Solving the Bose-Hubbard model in new ways

We introduce a new method for analysing the Bose-Hubbard model for an array of bosons with nearest neighbor interactions. It is based on a number-theoretic implementation of the creation and annihilation operators that constitute the model. One of the advantages of this approach is that it facilitates computation with arbitrary accuracy, enabling nearly perfect numerical experimentation. In particular, we provide a rigorous computer assisted proof of quantum phase transitions in finite systems of this type. Furthermore, we investigate properties of the infinite array via harmonic analysis on the multiplicative group of positive rationals. This furnishes an isomorphism that recasts the underlying Fock space as an infinite tensor product of Hecke spaces, i.e., spaces of square-integrable periodic functions that are a superposition of non-negative frequency harmonics. Under this isomorphism, the number-theoretic creation and annihilation operators are mapped into the Kastrup model of the harmonic oscillator on the circle. It also enables us to highlight a kinship of the model at hand with an array of spin moments with a local anisotropy field. This identifies an interesting physical system that can be mapped into the model at hand.Comment: 12 pages, 3 figures; submitte

Electron spin relaxation can enhance the performance of a cryptochrome-based magnetic compass sensor

The radical pair model of the avian magnetoreceptor relies on long‐lived electron spin coherence. Dephasing, resulting from interactions of the spins with their fluctuating environment, is generally assumed to degrade the sensitivity of this compass to the direction of the Earth's magnetic field. Here we argue that certain spin relaxation mechanisms can enhance its performance. We focus on the flavin‐tryptophan radical pair in cryptochrome, currently the only candidate magnetoreceptor molecule. Correlation functions for fluctuations in the distance between the two radicals in Arabidopsis thaliana cryptochrome 1 were obtained from molecular dynamics simulations and used to calculate the spin relaxation caused by modulation of the exchange and dipolar interactions. We find that intermediate spin relaxation rates afford substantial enhancements in the sensitivity of the reaction yields to an Earth‐strength magnetic field. Supported by calculations using toy radical pair models, we argue that these enhancements could be consistent with the molecular dynamics and magnetic interactions in avian cryptochromes

Modification of niobium surfaces using plasma electrolytic oxidation in silicate solutions

Herein, a study of the plasma electrolytic oxidation (PEO) of niobium in an anodising bath composed of potassium silicate (K2SiO3) and potassium hydroxide (KOH) is reported. The effects of the K2SiO3 concentration in the bath and the process voltage on the characteristics of the obtained oxide layers were assessed. Compact, barrier-type oxide layers were obtained when the process voltage did not exceed the breakdown potential of the oxide layer. When this threshold was breached, the morphology of the oxide layer changed markedly, which is typical of PEO. A significant amount of silicon, in the form of amorphous silica, was incorporated into the oxide coatings under these conditions compared with the amount obtained with conventional anodising. This surface modification technique led to an improvement in the corrosion resistance of niobium in Ringer’s solution, regardless of the imposed process conditions

An Introduction to Ontologies and Ontology Engineering

In the last decades, the use of ontologies in information systems has become more and more popular in various fields, such as web technologies, database integration, multi agent systems, natural language processing, etc. Artificial intelligent researchers have initially borrowed the word “ontology” from Philosophy, then the word spread in many scientific domain and ontologies are now used in several developments. The main goal of this chapter is to answer generic questions about ontologies, such as: Which are the different kinds of ontologies? What is the purpose of the use of ontologies in an application? Which methods can I use to build an ontology

A practical exploration of ontology interoperability

ISO Common Logic (CL, ISO/IEC 24707:2007) offers the Semantic Web (SW) a new and powerful dimension in achieving the effective discovery, automation, integration, and reuse across applications, data and knowledge. The paper shows how it is possible to explore such interoperability through small scale exemplar projects. As Conceptual Graphs (CG) is a key technology in CL, we focused on the Amine CG software and for the SW we focused on the Protégé OWL software, exploring the possible mappings between ontologies captured in OWL and in Amine. Through this practical exercise the dimensions and extent of the desired interoperability could be demonstrated. This small but significant experiment provided a practical insight into how CG Tools can actually interoperate towards achieving the wider goal of Ontology interoperability between CL and the SW.</p

ВЛИЯНИЕ ТРЕБОВАНИЙ ЭЛЕКТРОМАГНИТНОЙ СОВМЕСТИМОСТИ НА ВЫБОР УСТРОЙСТВ ОГРАНИЧЕНИЯ ПЕРЕНАПРЯЖЕНИЙ ТИПА 1

Reduction of the protection voltage levels of surge protective devices type 1 increased their fulness, enabling their application as the single-stage limiters, eliminating danger created by impulse s and currents. The paper deals with basic properties which the mentioned systems should be \racterized by. The particular attention was paid for the comparison of mentioned proprieties with threats mectric installation and with impulse strength levels of power supply connections of protected devices. pences 4, figures 2.Снижение напряженных уровней защиты устройств ограничивающих перенапряжен повысило га полезность давая возможность их употребления как одноградусных огр элиминирующих угрозу созданную ударными напряжениями и токами. В статье показань особенности которыми должны характеризоваться упомянутые ограничители. Особенное внимали на сравнение упомянутых особеностей с угрозами электропроводки и с уровнями ударной прочно электропитания защищаемых устройств. Библ.4, рис.2.Снижение напряженных уровней защиты устройств ограничивающих перенапряжен повысило га полезность давая возможность их употребления как одноградусных огр элиминирующих угрозу созданную ударными напряжениями и токами. В статье показань особенности которыми должны характеризоваться упомянутые ограничители. Особенное внимали на сравнение упомянутых особеностей с угрозами электропроводки и с уровнями ударной прочно электропитания защищаемых устройств. Библ.4, рис.2