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匹配条件: “Ognyan B. Todorov” ,找到相关结果约144137条。
Vertical Distribution of Species of the Subfamily Aphidiinae (Hymenoptera: Bracondae) from the Southwestern Bulgaria
Ognyan B. Todorov
Ecologia Balkanica , 2012,
Abstract: The vertical spreading of some species of the subfamily of Aphidiinae (Braconidae) from Southwest Bulgaria was investigated during the period 2002 – 2005. The research was carried out for four out of the six vegetation zones which are typical for this region: Xerothermic oak woods, Mesophyll oak woods, Beech woods, Coniferous woods, Subalpine sparse woods.
General conditions for approximate quantum error correction and near-optimal recovery channels
Cédric Bény,Ognyan Oreshkov
Physics , 2009, DOI: 10.1103/PhysRevLett.104.120501
Abstract: We derive necessary and sufficient conditions for the approximate correctability of a quantum code, generalizing the Knill-Laflamme conditions for exact error correction. Our measure of success of the recovery operation is the worst-case entanglement fidelity of the overall process. We show that the optimal recovery fidelity can be predicted exactly from a dual optimization problem on the environment causing the noise. We use this result to obtain an easy-to-calculate estimate of the optimal recovery fidelity as well as a way of constructing a class of near-optimal recovery channels that work within twice the minimal error. In addition to standard subspace codes, our results hold for subsystem codes and hybrid quantum-classical codes.
Enantioresolution of a Series of Chiral Benzyl Alcohols by HPLC on a Dinitrobenzoylphenylglycine Stationary Phase after Achiral Pre-Column Derivatization*  [PDF]
Svilen P. Simeonov, Anton P. Simeonov, Aleksandar R. Todorov, Vanya B. Kurteva
American Journal of Analytical Chemistry (AJAC) , 2010, DOI: 10.4236/ajac.2010.11001
Abstract: High performance liquid chromatography method for the separation of a series of chiral benzyl alcohols on N-(3,5-dinitrobenzoyl)-D-phenylglycine stationary phase (Macherey Nagel, Chiral-2) after pre-column achiral derivatization was developed. Cheap and easy available aromatic acid chlorides were used as derivatization agents. Good to excellent separations of the enantiomers were achieved in all cases in relatively short analytical runs. It was shown that the enantiorecognition depends on the substituents both in the starting alcohol and in the acid chloride. The method presents an efficient alternative to the direct analyses on polysaccharide and cyclodextrine-derived stationary phases.
Geometric Integrability of Some Generalizations of the Camassa-Holm Equation
Ognyan Christov
International Journal of Differential Equations , 2011, DOI: 10.1155/2011/738509
Abstract: We study the Camassa-Holm (CH) equation and recently introduced μCH equation from the geometric point of view. We show that Kupershmidt deformations of these equations describe pseudospherical surfaces and hence are geometrically integrable.
Records of Oedemeridae (Insecta: Coleoptera) species from Strandzha Mountain (Bulgaria and Turkey)
Ognyan Sivilov
ZooNotes , 2012,
Abstract: A list of 16 species from 5 genera of the family Oedemeridae and their localities in Strandzha Mountain was presented, five from which were reported for the first time to this mountain.
First record of Iphthiminus italicus (Coleoptera, Tenebrionidae) in Bulgaria
Ognyan Sivilov
ZooNotes , 2012,
Abstract: Iphthiminus italicus croaticus (Truqui, 1857) is reported from Bulgaria for the first time. Genus Iphthiminus Spilman, 1973 is also new to the Bulgarian fauna.
Journal of Engineering Studies and Research , 2012,
Abstract: The aim of this study is to justify a generalized basis model for investigating, evaluating and comparing the energy efficiency of the individual and the grouped mechanical handling machines and systems. Based on a conducted analysis and developed model technological schemes of the systems for continuous transport, dependencies are drawn for determining the basis power and minimizing the potential energy losses in loads passages, the losses of height and potential energy in the systems' auxiliary elements as well as the total energy losses. Additional indices for basis evaluation of the energy efficiency of the continuous-transport-systems technological schemes, regardless of the systems' type and scope, are developed and systematized.
Holonomic quantum computation in subsystems
Ognyan Oreshkov
Physics , 2009, DOI: 10.1103/PhysRevLett.103.090502
Abstract: We introduce a generalized method of holonomic quantum computation (HQC) based on encoding in subsystems. As an application, we propose a scheme for applying holonomic gates to unencoded qubits by the use of a noisy ancillary qubit. This scheme does not require initialization in a subspace since all dynamical effects factor out as a transformation on the ancilla. We use this approach to show how fault-tolerant HQC can be realized via 2-local Hamiltonians with perturbative gadgets.
Topics in quantum information and the theory of open quantum systems
Ognyan Oreshkov
Physics , 2008,
Abstract: This thesis examines seven topics in the areas of deterministic open-quantum-system dynamics, quantum measurements, and quantum error correction (QEC). The first topic concerns weak measurements and their universality as a means of generating quantum operations. It is shown that every generalized measurement can be implemented as a sequence of weak (infinitesimal) measurements. The second topic is an application of this result to the theory of entanglement. Necessary and sufficient differential conditions for entanglement monotones are derived and are used to find a new entanglement monotone for three-qubit states. The third topic is a study of the performance of different master equations for the description of non-Markovian dynamics. The system studied is a qubit coupled to a spin bath via the Ising interaction. The fourth topic investigates continuous QEC in the presence of non-Markovian noise. It is shown that due to the existence of a Zeno regime in non-Markovian dynamics, the performance of continuous QEC exhibits a quadratic improvement for a sufficiently high time resolution of the error-correcting operations. The fifth topic studies the conditions for correctability of subsystem codes under continuous dynamics. Necessary and sufficient conditions on the Lindbladian and the system-environment Hamiltonian are derived. The sixth topic examines the robustness of operator QEC codes against initialization errors. A new measure of fidelity for encoded information is introduced and is used to show that operator codes are robust against imperfect initialization without the need for restriction of the standard operator QEC conditions. The last topic concerns holonomic quantum computation (HQC) and stabilizer codes. A fault-tolerant scheme for HQC is presented, proving the scalability of the holonomic approach.
Robustness of operator quantum error correction with respect to initialization errors
Ognyan Oreshkov
Physics , 2007, DOI: 10.1103/PhysRevA.77.032333
Abstract: In the theory of operator quantum error correction (OQEC), the notion of correctability is defined under the assumption that states are perfectly initialized inside a particular subspace, a factor of which (a subsystem) contains the protected information. If the initial state of the system does not belong entirely to the subspace in question, the restriction of the state to the otherwise correctable subsystem may not remain invariant after the application of noise and error correction. It is known that in the case of decoherence-free subspaces and subsystems (DFSs) the condition for perfect unitary evolution inside the code imposes more restrictive conditions on the noise process if one allows imperfect initialization. It was believed that these conditions are necessary if DFSs are to be able to protect imperfectly encoded states from subsequent errors. By a similar argument, general OQEC codes would also require more restrictive error-correction conditions for the case of imperfect initialization. In this study, we examine this requirement by looking at the errors on the encoded state. In order to quantitatively analyze the errors in an OQEC code, we introduce a measure of the fidelity between the encoded information in two states for the case of subsystem encoding. A major part of the paper concerns the definition of the measure and the derivation of its properties. In contrast to what was previously believed, we obtain that more restrictive conditions are not necessary neither for DFSs nor for general OQEC codes. This is because the effective noise that can arise inside the code as a result of imperfect initialization is such that it can only increase the fidelity of an imperfectly encoded state with a perfectly encoded one.

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