Boundary Friction on Molecular Lubricants: Rolling Mode?

A theoretical model is proposed for low temperature friction between two smooth rigid solid surfaces separated by lubricant molecules, admitting their deformations and rotations. Appearance of different modes of energy dissipation (by ''rocking'' or ''rolling'' of lubricants) at slow relative displacement of the surfaces is shown to be accompanied by the stick-and-slip features and reveals a non-monotonic (mean) friction force {\it vs} external loadComment: revtex4, 4 pages, 5 figure

On the theory of high-TcT_\text{c} superconductivity of doped cuprates

A theoretical analysis is presented on possible effects of disorder by dopants in high-temperature superconducting cuprate perovskites, to define their basic spectra of spin and electronic excitations, and the subsequent observable properties, especially doping dependence of superconducting order parameter. The central point in the proposed physical picture is formation of specific impurity subband within the insulating bandgap of initial undoped material, serving as a source for the system metallization and further transition into superconducting state with anisotropic order parameter.Comment: 20 pages, 11 figure

ІНФОРМАЦІЙНО–АНАЛІТИЧНЕ ЗАБЕЗПЕЧЕННЯ ОЦІНЮВАННЯ В ЕКОНОМІЧНІЙ БЕЗПЕКОЛОГІЇ МІКРОРІВНЯ

One of the subject areas in economic security studies (a new direction in management science) is an assessment. Estimates of a particular object will most significantly reflect its state in case there is an information analytical support. Information analytical assessment provision in economic security studies must meet assessment information needs by providing such resource as indicators, using which it will be possible to have a high–quality economic security estimates of the objects selected for assessment. The indicators selection and further operations with them using the assessment methods to get the objects estimates in mіcrolevel economic security studies is performed taking into account an object of assessment, a research context of economic security, quality estimates requirements, availability and accessibility of information for determining values of indicators, estimates character (retrospective, current, predictive). There are some examples of indicators and methods of the objects assessment in the microlevel economic security studies considered that are eligible for assessment in a protective context of an enterprise economic security.Одной из предметных областей в науке об экономической безопасности (новое  направление в управленческой науке) является оценивание. Оценки конкретного объекта максимально достоверно будут отображать его состояние в случае наличия информационно–аналитического обеспечения. Информационно–аналитическое обеспечение оценивания в науке об экономической безопасности должно удовлетворять информационные потребности оценивания путем предоставления такого ресурса, как показатели, на основе которых можно получить качественные оценки экономической безопасности выбранных объектов оценивания. Выбор показателей и дальнейшие операции с ними с применением методов оценивания для получения оценок объектов в науке об экономической безопасности на микроуровне осуществляется с учетом объекта оценивания, контексты исследования экономической безопасности, требований к качеству оценок,  наличия и доступности информации для определения значений показателей, характера оценок (ретроспективные, текущие или прогнозные).  Как пример, представлено некоторые показатели и методы оценивания объектов в науке об экономической безопасности на микроуровне, которые подходят для оценивания в защитном контексте экономической безопасности предприятия.Однією з предметних областей в економічній безпекології (новий напрям в управлінській науці) є оцінювання. Оцінки конкретного об’єкта максимально достовірно будуть відображати його стан за наявності інформаційно–аналітичного забезпечення. Інформаційно–аналітичне забезпечення оцінювання в економічній безпекології має задовольнити інформаційні потреби оцінювання шляхом надання такого ресурсу як показники, з використанням яких можна отримати якісні оцінки економічної безпеки вибраних об’єктів оцінювання. Вибір показників та подальші операції з ними за допомогою методів оцінювання для отримання оцінок об’єктів в економічній безпекології макрорівня здійснюються з урахуванням об’єкта оцінювання, контексту дослідження економічної безпеки, вимог до якості оцінок, наявності та доступності інформації для визначення значень показників, характеру оцінок (ретроспективні, поточні, прогнозні). Як приклад надано деякі показники та методи оцінювання об’єктів в економічній безпекології мікрорівня, які придатні для оцінювання у захисному контексті економічної безпеки підприємства

Star Unfolding Convex Polyhedra via Quasigeodesic Loops

We extend the notion of star unfolding to be based on a quasigeodesic loop Q rather than on a point. This gives a new general method to unfold the surface of any convex polyhedron P to a simple (non-overlapping), planar polygon: cut along one shortest path from each vertex of P to Q, and cut all but one segment of Q.Comment: 10 pages, 7 figures. v2 improves the description of cut locus, and adds references. v3 improves two figures and their captions. New version v4 offers a completely different proof of non-overlap in the quasigeodesic loop case, and contains several other substantive improvements. This version is 23 pages long, with 15 figure

Transport Processes in Metal-Insulator Granular Layers

Tunnel transport processes are considered in a square lattice of metallic nanogranules embedded into insulating host to model tunnel conduction in real metal/insulator granular layers. Based on a simple model with three possible charging states ($\pm$, or 0) of a granule and three kinetic processes (creation or recombination of a $\pm$ pair, and charge transfer) between neighbor granules, the mean-field kinetic theory is developed. It describes the interplay between charging energy and temperature and between the applied electric field and the Coulomb fields by the non-compensated charge density. The resulting charge and current distributions are found to be essentially different in the free area (FA), between the metallic contacts, or in the contact areas (CA), beneath those contacts. Thus, the steady state dc transport is only compatible with zero charge density and ohmic resistivity in FA, but charge accumulation and non-ohmic behavior are \emph{necessary} for conduction over CA. The approximate analytic solutions are obtained for characteristic regimes (low or high charge density) of such conduction. The comparison is done with the measurement data on tunnel transport in related experimental systems.Comment: 10 pages, 11 figures, 1 reference corrected, acknowlegments adde

Specifics of impurity effects in ferropnictide superconductors

Effects of impurities and disorder on quasiparticle spectrum in superconducting iron pnictides are considered. Possibility for occurrence of localized energy levels due to impurities within the superconducting gap and the related modification of band structure and of superconducting order parameter are discussed. The evolution of superconducting state with impurity doping is traced.Comment: 9 pages, 8 figure

Low-temperature orientational order and possible domain structures in C(_{60}) fullerite

Based on a simple model for ordering of hexagons on square planar lattice, an attempt has been made to consider possible structure of C(_{60}) fullerite in its low temperature phase. It is shown that hexagons, imitating fullerens oriented along (C_{3}) axes of \emph{sc} lattice, can be ordered into an ideal structure with four non-equivalent molecules in unit cell. Then the energy degeneracy for each hexagon rotations by (\pi /3) around its (C_{3}) axis leaves the translational and orientational order in this structure, but leads to a random distribution of (\pi /3) rotations and hence to {}``averaged{}'' unit cell with two molecules. However the most relevant structural defects are not these intrinsic \char`\"{}misorientations\char`\"{} but certain walls between the domains with different sequencies of the above-mentioned two (non-ideal) sublattices. Numeric estimates have been made for the anisotropic inter-molecular potential showing that the anisotropy is noticeably smaller for molecules in walls than in domains

Quantum effects for ballistic transport in spintronic devices

Recent fabrication of atomic precision nanodevices for spintronics greatly boosted their performance and also revealed new interesting features, as oscillating magnetoresistance with number of atomic layers in a multilayered structure. This motivates the need to go beyond the usual theoretical approach of semi-classical continuous layers. Here the simple tight-binding dynamics is used to describe quantum conduction in a multicomponent system with spin-polarized electrodes separated by an ultrathin and atomically coherent non-magnetic spacer (either metallic or insulating). A possibility is indicated for obtaining a huge resonant enhancement of magnetoresistance in such device by a special choice of gate voltage on the spacer element.Comment: 9 pages, 9 figure

Remarks on the tight-binding model of graphene

We address a simple but fundamental issue arising in the study of graphene, as well as of other systems that have a crystalline structure with more than one atom per unit cell. For these systems, the choice of the tight-binding basis is not unique. For monolayer graphene two bases are widely used in the literature. While the expectation values of operators describing physical quantities should be independent of basis, the form of the operators may depend on the basis, especially in the presence of disorder or of an applied magnetic field. Using the inappropriate form of certain operators may lead to erroneous physical predictions. We discuss the two bases used to describe monolayer graphene, as well as the form of the most commonly used operators in the two bases. We repeat our analysis for the case of bilayer graphene.Comment: 15 pages, 4 figure