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| {{lead too long|date=August 2010}}
| | It is very common to have a dental emergency -- a fractured tooth, an abscess, or severe pain when chewing. Over-the-counter pain medication is just masking the problem. Seeing an emergency dentist is critical to getting the source of the problem diagnosed and corrected as soon as possible.<br><br>Here are some common dental emergencies:<br>Toothache: The most common dental emergency. This generally means a badly decayed tooth. As the pain affects the tooth's nerve, treatment involves gently removing any debris lodged in the cavity being careful not to poke deep as this will cause severe pain if the nerve is touched. Next rinse vigorously with warm water. Then soak a small piece of cotton in oil of cloves and insert it in the cavity. This will give temporary relief until a dentist can be reached.<br><br>At times the pain may have a more obscure location such as decay under an old filling. As this can be only corrected by a dentist there are two things you can do to help the pain. Administer a pain pill (aspirin or some other analgesic) internally or dissolve a tablet in a half glass (4 oz) of warm water holding it in the mouth for several minutes before spitting it out. DO NOT PLACE A WHOLE TABLET OR ANY PART OF IT IN THE TOOTH OR AGAINST THE SOFT GUM TISSUE AS IT WILL RESULT IN A NASTY BURN.<br><br>Swollen Jaw: This may be caused by several conditions the most probable being an abscessed tooth. In any case the treatment should be to reduce pain and swelling. An ice pack held on the outside of the jaw, (ten minutes on and ten minutes off) will take care of both. If this does not control the pain, an analgesic tablet can be given every four hours.<br><br>Other Oral Injuries: Broken teeth, cut lips, bitten tongue or lips if severe means a trip to a dentist as soon as possible. In the mean time rinse the mouth with warm water and place cold compression the face opposite the injury. If there is a lot of bleeding, apply direct pressure to the bleeding area. If bleeding does not stop get patient to the emergency room of a hospital as stitches may be necessary.<br><br>Prolonged Bleeding Following Extraction: Place a gauze pad or better still a moistened tea bag over the socket and have the patient bite down gently on it for 30 to 45 minutes. The tannic acid in the tea seeps into the tissues and often helps stop the bleeding. If bleeding continues after two hours, call the dentist or take patient to the emergency room of the nearest hospital.<br><br>Broken Jaw: If you suspect the patient's jaw is broken, bring the upper and lower teeth together. Put a necktie, handkerchief or towel under the chin, tying it over the head to immobilize the jaw until you can get the patient to a dentist or the emergency room of a hospital.<br><br>Painful Erupting Tooth: In young children teething pain can come from a loose baby tooth or from an erupting permanent tooth. Some relief can be given by crushing a little ice and wrapping it in gauze or a clean piece of cloth and putting it directly on the tooth or gum tissue where it hurts. The numbing effect of the cold, along with an appropriate dose of aspirin, usually provides temporary relief.<br><br>In young adults, an erupting 3rd molar (Wisdom tooth), especially if it is impacted, can cause the jaw to swell and be quite painful. Often the gum around the tooth will show signs of infection. Temporary relief can be had by giving aspirin or some other painkiller and by dissolving an aspirin in half a glass of warm water and holding this solution in the mouth over the sore gum. AGAIN DO NOT PLACE A TABLET DIRECTLY OVER THE GUM OR CHEEK OR USE THE ASPIRIN SOLUTION ANY STRONGER THAN RECOMMENDED TO PREVENT BURNING THE TISSUE. The swelling of the jaw can be reduced by using an ice pack on the outside of the face at intervals of ten minutes on and ten minutes off.<br><br>If you enjoyed this information and you would certainly such as to get even more information relating to [http://www.youtube.com/watch?v=90z1mmiwNS8 Washington DC Dentist] kindly see our own web-page. |
| '''Reversible computing''' is a model of [[computing]] where the [[computational process]] to some extent is reversible, i.e., [[DTIME|time]]-[[invertible function|invertible]]. In a [[computational model]] that uses [[transition function|transitions]] from one state of the abstract machine to another, a necessary condition for reversibility is that the relation of the mapping from states to their successors must be [[injective function|one-to-one]]. Reversible computing is generally considered an [[Unconventional computing|unconventional]] form of computing.
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| There are two major, closely related, types of reversibility that are of particular interest for this purpose: ''physical reversibility'' and ''logical reversibility''.<ref>http://www.cise.ufl.edu/research/revcomp/</ref>
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| A process is said to be ''physically reversible'' if it results in no increase in physical [[entropy]]; it is ''[[isentropic]]''. These circuits are also referred to as '''charge recovery logic''' or '''[[adiabatic]] computing'''. Although ''in practice'' no nonstationary physical process can be ''exactly'' physically reversible or isentropic, there is no known limit to the closeness with which we can approach perfect reversibility, in systems that are sufficiently well-isolated from interactions with unknown external environments, when the laws of physics describing the system's evolution are precisely known.
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| Probably the largest motivation for the study of technologies aimed at actually implementing reversible computing is that they offer what is predicted to be the only potential way to improve the [[Energy conversion efficiency|energy efficiency]] of computers beyond the fundamental [[von Neumann-Landauer limit]]<ref name="neumann">J. von Neumann, ''Theory of Self-Reproducing Automata'', Univ. of Illinois Press, 1966.</ref> of ''kT'' ln(2) energy dissipated per irreversible [[bit operation]].
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| As was first argued by [[Rolf Landauer]] of [[IBM]],<ref>R. Landauer, "Irreversibility and heat generation in the computing process," IBM Journal of Research and Development, vol. 5, pp. 183-191, 1961.</ref> in order for a computational process to be physically reversible, it must also be ''logically reversible''. [[Landauer's principle]] is the loosely formulated notion that the erasure of ''n'' bits of information must always incur a cost of ''nk'' ln(2) in thermodynamic [[entropy]]. 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]]; i.e. the output logical states uniquely defines the input logical states of the computational operation.
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| For computational processes that are nondeterministic (in the sense of being probabilistic or random), the relation between old and new states is not a [[single-valued function]], and the requirement needed to obtain physical reversibility becomes a slightly weaker condition, namely that the size of a given ensemble of possible initial computational states does not decrease, on average, as the computation proceeds forwards.
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| ==The reversibility of physics and reversible computing==
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| Landauer's principle (and indeed, the [[second law of thermodynamics]] itself) can also be understood to be a direct [[logical consequence]] of the underlying reversibility of [[physics]], as is reflected in the [[Hamiltonian mechanics|general Hamiltonian formulation of mechanics]], and in the [[time evolution|unitary time-evolution operator]] of [[quantum mechanics]] more specifically.
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| In the context of reversible physics, the phenomenon of entropy increase (and the observed [[arrow of time]]) can be understood to be consequences of the fact that our evolved predictive capabilities are rather limited, and cannot keep perfect track of the exact reversible evolution of complex physical systems, especially since these systems are never perfectly isolated from an unknown external environment, and even the laws of physics themselves are still not known with complete precision. Thus, we (and physical observers generally) always accumulate ''some'' uncertainty about the state of physical systems, even if the system's true underlying dynamics is a perfectly reversible one that is subject to ''no'' entropy increase if viewed from a hypothetical omniscient perspective in which the dynamical laws are precisely known. | |
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| The implementation of reversible computing thus amounts to learning how to characterize and control the physical dynamics of mechanisms to carry out desired computational operations so precisely that we can accumulate a negligible total amount of uncertainty regarding the complete physical state of the mechanism, per each logic operation that is performed. In other words, we would need to precisely track the state of the active energy that is involved in carrying out computational operations within the machine, and design the machine in such a way that the majority of this energy is recovered in an organized form that can be reused for subsequent operations, rather than being permitted to dissipate into the form of heat.
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| Although achieving this goal presents a significant challenge for the design, manufacturing, and characterization of ultra-precise new physical mechanisms for [[computing]], there is at present no fundamental reason to think that this goal cannot eventually be accomplished, allowing us to someday build computers that generate much less than 1 bit's worth of physical entropy (and dissipate much less than ''kT'' ln 2 energy to heat) for each useful logical operation that they carry out internally.
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| The motivation behind much of the research that has been done in reversible computing was the first seminal paper on the topic,<ref>C. H. Bennett, "Logical reversibility of computation," IBM Journal of Research and Development, vol. 17, no. 6, pp. 525-532, 1973.</ref><ref>C. H. Bennett, "The Thermodynamics of Computation -- A Review," International Journal of Theoretical Physics, vol. 21, no. 12, pp. 905-940, 1982.</ref> which was published by [[Charles H. Bennett (computer scientist)|Charles H. Bennett]] of IBM research in 1973. Today, the field has a substantial body of academic literature behind it. A wide variety of reversible device concepts, [[logic gate]]s, [[electronic circuit]]s, [[processor architecture]]s, [[programming language]]s, and application [[algorithm]]s have been designed and analyzed by [[physicist]]s, [[electrical engineer]]s, and [[computer scientist]]s. | |
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| This field of research awaits the detailed development of a high-quality, cost-effective, nearly reversible logic device technology, one that includes highly energy-efficient [[clocking]] and [[synchronization]] mechanisms. This sort of solid engineering progress will be needed before the large body of theoretical research on reversible computing can find practical application in enabling real computer technology to circumvent the various near-term barriers to its energy efficiency, including the von Neumann-Landauer bound. This may only be circumvented by the use of logically reversible computing, due to the [[Second Law of Thermodynamics]].
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| ==Reversible circuits==
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| To implement reversible computation, estimate its cost, and to judge its limits, it is formalized it in terms of gate-level circuits. For example, the [[inverter (logic gate)]] (NOT) gate is reversible because it can be ''undone''. The [[exclusive or]] (XOR) gate is irreversible because its inputs cannot be unambiguously reconstructed from an output value. However, a reversible version of the XOR gate—the [[controlled NOT gate]] (CNOT)—can be defined by preserving one of the inputs. The three-input variant of the CNOT gate is called the [[Toffoli gate]]. It preserves two of its inputs ''a,b'' and replaces the third ''c'' by <math>c\oplus (a\cdot b)</math>. With <math>c=0</math>, this gives the AND function, and with <math>a\cdot b=1</math> this gives the NOT function. Thus, the Toffoli gate is universal and can implement any reversible [[Boolean function]] (given enough zero-initialized ancillary bits). More generally, reversible gates have the same number of inputs and outputs. A reversible circuit connects reversible gates without fanouts and loops. Therefore, such circuits contain equal numbers of input and output wires, each going through an entire circuit.
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| Reversible logic circuits have been first motivated in the 1960s by theoretical considerations of zero-energy computation as well as practical improvement of [[bit manipulation|bit-manipulation]] transforms in cryptography and computer graphics. Since the 1980s, reversible circuits have attracted interest as components of [[quantum algorithm]]s, and more recently in photonic and nano-computing technologies where some switching devices offer no [[signal gain]].
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| Surveys of reversible circuits, their construction and optimization as well as recent research challenges is available.<ref>Rolf Drechsler, Robert Wille. From Truth Tables to Programming Languages: Progress in the Design of Reversible Circuits. International Symposium on Multiple-Valued Logic, 2011. http://www.informatik.uni-bremen.de/agra/doc/konf/11_ismvl_reversible_circuit_design_tutorial.pdf</ref><ref>Mehdi Saeedi, Igor L. Markov, Synthesis and Optimization of Reversible Circuits - A Survey, ACM Computing Surveys, 2012. http://arxiv.org/abs/1110.2574</ref><ref>Rolf Drechsler and Robert Wille. Reversible Circuits: Recent Accomplishments and Future Challenges for an Emerging Technology. International Symposium on VLSI Design and Test, 2012. http://www.informatik.uni-bremen.de/agra/doc/konf/2012_vdat_reversible_circuits_accompl_chall.pdf</ref>
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| ==See also==
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| *[[Reversible dynamics]]
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| *[[Maximum entropy thermodynamics]], on the uncertainty interpretation of the second law of thermodynamics
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| *[[Reversible process]]
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| *[[Toffoli gate]]
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| *[[Fredkin gate]]
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| *[[Quantum computing]]
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| *[[Billiard-ball computer]]
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| *[[Three-input universal logic gate]]
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| *[[Undo]]
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| *[[Reversible cellular automaton]]
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| * [[Adiabatic circuit]]
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| ==References==
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| <references/> | |
| Review of later theoretical work: P.M.B. Vitanyi, Time, space, and energy in reversible computing, Proceedings of the 2nd ACM conference on Computing frontiers, 2005, 435–444.
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| ==External links==
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| *[http://strangepaths.com/reversible-computation/2008/01/20/en/ Introductory article on reversible computing]
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| *[http://www.eng.fsu.edu/~mpf/CF05/RC05.htm First International Workshop on reversible computing]
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| *[http://www.eng.fsu.edu/~mpf/pubs.htm Recent publications of Michael P. Frank]
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| *[http://web.archive.org/web/20080626033214rn_1/revcomp.jot.com/WikiHome Internet Archive backup] of the "Reversible computing community Wiki" that was administered by Dr. Frank
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| *[http://www.reversible-computation.org/ Recent Workshops on Reversible Computation]
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| *[http://www.revkit.org/ Open-source toolkit for reversible circuit design]
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| {{DEFAULTSORT:Reversible Computing}}
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| [[Category:Digital electronics]]
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| [[Category:Models of computation]]
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It is very common to have a dental emergency -- a fractured tooth, an abscess, or severe pain when chewing. Over-the-counter pain medication is just masking the problem. Seeing an emergency dentist is critical to getting the source of the problem diagnosed and corrected as soon as possible.
Here are some common dental emergencies:
Toothache: The most common dental emergency. This generally means a badly decayed tooth. As the pain affects the tooth's nerve, treatment involves gently removing any debris lodged in the cavity being careful not to poke deep as this will cause severe pain if the nerve is touched. Next rinse vigorously with warm water. Then soak a small piece of cotton in oil of cloves and insert it in the cavity. This will give temporary relief until a dentist can be reached.
At times the pain may have a more obscure location such as decay under an old filling. As this can be only corrected by a dentist there are two things you can do to help the pain. Administer a pain pill (aspirin or some other analgesic) internally or dissolve a tablet in a half glass (4 oz) of warm water holding it in the mouth for several minutes before spitting it out. DO NOT PLACE A WHOLE TABLET OR ANY PART OF IT IN THE TOOTH OR AGAINST THE SOFT GUM TISSUE AS IT WILL RESULT IN A NASTY BURN.
Swollen Jaw: This may be caused by several conditions the most probable being an abscessed tooth. In any case the treatment should be to reduce pain and swelling. An ice pack held on the outside of the jaw, (ten minutes on and ten minutes off) will take care of both. If this does not control the pain, an analgesic tablet can be given every four hours.
Other Oral Injuries: Broken teeth, cut lips, bitten tongue or lips if severe means a trip to a dentist as soon as possible. In the mean time rinse the mouth with warm water and place cold compression the face opposite the injury. If there is a lot of bleeding, apply direct pressure to the bleeding area. If bleeding does not stop get patient to the emergency room of a hospital as stitches may be necessary.
Prolonged Bleeding Following Extraction: Place a gauze pad or better still a moistened tea bag over the socket and have the patient bite down gently on it for 30 to 45 minutes. The tannic acid in the tea seeps into the tissues and often helps stop the bleeding. If bleeding continues after two hours, call the dentist or take patient to the emergency room of the nearest hospital.
Broken Jaw: If you suspect the patient's jaw is broken, bring the upper and lower teeth together. Put a necktie, handkerchief or towel under the chin, tying it over the head to immobilize the jaw until you can get the patient to a dentist or the emergency room of a hospital.
Painful Erupting Tooth: In young children teething pain can come from a loose baby tooth or from an erupting permanent tooth. Some relief can be given by crushing a little ice and wrapping it in gauze or a clean piece of cloth and putting it directly on the tooth or gum tissue where it hurts. The numbing effect of the cold, along with an appropriate dose of aspirin, usually provides temporary relief.
In young adults, an erupting 3rd molar (Wisdom tooth), especially if it is impacted, can cause the jaw to swell and be quite painful. Often the gum around the tooth will show signs of infection. Temporary relief can be had by giving aspirin or some other painkiller and by dissolving an aspirin in half a glass of warm water and holding this solution in the mouth over the sore gum. AGAIN DO NOT PLACE A TABLET DIRECTLY OVER THE GUM OR CHEEK OR USE THE ASPIRIN SOLUTION ANY STRONGER THAN RECOMMENDED TO PREVENT BURNING THE TISSUE. The swelling of the jaw can be reduced by using an ice pack on the outside of the face at intervals of ten minutes on and ten minutes off.
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