Analytical stripe phase solution for the Hubbard model

The self-consistent solution for the spin-charge solitonic superstructure in quasi-one-dimensional electron system is obtained in the framework of the Hubbard model as a function of a hole doping. Effects of interchain interactions on the ground state are discussed. Results are used for the interpretation of the observed stripe phases in doped antiferromagnets.Comment: 9 pages, LaTex file, no figure

Conductivity in Two-Dimensional Disordered Model with Anisotropic Long-Range Hopping

We consider two-dimensional system of particles localized on randomly distributed sites of squared lattice with anisotropic transfer matrix elements between localized sites. By summing of "diffusion ladder" and "cooperon ladder" type vertices we calculated the conductivity for various sites and particles densities.Comment: Latex, 10 page

МЕТОДИЧНІ АСПЕКТИ ПОКРАЩЕННЯ ПІДГОТОВКИ СТУДЕНТІВ-ВИПУСКНИКІВ З ОРТОПЕДИЧНОЇ СТОМАТОЛОГІЇ ДО ПРАКТИЧНО-ОРІЄНТОВАНОГО ТА ТЕСТОВОГО ЛІЦЕНЗІЙНОГО ІСПИТІВ

The aim of the work – to search for ways to improve quality of knowledge 5th year students specialty “Dentistry”, improvement results of license test exam “KROK-2” and practical-oriented graduation exam. The research is based on the study of scienti c publications dedicated to optimizing educational process and own experience of using individualized approach for 5th year students specialty “Dentistry” to preparation for license test exam “KROK-2” and practical-oriented graduation exam.The main body. The article adduces the expediency and possibility of using methodology for practical training with 5th year students specialty “Dentistry” with practical skills training on phantoms. We proposed individualized approach to preparation for license test exam “KROK-2” and practical-oriented graduation exam. We make input test control at the rst lesson to identify topics, which require additional study. The advantages of memorizing theoretical material during practical work by students  were analyzed.Conclusions. Input test control for students at the rst lesson allows us to draw up plan for their study. The gradual repetition of previous topics make prerequisites for studying intricate topics of orthopedic treatment and patients rehabilitation. It is necessary to devote enough time to self-study of students on phantoms. Practical skills training during work on phantoms helps to prepare for the graduation exam and internship in future.Мета роботи – пошук шляхів підвищення якісної успішності студентів 5 курсу напрямку підготовки “Стоматологія”, поліпшення результатів складання ліцензійного тестового екзамену “КРОК-2” та практично-орієнтованого випускного іспиту. Дослідження базується на вивченні літературних джерел з оптимізації навчального процесу та власному досвіді застосування індивідуалізованого підходу до вивчення ортопедичної стоматології студентами 5 курсу напрямку підготовки “Стоматологія”, підготовки до складання тестового ліцензійного екзамену “КРОК-2” та практично-орієнтованого випускного іспиту.Основна частина. У статті розглянуто доцільність та можливість впровадження методики проведення практичного заняття зі студентами 5 курсу напрямку підготовки “Стоматологія” з відпрацюванням практичних навичок на фантомах та муляжах. Запропоновано індивідуалізований підхід до підготовки студентів для складання ліцензійного тестового екзамену “КРОК-2” та практично-орієнтованого випускного екзамену, що реалізується через проведення вхідного тестового контролю з метою визначення тем, що потребують додаткового вивчення студентами. Проаналізовано переваги закріплення вивченого теоретичного матеріалу запропонованою методикою.Висновки. Проведення на перших заняттях циклу вхідного тестового контролю знань, за результатами якого складається навчальний план студентів, робить можливим індивідуалізувати навчальний процес та покращити підготовку студентів. Поетапне повторення вивченого на попередніх курсах матеріалу створює базу для вивчення складних тем з ортопедичного лікування та реабілітації пацієнтів. Наглядне і теоретичне поєднання фантомів із роз’ясненням дозволяє покращити рівень підготовки з ортопедичної стоматології, дає можливість студентам краще підготуватися до державних іспитів. Необхідно приділяти достатньо часу на самостійне відпрацювання практичних навичок студентами на фантомах, що закріплює попередньо отримані теоретичні знання та сприяє швидшій адаптації до клінічного прийому хворих

Megamaser Disks in Active Galactic Nuclei

Recent spectroscopic and VLBI-imaging observations of bright extragalactic water maser sources have revealed that the megamaser emission often originates in thin circumnuclear disks near the centers of active galactic nuclei (AGNs). Using general radiative and kinematic considerations and taking account of the observed flux variability, we argue that the maser emission regions are clumpy, a conclusion that is independent of the detailed mechanism (X-ray heating, shocks, etc.) driving the collisionally pumped masers. We examine scenarios in which the clumps represent discrete gas condensations (i.e., clouds) and do not merely correspond to velocity irregularities in the disk. We show that even two clouds that overlap within the velocity coherence length along the line of sight could account (through self-amplification) for the entire maser flux of a high-velocity ``satellite'' feature in sources like NGC 4258 and NGC 1068, and we suggest that cloud self-amplification likely contributes also to the flux of the background-amplifying ``systemic'' features in these objects. Analogous interpretations have previously been proposed for water maser sources in Galactic star-forming regions. We argue that this picture provides a natural explanation of the time-variability characteristics of extragalactic megamaser sources and of their apparent association with Seyfert 2-like galaxies. We also show that the requisite cloud space densities and internal densities are consistent with the typical values of nuclear (broad emission-line region-type) clouds.Comment: 55 pages, 7 figures, AASTeX4.0, to appear in The Astrophysical Journal (1999 March 1 issue

Results from Beam Commissioning of an SRF Plug Gun Cavity Photoinjector

Superconducting rf photo electron injectors SRF photoinjectors hold the promise to deliver high brightness, high average current electron beams for future light sources or other applications demanding continuous wave operation of an electron injector. This paper discusses results from beam commissioning of a hybrid SRF photoinjector based on a Pb coated plug and a Nb rf gun cavity for beam energies up to 2.5MeV at Helmholtz Zentrum Berlin HZB . Emittance measurements and transverse phase space characterization with solenoid scan and slitmask methods will be presente

The level of air pollution in the impact zone of coal-fired power plant (Karaganda City) using the data of geochemical snow survey (Republic of Kazakhstan)

Coal-fired power plants emissions impact the air quality and human health. Of great significance is assessment of solid airborne particles emissions from those plants and distance of their transportation. The article presents the results of air pollution assessment in the zone of coal-fired power plant (Karaganda City) using snow survey. Based on the mass of solid airborne particles deposited in snow, time of their deposition on snow at the distance from 0.5 to 4.5 km a value of dust load has been determined. It is stated that very high level of pollution is observed at the distance from 0.5 to 1 km. there is a trend in decrease of dust burden value with the distance from the stacks of coal-fired power plant that may be conditioned by the particle size and washing out smaller ash particles by ice pellets forming at freezing water vapour in stacks of the coal-fired power plant. Study in composition of solid airborne particles deposited in snow has shown that they mainly contain particulates of underburnt coal, Al-Si- rich spheres, Fe-rich spheres, and coal dust. The content of the particles in samples decreases with the distance from the stacks of the coal-fired power plant

Expansion of the R4 Water Maser Arc Near Cepheus A HW 2

We present new (April 2000) MERLIN observations of the H2O masers located near the protostar Cepheus A HW2. The MERLIN observations detect many of the structures found in earlier (1996) VLBA observations of Torrelles and collaborators, and the changed positions of these structures are compatible with the VLBA proper motions and astrometric uncertainties. The radius of curvature of the R4 structure of maser arcs appears to have grown by a factor of two, and the displacement of the arcs between 1996 and 2000 are compatible with expansion about a common center. In addition, the MERLIN observations detect red-shifted masers not previously found; taken with the newly discovered masers, the R4 structure now resembles patchy emission from an elliptical ring. We demonstrate that a simple bow-shock model cannot simultaneously account for the shape and the velocity gradient of the R4 structure. A model involving a slow, hydromagnetic shock propagating into a rotating, circumstellar disk better describes the maser spot kinematics and luminosities. In this model, the central mass is 3 solar masses, and we demonstrate that the mass of the disk is negligible in comparison. The expansion velocity of the post-shock gas, roughly 5 km / s, is slow compared to the average shock velocity (roughly 13 km / s) suggesting that the post-shock gas is magnetically supported with a characteristic field strength of roughly 30 mG. We speculate that the expanding maser rings R4 and R5 may be generated by periodic, instability-driven winds from young stars that periodically send spherical shocks into the surrounding circumstellar material.Comment: 16 pages, 12 figures. Accepted for publication in the Astrophysical Journal. Uses emulateapj5.sty. Updated: removed previews from postscript figures to make them more arxiv-friendl

Experimental study of negative photoconductivity in n-PbTe(Ga) epitaxial films

We report on low-temperature photoconductivity (PC) in n-PbTe(Ga) epitaxial films prepared by the hot-wall technique on -BaF_2 substrates. Variation of the substrate temperature allowed us to change the resistivity of the films from 10^8 down to 10_{-2} Ohm x cm at 4.2 K. The resistivity reduction is associated with a slight excess of Ga concentration, disturbing the Fermi level pinning within the energy gap of n-PbTe(Ga). PC has been measured under continuous and pulse illumination in the temperature range 4.2-300 K. For films of low resistivity, the photoresponse is composed of negative and positive parts. Recombination processes for both effects are characterized by nonexponential kinetics depending on the illumination pulse duration and intensity. Analysis of the PC transient proves that the negative photoconductivity cannot be explained in terms of nonequilibrium charge carriers spatial separation of due to band modulation. Experimental results are interpreted assuming the mixed valence of Ga in lead telluride and the formation of centers with a negative correlation energy. Specifics of the PC process is determined by the energy levels attributed to donor Ga III, acceptor Ga I, and neutral Ga II states with respect to the crystal surrounding. The energy level corresponding to the metastable state Ga II is supposed to occur above the conduction band bottom, providing fast recombination rates for the negative PC. The superposition of negative and positive PC is considered to be dependent on the ratio of the densities of states corresponding to the donor and acceptor impurity centers.Comment: 7 pages, 4 figure

Determination of water content in clay and organic soil using microwave oven

The article deals with the techniques of soil water content determination using microwave radiation. Its practical application would allow solving the problems of resource efficiency in geotechnical survey due to reduction of energy and resource intensity of laboratory analysis as well as its acceleration by means of decreasing labour intensity and, as a result, cost reduction. The article presents a detail analysis of approaches to soil water content determination and soil drying, considers its features and application. The study in soil of different composition, typical for Western Siberia including organic and organic-mineral ones, is a peculiarity of the given article, which makes it rather topical. The article compares and analyzes the results of the investigation into soil water content, which are obtained via conventional techniques and the original one developed by the authors, consisting in microwave drying. The authors also give recommendation on microwave technique application to dry soil

The one dimensional Kondo lattice model at partial band filling

The Kondo lattice model introduced in 1977 describes a lattice of localized magnetic moments interacting with a sea of conduction electrons. It is one of the most important canonical models in the study of a class of rare earth compounds, called heavy fermion systems, and as such has been studied intensively by a wide variety of techniques for more than a quarter of a century. This review focuses on the one dimensional case at partial band filling, in which the number of conduction electrons is less than the number of localized moments. The theoretical understanding, based on the bosonized solution, of the conventional Kondo lattice model is presented in great detail. This review divides naturally into two parts, the first relating to the description of the formalism, and the second to its application. After an all-inclusive description of the bosonization technique, the bosonized form of the Kondo lattice hamiltonian is constructed in detail. Next the double-exchange ordering, Kondo singlet formation, the RKKY interaction and spin polaron formation are described comprehensively. An in-depth analysis of the phase diagram follows, with special emphasis on the destruction of the ferromagnetic phase by spin-flip disorder scattering, and of recent numerical results. The results are shown to hold for both antiferromagnetic and ferromagnetic Kondo lattice. The general exposition is pedagogic in tone.Comment: Review, 258 pages, 19 figure