversible Process For Forming Supramolecular Polymers Could Be The Basis Of Fibers, Molecular Transport Mechanisms
		In one process, a linear supramolecular pseudorotaxane polymer is formed that can be drawn into fibers.
		Within the glob are pockets of a specific size that can be used to trap target molecules, which can then be transported and released by reversing the construction of the dendrimer.
	www.eurekalert.org /pub_releases/1999-03/VT-RPFF-220399.php (415 words)

	Peace process is reversible, says ICG -DAWN - National; June 17, 2006
		ISLAMABAD, June 16: The International Crisis Group has expressed the fear that the process of normalisation of Pakistan-India relations is reversible and resumption of conflict is still possible unless the two nuclear powers work harder for advancing the peace process.
		It said Delhi and Islamabad needed to sustain the normalisation process by stabilising the ceasefire on the Line of Control through a gradual reduction of troops and by implementing confidence building measures such as regular meeting between the local commanders.
		To prevent Pakistan’s hardliners from undermining the peace process and to deprive its military of an excuse to opt out of the talks, India would be best served and would benefit by reaching an agreement about Siachen Glacier, it said.
	www.dawn.com /2006/06/17/nat6.htm (342 words)

	Pak-India peace process reversible: ICG
		It is in the interest of both countries to remove hurdles to the normalisation process.
		International support is essential to sustain the process and consolidate its gains.
		One of the greatest hurdles to sustaining the process is an asymmetry of perceptions and expectations.
	www.kashar.net /complete.asp?id=3682 (391 words)

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