Numerical study of vortex system quantum melting

We report a numerical study of the vortex system in the two dimensional II-type superconductors. We have proposed a phenomenological model that takes into account quantum fluctuations of Abrikosov's vortices. The results of the quantum Monte-Carlo simulations by the SSE algorithm show that the thermal fluctuations are dominated by quantum fluctuations at low temperatures. In particular, we demonstrate the possibility of the quantum melting transition for vortex system in the temperature region where thermal melting transition is improbable

Blue luminescence of Au nanoclusters embedded in silica matrix

Photoluminescence study using the 325 nm He-Cd excitation is reported for the Au nanoclusters embedded in SiO2 matrix. Au clusters are grown by ion beam mixing with 100 KeV Ar+ irradiation on Au [40 nm]/SiO2 at various fluences and subsequent annealing at high temperature. The blue bands above ~3 eV match closely with reported values for colloidal Au nanoclusters and supported Au nanoislands. Radiative recombination of sp electrons above Fermi level to occupied d-band holes are assigned for observed luminescence peaks. Peaks at 3.1 eV and 3.4 eV are correlated to energy gaps at the X- and L-symmetry points, respectively, with possible involvement of relaxation mechanism. The blue shift of peak positions at 3.4 eV with decreasing cluster size is reported to be due to the compressive strain in small clusters. A first principle calculation based on density functional theory using the full potential linear augmented plane wave plus local orbitals (FP-LAPW+LO) formalism with generalized gradient approximation (GGA) for the exchange correlation energy is used to estimate the band gaps at the X- and L-symmetry points by calculating the band structures and joint density of states (JDOS) for different strain values in order to explain the blueshift of ~0.1 eV with decreasing cluster size around L-symmetry point.Comment: 13 pages, 7 Figures Only in PDF format; To be published in J. of Chem. Phys. (Tentative issue of publication 8th December 2004

Universal SSE algorithm for Heisenberg model and Bose Hubbard model with interaction

We propose universal SSE method for simulation of Heisenberg model with arbitrary spin and Bose Hubbard model with interaction. We report on the first calculations of soft-core bosons with interaction by the SSE method. Moreover we develop a simple procedure for increase efficiency of the algorithm. From calculation of integrated autocorrelation times we conclude that the method is efficient for both models and essentially eliminates the critical slowing down problem.Comment: 6 pages, 5 figure

poST

Publisher Copyright: AuthorThis paper presents the core concepts for the poST language - a process-oriented extension of the IEC 61131-3 Structured Text (ST) language which intends to provide a conceptual consistency of the PLC source code with technological description of the plant operating procedure. The poST can be seamlessly used as a textual programming language for complex PLC software in the context of IEC 61131-3 (3rd Edition). The language combines the advantages of FSM-based programming with the conventional syntax of the ST language which would facilitate its adoption. The poST language assumes that a poST-program is a set of weakly connected concurrent processes, structurally and functionally corresponding to the technological description of the plant. Each process is specified by a sequential set of states. The states are specified by a set of the ST constructs, extended by TIMEOUT operation, SET STATE operation, and START / STOP / check state operations to communicate with other processes. The paper describes the basic syntax of the poST language, demonstrates the usage of the poST language by developing control software for an elevator, and compares the development in poST with pure Structured Text.Peer reviewe

Test of a simple and flexible S8 model molecule in alpha-s8 crystals

Alpha S8 is the most stable crystalline form, at ambient pressure and temperature (STP), of elemental sulfur. In this paper we analyze the zero pressure low temperature part of the phase diagram of this crystal, in order to test a simple and flexible model molecule. The calculations consist in a series of molecular dynamics (MD) simulations, performed in the constant pressure- constant temperature ensemble. Our calculations show that this model, that gives good results for three crystalline phases at STP and T>~300 K, fails at low temperatures, predicting a structural phase transition at 200 K where there should be none.Comment: 6 pages, 4 figures, submitted to Chem. Phys. Lett, a figure change

Temporal Logic for Programmable Logic Controllers

We address the formal verification of the control software of critical systems, i.e., ensuring the absence of design errors in a system with respect to requirements. Control systems are usually based on industrial controllers, also known as Programmable Logic Controllers (PLCs). A specific feature of a PLC is a scan cycle: 1) the inputs are read, 2) the PLC states change, and 3) the outputs are written. Therefore, in order to formally verify PLC, e.g., by model checking, it is necessary to describe the transition system taking into account this specificity and reason both in terms of state transitions within a cycle and in terms of larger state transitions according to the scan-cyclic semantics. We propose a formal PLC model as a hyperprocess transition system and temporal cycle-LTL logic based on LTL logic for formulating PLC property. A feature of the cycle-LTL logic is the possibility of viewing the scan cycle in two ways: as the effect of the environment (in particular, the control object) on the control system and as the effect of the control system on the environment. For both cases we introduce modified LTL temporal operators. We also define special modified LTL temporal operators to specify inside properties of scan cycles. We describe the translation of formulas of cycle-LTL into formulas of LTL, and prove its correctness. This implies the possibility ofmodel checking requirements expressed in logic cycle-LTL, by using well-known model checking tools with LTL as specification logic, e.g., Spin. We give the illustrative examples of requirements expressed in the cycle-LTL logic

Application of Raman spectroscopy to study the inactivation process of bacterial microorganisms

Raman spectroscopy (RS) is one of the promising approaches for structural and functional studies of various biological objects, including bacterial microorganisms. Both traditional biochemical tests and genetic methods which require expensive reagents, consumables and are time-consuming are used for bacterial analysis. Spectroscopic methods are positioned as noninvasive, highly sensitive, and requiring minimal sample preparation. In this work we investigated the possibility of using the RS method using optical sensors based on gold anisotropic nanoparticles. The applicability of the method was demonstrated by studying the effect of a broad-spectrum cephalosporin antibiotic and an extract of Viburnum opulus L (VO) on Escherichia coli (E. Coli) colonies. The studies were performed by Raman spectroscopy using a Virsa spectrometer (Renishaw). Raman signal amplification was carried out using two original optical sensors proposed by the authors. To create sensors, we used a chemical method of depositing gold nanostars on APTES-modified quartz glasses and a physical method for creating sensors based on anodizing titanium surfaces. The results of the study showed the high sensitivity and information content of the proposed method. The possibility of using the RS method for studying the inactivation of bacterial microorganisms is shown. Spectral Raman bands of E. Coli were determined and identified before and after exposure to VO extract and antibiotic as a control. A decrease in the intensity of spectral modes corresponding to amino acids and purine metabolites was found in the average Raman spectrum of E. Coli after exposure to VO extract. For the first time, a study of the antimicrobial effect of an aqueous extract of VO fruits was carried out by the method of Raman scattering. It has been shown that the use of plant extracts, including VO fruit extracts, to inactivate the vital activity of bacterial colonies is a promising approach to the search for new alternative antibacterial agents. The results obtained are in good agreement with the already known scientific studies and confirm the effectiveness of the proposed method

Методы специализации онтологии процессов, ориентированной на верификацию

User-friendly formal specifications and verification of parallel and distributed systems from various subject fields, such as automatic control, telecommunications, business processes, are active research topics due to its practical significance. In this paper, we present methods for the development of verification-oriented domain-specific process ontologies which are used to describe parallel and distributed systems of subject fields. One of the advantages of such ontologies is their formal semantics which make possible formal verification of the described systems. Our method is based on the abstract verification-oriented process ontology. We use two methods of specialization of the abstract process ontology. The declarative method uses the specialization of the classes of the original ontology, introduction of new declarative classes, as well as use of new axioms system, which restrict the classes and relations of the abstract ontology. The constructive method uses semantic markup and pattern matching techniques to link sublect fields with classes of the abstract process ontology. We provide detailed ontological specifications for these techniques. Our methods preserve the formal semantics of the original process ontology and, therefore, the possibility of applying formal verification methods to the specialized process ontologies. We show that the constructive method is a refinement of the declarative method. The construction of ontology of the typical elements of automatic control systems illustrates our methods: we develop a declarative description of the classes and restrictions for the specialized ontology in the Prot´eg´e system in the OWL language using the deriving rules written in the SWRL language and we construct the system of semantic markup templates which implements typical elements of automatic control systems.Удобная для пользователя формальная спецификация и верификация параллельных и распределённых систем, принадлежащих различным предметным областям, таким как системы автоматического управления, телекоммуникации, бизнес-процессы, являются активными темами исследований в силу их практической значимости. В этой статье мы представляем методы разработки специализированных ориентированных на верификацию онтологий процессов, которые используются для описания параллельных и распределенных систем предметных областей. Одним из преимуществ таких онтологий является их формальная семантика, которая делает возможной формальную верификацию описанных систем. Наш метод основан на абстрактной онтологии процессов, ориентированной на верификацию. Мы используем два метода специализации абстрактной онтологии процессов. Декларативный метод с помощью специализации классов исходной онтологии, введения новых декларативных классов, а также системы аксиом задаёт ограничения для классов и отношений абстрактной онтологии. Конструктивный метод использует техники семантической разметки и сопоставления с образцом, чтобы связать понятия предметной области с классами абстрактной онтологии процессов. Мы даём подробные онтологические спецификации этих техник. Наши методы сохраняют формальную семантику исходной онтологии процессов и, следовательно, возможность применения формальных методов верификации к специализированным онтологиям процессов. Мы показываем, что конструктивный метод является уточнением декларативного метода. Построение онтологии типовых элементов систем автоматического управления иллюстрирует наши методы: разработано декларативное описание классов и ограничений специализированной онтологии в системе Protege на языке OWL с использованием правил вывода на языке SWRL и построена система шаблонов семантической разметки, которая реализует типовые элементы систем автоматического управления

First principles high throughput screening of oxynitrides for water-splitting photocatalysts

In this paper, we present a first principles high throughput screening system to search for new water-splitting photocatalysts. We use the approach to screen through nitrides and oxynitrides. Most of the known photocatalytic materials in the screened chemical space are reproduced. In addition, sixteen new materials are suggested by the screening approach as promising photocatalysts, including three binary nitrides, two ternary oxynitrides and eleven quaternary oxynitrides.United States. Dept. of Energy (contract DE-FG02-96ER4557)National Science Foundation (U.S.) (TeraGrid resources under Grant No. TG-DMR970008S)Pittsburgh Supercomputing CenterUniversity of Texas at Austin. Texas Advanced Computing CenterEni-MIT Solar Frontiers Cente

Темпоральная логика для программируемых логических контроллеров

We address the formal verification of the control software of critical systems, i.e., ensuring the absence of design errors in a system with respect to requirements. Control systems are usually based on industrial controllers, also known as Programmable Logic Controllers (PLCs). A specific feature of a PLC is a scan cycle: 1) the inputs are read, 2) the PLC states change, and 3) the outputs are written. Therefore, in order to formally verify PLC, e.g., by model checking, it is necessary to describe the transition system taking into account this specificity and reason both in terms of state transitions within a cycle and in terms of larger state transitions according to the scan-cyclic semantics. We propose a formal PLC model as a hyperprocess transition system and temporal cycle-LTL logic based on LTL logic for formulating PLC property. A feature of the cycle-LTL logic is the possibility of viewing the scan cycle in two ways: as the effect of the environment (in particular, the control object) on the control system and as the effect of the control system on the environment. For both cases we introduce modified LTL temporal operators. We also define special modified LTL temporal operators to specify inside properties of scan cycles. We describe the translation of formulas of cycle-LTL into formulas of LTL, and prove its correctness. This implies the possibility ofmodel checking requirements expressed in logic cycle-LTL, by using well-known model checking tools with LTL as specification logic, e.g., Spin. We give the illustrative examples of requirements expressed in the cycle-LTL logic.Мы исследуем формальную верификацию управляющего программного обеспечения критических систем, т. е. проверку соответствия функционирования проектируемой системы предъявленным требованиям. Важнейший класс управляющего программного обеспечения составляют программы для программируемых логических контроллеров (ПЛК). Особенностью программ ПЛК является цикл управления: 1) считываются входы, 2) изменяются состояния ПЛК и 3) записываются выходы. Поэтому для формальной верификации программ ПЛК нужна возможность описывать учитывающие эту специфику системы переходов, а также определять свойства систем, моделирующих программы ПЛК, как относительно переходов внутри цикла, так и относительно более крупных переходов в соответствии с семантикой цикла управления. Мы предлагаем формальную модель программы ПЛК как систему переходов гиперпроцессов и темпоральную логику cycle-LTL для формализации свойств ПЛК. Особенностью логики cycle-LTL является возможность рассматривать свойства систем управления двояким образом: воздействие окружения на систему управления и воздействие системы управления на окружение. Мы определяем модификации стандартных темпоральных операторов логики LTL для каждого из этих случаев, а также для свойств внутри цикла управления. Рассмотрены примеры требований, определенных в нашей логике. Описана трансляция формул cycle-LTL в формулы LTL и показана её корректность. Доказана возможность сведения задачи верификации методом проверки моделей для требований, определенных в логике cycle-LTL, к задаче верификации требований, определенных в стандартной логике LTL