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very quantum nature, the retrieval process is thus probabilistic. Because quantum associative memories are free from cross-talk, however, spurious memories are never generated. Correspondingly, they have a superior capacity than classical ones. The number of parameters in the unitary matrix U is O ( p n ) {\displaystyle O(pn)} . One can thus have efficient, spurious-memory-free quantum associative memories for any polynomial number of patterns. === Linear algebra simulation with quantum amplitudes === A number of quantum algorithms for machine learning are based on the idea of amplitude encoding, that is, to associate the amplitudes of a quantum state with the inputs and outputs of computations. Since a state of n {\displaystyle n} qubits is described by 2 n {\displaystyle 2^{n}} complex amplitudes, this information encoding can allow for an exponentially compact representation. Intuitively, this corresponds to associating a discrete probability distribution over binary random variables with a classical vector. The goal of algorithms based on amplitude encoding is to formulate quantum algorithms whose resources grow polynomially in the number of qubits n {\displaystyle n} , which amounts to a logarithmic time complexity in the number of amplitudes and thereby the dimension of the input. Many quantum machine learning algorithms in this category are based on variations of the quantum algorithm for linear systems of equations (colloquially called HHL, after the paper's authors) which, under specific conditions, performs a matrix inversion using an amount of physical resources growing only logarithmically in the dimensions of the matrix. One of these conditions is that a Hamiltonian which entry wise corresponds to the matrix can be simulated efficiently, which is known to be possible if the matrix is sparse or low rank. For reference, any known classical algorithm for matrix inversion requires a number of operations that grows more than quadratically in the
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dimension of the matrix (e.g. O ( n 2.373 ) {\displaystyle O{\mathord {\left(n^{2.373}\right)}}} ), but they are not restricted to sparse matrices. Quantum matrix inversion can be applied to machine learning methods in which the training reduces to solving a linear system of equations, for example in least-squares linear regression, the least-squares version of support vector machines, and Gaussian processes. A crucial bottleneck of methods that simulate linear algebra computations with the amplitudes of quantum states is state preparation, which often requires one to initialise a quantum system in a state whose amplitudes reflect the features of the entire dataset. Although efficient methods for state preparation are known for specific cases, this step easily hides the complexity of the task. === Variational Quantum Algorithms (VQAs) === VQAs are one of the most studied classes of quantum algorithms, as modern research demonstrates their applicability to the vast majority of known major applications of the quantum computer, and they appear to be a leading hope for gaining quantum supremacy. VQAs are a mixed quantum-classical approach where the quantum processor prepares quantum states and measurement is made and the optimization is done by a classical computer. VQAs are considered best for NISQ as VQAs are noise tolerant compared to other algorithms and give quantum superiority with only a few hundred qubits. Researchers have studied circuit-based algorithms to solve optimization problems and find the ground state energy of complex systems, which were difficult to solve or required a large time to perform the computation using a classical computer. === Variational quantum circuits (VQCs) === Variational Quantum Circuits also known as Parametrized Quantum Circuits (PQCs) are based on Variational Quantum Algorithms (VQAs). VQCs consist of three parts: preparation of initial states, quantum circuit, and measurement. Researchers are extensively studying VQCs, as it uses the power
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of quantum computation to learn in a short time and also use fewer parameters than its classical counterparts. It is theoretically and numerically proven that we can approximate non-linear functions, like those used in neural networks, on quantum circuits. Due to VQCs superiority, neural network has been replaced by VQCs in Reinforcement Learning tasks and Generative Algorithms. The intrinsic nature of quantum devices towards decoherence, random gate error and measurement errors caused to have high potential to limit the training of the variation circuits. Training the VQCs on the classical devices before employing them on quantum devices helps to overcome the problem of decoherence noise that came through the number of repetitions for training. === Quantum binary classifier === Pattern reorganization is one of the important tasks of machine learning, binary classification is one of the tools or algorithms to find patterns. Binary classification is used in supervised learning and in unsupervised learning. In quantum machine learning, classical bits are converted to qubits and they are mapped to Hilbert space; complex value data are used in a quantum binary classifier to use the advantage of Hilbert space. By exploiting the quantum mechanic properties such as superposition, entanglement, interference the quantum binary classifier produces the accurate result in short period of time. === Quantum machine learning algorithms based on Grover search === Another approach to improving classical machine learning with quantum information processing uses amplitude amplification methods based on Grover's search algorithm, which has been shown to solve unstructured search problems with a quadratic speedup compared to classical algorithms. These quantum routines can be employed for learning algorithms that translate into an unstructured search task, as can be done, for instance, in the case of the k-medians and the k-nearest neighbors algorithms. Other applications include quadratic speedups in the training of
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perceptron and the computation of attention. An example of amplitude amplification being used in a machine learning algorithm is Grover's search algorithm minimization. In which a subroutine uses Grover's search algorithm to find an element less than some previously defined element. This can be done with an oracle that determines whether or not a state with a corresponding element is less than the predefined one. Grover's algorithm can then find an element such that our condition is met. The minimization is initialized by some random element in our data set, and iteratively does this subroutine to find the minimum element in the data set. This minimization is notably used in quantum k-medians, and it has a speed up of at least O ( n k ) {\displaystyle {\mathcal {O}}\left({\sqrt {\frac {n}{k}}}\right)} compared to classical versions of k-medians, where n {\displaystyle n} is the number of data points and k {\displaystyle k} is the number of clusters. Amplitude amplification is often combined with quantum walks to achieve the same quadratic speedup. Quantum walks have been proposed to enhance Google's PageRank algorithm as well as the performance of reinforcement learning agents in the projective simulation framework. === Quantum-enhanced reinforcement learning === Reinforcement learning is a branch of machine learning distinct from supervised and unsupervised learning, which also admits quantum enhancements. In quantum-enhanced reinforcement learning, a quantum agent interacts with a classical or quantum environment and occasionally receives rewards for its actions, which allows the agent to adapt its behavior—in other words, to learn what to do in order to gain more rewards. In some situations, either because of the quantum processing capability of the agent, or due to the possibility to probe the environment in superpositions, a quantum speedup may be achieved. Implementations of these kinds of protocols have been proposed for
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systems of trapped ions and superconducting circuits. A quantum speedup of the agent's internal decision-making time has been experimentally demonstrated in trapped ions, while a quantum speedup of the learning time in a fully coherent (`quantum') interaction between agent and environment has been experimentally realized in a photonic setup. === Quantum annealing === Quantum annealing is an optimization technique used to determine the local minima and maxima of a function over a given set of candidate functions. This is a method of discretizing a function with many local minima or maxima in order to determine the observables of the function. The process can be distinguished from Simulated annealing by the Quantum tunneling process, by which particles tunnel through kinetic or potential barriers from a high state to a low state. Quantum annealing starts from a superposition of all possible states of a system, weighted equally. Then the time-dependent Schrödinger equation guides the time evolution of the system, serving to affect the amplitude of each state as time increases. Eventually, the ground state can be reached to yield the instantaneous Hamiltonian of the system. === NISQ Circuit as Quantum Model === As the depth of the quantum circuit advances on NISQ devices, the noise level rises, posing a significant challenge to accurately computing costs and gradients on training models. The noise tolerance will be improved by using the quantum perceptron and the quantum algorithm on the currently accessible quantum hardware. A regular connection of similar components known as neurons forms the basis of even the most complex brain networks. Typically, a neuron has two operations: the inner product and an activation function. As opposed to the activation function, which is typically nonlinear, the inner product is a linear process. With quantum computing, linear processes may be easily accomplished additionally, due to
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the simplicity of implementation, the threshold function is preferred by the majority of quantum neurons for activation functions. === Quantum sampling techniques === Sampling from high-dimensional probability distributions is at the core of a wide spectrum of computational techniques with important applications across science, engineering, and society. Examples include deep learning, probabilistic programming, and other machine learning and artificial intelligence applications. A computationally hard problem, which is key for some relevant machine learning tasks, is the estimation of averages over probabilistic models defined in terms of a Boltzmann distribution. Sampling from generic probabilistic models is hard: algorithms relying heavily on sampling are expected to remain intractable no matter how large and powerful classical computing resources become. Even though quantum annealers, like those produced by D-Wave Systems, were designed for challenging combinatorial optimization problems, it has been recently recognized as a potential candidate to speed up computations that rely on sampling by exploiting quantum effects. Some research groups have recently explored the use of quantum annealing hardware for training Boltzmann machines and deep neural networks. The standard approach to training Boltzmann machines relies on the computation of certain averages that can be estimated by standard sampling techniques, such as Markov chain Monte Carlo algorithms. Another possibility is to rely on a physical process, like quantum annealing, that naturally generates samples from a Boltzmann distribution. The objective is to find the optimal control parameters that best represent the empirical distribution of a given dataset. The D-Wave 2X system hosted at NASA Ames Research Center has been recently used for the learning of a special class of restricted Boltzmann machines that can serve as a building block for deep learning architectures. Complementary work that appeared roughly simultaneously showed that quantum annealing can be used for supervised learning in classification tasks. The same device
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was later used to train a fully connected Boltzmann machine to generate, reconstruct, and classify down-scaled, low-resolution handwritten digits, among other synthetic datasets. In both cases, the models trained by quantum annealing had a similar or better performance in terms of quality. The ultimate question that drives this endeavour is whether there is quantum speedup in sampling applications. Experience with the use of quantum annealers for combinatorial optimization suggests the answer is not straightforward. Reverse annealing has been used as well to solve a fully connected quantum restricted Boltzmann machine. Inspired by the success of Boltzmann machines based on classical Boltzmann distribution, a new machine learning approach based on quantum Boltzmann distribution of a transverse-field Ising Hamiltonian was recently proposed. Due to the non-commutative nature of quantum mechanics, the training process of the quantum Boltzmann machine can become nontrivial. This problem was, to some extent, circumvented by introducing bounds on the quantum probabilities, allowing the authors to train the model efficiently by sampling. It is possible that a specific type of quantum Boltzmann machine has been trained in the D-Wave 2X by using a learning rule analogous to that of classical Boltzmann machines. Quantum annealing is not the only technology for sampling. In a prepare-and-measure scenario, a universal quantum computer prepares a thermal state, which is then sampled by measurements. This can reduce the time required to train a deep restricted Boltzmann machine, and provide a richer and more comprehensive framework for deep learning than classical computing. The same quantum methods also permit efficient training of full Boltzmann machines and multi-layer, fully connected models and do not have well-known classical counterparts. Relying on an efficient thermal state preparation protocol starting from an arbitrary state, quantum-enhanced Markov logic networks exploit the symmetries and the locality structure of the probabilistic graphical model
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generated by a first-order logic template. This provides an exponential reduction in computational complexity in probabilistic inference, and, while the protocol relies on a universal quantum computer, under mild assumptions it can be embedded on contemporary quantum annealing hardware. === Quantum neural networks === Quantum analogues or generalizations of classical neural nets are often referred to as quantum neural networks. The term is claimed by a wide range of approaches, including the implementation and extension of neural networks using photons, layered variational circuits or quantum Ising-type models. Quantum neural networks are often defined as an expansion on Deutsch's model of a quantum computational network. Within this model, nonlinear and irreversible gates, dissimilar to the Hamiltonian operator, are deployed to speculate the given data set. Such gates make certain phases unable to be observed and generate specific oscillations. Quantum neural networks apply the principals quantum information and quantum computation to classical neurocomputing. Current research shows that QNN can exponentially increase the amount of computing power and the degrees of freedom for a computer, which is limited for a classical computer to its size. A quantum neural network has computational capabilities to decrease the number of steps, qubits used, and computation time. The wave function to quantum mechanics is the neuron for Neural networks. To test quantum applications in a neural network, quantum dot molecules are deposited on a substrate of GaAs or similar to record how they communicate with one another. Each quantum dot can be referred as an island of electric activity, and when such dots are close enough (approximately 10 - 20 nm) electrons can tunnel underneath the islands. An even distribution across the substrate in sets of two create dipoles and ultimately two spin states, up or down. These states are commonly known as qubits with corresponding states
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of | 0 ⟩ {\displaystyle |0\rangle } and | 1 ⟩ {\displaystyle |1\rangle } in Dirac notation. === Quantum Convolution Neural Network === A novel design for multi-dimensional vectors that uses circuits as convolution filters is QCNN. It was inspired by the advantages of CNNs and the power of QML. It is made using a combination of a variational quantum circuit(VQC) and a deep neural network(DNN), fully utilizing the power of extremely parallel processing on a superposition of a quantum state with a finite number of qubits. The main strategy is to carry out an iterative optimization process in the NISQ devices, without the negative impact of noise, which is possibly incorporated into the circuit parameter, and without the need for quantum error correction. The quantum circuit must effectively handle spatial information in order for QCNN to function as CNN. The convolution filter is the most basic technique for making use of spatial information. One or more quantum convolutional filters make up a quantum convolutional neural network (QCNN), and each of these filters transforms input data using a quantum circuit that can be created in an organized or randomized way. Three parts that make up the quantum convolutional filter are: the encoder, the parameterized quantum circuit (PQC), and the measurement. The quantum convolutional filter can be seen as an extension of the filter in the traditional CNN because it was designed with trainable parameters. Quantum neural networks take advantage of the hierarchical structures, and for each subsequent layer, the number of qubits from the preceding layer is decreased by a factor of two. For n input qubits, these structure have O(log(n)) layers, allowing for shallow circuit depth. Additionally, they are able to avoid "barren plateau," one of the most significant issues with PQC-based algorithms, ensuring trainability. Despite the fact that
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the QCNN model does not include the corresponding quantum operation, the fundamental idea of the pooling layer is also offered to assure validity. In QCNN architecture, the pooling layer is typically placed between succeeding convolutional layers. Its function is to shrink the representation's spatial size while preserving crucial features, which allows it to reduce the number of parameters, streamline network computing, and manage over-fitting. Such process can be accomplished applying full Tomography on the state to reduce it all the way down to one qubit and then processed it in subway. The most frequently used unit type in the pooling layer is max pooling, although there are other types as well. Similar to conventional feed-forward neural networks, the last module is a fully connected layer with full connections to all activations in the preceding layer. Translational invariance, which requires identical blocks of parameterized quantum gates within a layer, is a distinctive feature of the QCNN architecture. ==== Dissipative Quantum Neural Network ==== Dissipative QNNs (DQNNs) are constructed from layers of qubits coupled by perceptron called building blocks, which have an arbitrary unitary design. Each node in the network layer of a DQNN is given a distinct collection of qubits, and each qubit is also given a unique quantum perceptron unitary to characterize it. The input states information are transported through the network in a feed-forward fashion, layer-to-layer transition mapping on the qubits of the two adjacent layers, as the name implies. Dissipative term also refers to the fact that the output layer is formed by the ancillary qubits while the input layers are dropped while tracing out the final layer. When performing a broad supervised learning task, DQNN are used to learn a unitary matrix connecting the input and output quantum states. The training data for this task consists of
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the quantum state and the corresponding classical labels. Inspired by the extremely successful classical Generative adversarial network(GAN), dissipative quantum generative adversarial network (DQGAN) is introduced for unsupervised learning of the unlabeled training data . The generator and the discriminator are the two DQNNs that make up a single DQGAN. The generator's goal is to create false training states that the discriminator cannot differentiate from the genuine ones, while the discriminator's objective is to separate the real training states from the fake states created by the generator. The relevant features of the training set are learned by the generator by alternate and adversarial training of the networks that aid in the production of sets that extend the training set. DQGAN has a fully quantum architecture and is trained in quantum data. === Hidden quantum Markov models === Entangled Hidden Markov Models An Entangled Hidden Markov Model (EHMM) is a quantum extension of the classical Hidden Markov Model (HMM), introduced by Abdessatar Souissi and El Gheteb Souedidi. EHMMs establish a bridge between classical probability and quantum entanglement, providing a more profound understanding of quantum systems using observational data. == Mathematical Formulation == Let \( d_H, d_O \) be two positive integers representing the dimensions of the hidden and observable states, respectively. Define: - \( \mathcal{M}_{d_H} \) as the \( C^* \)-algebra of \( d_H \times d_H \) matrices. - \( \mathcal{M}_{d_O} \) as the \( C^* \)-algebra of \( d_O \times d_O \) matrices. - The identity element in \( \mathcal{M}_{d_H} \) is denoted by \( \mathbb{I}_{d_H} \). - The Schur (Hadamard) product for two matrices \( A, B \in \mathcal{M}_{d_H} \) is defined as: \[ A \diamond B = (a_{ij} b_{ij})_{1 \leq i,j \leq d_H}. \] Define the hidden and observable sample algebras: \[ \mathcal{A}_H = \bigotimes_{\mathbb{N}} \mathcal{M}_{d_H}, \quad \mathcal{A}_O =
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\bigotimes_{\mathbb{N}} \mathcal{M}_{d_O}, \] with the full sample algebra: \[ \mathcal{A}_{H,O} = \bigotimes_{\mathbb{N}} (\mathcal{M}_{d_H} \otimes \mathcal{M}_{d_O}). \] == Hidden Quantum Markov Models == Hidden Quantum Markov Models (HQMMs) are a quantum-enhanced version of classical Hidden Markov Models (HMMs), which are typically used to model sequential data in various fields like robotics and natural language processing. Unlike other quantum-enhanced machine learning algorithms, HQMMs can be viewed as models inspired by quantum mechanics that can be run on classical computers as well. Where classical HMMs use probability vectors to represent hidden 'belief' states, HQMMs use the quantum analogue: density matrices. Recent work has extended HQMMs through the introduction of **Entangled Hidden Markov Models (EHMMs)**, which incorporate quantum entanglement into their structure. The EHMM framework builds upon classical HQMMs by defining entangled transition expectations, which allow for enhanced modeling of quantum systems. Additionally, EHMMs have been linked to Matrix Product States (MPS) and provide a new perspective on probabilistic graphical models in quantum settings. Since classical HMMs are a particular kind of Bayes net, HQMMs and EHMMs provide insights into quantum-analogous Bayesian inference, offering new pathways for modeling quantum probability and non-classical correlations in quantum information processing. Furthermore, empirical studies suggest that EHMMs improve the ability to model sequential data when compared to their classical counterparts, though further research is required to fully understand these benefits. == Transition Expectation and Emission Operators == A linear map \( \mathcal{E}_H : \mathcal{M}_{d_H} \otimes \mathcal{M}_{d_H} \to \mathcal{M}_{d_H} \) is called a **transition expectation** if it is completely positive and identity-preserving \cite{SSB23}. Similarly, a linear map \( \mathcal{E}_{H,O} : \mathcal{M}_{d_H} \otimes \mathcal{M}_{d_O} \to \mathcal{M}_{d_H} \) is called an **emission operator** if it is completely positive and identity-preserving. === Fully quantum machine learning === In the most general case of quantum machine learning, both the learning device and the
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system under study, as well as their interaction, are fully quantum. This section gives a few examples of results on this topic. One class of problem that can benefit from the fully quantum approach is that of 'learning' unknown quantum states, processes or measurements, in the sense that one can subsequently reproduce them on another quantum system. For example, one may wish to learn a measurement that discriminates between two coherent states, given not a classical description of the states to be discriminated, but instead a set of example quantum systems prepared in these states. The naive approach would be to first extract a classical description of the states and then implement an ideal discriminating measurement based on this information. This would only require classical learning. However, one can show that a fully quantum approach is strictly superior in this case. (This also relates to work on quantum pattern matching.) The problem of learning unitary transformations can be approached in a similar way. Going beyond the specific problem of learning states and transformations, the task of clustering also admits a fully quantum version, wherein both the oracle which returns the distance between data-points and the information processing device which runs the algorithm are quantum. Finally, a general framework spanning supervised, unsupervised and reinforcement learning in the fully quantum setting was introduced in, where it was also shown that the possibility of probing the environment in superpositions permits a quantum speedup in reinforcement learning. Such a speedup in the reinforcement-learning paradigm has been experimentally demonstrated in a photonic setup. === Explainable quantum machine learning === The need for models that can be understood by humans emerges in quantum machine learning in analogy to classical machine learning and drives the research field of explainable quantum machine learning (or XQML in analogy to
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XAI/XML). These efforts are often also referred to as Interpretable Machine Learning (IML, and by extension IQML). XQML/IQML can be considered as an alternative research direction instead of finding a quantum advantage. For example, XQML has been used in the context of mobile malware detection and classification. Quantum Shapley values have also been proposed to interpret gates within a circuit based on a game-theoretic approach. For this purpose, gates instead of features act as players in a coalitional game with a value function that depends on measurements of the quantum circuit of interest. Additionally, a quantum version of the classical technique known as LIME (Linear Interpretable Model-Agnostic Explanations) has also been proposed, known as Q-LIME. == Classical learning applied to quantum problems == The term "quantum machine learning" sometimes refers to classical machine learning performed on data from quantum systems. A basic example of this is quantum state tomography, where a quantum state is learned from measurement. Other applications include learning Hamiltonians and automatically generating quantum experiments. == Quantum learning theory == Quantum learning theory pursues a mathematical analysis of the quantum generalizations of classical learning models and of the possible speed-ups or other improvements that they may provide. The framework is very similar to that of classical computational learning theory, but the learner in this case is a quantum information processing device, while the data may be either classical or quantum. Quantum learning theory should be contrasted with the quantum-enhanced machine learning discussed above, where the goal was to consider specific problems and to use quantum protocols to improve the time complexity of classical algorithms for these problems. Although quantum learning theory is still under development, partial results in this direction have been obtained. The starting point in learning theory is typically a concept class, a set of possible
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concepts. Usually a concept is a function on some domain, such as { 0 , 1 } n {\displaystyle \{0,1\}^{n}} . For example, the concept class could be the set of disjunctive normal form (DNF) formulas on n bits or the set of Boolean circuits of some constant depth. The goal for the learner is to learn (exactly or approximately) an unknown target concept from this concept class. The learner may be actively interacting with the target concept, or passively receiving samples from it. In active learning, a learner can make membership queries to the target concept c, asking for its value c(x) on inputs x chosen by the learner. The learner then has to reconstruct the exact target concept, with high probability. In the model of quantum exact learning, the learner can make membership queries in quantum superposition. If the complexity of the learner is measured by the number of membership queries it makes, then quantum exact learners can be polynomially more efficient than classical learners for some concept classes, but not more. If complexity is measured by the amount of time the learner uses, then there are concept classes that can be learned efficiently by quantum learners but not by classical learners (under plausible complexity-theoretic assumptions). A natural model of passive learning is Valiant's probably approximately correct (PAC) learning. Here the learner receives random examples (x,c(x)), where x is distributed according to some unknown distribution D. The learner's goal is to output a hypothesis function h such that h(x)=c(x) with high probability when x is drawn according to D. The learner has to be able to produce such an 'approximately correct' h for every D and every target concept c in its concept class. We can consider replacing the random examples by potentially more powerful quantum examples ∑
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x D ( x ) | x , c ( x ) ⟩ {\displaystyle \sum _{x}{\sqrt {D(x)}}|x,c(x)\rangle } . In the PAC model (and the related agnostic model), this doesn't significantly reduce the number of examples needed: for every concept class, classical and quantum sample complexity are the same up to constant factors. However, for learning under some fixed distribution D, quantum examples can be very helpful, for example for learning DNF under the uniform distribution. When considering time complexity, there exist concept classes that can be PAC-learned efficiently by quantum learners, even from classical examples, but not by classical learners (again, under plausible complexity-theoretic assumptions). This passive learning type is also the most common scheme in supervised learning: a learning algorithm typically takes the training examples fixed, without the ability to query the label of unlabelled examples. Outputting a hypothesis h is a step of induction. Classically, an inductive model splits into a training and an application phase: the model parameters are estimated in the training phase, and the learned model is applied an arbitrary many times in the application phase. In the asymptotic limit of the number of applications, this splitting of phases is also present with quantum resources. == Implementations and experiments == The earliest experiments were conducted using the adiabatic D-Wave quantum computer, for instance, to detect cars in digital images using regularized boosting with a nonconvex objective function in a demonstration in 2009. Many experiments followed on the same architecture, and leading tech companies have shown interest in the potential of quantum machine learning for future technological implementations. In 2013, Google Research, NASA, and the Universities Space Research Association launched the Quantum Artificial Intelligence Lab which explores the use of the adiabatic D-Wave quantum computer. A more recent example trained a probabilistic generative models with
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arbitrary pairwise connectivity, showing that their model is capable of generating handwritten digits as well as reconstructing noisy images of bars and stripes and handwritten digits. Using a different annealing technology based on nuclear magnetic resonance (NMR), a quantum Hopfield network was implemented in 2009 that mapped the input data and memorized data to Hamiltonians, allowing the use of adiabatic quantum computation. NMR technology also enables universal quantum computing, and it was used for the first experimental implementation of a quantum support vector machine to distinguish hand written number ‘6’ and ‘9’ on a liquid-state quantum computer in 2015. The training data involved the pre-processing of the image which maps them to normalized 2-dimensional vectors to represent the images as the states of a qubit. The two entries of the vector are the vertical and horizontal ratio of the pixel intensity of the image. Once the vectors are defined on the feature space, the quantum support vector machine was implemented to classify the unknown input vector. The readout avoids costly quantum tomography by reading out the final state in terms of direction (up/down) of the NMR signal. Photonic implementations are attracting more attention, not the least because they do not require extensive cooling. Simultaneous spoken digit and speaker recognition and chaotic time-series prediction were demonstrated at data rates beyond 1 gigabyte per second in 2013. Using non-linear photonics to implement an all-optical linear classifier, a perceptron model was capable of learning the classification boundary iteratively from training data through a feedback rule. A core building block in many learning algorithms is to calculate the distance between two vectors: this was first experimentally demonstrated for up to eight dimensions using entangled qubits in a photonic quantum computer in 2015. Recently, based on a neuromimetic approach, a novel ingredient has been added
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to the field of quantum machine learning, in the form of a so-called quantum memristor, a quantized model of the standard classical memristor. This device can be constructed by means of a tunable resistor, weak measurements on the system, and a classical feed-forward mechanism. An implementation of a quantum memristor in superconducting circuits has been proposed, and an experiment with quantum dots performed. A quantum memristor would implement nonlinear interactions in the quantum dynamics which would aid the search for a fully functional quantum neural network. Since 2016, IBM has launched an online cloud-based platform for quantum software developers, called the IBM Q Experience. This platform consists of several fully operational quantum processors accessible via the IBM Web API. In doing so, the company is encouraging software developers to pursue new algorithms through a development environment with quantum capabilities. New architectures are being explored on an experimental basis, up to 32 qubits, using both trapped-ion and superconductive quantum computing methods. In October 2019, it was noted that the introduction of Quantum Random Number Generators (QRNGs) to machine learning models including Neural Networks and Convolutional Neural Networks for random initial weight distribution and Random Forests for splitting processes had a profound effect on their ability when compared to the classical method of Pseudorandom Number Generators (PRNGs). However, in a more recent publication from 2021, these claims could not be reproduced for Neural Network weight initialization and no significant advantage of using QRNGs over PRNGs was found. The work also demonstrated that the generation of fair random numbers with a gate quantum computer is a non-trivial task on NISQ devices, and QRNGs are therefore typically much more difficult to use in practice than PRNGs. A paper published in December 2018 reported on an experiment using a trapped-ion system demonstrating a quantum speedup
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of the deliberation time of reinforcement learning agents employing internal quantum hardware. In March 2021, a team of researchers from Austria, The Netherlands, the US and Germany reported the experimental demonstration of a quantum speedup of the learning time of reinforcement learning agents interacting fully quantumly with the environment. The relevant degrees of freedom of both agent and environment were realized on a compact and fully tunable integrated nanophotonic processor. == Skepticism == While machine learning itself is now not only a research field but an economically significant and fast growing industry and quantum computing is a well established field of both theoretical and experimental research, quantum machine learning remains a purely theoretical field of studies. Attempts to experimentally demonstrate concepts of quantum machine learning remain insufficient. Further, another obstacle exists at the prediction stage because the outputs of quantum learning models are inherently random. This creates an often considerable overhead, as many executions of a quantum learning model have to be aggregated to obtain an actual prediction. Many of the leading scientists that extensively publish in the field of quantum machine learning warn about the extensive hype around the topic and are very restrained if asked about its practical uses in the foreseeable future. Sophia Chen collected some of the statements made by well known scientists in the field: "I think we haven't done our homework yet. This is an extremely new scientific field," - physicist Maria Schuld of Canada-based quantum computing startup Xanadu. “When mixing machine learning with ‘quantum,’ you catalyse a hype-condensate.” - Jacob Biamonte a contributor to the theory of quantum computation. "There is a lot more work that needs to be done before claiming quantum machine learning will actually work," - computer scientist Iordanis Kerenidis, the head of quantum algorithms at the Silicon Valley-based quantum
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computing startup QC Ware. "I have not seen a single piece of evidence that there exists a meaningful [machine learning] task for which it would make sense to use a quantum computer and not a classical computer," - physicist Ryan Sweke of the Free University of Berlin in Germany. “Don't fall for the hype!” - Frank Zickert, who is the author of probably the most practical book related to the subject beware that ”quantum computers are far away from advancing machine learning for their representation ability”, and even speaking about evaluation and optimization for any kind of useful task quantum supremacy is not yet achieved. Furthermore, nobody among the active researchers in the field make any forecasts about when it could possibly become practical. == See also == Differentiable programming Quantum computing Quantum algorithm for linear systems of equations Quantum annealing Quantum neural network Quantum image == References ==
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"title": "Quantum machine learning"
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The Korean Biology Olympiad (KBO) is a biology olympiad held by Korean Biology Educational Society. The top four finalists become eligible to join the International Biology Olympiad. == See also == List of biology awards == References ==
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"page_id": 57019357,
"source": null,
"title": "Korean Biology Olympiad"
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In chemistry, an acid–base reaction is a chemical reaction that occurs between an acid and a base. It can be used to determine pH via titration. Several theoretical frameworks provide alternative conceptions of the reaction mechanisms and their application in solving related problems; these are called the acid–base theories, for example, Brønsted–Lowry acid–base theory. Their importance becomes apparent in analyzing acid–base reactions for gaseous or liquid species, or when acid or base character may be somewhat less apparent. The first of these concepts was provided by the French chemist Antoine Lavoisier, around 1776. It is important to think of the acid–base reaction models as theories that complement each other. For example, the current Lewis model has the broadest definition of what an acid and base are, with the Brønsted–Lowry theory being a subset of what acids and bases are, and the Arrhenius theory being the most restrictive. == Acid–base definitions == === Historic development === The concept of an acid–base reaction was first proposed in 1754 by Guillaume-François Rouelle, who introduced the word "base" into chemistry to mean a substance which reacts with an acid to give it solid form (as a salt). Bases are mostly bitter in nature. ==== Lavoisier's oxygen theory of acids ==== The first scientific concept of acids and bases was provided by Lavoisier in around 1776. Since Lavoisier's knowledge of strong acids was mainly restricted to oxoacids, such as HNO3 (nitric acid) and H2SO4 (sulfuric acid), which tend to contain central atoms in high oxidation states surrounded by oxygen, and since he was not aware of the true composition of the hydrohalic acids (HF, HCl, HBr, and HI), he defined acids in terms of their containing oxygen, which in fact he named from Greek words meaning "acid-former" (from Greek ὀξύς (oxys) 'acid, sharp' and γεινομαι
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"page_id": 3038,
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(geinomai) 'engender'). The Lavoisier definition held for over 30 years, until the 1810 article and subsequent lectures by Sir Humphry Davy in which he proved the lack of oxygen in hydrogen sulfide (H2S), hydrogen telluride (H2Te), and the hydrohalic acids. However, Davy failed to develop a new theory, concluding that "acidity does not depend upon any particular elementary substance, but upon peculiar arrangement of various substances". One notable modification of oxygen theory was provided by Jöns Jacob Berzelius, who stated that acids are oxides of nonmetals while bases are oxides of metals. ==== Liebig's hydrogen theory of acids ==== In 1838, Justus von Liebig proposed that an acid is a hydrogen-containing compound whose hydrogen can be replaced by a metal. This redefinition was based on his extensive work on the chemical composition of organic acids, finishing the doctrinal shift from oxygen-based acids to hydrogen-based acids started by Davy. Liebig's definition, while completely empirical, remained in use for almost 50 years until the adoption of the Arrhenius definition. === Arrhenius definition === The first modern definition of acids and bases in molecular terms was devised by Svante Arrhenius. A hydrogen theory of acids, it followed from his 1884 work with Friedrich Wilhelm Ostwald in establishing the presence of ions in aqueous solution and led to Arrhenius receiving the Nobel Prize in Chemistry in 1903. As defined by Arrhenius: An Arrhenius acid is a substance that ionises in water to form hydrogen ions (H+); that is, an acid increases the concentration of H+ ions in an aqueous solution. This causes the protonation of water, or the creation of the hydronium (H3O+) ion. Thus, in modern times, the symbol H+ is interpreted as a shorthand for H3O+, because it is now known that a bare proton does not exist as a free species
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in aqueous solution. This is the species which is measured by pH indicators to measure the acidity or basicity of a solution. An Arrhenius base is a substance that dissociates in water to form hydroxide (OH−) ions; that is, a base increases the concentration of OH− ions in an aqueous solution. The Arrhenius definitions of acidity and alkalinity are restricted to aqueous solutions and are not valid for most non-aqueous solutions, and refer to the concentration of the solvent ions. Under this definition, pure H2SO4 and HCl dissolved in toluene are not acidic, and molten NaOH and solutions of calcium amide in liquid ammonia are not alkaline. This led to the development of the Brønsted–Lowry theory and subsequent Lewis theory to account for these non-aqueous exceptions. The reaction of an acid with a base is called a neutralization reaction. The products of this reaction are a salt and water. acid + base ⟶ salt + water {\displaystyle {\text{acid}}\ +\ {\text{base}}\ \longrightarrow \ {\text{salt}}\ +\ {\text{water}}} In this traditional representation an acid–base neutralization reaction is formulated as a double-replacement reaction. For example, the reaction of hydrochloric acid (HCl) with sodium hydroxide (NaOH) solutions produces a solution of sodium chloride (NaCl) and some additional water molecules. HCl ( aq ) + NaOH ( aq ) ⟶ NaCl ( aq ) + H 2 O {\displaystyle {\ce {HCl_{(aq)}{}+ NaOH_{(aq)}-> NaCl_{(aq)}{}+ H2O}}} The modifier (aq) in this equation was implied by Arrhenius, rather than included explicitly. It indicates that the substances are dissolved in water. Though all three substances, HCl, NaOH and NaCl are capable of existing as pure compounds, in aqueous solutions they are fully dissociated into the aquated ions H+, Cl−, Na+ and OH−. ==== Example: Baking powder ==== Baking powder is used to cause the dough for breads and cakes to
|
{
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"rise" by creating millions of tiny carbon dioxide bubbles. Baking powder is not to be confused with baking soda, which is sodium bicarbonate (NaHCO3). Baking powder is a mixture of baking soda (sodium bicarbonate) and acidic salts. The bubbles are created because, when the baking powder is combined with water, the sodium bicarbonate and acid salts react to produce gaseous carbon dioxide. Whether commercially or domestically prepared, the principles behind baking powder formulations remain the same. The acid–base reaction can be generically represented as shown: NaHCO 3 + H + ⟶ Na + + CO 2 + H 2 O {\displaystyle {\ce {NaHCO3 + H+ -> Na+ + CO2 + H2O}}} The real reactions are more complicated because the acids are complicated. For example, starting with sodium bicarbonate and monocalcium phosphate (Ca(H2PO4)2), the reaction produces carbon dioxide by the following stoichiometry: 14 NaHCO 3 + 5 Ca ( H 2 PO 4 ) 2 ⟶ 14 CO 2 + Ca 5 ( PO 4 ) 3 OH + 7 Na 2 HPO 4 + 13 H 2 O {\displaystyle {\ce {14 NaHCO3 + 5 Ca(H2PO4)2 -> 14 CO2 + Ca5(PO4)3OH + 7 Na2HPO4 + 13 H2O}}} A typical formulation (by weight) could call for 30% sodium bicarbonate, 5–12% monocalcium phosphate, and 21–26% sodium aluminium sulfate. Alternately, a commercial baking powder might use sodium acid pyrophosphate as one of the two acidic components instead of sodium aluminium sulfate. Another typical acid in such formulations is cream of tartar (KC4H5O6), a derivative of tartaric acid. === Brønsted–Lowry definition === The Brønsted–Lowry definition, formulated in 1923, independently by Johannes Nicolaus Brønsted in Denmark and Martin Lowry in England, is based upon the idea of protonation of bases through the deprotonation of acids – that is, the ability of acids to "donate" hydrogen ions
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(H+) – otherwise known as protons – to bases, which "accept" them. An acid–base reaction is, thus, the removal of a hydrogen ion from the acid and its addition to the base. The removal of a hydrogen ion from an acid produces its conjugate base, which is the acid with a hydrogen ion removed. The reception of a proton by a base produces its conjugate acid, which is the base with a hydrogen ion added. Unlike the previous definitions, the Brønsted–Lowry definition does not refer to the formation of salt and solvent, but instead to the formation of conjugate acids and conjugate bases, produced by the transfer of a proton from the acid to the base. In this approach, acids and bases are fundamentally different in behavior from salts, which are seen as electrolytes, subject to the theories of Debye, Onsager, and others. An acid and a base react not to produce a salt and a solvent, but to form a new acid and a new base. The concept of neutralization is thus absent. Brønsted–Lowry acid–base behavior is formally independent of any solvent, making it more all-encompassing than the Arrhenius model. The calculation of pH under the Arrhenius model depended on alkalis (bases) dissolving in water (aqueous solution). The Brønsted–Lowry model expanded what could be pH tested using insoluble and soluble solutions (gas, liquid, solid). The general formula for acid–base reactions according to the Brønsted–Lowry definition is: HA + B ⟶ BH + + A − {\displaystyle {\ce {HA + B -> BH+ + A-}}} where HA represents the acid, B represents the base, BH+ represents the conjugate acid of B, and A− represents the conjugate base of HA. For example, a Brønsted–Lowry model for the dissociation of hydrochloric acid (HCl) in aqueous solution would be the following: HCl acid
|
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+ H 2 O base ↽ − − ⇀ H 3 O + conjugate acid + Cl − conjugate base {\displaystyle {\underset {\text{acid}}{{\ce {HCl_{\,}}}}}\ +\ {\underset {\text{base}}{{\ce {H2O}}}}\quad {\ce {<=>}}\quad {\underset {{\text{conjugate }} \atop {\text{acid }}}{{\ce {H3O+}}}}\ +{\underset {{\text{conjugate}} \atop {\text{base}}}{{\ce {Cl_{\,}-}}}}} The removal of H+ from the HCl produces the chloride ion, Cl−, the conjugate base of the acid. The addition of H+ to the H2O (acting as a base) forms the hydronium ion, H3O+, the conjugate acid of the base. Water is amphoteric – that is, it can act as both an acid and a base. The Brønsted–Lowry model explains this, showing the dissociation of water into low concentrations of hydronium and hydroxide ions: H 2 O + H 2 O ↽ − − ⇀ H 3 O + + OH − {\displaystyle {\ce {H2O + H2O <=> H3O+ + OH-}}} This equation is demonstrated in the image below: Here, one molecule of water acts as an acid, donating an H+ and forming the conjugate base, OH−, and a second molecule of water acts as a base, accepting the H+ ion and forming the conjugate acid, H3O+. As an example of water acting as an acid, consider an aqueous solution of pyridine, C5H5N. C 5 H 5 N + H 2 O ↽ − − ⇀ [ C 5 H 5 NH ] + + OH − {\displaystyle {\ce {C5H5N + H2O <=> [C5H5NH]+ + OH-}}} In this example, a water molecule is split into a hydrogen ion, which is donated to a pyridine molecule, and a hydroxide ion. In the Brønsted–Lowry model, the solvent does not necessarily have to be water, as is required by the Arrhenius Acid–Base model. For example, consider what happens when acetic acid, CH3COOH, dissolves in liquid ammonia. CH 3 COOH + NH
|
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3 ↽ − − ⇀ NH 4 + + CH 3 COO − {\displaystyle {\ce {CH3COOH + NH3 <=> NH4+ + CH3COO-}}} An H+ ion is removed from acetic acid, forming its conjugate base, the acetate ion, CH3COO−. The addition of an H+ ion to an ammonia molecule of the solvent creates its conjugate acid, the ammonium ion, NH+4. The Brønsted–Lowry model calls hydrogen-containing substances (like HCl) acids. Thus, some substances, which many chemists considered to be acids, such as SO3 or BCl3, are excluded from this classification due to lack of hydrogen. Gilbert N. Lewis wrote in 1938, "To restrict the group of acids to those substances that contain hydrogen interferes as seriously with the systematic understanding of chemistry as would the restriction of the term oxidizing agent to substances containing oxygen." Furthermore, KOH and KNH2 are not considered Brønsted bases, but rather salts containing the bases OH− and NH−2. === Lewis definition === The hydrogen requirement of Arrhenius and Brønsted–Lowry was removed by the Lewis definition of acid–base reactions, devised by Gilbert N. Lewis in 1923, in the same year as Brønsted–Lowry, but it was not elaborated by him until 1938. Instead of defining acid–base reactions in terms of protons or other bonded substances, the Lewis definition defines a base (referred to as a Lewis base) to be a compound that can donate an electron pair, and an acid (a Lewis acid) to be a compound that can receive this electron pair. For example, boron trifluoride, BF3 is a typical Lewis acid. It can accept a pair of electrons as it has a vacancy in its octet. The fluoride ion has a full octet and can donate a pair of electrons. Thus BF 3 + F − ⟶ BF 4 − {\displaystyle {\ce {BF3 + F- -> BF4-}}}
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is a typical Lewis acid, Lewis base reaction. All compounds of group 13 elements with a formula AX3 can behave as Lewis acids. Similarly, compounds of group 15 elements with a formula DY3, such as amines, NR3, and phosphines, PR3, can behave as Lewis bases. Adducts between them have the formula X3A←DY3 with a dative covalent bond, shown symbolically as ←, between the atoms A (acceptor) and D (donor). Compounds of group 16 with a formula DX2 may also act as Lewis bases; in this way, a compound like an ether, R2O, or a thioether, R2S, can act as a Lewis base. The Lewis definition is not limited to these examples. For instance, carbon monoxide acts as a Lewis base when it forms an adduct with boron trifluoride, of formula F3B←CO. Adducts involving metal ions are referred to as co-ordination compounds; each ligand donates a pair of electrons to the metal ion. The reaction [ Ag ( H 2 O ) 4 ] + + 2 NH 3 ⟶ [ Ag ( NH 3 ) 2 ] + + 4 H 2 O {\displaystyle {\ce {[Ag(H2O)4]+ + 2 NH3 -> [Ag(NH3)2]+ + 4 H2O}}} can be seen as an acid–base reaction in which a stronger base (ammonia) replaces a weaker one (water). The Lewis and Brønsted–Lowry definitions are consistent with each other since the reaction H + + OH − ↽ − − ⇀ H 2 O {\displaystyle {\ce {H+ + OH- <=> H2O}}} is an acid–base reaction in both theories. === Solvent system definition === One of the limitations of the Arrhenius definition is its reliance on water solutions. Edward Curtis Franklin studied the acid–base reactions in liquid ammonia in 1905 and pointed out the similarities to the water-based Arrhenius theory. Albert F.O. Germann, working with liquid phosgene, COCl2,
|
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formulated the solvent-based theory in 1925, thereby generalizing the Arrhenius definition to cover aprotic solvents. Germann pointed out that in many solutions, there are ions in equilibrium with the neutral solvent molecules: solvonium ions: a generic name for positive ions. These are also sometimes called solvo-acids; when protonated solvent, they are lyonium ions. solvate ions: a generic name for negative ions. These are also sometimes called solve-bases; when deprotonated solvent, they are lyate ions. For example, water and ammonia undergo such dissociation into hydronium and hydroxide, and ammonium and amide, respectively: H3O+ + OH-}}\\[4pt]{\ce {2 NH3}}&{\ce {\, <=> NH4+ + NH2-}}\end{aligned}}}"> 2 H 2 O ↽ − − ⇀ H 3 O + + OH − 2 NH 3 ↽ − − ⇀ NH 4 + + NH 2 − {\displaystyle {\begin{aligned}{\ce {2 H2O}}&{\ce {\, <=> H3O+ + OH-}}\\[4pt]{\ce {2 NH3}}&{\ce {\, <=> NH4+ + NH2-}}\end{aligned}}} Some aprotic systems also undergo such dissociation, such as dinitrogen tetroxide into nitrosonium and nitrate, antimony trichloride into dichloroantimonium and tetrachloroantimonate, and phosgene into chlorocarboxonium and chloride: NO+ + NO3-}}\\[4pt]{\ce {2 SbCl3}}&{\ce {\, <=> SbCl2+ + SbCl4-}}\\[4pt]{\ce {COCl2}}&{\ce {\, <=> COCl+ + Cl-}}\end{aligned}}}"> N 2 O 4 ↽ − − ⇀ NO + + NO 3 − 2 SbCl 3 ↽ − − ⇀ SbCl 2 + + SbCl 4 − COCl 2 ↽ − − ⇀ COCl + + Cl − {\displaystyle {\begin{aligned}{\ce {N2O4}}&{\ce {\, <=> NO+ + NO3-}}\\[4pt]{\ce {2 SbCl3}}&{\ce {\, <=> SbCl2+ + SbCl4-}}\\[4pt]{\ce {COCl2}}&{\ce {\, <=> COCl+ + Cl-}}\end{aligned}}} A solute that causes an increase in the concentration of the solvonium ions and a decrease in the concentration of solvate ions is defined as an acid. A solute that causes an increase in the concentration of the solvate ions and a decrease in the concentration of the solvonium ions is
|
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defined as a base. Thus, in liquid ammonia, KNH2 (supplying NH−2) is a strong base, and NH4NO3 (supplying NH+4) is a strong acid. In liquid sulfur dioxide (SO2), thionyl compounds (supplying SO2+) behave as acids, and sulfites (supplying SO2−3) behave as bases. The non-aqueous acid–base reactions in liquid ammonia are similar to the reactions in water: 2 NaNH 2 base + Zn ( NH 2 ) 2 amphiphilic amide ⟶ Na 2 [ Zn ( NH 2 ) 4 ] 2 NH 4 I acid + Zn ( NH 2 ) 2 ⟶ [ Zn ( NH 3 ) 4 ] I 2 {\displaystyle {\begin{aligned}{\underset {\text{base}}{{\ce {2 NaNH2}}}}+{\underset {{\text{amphiphilic}} \atop {\text{amide}}}{{\ce {Zn(NH2)2}}}}&\longrightarrow {\ce {Na2[Zn(NH2)4]}}\\[4pt]{\underset {\text{acid}}{{\ce {2 NH4I}}}}\ +\ {\ce {Zn(NH2)2}}&\longrightarrow {\ce {[Zn(NH3)4]I2}}\end{aligned}}} Nitric acid can be a base in liquid sulfuric acid: HNO 3 base + 2 H 2 SO 4 ⟶ NO 2 + + H 3 O + + 2 HSO 4 − {\displaystyle {\underset {\text{base}}{{\ce {HNO3}}}}+{\ce {2 H2SO4 -> NO2+ + H3O+ + 2 HSO4-}}} The unique strength of this definition shows in describing the reactions in aprotic solvents; for example, in liquid N2O4: AgNO 3 base + NOCl acid ⟶ N 2 O 4 solvent + AgCl salt {\displaystyle {\underset {\text{base}}{{\ce {AgNO3}}}}+{\underset {\text{acid}}{{\ce {NOCl_{\ }}}}}\longrightarrow {\underset {\text{solvent}}{{\ce {N2O4}}}}+{\underset {\text{salt}}{{\ce {AgCl_{\ }}}}}} Because the solvent system definition depends on the solute as well as on the solvent itself, a particular solute can be either an acid or a base depending on the choice of the solvent: HClO4 is a strong acid in water, a weak acid in acetic acid, and a weak base in fluorosulfonic acid; this characteristic of the theory has been seen as both a strength and a weakness, because some substances (such as SO3 and NH3) have been seen to be acidic or basic
|
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on their own right. On the other hand, solvent system theory has been criticized as being too general to be useful. Also, it has been thought that there is something intrinsically acidic about hydrogen compounds, a property not shared by non-hydrogenic solvonium salts. === Lux–Flood definition === This acid–base theory was a revival of the oxygen theory of acids and bases proposed by German chemist Hermann Lux in 1939, further improved by Håkon Flood c. 1947 and is still used in modern geochemistry and electrochemistry of molten salts. This definition describes an acid as an oxide ion (O2−) acceptor and a base as an oxide ion donor. For example: (base) (acid) MgO + CO 2 ⟶ MgCO 3 CaO + SiO 2 ⟶ CaSiO 3 NO 3 − + S 2 O 7 2 − ⟶ NO 2 + + 2 SO 4 2 − {\displaystyle {\begin{array}{ccccl}_{\text{(base)}}&&_{\text{(acid)}}\\[4pt]{\ce {MgO}}&+&{\ce {CO2}}&\longrightarrow &{\ce {MgCO3}}\\[4pt]{\ce {CaO}}&+&{\ce {SiO2}}&\longrightarrow &{\ce {CaSiO3}}\\[4pt]{\ce {NO3-}}&+&{\ce {S2O7^2-}}\!\!&\longrightarrow &{\ce {NO2+ + 2 SO4^2-}}\end{array}}} This theory is also useful in the systematisation of the reactions of noble gas compounds, especially the xenon oxides, fluorides, and oxofluorides. === Usanovich definition === Mikhail Usanovich developed a general theory that does not restrict acidity to hydrogen-containing compounds, but his approach, published in 1938, was even more general than Lewis theory. Usanovich's theory can be summarized as defining an acid as anything that accepts negative species or donates positive ones, and a base as the reverse. This defined the concept of redox (oxidation-reduction) as a special case of acid–base reactions. Some examples of Usanovich acid–base reactions include: (base) (acid) Na 2 O + SO 3 ⟶ 2 Na + + SO 4 2 − (species exchanged: O 2 − anion) 3 ( NH 4 ) 2 S + Sb 2 S 5 ⟶ 6 NH 4
|
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"page_id": 3038,
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+ + 2 SbS 4 3 − (species exchanged: 3 S 2 − anions) 2 Na + Cl 2 ⟶ 2 Na + + 2 Cl − (species exchanged: 2 electrons) {\displaystyle {\begin{array}{ccccll}_{\text{(base)}}&&_{\text{(acid)}}\\[4pt]{\ce {Na2O}}&+&{\ce {SO3}}&\longrightarrow &{\ce {2Na+{}+\ SO4^{2}-}}&{\text{(species exchanged: }}{\ce {O^{2}-}}{\text{anion)}}\\[4pt]{\ce {3(NH4)2S}}&+&{\ce {Sb2S5}}&\longrightarrow &{\ce {6NH4+{}+\ 2SbS4^{3}-}}&{\text{(species exchanged: }}{\ce {3S^{2}-}}{\text{ anions)}}\\[4pt]{\ce {2Na}}&+&{\ce {Cl2}}&\longrightarrow &{\ce {2Na+{}+\ 2Cl-}}&{\text{(species exchanged: 2 electrons)}}\end{array}}} == Rationalizing the strength of Lewis acid–base interactions == === HSAB theory === In 1963, Ralph Pearson proposed a qualitative concept known as the Hard and Soft Acids and Bases principle. later made quantitative with help of Robert Parr in 1984. 'Hard' applies to species that are small, have high charge states, and are weakly polarizable. 'Soft' applies to species that are large, have low charge states and are strongly polarizable. Acids and bases interact, and the most stable interactions are hard–hard and soft–soft. This theory has found use in organic and inorganic chemistry. === ECW model === The ECW model created by Russell S. Drago is a quantitative model that describes and predicts the strength of Lewis acid base interactions, −ΔH. The model assigned E and C parameters to many Lewis acids and bases. Each acid is characterized by an EA and a CA. Each base is likewise characterized by its own EB and CB. The E and C parameters refer, respectively, to the electrostatic and covalent contributions to the strength of the bonds that the acid and base will form. The equation is − Δ H = E A E B + C A C B + W {\displaystyle -\Delta H=E_{\rm {A}}E_{\rm {B}}+C_{\rm {A}}C_{\rm {B}}+W} The W term represents a constant energy contribution for acid–base reaction such as the cleavage of a dimeric acid or base. The equation predicts reversal of acids and base strengths. The graphical presentations of the
|
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equation show that there is no single order of Lewis base strengths or Lewis acid strengths. == Acid–base equilibrium == The reaction of a strong acid with a strong base is essentially a quantitative reaction. For example, HCl ( aq ) + Na ( OH ) ( aq ) ⟶ H 2 O + NaCl ( aq ) {\displaystyle {\ce {HCl_{(aq)}{}+ Na(OH)_{(aq)}-> H2O + NaCl_{(aq)}}}} In this reaction both the sodium and chloride ions are spectators as the neutralization reaction, H + OH − ⟶ H 2 O {\displaystyle {\ce {H + OH- -> H2O}}} does not involve them. With weak bases addition of acid is not quantitative because a solution of a weak base is a buffer solution. A solution of a weak acid is also a buffer solution. When a weak acid reacts with a weak base an equilibrium mixture is produced. For example, adenine, written as AH, can react with a hydrogen phosphate ion, HPO2−4. AH + HPO 4 2 − ↽ − − ⇀ A − + H 2 PO 4 − {\displaystyle {\ce {AH + HPO4^2- <=> A- + H2PO4-}}} The equilibrium constant for this reaction can be derived from the acid dissociation constants of adenine and of the dihydrogen phosphate ion. [ A − ] [ H + ] = K a 1 [ AH ] [ HPO 4 2 − ] [ H + ] = K a 2 [ H 2 PO 4 − ] {\displaystyle {\begin{aligned}\left[{\ce {A-}}\right]\!\left[{\ce {H+}}\right]&=K_{a1}{\bigl [}{\ce {AH}}{\bigr ]}\\[4pt]\left[{\ce {HPO4^2-}}\right]\!\left[{\ce {H+}}\right]&=K_{a2}\left[{\ce {H2PO4-}}\right]\end{aligned}}} The notation [X] signifies "concentration of X". When these two equations are combined by eliminating the hydrogen ion concentration, an expression for the equilibrium constant, K is obtained. [ A − ] [ H 2 PO 4 − ] = K [ AH ] [ HPO 4
|
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2 − ] ; K = K a 1 K a 2 {\displaystyle \left[{\ce {A-}}\right]\!\left[{\ce {H2PO4-}}\right]=K{\bigl [}{\ce {AH}}{\bigr ]}\!\left[{\ce {HPO4^2-}}\right];\quad K={\frac {K_{a1}}{K_{a2}}}} == Acid–alkali reaction == An acid–alkali reaction is a special case of an acid–base reaction, where the base used is also an alkali. When an acid reacts with an alkali salt (a metal hydroxide), the product is a metal salt and water. Acid–alkali reactions are also neutralization reactions. In general, acid–alkali reactions can be simplified to OH ( aq ) − + H ( aq ) + ⟶ H 2 O {\displaystyle {\ce {OH_{(aq)}- + H+_{(aq)}-> H2O}}} by omitting spectator ions. Acids are in general pure substances that contain hydrogen cations (H+) or cause them to be produced in solutions. Hydrochloric acid (HCl) and sulfuric acid (H2SO4) are common examples. In water, these break apart into ions: HCl ⟶ H ( aq ) + + Cl ( aq ) − H 2 SO 4 ⟶ H ( aq ) + + HSO 4 ( aq ) − {\displaystyle {\begin{aligned}{\ce {HCl}}&\longrightarrow {\ce {H_{(aq)}+ {}+ Cl_{(aq)}-}}\\[4pt]{\ce {H2SO4}}&\longrightarrow {\ce {H_{(aq)}+ {}+ HSO4_{\,(aq)}-}}\end{aligned}}} The alkali breaks apart in water, yielding dissolved hydroxide ions: NaOH ⟶ Na ( aq ) + + OH ( aq ) − {\displaystyle {\ce {NaOH -> Na^+_{(aq)}{}+ OH_{(aq)}-}}} . == See also == Acid–base titration Deprotonation Donor number Electron configuration Gutmann–Beckett method Lewis structure Nucleophilic substitution Neutralization (chemistry) Protonation Redox reactions Resonance (chemistry) == Notes == == References == === Sources === Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2015). Organic Chemistry (First ed.). Oxford University Press. Finston, H.L.; Rychtman, A.C. (1983). A New View of Current Acid–Base Theories. New York: John Wiley & Sons. Meyers, R. (2003). The Basics of Chemistry. Greenwood Press. Miessler, G.L.; Tarr, D.A. (1991). Inorganic Chemistry. == External links == Acid–base Physiology
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{
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– an on-line text John W. Kimball's online biology book section of acid and bases.
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Copper sulfate may refer to: Copper(II) sulfate, CuSO4, a common, greenish blue compound used as a fungicide and herbicide Copper(I) sulfate, Cu2SO4, an unstable white solid which is uncommonly used
|
{
"page_id": 592865,
"source": null,
"title": "Copper sulfate"
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Auger architectomics is a scientific imaging technique that allows biologists, working in the field of nano-technology, to slice open the cells of living organisms to view and assess their internal workings. Using argon gas etching to open the cells and a scanning electron microscope to create a three-dimensional view, researchers can harness this technique to track how cells function. This is most importantly used to assess how cells react to medication, for instance in the field of cancer research. It was first discovered in 2010 by Professor Lodewyk Kock and his team working in the biotechnology department at the University of the Free State in South Africa. The technique was adapted from Nano Scanning Auger Microscopy (NanoSAM), a technique used by physical scientists to study the surface structures of metal and inanimate materials such as semiconductors. Originally designed to observe yeast cells to find out more about how they manufactured the gas that causes bread to rise, the scientists discovered that the process could also be used in observing other living cells. In 2012 the technique was successfully applied to human cell tissue. == History == The project was initiated at the University of the Free State by the Kock group in 1982, with the major inputs and breakthroughs occurring between 2007 and 2012. The initial aim was to explore lipid biochemical routes, which would uncover unique lipids in yeasts, and to develop new taxonomies on the structures of these lipids. This unfolded into the development of the anti-mitochondrial antifungal assay (3A system), where yeast sensors are used to indicate anti-mitochondrial activity in compounds. These compounds, aimed at selectively switching off the mitochondria, therefore, might find application in combating various diseases such as fungal infections and cancer. Auger architectomics, which opens up individual cells to scan them, can be used
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{
"page_id": 39455714,
"source": null,
"title": "Auger architectomics"
}
|
to assess the effectiveness of such drugs by determining if a single cell can be "powered down" with targeted treatment. Based on the development of the anti-mitochondrial antifungal assay system, the University of the Free State scientists felt there was a need to analyse the system in more detail. As a result, they adapted Nano Scanning Auger Microscopy, a technique used to scan the properties of metals in physics, to apply it to cells. The result was a combination of auger atom electron physics, electron microscopy, and argon etching. The main challenge in applying the technology to biological material was to invent a sample preparation procedure that would ensure that the atom and 3D structure remained stable while argon nano-etching occurred. During the NanoSAM scanning electron microscope visualisation, an electron beam at 25 kV is used instead of the normal 5 kV beam. Sample fixation and dehydration methods had to be developed and optimised to fit NanoSAM without creating sample distortions. Dehydration regimes based on alcohol extraction procedures were installed and optimised, while fixation using various fixatives was included. Electron conductivity of samples throughout Argon etching was assured by optimised gold sputtering. == Procedure == Firstly, the biological sample is plated with gold to stabilise the outer structure and make it electron conductive. It is then scanned in SEM mode and the surface visually enlarged. Auger atom electron physics are applied and selected areas on the sample surface are beamed with electrons. The incident beam ejects an electron in the inner orbital of the atom, leaving an open space. This is filled by an electron from an outer orbital by relaxation. Energy is released, causing the ejection of an electron from the outer orbital. This electron is called the Auger electron. The amount of energy that is released is measured
|
{
"page_id": 39455714,
"source": null,
"title": "Auger architectomics"
}
|
by auger electron spectroscopy (AES) and used to identify the atom and its intensity. Similarly, the surface area can be screened by an electron beam eventually yielding auger electrons that are mapped, showing the distribution of atoms in different colours covering a surface area of predetermined size. The previously-screened surface of the sample is etched with argon, exposing a new surface of the sample that is then again analysed. In this way, a 3-dimensional image and element composition architecture of the whole cell is visualised. == Discoveries == This process in nanotechnology led to the discovery of gas bubbles inside yeasts. This is considered a paradigm shift, since naked gas bubbles are not expected inside any type of cell due to structured water in the cytoplasm. This was exposed in a fluconazole-treated bubble-like sensor of the yeast Nadsonia. This is the only technology known at present that can accomplish this type of nano-analysis on biological material. == Use in medicine == Nanotechnology developments in medicine allow microdoses of drugs and therapies to be delivered directly to infected cells, instead of killing large groups of cells, often at the expense of healthy cells. Gold at a nano-level has the ability to bind to certain types of biological material, which means that certain types of cells can be targeted. The technique of auger architectomics may be used to map the success or otherwise of targeted drug delivery by analysing cells. The team at the University of the Free State is working with the Mayo Clinic to use the technology as a part of their cancer research. == References ==
|
{
"page_id": 39455714,
"source": null,
"title": "Auger architectomics"
}
|
The molecular formula C10H14N2 (molar mass: 162.23 g/mol, exact mass: 162.1157 u) may refer to: Anabasine Nicotine Phenylpiperazine Rivanicline
|
{
"page_id": 23661539,
"source": null,
"title": "C10H14N2"
}
|
In forest ecology, a snag refers to a standing dead or dying tree, often missing a top or most of the smaller branches. In freshwater ecology it refers to trees, branches, and other pieces of naturally occurring wood found sunken in rivers and streams; it is also known as coarse woody debris. Snags provide habitat for a wide variety of wildlife but pose hazards to river navigation. When used in manufacturing, especially in Scandinavia, they are often called dead wood and in Finland, kelo wood. == Forest snags == Snags are an important structural component in forest communities, making up 10–20% of all trees present in old-growth tropical, temperate, and boreal forests. Snags and downed coarse woody debris represent a large portion of the woody biomass in a healthy forest. In temperate forests, snags provide critical habitat for more than 100 species of bird and mammal, and snags are often called 'wildlife trees' by foresters. Dead, decaying wood supports a rich community of decomposers like bacteria and fungi, insects, and other invertebrates. These organisms and their consumers, along with the structural complexity of cavities, hollows, and broken tops make snags important habitat for birds, bats, and small mammals, which in turn feed larger mammalian predators. Snags are optimal habitat for primary cavity nesters such as woodpeckers which create the majority of cavities used by secondary cavity users in forest ecosystems. Woodpeckers excavate cavities for more than 80 other species and the health of their populations relies on snags. Most snag-dependent birds and mammals are insectivorous and represent a major portion of the insectivorous forest fauna, and are important factors in controlling forest insect populations. There are many instances in which birds reduced outbreak populations of forest insects, such as woodpeckers affecting outbreaks of southern hardwood borers and Engelmann spruce beetles.
|
{
"page_id": 2165732,
"source": null,
"title": "Snag (ecology)"
}
|
Snag creation occurs naturally as trees die due to old age, disease, drought, or wildfire. A snag undergoes a series of changes from the time the tree dies until final collapse, and each stage in the decay process has particular value to certain wildlife species. Snag persistence depends on two factors, the size of the stem, and the durability of the wood of the species concerned. The snags of some large conifers, such as Giant Sequoia and Coast Redwood on the Pacific Coast of North America, and the Alerce of Patagonia, can remain intact for 100 years or more, becoming progressively shorter with age, while other snags with rapidly decaying wood, such as aspen and birch, break up and collapse in 2–10 years. Snag forests, or complex early seral forests, are ecosystems that occupy potentially forested sites after a stand-replacement disturbance and before re-establishment of a closed-forest canopy. They are generated by natural disturbances such as wildfire or insect outbreaks that reset ecological succession processes and follow a pathway that is influenced by biological legacies (e.g., large live trees and snags downed logs, seed banks, resprout tissue, fungi, and other live and dead biomass) that were not removed during the initial disturbance. Water hunting birds like the osprey or kingfishers can be found near water, perched in a snag tree, or feeding upon their fish catch. == Freshwater snags == In freshwater ecology in Australia and the United States, the term snag is used to refer to the trees, branches and other pieces of naturally occurring wood found in a sunken form in rivers and streams. Such snags have been identified as being critical for shelter and as spawning sites for fish, and are one of the few hard substrates available for biofilm growth supporting aquatic invertebrates in lowland rivers
|
{
"page_id": 2165732,
"source": null,
"title": "Snag (ecology)"
}
|
flowing through alluvial flood plains. Snags are important as sites for biofilm growth and for shelter and feeding of aquatic invertebrates in both lowland and upland rivers and streams. In Australia, the role of freshwater snags has been largely ignored until recently, and more than one million snags have been removed from the Murray-Darling basin. Large tracts of the lowland reaches of the Murray-Darling system are now devoid of the snags that native fish like Murray cod require for shelter and breeding. The damage such wholesale snag removal has caused is enormous but difficult to quantify, however some quantification attempts have been made. Most snags in these systems are river red gum snags. As the dense wood of river red gum is almost impervious to rot it is thought that some of the river red gum snags removed in past decades may have been several thousand years old. == Maritime hazard == Also known as deadheads, partially submerged snags posed hazards to early riverboat navigation and commerce. If hit, snags punctured the wooden hulls used in the 19th century and early 20th century. Snags were, in fact, the most commonly encountered hazard, especially in the early years of steamboat travel. As described by a British traveller on the Mississippi in 1858, "We see plenty of snags, which are trees that have floated down; their roots in the water then catch fast in the mud; the stream breaks off the branches, and the sharp end of the tree sticks up, just at the right angles for catching any up-river boat, and often runs right through them, making a large leak, and sinking the unfortunate steamer." In the United States, the U.S. Army Corps of Engineers operated "snagboats" such as the W. T. Preston in the Puget Sound of Washington State and
|
{
"page_id": 2165732,
"source": null,
"title": "Snag (ecology)"
}
|
the Montgomery in the rivers of Alabama to pull out and clear snags. Starting in 1824, there were successful efforts to remove snags from the Mississippi and its tributaries. By 1835, a lieutenant reported to the Chief of Engineers that steamboat travel had become much safer, but by the mid-1840s the appropriations for snag removal dried up and snags re-accumulated until after the Civil War. == Dead wood products == In Scandinavia and Finland, snags, invariably pine trees, known in Finnish as kelo and in Swedish as torraka, are collected for the production of different objects, from furniture to entire log houses. Commercial enterprises market them abroad as "dead wood" or in Finland as "kelo wood". They have been especially prized for their silver-grey weathered surface in the manufacture of vernacular or national romantic products. The suppliers of "dead wood" emphasise its age: the wood has developed with dehydration in the dry coldness of the subarctic zones, the tree having stopped growing after some 300–400 years, and the tree has remained upright for another few hundred years. "Dead wood" logs are easier to transport and handle than normal logs due to their lightness. == See also == Coarse woody debris Complex early seral forest Large woody debris Stream restoration Tree hollow == References == == External links == Media related to Snag at Wikimedia Commons
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{
"page_id": 2165732,
"source": null,
"title": "Snag (ecology)"
}
|
Hybrid speciation is a form of speciation where hybridization between two different species leads to a new species, reproductively isolated from the parent species. Previously, reproductive isolation between two species and their parents was thought to be particularly difficult to achieve, and thus hybrid species were thought to be very rare. With DNA analysis becoming more accessible in the 1990s, hybrid speciation has been shown to be a somewhat common phenomenon, particularly in plants. In botanical nomenclature, a hybrid species is also called a nothospecies. Hybrid species are by their nature polyphyletic. == Ecology == A hybrid may occasionally be better fitted to the local environment than the parental lineage, and as such, natural selection may favor these individuals. If reproductive isolation is subsequently achieved, a separate species may arise. Reproductive isolation may be genetic, ecological, behavioral, spatial, or a combination of these. If reproductive isolation fails to establish, the hybrid population may merge with either or both parent species. This will lead to an influx of foreign genes into the parent population, a situation called an introgression. Introgression is a source of genetic variation, and can in itself facilitate speciation. There is evidence that introgression is a ubiquitous phenomenon in plants and animals, even in humans, where genetic material from Neanderthals and Denisovans is responsible for much of the immune genes in non-African populations. === Ecological constraints === For a hybrid form to persist, it must be able to exploit the available resources better than either parent species, which, in most cases, it will have to compete with. For example: while grizzly bears and polar bears may be able to mate and produce offspring, a grizzly–polar bear hybrid is apparently less- suited in either of the parents' ecological niches than the original parent species themselves. So: although the hybrid
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{
"page_id": 7474152,
"source": null,
"title": "Hybrid speciation"
}
|
is fertile (i.e. capable of reproduction and thus theoretically could propagate), this poor adaptation would be unlikely to support the establishment of a permanent population. Likewise, lions and tigers have historically overlapped in a portion of their range and can theoretically produce wild hybrids: ligers, which are a cross between a male lion and female tiger, and tigons, which are a cross between a male tiger and a female lion; however, tigers and lions have thus far only hybridized in captivity. In both ligers and tigons, the females are fertile and the males are sterile. One of these hybrids (the tigon) carries growth-inhibitor genes from both parents and thus is smaller than either parent species and might in the wild come into competition with smaller carnivores, e.g. the leopard. The other hybrid, the liger, ends up larger than either of its parents: about a thousand pounds (450 kilograms) fully grown. No tiger-lion hybrids are known from the wild, and the ranges of the two species no longer overlap (tigers are not found in Africa, and while there was formerly overlap in the distribution of the two species in Asia, both have been extirpated from much of their respective historic ranges, and the Asiatic lion is now restricted to the Gir Forest National Park, where tigers are mostly absent). Some situations may favor hybrid population. One example is rapid turnover of available environment types, like the historical fluctuation of water level in Lake Malawi, a situation that generally favors speciation. A similar situation can be found where closely related species occupy a chain of islands. This will allow any present hybrid population to move into new, unoccupied habitats, avoiding direct competition with parent species and giving a hybrid population time and space to establish. Genetics, too, can occasionally favor hybrids. In
|
{
"page_id": 7474152,
"source": null,
"title": "Hybrid speciation"
}
|
the Amboseli National Park in Kenya, yellow baboons and anubis baboons regularly interbreed. The hybrid males reach maturity earlier than their pure-bred cousins, setting up a situation where the hybrid population may over time replace one or both of the parent species in the area. == Genetics of hybridization == Genetics are more variable and malleable in plants than in animals, probably reflecting the higher activity level in animals. Hybrids' genetics will necessarily be less stable than those of species evolving through isolation, which explains why hybrid species appear more common in plants than in animals. Many agricultural crops are hybrids with double or even triple chromosome sets. Having multiple sets of chromosomes is called polyploidy. Polyploidy is usually fatal in animals where extra chromosome sets upset fetal development, but is often found in plants. A form of hybrid speciation that is relatively common in plants occurs when an infertile hybrid becomes fertile after doubling of the chromosome number. Hybridization without change in chromosome number is called homoploid hybrid speciation. This is the situation found in most animal hybrids. For a hybrid to be viable, the chromosomes of the two organisms will have to be very similar, i.e., the parent species must be closely related, or else the difference in chromosome arrangement will make mitosis problematic. With polyploid hybridization, this constraint is less acute. Super-numerary chromosome numbers can be unstable, which can lead to instability in the genetics of the hybrid. The European edible frog appears to be a species, but is actually a triploid semi-permanent hybrid between pool frogs and marsh frogs. In most populations, the edible frog population is dependent on the presence of at least one of the parent species to be maintained, as each individual need two gene sets from one parent species and one from
|
{
"page_id": 7474152,
"source": null,
"title": "Hybrid speciation"
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the other. Also, the male sex determination gene in the hybrids is only found in the genome of the pool frog, further undermining stability. Such instability can also lead to rapid reduction of chromosome numbers, creating reproductive barriers and thus allowing speciation. == Hybrid speciation in animals == === Homoploid hybrid speciation === Hybrid speciation in animals is primarily homoploid. While thought not to be very common, a few animal species are the result of hybridization, mostly insects such as tephritid fruitflies that inhabit Lonicera plants and Heliconius butterflies, as well as some fish, one marine mammal, the clymene dolphin, a few birds. and certain Bufotes toads. One bird is an unnamed form of Darwin's finch from the Galapagos island of Daphne Major, described in 2017 and likely founded in the early 1980s by a male Española cactus finch from Española Island and a female medium ground finch from Daphne Major. Another is the great skua, which has a surprising genetic similarity to the physically very different pomarine skua; most ornithologists now assume it to be a hybrid between the pomarine skua and one of the southern skuas. The golden-crowned manakin was formed 180,000 years ago by hybridization between snow-capped and opal-crowned manakins. A 2021 DNA study determined that the Columbian mammoth of North America was a hybrid species between woolly mammoths and another lineage, discovered in Krestovka, descended from steppe mammoths. The two populations had diverged from the ancestral steppe mammoth earlier in the Pleistocene. Analysis of genetic material recovered from their remains showed that half of the ancestry of the Columbian mammoths originated from the Krestovka lineage and the other half from woolly mammoths, with the hybridization happening more than 420,000 years ago, during the Middle Pleistocene. This is the first evidence of hybrid speciation obtained from prehistoric
|
{
"page_id": 7474152,
"source": null,
"title": "Hybrid speciation"
}
|
DNA. === Multiple hybrids during rapid divergence === Rapidly diverging species can sometimes form multiple hybrid species, giving rise to a species complex, like several physically divergent but closely related genera of cichlid fishes in Lake Malawi. The duck genus Anas (mallards and teals) has a very recent divergence history, many of the species are inter-fertile, and quite a few of them are thought to be hybrids. While hybrid species generally appear rare in mammals, the American red wolf appears to be a hybrid species of the Canis species complex, between gray wolf and coyote. Hybridization may have led to the species-rich Heliconius butterflies, though this conclusion has been criticized. == Hybrid speciation in plants == Hybrid speciation occurs when two divergent lineages (e.g., species) with independent evolutionary histories come into contact and interbreed. Hybridization can result in speciation when hybrid populations become isolated from the parental lineages, leading to divergence from the parent populations. === Polyploid hybrid speciation === In cases where the first-generation hybrids are viable but infertile, fertility can be restored by whole genome duplication (polyploidy), resulting in reproductive isolation and polyploid speciation. Polyploid speciation is commonly observed in plants because their nature allows them to support genome duplications. Polyploids are considered a new species because the occurrence of a whole genome duplication imposes post-zygotic barriers, which enable reproductive isolation between parent populations and hybrid offspring. Polyploids can arise through single step mutations or through triploid bridges. In single step mutations, allopolyploids are the result of unreduced gametes in crosses between divergent lineages. The F1 hybrids produced from these mutations are infertile due to failure of bivalent pairing of chromosomes and segregation into gametes which leads to the production of unreduced gametes by single division meiosis, which results in unreduced, diploid (2N) gametes. Triploid bridges occur in
|
{
"page_id": 7474152,
"source": null,
"title": "Hybrid speciation"
}
|
low frequencies in populations and are produced when unreduced gametes combine with haploid (1N) gametes to produce a triploid offspring that can function as a bridge to the formation of tetraploids. In both paths, the polyploid hybrids are reproductively isolated from the parents due to the difference in ploidy. Polyploids manage to remain in populations because they generally experience less inbreeding depression and have higher self-fertility. === Homoploid hybrid speciation === Homoploid (diploid) speciation is another result of hybridization, but the hybrids remain diploid. It is less common in plants than polyploid speciation because, without genome duplication, genetic isolation must develop through other mechanisms. Studies on diploid hybrid populations of Louisiana irises show how these populations occur in Hybrid zones created by disturbances and ecotones (Anderson 1949). Novel niches can allow for the persistence of hybrid lineages. For example, established sunflower (Helianthus) hybrid species show transgressive phenotypes and display genomic divergence separating them from the parent species. == See also == Clymene dolphin Eastern coyote Coywolf Genetic pollution Hybrid name New Mexico whiptail Secondary contact Ring species Chimera (genetics) == References ==
|
{
"page_id": 7474152,
"source": null,
"title": "Hybrid speciation"
}
|
Pteropsida is a subdivision of vascular plants that is no longer in use. It included all flowering plants and ferns and was divided into Filicinae, Gymnospermae, and Angiospermae. == References ==
|
{
"page_id": 1772523,
"source": null,
"title": "Pteropsida"
}
|
Quantum contextuality is a feature of the phenomenology of quantum mechanics whereby measurements of quantum observables cannot simply be thought of as revealing pre-existing values. Any attempt to do so in a realistic hidden-variable theory leads to values that are dependent upon the choice of the other (compatible) observables which are simultaneously measured (the measurement context). More formally, the measurement result (assumed pre-existing) of a quantum observable is dependent upon which other commuting observables are within the same measurement set. Contextuality was first demonstrated to be a feature of quantum phenomenology by the Bell–Kochen–Specker theorem. The study of contextuality has developed into a major topic of interest in quantum foundations as the phenomenon crystallises certain non-classical and counter-intuitive aspects of quantum theory. A number of powerful mathematical frameworks have been developed to study and better understand contextuality, from the perspective of sheaf theory, graph theory, hypergraphs, algebraic topology, and probabilistic couplings. Nonlocality, in the sense of Bell's theorem, may be viewed as a special case of the more general phenomenon of contextuality, in which measurement contexts contain measurements that are distributed over spacelike separated regions. This follows from Fine's theorem. Quantum contextuality has been identified as a source of quantum computational speedups and quantum advantage in quantum computing. Contemporary research has increasingly focused on exploring its utility as a computational resource. == Kochen and Specker == The need for contextuality was discussed informally in 1935 by Grete Hermann, but it was more than 30 years later when Simon B. Kochen and Ernst Specker, and separately John Bell, constructed proofs that any realistic hidden-variable theory able to explain the phenomenology of quantum mechanics is contextual for systems of Hilbert space dimension three and greater. The Kochen–Specker theorem proves that realistic noncontextual hidden-variable theories cannot reproduce the empirical predictions of quantum mechanics.
|
{
"page_id": 38407148,
"source": null,
"title": "Quantum contextuality"
}
|
Such a theory would suppose the following. All quantum-mechanical observables may be simultaneously assigned definite values (this is the realism postulate, which is false in standard quantum mechanics, since there are observables that are indefinite in every given quantum state). These global value assignments may deterministically depend on some "hidden" classical variable, which in turn may vary stochastically for some classical reason (as in statistical mechanics). The measured assignments of observables may therefore finally stochastically change. This stochasticity is, however, epistemic and not ontic, as in the standard formulation of quantum mechanics. Value assignments pre-exist and are independent of the choice of any other observables, which, in standard quantum mechanics, are described as commuting with the measured observable, and they are also measured. Some functional constraints on the assignments of values for compatible observables are assumed (e.g., they are additive and multiplicative, there are, however, several versions of this functional requirement). In addition, Kochen and Specker constructed an explicitly noncontextual hidden-variable model for the two-dimensional qubit case in their paper on the subject, thereby completing the characterisation of the dimensionality of quantum systems that can demonstrate contextual behaviour. Bell's proof invoked a weaker version of Gleason's theorem, reinterpreting the theorem to show that quantum contextuality exists only in Hilbert space dimension greater than two. == Frameworks for contextuality == === Sheaf-theoretic framework === The sheaf-theoretic, or Abramsky–Brandenburger, approach to contextuality initiated by Samson Abramsky and Adam Brandenburger is theory-independent and can be applied beyond quantum theory to any situation in which empirical data arises in contexts. As well as being used to study forms of contextuality arising in quantum theory and other physical theories, it has also been used to study formally equivalent phenomena in logic, relational databases, natural language processing, and constraint satisfaction. In essence, contextuality arises when empirical
|
{
"page_id": 38407148,
"source": null,
"title": "Quantum contextuality"
}
|
data is locally consistent but globally inconsistent. This framework gives rise in a natural way to a qualitative hierarchy of contextuality: (Probabilistic) contextuality may be witnessed in measurement statistics, e.g. by the violation of an inequality. A representative example is the KCBS proof of contextuality. Logical contextuality may be witnessed in the "possibilistic" information about which outcome events are possible and which are not possible. A representative example is Hardy's nonlocality proof of nonlocality. Strong contextuality is a maximal form of contextuality. Whereas (probabilistic) contextuality arises when measurement statistics cannot be reproduced by a mixture of global value assignments, strong contextuality arises when no global value assignment is even compatible with the possible outcome events. A representative example is the original Kochen–Specker proof of contextuality. Each level in this hierarchy strictly includes the next. An important intermediate level that lies strictly between the logical and strong contextuality classes is all-versus-nothing contextuality, a representative example of which is the Greenberger–Horne–Zeilinger proof of nonlocality. === Graph and hypergraph frameworks === Adán Cabello, Simone Severini, and Andreas Winter introduced a general graph-theoretic framework for studying contextuality of different physical theories. Within this framework experimental scenarios are described by graphs, and certain invariants of these graphs were shown have particular physical significance. One way in which contextuality may be witnessed in measurement statistics is through the violation of noncontextuality inequalities (also known as generalized Bell inequalities). With respect to certain appropriately normalised inequalities, the independence number, Lovász number, and fractional packing number of the graph of an experimental scenario provide tight upper bounds on the degree to which classical theories, quantum theory, and generalised probabilistic theories, respectively, may exhibit contextuality in an experiment of that kind. A more refined framework based on hypergraphs rather than graphs is also used. === Contextuality-by-default (CbD) framework ===
|
{
"page_id": 38407148,
"source": null,
"title": "Quantum contextuality"
}
|
In the CbD approach, developed by Ehtibar Dzhafarov, Janne Kujala, and colleagues, (non)contextuality is treated as a property of any system of random variables, defined as a set R = { R q c : q ∈ Q , q ≺ c , c ∈ C } {\displaystyle {\mathcal {R}}=\{R_{q}^{c}:q\in Q,q\prec c,c\in C\}} in which each random variable R q c {\displaystyle R_{q}^{c}} is labeled by its content q {\displaystyle q} – the property it measures, and its context c {\displaystyle c} – the set of recorded circumstances under which it is recorded (including but not limited to which other random variables it is recorded together with); q ≺ c {\displaystyle q\prec c} stands for " q {\displaystyle q} is measured in c {\displaystyle c} ". The variables within a context are jointly distributed, but variables from different contexts are stochastically unrelated, defined on different sample spaces. A (probabilistic) coupling of the system R {\displaystyle {\mathcal {R}}} is defined as a system S {\displaystyle S} in which all variables are jointly distributed and, in any context c {\displaystyle c} , R c = { R q c : q ∈ Q , q ≺ c } {\displaystyle R^{c}=\{R_{q}^{c}:q\in Q,q\prec c\}} and S c = { S q c : q ∈ Q , q ≺ c } {\displaystyle S^{c}=\{S_{q}^{c}:q\in Q,q\prec c\}} are identically distributed. The system is considered noncontextual if it has a coupling S {\displaystyle S} such that the probabilities Pr [ S q c = S q c ′ ] {\displaystyle \Pr[S_{q}^{c}=S_{q}^{c'}]} are maximal possible for all contexts c , c ′ {\displaystyle c,c'} and contents q {\displaystyle q} such that q ≺ c , c ′ {\displaystyle q\prec c,c'} . If such a coupling does not exist, the system is contextual. For the important class of cyclic
|
{
"page_id": 38407148,
"source": null,
"title": "Quantum contextuality"
}
|
systems of dichotomous ( ± 1 {\displaystyle \pm 1} ) random variables, C n = { ( R 1 1 , R 2 1 ) , ( R 2 2 , R 3 2 ) , … , ( R n n , R 1 n ) } {\displaystyle {\mathcal {C}}_{n}={\big \{}(R_{1}^{1},R_{2}^{1}),(R_{2}^{2},R_{3}^{2}),\ldots ,(R_{n}^{n},R_{1}^{n}){\big \}}} ( n ≥ 2 {\displaystyle n\geq 2} ), it has been shown that such a system is noncontextual if and only if D ( C n ) ≤ Δ ( C n ) , {\displaystyle D({\mathcal {C}}_{n})\leq \Delta ({\mathcal {C}}_{n}),} where Δ ( C n ) = ( n − 2 ) + | R 1 1 − R 1 n | + | R 2 1 − R 2 2 | + … + | R n n − 1 − R n n | , {\displaystyle \Delta ({\mathcal {C}}_{n})=(n-2)+|R_{1}^{1}-R_{1}^{n}|+|R_{2}^{1}-R_{2}^{2}|+\ldots +|R_{n}^{n-1}-R_{n}^{n}|,} and D ( C n ) = max ( λ 1 ⟨ R 1 1 R 2 1 ⟩ + λ 2 ⟨ R 2 2 R 3 2 ⟩ + … + λ n ⟨ R n n R 1 n ⟩ ) , {\displaystyle D({\mathcal {C}}_{n})=\max {\big (}\lambda _{1}\langle R_{1}^{1}R_{2}^{1}\rangle +\lambda _{2}\langle R_{2}^{2}R_{3}^{2}\rangle +\ldots +\lambda _{n}\langle R_{n}^{n}R_{1}^{n}\rangle {\big )},} with the maximum taken over all λ i = ± 1 {\displaystyle \lambda _{i}=\pm 1} whose product is − 1 {\displaystyle -1} . If R q c {\displaystyle R_{q}^{c}} and R q c ′ {\displaystyle R_{q}^{c'}} , measuring the same content in different context, are always identically distributed, the system is called consistently connected (satisfying "no-disturbance" or "no-signaling" principle). Except for certain logical issues, in this case CbD specializes to traditional treatments of contextuality in quantum physics. In particular, for consistently connected cyclic systems the noncontextuality criterion above reduces to D ( C
|
{
"page_id": 38407148,
"source": null,
"title": "Quantum contextuality"
}
|
n ) ≤ n − 2 , {\displaystyle D({\mathcal {C}}_{n})\leq n-2,} which includes the Bell/CHSH inequality ( n = 4 {\displaystyle n=4} ), KCBS inequality ( n = 5 {\displaystyle n=5} ), and other famous inequalities. That nonlocality is a special case of contextuality follows in CbD from the fact that being jointly distributed for random variables is equivalent to being measurable functions of one and the same random variable (this generalizes Arthur Fine's analysis of Bell's theorem). CbD essentially coincides with the probabilistic part of Abramsky's sheaf-theoretic approach if the system is strongly consistently connected, which means that the joint distributions of { R q 1 c , … , R q k c } {\displaystyle \{R_{q_{1}}^{c},\ldots ,R_{q_{k}}^{c}\}} and { R q 1 c ′ , … , R q k c ′ } {\displaystyle \{R_{q_{1}}^{c'},\ldots ,R_{q_{k}}^{c'}\}} coincide whenever q 1 , … , q k {\displaystyle q_{1},\ldots ,q_{k}} are measured in contexts c , c ′ {\displaystyle c,c'} . However, unlike most approaches to contextuality, CbD allows for inconsistent connectedness, with R q c {\displaystyle R_{q}^{c}} and R q c ′ {\displaystyle R_{q}^{c'}} differently distributed. This makes CbD applicable to physics experiments in which no-disturbance condition is violated, as well as to human behavior where this condition is violated as a rule. In particular, Vctor Cervantes, Ehtibar Dzhafarov, and colleagues have demonstrated that random variables describing certain paradigms of simple decision making form contextual systems, whereas many other decision-making systems are noncontextual once their inconsistent connectedness is properly taken into account. === Operational framework === An extended notion of contextuality due to Robert Spekkens applies to preparations and transformations as well as to measurements, within a general framework of operational physical theories. With respect to measurements, it removes the assumption of determinism of value assignments that is present
|
{
"page_id": 38407148,
"source": null,
"title": "Quantum contextuality"
}
|
in standard definitions of contextuality. This breaks the interpretation of nonlocality as a special case of contextuality, and does not treat irreducible randomness as nonclassical. Nevertheless, it recovers the usual notion of contextuality when outcome determinism is imposed. Spekkens' contextuality can be motivated using Leibniz's law of the identity of indiscernibles. The law applied to physical systems in this framework mirrors the entended definition of noncontextuality. This was further explored by Simmons et al, who demonstrated that other notions of contextuality could also be motivated by Leibnizian principles, and could be thought of as tools enabling ontological conclusions from operational statistics. === Extracontextuality and extravalence === Given a pure quantum state | ψ ⟩ {\displaystyle |\psi \rangle } , Born's rule tells that the probability to obtain another state | ϕ ⟩ {\displaystyle |\phi \rangle } in a measurement is | ⟨ ϕ | ψ ⟩ | 2 {\displaystyle |\langle \phi |\psi \rangle |^{2}} . However, such a number does not define a full probability distribution, i.e. values over a set of mutually exclusive events, summing up to 1. In order to obtain such a set one needs to specify a context, that is a complete set of commuting operators (CSCO), or equivalently a set of N orthogonal projectors | ϕ n ⟩ ⟨ ϕ n | {\displaystyle |\phi _{n}\rangle \langle \phi _{n}|} that sum to identity, where N {\displaystyle N} is the dimension of the Hilbert space. Then one has ∑ n | ⟨ ϕ n | ψ ⟩ | 2 = 1 {\displaystyle \sum _{n}|\langle \phi _{n}|\psi \rangle |^{2}=1} as expected. In that sense, one can tell that a state vector | ψ ⟩ {\displaystyle |\psi \rangle } alone is predictively incomplete, as long a context has not been specified. The actual physical state, now defined by |
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"page_id": 38407148,
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ϕ n ⟩ {\displaystyle |\phi _{n}\rangle } within a specified context, has been called a modality by Auffèves and Grangier Since it is clear that | ψ ⟩ {\displaystyle |\psi \rangle } alone does not define a modality, what is its status ? If N ≥ 3 {\displaystyle N\geq 3} , one sees easily that | ψ ⟩ {\displaystyle |\psi \rangle } is associated with an equivalence class of modalities, belonging to different contexts, but connected between themselves with certainty, even if the different CSCO observables do not commute. This equivalence class is called an extravalence class, and the associated transfer of certainty between contexts is called extracontextuality. As a simple example, the usual singlet state for two spins 1/2 can be found in the (non commuting) CSCOs associated with the measurement of the total spin (with S = 0 , m = 0 {\displaystyle S=0,\;m=0} ), or with a Bell measurement, and actually it appears in infinitely many different CSCOs - but obviously not in all possible ones. The concepts of extravalence and extracontextuality are very useful to spell out the role of contextuality in quantum mechanics, that is not non-contextual (like classical physical would be), but not either fully contextual, since modalities belonging to incompatible (non-commuting) contexts may be connected with certainty. Starting now from extracontextuality as a postulate, the fact that certainty can be transferred between contexts, and is then associated with a given projector, is the very basis of the hypotheses of Gleason's theorem, and thus of Born's rule. Also, associating a state vector with an extravalence class clarifies its status as a mathematical tool to calculate probabilities connecting modalities, which correspond to the actual observed physical events or results. This point of view is quite useful, and it can be used everywhere in quantum mechanics.
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"page_id": 38407148,
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=== Other frameworks and extensions === A form of contextuality that may present in the dynamics of a quantum system was introduced by Shane Mansfield and Elham Kashefi, and has been shown to relate to computational quantum advantages. As a notion of contextuality that applies to transformations it is inequivalent to that of Spekkens. Examples explored to date rely on additional memory constraints which have a more computational than foundational motivation. Contextuality may be traded-off against Landauer erasure to obtain equivalent advantages. == Fine's theorem == The Kochen–Specker theorem proves that quantum mechanics is incompatible with realistic noncontextual hidden variable models. On the other hand Bell's theorem proves that quantum mechanics is incompatible with factorisable hidden variable models in an experiment in which measurements are performed at distinct spacelike separated locations. Arthur Fine showed that in the experimental scenario in which the famous CHSH inequalities and proof of nonlocality apply, a factorisable hidden variable model exists if and only if a noncontextual hidden variable model exists. This equivalence was proven to hold more generally in any experimental scenario by Samson Abramsky and Adam Brandenburger. It is for this reason that we may consider nonlocality to be a special case of contextuality. == Measures of contextuality == === Contextual fraction === A number of methods exist for quantifying contextuality. One approach is by measuring the degree to which some particular noncontextuality inequality is violated, e.g. the KCBS inequality, the Yu–Oh inequality, or some Bell inequality. A more general measure of contextuality is the contextual fraction. Given a set of measurement statistics e, consisting of a probability distribution over joint outcomes for each measurement context, we may consider factoring e into a noncontextual part eNC and some remainder e', e = λ e N C + ( 1 − λ ) e
|
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"page_id": 38407148,
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′ . {\displaystyle e=\lambda e^{NC}+(1-\lambda )e'\,.} The maximum value of λ over all such decompositions is the noncontextual fraction of e denoted NCF(e), while the remainder CF(e)=(1-NCF(e)) is the contextual fraction of e. The idea is that we look for a noncontextual explanation for the highest possible fraction of the data, and what is left over is the irreducibly contextual part. Indeed, for any such decomposition that maximises λ the leftover e' is known to be strongly contextual. This measure of contextuality takes values in the interval [0,1], where 0 corresponds to noncontextuality and 1 corresponds to strong contextuality. The contextual fraction may be computed using linear programming. It has also been proved that CF(e) is an upper bound on the extent to which e violates any normalised noncontextuality inequality. Here normalisation means that violations are expressed as fractions of the algebraic maximum violation of the inequality. Moreover, the dual linear program to that which maximises λ computes a noncontextual inequality for which this violation is attained. In this sense the contextual fraction is a more neutral measure of contextuality, since it optimises over all possible noncontextual inequalities rather than checking the statistics against one inequality in particular. === Measures of (non)contextuality within the Contextuality-by-Default (CbD) framework === Several measures of the degree of contextuality in contextual systems were proposed within the CbD framework, but only one of them, denoted CNT2, has been shown to naturally extend into a measure of noncontextuality in noncontextual systems, NCNT2. This is important, because at least in the non-physical applications of CbD contextuality and noncontextuality are of equal interest. Both CNT2 and NCNT2 are defined as the L 1 {\displaystyle L_{1}} -distance between a probability vector p {\displaystyle \mathbf {p} } representing a system and the surface of the noncontextuality polytope P {\displaystyle \mathbb
|
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"page_id": 38407148,
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{P} } representing all possible noncontextual systems with the same single-variable marginals. For cyclic systems of dichotomous random variables, it is shown that if the system is contextual (i.e., D ( C n ) > Δ ( C n ) {\displaystyle D\left({\mathcal {C}}_{n}\right)>\Delta \left({\mathcal {C}}_{n}\right)} ), C N T 2 = D ( C n ) − Δ ( C n ) , {\displaystyle \mathrm {CNT} _{2}=D\left({\mathcal {C}}_{n}\right)-\Delta \left({\mathcal {C}}_{n}\right),} and if it is noncontextual ( D ( C n ) ≤ Δ ( C n ) {\displaystyle D\left({\mathcal {C}}_{n}\right)\leq \Delta \left({\mathcal {C}}_{n}\right)} ), N C N T 2 = min ( Δ ( C n ) − D ( C n ) , m ( C n ) ) , {\displaystyle \mathrm {NCNT} _{2}=\min \left(\Delta \left({\mathcal {C}}_{n}\right)-D\left({\mathcal {C}}_{n}\right),m\left({\mathcal {C}}_{n}\right)\right),} where m ( C n ) {\displaystyle m\left({\mathcal {C}}_{n}\right)} is the L 1 {\displaystyle L_{1}} -distance from the vector p ∈ P {\displaystyle \mathbf {p} \in \mathbb {P} } to the surface of the box circumscribing the noncontextuality polytope. More generally, NCNT2 and CNT2 are computed by means of linear programming. The same is true for other CbD-based measures of contextuality. One of them, denoted CNT3, uses the notion of a quasi-coupling, that differs from a coupling in that the probabilities in the joint distribution of its values are replaced with arbitrary reals (allowed to be negative but summing to 1). The class of quasi-couplings S {\displaystyle S} maximizing the probabilities Pr [ S q c = S q c ′ ] {\displaystyle \Pr \left[S_{q}^{c}=S_{q}^{c'}\right]} is always nonempty, and the minimal total variation of the signed measure in this class is a natural measure of contextuality. == Contextuality as a resource for quantum computing == Recently, quantum contextuality has been investigated as a source of quantum advantage and computational speedups
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"page_id": 38407148,
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in quantum computing. === Magic state distillation === Magic state distillation is a scheme for quantum computing in which quantum circuits constructed only of Clifford operators, which by themselves are fault-tolerant but efficiently classically simulable, are injected with certain "magic" states that promote the computational power to universal fault-tolerant quantum computing. In 2014, Mark Howard, et al. showed that contextuality characterizes magic states for qubits of odd prime dimension and for qubits with real wavefunctions. Extensions to the qubit case have been investigated by Juani Bermejo Vega et al. This line of research builds on earlier work by Ernesto Galvão, which showed that Wigner function negativity is necessary for a state to be "magic"; it later emerged that Wigner negativity and contextuality are in a sense equivalent notions of nonclassicality. === Measurement-based quantum computing === Measurement-based quantum computation (MBQC) is a model for quantum computing in which a classical control computer interacts with a quantum system by specifying measurements to be performed and receiving measurement outcomes in return. The measurement statistics for the quantum system may or may not exhibit contextuality. A variety of results have shown that the presence of contextuality enhances the computational power of an MBQC. In particular, researchers have considered an artificial situation in which the power of the classical control computer is restricted to only being able to compute linear Boolean functions, i.e. to solve problems in the Parity L complexity class ⊕L. For interactions with multi-qubit quantum systems a natural assumption is that each step of the interaction consists of a binary choice of measurement which in turn returns a binary outcome. An MBQC of this restricted kind is known as an l2-MBQC. ==== Anders and Browne ==== In 2009, Janet Anders and Dan Browne showed that two specific examples of nonlocality and contextuality
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were sufficient to compute a non-linear function. This in turn could be used to boost computational power to that of a universal classical computer, i.e. to solve problems in the complexity class P. This is sometimes referred to as measurement-based classical computation. The specific examples made use of the Greenberger–Horne–Zeilinger nonlocality proof and the supra-quantum Popescu–Rohrlich box. ==== Raussendorf ==== In 2013, Robert Raussendorf showed more generally that access to strongly contextual measurement statistics is necessary and sufficient for an l2-MBQC to compute a non-linear function. He also showed that to compute non-linear Boolean functions with sufficiently high probability requires contextuality. ==== Abramsky, Barbosa and Mansfield ==== A further generalization and refinement of these results due to Samson Abramsky, Rui Soares Barbosa and Shane Mansfield appeared in 2017, proving a precise quantifiable relationship between the probability of successfully computing any given non-linear function and the degree of contextuality present in the l2-MBQC as measured by the contextual fraction. Specifically, ( 1 − p s ) ≥ ( 1 − C F ( e ) ) . ν ( f ) {\displaystyle (1-p_{s})\geq \left(1-CF(e)\right).\nu (f)} where p s , C F ( e ) , ν ( f ) ∈ [ 0 , 1 ] {\displaystyle p_{s},CF(e),\nu (f)\in [0,1]} are the probability of success, the contextual fraction of the measurement statistics e, and a measure of the non-linearity of the function to be computed f {\displaystyle f} , respectively. === Further examples === The above inequality was also shown to relate quantum advantage in non-local games to the degree of contextuality required by the strategy and an appropriate measure of the difficulty of the game. Similarly the inequality arises in a transformation-based model of quantum computation analogous to l2-MBQC where it relates the degree of sequential contextuality present in the dynamics
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"page_id": 38407148,
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"title": "Quantum contextuality"
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of the quantum system to the probability of success and the degree of non-linearity of the target function. Preparation contextuality has been shown to enable quantum advantages in cryptographic random-access codes and in state-discrimination tasks. In classical simulations of quantum systems, contextuality has been shown to incur memory costs. == See also == Kochen–Specker theorem Mermin–Peres square KCBS pentagram Quantum nonlocality Quantum foundations Quantum indeterminacy == References ==
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"page_id": 38407148,
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"title": "Quantum contextuality"
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Peanut butter is a viscoelastic food that exhibits both solid and fluid behaviors. It consists of ground up peanuts and may contain additional additives, such as stabilizers, sugars, or salt. Its characteristic soft, spreadable texture can be further defined through rheology – the study of flow and deformation of matter, affecting texture, consistency, and mouthfeel. Specifically for peanut butter, rheology can be used to more accurately define characteristics, such as spreadability and grittiness. == Soft matter context == In a soft matter context, peanut butter can be considered as a colloidal dispersion, where solid, insoluble peanut particles are suspended in liquid oil. There are two types of peanut butter, and at room temperature, these two types of peanut butter behave differently. Non-stabilized peanut butter, also known as "natural" or "100%" peanut butter consists only of ground peanuts and peanut oil and may contain seasonings, such as salt. In natural peanut butter at room temperature, the insoluble peanut particles separate from peanut oil, and the difference in density causes the peanut oil to float upwards. Stabilized peanut butter contains additional ingredients, such as vegetable oil, to prevent the grounded peanuts and peanut oil from separating into two layers. During the grinding process, the peanuts release oils, forming a peanut paste consisting of peanut oil and peanut grounds. The grinding process also causes an increase in the overall product temperature, and at this point a stabilizer might be added, such as hydrogenated vegetable oils. At this temperature, the stabilizer melts, uniformly dispersing into the peanut paste. This oil then crystallizes once the product returns to ambient temperatures, and the formed crystalline lattices trap the stabilizer particles within the paste. This prevents the final peanut butter from separating into two separate phases. Without the stabilizer, the peanut oil alone is not enough, as
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"page_id": 76090350,
"source": null,
"title": "Rheology of peanut butter"
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it is unable to crystallize at room temperature. The melting point of peanut oil is 3 °C (37 °F). At room temperature, the oils in natural peanut butter remain liquid, causing a phase separation. Within the stabilized peanut butter, the microstructural features are able to remain well-dispersed in a matrix of stabilized oil due to crystallization, while in the unstabilized peanut butter, the features are not able to retain the same uniformity. == Methods to characterize peanut butter rheology == For most viscous semi-liquid foods, rheological characteristics are determined in shear flow using a coaxial viscometer. However, as peanut butter is not only a highly viscous material, it is also self-lubricating, meaning it releases oils under shear. If placed in a typical coaxial viscometer, the resulting flow pattern a distorted shear flow or plug flow. For accurate data, rheometers typically require no-slip, and the properties of peanut butter do not satisfy this condition. This causes it to be particularly difficult to study its rheology. There have been a few methods devised to overcome this. === Squeezing flow viscosimetry === Squeezing flow viscosimetery uses two parallel plates to compress a fluid uniaxially. This method can be used to better understand the viscoelastic properties of peanut butter. Peanut butter samples can be placed between two lubricated plates, and samples can be subjected to either uniaxial deformation at various constant displacement rates, or to uniaxial creep deformation under various constant loads. As the plates compressed the sample, if the sample retained a cylindrical shape without bulging, this is evident that there is a lack of shear flow. Using this method, peanut butter has been determined to be a power-law fluid with shear thinning properties. In other words, under high shear rates, there is a lower apparent viscosity. This is likely due to the
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"page_id": 76090350,
"source": null,
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size difference in peanut and oil particles. The larger peanut particles likely form loosely bound aggregates that break down as shear rate increases (e.g. mixing), which allow the oil to better disperse between peanut particles, resulting in a reduced viscosity. === Rough plates with parallel plate rheometers === Another way to overcome the wall-slip effects, is to rough up the contact surface of parallel plate rheometers using a material such as sandpaper. In order to determine if this method sufficiently reduces the wall-slip effects, stress growth experiments can be conducted. If the stress over time is independent of gap size, then wall slip has been successfully reduced. == Rheological properties == The apparent yield stress for the stabilized suspension (374 Pa) was significantly larger than the unstabilized sample (27 Pa) under the Bingham model. This is likely due to the effects of the stabilizing agent. During the grinding stage, the stabilizer dispersed around the peanut particles. At room temperature, the stabilizer crystallized around the particles, creating a strong network of particles within the suspension that can resist the onset of flow. In unstabilized peanut butter, the peanut oil remains in a liquid state. Even when the peanut particles are mixed in homogeneously, the peanut butter remains more liquid-like. Previously conducted creep (stress vs. strain) experiments were conducted to determine the viscosity of peanut butter. In the stabilized peanut butter, under stresses of 250 MPa, the viscosity increases rapidly with increasing strain, exemplifying solid-like behavior. With stresses greater than 250 MPa, stabilized peanut butter displays liquid-like behavior. In an unstabilized sample, the same viscoelastic transitional behavior was found at 10 MPa. Both stabilized and unstabilized peanut butter displayed highly non-linear behavior, and the storage (G’) and loss (G’’) modulus was determined. Both peanut butter types have a decrease in G’ and
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{
"page_id": 76090350,
"source": null,
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G’’ until critical strain amplitude is reached. Beyond this critical point, both moduli start to increase. The initial observed decrease was likely due to a structure breakdown under strain. Mentioned previously, the increase in strain causes loosely aggregated peanut particles to break, allowing a more homogeneous oil-peanut mixture to form. However, the increase in moduli at a critical strain implies a less homogenous structure is being formed, causing a greater resistance to flow. This might mean at some critical strain, the particles start to behave in a shear thickening manner. A possible reason could be that the maximum volume packing fraction changes with strain amplitude. Meaning at a critical strain, the flow would cause particles to create a less ordered structure resulting in an increase in viscosity. Complex viscosity is a measure of the total resistance to flow as a function of angular frequency. For peanut butter, it was found that the initial complex viscosity as angular frequency increased was very high. However, if the angular frequency was decreased and increased again, a different behavior emerged, and the peanut butter was unable to retain the same initial complex viscosity. This shows that once the existing structure of the sample was broken, the sample's thixotropic effects, or the rheological properties dependent on flow history, are less pronounced. == Other factors == By varying the grinding time of peanuts, the resulting rheology and texture of natural peanut butter (with no stabilizer) can be affected. More specifically, as grinding time increases, the apparent viscosity decreases. This is likely due to an increase in peanut oil produced by a higher grinding time, causing a lubricating effect to decrease viscosity. Increasing the grinding time also produced peanut butter with a narrower particle size distribution with high densities. As smaller particles can compact better with less
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{
"page_id": 76090350,
"source": null,
"title": "Rheology of peanut butter"
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void space than larger particles, density would increase as grinding time increased. For shorter grinding times, there is a wider particle size distribution, meaning the overall peanut particle size is less uniform. This results in a wider linear viscoelastic region, and allows unstabilized peanut butter to behave more similarly to stabilized peanut butter. This is because in stabilized peanut butter, the peanuts' protein bodies and cell wall fragments are able to be more uniformly distributed throughout the peanut butter, rather than clumping. If the particle size is more widely distributed, it mimics the particle size distribution of stabilized peanut butter, resulting in a more stable natural peanut butter. == Applications == The rheology of peanut butter may affect its best texture, flavor, storage stability, and overall quality. This understanding can be applied when determining better or alternative stabilizers for peanut butter or better grinding manufacturing processes for unstabilized peanut butter to prevent oil separation more effectively. == References ==
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{
"page_id": 76090350,
"source": null,
"title": "Rheology of peanut butter"
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Glucuronidase may refer to several enzymes: Alpha-glucuronidase Beta-glucuronidase Glycyrrhizinate beta-glucuronidase Glucuronosyl-disulfoglucosamine glucuronidase
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{
"page_id": 20712430,
"source": null,
"title": "Glucuronidase"
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In condensed matter physics, the Fermi surface is the surface in reciprocal space which separates occupied electron states from unoccupied electron states at zero temperature. The shape of the Fermi surface is derived from the periodicity and symmetry of the crystalline lattice and from the occupation of electronic energy bands. The existence of a Fermi surface is a direct consequence of the Pauli exclusion principle, which allows a maximum of one electron per quantum state. The study of the Fermi surfaces of materials is called fermiology. == Theory == Consider a spin-less ideal Fermi gas of N {\displaystyle N} particles. According to Fermi–Dirac statistics, the mean occupation number of a state with energy ϵ i {\displaystyle \epsilon _{i}} is given by ⟨ n i ⟩ = 1 e ( ϵ i − μ ) / k B T + 1 , {\displaystyle \langle n_{i}\rangle ={\frac {1}{e^{(\epsilon _{i}-\mu )/k_{\rm {B}}T}+1}},} where ⟨ n i ⟩ {\displaystyle \left\langle n_{i}\right\rangle } is the mean occupation number of the i {\displaystyle i} th state ϵ i {\displaystyle \epsilon _{i}} is the kinetic energy of the i {\displaystyle i} th state μ {\displaystyle \mu } is the chemical potential (at zero temperature, this is the maximum kinetic energy the particle can have, i.e. Fermi energy E F {\displaystyle E_{\rm {F}}} ) T {\displaystyle T} is the absolute temperature k B {\displaystyle k_{\rm {B}}} is the Boltzmann constant Suppose we consider the limit T → 0 {\displaystyle T\to 0} . Then we have, ⟨ n i ⟩ → { 1 ( ϵ i < μ ) 0 ( ϵ i > μ ) . {\displaystyle \left\langle n_{i}\right\rangle \to {\begin{cases}1&(\epsilon _{i}<\mu )\\0&(\epsilon _{i}>\mu )\end{cases}}.} By the Pauli exclusion principle, no two fermions can be in the same state. Additionally, at zero temperature the enthalpy of the electrons
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"page_id": 986096,
"source": null,
"title": "Fermi surface"
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must be minimal, meaning that they cannot change state. If, for a particle in some state, there existed an unoccupied lower state that it could occupy, then the energy difference between those states would give the electron an additional enthalpy. Hence, the enthalpy of the electron would not be minimal. Therefore, at zero temperature all the lowest energy states must be saturated. For a large ensemble the Fermi level will be approximately equal to the chemical potential of the system, and hence every state below this energy must be occupied. Thus, particles fill up all energy levels below the Fermi level at absolute zero, which is equivalent to saying that is the energy level below which there are exactly N {\displaystyle N} states. In momentum space, these particles fill up a ball of radius k F {\displaystyle k_{\rm {F}}} , the surface of which is called the Fermi surface. The linear response of a metal to an electric, magnetic, or thermal gradient is determined by the shape of the Fermi surface, because currents are due to changes in the occupancy of states near the Fermi energy. In reciprocal space, the Fermi surface of an ideal Fermi gas is a sphere of radius k F = p F ℏ = 2 m E F ℏ {\displaystyle k_{\rm {F}}={\frac {p_{\rm {F}}}{\hbar }}={\frac {\sqrt {2mE_{\rm {F}}}}{\hbar }}} , determined by the valence electron concentration where ℏ {\displaystyle \hbar } is the reduced Planck constant. A material whose Fermi level falls in a gap between bands is an insulator or semiconductor depending on the size of the bandgap. When a material's Fermi level falls in a bandgap, there is no Fermi surface. Materials with complex crystal structures can have quite intricate Fermi surfaces. Figure 2 illustrates the anisotropic Fermi surface of graphite, which has
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"page_id": 986096,
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"title": "Fermi surface"
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both electron and hole pockets in its Fermi surface due to multiple bands crossing the Fermi energy along the k z {\displaystyle \mathbf {k} _{z}} direction. Often in a metal, the Fermi surface radius k F {\displaystyle k_{\rm {F}}} is larger than the size of the first Brillouin zone, which results in a portion of the Fermi surface lying in the second (or higher) zones. As with the band structure itself, the Fermi surface can be displayed in an extended-zone scheme where k {\displaystyle \mathbf {k} } is allowed to have arbitrarily large values or a reduced-zone scheme where wavevectors are shown modulo 2 π a {\textstyle {\frac {2\pi }{a}}} (in the 1-dimensional case) where a is the lattice constant. In the three-dimensional case the reduced zone scheme means that from any wavevector k {\displaystyle \mathbf {k} } there is an appropriate number of reciprocal lattice vectors K {\displaystyle \mathbf {K} } subtracted that the new k {\displaystyle \mathbf {k} } now is closer to the origin in k {\displaystyle \mathbf {k} } -space than to any K {\displaystyle \mathbf {K} } . Solids with a large density of states at the Fermi level become unstable at low temperatures and tend to form ground states where the condensation energy comes from opening a gap at the Fermi surface. Examples of such ground states are superconductors, ferromagnets, Jahn–Teller distortions and spin density waves. The state occupancy of fermions like electrons is governed by Fermi–Dirac statistics so at finite temperatures the Fermi surface is accordingly broadened. In principle all fermion energy level populations are bound by a Fermi surface although the term is not generally used outside of condensed-matter physics. == Experimental determination == Electronic Fermi surfaces have been measured through observation of the oscillation of transport properties in magnetic fields H
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{\displaystyle H} , for example the de Haas–van Alphen effect (dHvA) and the Shubnikov–de Haas effect (SdH). The former is an oscillation in magnetic susceptibility and the latter in resistivity. The oscillations are periodic versus 1 / H {\displaystyle 1/H} and occur because of the quantization of energy levels in the plane perpendicular to a magnetic field, a phenomenon first predicted by Lev Landau. The new states are called Landau levels and are separated by an energy ℏ ω c {\displaystyle \hbar \omega _{\rm {c}}} where ω c = e H / m ∗ c {\displaystyle \omega _{\rm {c}}=eH/m^{*}c} is called the cyclotron frequency, e {\displaystyle e} is the electronic charge, m ∗ {\displaystyle m^{*}} is the electron effective mass and c {\displaystyle c} is the speed of light. In a famous result, Lars Onsager proved that the period of oscillation Δ H {\displaystyle \Delta H} is related to the cross-section of the Fermi surface (typically given in Å−2) perpendicular to the magnetic field direction A ⊥ {\displaystyle A_{\perp }} by the equation A ⊥ = 2 π e Δ H ℏ c {\displaystyle A_{\perp }={\frac {2\pi e\Delta H}{\hbar c}}} . Thus the determination of the periods of oscillation for various applied field directions allows mapping of the Fermi surface. Observation of the dHvA and SdH oscillations requires magnetic fields large enough that the circumference of the cyclotron orbit is smaller than a mean free path. Therefore, dHvA and SdH experiments are usually performed at high-field facilities like the High Field Magnet Laboratory in Netherlands, Grenoble High Magnetic Field Laboratory in France, the Tsukuba Magnet Laboratory in Japan or the National High Magnetic Field Laboratory in the United States. The most direct experimental technique to resolve the electronic structure of crystals in the momentum-energy space (see reciprocal lattice), and, consequently,
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the Fermi surface, is the angle-resolved photoemission spectroscopy (ARPES). An example of the Fermi surface of superconducting cuprates measured by ARPES is shown in Figure 3. === Measurement using ACAR === With positron annihilation it is also possible to determine the Fermi surface as the annihilation process conserves the momentum of the initial particle. Since a positron in a solid will thermalize prior to annihilation, the annihilation radiation carries the information about the electron momentum. The corresponding experimental technique is called Angular Correlation of electron-positron Annihilation Radiation (ACAR) as it measures the angular deviation from 180° of both annihilation quanta. In this way it is possible to probe the electron momentum density of a solid and determine the Fermi surface. Furthermore, using spin polarized positrons, the momentum distribution for the two spin states in magnetized materials can be obtained. ACAR has many advantages and disadvantages compared to other experimental techniques: It does not rely on UHV conditions, cryogenic temperatures, high magnetic fields or fully ordered alloys. However, ACAR needs samples with a low vacancy concentration as they act as effective traps for positrons. In this way, the first determination of a smeared Fermi surface in a 30% alloy was obtained in 1978. == See also == Fermi energy Brillouin zone Fermi surface of superconducting cuprates Kelvin probe force microscope Luttinger's theorem == References == == External links == Experimental Fermi surfaces of some superconducting cuprates and strontium ruthenates in "Angle-resolved photoemission spectroscopy of the cuprate superconductors (Review Article)" (2002) Experimental Fermi surfaces of some cuprates, transition metal dichalcogenides, ruthenates, and iron-based superconductors in "ARPES experiment in fermiology of quasi-2D metals (Review Article)" (2014) Dugdale, S. B. (2016-01-01). "Life on the edge: a beginner's guide to the Fermi surface". Physica Scripta. 91 (5): 053009. Bibcode:2016PhyS...91e3009D. doi:10.1088/0031-8949/91/5/053009. hdl:1983/18576e8a-c769-424d-8ac2-1c52ef80700e. ISSN 1402-4896.
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Tiago de Paula Peixoto is a Brazilian physicist who works in the areas of network science, statistical physics, and complex systems. He is currently an full professor of Complex Systems and Network Science at the Interdisciplinary Transformation University. == Career == Peixoto is mostly known for his work in statistical inference in networks. He developed and maintains the graph manipulation library graph-tool, which contains readily available implementations of the methods he proposes in his publications. Peixoto graduated with a bachelor's degree in physics from the University of São Paulo in 2003. He earned a PhD in Physics from the same university in 2007, advised by Carmen Pimentel Cintra do Prado with a dissertation entitled "Dynamics of the epicenters of the Olami-Feder-Christensen model of earthquakes (OFC)". In 2017 he obtained his Habilitation in Theoretical Physics at the University of Bremen. Peixoto worked as a post-doctoral fellow in Germany (2008–2016) at the Technische Universität Darmstadt and University of Bremen before becoming an assistant professor (lecturer), in 2016, at the Department of Mathematics of the University of Bath. In 2019, he joined the faculty of the Central European University as an associate professor. As of 2024, he's a full professor at the Interdisciplinary Transformation University in Linz, Austria. == Awards and honors == In 2019, Peixoto was awarded the prestigious Erdős–Rényi Prize in Network Science for his contributions for the statistical inference of network modules (aka communities), statistical analysis and network visualization. He was also the sixth recipient of the Zachary Karate Club CLUB prize. == References == == External links == Tiago P. Peixoto publications indexed by Google Scholar Web Page at Interdisciplinary Transformation University. Web Page at the Central European University. Web Page at the ISI Foundation. LinkedIn Profile
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A time-of-flight (TOF) detector is a particle detector which can discriminate between a lighter and a heavier elementary particle of same momentum using their time of flight between two scintillators. The first of the scintillators activates a clock upon being hit while the other stops the clock upon being hit. If the two masses are denoted by m 1 {\displaystyle m_{1}} and m 2 {\displaystyle m_{2}} and have velocities v 1 {\displaystyle v_{1}} and v 2 {\displaystyle v_{2}} then the time of flight difference is given by Δ t = L ( 1 v 1 − 1 v 2 ) ≈ L c 2 p 2 ( m 1 2 − m 2 2 ) {\displaystyle \Delta t=L\left({\frac {1}{v_{1}}}-{\frac {1}{v_{2}}}\right)\approx {\frac {Lc}{2p^{2}}}(m_{1}^{2}-m_{2}^{2})} where L {\displaystyle L} is the distance between the scintillators. The approximation is in the relativistic limit at momentum p {\displaystyle p} and c {\displaystyle c} denotes the speed of light in vacuum. == See also == Time-of-flight mass spectrometry == References ==
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{
"page_id": 1379315,
"source": null,
"title": "Time-of-flight detector"
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Anti-Cancer Agents in Medicinal Chemistry is a peer-reviewed academic journal covering the disciplines of medicinal chemistry and drug design relating to chemotherapeutic agents in cancer. It is published by Bentham Science Publishers and the editor-in-chief is Simone Carradori ("G. d'Annunzio" University of Chieti-Pescara). The journal covers developments in "medicinal chemistry and rational drug design for the discovery of anti-cancer agents" and publishes original research reports and review papers. It is related to the journal Current Medicinal Chemistry and was established in 2001 as Current Medicinal Chemistry – Anti-Cancer Agents. The journal obtained its present title in 2006. == Abstracting and indexing == The journal is abstracted and indexed in: According to the Journal Citation Reports, the journal has a 2022 impact factor of 2.8. == References == == External links == Official website
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{
"page_id": 60034038,
"source": null,
"title": "Anti-Cancer Agents in Medicinal Chemistry"
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Freezer burn is a condition that occurs when frozen food has been damaged by dehydration and oxidation due to air reaching the food. It is generally caused by food not being securely wrapped in air-tight packaging. Freezer burn appears as grayish-brown leathery spots on frozen food and occurs when air reaches the food's surface and dries the product. Color changes result from chemical changes in the food's pigment. Freezer burn does not make the food unsafe; it merely causes dry spots in foods. The food remains usable and edible, but removing the freezer burns will improve the flavor. The dehydration of freezer-burned food is caused by water sublimating from the food into the surrounding atmosphere. The lost water may then be deposited elsewhere in the food and packaging as snow-like crystals. Fluctuation of temperatures in a freezer, such that the temperature does not remain consistently below -18°C, can also speed up freezer burn. == See also == Freeze drying Ice crystals == References == === Inline citations === === General and cited references === Are You Storing Food Safely?—United States Food and Drug Administration
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"page_id": 1641463,
"source": null,
"title": "Freezer burn"
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Pharmaceutical drugs become known for off-label use when publications begin discussing how they can be used for off-label treatment of medical conditions. == List == Actiq (oral transmucosal fentanyl citrate), a controlled substance, is used off-label to treat moderate to severe chronic, non-malignant pain even though it is approved in the United States solely for breakthrough pain in cancer patients. Bevacizumab (Avastin) has been used against wet age-related macular degeneration, as well as macular edema from diseases such as diabetic retinopathy and central retinal vein occlusion. Buprenorphine has been shown experimentally (1982–1995) to be effective against severe, refractory depression. Bupropion, when sold under the brand name Wellbutrin is indicated for depression. It is also sold as a smoking cessation drug, under the name Zyban. In Ontario, Canada, smoking cessation drugs are not covered by provincial drug plans. Thus, a physician can write a prescription for Wellbutrin to assist with giving up the habit of smoking. Sometimes it is also prescribed as second-line treatment of ADHD, often in combination with the stimulant being used, but it was also shown to work on its own as a norepinephrine–dopamine reuptake inhibitor. It is also given to counter the negative effects of SSRIs on libido, anorgasmia and anhedonia. Carbamazepine, or Tegretol, has been used as a mood stabilizer and is accepted treatment for bipolar disorder. Clomiphene (Clomid) for male infertility: clomiphene is approved for female infertility due to ovulatory disorder. Clonidine (Catapres) for ADHD: clonidine is approved and commonly used for the treatment of hypertension. Other off-label uses include cancer pain, hot sweats, certain psychiatric disorders, nicotine dependence, opioid withdrawal, migraine headaches, and restless leg syndrome. Colchicine (Colcrys) for pericarditis: colchicine is indicated for the treatment and prevention of gout, though it is also generally considered first-line treatment for acute pericarditis, as well as
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preventing recurrent episodes. Although the exact mechanism of colchicine is not fully understood, its anti-inflammatory effect for pericarditis appears to be related to its ability to inhibit microtubule self-assembly, resulting in decreased leucocyte motility and phagocytosis. Other non-FDA-approved uses include actinic keratosis, amyloidosis, Peyronie's disease, and psoriasis. Dexamethasone and betamethasone in premature labor, to enhance pulmonary maturation of the fetus. Doxepin has been used to treat angiodema and severe allergic reactions due to its strong antihistamine properties. Diphenhydramine, known in the US as Benadryl, is approved for treatment of allergies, but is also used off label for nausea, anxiety, and more. Gabapentin, approved for treatment of seizures and postherpetic neuralgia in adults, is used off-label for a variety of conditions including bipolar disorder, essential tremor, hot flashes, migraine prophylaxis, neuropathic pain syndromes, phantom limb syndrome, and restless leg syndrome. Lithium is approved by the FDA for the treatment of bipolar disorder and is widely prescribed off-label as a treatment for major depressive disorder, often as an augmentation agent. Lithium is recommended for the treatment of schizophrenic disorders only after other antipsychotics have failed; it has limited effectiveness when used alone. Magnesium sulfate is used in obstetrics for premature labor and preeclampsia. Memantine (Namenda) for OCD: memantine is approved for the treatment of Alzheimer's disease. Methotrexate (MTX), approved for the treatment of choriocarcinoma, is frequently used for the medical treatment of an unruptured ectopic pregnancy. There is no FDA-approved drug for this purpose and there is little incentive to sponsor an unpatented drug such as MTX for FDA-approval. Misoprostol is approved for medical abortion regimens when administered at the office, but clinicians often give abortion patients the drug to be taken at home. Modafinil is a central nervous system (CNS) stimulant medication used to treat sleepiness due to narcolepsy, shift work
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"page_id": 53677048,
"source": null,
"title": "List of drugs known for off-label use"
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sleep disorder, and obstructive sleep apnea. It is often used off-label as a nootropic. Prazosin (Minipress) for nightmares: prazosin is approved for the use of hypertension. A 2012 systematic review showed a small benefit for the treatment of PTSD-associated night terrors. Other non-FDA-approved uses for prazosin include the treatment of Raynaud's disease and poisoning due to scorpion venom. Propranolol (Inderal) for performance anxiety: propranolol is a non-selective beta-blocker used for the treatment of hypertension and the prophylaxis of angina pectoris. In 1991, a published study showed that a single dose of propranolol immediately before the Scholastic Aptitude Test (SAT) significantly improved performance in high school students prone to cognitive dysfunction due to test anxiety. In addition to test taking, propranolol has been tested for public speaking, performing surgery, musical recitals, and sports, all with varying degrees of benefit. Other off-label uses for propranolol include the treatment of thyroid storm, portal hypertension, and neuroleptic-induced akathisia. Quetiapine (Seroquel) for insomnia: quetiapine is approved for the treatment of schizophrenia and bipolar disorder. Retigabine (INN) is an anticonvulsant used as an adjunctive treatment for partial epilepsies in treatment-experienced adult patients. Currently, it is being tested in the treatment of Tinnitus. The SSRI medication sertraline (Zoloft) is approved as an anti-depressant but is also commonly prescribed off-label to help men suffering from premature ejaculation. Tramadol, an opioid painkiller, is used to treat premature ejaculation, and may also be applied against restless legs syndrome. Low-dose naltrexone is cheap without side effects and used to treat cancer and autoimmune diseases like focal segmental glomerulosclerosis. Naltrexone (Revia) for behavioral addiction: there is some belief that low-dose naltrexone may benefit the treatment of cancer, HIV, and multiple sclerosis by “normalizing” the immune system; however, data is lacking. Naltrexone is approved for the treatment of alcohol and opioid dependence ==
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"page_id": 53677048,
"source": null,
"title": "List of drugs known for off-label use"
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|
See also == Lists of drugs List of off-label promotion pharmaceutical settlements Marketing of off-label use == References ==
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"page_id": 53677048,
"source": null,
"title": "List of drugs known for off-label use"
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Sympathetic cooling is a process in which particles of one type cool particles of another type. Typically, atomic ions that can be directly laser cooled are used to cool nearby ions or atoms, by way of their mutual Coulomb interaction. This technique is used to cool ions and atoms that cannot be cooled directly by laser cooling, which includes most molecular ion species, especially large organic molecules. However, sympathetic cooling is most efficient when the mass/charge ratios of the sympathetic- and laser-cooled ions are similar. The cooling of neutral atoms in this manner was first demonstrated by Christopher Myatt et al. in 1997. Here, a technique with electric and magnetic fields were used, where atoms with spin in one direction were more weakly confined than those with spin in the opposite direction. The weakly confined atoms with a high kinetic energy were allowed to more easily escape, lowering the total kinetic energy, resulting in a cooling of the strongly confined atoms. Myatt et al. also showed the utility of their version of sympathetic cooling for the creation of Bose–Einstein condensates. == References ==
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{
"page_id": 11996151,
"source": null,
"title": "Sympathetic cooling"
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A vaccine passport or proof of vaccination is an immunity passport employed as a credential in countries and jurisdictions as part of efforts to control the COVID-19 pandemic via vaccination. A vaccine passport is typically issued by a government or health authority, and usually consists of a digital or printed record. Some credentials may include a scannable QR code, which can also be provisioned via mobile app. It may or may not use a COVID-19 vaccine card as a basis of authentication. The use of vaccine passports is based on the general presumption that a vaccinated individual would be less likely to transmit SARS-CoV-2 to others, and less likely to experience a severe outcome (hospitalization or death) if they were to be infected, thus making it relatively safer for them to congregate. A vaccine passport is typically coordinated with policies enforced by individual businesses, or enforceable public health orders, that require patrons to present proof of vaccination for COVID-19 as a condition of entry or service. Government-mandated use of vaccine passports typically applies to discretionary public spaces and events (such as indoor restaurants, bars, or large-scale in-person events, such as concerts and sports), and not essential businesses, such as retail stores or health care. In France, Italy, Ireland, and Canada, vaccine uptake increased after various levels of governments announced plans to introduce vaccine passports. An intention by some jurisdictions is to prevent future lockdowns and restrictions. Vaccine passports are controversial and have raised scientific, ethical and legal concerns. Critics have also argued that vaccine passports violate civil liberties via coercion. In the United States, there is no vaccine passport at a federal level, and some US states have preemptively banned vaccine passports in certain public and private sector contexts, citing discrimination and privacy concerns. England initially decided against mandating vaccine
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passports due to worries that discrimination and economic harm would occur, but later joined the other nations of the United Kingdom in mandating vaccine passports due to the threat of the Omicron variant. == History and background == Many governments, including Finland and Germany, expressed early interest in the concept. Vaccine passports were seen as a potential way to permit a faster economic recovery from large-scale lockdowns that apply to all residents (especially within the travel and tourism industries), improve the confidence of patrons concerned for their health and safety, and to incentivize vaccination in order for a population to potentially reach "herd immunity". In May 2020, Chile started issuing "release certificates" to patients who had recovered from COVID-19, but "the documents will not yet certify immunity". Many governments including Finland, Germany, the United Kingdom, and the United States expressed interest in the concept. The Royal Society published a report on 19 February 2021 where a lead author of the report, Professor Melinda Mills, Director of the Leverhulme Centre for Demographic Science at the University of Oxford said: “Understanding what a vaccine passport could be used for is a fundamental question – is it literally a passport to allow international travel or could it be used domestically to allow holders greater freedoms? The intended use will have significant implications across a wide range of legal and ethical issues that need to be fully explored and could inadvertently discriminate or exacerbate existing inequalities.” The report lists 12 essential criteria for an international standard. On 12 March 2021, Ecma International announced its intention to create an international standard which prevents counterfeits and protects private data as much as possible in a "Call for Participation on Vaccine Passports International Standardization" that referenced the earlier report from the UK's Royal Society. In August 2021,
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Ecma International announced revisions to Ecma-417 (Architectures for distributed real-time access systems) relevant to standards for vaccine passports. An early advocate of immunity passports during the COVID-19 pandemic was Sam Rainsy, the Cambodian opposition leader. In exile and under confinement in Paris, he proposed immunity passports as a way to help restart the economy in a series of articles which he began in March 2020 and published in The Geopolitics and The Brussels Times. The proposals were also published in French. The idea became increasingly relevant as evidence of lasting acquired immunity became clear. Proponents of the idea such as Sam Rainsy, co-founder of the opposition Cambodia National Rescue Party (CNRP) have argued that immunity, whether acquired naturally or through vaccination, is a resource which needs to be used to limit the impact of the pandemic on the global economy. Many people in Cambodia depend entirely for their living on a tourism industry which has been wiped out. Poor countries can also benefit from recording immunological status as this will reduce wastage of scarce vaccines. The immunity passport proposed by Rainsy was effectively adopted in the EU under the name of "health pass". As of 4 April 2021, it was not yet clear whether vaccinated people that remain asymptomatic are still contagious and are thus silent spreaders of the virus putting unvaccinated people at risk. "A lot of people are thinking that once they get vaccinated, they’re not going to have to wear masks anymore," said Michal Tal, an immunologist at Stanford University. "It’s really going to be critical for them to know if they have to keep wearing masks, because they could still be contagious." In January 2021, Israel announced that Israelis who had received their second vaccination and those who had proof of recovery from infection would be
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eligible for a Green Pass, exempting them from isolation requirements and mandatory COVID-19 tests, including those on arrival from overseas. In February 2021, Israel became one of the first countries to implement a vaccine passport system, dubbed the Green Pass. They are required in order to access venues such as gyms, hotels, bars, and restaurants. In October 2021, Israel announced an update to its guidelines, requiring that the most recent vaccine dose (or proof of recovery) to have been during the past six months. This change made Israel the first country to make a booster shot a requirement for its vaccine passport system. == By region == === Africa === ==== Morocco ==== In August 2021, Morocco established a nightly curfew between 23:00 and 04:30, exempting those fully vaccinated. The curfew was lifted in November 2021. === Asia === ==== Azerbaijan ==== Beginning on 1 September 2021, Azerbaijan required proof of vaccination for people over 18 to enter virtually all public spaces, and a national mandate of 1 October required vaccination of all state-regulated workers. ==== China ==== In February 2020, China started to use digital "health codes", available on a variety of platforms including WeChat and Alipay with scannable QR barcodes displaying a "traffic light" system of colours to enter public transport, shops, restaurants and malls. It was used 40 billion times between February and March. In March 2021, an "International Travel Health Certificate" was created. In March 2021, the government of China rolled out the world's first COVID-19 vaccine passport system through a partnership with Alipay and WeChat. The system provides a health certificate that includes an individual's vaccine status and the results of COVID-19 testing. Initially, the system would only indicate that an individual had been vaccinated if they received a Chinese-made coronavirus vaccine, leading to criticism,
|
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though by April 2021 the system began to accept records of receiving the Pfizer-BioNTech, Moderna, and Janssen vaccines. As of March 2021, the app was optional and its use was restricted to Chinese citizens. The digital health passport is intended to better facilitate travel. Privacy advocates and Chinese netizens have expressed concerns regarding the potential invasive data collection and the use of data for non-health monitoring purposes. ==== Iran ==== According to Minister of health and education requires passport number, Iranian national ID card code for issuing vaccine digital foreign travel card. ==== Israel ==== Israel was one of the first countries to issue what is known as a Green Pass in February 2021. The pass was discontinued on 1 June 2021, but following a surge of new infections, it was reinstated on 29 July 2021. In October 2021, all existing Green Passes were voided if the most recent shot was administered more than 6 months ago. A new pass would be issued upon proof of a third (booster) dose or a recovery within the past 6 months. A temporary Green Pass could also be obtained with a negative viral test, but must be paid for by the individual unless ineligible for vaccination. Starting 1 March 2022, most COVID-19 regulations were relaxed, and a Green Pass is now only required to enter old age homes. ==== Japan ==== On 19 July 2021, Japan began accepting applications for its COVID-19 vaccination passport program. When issued, the passports will be in paper form in both Japanese and English, showing the holder's date(s) of inoculation and the vaccine type, and are available free of charge. As of 20 December 2021, entry restrictions were relaxed for Japan vaccine passport holders in 76 countries. ==== Saudi Arabia ==== Residents attending restaurants, cafes and public spaces
|
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"title": "Vaccine passports during the COVID-19 pandemic"
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like malls, shopping centres and markets must be fully vaccinated. The country uses the Tawakkalna app which includes information for health appointments, vaccination status and alerts users to COVID-19 exposure for contact tracing purposes. ==== Singapore ==== Since 10 August 2021, all residents dining out must be fully vaccinated by showing proof of vaccination using the TraceTogether or HealthHub app, or use the TraceTogether token. Proof of vaccination has been progressively implemented in almost all public venues since 13 October 2021, starting with shopping malls, retail shops, entertainment venues except bars, nightclubs and karaoke parlours, attractions, cruises and eateries. It has since been expanded to include large events, public libraries, selected events at community buildings and will be expanded to tertiary institutions, places of lodging, small events and workplaces from January 2022. ==== South Korea ==== On 1 November 2021, a vaccine passport system went into effect in South Korea as part of a "living with COVID-19" strategy, requiring vaccination of all residents wishing to access high-risk areas such as bars, restaurants, gyms and saunas must be vaccinated. ==== Taiwan ==== On 25 October 2021, the Taiwanese government announced that the digital COVID certificate system in the country had been completed. In December 2021, the system was also recognised by the EU as an equivalent of the EU Digital Covid Certificate. On 20 January 2022, Taiwan officially released the certificate and implemented rules that it be required before entering bars or karaoke alike. === Europe === ==== European Union ==== The European Union offers an EU Digital COVID Certificate (EUDCC), also known as the Green Pass, a digitally-signed proof of vaccination, proof of a recent recovery, or a recent negative test, for use when travelling within the Schengen area with fewer restrictions. ===== Bulgaria ===== On 19 October 2021, the
|
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caretaker Minister of Health of Bulgaria, Stoycho Katsarov, introduced the Green Certificate (Bulgarian: Зелен Сертификат). Since 21 October 2021, all visitors to cinemas, theaters, concerts, museums, galleries, supermarkets over 300 square meters, fitness centers, gyms, restaurants and entertainment centers in Bulgaria have to prove that they are vaccinated, have a valid negative test from last 72 hours or have been ill recently. The restrictions ended on 10 March 2022. ===== Denmark ===== Denmark introduced a Coronapas on 21 April 2021. Those unvaccinated with a recently negative test of 72 hours or previous infection of COVID-19 of up to 12 weeks prior were included in the pass system. Due to the high uptake of vaccines, Denmark retired their system on 10 September 2021. ===== France ===== France issued a Health Pass (or Pass Sanitaire in French) on 9 August 2021, for use in non-essential settings for those 18 and older. To obtain the pass people must be fully vaccinated or undertake a test within 72 hours of attending a non-essential space or have recovered recently from an infection of the virus. The initial announcement of the pass system is believed to have encouraged an additional one million people to sign up for vaccination the day following the announcement, and is credited to encouraging a further 3.7 million people to sign up for vaccination in the following week. Starting 1 October 2021, those age 12 and older will require a Pass Sanitaire to enter public sites like restaurants, cinemas, and sporting events. ===== Germany ===== In Germany, proof of COVID vaccinations or recent recovery, is typically entered in the International Certificate of Vaccination or Prophylaxis (German: Impfausweis), similar to how other vaccinations for other diseases are recorded. The entry in this booklet can be used to acquire an EU Digital COVID Certificate,
|
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"title": "Vaccine passports during the COVID-19 pandemic"
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in accordance with EU Directive 2021/953, effective 1 July 2021. ===== Hungary ===== Outside of the application of the EUDCC, Hungary recognises Kazakh and Indian vaccine passports. ===== Ireland ===== In July 2021, Ireland introduced a vaccine certificate program (EU Digital COVID Certificate) which allowed vaccinated individuals to attend cafes, bars and restaurants. Due to one of the highest uptakes of COVID-19 vaccines in the world, the Republic of Ireland (but not Northern Ireland) had plans to retire their vaccine passport program on 22 October 2021 however this was postponed due to increased COVID-19 cases and hospital numbers. On 22 January 2022, the Republic of Ireland's vaccine passport programme was retired, except for international travel. ===== Italy ===== In August 2021 the Italian government extended the requirement of the EU Digital COVID Certificate, also known as a Green Pass, to the participation in sports events and music festivals, but also to access to indoor places like bars, restaurants and gyms, as well as to long-distance public transportation. On 15 October 2021, Italy became the first country in the world to require its entire workforce, public and private, to have a government-issued health pass. ===== Sweden ===== On 1 December 2021 the Swedish government introduced vaccine passports for indoor events with more than 100 people. Indoor events with more than 100 participants who do not use vaccination certificates must follow specific guidelines to avoid spreading the disease. ===== Ukraine ===== In Ukraine, citizens with at least one dose of a vaccine are allowed to attend certain high-risk indoor settings which would normally be closed or heavily restricted in hot spots. ===== United Kingdom ===== Proof of vaccination programs exist in the Home Nations of the United Kingdom, with England and Wales referring to them as "NHS COVID Pass", Scotland as "NHS
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Scotland Covid Status", and Northern Ireland as "COVIDCert NI". By December 2021, all four nations had mandated proof of vaccination or a recent negative test in specific settings. The exact rules vary by nation, but they primarily applied to venues such as cinemas, nightclubs, and venues hosting large organized events (including but not limited to concerts and sporting events). In September 2021, Secretary of Health Sajid Javid stated that England would not implement a mandate for proof of vaccination, following pushback from Conservative members of parliament and business leaders over potential discrimination and economic harm. Prime Minister Boris Johnson subsequently stated that England would focus on a strategy of contact tracing, rapid testing, and the rollout of vaccine boosters, and only included mandatory proof of vaccination in a package of "plan B" measures (including a reintroduction of mask mandates) in the event of another surge of COVID-19 cases. The spread of Omicron variant in England would lead to the implementation of "plan B", resulting in proof of vaccination for nightclubs and large events becoming mandatory beginning 15 December. These restrictions ended on 27 January 2022. ===== North Macedonia ===== Residents wishing to attend events, bars, restaurants, and other dining establishments must present proof of vaccination. === North America === ==== Canada ==== The implementation of digital proof of vaccination in Canada has largely been conducted at the provincial and territorial level, with the federal government specifying the SMART Health Card document and QR code standard designed to be suitable for international travel. As of November 2021, all ten provinces in Canada, and two of the three territories, had implemented or announced plans to implement a provincially-regulated vaccine passport. ==== Federal requirements and mandates ==== Beginning 30 October 2021 proof of vaccination became mandatory for all passengers aged 12 and older
|
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"source": null,
"title": "Vaccine passports during the COVID-19 pandemic"
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boarding domestic and/or international commercial airplanes departing from most Canada-based airports, and those riding on the cross-country Via Rail services. Travellers by land (via the United States border) are required to be fully vaccinated to enter Canada and must provide a negative test 72-hours before land crossing. An exception was made for essential workers, until January 15, 2022 when essential workers (mainly truckers) were required to be fully vaccinated to re-enter the country. In late-January 2022, a convoy to and demonstration in the federal capital of Ottawa—supported primarily by far-right activists and groups—was held to protest this change. ===== Alberta ===== Alberta implemented the Restrictions Exemption Program (REP) from 20 September 2021 to 8 February 2022, after re-establishing a state of emergency on 15 September 2021. The government described the program as an opt-in system, allowing establishments to operate with fewer restrictions. Visitors at these establishments were required to present a proof of vaccination or a recent negative test. If a facility does not participate, or is prohibited from participating, it was required to comply with all public health orders, such as reduced capacity and/or being prohibited from offering indoor dining. Due to Omicron variant, even establishments participating in REP became subject to restrictions in December 2021, including restrictions on the capacity of large venues (50%), and restaurants subject to limits on table sizes, a prohibition on entertainment, and operating hours. The city of Calgary passed a municipal bylaw on 23 September 2021 to mandate participation in REP by all industries that are eligible to do so. The bylaw ceased on 9 February 2022 due to the lifting of the REP by the provincial government. The city considered reimplementing the mandate at the municipal level (as haveseveral U.S. cities) but such a proposal was rejected by the city council committee.
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===== Manitoba ===== Manitoba was the first province to introduce a passport system in Canada on 17 July 2021. The passport requirement was removed for movie theatres, museums and galleries on 7 August 2021, only to be reinstated on 3 September 2021, upon Manitoba expanding its passport system. The province utilized physical Immunization Cards which faced supply shortages in production. ===== Quebec ===== Quebec was the second province to implement a vaccine passport system on 1 September 2021, using QR codes. ===== Northwest Territories ===== The Northwest Territories will implement an opt-in vaccine passport system on 22 October 2021 using original vaccination receipts. ===== Other provinces ===== British Columbia has created a Proof of vaccination system which utilises a QR code. The system initially relied on paper receipts of the BC vaccine receipt and gradually migrated to a digital system. The QR code can also be physically printed out. New Brunswick requires a Proof of Vaccination system using original immunisation records. Newfoundland and Labrador has plans to release a QR code based system for their vaccine passport. Nova Scotia has a Proof of Full Vaccination Policy using original government issued proof of vaccination. Ontario introduced a vaccine passport system on 22 September 2021. The system initially relied on original vaccine paper receipts, but gradually began switching over to verifiable QR codes along with the introduction of the "Verify Ontario" mobile app on 22 October 2021. As of 4 January 2022, only vaccine receipts with verifiable QR codes and the "Verify Ontario" mobile app will be accepted at venues where proof of vaccine is required. Prince Edward Island uses the PEI Vax Pass Program using original government issued vaccination information. Saskatchewan has a Proof of vaccination mandate, effective from 1 October 2021 to 13 February 2022. Yukon territory will implement a
|
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"page_id": 68750333,
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"title": "Vaccine passports during the COVID-19 pandemic"
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passport system on 30 November 2021 to access non-essential indoor facilities. ==== United States ==== Although the Centers for Disease Control and Prevention (CDC) issues a COVID-19 vaccine card that may be accepted as proof of vaccination (but is vulnerable to forgery and counterfeiting, and thus not a verifiable proof of vaccination), the United States does not have a federal framework for a digital vaccine passport, and federal officials explicitly ruled out doing so, citing privacy and human rights concerns. This leaves their implementations up to individual states and territories. Prior to the issue becoming politicised, public views on vaccine passports were evenly split and the divide crossed, rather than followed, political and ideological lines. Since then, criticism and conspiracy theories surrounding the vaccines in general, and in turn vaccine mandates, largely came from the political right; for example, U.S. representative for Georgia's 14th congressional district Marjorie Taylor Greene, a Republican, asserted that requesting the disclosure of one's vaccine status was a violation of data privacy rules for the health care industry, even though said rules only apply to entities such as health insurers. The state governments of California, Hawaii, Louisiana, New York, North Carolina, Delaware, and Virginia have each rolled out mechanisms where residents can choose to receive proof of COVID-19 vaccination in the form of a scannable QR code by linking to records within each state's immunization registry. Illinois has a Vax Verify website, where residents can download proof of COVID-19 vaccination for businesses that require it. In New Jersey, residents can obtain a digital COVID-19 vaccination record through its mobile app Docket; Governor Phil Murphy specifically avoided using the term "vaccine passport" to describe the service. Each state credential has varying degrees of interoperability with other state and foreign governments; some states have closed systems, with QR
|
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"page_id": 68750333,
"source": null,
"title": "Vaccine passports during the COVID-19 pandemic"
}
|
codes that are only usable within the issuing state, and others have broad interoperability, with New York offering both types of credentials for its residents. Arizona, Maryland, Mississippi, North Dakota, Washington, West Virginia, Puerto Rico, and the District of Columbia have contracted with the organization MyIR that interfaces with governmental vaccination records to produce a PDF proof of vaccination, but has also moved toward scannable QR codes. Health departments in Indiana, Colorado, and Georgia can provide proof of vaccination in PDF form but not via a QR code. At least 20 states have prohibited public agencies from issuing or requiring a vaccine passport, while Alabama, Florida, Iowa, Montana, and Texas also made it illegal for any private entity to request proof of vaccination as a condition of service, under the assertion that they discriminate against those who have made a personal choice to not receive the vaccine. ===== Los Angeles County ===== Los Angeles County began a proof of vaccination system for indoor bars, restaurants, venues and nightclubs on 7 October 2021. ===== New York City ===== New York City began its Excelsior Pass or Key to NYC vaccine passport system for dining, fitness, events and indoor entertainment on 13 September 2021. ===== New Orleans ===== New Orleans began to require proof of vaccination or a negative test to enter indoor bars, restaurants, events, fitness, and sporting events on 16 August 2021. === South America === ==== Brazil ==== In December 2020, the Brazilian Senate approved a document giving digital proof of all vaccinations – not just those in respect of COVID-19. However, the urgency for creating such a digital proof of vaccination came from the COVID-19 pandemic. ==== Chile ==== In May 2021, then Health Ministry Subsecretary, Paula Daza, mandated the "mobility pass" (pase de movilidad) in gyms, restaurants
|
{
"page_id": 68750333,
"source": null,
"title": "Vaccine passports during the COVID-19 pandemic"
}
|
and swimming pools. This document was given to people with two doses of the COVID-19 vaccine, later it was upscaled to three doses and later on in the same year four doses were required, being one of the most drastic vaccines passports in the world. Chile is the only country in the world with entry procedures such as requiring homologation of vaccines to travel to. === Oceania === ==== New Zealand ==== On 17 November 2021, the New Zealand Government launched a vaccine certificate called My Vaccine Pass for individuals who have been vaccinated against COVID-19. The vaccine pass is required to enter hospitality venues, community, sport and faith-based gatherings as defined by the COVID-19 Protection Framework. They came into force on 29 November 2021. On 23 November, the New Zealand Government launched the NZ Pass Verifier to scan the passes. On April 5, 2022, vaccine passes will no longer be required for most venues. On June 1, 2022, all vaccine passes will become invalid, and will no longer be required for any venue. == Arguments and controversy == As of September 2021, the World Health Organization (WHO) acknowledged that mandatory COVID-19 vaccine passports would be discriminatory against countries with little access to vaccinations, but could eventually be considered for international travel when vaccine access improves. === Effect on vaccine uptake === In some jurisdictions, vaccine uptake increased after various levels of governments announced plans to mandate their use. === Ethical and social issues === The ethical issues that arise in the acceptability of vaccine passports revolve around the policy objectives and the intended use. The public health restriction on implementing vaccine passports limits the freedom of an individual to perform social activities. People who are privileged to receive the vaccination will have gained access to going back to normal
|
{
"page_id": 68750333,
"source": null,
"title": "Vaccine passports during the COVID-19 pandemic"
}
|
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