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methods have been proposed to overcome these susceptibilities, in the most recent studies it has been shown that these proposed solutions are far from providing an accurate representation of current vulnerabilities of deep reinforcement learning policies. === Fuzzy reinforcement learning === By introducing fuzzy inference in reinforcement learning, approximating the state-action value function with fuzzy rules in continuous space becomes possible. The IF - THEN form of fuzzy rules make this approach suitable for expressing the results in a form close to natural language. Extending FRL with Fuzzy Rule Interpolation allows the use of reduced size sparse fuzzy rule-bases to emphasize cardinal rules (most important state-action values). === Inverse reinforcement learning === In inverse reinforcement learning (IRL), no reward function is given. Instead, the reward function is inferred given an observed behavior from an expert. The idea is to mimic observed behavior, which is often optimal or close to optimal. One popular IRL paradigm is named maximum entropy inverse reinforcement learning (MaxEnt IRL). MaxEnt IRL estimates the parameters of a linear model of the reward function by maximizing the entropy of the probability distribution of observed trajectories subject to constraints related to matching expected feature counts. Recently it has been shown that MaxEnt IRL is a particular case of a more general framework named random utility inverse reinforcement learning (RU-IRL). RU-IRL is based on random utility theory and Markov decision processes. While prior IRL approaches assume that the apparent random behavior of an observed agent is due to it following a random policy, RU-IRL assumes that the observed agent follows a deterministic policy but randomness in observed behavior is due to the fact that an observer only has partial access to the features the observed agent uses in decision making. The utility function is modeled as a random variable to
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account for the ignorance of the observer regarding the features the observed agent actually considers in its utility function. === Multi-objective reinforcement learning === Multi-objective reinforcement learning (MORL) is a form of reinforcement learning concerned with conflicting alternatives. It is distinct from multi-objective optimization in that it is concerned with agents acting in environments. === Safe reinforcement learning === Safe reinforcement learning (SRL) can be defined as the process of learning policies that maximize the expectation of the return in problems in which it is important to ensure reasonable system performance and/or respect safety constraints during the learning and/or deployment processes. An alternative approach is risk-averse reinforcement learning, where instead of the expected return, a risk-measure of the return is optimized, such as the conditional value at risk (CVaR). In addition to mitigating risk, the CVaR objective increases robustness to model uncertainties. However, CVaR optimization in risk-averse RL requires special care, to prevent gradient bias and blindness to success. === Self-reinforcement learning === Self-reinforcement learning (or self-learning), is a learning paradigm which does not use the concept of immediate reward R a ( s , s ′ ) {\displaystyle R_{a}(s,s')} after transition from s {\displaystyle s} to s ′ {\displaystyle s'} with action a {\displaystyle a} . It does not use an external reinforcement, it only uses the agent internal self-reinforcement. The internal self-reinforcement is provided by mechanism of feelings and emotions. In the learning process emotions are backpropagated by a mechanism of secondary reinforcement. The learning equation does not include the immediate reward, it only includes the state evaluation. The self-reinforcement algorithm updates a memory matrix W = | | w ( a , s ) | | {\displaystyle W=||w(a,s)||} such that in each iteration executes the following machine learning routine: In situation s {\displaystyle s} perform action a
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{\displaystyle a} . Receive a consequence situation s ′ {\displaystyle s'} . Compute state evaluation v ( s ′ ) {\displaystyle v(s')} of how good is to be in the consequence situation s ′ {\displaystyle s'} . Update crossbar memory w ′ ( a , s ) = w ( a , s ) + v ( s ′ ) {\displaystyle w'(a,s)=w(a,s)+v(s')} . Initial conditions of the memory are received as input from the genetic environment. It is a system with only one input (situation), and only one output (action, or behavior). Self-reinforcement (self-learning) was introduced in 1982 along with a neural network capable of self-reinforcement learning, named Crossbar Adaptive Array (CAA). The CAA computes, in a crossbar fashion, both decisions about actions and emotions (feelings) about consequence states. The system is driven by the interaction between cognition and emotion. === Reinforcement Learning in Natural Language Processing === In recent years, Reinforcement learning has become a significant concept in Natural Language Processing (NLP), where tasks are often sequential decision-making rather than static classification. Reinforcement learning is where an agent take actions in an environment to maximize the accumulation of rewards. This framework is best fit for many NLP tasks, including dialogue generation, text summarization, and machine translation, where the quality of the output depends on optimizing long-term or human-centered goals rather than the prediction of single correct label. Early application of RL in NLP emerged in dialogue systems, where conversation was determined as a series of actions optimized for fluency and coherence. These early attempts, including policy gradient and sequence-level training techniques, laid a foundation for the broader application of reinforcement learning to other areas of NLP. A major breakthrough happened with the introduction of Reinforcement Learning from Human Feedback (RLHF), a method in which human feedbacks are used to
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"page_id": 66294,
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train a reward model that guides the RL agent. Unlike traditional rule-based or supervised systems, RLHF allows models to align their behavior with human judgments on complex and subjective tasks. This technique was initially used in the development of InstructGPT, an effective language model trained to follow human instructions and later in ChatGPT which incorporates RLHF for improving output responses and ensuring safety. More recently, researchers have explored the use of offline RL in NLP to improve dialogue systems without the need of live human interaction. These methods optimize for user engagement, coherence, and diversity based on past conversation logs and pre-trained reward models. == Statistical comparison of reinforcement learning algorithms == Efficient comparison of RL algorithms is essential for research, deployment and monitoring of RL systems. To compare different algorithms on a given environment, an agent can be trained for each algorithm. Since the performance is sensitive to implementation details, all algorithms should be implemented as closely as possible to each other. After the training is finished, the agents can be run on a sample of test episodes, and their scores (returns) can be compared. Since episodes are typically assumed to be i.i.d, standard statistical tools can be used for hypothesis testing, such as T-test and permutation test. This requires to accumulate all the rewards within an episode into a single number—the episodic return. However, this causes a loss of information, as different time-steps are averaged together, possibly with different levels of noise. Whenever the noise level varies across the episode, the statistical power can be improved significantly, by weighting the rewards according to their estimated noise. == Challenges and Limitations == Despite significant advancements, reinforcement learning (RL) continues to face several challenges and limitations that hinder its widespread application in real-world scenarios. === Sample Inefficiency === RL algorithms
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often require a large number of interactions with the environment to learn effective policies, leading to high computational costs and time-intensive to train the agent. For instance, OpenAI's Dota-playing bot utilized thousands of years of simulated gameplay to achieve human-level performance. Techniques like experience replay and curriculum learning have been proposed to deprive sample inefficiency, but these techniques add more complexity and are not always sufficient for real-world applications. === Stability and Convergence Issues === Training RL models, particularly for deep neural network-based models, can be unstable and prone to divergence. A small change in the policy or environment can lead to extreme fluctuations in performance, making it difficult to achieve consistent results. This instability is further enhanced in the case of the continuous or high-dimensional action space, where the learning step becomes more complex and less predictable. === Generalization and Transferability === The RL agents trained in specific environments often struggle to generalize their learned policies to new, unseen scenarios. This is the major setback preventing the application of RL to dynamic real-world environments where adaptability is crucial. The challenge is to develop such algorithms that can transfer knowledge across tasks and environments without extensive retraining. === Bias and Reward Function Issues === Designing appropriate reward functions is critical in RL because poorly designed reward functions can lead to unintended behaviors. In addition, RL systems trained on biased data may perpetuate existing biases and lead to discriminatory or unfair outcomes. Both of these issues requires careful consideration of reward structures and data sources to ensure fairness and desired behaviors. == See also == == References == == Further reading == Annaswamy, Anuradha M. (3 May 2023). "Adaptive Control and Intersections with Reinforcement Learning". Annual Review of Control, Robotics, and Autonomous Systems. 6 (1): 65–93. doi:10.1146/annurev-control-062922-090153. ISSN 2573-5144. S2CID 255702873.
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Auer, Peter; Jaksch, Thomas; Ortner, Ronald (2010). "Near-optimal regret bounds for reinforcement learning". Journal of Machine Learning Research. 11: 1563–1600. Bertsekas, Dimitri P. (2023) [2019]. REINFORCEMENT LEARNING AND OPTIMAL CONTROL (1st ed.). Athena Scientific. ISBN 978-1-886-52939-7. Busoniu, Lucian; Babuska, Robert; De Schutter, Bart; Ernst, Damien (2010). Reinforcement Learning and Dynamic Programming using Function Approximators. Taylor & Francis CRC Press. ISBN 978-1-4398-2108-4. François-Lavet, Vincent; Henderson, Peter; Islam, Riashat; Bellemare, Marc G.; Pineau, Joelle (2018). "An Introduction to Deep Reinforcement Learning". Foundations and Trends in Machine Learning. 11 (3–4): 219–354. arXiv:1811.12560. Bibcode:2018arXiv181112560F. doi:10.1561/2200000071. S2CID 54434537. Li, Shengbo Eben (2023). Reinforcement Learning for Sequential Decision and Optimal Control (1st ed.). Springer Verlag, Singapore. doi:10.1007/978-981-19-7784-8. ISBN 978-9-811-97783-1. Powell, Warren (2011). Approximate dynamic programming: solving the curses of dimensionality. Wiley-Interscience. Archived from the original on 2016-07-31. Retrieved 2010-09-08. Sutton, Richard S. (1988). "Learning to predict by the method of temporal differences". Machine Learning. 3: 9–44. doi:10.1007/BF00115009. Sutton, Richard S.; Barto, Andrew G. (2018) [1998]. Reinforcement Learning: An Introduction (2nd ed.). MIT Press. ISBN 978-0-262-03924-6. Szita, Istvan; Szepesvari, Csaba (2010). "Model-based Reinforcement Learning with Nearly Tight Exploration Complexity Bounds" (PDF). ICML 2010. Omnipress. pp. 1031–1038. Archived from the original (PDF) on 2010-07-14. == External links == Dissecting Reinforcement Learning Series of blog post on reinforcement learning with Python code A (Long) Peek into Reinforcement Learning
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Presentism (sometimes 'philosophical presentism') is the view of time which states that only present entities exist (or, equivalently, that everything which is exists presently) and what is present (i.e., what exists) changes as time passes. According to presentism, there are no past or future entities at all, though some entities have existed and other entities will exist. In a sense, the past and the future do not exist for presentists—past events have happened (have existed, or have been present) and future events will happen (will exist, or will be present), but neither exist at all since they do not exist now. Presentism is a view about temporal ontology, i.e., a view about what exists in time, that contrasts with eternalism—the view that past, present and future entities exist (that is, the ontological thesis of the 'block universe')—and with no-futurism—the view that only past and present entities exist (that is, the ontological thesis of the 'growing block universe'). == Historical antecedents == Augustine of Hippo proposed that the present is analogous to a knife edge placed exactly between the perceived past and the imaginary future and does not include the concept of time. Proponents claim this should be self-evident because, if the present is extended, it must have separate parts. These parts must be simultaneous if they are truly a part of the present. According to early philosophers, time cannot be simultaneously past and present and hence not extended. Contrary to Saint Augustine, some philosophers propose that conscious experience is extended in time. For instance, William James said that time is "the short duration of which we are immediately and incessantly sensible". Other early presentist philosophers include the Indian Buddhist tradition. Fyodor Shcherbatskoy, a leading scholar of the modern era on Buddhist philosophy, has written extensively on Buddhist presentism: "Everything past
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is unreal, everything future is unreal, everything imagined, absent, mental... is unreal. Ultimately, real is only the present moment of physical efficiency [i.e., causation]." According to J. M. E. McTaggart's "The Unreality of Time", there are two ways of referring to events: the 'A Series' (or 'tensed time': yesterday, today, tomorrow) and the 'B Series' (or 'untensed time': Monday, Tuesday, Wednesday). Presentism posits that the A Series is fundamental and that the B Series alone is not sufficient. Presentists maintain that temporal discourse requires the use of tenses, whereas the "Old B-Theorists" argued that tensed language could be reduced to tenseless facts (Dyke, 2004). Arthur N. Prior has argued against un-tensed theories with the following ideas: the meaning of statements such as "Thank goodness that's over" is much easier to see in a tensed theory with a distinguished, present now. Similar arguments can be made to support the theory of egocentric presentism (or perspectival realism), which holds that there is a distinguished, present self. Vincent Conitzer has made a similar argument connecting A-theory with the vertiginous question. According to Conitzer, arguments in favor of A-theory are more effective as arguments for the combined position of both A-theory being true and the "I" being metaphysically privileged from other perspectives. == Philosophical objections == One main objection to presentism comes from the idea that what is true substantively depends upon what exists (or, that truth depends or 'supervenes' upon being). According to this critique, presentism is said to be in conflict with truth-maker theory. Truth-maker theory looks to capture the dependence of truth upon being with the idea that truths (e.g., true propositions) are true in virtue of the existence of some entity or entities ('truth-makers'). The conflict arises because most presentists accept that there are evidence-transcendent and objective truths about the
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past (and some accept that there are truths about the future, pace concerns about fatalism), but presentists deny the existence of the past and the future. For instance, most presentists accept that it is true that Marie Curie discovered polonium, but they deny that the event of her discovery exists (because it is a wholly past event). Since the mid-1990s, truth-maker theorists have been trying to accuse Presentists with violating their principle (that truths require truth-makers) and ontologically 'cheating'. To resolve the truth-maker theorists' counter, presentists can argue that there are truth-makers for the past, but they either exist presently or outside of time. For a second option, some presentists posit the existence of "atemporal" objects which function as truth-makers, though some justification would be needed for how something outside of time would not conflict with the proposition that only present entities exist. Presentists can as well reject that propositions about the past are made true by truth-makers. However, this leaves unclear what exactly makes truths about the past true. As a result, few philosophers support this method of resolving the objection. == Ersatz Presentism == Presentists who make the claim that there are “atemporal” entities (atemporal in a similar sense as numbers) which are truth-making endorse a view called “ersatz presentism.” Ersatz (German for "substitute"/"alternative") presentists believe that the truth of propositions about the past like “Churchill existed” are made true by a theoretical time which is a representation of how things were (i.e. ersatz rather than concrete). Ersatz times are, in a sense, akin to ersatz possible worlds. Alyssa Ney describes ersatz modal realism as positing “that there are possible worlds (worlds that can play a similar role to the concrete worlds of the modal realist), but that these are not additional universes in the same sense as
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our universe.” In a similar way, ersatz times would exist, but not in the same sense that actual time currently exists. Rather, they would be theoretical times which represent the moment when in which the proposition was true. Ersatz presentists must, though, postulate an ordering relationship between ersatz times which is equivalent to an earlier/later-than relation (such that t1 is later than t2). For example, when ersatz presentists claim “Churchill existed,” such a proposition is true only if a) there is an ersatz time (t2) which represents the present time and b) there is an ersatz time which represents (t1) a prior time when Churchill existed. For the ersatz presentist, the theoretical ersatz times ground or make true propositions about the past. As a result of postulating presently existing entities which ground past entities, ersatz presentists do not need to accept the existence of anything which does not presently exist in order to explain the distinction between consecutive moments. == Relativity == Many philosophers have argued that relativity implies eternalism, the idea that the past and future exist in a real sense, not only as changes that occurred or will occur to the present. Philosopher of science Dean Rickles disagrees with some qualifications, but notes that "the consensus among philosophers seems to be that special and general relativity are incompatible with presentism". Some philosophers view time as a dimension equal to spatial dimensions, that future events are "already there" in the same sense different places exist, and that there is no objective flow of time; however, this view is disputed. Since relativity has been confirmed by experiment, and it posits that time is a coordinate or "dimension" between two points in spacetime, it gave rise to a philosophical viewpoint known as four dimensionalism. Observers in motion with respect to each
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other are said to be in different frames of reference. These observers may disagree on whether two events at different locations occurred simultaneously, which is referred to as the relativity of simultaneity. Presentism in classical spacetime deems that only the present exists; this is not reconcilable with the relativity of simultaneity in special relativity, shown in the following example: Alice and Bob are simultaneous observers of event O. For Alice, some event E is simultaneous with O, but for Bob, event E is in the past or future. Therefore, Alice and Bob disagree about what exists in the present, which contradicts classical presentism. "Here-now presentism" attempts to reconcile this by only acknowledging the time and space of a single point; this is unsatisfactory because objects coming and going from the "here-now" alternate between real and unreal, in addition to the lack of a privileged "here-now" that would be the "real" present. "Relativized presentism" acknowledges that there are infinite frames of reference, each of them having a different set of simultaneous events, which makes it impossible to distinguish a single "real" present, and hence either all events in time are real—blurring the difference between presentism and eternalism—or each frame of reference exists in its own reality. Options for presentism in special relativity appear to be exhausted, but Gödel and others suspect presentism may be valid for some forms of general relativity. Generally, the idea of absolute time and space is considered incompatible with general relativity; there is no universal truth about the absolute position of events which occur at different times, and thus no way to determine which point in space at one time is at the universal "same position" at another time, and all coordinate systems are on equal footing as given by the principle of diffeomorphism invariance. == See
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also == A-series and B-series Appeal to novelty Arrow of time Centered worlds Endurantism Eternity Growing block universe Perdurantism Problem of future contingents Specious present == References == == External links == Balashov, Y; Janssen, M (2002), "Presentism and Relativity" (PDF), British Journal for the Philosophy of Science (preprint of article), 54 (2): 327–346, CiteSeerX 10.1.1.114.5886, doi:10.1093/bjps/54.2.327. Bourne, Craig (2006), A Future for presentism, Oxford: Oxford University Press, ISBN 978-0-19-921280-4, archived from the original on 2007-09-29. Dowden, Bradley. "Time". Internet Encyclopedia of Philosophy. Ingram, David; Tallant, Jonathan (2018). Presentism. Metaphysics Research Lab, Stanford University. {{cite book}}: |website= ignored (help) McKinnon, N (2003), "Presentism and Consciousness", Australasian Journal of Philosophy, 81 (3): 305–323, doi:10.1093/ajp/jag301 (inactive 1 November 2024), archived from the original (Geocities) on 2009-10-26{{citation}}: CS1 maint: DOI inactive as of November 2024 (link). Petkov, Vesselin (2005), Is There an Alternative to the Block Universe View?, Pitt. Rea, MC, "Four Dimensionalism", The Oxford Handbook for Metaphysics (PDF), ND, archived from the original (PDF) on 2005-11-25. Describes Presentism and how four dimensionalism contradicts it.
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A dasymeter was meant initially as a device to demonstrate the buoyant effect of gases like air (as shown in the adjacent pictures). A dasymeter which allows weighing acts as a densimeter used to measure the density of gases. == Principle == The Principle of Archimedes permits to derive a formula which does not rely on any information of volume: a sample, the big sphere in the adjacent images, of known mass-density is weighed in vacuum and then immersed into the gas and weighed again. density of sphere density of gas = weight of sphere weight of sphere − weight of immersed sphere {\displaystyle {\frac {\text{density of sphere}}{\text{density of gas}}}={\frac {\text{weight of sphere}}{{\text{weight of sphere}}-{\text{weight of immersed sphere}}}}\,} (The above formula was taken from the article buoyancy and still has to be solved for the density of the gas.) From the known mass density of the sample (sphere) and its two weight-values, the mass-density of the gas can be calculated as: density of gas = weight of sphere − weight of immersed sphere weight of sphere × density of sphere {\displaystyle {\text{density of gas}}={\frac {{\text{weight of sphere}}-{\text{weight of immersed sphere}}}{\text{weight of sphere}}}\times {\text{density of sphere}}} == Construction and use == It consists of a thin sphere made of glass, ideally with an average density close to that of the gas to be investigated. This sphere is immersed in the gas and weighed. == History of the dasymeter == The dasymeter was invented in 1650 by Otto von Guericke. Archimedes used a pair of scales which he immersed into water to demonstrate the buoyant effect of water. A dasymeter can be seen as a variant of that pair of scales, only immersed into gas. == References == == External links == Volume Conversion
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"page_id": 4129530,
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"title": "Dasymeter"
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The molecular formula C10H19O6PS2 (molar mass: 330.36 g/mol, exact mass: 330.0361 u) may refer to: Isomalathion Malathion
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{
"page_id": 23593722,
"source": null,
"title": "C10H19O6PS2"
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Diaphorase may refer to: Cytochrome b5 reductase, an enzyme NADH dehydrogenase, an enzyme NADPH dehydrogenase, an enzyme == See also == NADPH-diaphorase (disambiguation)
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"page_id": 11928316,
"source": null,
"title": "Diaphorase"
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In chemistry, a resorcinarene (also resorcarene or calix[4]resorcinarene) is a macrocycle, or a cyclic oligomer, based on the condensation of resorcinol (1,3-dihydroxybenzene) and an aldehyde. Resorcinarenes are a type of calixarene. Other types of resorcinarenes include the related pyrogallolarenes and octahydroxypyridines, derived from pyrogallol and 2,6-dihydroxypyridine, respectively. Resorcinarenes interact with other molecules forming a host–guest complex. Resorcinarenes and pyrogallolarenes self-assemble into larger supramolecular structures. Both in the crystalline state and in organic solvents, six resorcinarene molecules are known to form hexamers with an internal volume of around one cubic nanometer (nanocapsules) and shapes similar to the Archimedean solids. Hydrogen bonds appear to hold the assembly together. A number of solvent or other molecules reside inside. The resorcinarene is also the basic structural unit for other molecular recognition scaffolds, typically formed by bridging the phenolic oxygens with alkyl or aromatic spacers. A number of molecular structures are based on this macrocycle, namely cavitands and carcerands. == Synthesis == The resorcinarenes are typically prepared by condensation of resorcinol and an aldehyde in acid solution. This reaction was first described by Adolf von Baeyer who described the condensation of resorcinol and benzaldehyde but was unable to elucidate the nature of the product(s). The methods have since been refined. Recrystallization typically gives the desired isomer in quite pure form. However, for certain aldehydes, the reaction conditions lead to significant by-products. Alternative condensation conditions have been developed, including the use of Lewis acid catalysts. A green chemistry procedure uses solvent-free conditions: resorcinol, an aldehyde, and p-toluenesulfonic acid are ground together in a mortar and pestle at low temperature. == Structure == Resorcinarenes can be characterized by a wide upper rim and a narrow lower rim. The upper rim includes eight hydroxyl groups that can participate in hydrogen bonding interactions. Depending on the aldehyde starting material,
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"page_id": 3998467,
"source": null,
"title": "Resorcinarene"
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the lower rim includes four appending groups, usually chosen to give optimal solubility. The resorcin[n]arene nomenclature is analogous to that of calix[n]arenes, in which 'n' represents the number of repeating units in the ring. Pyrogallolarenes are related macrocycles derived from the condensation of pyrogallol (1,2,3-trihydroxybenzene) with an aldehyde. Resorcinarenes and pyrogallolarenes self-assemble to give supramolecular assemblies. Both in the crystalline state and in solution, they are known to form hexamers that are akin to certain Archimedean solids with an internal volume of around one cubic nanometer (nanocapsules). (Isobutylpyrogallol[4]arene)6 is held together by 48 intermolecular hydrogen bonds. The remaining 24 hydrogen bonds are intramolecular. The cavity is filled by solvent. == Catalysis == The resorcinarene hexamer has been described as a yoctolitre reaction vessel. Within the confines of the container, terpene cyclizations and iminium catalyzed reactions have been observed. == References == Palmer LC, Shivanyuk A, Yamanaka M, Rebek J (2005). "Resorcinarene assemblies as synthetic receptors". Chemical Communications. 2005 (7): 857–858. doi:10.1039/b414252g. PMID 15700060.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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"page_id": 3998467,
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"title": "Resorcinarene"
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The nonequilibrium partition identity (NPI) is a remarkably simple and elegant consequence of the fluctuation theorem previously known as the Kawasaki identity: ⟨ exp [ − Σ ¯ t t ] ⟩ = 1 , ∀ t {\displaystyle \left\langle {\exp[-{\overline {\Sigma }}_{t}\;t]}\right\rangle =1,\quad \forall t} (Carberry et al. 2004). Thus in spite of the second law inequality which might lead one to expect that the average would decay exponentially with time, the exponential probability ratio given by the FT exactly cancels the negative exponential in the average above leading to an average which is unity for all time. The first derivation of the nonequilibrium partition identity for Hamiltonian systems was by Yamada and Kawasaki in 1967. For thermostatted deterministic systems the first derivation was by Morriss and Evans in 1985. == Bibliography == Kawasaki, Kyozi; Gunton, James D. (1973-10-01). "Theory of Nonlinear Transport Processes: Nonlinear Shear Viscosity and Normal Stress Effects". Physical Review A. 8 (4). American Physical Society (APS): 2048–2064. Bibcode:1973PhRvA...8.2048K. doi:10.1103/physreva.8.2048. ISSN 0556-2791. Yamada, Tomoji; Kawasaki, Kyozi (1967). "Nonlinear Effects in the Shear Viscosity of Critical Mixtures". Progress of Theoretical Physics. 38 (5). Oxford University Press (OUP): 1031–1051. Bibcode:1967PThPh..38.1031Y. doi:10.1143/ptp.38.1031. ISSN 0033-068X. Morriss, G.P.; Evans, Denis J. (1985-02-20). "Isothermal response theory". Molecular Physics. 54 (3). Informa UK Limited: 629–636. Bibcode:1985MolPh..54..629M. doi:10.1080/00268978500100481. ISSN 0026-8976. Carberry, D. M.; Williams, S. R.; Wang, G. M.; Sevick, E. M.; Evans, Denis J. (2004). "The Kawasaki identity and the Fluctuation Theorem" (PDF). The Journal of Chemical Physics. 121 (17). AIP Publishing: 8179–82. Bibcode:2004JChPh.121.8179C. doi:10.1063/1.1802211. hdl:1885/15803. ISSN 0021-9606. PMID 15511135. == See also == Fluctuation theorem – Provides an equality that quantifies fluctuations in time averaged entropy production in a wide variety of nonequilibrium systems Crooks fluctuation theorem – Provides a fluctuation theorem between two equilibrium states; implies the Jarzynski equality == External
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"page_id": 16384773,
"source": null,
"title": "Nonequilibrium partition identity"
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links == Marconi, U; Puglisi, A; Rondoni, L; Vulpiani, A (2008). "Fluctuation–dissipation: Response theory in statistical physics". Physics Reports. 461 (4–6). Elsevier BV: 111–195. arXiv:0803.0719. Bibcode:2008PhR...461..111M. doi:10.1016/j.physrep.2008.02.002. ISSN 0370-1573. S2CID 118575899.
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"page_id": 16384773,
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Koenig's manometric flame apparatus was a laboratory instrument invented in 1862 by the German physicist Rudolph Koenig, and used to visualize sound waves. It was the nearest equivalent of the modern oscilloscope in the late nineteenth and early twentieth centuries. == Description == The manometric flame apparatus consisted of a chamber which acted in the same way as a modern microphone. Sound from the source to be measured was concentrated by means of a horn or tube into one half of the capsule chamber. The chamber was divided in two by an elastic diaphragm, usually rubber. The sound caused the diaphragm to vibrate which modulated a flow of flammable illumination gas passing through the other half of the chamber. The illumination gas was passed to a Bunsen burner, the flame of which would then increase or decrease in size at the same frequency as the sound source. The change in flame size was too fast to be easily seen with the naked eye, and a stroboscope — usually in the form of a rotating many sided mirror — was used to view the flame. The frequency of the sound could then be calculated from the apparent distance between the flame images in the mirror and the known speed of its rotation. Alexander Graham Bell used this type of equipment to study the performance of his microphones and demonstrated it in his display at the 1876 Philadelphia Centenarian Exhibition. He replaced the rubber diaphragm with an iron disc which was driven by an electromagnet with current fed from a microphone. This apparatus was capable of giving quantitative measures of the performance of his microphones. A type of Fourier analyzer can be constructed by connecting a number of manometric flame capsules each to a Helmholtz resonator tuned to either the fundamental frequency
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"page_id": 16646920,
"source": null,
"title": "Koenig's manometric flame apparatus"
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of the sound to be analyzed, or one of its harmonics. The flames produced from each capsule are then an indication of the strength of each of the Fourier components of the sound. == Notes == == References == 1. The Koinge manometric flame apparatus Jim & Rhoda Morris at SciTechAntiques. Accessed March 2008 2.Manometric Flame Apparatus Kenyon College. Gambier, Ohio. Accessed March 2008 3.Fourier Analysis Kenyon College. Gambier, Ohio. Accessed March 2008 4.Flame manometer Case Western Reserve University Physics Department. Accessed March 2008
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Redox ( RED-oks, REE-doks, reduction–oxidation or oxidation–reduction: 150 ) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a decrease in the oxidation state. The oxidation and reduction processes occur simultaneously in the chemical reaction. There are two classes of redox reactions: Electron-transfer – Only one (usually) electron flows from the atom, ion, or molecule being oxidized to the atom, ion, or molecule that is reduced. This type of redox reaction is often discussed in terms of redox couples and electrode potentials. Atom transfer – An atom transfers from one substrate to another. For example, in the rusting of iron, the oxidation state of iron atoms increases as the iron converts to an oxide, and simultaneously, the oxidation state of oxygen decreases as it accepts electrons released by the iron. Although oxidation reactions are commonly associated with forming oxides, other chemical species can serve the same function. In hydrogenation, bonds like C=C are reduced by transfer of hydrogen atoms. == Terminology == "Redox" is a portmanteau of the words "REDuction" and "OXidation." The term "redox" was first used in 1928. Oxidation is a process in which a substance loses electrons. Reduction is a process in which a substance gains electrons. The processes of oxidation and reduction occur simultaneously and cannot occur independently. In redox processes, the reductant transfers electrons to the oxidant. Thus, in the reaction, the reductant or reducing agent loses electrons and is oxidized, and the oxidant or oxidizing agent gains electrons and is reduced. The pair of an oxidizing and reducing agent that is involved in a particular reaction is called a redox pair. A redox couple is a reducing
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species and its corresponding oxidizing form, e.g., Fe2+/ Fe3+.The oxidation alone and the reduction alone are each called a half-reaction because two half-reactions always occur together to form a whole reaction. In electrochemical reactions the oxidation and reduction processes do occur simultaneously but are separated in space. === Oxidants === Oxidation originally implied a reaction with oxygen to form an oxide. Later, the term was expanded to encompass substances that accomplished chemical reactions similar to those of oxygen. Ultimately, the meaning was generalized to include all processes involving the loss of electrons or the increase in the oxidation state of a chemical species.: A49 Substances that have the ability to oxidize other substances (cause them to lose electrons) are said to be oxidative or oxidizing, and are known as oxidizing agents, oxidants, or oxidizers. The oxidant removes electrons from another substance, and is thus itself reduced.: A50 Because it "accepts" electrons, the oxidizing agent is also called an electron acceptor. Oxidants are usually chemical substances with elements in high oxidation states: 159 (e.g., N2O4, MnO−4, CrO3, Cr2O2−7, OsO4), or else highly electronegative elements (e.g. O2, F2, Cl2, Br2, I2) that can gain extra electrons by oxidizing another substance.: 909 Oxidizers are oxidants, but the term is mainly reserved for sources of oxygen, particularly in the context of explosions. Nitric acid is a strong oxidizer. === Reductants === Substances that have the ability to reduce other substances (cause them to gain electrons) are said to be reductive or reducing and are known as reducing agents, reductants, or reducers. The reductant transfers electrons to another substance and is thus itself oxidized.: 159 Because it donates electrons, the reducing agent is also called an electron donor. Electron donors can also form charge transfer complexes with electron acceptors. The word reduction originally referred to
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the loss in weight upon heating a metallic ore such as a metal oxide to extract the metal. In other words, ore was "reduced" to metal. Antoine Lavoisier demonstrated that this loss of weight was due to the loss of oxygen as a gas. Later, scientists realized that the metal atom gains electrons in this process. The meaning of reduction then became generalized to include all processes involving a gain of electrons. Reducing equivalent refers to chemical species which transfer the equivalent of one electron in redox reactions. The term is common in biochemistry. A reducing equivalent can be an electron or a hydrogen atom as a hydride ion. Reductants in chemistry are very diverse. Electropositive elemental metals, such as lithium, sodium, magnesium, iron, zinc, and aluminium, are good reducing agents. These metals donate electrons relatively readily. Hydride transfer reagents, such as NaBH4 and LiAlH4, reduce by atom transfer: they transfer the equivalent of hydride or H−. These reagents are widely used in the reduction of carbonyl compounds to alcohols. A related method of reduction involves the use of hydrogen gas (H2) as sources of H atoms.: 288 == Rates, mechanisms, and energies == Redox reactions can occur slowly, as in the formation of rust, or rapidly, as in the case of burning fuel. Electron transfer reactions are generally fast, occurring within the time of mixing. The mechanisms of atom-transfer reactions are highly variable because many kinds of atoms can be transferred. Such reactions can also be quite complex, involving many steps. The mechanisms of electron-transfer reactions occur by two distinct pathways, inner sphere electron transfer and outer sphere electron transfer. Analysis of bond energies and ionization energies in water allows calculation of the thermodynamic aspects of redox reactions. == Standard electrode potentials (reduction potentials) == Each half-reaction has a
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standard electrode potential (Eocell), which is equal to the potential difference or voltage at equilibrium under standard conditions of an electrochemical cell in which the cathode reaction is the half-reaction considered, and the anode is a standard hydrogen electrode where hydrogen is oxidized: 1⁄2H2 → H+ + e− The electrode potential of each half-reaction is also known as its reduction potential (Eored), or potential when the half-reaction takes place at a cathode. The reduction potential is a measure of the tendency of the oxidizing agent to be reduced. Its value is zero for H+ + e− → 1⁄2H2 by definition, positive for oxidizing agents stronger than H+ (e.g., +2.866 V for F2) and negative for oxidizing agents that are weaker than H+ (e.g., −0.763V for Zn2+).: 873 For a redox reaction that takes place in a cell, the potential difference is: Eocell = Eocathode − Eoanode However, the potential of the reaction at the anode is sometimes expressed as an oxidation potential: Eoox = −Eored The oxidation potential is a measure of the tendency of the reducing agent to be oxidized but does not represent the physical potential at an electrode. With this notation, the cell voltage equation is written with a plus sign Eocell = Eored(cathode) + Eoox(anode) == Examples of redox reactions == In the reaction between hydrogen and fluorine, hydrogen is being oxidized and fluorine is being reduced: H2 + F2 → 2 HF This spontaneous reaction releases a large amount of energy (542 kJ per 2 g of hydrogen) because two H-F bonds are much stronger than one H-H bond and one F-F bond. This reaction can be analyzed as two half-reactions. The oxidation reaction converts hydrogen to protons: H2 → 2 H+ + 2 e− The reduction reaction converts fluorine to the fluoride anion: F2
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+ 2 e− → 2 F− The half-reactions are combined so that the electrons cancel: The protons and fluoride combine to form hydrogen fluoride in a non-redox reaction: 2 H+ + 2 F− → 2 HF The overall reaction is: H2 + F2 → 2 HF === Metal displacement === In this type of reaction, a metal atom in a compound or solution is replaced by an atom of another metal. For example, copper is deposited when zinc metal is placed in a copper(II) sulfate solution: Zn (s) + CuSO4 (aq) → ZnSO4 (aq) + Cu (s) In the above reaction, zinc metal displaces the copper(II) ion from the copper sulfate solution, thus liberating free copper metal. The reaction is spontaneous and releases 213 kJ per 65 g of zinc. The ionic equation for this reaction is: Zn + Cu2+ → Zn2+ + Cu As two half-reactions, it is seen that the zinc is oxidized: Zn → Zn2+ + 2 e− And the copper is reduced: Cu2+ + 2 e− → Cu === Other examples === The reduction of nitrate to nitrogen in the presence of an acid (denitrification): 2 NO−3 + 10 e− + 12 H+ → N2 + 6 H2O The combustion of hydrocarbons, such as in an internal combustion engine, produces water, carbon dioxide, some partially oxidized forms such as carbon monoxide, and heat energy. Complete oxidation of materials containing carbon produces carbon dioxide. The stepwise oxidation of a hydrocarbon by oxygen, in organic chemistry, produces water and, successively: an alcohol, an aldehyde or a ketone, a carboxylic acid, and then a peroxide. === Corrosion and rusting === The term corrosion refers to the electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Rusting, the formation of iron oxides, is a well-known example of
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electrochemical corrosion: it forms as a result of the oxidation of iron metal. Common rust often refers to iron(III) oxide, formed in the following chemical reaction: 4 Fe + 3 O2 → 2 Fe2O3 The oxidation of iron(II) to iron(III) by hydrogen peroxide in the presence of an acid: Fe2+ → Fe3+ + e− H2O2 + 2 e− → 2 OH− Here the overall equation involves adding the reduction equation to twice the oxidation equation, so that the electrons cancel: 2 Fe2+ + H2O2 + 2 H+ → 2 Fe3+ + 2 H2O === Disproportionation === A disproportionation reaction is one in which a single substance is both oxidized and reduced. For example, thiosulfate ion with sulfur in oxidation state +2 can react in the presence of acid to form elemental sulfur (oxidation state 0) and sulfur dioxide (oxidation state +4). S2O2−3 + 2 H+ → S + SO2 + H2O Thus one sulfur atom is reduced from +2 to 0, while the other is oxidized from +2 to +4.: 176 == Redox reactions in industry == Cathodic protection is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects protected metal to a more easily corroded "sacrificial anode" to act as the anode. The sacrificial metal, instead of the protected metal, then corrodes. Oxidation is used in a wide variety of industries, such as in the production of cleaning products and oxidizing ammonia to produce nitric acid. Redox reactions are the foundation of electrochemical cells, which can generate electrical energy or support electrosynthesis. Metal ores often contain metals in oxidized states, such as oxides or sulfides, from which the pure metals are extracted by smelting at high temperatures in the presence of a
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reducing agent. The process of electroplating uses redox reactions to coat objects with a thin layer of a material, as in chrome-plated automotive parts, silver plating cutlery, galvanization and gold-plated jewelry. == Redox reactions in biology == Many essential biological processes involve redox reactions. Before some of these processes can begin, iron must be assimilated from the environment. Cellular respiration, for instance, is the oxidation of glucose (C6H12O6) to CO2 and the reduction of oxygen to water. The summary equation for cellular respiration is: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy The process of cellular respiration also depends heavily on the reduction of NAD+ to NADH and the reverse reaction (the oxidation of NADH to NAD+). Photosynthesis and cellular respiration are complementary, but photosynthesis is not the reverse of the redox reaction in cellular respiration: 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2 Biological energy is frequently stored and released using redox reactions. Photosynthesis involves the reduction of carbon dioxide into sugars and the oxidation of water into molecular oxygen. The reverse reaction, respiration, oxidizes sugars to produce carbon dioxide and water. As intermediate steps, the reduced carbon compounds are used to reduce nicotinamide adenine dinucleotide (NAD+) to NADH, which then contributes to the creation of a proton gradient, which drives the synthesis of adenosine triphosphate (ATP) and is maintained by the reduction of oxygen. In animal cells, mitochondria perform similar functions. The term redox state is often used to describe the balance of GSH/GSSG, NAD+/NADH and NADP+/NADPH in a biological system such as a cell or organ. The redox state is reflected in the balance of several sets of metabolites (e.g., lactate and pyruvate, beta-hydroxybutyrate and acetoacetate), whose interconversion is dependent on these ratios. Redox mechanisms also control some
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cellular processes. Redox proteins and their genes must be co-located for redox regulation according to the CoRR hypothesis for the function of DNA in mitochondria and chloroplasts. === Redox cycling === Wide varieties of aromatic compounds are enzymatically reduced to form free radicals that contain one more electron than their parent compounds. In general, the electron donor is any of a wide variety of flavoenzymes and their coenzymes. Once formed, these anion free radicals reduce molecular oxygen to superoxide and regenerate the unchanged parent compound. The net reaction is the oxidation of the flavoenzyme's coenzymes and the reduction of molecular oxygen to form superoxide. This catalytic behavior has been described as a futile cycle or redox cycling. == Redox reactions in geology == Minerals are generally oxidized derivatives of metals. Iron is mined as ores such as magnetite (Fe3O4) and hematite (Fe2O3). Titanium is mined as its dioxide, usually in the form of rutile (TiO2). These oxides must be reduced to obtain the corresponding metals, often achieved by heating these oxides with carbon or carbon monoxide as reducing agents. Blast furnaces are the reactors where iron oxides and coke (a form of carbon) are combined to produce molten iron. The main chemical reaction producing the molten iron is: Fe2O3 + 3 CO → 2 Fe + 3 CO2 == Redox reactions in soils == Electron transfer reactions are central to myriad processes and properties in soils, and redox potential, quantified as Eh (platinum electrode potential (voltage) relative to the standard hydrogen electrode) or pe (analogous to pH as −log electron activity), is a master variable, along with pH, that controls and is governed by chemical reactions and biological processes. Early theoretical research with applications to flooded soils and paddy rice production was seminal for subsequent work on thermodynamic aspects of
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redox and plant root growth in soils. Later work built on this foundation, and expanded it for understanding redox reactions related to heavy metal oxidation state changes, pedogenesis and morphology, organic compound degradation and formation, free radical chemistry, wetland delineation, soil remediation, and various methodological approaches for characterizing the redox status of soils. == Mnemonics == The key terms involved in redox can be confusing. For example, a reagent that is oxidized loses electrons; however, that reagent is referred to as the reducing agent. Likewise, a reagent that is reduced gains electrons and is referred to as the oxidizing agent. These mnemonics are commonly used by students to help memorise the terminology: "OIL RIG" — oxidation is loss of electrons, reduction is gain of electrons "LEO the lion says GER [grr]" — loss of electrons is oxidation, gain of electrons is reduction "LEORA says GEROA" — the loss of electrons is called oxidation (reducing agent); the gain of electrons is called reduction (oxidizing agent). "RED CAT" and "AN OX", or "AnOx RedCat" ("an ox-red cat") — reduction occurs at the cathode and the anode is for oxidation "RED CAT gains what AN OX loses" – reduction at the cathode gains (electrons) what anode oxidation loses (electrons) "PANIC" – Positive Anode and Negative is Cathode. This applies to electrolytic cells which release stored electricity, and can be recharged with electricity. PANIC does not apply to cells that can be recharged with redox materials. These galvanic or voltaic cells, such as fuel cells, produce electricity from internal redox reactions. Here, the positive electrode is the cathode and the negative is the anode. == See also == == References == == Further reading == Schüring, J.; Schulz, H. D.; Fischer, W. R.; Böttcher, J.; Duijnisveld, W. H., eds. (1999). Redox: Fundamentals, Processes and
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Applications. Heidelberg: Springer-Verlag. p. 246. hdl:10013/epic.31694.d001. ISBN 978-3-540-66528-1. Tratnyek, Paul G.; Grundl, Timothy J.; Haderlein, Stefan B., eds. (2011). Aquatic Redox Chemistry. ACS Symposium Series. Vol. 1071. doi:10.1021/bk-2011-1071. ISBN 978-0-8412-2652-4. == External links ==
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Solid-state chemistry, also sometimes referred as materials chemistry, is the study of the synthesis, structure, and properties of solid phase materials. It therefore has a strong overlap with solid-state physics, mineralogy, crystallography, ceramics, metallurgy, thermodynamics, materials science and electronics with a focus on the synthesis of novel materials and their characterization. A diverse range of synthetic techniques, such as the ceramic method and chemical vapour depostion, make solid-state materials. Solids can be classified as crystalline or amorphous on basis of the nature of order present in the arrangement of their constituent particles. Their elemental compositions, microstructures, and physical properties can be characterized through a variety of analytical methods. == History == Because of its direct relevance to products of commerce, solid state inorganic chemistry has been strongly driven by technology. Progress in the field has often been fueled by the demands of industry, sometimes in collaboration with academia. Applications discovered in the 20th century include zeolite and platinum-based catalysts for petroleum processing in the 1950s, high-purity silicon as a core component of microelectronic devices in the 1960s, and “high temperature” superconductivity in the 1980s. The invention of X-ray crystallography in the early 1900s by William Lawrence Bragg was an enabling innovation. Our understanding of how reactions proceed at the atomic level in the solid state was advanced considerably by Carl Wagner's work on oxidation rate theory, counter diffusion of ions, and defect chemistry. Because of his contributions, he has sometimes been referred to as the father of solid state chemistry. == Synthetic methods == Given the diversity of solid-state compounds, an equally diverse array of methods are used for their preparation. Synthesis can range from high-temperature methods, like the ceramic method, to gas methods, like chemical vapour deposition. Often, the methods prevent defect formation or produce high-purity products. === High-temperature
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methods === ==== Ceramic method ==== The ceramic method is one of the most common synthesis techniques. The synthesis occurs entirely in the solid state. The reactants are ground together, formed into a pellet using a pellet press and hydraulic press, and heated at high temperatures. When the temperature of the reactants are sufficient, the ions at the grain boundaries react to form desired phases. Generally ceramic methods give polycrystalline powders, but not single crystals. Using a mortar and pestle, ResonantAcoustic mixer, or ball mill, the reactants are ground together, which decreases size and increases surface area of the reactants. If the mixing is not sufficient, we can use techniques such as co-precipitation and sol-gel. A chemist forms pellets from the ground reactants and places the pellets into containers for heating. The choice of container depends on the precursors, the reaction temperature and the expected product. For example, metal oxides are typically synthesized in silica or alumina containers. A tube furnace heats the pellet. Tube furnaces are available up to maximum temperatures of 2800oC. ==== Molten flux synthesis ==== Molten flux synthesis can be an efficient method for obtaining single crystals. In this method, the starting reagents are combined with flux, an inert material with a melting point lower than that of the starting materials. The flux serves as a solvent. After the reaction, the excess flux can be washed away using an appropriate solvent or it can be heat again to remove the flux by sublimation if it is a volatile compound. Crucible materials have a great role to play in molten flux synthesis. The crucible should not react with the flux or the starting reagent. If any of the material is volatile, it is recommended to conduct the reaction in a sealed ampule. If the target phase is
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sensitive to oxygen, a carbon- coated fused silica tube or a carbon crucible inside a fused silica tube is often used which prevents the direct contact between the tube wall and reagents. ==== Chemical vapour transport ==== Chemical vapour transport results in very pure materials. The reaction typically occurs in a sealed ampoule. A transporting agent, added to the sealed ampoule, produces a volatile intermediate species from the solid reactant. For metal oxides, the transporting agent is usually Cl2 or HCl. The ampoule has a temperature gradient, and, as the gaseous reactant travels along the gradient, it eventually deposits as a crystal. An example of an industrially-used chemical vapor transport reaction is the Mond process. The Mond process involves heating impure nickel in a stream of carbon monoxide to produce pure nickel. === Low-temperature methods === ==== Intercalation method ==== Intercalation synthesis is the insertion of molecules or ions between layers of a solid. The layered solid has weak intermolecular bonds holding its layers together. The process occurs via diffusion. Intercalation is further driven by ion exchange, acid-base reactions or electrochemical reactions. The intercalation method was first used in China with the discovery of porcelain. Also, graphene is produced by the intercalation method, and this method is the principle behind lithium-ion batteries. === Solution methods === It is possible to use solvents to prepare solids by precipitation or by evaporation. At times, the solvent is a hydrothermal that is under pressure at temperatures higher than the normal boiling point. A variation on this theme is the use of flux methods, which use a salt with a relatively low melting point as the solvent. === Gas methods === Many solids react vigorously with gas species like chlorine, iodine, and oxygen. Other solids form adducts, such as CO or ethylene. Such reactions
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are conducted in open-ended tubes, which the gasses are passed through. Also, these reactions can take place inside a measuring device such as a TGA. In that case, stoichiometric information can be obtained during the reaction, which helps identify the products. ==== Chemical vapour deposition ==== Chemical vapour deposition is a method widely used for the preparation of coatings and semiconductors from molecular precursors. A carrier gas transports the gaseous precursors to the material for coating. == Characterization == This is the process in which a material’s chemical composition, structure, and physical properties are determined using a variety of analytical techniques. === New phases === Synthetic methodology and characterization often go hand in hand in the sense that not one but a series of reaction mixtures are prepared and subjected to heat treatment. Stoichiometry, a numerical relationship between the quantities of reactant and product, is typically varied systematically. It is important to find which stoichiometries will lead to new solid compounds or solid solutions between known ones. A prime method to characterize the reaction products is powder diffraction because many solid-state reactions will produce polycrystalline molds or powders. Powder diffraction aids in the identification of known phases in the mixture. If a pattern is found that is not known in the diffraction data libraries, an attempt can be made to index the pattern. The characterization of a material's properties is typically easier for a product with crystalline structures. === Compositions and structures === Once the unit cell of a new phase is known, the next step is to establish the stoichiometry of the phase. This can be done in several ways. Sometimes the composition of the original mixture will give a clue, under the circumstances that only a product with a single powder pattern is found or a phase of
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a certain composition is made by analogy to known material, but this is rare. Often, considerable effort in refining the synthetic procedures is required to obtain a pure sample of the new material. If it is possible to separate the product from the rest of the reaction mixture, elemental analysis methods such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) can be used. The detection of scattered and transmitted electrons from the surface of the sample provides information about the surface topography and composition of the material. Energy dispersive X-ray spectroscopy (EDX) is a technique that uses electron beam excitation. Exciting the inner shell of an atom with incident electrons emits characteristic X-rays with specific energy to each element. The peak energy can identify the chemical composition of a sample, including the distribution and concentration.Similar to EDX, X-ray diffraction analysis (XRD) involves the generation of characteristic X-rays upon interaction with the sample. The intensity of diffracted rays scattered at different angles is used to analyze the physical properties of a material such as phase composition and crystallographic structure. These techniques can also be coupled to achieve a better effect. For example, SEM is a useful complement to EDX due to its focused electron beam, it produces a high-magnification image that provides information on the surface topography. Once the area of interest has been identified, EDX can be used to determine the elements present in that specific spot. Selected area electron diffraction can be coupled with TEM or SEM to investigate the level of crystallinity and the lattice parameters of a sample. ==== More information ==== X-ray diffraction is also used due to its imaging capabilities and speed of data generation. The latter often requires revisiting and refining the preparative procedures and that are linked to the question of
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which phases are stable at what composition and what stoichiometry. In other words, what the phase diagram looks like. An important tool in establishing this are thermal analysis techniques like DSC or DTA and increasingly also, due to the advent of synchrotrons, temperature-dependent powder diffraction. Increased knowledge of the phase relations often leads to further refinement in synthetic procedures in an iterative way. New phases are thus characterized by their melting points and their stoichiometric domains. The latter is important for the many solids that are non-stoichiometric compounds. The cell parameters obtained from XRD are particularly helpful to characterize the homogeneity ranges of the latter. === Local structure === In contrast to the large structures of crystals, the local structure describes the interaction of the nearest neighbouring atoms. Methods of nuclear spectroscopy use specific nuclei to probe the electric and magnetic fields around the nucleus. E.g. electric field gradients are very sensitive to small changes caused by lattice expansion/compression (thermal or pressure), phase changes, or local defects. Common methods are Mössbauer spectroscopy and perturbed angular correlation. === Optical properties === For metallic materials, their optical properties arise from the collective excitation of conduction electrons. The coherent oscillations of electrons under electromagnetic radiation along with associated oscillations of the electromagnetic field are called surface plasmon resonances. The excitation wavelength and frequency of the plasmon resonances provide information on the particle's size, shape, composition, and local optical environment. For non-metallic materials or semiconductors, they can be characterized by their band structure. It contains a band gap that represents the minimum energy difference between the top of the valence band and the bottom of the conduction band. The band gap can be determined using Ultraviolet-visible spectroscopy to predict the photochemical properties of the semiconductors. === Further characterization === In many cases, new solid
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compounds are further characterized by a variety of techniques that straddle the fine line that separates solid-state chemistry from solid-state physics. See Characterisation in material science for additional information. == References == == External links == Media related to Solid state chemistry at Wikimedia Commons [1], Sadoway, Donald. 3.091SC; Introduction to Solid State Chemistry, Fall 2010. (Massachusetts Institute of Technology: MIT OpenCourseWare)
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Homi Jehangir Bhabha, FNI, FASc, FRS(30 October 1909 – 24 January 1966) was an Indian nuclear physicist who is widely credited as the "father of the Indian nuclear programme". He was the founding director and professor of physics at the Tata Institute of Fundamental Research (TIFR), as well as the founding director of the Atomic Energy Establishment, Trombay (AEET) which was renamed the Bhabha Atomic Research Centre in his honour. TIFR and AEET served as the cornerstone to the Indian nuclear energy and weapons programme. He was the first chairman of the Indian Atomic Energy Commission (AEC) and secretary of the Department of Atomic Energy (DAE). By supporting space science projects which initially derived their funding from the AEC, he played an important role in the birth of the Indian space programme. Bhabha was awarded the Adams Prize (1942) and Padma Bhushan (1954), and nominated for the Nobel Prize for Physics in 1951 and 1953–1956. He died in the crash of Air India Flight 101 in 1966, at the age of 56. == Early life == === Childhood === Homi Jehangir Bhabha was born on 30 October 1909 into a wealthy Parsi family comprising Jehangir Hormusji Bhabha, a well-known lawyer, and Meherbai Framji Panday, granddaughter of Sir Dinshaw Maneckji Petit. He was named Hormusji after his paternal grandfather, Hormusji Bhabha, who was Inspector-General of Education in Mysore. He received his early studies at Mumbai's Cathedral and John Connon School. Bhabha's upbringing instilled in him an appreciation for music, painting and gardening. He often visited his paternal aunt Meherbai Tata, who owned a Western classical music collection which included the works of Beethoven, Mozart, Haydn and Schubert. Together with his brother and his cousin, it was a ritual for him to listen to records from this collection over the gramophone. Bhabha
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also received special violin and piano lessons. His tutor in sketching and painting was the artist Jehangir Lalkala. At seventeen, Bhabha's self-portrait won second place at the prestigious Bombay Art Society's exhibition. Tending to a terrace garden of exotic plants and cross-bred bougainvillea and roses, Hormusji was an expert on trees, plants and flowers. He kept books on gardening in the house's large private library. Bhabha showed signs of precocity in the sciences. As a child, he spent hours playing with Meccano sets, and was fond of building his own models rather than following the booklets that accompanied the sets. By fifteen, he had studied general relativity. Bhabha frequently visited the home of his uncle Dorabji Tata, chairman of the conglomerate Tata Group and then one of the wealthiest men in India. There, he was privy to conversations Dorabji had with national leaders of the independence movement, like Mahatma Gandhi and Motilal Nehru, as well as business dealings in industries like steel, heavy chemicals and hydroelectric power which the Tata Group invested in. John Cockcroft remarked that overhearing these conversations should have inspired Bhabha's career as a scientific organizer. === University studies in India === Though he passed his Senior Cambridge Examination with honours at the age of fifteen, he was too young to join any college abroad. So, he enrolled in Elphinstone College. He then attended the Royal Institute of Science in 1927, where he witnessed a public lecture by Arthur Compton, who would win the Nobel Prize in physics the next year for his 1923 discovery of the Compton effect. Bhabha later said that he first heard of cosmic rays, the subject of his future research, at this lecture. === University studies in Cambridge === The following year, he joined Gonville and Caius College of Cambridge University. This
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was due to the insistence of his father and his uncle Dorabji, who planned for Bhabha to obtain a degree in mechanical engineering from Cambridge and then return to India, where he would join the Tata Steel mills in Jamshedpur as a metallurgist. Within a year of joining Cambridge University, Bhabha wrote to his father:I seriously say to you that business or job as an engineer is not the thing for me. It is totally foreign to my nature and radically opposed to my temperament and opinions. Physics is my line. I know I shall do great things here. For, each man can do best and excel in only that thing of which he is passionately fond, in which he believes, as I do, that he has the ability to do it, that he is in fact born and destined to do it … I am burning with a desire to do physics. I will and must do it sometime. It is my only ambition. I have no desire to be a "successful" man or the head of a big firm. There are intelligent people who like that and let them do it. … It is no use saying to Beethoven "You must be a scientist for it is great thing" when he did not care two hoots for science; or to Socrates "Be an engineer; it is work of intelligent man". It is not in the nature of things. I therefore earnestly implore you to let me do physics.Sympathetic to his son's predicament, Bhabha's father agreed to finance his studies in mathematics provided that he obtain first class on his Mechanical Tripos. Bhabha sat the Mechanical Tripos in June 1930 and the Mathematics Tripos two years later, passing both with first-class honours. Bhabha coxed for his college in boat
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"page_id": 1245965,
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races and designed the cover of his college magazine the Caian. He also designed the sets for a student performance of Pedro Calderón de la Barca's play Life is a Dream and Mozart's Idomeneo for the Cambridge Musical Society. Encouraged by the English artist and art critic Roger Fry, who praised his sketches, Bhabha seriously considered becoming an artist. However, exposure to work being done at the Cavendish Laboratory at the time motivated Bhabha to focus on theoretical physics. When he registered as a research student in mathematics, he decided to change his name to Homi Jehangir Bhabha, the name he would keep for the rest of his life. == Early research in nuclear physics == Bhabha worked at the Cavendish Laboratory while working towards his PhD degree in theoretical physics supervised by Ralph Fowler. At the time, the laboratory was the centre of several breakthroughs in experimental physics. James Chadwick had discovered the neutron, John Cockcroft and Ernest Walton had transmuted lithium with high-energy protons, Francis Aston had discovered chemical isotopes, and Patrick Blackett and Giuseppe Occhialini had used cloud chambers to demonstrate the production of electron pairs and showers by gamma radiation. In 1931, Bhabha held the Salomons studentship in engineering. In 1932, on a Rouse Ball travelling studentship, he visited Copenhagen, Zurich and Utretcht. Niels Bohr's institute at Copenhagen was a major hub of theoretical physics research. At Zurich, Bhabha wrote his first paper in July 1933 with Wolfgang Pauli, which was published in the Zeitschrift fur physik in October 1933. During his studentship, Bhabha also visited Hans Kramers, who was then a professor conducting theoretical research in the interaction of electromagnetic waves with matter at Utrecht University. In 1933, Bhabha was selected for the Isaac Newton scholarship, which he held for the next three years and
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"page_id": 1245965,
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used to fund his time working with Enrico Fermi at the Institute of Physics in Rome. The same year, Bhabha published his first paper on the role of electron showers in absorbing gamma radiation. The discovery of the positron in 1932 and the formulation of Dirac's hole theory to explain its properties had catalysed the creation of the field of high-energy physics. Bhabha chose to make this field the focus of his career, publishing over fifty papers on the topic during his lifetime. He played a key role in the early development of quantum electrodynamics. Bhabha received his doctorate in nuclear physics in 1935 for his thesis titled "On cosmic radiation and the creation and annihilation of positrons and electrons". In 1935, Bhabha published a paper in the Proceedings of the Royal Society in which he first calculated the cross-section of electron-positron scattering. Electron-positron scattering was later named Bhabha scattering after him. In 1937, with Walter Heitler, he co-authored a paper, "The passage of fast electrons and the theory of cosmic showers" in the Proceedings of the Royal Society, Series A, in which they used their theory to describe how primary cosmic rays from outer space interact with the upper atmosphere to produce particles observed at the ground level. Bhabha and Heitler then made numerical estimates of the number of electrons in the cascade process at different altitudes for different electron initiation energies. The calculations agreed with the experimental observations of cosmic ray showers made by Bruno Rossi and Pierre Victor Auger a few years before. Bhabha and Heitler postulated that the penetrating component of cosmic radiation comprised "heavy electrons", most of which "must have masses nearer to hundred times the electron mass". The paper was announced in a letter in Nature. The same year, Seth Neddermeyer and Carl David
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"page_id": 1245965,
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Anderson, among others, also reached similar conclusions in independently published papers in Physical Review. Before pions were discovered, observers often confused muons with mesons. When Bhabha's collaborator Heitler made him aware of Hideki Yukawa's 1935 paper on the theory of the meson, Bhabha realized that this particle was the postulated "heavy electron". In a 1939 note to Nature, Bhabha argued the particle should be christened the "meson" in line with the word's Greek etymology, not "mesotron" as Anderson had proposed. Bhabha later concluded that observations of the properties of the meson would lead to the straightforward experimental verification of the time dilation phenomenon predicted by Albert Einstein's theory of relativity. So far, Bhabha's work had been supported by the Senior Studentship of the 1851 exhibition, which he had received for three years, starting in 1936, while continuing to be based in Gonville and Caius College. In 1939, Bhabha was awarded a Royal Society grant to work in P. M. S. Blackett's laboratory in Manchester. However, when World War II broke out, Bhabha found himself unable to return to England to take up the assignment. == Career == === Indian Institute of Science === Bhabha had returned to India for his annual vacation before the start of World War II in September 1939. War prompted him to remain in India, where he accepted a post of reader in physics at the Indian Institute of Science in Bengaluru headed by Nobel laureate C.V. Raman. In 1940, the Sir Dorabji Tata Trust supported his experimental cosmic ray physics research with a grant. Bhabha was made a Fellow of the Royal Society in 1941, and the following year he became the first Indian to receive the Adams Prize. Soon after receiving the Adams Prize, Bhabha was also made a Fellow of the Indian Academy
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{
"page_id": 1245965,
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of Sciences and President of the Physics section of the Indian Sciences Congress. While introducing him at the 1941 Annual Meeting of the Indian Academy of Sciences, C.V. Raman described the 32-year-old Bhabha as "the modern equivalent of Leonardo da Vinci". On 20 January 1942, Bhabha formally accepted professorship and leadership of the Cosmic Ray Research Unit. As late as 1940, Bhabha was listing his affiliation as "at present at the Department of Physics, Indian Institute of Science, Bangalore", suggesting that he viewed his time in India as a temporary period before his return to the UK. In 1941, he wrote to Robert Millikan that he hoped that the war would be over soon, so that "we can all turn again in more favourable conditions to purely scientific activity". Though he had hoped to work in Caltech, it was impossible for Millikan to invite him there. The restrictions on finance imposed by the war also made it impossible for Wolfgang Pauli to invite Bhabha to Princeton. During his time in Bengaluru, Bhabha met Vikram and Mrinalini Sarabhai as part of a group interested in Indian culture, and developed an appreciation for Indian architectural and artistic heritage on his tours around the country. In a 1944 letter, he expressed a change of mind and a desire to stay in India:I had the idea that after the war I would accept a job in a good university in Europe or America. … But in the last two years I have come more and more to the view that provided proper appreciation and financial support are forthcoming, it is one's duty to stay in one's own country. === Tata Institute of Fundamental Research === In 1943, Bhabha wrote to J. R. D. Tata proposing the establishment of an institute of fundamental research. Tata
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"page_id": 1245965,
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wrote back:If you and some of your friends in the scientific world will put up concrete proposals backed by a sound case I think there is a very good chance that the Sir Dorabji Tata Trust will respond. After all, the advancement of science of one of the fundamental objectives with which the Tata Trusts were founded, and they have already rendered useful service in that field. If they are shown that they can give still more valuable help in a new way, I am quite sure that they will give it their most serious consideration. In a letter to the astrophysicist Subrahmanyan Chandrasekhar, Bhabha described that his ambition was to "bring together as many outstanding scientists as possible … so as to build up in time an intellectual atmosphere approaching what we knew in places like Cambridge and Paris." J. R. D. Tata's enthusiasm encouraged Bhabha to send a proposal in March 1944 to Sir Sorab Saklavata, the chairman of the Sir Dorabji Tata Trust, for establishing a school dedicated to research in fundamental physics. In his proposal he wrote: There is at the moment in India no big school of research in the fundamental problems of physics, both theoretical and experimental. There are, however, scattered all over India competent workers who are not doing as good work as they would do if brought together in one place under proper direction. It is absolutely in the interest of India to have a vigorous school of research in fundamental physics, for such a school forms the spearhead of research not only in less advanced branches of physics but also in problems of immediate practical application in industry. If much of the applied research done in India today is disappointing or of very inferior quality it is entirely due to the
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"page_id": 1245965,
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absence of a sufficient number of outstanding pure research workers who would set the standard of good research and act on the directing boards in an advisory capacity ... Moreover, when nuclear energy has been successfully applied for power production in say a couple of decades from now, India will not have to look abroad for its experts but will find them ready at hand.The trustees of Sir Dorabji Tata Trust decided to accept Bhabha's proposal and financial responsibility for starting the Institute in April 1944. In June 1945, with a grant from the Trust, he established the Tata Institute of Fundamental Research. While TIFR began functioning in the Cosmic Ray Unit of the Indian Institute of Science Bangalore, by October that year, it had moved to Bombay. TIFR initially operated in 6,000 square feet of the bungalow where Bhabha had been born, with Bhabha taking as his office the very room where he had been born. The institute was moved into the old buildings of the Royal Yacht club in 1948. In 1962, an art gallery designed the Chicago-based firm Holabird & Root architect Helmuth Bartsch was inaugurated at TIFR. Bombay was chosen as the location as the Government of Bombay showed interest in becoming a joint founder of the proposed institute. Inaugurating the Bombay premises in December 1945, the Governor of Bombay Sir John Colville said:We are embarking on an enterprise of importance to the country's development, in which great wealth, wisely husbanded and applied, individual initiative and government support are all blended. I do not think there could be a better combination for progress.A former director of TIFR, M. G. K. Menon, said that the institute's budget "grew at the rate of about 30% per annum over the first ten years, and about 15% per annum over
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{
"page_id": 1245965,
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the second decade". By 1954, Bhabha had stopped publishing scientific papers but continued to carry out a range of administrative tasks aimed at growing TIFR. Some of TIFR's research groups focused on nuclear chemistry and metallurgy; these were later moved to Trombay to provide the basis for a 1958 plan to integrate nuclear energy into the national power grid. By 1954, the Institute contained an in-house electronics production unit. Under Bhabha's leadership, the Institute established a research group under Bernard Peters' supervision to conduct research on cosmic rays, and later geophysics. This group was the first to identify K minus strange particles. Bhabha remained the institute's Director till his death in 1966. === India's nuclear energy programme === ==== Atomic Energy Commission ==== On 26 April 1948, Bhabha wrote to Prime Minister Jawaharlal Nehru that "the development of atomic energy should be entrusted to a very small and high-powered body composed of say three people with executive power, and answerable directly to the Prime Minister without any intervening link. For brevity, this body may be referred to as the Atomic Energy Commission." Pursuant to the Atomic Energy Act, the Atomic Energy Commission (AEC) was established on 10 August 1948. Nehru appointed Bhabha as the commission's first chairman. The three-member Commission included S. S. Bhatnagar and K. S. Krishnan. Bhabha, Bhatnagar and Krishnan were also named to the Scientific Advisory Committee to the Ministry of Defence created in July 1948. The details of the workings of the AEC were declared state secrets for two reasons according to Nehru: "the advantage of our research would go to others before we even reaped it, and secondly it would become impossible for us to cooperate with any country which is prepared to cooperate with us in this matter, because it will not be prepared
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{
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for the results of researches to become public." The scholar George Perkovich argues that due to this secrecy and the AEC's relative freedom from government control, the "Nehru-Bhabha relationship constituted the only potentially real mechanism to check and balance the nuclear programme". Yet, rather than being "watchful and balancing", the relationship was "friendly and symbiotic". Twenty years younger than Nehru, Bhabha addressed him as "Dear Bhai", or "Dear Brother", while Nehru addressed Bhabha as "My dear Homi". Indira Gandhi later recalled that her father always found the time to speak to Bhabha, both because, she claimed, Bhabha brought to him urgent matters that required immediate attention, and because conversations with him afforded Nehru "warm moments of sensitivity that other people take for granted in their everyday life", but which are harder to come by in the life of a politician. When Bhabha realised that technology development for the atomic energy programme could no longer be carried out within TIFR he proposed to the government to build a new laboratory entirely devoted to this purpose. For this purpose, 1,200 acres (490 ha) of land was acquired at Trombay from the Bombay Government. Thus, the Atomic Energy Establishment Trombay (AEET) started functioning in 1954. The same year, Bhabha was appointed the secretary of the Department of Atomic Energy (DAE) under the direct charge of the Prime Minister. Atomic Energy was established as a separate ministry, where earlier the AEC fell under the umbrella of the Ministry of Natural Resources and Scientific Research. In a 1957 paper in Nature summarizing the Indian nuclear energy programme's ambitions and work, Bhabha claimed that "[a]lthough the Atomic Energy Commission was established as an advisory body in 1948 in the Ministry of Natural Resources and Scientific Research, no important effort to develop this work was made until
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"page_id": 1245965,
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a separate department of the Government of India with the full powers of a ministry was established in August 1954." A former chairman of the AEC, H. N. Sethna, said that until the establishment of the DAE in 1954, "the work of the Atomic Energy Commission had been restricted to the survey of radioactive minerals, setting up plants for processing monazite and limited research activity in the area of electronics, methods of chemical analysis of minerals and the recovery of valuable elements from available minerals." At the DAE, Bhabha maintained relative autonomy over priority-setting, and throughout the 1950s and the early 1960s, nuclear policy remained little-discussed in the Parliament and in public life. ==== Three-stage plan ==== Bhabha is credited with formulating a strategy of focusing on extracting power from the country's vast thorium reserves rather than its meagre uranium reserves. He presented this plan to the Conference on the Development of Atomic Energy for Peaceful Purposes in New Delhi in November 1954. This thorium-focused strategy stood in marked contrast to all other countries in the world. It became formally adopted by the Indian government in 1958 as India's three-stage nuclear power programme. Bhabha paraphrased the three-stage approach as follows: The total reserves of thorium in India amount to over 500,000 tons in the readily extractable form, while the known reserves of uranium are less than a tenth of this. The aim of a long-range atomic power programme in India must therefore be to base the nuclear power generation as soon as possible on thorium rather than uranium... The first generation of atomic power stations based on natural uranium can only be used to start an atomic power programme... The plutonium produced by the first-generation of power stations can be used in a second-generation of power stations designed to produce
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"page_id": 1245965,
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electric power and convert thorium into U-233, or depleted uranium into more plutonium with breeding gain... The second generation of power stations may be regarded as an intermediate step for the breeder power stations of the third generation all of which would produce more U-238 than they burn in the course of producing power.In 1952, Indian Rare Earths Limited, a Government-owned company, was established to extract rare earths and thorium from Kerala's monazite sands, with Bhabha serving as its director. In August 1956, the one-megawatt "swimming-pool" research reactor APSARA was commissioned, making India the first Asian country besides the Soviet Union to have a nuclear reactor. Running on enriched natural uranium fuel supplied by the United Kingdom Atomic Energy Commission and thorium, APSARA represented the first stage of Bhabha's plan: it would be useful in producing plutonium. It also allowed Indian nuclear scientists to carry out experiments, whereas national research in atomic energy earlier had been largely theoretical. Bhabha was able to secure favourable terms for India partly due to his friendship with Sir John Cockcroft, who had been his colleague at the Cavendish laboratory in Cambridge. That year, India and Canada signed an agreement for the construction of a natural uranium, heavy water-moderated National Research Experimental (NRX) reactor in Trombay. Bhabha's personal friendship with WB Lewis, who headed the Canadian Atomic Energy Agency at the time, proved useful to securing the deal. The reactor, named the Canada India Reactor Utility Service (CIRUS), went critical on 10 July 1960. At forty megawatts, it was the highest-output reactor in Asia at the time, and India's first plutonium source. CIRUS also served as the prototype of the successful Canada Deuterium Uranium (CANDU) reactor type. The reactor's low burn produced a large amount of weapons-grade plutonium, some of which was used in India's
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1974 peaceful nuclear explosion. To supply CIRUS with heavy water, a heavy water plant with an output of 14 metric tonnes per year was commissioned in Nangal. It began operation on 2 August 1962. In July 1958, Bhabha decided to build a plutonium reprocessing plant in Trombay. Construction of the Phoenix plant, based on the Purex (plutonium-uranium extraction) technique for extracting plutonium from spent fuel, began in 1961 and was completed in mid-1964. Paired with CIRUS, Phoenix produced India's first weapons-grade plutonium in 1964. Even after the establishment of APSARA, CIRUS, Phoenix and the indigenously produced zero-energy critical reactor ZERLINA, India hadn't actually produced nuclear energy. To remedy this, in 1962, General Electric was commissioned to build two light water-moderated nuclear reactors in Tarapur. Because the Tarapur Atomic Power Stations (TAPS) were fueled by enriched uranium, they didn't fit into Bhabha's three-stage plan. The US' terms for the Tarapur deal, an $80 million loan at 0.75% interest, were highly favourable to India. Bhabha also managed to negotiate the limitation of International Atomic Energy Agency safeguards to the TAPS facility. M. R. Srinivasan, former chairman of the AEC, remarked that Bhabha's success in the Tarapur negotiation would have been a proud achievement for an experienced professional diplomat. ==== International Atomic Energy Agency ==== In the 1950s, Bhabha represented India in International Atomic Energy Agency conferences, and served as President of the United Nations Conference on the Peaceful Uses of Atomic Energy in Geneva, Switzerland in 1955. According to the IAEA's 10 September 1956 draft statute, plutonium and other special fissionable materials would be deposited with the agency, which would have the discretion to provide states with quantities deemed suitable for nonmilitary use under safeguards. Bhabha successfully lobbied against the agency's broad authority, arguing in a 27 September 1956 conference that it
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was the "inalienable right of States to produce and hold the fissionable material required for the peaceful power programmes". The IAEA's final statute required only safeguards on fissile materials and reactors to ensure these weren't diverted to military use. Of Bhabha's negotiating skills, the US Atomic Energy Commission chairman Glenn Seaborg said: "He was not easy to argue with. Polite but very sure of himself, he was never at a loss for words, and was most articulate. He was a very imposing presence." ==== Allegations of developing nuclear explosives capability ==== Aware that the negotiated IAEA safeguards weren't sufficient to deter a state from developing weapons capability, Bhabha had remarked in his 27 September 1957 speech at the IAEA:[T]here are many States, technically advanced, which may undertake with Agency aid, fulfilling all the present safeguards, but in addition run their own parallel programmes independently of the Agency in which they could use the experience and know-how obtained in Agency-aided projects, without being subject in any way to the system of safeguards.In December 1959, in light of concerns about a possible Chinese nuclear weapons programme, Bhabha claimed to the Parliamentary Consultative Committee on Atomic Energy that India's nuclear energy research had progressed to the point where it could build nuclear weapons without external aid. In 1960, in a meeting with Nehru and Kenneth Nichols, who was visiting India as a consultant to Westinghouse, Bhabha estimated that it would take India "about a year" to build a nuclear bomb. A 1964 US State Department Bureau of Intelligence and Research report concluded that although there was no "direct evidence" of an Indian nuclear weapons programme and that it was "unlikely" that India had made a decision to pursue weapons capability, it was "probably no accident" that "everything the Indians [had] done so far
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{
"page_id": 1245965,
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would be compatible with a weapons programme if at some future date it appeared desirable to start one". A year after Bhabha's death, at a memorial lecture held in his honour, John Cockcroft stated that "it was a declared policy of the government of India not to develop nuclear weapons, and Homi Bhabha of course in his official pronouncements followed the policy of his government," but that Cockcroft "always thought, from private discussions, that his attitude was somewhat ambivalent. After the Chinese nuclear bomb test, he certainly wished to put India into the position of being able to make plutonium bombs, if the government so desired." However, M. G. K. Menon, the new director of TIFR, pushed back against Cockcroft's statement, arguing that the motivation behind setting up the Indian plutonium reprocessing plant "has sometimes been misunderstood". He said that because the decision to build the plant was taken before the 1962 Indo-China war, it could not have been built for security reasons and was purely for reprocessing fuel rods. However, Menon conceded that mistrust between the two nations had been public since 1950. India also had knowledge of the Chinese nuclear weapons program before the 1962 war. In a 2006 interview, P. K. Iyengar, a former chairman of the AEC, was asked whether Bhabha was "keen" on India becoming a nuclear weapons state. In response, Iyengar stated: "Dr Bhabha had in his mind from the very beginning that India should become a Nuclear Weapons State. His emphasis on self-reliance is essentially due to the fact he wanted India to be a nuclear weapons country." ==== Lobbying to build nuclear explosives ==== After the Chinese nuclear test on 16 October 1964, Bhabha began to publicly call for building nuclear explosives. On the other hand, Prime Minister Lal Bahadur Shastri, Nehru's
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{
"page_id": 1245965,
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successor, sought security guarantees from the existing nuclear powers, while declaring at the Cairo Conference of Non-aligned Nations that India's nuclear establishment was "under firm orders not to make a single experiment, not to perfect a single device which is not needed for peaceful uses of atomic energy". On a visit to London on 4 October 1964, anticipating the Chinese test, Bhabha said that India could conduct a nuclear test within a year and a half of a decision to do so, but that he did not "think such a decision will be taken". A 28 October 1964 Indian Express survey found that public opinion leaders across India now took "for granted" Bhabha's claim that India could develop a nuclear bomb within a year and a half. Yet, this figure was likely an overestimate. In 1996, Raja Ramanna, the physicist tasked in 1965 with directing the nuclear weapons project, said: "I don't think it would have been possible to do what Bhabha said—build a device in 18 months. A crash program could have been done, I suppose, but it would have been very expensive." By 1965, Bhabha had updated his estimate from eighteen months to at least five years. About a week after the Chinese test, Bhabha said in an All India Radio broadcast:Atomic weapons give a State possessing them in adequate numbers a deterrent power against attack from a much stronger State. … A two megaton explosion, i.e., one equivalent to 2 million tons of TNT, would cost $600,000 or Rs. 30 lakhs. On the other hand, at current prices of TNT, 2 million tons of it would cost some Rs. 150 crores [$300 million]. This cost estimate ignored the expenses on reactors, reprocessing facilities and infrastructure necessary to design and produce weapons. Nevertheless, despite efforts by the US
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"page_id": 1245965,
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government and other Indian scientists to correct this estimate, Bhabha's arguments supporting the affordability of a nuclear weapons programme continued to be used by the Indian pro-bomb lobby. On 26 October 1964, the Hindu nationalist Jana Sangh editorialized: "We had the chance to do it [detonate a nuclear bomb] before China did it and so we could tell that we meant business and that we were ahead of China. In our criminal folly we missed it." A 29 October 1964 US Embassy cable cited an informed source from the Indian Ministry of External Affairs as saying that "pressures within GOI [Government of India] for India to develop its own bomb were building up" and that "Bhabha was the leading advocate for this group and he was actively campaigning to go down nuclear the road". A six-hour cabinet discussion of nuclear policy had culminated in the Minister of External Affairs Swaran Singh and the influential Minister of Railways S. K. Patil supporting Bhabha, who was attending as an observer, in his proposal for a nuclear weapon-building program. Only two cabinet ministers were against. Prime Minister Lal Bahadur Shastri, Nehru's successor, authorized Bhabha to "come up with estimate of what was involved in India's attempting an underground 'explosion'." This repudiated Shastri's policy preferences, who, as a Gandhian, showed a strong moral revulsion to building nuclear weapons, and did not wish to increase defence spending during the nation's ongoing food crisis. Shastri sought British assistance in making more objective cost estimates. In a November 1964 All India Congress Committee meeting, he disputed Bhabha's numbers, arguing that the production of a single nuclear bomb would cost Rs 400 to 500 million, more than two hundred times Bhabha's estimate. In a remark likely aimed at Bhabha's All India Radio broadcast, Shastri added that "scientists should
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realise that it was the responsibility of the Government to defend the country and adopt appropriate measures". Beyond economic considerations, he warned that with the development of an initial weapons capability, India "could not be content with one or two bombs. The spirit of competition was bound to capture her". As "the majority of speakers [had come] out strongly and frankly in favour of India manufacturing atom bombs" at the meeting, the Hindustan Times called Shastri's successful opposing address "nothing short of a miracle". After Shastri's address, Bhabha clarified that his figures came from an American study on "the peaceful uses of atomic explosions" for civil engineering projects, but maintained that nuclear explosive power could be cost-effective. On 23 and 24 November 1964, when the Lok Sabha met to discuss India's foreign policy, speakers generally assumed that Bhabha's eighteen-month timeline for building a nuclear bomb was accurate, and did not suggest that a Soviet or US nuclear umbrella would extend over India in case of a nuclear attack. Ultimately, in part due to uncertainty around the cost of developing a nuclear bomb and its appropriate delivery platforms, the Parliament deferred a decision for or against nuclear weapons. The parliamentarians moved instead to speed the development of technology and know-how which would enable them to establish a nuclear weapons programme if they later decided to do so. Shastri hedged, though, that this policy was subject to change:I cannot say that the present policy is deep-rooted, that it cannot be set aside, that it can never be changed. … Here situations alter, changes take place, and we have to mould our policies accordingly. If there is a need to amend what we have said today, then we will say—all right, let us go ahead and do so. Historians have argued that this
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{
"page_id": 1245965,
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marked the beginning of India's policy of keeping a "nuclear option". On 27 November 1964, the Jana Sangh introduced a motion in the Lok Sabha calling for the development of nuclear weapons. Shastri, reiterating his moral stand for nuclear disarmament, won a voice vote against the motion. However, he reminded the Parliament that the manufacture of nuclear weapons could be completed in "two or three years" if necessary. Then, for the first time, he said that India's work on nuclear energy for nonmilitary use would include the development of peaceful nuclear explosives, which he called "nuclear devices":Dr. Bhabha has made it quite clear to me that as far as we can progress and improve upon nuclear devices, we should do so, as far as development is possible, we should resort to it so that we can reap its peaceful benefits and we can use it for the development of our nation. … Just assume that we have to use big tunnels and we have to clear huge areas, we have to wipe out mountains for development parks, and in this context if it is required to use nuclear devices for the good of the country as well as for the good of the world, so then our Atomic Energy Commission is pursuing these same objectives.Shastri's announcement of a program to develop peaceful nuclear explosives fell short of sanctioning an explicit nuclear weapons programme. However, though intended for different purposes, the two kinds of devices are technically similar. Speaking to the Press Trust of India in 1997, Raja Ramanna said:The Pokhran test was a bomb, I can tell you now. … An explosion is an explosion, a gun is a gun, whether you shoot at someone or shoot at the ground. … I just want to make clear that the test
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"page_id": 1245965,
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was not all that peaceful.Ramanna speculated that the Shastri endorsement of peaceful nuclear explosive research "must have come from Bhabha". In an interview with the scholar George Perkovich in 1997, Homi Sethna, a former AEC chairman, agreed that Bhabha had prompted this statement, though he added that "Bhabha was able to obtain approval to do theoretical studies only". Historians have interpreted the shift in Shastri's no-bomb position as a concession to the pro-bomb officials within the Congress party and an attempt to win Bhabha's support, which could shield Shastri against further attacks on nuclear policy in the Parliament. The new nuclear policy of doing theoretical research on peaceful nuclear explosives also avoided the large economic costs and international recriminations that would follow a full-fledged nuclear weapons programme. The concession apparently did win Bhabha's alignment. After the 1965 Indo-Pakistani war, pressure to build nuclear weapons intensified as the threat from Pakistan introduced new security concerns. Rather than using the renewed political debate to gain additional authorizations, Bhabha denied in an interview that he had received any new instructions from Shastri, saying: "The emergency changed nothing. Why should it?" Historians have interpreted Bhabha's comments as an indication that the constraint to building nuclear explosives was not policy, but unmet technological requirements. After realizing that the eighteen-month timeline for building nuclear weapons capability was too ambitious, Bhabha held several meetings with US officials in secret between 1964 and 1965. In these, he explored the option of importing nuclear explosive capability, especially fissile plutonium and designs of a nuclear device, from the US Atomic Energy Commission as part of Project Plowshare. However, with the emergence of the Nuclear Nonproliferation Treaty, this option eventually closed. After Bhabha's death, dissatisfied with the NPT's refusal to meet India's security concerns, scientists at the Bhabha Atomic Research Centre
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{
"page_id": 1245965,
"source": null,
"title": "Homi J. Bhabha"
}
|
and the Defence Research and Development Organization began work on the nuclear device used in the 1974 Pokhran test. == Interest in and patronage of the arts == A classical music and opera enthusiast, Bhabha pushed for Vienna to be the headquarters of the IAEA in part to be able to attend the state opera when attending IAEA meetings. According to his brother Jamshed Bhabha,For Homi Bhabha, the arts were not just a form of recreation or pleasant relaxation; they were among the most serious pursuits of life and he attached just as much importance to them as to his work in mathematics and physics. For him, the arts were, in his own words, 'what made life worth living'.Bhabha was an avid painter, decorating his house with abstracts he painted during the 1930s in England. He was a key patron of the Progressive Artists’ Group, formed in Bombay in 1947 to establish new ways of expressing India's post-colonial identity. This group produced artists like F. N. Souza, M. F. Husain, Tyeb Mehta, K. H. Ara and S. H. Raza, some of whose early works Bhabha selected for the TIFR collection. Unique among scientific institutions around the world, TIFR still hosts a large collection of contemporary Indian art, which was opened to the public in 2018. == Awards and honours == Bhabha's doctoral thesis won him the Adams Prize in 1942, making him the first Indian to receive the honour. This was followed by a Hopkins Prize by the Cambridge Philosophical Society in 1948. He gained international prominence after deriving a correct expression for the probability of scattering positrons by electrons, a process now known as Bhabha scattering. His major contributions included work on Compton scattering, R-process, and the advancement of nuclear physics. He was nominated for the Nobel Prize for
|
{
"page_id": 1245965,
"source": null,
"title": "Homi J. Bhabha"
}
|
Physics in 1951 and 1953–1956. He was awarded Padma Bhushan, India's third-highest civilian honour, in 1954. In 1957, he was elected an honorary fellow of Gonville and Caius College and of the Royal Society of Edinburgh. He was elected a Foreign Honorary Fellow of the American Academy of Arts and Sciences in 1958, and appointed the President of the International Union of Pure and Applied Physics from 1960 to 1963. Bhabha received several honorary doctoral degrees in science throughout his career: Patna (1944), Lucknow (1949), Banaras (1950), Agra (1952), Perth (1954), Allahabad (1958), Cambridge (1959), London (1960) and Padova (1961). == Death == On 24 January 1966, Bhabha was on board Air India Flight 101, a Boeing 707-420, when it crashed near Mont Blanc in a controlled flight terrain while trying to land at Geneva Airport. All 106 passengers, including Bhabha, and 11 crew members died in the crash. A misunderstanding between Geneva Airport ATC and the pilots about the aircraft position near the mountain was noted to be the official reason of the crash. In a ceremony mourning his death, then Prime Minister Indira Gandhi quoted:To lose Dr Homi Bhabha at this crucial moment in the development of our atomic energy programme is a terrible blow for our nation. He had his most creative years ahead of him. When we take up the unfinished work he has left behind, we will realize in how many fields he served us. For me, it is a personal loss. I shall miss his wide-ranging mind and many talents, his determination to strengthen our country’s science and enthusiastic interest in life’s many facets. We mourn a great son of India. === Assassination claims === Many possible theories have been advanced for the air crash, including a claim that the Central Intelligence Agency (CIA)
|
{
"page_id": 1245965,
"source": null,
"title": "Homi J. Bhabha"
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|
was involved in paralysing India's nuclear program. An Indian diplomatic bag containing calendars and a personal letter was recovered near the crash site in 2012. Gregory Douglas, a journalist, conspiracy theorist, forger, and holocaust denier who claimed to have conducted telephone conversations with former CIA operative Robert Crowley in 1993, published a book titled Conversations with the Crow in 2013. According to Douglas, Crowley claimed that the CIA was responsible for assassinating Homi Bhabha and Prime Minister Shastri in 1966, thirteen days apart, to thwart India's nuclear programme. Douglas asserted that Crowley told him a bomb in the cargo section of the plane exploded mid-air, bringing down the commercial Boeing 707 airliner in Alps with few traces. Per Douglas, Crowley said: "We could have blown it up over Vienna but we decided the high mountains were much better for the bits and pieces to come down on". Conspiracy theorists point to the circumstances surrounding the death of Vikram Sarabhai, who showed no signs of illness prior to his death from a heart attack and was cremated without autopsy, as additional evidence of foreign involvement. == Legacy == Bhabha is considered the "father of the Indian nuclear programme" and one of the most prominent scientists in the country's history. After his death, the Atomic Energy Establishment at Mumbai was renamed the Bhabha Atomic Research Centre in his honour. In 1967, TIFR showcased an exhibition of Bhabha's life at the Royal Society, which was later moved to TIFR's auditorium foyer. The auditorium was named the Homi Bhabha Auditorium in the late scientist's honour and inaugurated by Prime Minister Indira Gandhi on 9 November 1968. Bhabha encouraged research in electronics, space science, microbiology and radio astronomy. The radio telescope in Ooty, India, which is one of the world's largest steerable telescopes, was built
|
{
"page_id": 1245965,
"source": null,
"title": "Homi J. Bhabha"
}
|
at Bhabha's initiative in 1970. A number of research institutes received their initial funding from the Department of Atomic Energy under Bhabha's supervision, including the Tata Memorial Hospital, the Indian Cancer Research Centre, the Saha Institute of Nuclear Physics and the Physical Research Laboratory in Ahmedabad. As a member of the Indian Cabinet's Scientific Advisory Committee to the Cabinet, Bhabha played a key role in helping Vikram Sarabhai set up the Indian National Committee for Space Research. The Homi Bhabha Fellowship Council has been giving Homi Bhabha Fellowships since 1967. Other noted institutions in his name are the Homi Bhabha National Institute, an Indian-deemed university and the Homi Bhabha Centre for Science Education, Mumbai, India. At Bhabha's death, his estate, including Mehrangir, the sprawling colonial bungalow at Malabar Hill where he spent most of his life, was inherited by his brother Jamshed Bhabha. Jamshed, an avid patron of arts and culture, bequeathed the bungalow and its contents to the National Centre for the Performing Arts, which auctioned the property for Rs 372 crores in 2014 to raise funds for upkeep and development of the centre. The bungalow was demolished in June 2016 by the owner, Smita-Crishna Godrej of the Godrej family, despite some efforts to have it preserved as a memorial to Homi Bhabha. == In popular culture == Rocket Boys (2022) is a web series inspired by the lives of Homi J. Bhabha, Vikram Sarabhai and A. P. J. Abdul Kalam, in which Bhabha is played by Jim Sarbh. In 2023, the second season was released. == See also == India's three-stage nuclear power programme Abdul Qadeer Khan Bertrand Goldschmidt Deng Jiaxian Homi Bhabha Medal and Prize Igor Kurchatov J. Robert Oppenheimer Leo Szilard John von Neumann William Penney, Baron Penney == References == == Bibliography == Nath, Biman
|
{
"page_id": 1245965,
"source": null,
"title": "Homi J. Bhabha"
}
|
(2022). Homi J Bhabha: A Renaissance Man among Scientists. Niyogi Books. ISBN 9789391125110. Chowdhury, Indira; Dasgupta, Ananya (2010). A masterful spirit : Homi J. Bhabha, 1909-1966. New Delhi: Penguin Books. ISBN 978-0-14-306672-9. OCLC 680165938. Deśamukha, Cintāmaṇī.; National Book Trust (2003). Homi Jehangir Bhabha. New Delhi: National Book Trust. ISBN 81-237-4106-5. OCLC 55680312. Perkovich, George (1999). India's nuclear bomb : the impact on global proliferation. Berkeley: University of California Press. ISBN 0-520-21772-1. OCLC 41612482. == External links == Annotated Bibliography for Homi J. Bhabha from the Alsos Digital Library for Nuclear Issues. The Woodrow Wilson Center's Nuclear Proliferation International History Project. NPIHP has a series of primary source documents about and by Homi Bhabha. "Film on Dr Homi Bhabha by TIFR marking his birth centenary in 2009". YouTube. International Centre for Theoretical Sciences. 25 May 2016. "Homi Bhabha A Scientist in Action". YouTube. Films Division. 27 September 2016. "Homi Jehangir Bhabha". YouTube. Chandigarh-VSP. 17 February 2022.
|
{
"page_id": 1245965,
"source": null,
"title": "Homi J. Bhabha"
}
|
Morphological freedom refers to a proposed civil right of a person to either maintain or modify their own body, on their own terms, through informed, consensual recourse to, or refusal of, available therapeutic or enabling medical technology. The term may have been coined by transhumanist Max More in his 1993 article, “Technological Self-Transformation: Expanding Personal Extropy”, where he defined it as "the ability to alter bodily form at will through technologies such as surgery, genetic engineering, nanotechnology, uploading". The term was later used by science debater and futurist Anders Sandberg as "an extension of one’s right to one’s body, not just self-ownership but also the right to modify oneself according to one’s desires." The Massachusetts-headquartered charity, the Freedom of Form Foundation, was founded in 2018 to advocate and fund scientific research furthering progress on morphological freedom, the tools required to achieve it and its general acceptance in society at large. == Politics == According to technocritic Dale Carrico, the politics of morphological freedom imply a commitment to the value, standing, and social legibility of the widest possible variety of desired morphologies and lifestyles. More specifically, morphological freedom is an expression of liberal pluralism, secularism, progressive cosmopolitanism, and posthumanist multiculturalisms applied to the ongoing and upcoming transformation of the understanding of medical practice from one of conventional therapy to one of consensual self-determination, via genetic, prosthetic, and cognitive modification. == Religion == According to authors Calvin Mercer and Tracy J. Trothen there is tension between religion and transhumanists, particularly the Abrahamic traditions, with regards to morphological freedom. While religion generally recognizes the need to heal people and improve their situation from a medical perspective they are generally hesitant to promote a wholesale modification of the body as they see it ultimately belonging to God. == See also == == References ==
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{
"page_id": 1311504,
"source": null,
"title": "Morphological freedom"
}
|
== External links == Carrico, Dale (2006). "The Politics of Morphological Freedom". Amor Munro blog. Retrieved 2007-01-28. Sandberg, Anders (2001). "Morphological Freedom -- Why We not just Want it, but Need it". Retrieved 2024-03-07.
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{
"page_id": 1311504,
"source": null,
"title": "Morphological freedom"
}
|
In molecular biology mir-187 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms. miR-187 has been found to be expressed at higher levels in ovarian cancers compared with benign tumours. It is known to target DAB2 (disabled homolog-2), a protein encoded by the DAB2 gene, with miR-187's target site at the 3'UTR of the DAB2 gene. DAB2 has been seen to play roles in both cell proliferation and tumour progression, and initial expression of miR-187 in cancer cells promotes cell proliferation. However, overexpression suppresses DAB2 and inhibits epithelial to mesenchymal cell transition. High miR-187 levels have accordingly been associated with higher survival rates in ovarian cancer patients. == See also == MicroRNA == Further reading == == External links == Page for mir-187 microRNA precursor family at Rfam
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{
"page_id": 36373264,
"source": null,
"title": "Mir-187 microRNA precursor family"
}
|
Naturalist is an autobiography by naturalist, entomologist, and sociobiologist Edward O. Wilson first published in 1994 by Island Press. In it he writes on his childhood and the beginnings of his interest in biology, on his work in entomology and myrmecology, on his work with biogeography, and on several of his writings including on his controversial work Sociobiology: The New Synthesis (1975), as well as several other subjects. It was awarded the 1995 Los Angeles Times book prize for Science and Technology publication. In 2020, a graphic novel version was published, adapted by Jim Ottaviani and C.M. Butzer. == References == == External links == Official publisher's website
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{
"page_id": 14484242,
"source": null,
"title": "Naturalist (book)"
}
|
In mathematics, a Relevance Vector Machine (RVM) is a machine learning technique that uses Bayesian inference to obtain parsimonious solutions for regression and probabilistic classification. A greedy optimisation procedure and thus fast version were subsequently developed. The RVM has an identical functional form to the support vector machine, but provides probabilistic classification. It is actually equivalent to a Gaussian process model with covariance function: k ( x , x ′ ) = ∑ j = 1 N 1 α j φ ( x , x j ) φ ( x ′ , x j ) {\displaystyle k(\mathbf {x} ,\mathbf {x'} )=\sum _{j=1}^{N}{\frac {1}{\alpha _{j}}}\varphi (\mathbf {x} ,\mathbf {x} _{j})\varphi (\mathbf {x} ',\mathbf {x} _{j})} where φ {\displaystyle \varphi } is the kernel function (usually Gaussian), α j {\displaystyle \alpha _{j}} are the variances of the prior on the weight vector w ∼ N ( 0 , α − 1 I ) {\displaystyle w\sim N(0,\alpha ^{-1}I)} , and x 1 , … , x N {\displaystyle \mathbf {x} _{1},\ldots ,\mathbf {x} _{N}} are the input vectors of the training set. Compared to that of support vector machines (SVM), the Bayesian formulation of the RVM avoids the set of free parameters of the SVM (that usually require cross-validation-based post-optimizations). However RVMs use an expectation maximization (EM)-like learning method and are therefore at risk of local minima. This is unlike the standard sequential minimal optimization (SMO)-based algorithms employed by SVMs, which are guaranteed to find a global optimum (of the convex problem). The relevance vector machine was patented in the United States by Microsoft (patent expired September 4, 2019). == See also == Kernel trick Platt scaling: turns an SVM into a probability model == References == == Software == dlib C++ Library The Kernel-Machine Library rvmbinary: R package for binary classification scikit-rvm
|
{
"page_id": 4195092,
"source": null,
"title": "Relevance vector machine"
}
|
fast-scikit-rvm, rvm tutorial == External links == Tipping's webpage on Sparse Bayesian Models and the RVM A Tutorial on RVM by Tristan Fletcher Applied tutorial on RVM Comparison of RVM and SVM
|
{
"page_id": 4195092,
"source": null,
"title": "Relevance vector machine"
}
|
Samer Hassan is a computer scientist, social scientist, activist and researcher, focused on the study of the collaborative economy, online communities and decentralized technologies. He is Associate Professor at Universidad Complutense de Madrid (Spain) and Faculty Associate at the Berkman Klein Center for Internet & Society at Harvard University. He is the recipient of an ERC Grant of 1.5M€ with the P2P Models project, to research blockchain-based decentralized autonomous organizations for the collaborative economy. == Education & career == Samer Hassan is a scholar with an interdisciplinary background, which combines computer sciences with social sciences and activism. He received a degree in Computer Science and MSc in Artificial Intelligence from the Universidad Complutense de Madrid (UCM) in Spain. He also studied 3 years of Political Science at the distance learning university UNED. He has then undertaken a PhD in Social Simulation at the department of Software Engineering and Artificial Intelligence of UCM, supervised by the computer scientist Juan Pavón and the sociologist Millán Arroyo-Menéndez. He has been researching in several institutions, funded by several scholarships and awards, most notably Harvard's Real Colegio Complutense, and the Spanish postdoctoral grants Juan de la Cierva and José Castillejo. Thus, he was a visiting researcher at the Centre for Research in Social Simulation, in the Department of Sociology at the University of Surrey in the UK, working under the supervision of Nigel Gilbert (2007-2008), and a lecturer at the American University of Science and Technology in Lebanon (2010–11). He was selected as Fellow at the Berkman-Klein Center for Internet and Society at Harvard University (2015-2017) and is presently a Faculty Associate at the same structure. == Activism & social engagement == As an activist, Samer Hassan has been engaged in both offline (La Tabacalera de Lavapiés, Medialab-Prado) and online (Ourproject.org, Barrapunto, Wikipedia) initiatives. He
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"page_id": 57475860,
"source": null,
"title": "Samer Hassan"
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|
was accredited as a grassroots facilitator by the Altekio Cooperative. He co-founded the Comunes Nonprofit in 2009 and the Move Commons webtool project in 2010. He has co-organized practitioner-oriented workshops on platform co-ops and free/open source decentralized tools for communities, and has presented his work in non-academic conferences of Mozilla, the Internet Archive, and others. As a privacy advocate, he co-created a course on cyber-ethics which has been teaching since 2013 (as of 2021). He was co-founder of the Sci-Fdi Spanish science-fiction magazine. == Work == Hassan's interdisciplinary research spans multiple fields, including online communities, online governance, online collaboration, decentralized technologies, blockchain-based decentralized autonomous organizations, free/libre/open source software, Commons-based peer production, agent-based social simulation, social movements and cyberethics. He has published more than 60 works in these fields. Samer Hassan's PhD thesis focused on the methodological challenges for building data-driven social simulation models. The main model built simulated the transition from modern values to postmodern values in Spain. His methodological work also explored the combination of different Artificial Intelligence technologies, i.e. software agents with fuzzy logic, data mining, natural language processing, and microsimulation. In his postdoctoral period, he focused on experimenting with multiple software systems to facilitate the collaborative economy, e.g. semantic-web labelling for commons-based initiatives, distribution of value in peer production communities, agent-supported online assemblies, decentralized real-time collaborative software, decentralized blockchain based reputation, or blockchain-enabled commons governance. Hassan was Principal Investigator of the UCM partner in the EU-funded P2Pvalue project on building decentralized web-tools for collaborative communities. As such, he led the team that created SwellRT, a federated backend-as-a-service focused to ease development of apps featuring real-time collaboration. Intellectual Property of this project was transferred to the Apache Software Foundation in 2017. As part of this research line, Hassan's team also develop two SwellRT-based apps, "Teem" for management of
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{
"page_id": 57475860,
"source": null,
"title": "Samer Hassan"
}
|
social collectives and Jetpad, a federated real time editor. He presented the innovations concerning these software at Harvard's Berkman Klein Center and Harvard's Center for Research on Computation and Society. Other research lines offered outcomes beyond publications. "Wikichron", coled by Javier Arroyo, is a web tool to visualize MediaWiki community metrics, currently in production and available for third-parties. "Decentralized Science", led by Hassan's PhD student Ámbar Tenorio-Fornés, is a framework to facilitate decentralized infrastructure and open peer review in the scientific publication process, which has been selected by the European Commission to receive funding as a spin-off social enterprise. His research on blockchain and crowdfunding models awarded him with a commission from Triple Canopy. His team pushed forward a mapping of the ecosystem of blockchain for social good, led by the Joint Research Centre and published by the European Commission. As part of his ERC project P2P Models, Samer Hassan and his team –including Silvia Semenzin– are investigating whether blockchain technology and Decentralized Autonomous Organizations could contribute to improving the governance of commons-oriented communities, both online and offline. Their work has been showcased for tackling the impact of blockchain on governance, proposing alternatives to the current sharing economy, emerging forms of techno-social systems like NFTs, or giving relevance to gender issues in the field. Hassan was invited to present the project achievements in Harvard Kennedy School, MIT Media Lab, Harvard's Data Privacy Lab, Harvard's Center for Research on Computation and Society, and Harvard's SEAS EconCS. British MP and Opposition Leader Ed Miliband showcased his research and its potential impact on policy. The project made public its way of organizing and its core values. In particular, it has shown a commitment to diversity as a core value in hiring, or choosing case studies. This may be related to Hassan being Spanish/Lebanese
|
{
"page_id": 57475860,
"source": null,
"title": "Samer Hassan"
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|
or using "he/they" as pronouns. == Selected works == Arroyo, Javier; Davó, David; Martínez-Vicente, Elena; Faqir-Rhazoui, Youssef; Hassan, Samer (8 November 2022). "DAO-Analyzer: Exploring Activity and Participation in Blockchain Organizations" (PDF). Companion Publication of the 2022 Conference on Computer Supported Cooperative Work and Social Computing. CSCW'22 Companion. New York, NY, USA: Association for Computing Machinery. pp. 193–196. doi:10.1145/3500868.3559707. ISBN 978-1-4503-9190-0. Rozas, David; Tenorio-Fornés, Antonio; Díaz-Molina, Silvia; Hassan, Samer (2021). "When Ostrom Meets Blockchain: Exploring the Potentials of Blockchain for Commons Governance". SAGE Open. 11 (1): 215824402110025. doi:10.1177/21582440211002526. ISSN 2158-2440. Faqir-Rhazoui, Youssef; Ariza-Garzón, Miller-Janny; Arroyo, Javier; Hassan, Samer (8 May 2021). "Effect of the Gas Price Surges on User Activity in the DAOs of the Ethereum Blockchain" (PDF). Extended Abstracts of the 2021 CHI Conference on Human Factors in Computing Systems. CHI EA '21. New York, NY, USA: Association for Computing Machinery. pp. 1–7. doi:10.1145/3411763.3451755. ISBN 978-1-4503-8095-9. Hassan, Samer; Filippi, Primavera De (20 April 2021). "Decentralized Autonomous Organization". Internet Policy Review. 10 (2). doi:10.14763/2021.2.1556. ISSN 2197-6775. Joint Research Centre (European Commission); Hassan, Samer; Hakami, Anna; Brekke, Jaya Klara; De Filippi, Primavera; Lopéz Morales, Genoveva; Pólvora, Alexandre; Orgaz Alonso, Christian; Bodó, Balázs (2020). Scanning the European ecosystem of distributed ledger technologies for social and public good: what, why, where, how, and ways to move forward. LU: Publications Office of the European Union. doi:10.2760/300796. ISBN 978-92-76-21578-3. Filippi, Primavera De; Hassan, Samer (14 November 2016). "Blockchain technology as a regulatory technology: From code is law to law is code". First Monday. arXiv:1801.02507. doi:10.5210/fm.v21i12.7113. ISSN 1396-0466. == See also == P2Pvalue project at WikiMedia Meta SwellRT Decentralized autonomous organization Harvard's Berkman Klein Center for Internet & Society == References == == External links == Personal webpage Bio at Berkman Klein Center at Harvard P2P Models webpage
|
{
"page_id": 57475860,
"source": null,
"title": "Samer Hassan"
}
|
A flight interception trap (or FIT) is a widely used trapping, killing, and preserving system for flying insects. It is especially well-suited for collecting beetles, since these animals usually drop themselves after flying into an object, rather than flying upward (in which case a Malaise trap is a better option). Flight Interception Traps are mainly used to collect flying species which are not likely to be attracted to bait or light. == Construction == The basis of any Flight Interception Trap consists of an upright placed see-through barrier under which one or more small basins are placed. The barrier may consist of such materials as plastic mesh, a transparent plastic sheet or even Plexiglas, although the latter does not work well for day-active insects since it is visible to them due to its specific refraction. The basins are filled with a preserving fluid such as ethanol (which should be mixed with something bad-tasting (like denatonium) to prevent wild animals drinking it), propylene glycol, salt-saturated water or even plain water. The best preservative to keep internal organs in good condition is FAACC, a solution of formaldehyde. A small amount of detergent is added to break the surface tension, causing the insects to sink. Yellow (a colour which attracts many insects) pans with soapy water may be used alone. The water itself can be an attractant in dry environments [2]. == Location == Depending on either the desired information (for research) or desired species (for collection and/or trade) the construction can be put in open land or in the forest. It is important to place the barrier in a straight angle with the most likely flying route for insects (e.g. blocking a forest corridor), so as to maximize results. == Checking == The basins can be checked daily (when it is e.g.
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{
"page_id": 25559829,
"source": null,
"title": "Flight interception trap"
}
|
important to check the activity of the desired insects under different weather conditions), weekly or even less often. Maximum time between two checks depends on the used preservatives, since not all preservatives are equally suited for preserving insects for a longer time. == Cover == To prevent the basins from filling up with litter, most researchers place some kind of roof over the trap. This keeps leaves from falling in while it also keeps the rain out (which could otherwise dilute the preservative or cause an overflow). == References ==
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{
"page_id": 25559829,
"source": null,
"title": "Flight interception trap"
}
|
The principle of microscopic reversibility in physics and chemistry is twofold: First, it states that the microscopic detailed dynamics of particles and fields is time-reversible because the microscopic equations of motion are symmetric with respect to inversion in time (T-symmetry); Second, it relates to the statistical description of the kinetics of macroscopic or mesoscopic systems as an ensemble of elementary processes: collisions, elementary transitions or reactions. For these processes, the consequence of the microscopic T-symmetry is: Corresponding to every individual process there is a reverse process, and in a state of equilibrium the average rate of every process is equal to the average rate of its reverse process. == History of microscopic reversibility == The idea of microscopic reversibility was born together with physical kinetics. In 1872, Ludwig Boltzmann represented kinetics of gases as statistical ensemble of elementary collisions. Equations of mechanics are reversible in time, hence, the reverse collisions obey the same laws. This reversibility of collisions is the first example of microreversibility. According to Boltzmann, this microreversibility implies the principle of detailed balance for collisions: at the equilibrium ensemble each collision is equilibrated by its reverse collision. These ideas of Boltzmann were analyzed in detail and generalized by Richard C. Tolman. In chemistry, J. H. van't Hoff (1884) came up with the idea that equilibrium has dynamical nature and is a result of the balance between the forward and backward reaction rates. He did not study reaction mechanisms with many elementary reactions and could not formulate the principle of detailed balance for complex reactions. In 1901, Rudolf Wegscheider introduced the principle of detailed balance for complex chemical reactions. He found that for a complex reaction the principle of detailed balance implies important and non-trivial relations between reaction rate constants for different reactions. In particular, he demonstrated that the
|
{
"page_id": 3408660,
"source": null,
"title": "Microscopic reversibility"
}
|
irreversible cycles of reaction are impossible and for the reversible cycles the product of constants of the forward reactions (in the "clockwise" direction) is equal to the product of constants of the reverse reactions (in the "anticlockwise" direction). Lars Onsager (1931) used these relations in his well-known work, without direct citation but with the following remark: "Here, however, the chemists are accustomed to impose a very interesting additional restriction, namely: when the equilibrium is reached each individual reaction must balance itself. They require that the transition A → B {\displaystyle A\to B} must take place just as frequently as the reverse transition B → A {\displaystyle B\to A} etc." The quantum theory of emission and absorption developed by Albert Einstein (1916, 1917) gives an example of application of the microreversibility and detailed balance to development of a new branch of kinetic theory. Sometimes, the principle of detailed balance is formulated in the narrow sense, for chemical reactions only but in the history of physics it has the broader use: it was invented for collisions, used for emission and absorption of quanta, for transport processes and for many other phenomena. In its modern form, the principle of microreversibility was published by Lewis (1925). In the classical textbooks full theory and many examples of applications are presented. == Time-reversibility of dynamics == The Newton and the Schrödinger equations in the absence of the macroscopic magnetic fields and in the inertial frame of reference are T-invariant: if X(t) is a solution then X(-t) is also a solution (here X is the vector of all dynamic variables, including all the coordinates of particles for the Newton equations and the wave function in the configuration space for the Schrödinger equation). There are two sources of the violation of this rule: First, if dynamics depend on
|
{
"page_id": 3408660,
"source": null,
"title": "Microscopic reversibility"
}
|
a pseudovector like the magnetic field or the rotation angular speed in the rotating frame then the T-symmetry does not hold. Second, in microphysics of weak interaction the T-symmetry may be violated and only the combined CPT symmetry holds. == Macroscopic consequences of the time-reversibility of dynamics == In physics and chemistry, there are two main macroscopic consequences of the time-reversibility of microscopic dynamics: the principle of detailed balance and the Onsager reciprocal relations. The statistical description of the macroscopic process as an ensemble of the elementary indivisible events (collisions) was invented by L. Boltzmann and formalised in the Boltzmann equation. He discovered that the time-reversibility of the Newtonian dynamics leads to the detailed balance for collision: in equilibrium collisions are equilibrated by their reverse collisions. This principle allowed Boltzmann to deduce simple and nice formula for entropy production and prove his famous H-theorem. In this way, microscopic reversibility was used to prove macroscopic irreversibility and convergence of ensembles of molecules to their thermodynamic equilibria. Another macroscopic consequence of microscopic reversibility is the symmetry of kinetic coefficients, the so-called reciprocal relations. The reciprocal relations were discovered in the 19th century by Thomson and Helmholtz for some phenomena but the general theory was proposed by Lars Onsager in 1931. He found also the connection between the reciprocal relations and detailed balance. For the equations of the law of mass action the reciprocal relations appear in the linear approximation near equilibrium as a consequence of the detailed balance conditions. According to the reciprocal relations, the damped oscillations in homogeneous closed systems near thermodynamic equilibria are impossible because the spectrum of symmetric operators is real. Therefore, the relaxation to equilibrium in such a system is monotone if it is sufficiently close to the equilibrium. == References == == See also == Detailed balance
|
{
"page_id": 3408660,
"source": null,
"title": "Microscopic reversibility"
}
|
Onsager reciprocal relations
|
{
"page_id": 3408660,
"source": null,
"title": "Microscopic reversibility"
}
|
The Apprentice is a novel by Lewis Libby, former Chief of Staff to United States Vice President Dick Cheney, first published in hardback in 1996, reprinted in trade paperback in 2002, and reissued in mass market paperback in 2005 after Libby's indictment in the CIA leak grand jury investigation. It is set in northern Japan in winter 1903, and centers on a group of travelers stranded at a remote inn due to a smallpox epidemic. It has been described as "a thriller ... that includes references to bestiality, pedophilia and rape." It is the first and only novel that Libby has written. == Publication history == After being published in hardback by Graywolf Press (St. Paul, Minnesota) in August 1996 (now out of print), it was published as a trade paperback by St. Martin's Thomas Dunne Books in February 2002, and then reissued as a mass market paperback reprint of 25,000 copies by St. Martin's Griffin imprint in December 2005, after Libby's indictment that October, as a result of the CIA leak grand jury investigation. == First edition publicity == In 2002, during an interview on Larry King Live promoting his novel's first publication in paperback, King asked Libby: "Are you a novelist working part-time for the vice president?" Libby told King, "Well, I've never quite figured that out. ... I'm a great fan of the Vice President. I think he's one of the smartest, most honorable people I've ever met. So, I'd like to consider myself fully on his team, but there's always a novel kicking around in the back somewhere." After hearing a brief plot summary, King wondered why Libby had set the novel in Japan, and Libby responded: I first wrote it in Japan -- contemporary Japan -- in college for a credit. Had a good reason
|
{
"page_id": 3080986,
"source": null,
"title": "The Apprentice (Libby novel)"
}
|
-- I wanted to graduate. ... But the story sort of wouldn't let me go, and I sort of said, why am I writing about -- this about Japan? ... And I went back and rewrote the book entirely in New England -- set in New England. Went out to Colorado, drank tequila and wrote. And sort of the dream life. ... But what eventually happened was, that didn't seem right. I took that 300 pages and threw it away, never showed it. [KING: It's a classic first novel.] ... And then I started to think, you know, what I need is more distance for the characters, more sort of isolation. I wanted a land before telephones, before fingerprints -- give the reader even a greater sense [of isolation]. At that time, Libby also appeared on The Diane Rehm Show on National Public Radio to talk about the novel. Libby said that he had chosen to set the novel in Japan in 1903, because it was a pivotal time in its history that had intrigued him. == Plot summary == According to the description of the book by St. Martin's Press: The Apprentice takes place in a remote mountain inn in northernmost Japan, where a raging blizzard has brought together wayfarers who share only fear and suspicion of one another. It is the winter of 1903, the country is beset with smallpox and war is brewing with Russia. In the flickering shadows of the crowded room, the apprentice, charged with running the inn during the owner's absence, finds himself strongly attracted to one of the performers lodged there. His involvement with the mysterious travelers plunges him headlong into murder, passion and heart-stopping chases through the snow. == Reprint publicity == Following his indictment on October 28, 2005, for obstruction of
|
{
"page_id": 3080986,
"source": null,
"title": "The Apprentice (Libby novel)"
}
|
justice, perjury, and making false statements to federal investigators in Special Counsel Patrick Fitzgerald's CIA leak grand jury investigation, relating to the Plame affair, after the novel was reissued and promoted by its publisher and Libby in media interviews and the subject of subsequent reviews, it gained renewed attention. Notably, The Apprentice and Lewis Libby were the focus of the following week's New Yorker "Talk of the Town" column, by Lauren Collins, entitled "Scooter's Sex Shocker". Observing that "Libby has a lot to live up to as a conservative author of erotic fiction," Collins compares the novel to other so-called "sex shockers" written by conservative politicians and pundits and discusses themes of homoeroticism and incest in The Apprentice. She documents her view that "Like his predecessors, Libby does not shy from the scatological" with quotations from the book, regarding it as "Libby’s 1996 entry in the long and distinguished annals of the right-wing dirty novel." == Reception == Although the sexual passages and references make up only a few pages of the novel, one passage in particular — combining bestiality, pedophilia, prostitution, biastophilia, and voyeurism in just three sentences—has received wide attention: Then the young samurai's mother had the child sold to a brothel, where she swept the floors and oiled the women and watched the secret ways. At age ten the madam put the child in a cage with a bear trained to couple with young girls so the girls would be frigid and not fall in love with their patrons. They fed her through the bars and aroused the bear with a stick when it seemed to lose interest. Groups of men paid to watch. Like other girls who have been trained this way, she learned to handle many men in a single night and her skin turned
|
{
"page_id": 3080986,
"source": null,
"title": "The Apprentice (Libby novel)"
}
|
a milky white. Another sentence in the book introduces necrophilia in addition to bestiality, as a hunter copulates with a freshly killed deer: "The man called out to the others that the deer was still warm. He asked if they should fuck the deer" (127). In his June 7, 2007 Wall Street Journal op-ed calling for Presidential pardon of Scooter Libby, conservative academic Fouad Ajami praised The Apprentice as a "remarkably lyrical novel ... [which] bears witness to an eye for human folly and disappointment." == References == == External links == The Apprentice at Google Book Search. ("Preview" includes scans of front and back covers; title page; copyright page (back of title page); and selected pages from chapters 2, 4 and 5, with excluded pages identified. This preview includes pages cited above.)
|
{
"page_id": 3080986,
"source": null,
"title": "The Apprentice (Libby novel)"
}
|
This page provides supplementary chemical data on boron trioxide. == Material Safety Data Sheet == MSDS from SIRI == Structure and properties == == Thermodynamic properties == == Spectral data == == References ==
|
{
"page_id": 8323870,
"source": null,
"title": "Boron trioxide (data page)"
}
|
In quantum chaos, a branch of mathematical physics, quantum ergodicity is a property of the quantization of classical mechanical systems that are chaotic in the sense of exponential sensitivity to initial conditions. Quantum ergodicity states, roughly, that in the high-energy limit, the probability distributions associated to energy eigenstates of a quantized ergodic Hamiltonian tend to a uniform distribution in the classical phase space. This is consistent with the intuition that the flows of ergodic systems are equidistributed in phase space. By contrast, classical completely integrable systems generally have periodic orbits in phase space, and this is exhibited in a variety of ways in the high-energy limit of the eigenstates: typically, some form of concentration occurs in the semiclassical limit ℏ → 0 {\displaystyle \hbar \rightarrow 0} . The model case of a Hamiltonian is the geodesic Hamiltonian on the cotangent bundle of a compact Riemannian manifold. The quantization of the geodesic flow is given by the fundamental solution of the Schrödinger equation U t = exp ( i t Δ ) {\displaystyle U_{t}=\exp(it{\sqrt {\Delta }})} where Δ {\displaystyle {\sqrt {\Delta }}} is the square root of the Laplace–Beltrami operator. The quantum ergodicity theorem of Shnirelman 1974, Zelditch, and Yves Colin de Verdière states that a compact Riemannian manifold whose unit tangent bundle is ergodic under the geodesic flow is also ergodic in the sense that the probability density associated to the nth eigenfunction of the Laplacian tends weakly to the uniform distribution on the unit cotangent bundle as n → ∞ in a subset of the natural numbers of natural density equal to one. Quantum ergodicity can be formulated as a non-commutative analogue of the classical ergodicity (T. Sunada). Since a classically chaotic system is also ergodic, almost all of its trajectories eventually explore uniformly the entire accessible phase
|
{
"page_id": 23855903,
"source": null,
"title": "Quantum ergodicity"
}
|
space. Thus, when translating the concept of ergodicity to the quantum realm, it is natural to assume that the eigenstates of the quantum chaotic system would fill the quantum phase space evenly (up to random fluctuations) in the semiclassical limit ℏ → 0 {\displaystyle \hbar \rightarrow 0} . The quantum ergodicity theorems of Shnirelman, Zelditch, and Yves Colin de Verdière proves that the expectation value of an operator converges in the semiclassical limit to the corresponding microcanonical classical average. However, the quantum ergodicity theorem leaves open the possibility of eigenfunctions become sparse with serious holes as ℏ → 0 {\displaystyle \hbar \rightarrow 0} , leaving large but not macroscopic gaps on the energy manifolds in the phase space. In particular, the theorem allows the existence of a subset of macroscopically nonergodic states which on the other hand must approach zero measure, i.e., the contribution of this set goes towards zero percent of all eigenstates when ℏ → 0 {\displaystyle \hbar \rightarrow 0} . For example, the theorem do not exclude quantum scarring, as the phase space volume of the scars also gradually vanishes in this limit. A quantum eigenstate is scarred by periodic orbit if its probability density is on the classical invariant manifolds near and all along that periodic orbit is systematically enhanced above the classical, statistically expected density along that orbit. In a simplified manner, a quantum scar refers to an eigenstate of whose probability density is enhanced in the neighborhood of a classical periodic orbit when the corresponding classical system is chaotic. In conventional scarring, the responsive periodic orbit is unstable. The instability is a decisive point that separates quantum scars from a more trivial finding that the probability density is enhanced near stable periodic orbits due to the Bohr's correspondence principle. The latter can be viewed
|
{
"page_id": 23855903,
"source": null,
"title": "Quantum ergodicity"
}
|
as a purely classical phenomenon, whereas in the former quantum interference is important. On the other hand, in the perturbation-induced quantum scarring, some of the high-energy eigenstates of a locally perturbed quantum dot contain scars of short periodic orbits of the corresponding unperturbed system. Even though similar in appearance to ordinary quantum scars, these scars have a fundamentally different origin., In this type of scarring, there are no periodic orbits in the perturbed classical counterpart or they are too unstable to cause a scar in a conventional sense. Conventional and perturbation-induced scars are both a striking visual example of classical-quantum correspondence and of a quantum suppression of chaos (see the figure). In particular, scars are a significant correction to the assumption that the corresponding eigenstates of a classically chaotic Hamiltonian are only featureless and random. In some sense, scars can be considered as an eigenstate counterpart to the quantum ergodicity theorem of how short periodic orbits provide corrections to the universal random matrix theory eigenvalue statistics. == See also == Eigenstate thermalization hypothesis Ergodic hypothesis Quantum chaos Scar (physics) == External links == Shnirelman theorem, Scholarpedia article == References == Shnirelman, A I (1974), Ergodic properties of eigenfunctions, vol. 29(6(180)), Uspekhi Mat. Nauk, Moscow, pp. 181–182 Zelditch, S (2006), "Quantum ergodicity and mixing of eigenfunctions", in Françoise, Jean-Pierre; Naber, Gregory L.; Tsun, Tsou Sheung (eds.), Encyclopedia of mathematical physics. Vol. 1, 2, 3, 4, 5, Academic Press/Elsevier Science, Oxford, ISBN 9780125126601, MR 2238867 Sunada, T (1997), "Quantum ergodicity", Trend in Mathematics, Birkhauser Verlag, Basel, pp. 175–196
|
{
"page_id": 23855903,
"source": null,
"title": "Quantum ergodicity"
}
|
Expandable. We make separate entries for proteins, etc. Why not these? In molecular biology mir-188 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms. == See also == MicroRNA == References == == Further reading == == External links == Page for mir-188 microRNA precursor family at Rfam
|
{
"page_id": 36373280,
"source": null,
"title": "Mir-188 microRNA precursor family"
}
|
Solid hydrogen is the solid state of the element hydrogen. At standard pressure, this is achieved by decreasing the temperature below hydrogen's melting point of 14.01 K (−259.14 °C; −434.45 °F). It was collected for the first time by James Dewar in 1899 and published with the title "Sur la solidification de l'hydrogène" (English: On the freezing of hydrogen) in the Annales de Chimie et de Physique, 7th series, vol. 18, Oct. 1899. Solid hydrogen has a density of 0.086 g/cm3 making it one of the lowest-density solids. == Molecular solid hydrogen == At low temperatures and at pressures up to around 400 GPa (3,900,000 atm), hydrogen forms a series of solid phases formed from discrete H2 molecules. Phase I occurs at low temperatures and pressures, and consists of a hexagonal close-packed array of freely rotating H2 molecules. Upon increasing the pressure at low temperature, a transition to Phase II occurs at up to 110 GPa. Phase II is a broken-symmetry structure in which the H2 molecules are no longer able to rotate freely. If the pressure is further increased at low temperature, a Phase III is encountered at about 160 GPa. Upon increasing the temperature, a transition to a Phase IV occurs at a temperature of a few hundred kelvin at a range of pressures above 220 GPa. Identifying the atomic structures of the different phases of molecular solid hydrogen is extremely challenging, because hydrogen atoms interact with X-rays very weakly and only small samples of solid hydrogen can be achieved in diamond anvil cells, so that X-ray diffraction provides very limited information about the structures. Nevertheless, phase transitions can be detected by looking for abrupt changes in the Raman spectra of samples. Furthermore, atomic structures can be inferred from a combination of experimental Raman spectra and first-principles modelling.
|
{
"page_id": 19137315,
"source": null,
"title": "Solid hydrogen"
}
|
Density functional theory calculations have been used to search for candidate atomic structures for each phase. These candidate structures have low free energies and Raman spectra in agreement with the experimental spectra. Quantum Monte Carlo methods together with a first-principles treatment of anharmonic vibrational effects have then been used to obtain the relative Gibbs free energies of these structures and hence to obtain a theoretical pressure-temperature phase diagram that is in reasonable quantitative agreement with experiment. On this basis, Phase II is believed to be a molecular structure of P21/c symmetry; Phase III is (or is similar to) a structure of C2/c symmetry consisting of flat layers of molecules in a distorted hexagonal arrangement; and Phase IV is (or is similar to) a structure of Pc symmetry, consisting of alternate layers of strongly bonded molecules and weakly bonded graphene-like sheets. == See also == Compressed hydrogen Liquid hydrogen Metallic hydrogen Slush hydrogen Timeline of hydrogen technologies == References == == Further reading == Melting Characteristics and Bulk Thermophysical Properties of Solid Hydrogen", Air Force Rocket Propulsion Laboratory, Technical Report, 1972 == External links == "Properties of solid hydrogen at very low temperatures" (2001) "Solid hydrogen experiments for atomic propellants"
|
{
"page_id": 19137315,
"source": null,
"title": "Solid hydrogen"
}
|
The cross-entropy (CE) method is a Monte Carlo method for importance sampling and optimization. It is applicable to both combinatorial and continuous problems, with either a static or noisy objective. The method approximates the optimal importance sampling estimator by repeating two phases: Draw a sample from a probability distribution. Minimize the cross-entropy between this distribution and a target distribution to produce a better sample in the next iteration. Reuven Rubinstein developed the method in the context of rare-event simulation, where tiny probabilities must be estimated, for example in network reliability analysis, queueing models, or performance analysis of telecommunication systems. The method has also been applied to the traveling salesman, quadratic assignment, DNA sequence alignment, max-cut and buffer allocation problems. == Estimation via importance sampling == Consider the general problem of estimating the quantity ℓ = E u [ H ( X ) ] = ∫ H ( x ) f ( x ; u ) d x {\displaystyle \ell =\mathbb {E} _{\mathbf {u} }[H(\mathbf {X} )]=\int H(\mathbf {x} )\,f(\mathbf {x} ;\mathbf {u} )\,{\textrm {d}}\mathbf {x} } , where H {\displaystyle H} is some performance function and f ( x ; u ) {\displaystyle f(\mathbf {x} ;\mathbf {u} )} is a member of some parametric family of distributions. Using importance sampling this quantity can be estimated as ℓ ^ = 1 N ∑ i = 1 N H ( X i ) f ( X i ; u ) g ( X i ) {\displaystyle {\hat {\ell }}={\frac {1}{N}}\sum _{i=1}^{N}H(\mathbf {X} _{i}){\frac {f(\mathbf {X} _{i};\mathbf {u} )}{g(\mathbf {X} _{i})}}} , where X 1 , … , X N {\displaystyle \mathbf {X} _{1},\dots ,\mathbf {X} _{N}} is a random sample from g {\displaystyle g\,} . For positive H {\displaystyle H} , the theoretically optimal importance sampling density (PDF) is given by g
|
{
"page_id": 5767980,
"source": null,
"title": "Cross-entropy method"
}
|
∗ ( x ) = H ( x ) f ( x ; u ) / ℓ {\displaystyle g^{*}(\mathbf {x} )=H(\mathbf {x} )f(\mathbf {x} ;\mathbf {u} )/\ell } . This, however, depends on the unknown ℓ {\displaystyle \ell } . The CE method aims to approximate the optimal PDF by adaptively selecting members of the parametric family that are closest (in the Kullback–Leibler sense) to the optimal PDF g ∗ {\displaystyle g^{*}} . == Generic CE algorithm == Choose initial parameter vector v ( 0 ) {\displaystyle \mathbf {v} ^{(0)}} ; set t = 1. Generate a random sample X 1 , … , X N {\displaystyle \mathbf {X} _{1},\dots ,\mathbf {X} _{N}} from f ( ⋅ ; v ( t − 1 ) ) {\displaystyle f(\cdot ;\mathbf {v} ^{(t-1)})} Solve for v ( t ) {\displaystyle \mathbf {v} ^{(t)}} , where v ( t ) = argmax v 1 N ∑ i = 1 N H ( X i ) f ( X i ; u ) f ( X i ; v ( t − 1 ) ) log f ( X i ; v ) {\displaystyle \mathbf {v} ^{(t)}=\mathop {\textrm {argmax}} _{\mathbf {v} }{\frac {1}{N}}\sum _{i=1}^{N}H(\mathbf {X} _{i}){\frac {f(\mathbf {X} _{i};\mathbf {u} )}{f(\mathbf {X} _{i};\mathbf {v} ^{(t-1)})}}\log f(\mathbf {X} _{i};\mathbf {v} )} If convergence is reached then stop; otherwise, increase t by 1 and reiterate from step 2. In several cases, the solution to step 3 can be found analytically. Situations in which this occurs are When f {\displaystyle f\,} belongs to the natural exponential family When f {\displaystyle f\,} is discrete with finite support When H ( X ) = I { x ∈ A } {\displaystyle H(\mathbf {X} )=\mathrm {I} _{\{\mathbf {x} \in A\}}} and f ( X i ; u ) =
|
{
"page_id": 5767980,
"source": null,
"title": "Cross-entropy method"
}
|
f ( X i ; v ( t − 1 ) ) {\displaystyle f(\mathbf {X} _{i};\mathbf {u} )=f(\mathbf {X} _{i};\mathbf {v} ^{(t-1)})} , then v ( t ) {\displaystyle \mathbf {v} ^{(t)}} corresponds to the maximum likelihood estimator based on those X k ∈ A {\displaystyle \mathbf {X} _{k}\in A} . == Continuous optimization—example == The same CE algorithm can be used for optimization, rather than estimation. Suppose the problem is to maximize some function S {\displaystyle S} , for example, S ( x ) = e − ( x − 2 ) 2 + 0.8 e − ( x + 2 ) 2 {\displaystyle S(x)={\textrm {e}}^{-(x-2)^{2}}+0.8\,{\textrm {e}}^{-(x+2)^{2}}} . To apply CE, one considers first the associated stochastic problem of estimating P θ ( S ( X ) ≥ γ ) {\displaystyle \mathbb {P} _{\boldsymbol {\theta }}(S(X)\geq \gamma )} for a given level γ {\displaystyle \gamma \,} , and parametric family { f ( ⋅ ; θ ) } {\displaystyle \left\{f(\cdot ;{\boldsymbol {\theta }})\right\}} , for example the 1-dimensional Gaussian distribution, parameterized by its mean μ t {\displaystyle \mu _{t}\,} and variance σ t 2 {\displaystyle \sigma _{t}^{2}} (so θ = ( μ , σ 2 ) {\displaystyle {\boldsymbol {\theta }}=(\mu ,\sigma ^{2})} here). Hence, for a given γ {\displaystyle \gamma \,} , the goal is to find θ {\displaystyle {\boldsymbol {\theta }}} so that D K L ( I { S ( x ) ≥ γ } ‖ f θ ) {\displaystyle D_{\mathrm {KL} }({\textrm {I}}_{\{S(x)\geq \gamma \}}\|f_{\boldsymbol {\theta }})} is minimized. This is done by solving the sample version (stochastic counterpart) of the KL divergence minimization problem, as in step 3 above. It turns out that parameters that minimize the stochastic counterpart for this choice of target distribution and parametric family are the sample mean and sample variance
|
{
"page_id": 5767980,
"source": null,
"title": "Cross-entropy method"
}
|
corresponding to the elite samples, which are those samples that have objective function value ≥ γ {\displaystyle \geq \gamma } . The worst of the elite samples is then used as the level parameter for the next iteration. This yields the following randomized algorithm that happens to coincide with the so-called Estimation of Multivariate Normal Algorithm (EMNA), an estimation of distribution algorithm. === Pseudocode === // Initialize parameters μ := −6 σ2 := 100 t := 0 maxits := 100 N := 100 Ne := 10 // While maxits not exceeded and not converged while t < maxits and σ2 > ε do // Obtain N samples from current sampling distribution X := SampleGaussian(μ, σ2, N) // Evaluate objective function at sampled points S := exp(−(X − 2) ^ 2) + 0.8 exp(−(X + 2) ^ 2) // Sort X by objective function values in descending order X := sort(X, S) // Update parameters of sampling distribution via elite samples μ := mean(X(1:Ne)) σ2 := var(X(1:Ne)) t := t + 1 // Return mean of final sampling distribution as solution return μ == Related methods == Simulated annealing Genetic algorithms Harmony search Estimation of distribution algorithm Tabu search Natural Evolution Strategy Ant colony optimization algorithms == See also == Cross entropy Kullback–Leibler divergence Randomized algorithm Importance sampling == Journal papers == De Boer, P.-T., Kroese, D.P., Mannor, S. and Rubinstein, R.Y. (2005). A Tutorial on the Cross-Entropy Method. Annals of Operations Research, 134 (1), 19–67.[1] Rubinstein, R.Y. (1997). Optimization of Computer Simulation Models with Rare Events, European Journal of Operational Research, 99, 89–112. == Software implementations == CEopt Matlab package CEoptim R package Novacta.Analytics .NET library == References ==
|
{
"page_id": 5767980,
"source": null,
"title": "Cross-entropy method"
}
|
The factored language model (FLM) is an extension of a conventional language model introduced by Jeff Bilmes and Katrin Kirchoff in 2003. In an FLM, each word is viewed as a vector of k factors: w i = { f i 1 , . . . , f i k } . {\displaystyle w_{i}=\{f_{i}^{1},...,f_{i}^{k}\}.} An FLM provides the probabilistic model P ( f | f 1 , . . . , f N ) {\displaystyle P(f|f_{1},...,f_{N})} where the prediction of a factor f {\displaystyle f} is based on N {\displaystyle N} parents { f 1 , . . . , f N } {\displaystyle \{f_{1},...,f_{N}\}} . For example, if w {\displaystyle w} represents a word token and t {\displaystyle t} represents a Part of speech tag for English, the expression P ( w i | w i − 2 , w i − 1 , t i − 1 ) {\displaystyle P(w_{i}|w_{i-2},w_{i-1},t_{i-1})} gives a model for predicting current word token based on a traditional Ngram model as well as the Part of speech tag of the previous word. A major advantage of factored language models is that they allow users to specify linguistic knowledge such as the relationship between word tokens and Part of speech in English, or morphological information (stems, root, etc.) in Arabic. Like N-gram models, smoothing techniques are necessary in parameter estimation. In particular, generalized back-off is used in training an FLM. == References == J Bilmes and K Kirchhoff (2003). "Factored Language Models and Generalized Parallel Backoff" (PDF). Human Language Technology Conference. Archived from the original (PDF) on 17 July 2012.
|
{
"page_id": 2229040,
"source": null,
"title": "Factored language model"
}
|
Tirpitz was a pig captured from the Imperial German Navy after a naval skirmish (the Battle of Más a Tierra) following the Battle of the Falkland Islands in 1914. She became the mascot of the cruiser HMS Glasgow. == Early life == Pigs were often kept on board warships to supply fresh meat. Tirpitz was aboard SMS Dresden, when she was ordered into the South Atlantic to join with the forces of Vice Admiral Maximilian von Spee to raid Allied merchants. The ship's first encounter with HMS Glasgow was at the Battle of Coronel, where the German fleet was victorious. They were later defeated at the Battle of the Falkland Islands, though the faster Dresden managed to escape. She was located in Cumberland Bay on the Chilean island of Más a Tierra (today known as Robinson Crusoe Island), by HMS Glasgow and HMS Kent off the coast of South America on 15 March 1915. The Germans scuttled the ship, but Tirpitz was left on board as she sank. == Capture and Royal Navy service == Tirpitz was able to make her way above deck and swim clear of the sinking Dresden. She struck out for the nearby Royal Navy ships and was spotted an hour later by a petty officer aboard HMS Glasgow. The officer entered the water, but the frightened Tirpitz nearly drowned him. He was however eventually able to rescue the pig and bring her aboard. The animal was adopted by the crew of HMS Glasgow, who made her their mascot, and named her 'Tirpitz', after Alfred von Tirpitz, the German Admiral, and Secretary of State of the Imperial Naval Office. Tirpitz remained with the Glasgow for a year and was then placed in quarantine until she was allowed to be adopted by the Petty Officer who had
|
{
"page_id": 13304626,
"source": null,
"title": "Tirpitz (pig)"
}
|
first seen her, who transferred her to Whale Island Gunnery School, Portsmouth for the rest of her career. The Times newspaper reported: The animal, which is known as 'Tirpitz', was once owned by the German light cruiser Dresden, and when, during the action with Glasgow, Kent, and Orama, the Germans escaped to the shore after causing an explosion which sank the Dresden, and 'Tirpitz' was left to its fate, the pig struck out boldly, and was seen swimming near the Glasgow. Two sailors dived into the sea, and the animal was brought safely aboard. The ship's company of the Glasgow awarded 'Tirpitz' an 'Iron Cross' for having remained in the ship after its shipmates had left, and it became a great pet. == As a fundraiser == Tirpitz was eventually auctioned off for charity as pork in 1919. She ultimately raised £1,785 for the British Red Cross. Tirpitz was bought by William Cavendish-Bentinck, 6th Duke of Portland, who donated Tirpitz's stuffed head to the Imperial War Museum. Tirpitz's head was put on display as part of the museum's original exhibition at The Crystal Palace in 1920, and also featured in the museum's 2006 temporary exhibition 'The Animals' War'. Another of Tirpitz's legacies was bequeathed to the next HMS Glasgow, which retained a pair of silver mounted carvers made from Tirpitz's trotters. These carvers were later also acquired by the Imperial War Museum. == See also == List of individual pigs == Notes == == References == 'Pig in the Post' - A presentation to the Royal Philatelic Society London by Colin Mount FBSAP
|
{
"page_id": 13304626,
"source": null,
"title": "Tirpitz (pig)"
}
|
COMET (Coherent Muon to Electron Transition) is a nuclear physics experiment in J-PARC, Tokai, Japan. In contrast to the usual muon decay to an electron and neutrino, COMET seeks to look for neutrinoless muon to electron conversion, where the electron flies away with an energy of 104.8 MeV. Muon to electron conversion is not forbidden in the Standard Model but the branching ratio is about O ( 10 − 54 ) {\displaystyle {\mathcal {O}}(10^{-54})} considering neutrino oscillations. In beyond the Standard Model approaches the muon to electron conversion process can be as high as O ( 10 − 15 ) {\displaystyle {\mathcal {O}}(10^{-15})} e.g. via the supersymmetric χ 0 ~ {\displaystyle {\tilde {\chi _{0}}}} . COMET will be using a new beamline connecting the J-PARC main ring and the J-PARC Nuclear and particle Physics Experimental Hall (NP hall). The current spokesperson is Kuno Yoshitaka alongside project manager Mihara Satoshi. The collaboration consists of universities coming from 15 countries. == See also == Mu2e experiment == References == == External links == SINDRUM MECO
|
{
"page_id": 53281588,
"source": null,
"title": "Comet (experiment)"
}
|
In molecular biology mir-190 microRNA is a short RNA molecule. MicroRNAs function is to regulate the expression levels of other genes by several mechanisms. == See also == MicroRNA == References == == Further reading == == External links == Page for mir-190 microRNA precursor family at Rfam
|
{
"page_id": 36373301,
"source": null,
"title": "Mir-190 microRNA precursor family"
}
|
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