Nonlinear acoustic waves in channels with variable cross sections

The point symmetry group is studied for the generalized Webster-type equation describing non-linear acoustic waves in lossy channels with variable cross sections. It is shown that, for certain types of cross section profiles, the admitted symmetry group is extended and the invariant solutions corresponding to these profiles are obtained. Approximate analytic solutions to the generalized Webster equation are derived for channels with smoothly varying cross sections and arbitrary initial conditions.Comment: Revtex4, 10 pages, 2 figure. This is an enlarged contribution to Acoustical Physics, 2012, v.58, No.3, p.269-276 with modest stylistic corrections introduced mainly in the Introduction and References. Several typos were also correcte

Universal Model of Finite-Reynolds Number Turbulent Flow in Channels and Pipes

In this Letter we suggest a simple and physically transparent analytical model of the pressure driven turbulent wall-bounded flows at high but finite Reynolds numbers Re. The model gives accurate qualitative description of the profiles of the mean-velocity and Reynolds-stresses (second order correlations of velocity fluctuations) throughout the entire channel or pipe in the wide range of Re, using only three Re-independent parameters. The model sheds light on the long-standing controversy between supporters of the century-old log-law theory of von-K\`arm\`an and Prandtl and proposers of a newer theory promoting power laws to describe the intermediate region of the mean velocity profile.Comment: 4 pages, 6 figs, re-submitted PRL according to referees comment

Determination of the electric field strength of high-voltage substations

The electric field strength is one of the main factors influencing sensitive microprocessor equipment and personnel on power stations and substations, power lines. Determining its level is an important applied task for ensuring the safe operation of electrical installations. The aim is to develop calculation relationships for determining the electric field strength created by the busbar of high-voltage substations in the working areas of personnel. The solution of the problem was based on the use of the method of equivalent charges to determine the strength of the electric field created by the complex busbar of high-voltage substations. Methodology. The development was based on solving the problem of the potential of the electric field of a point charge located in a dielectric half-space for a cylindrical coordinate system. By representing the electrode in the form of a set of point charges and subsequent integration, an expression for calculating the potential is obtained, created by a busbar of arbitrary orientation of finite length in an analytical form. Using the principle of superposition of fields and the definition of the derivative, expressions were obtained for calculating the vertical component of the electric field strength at given heights. Results. Based on the obtained expressions, using Visual Basic, the simulation of the distribution of the electric field strength under a three-phase power line with a voltage of 150 kV was performed. Comparison with the known calculation results obtained on the basis of analytical expressions for infinitely long conductors showed that the obtained expressions have an error of no more than 7%. The scientific novelty lies in the fact that for the first time expressions were obtained for determining the electric field strength created by a system of electrodes of finite length, based on the analytical method for solving differential equations. Practical significance. The proposed technique is implemented as a test module of the LiGro specialized software package, which allows modeling complex busbar systems typical for power stations and substations and power lines. A test calculation was carried out for an operating substation of regional electric networks with a voltage class of 110 kV. By comparing the duration of the calculation of switchgears with a diagonal of about 500 m, it was found that the calculation time in the LiGro complex based on the analytical method is several tens of times less than the calculation based on the finite element method. In addition, a more powerful computer was used for the end element simulation.В електричних станціях та підстанціях, лініях електропередачі напруженість електричного поля є одним з головних факторів впливу на чутливе мікропроцесорне обладнання та персонал. Визначення її рівня є важливою прикладною задачею для забезпечення безпечної експлуатації електроустановок. Мета роботи – розробка розрахункових співвідношень для визначення напруженості електричного поля, що створюється ошиновкою високовольтних підстанцій в робочих зонах персоналу. Розв'язання задачі базувалося на використанні методу еквівалентних зарядів для визначення напруженості електричного поля, створюваного складною ошиновкою високовольтних підстанцій. Методика. В основу розробки покладено розв’язання задачі про потенціал електричного поля точкового заряду, розташованого в діелектричному наппівпросторі, для циліндричної системи координат. Шляхом представлення електроду у вигляді множини точкових зарядів та подальшого інтегрування отримано вираз для розрахунку потенціалу, що створений ошиновкою довільної орієнтації кінцевої довжини в аналітичному вигляді. Використовуючи принцип суперпозиції полів і визначення похідної, отримано вирази для розрахунку вертикальної складової напруженості електричного поля на заданих висотах. Результати. На основі отриманих виразів за допомогою Visual Basic виконано моделювання розподілу напруженості електричного поля під трифазною лінією електропередачі напругою 150 кВ. Порівняння з відомими результатами розрахунків, отриманими на основі аналітичних виразів для нескінченно довгих провідників, показало, що отримані вирази мають похибку не більше 7%. Наукова новизна полягає в тому, що вперше отримано вирази для визначення напруженості електричного поля, створюваного системою електродів скінченної довжини, на основі аналітичного методу розв’язування диференціальних рівнянь. Практична значимість. Запропонований спосіб реалізовано у вигляді тестового модулю спеціалізованого програмного комплексу LiGro, що дозволяє виконувати моделювання складних систем ошиновок, характерних для електричних станцій та підстанцій і ліній електропередачі. Виконано тестовий розрахунок для діючої підстанції регіональних електричних мереж класом напруги 110 кВ. Шляхом порівняння тривалості розрахунку розподільчих пристроїв з діагоналлю близько 500 м встановлено, що час розрахунку в комплексі LiGro на основі аналітичного методу в декілька десятків разів менший, ніж розрахунок на основі методу кінцевих елементів. Крім того, для моделювання методом кінцевих елементів використовувався комп’ютер з більш потужними характеристиками

Very high frequency gravitational wave background in the universe

Astrophysical sources of high frequency gravitational radiation are considered in association with a new interest to very sensitive HFGW receivers required for the laboratory GW Hertz experiment. A special attention is paid to the phenomenon of primordial black holes evaporation. They act like black body to all kinds of radiation, including gravitons, and, therefore, emit an equilibrium spectrum of gravitons during its evaporation. Limit on the density of high frequency gravitons in the Universe is obtained, and possibilities of their detection are briefly discussed.Comment: 14 page

Energy Spectra of Quantum Turbulence: Large-scale Simulation and Modeling

In $2048^3$ simulation of quantum turbulence within the Gross-Pitaevskii equation we demonstrate that the large scale motions have a classical Kolmogorov-1941 energy spectrum E(k) ~ k^{-5/3}, followed by an energy accumulation with E(k) ~ const at k about the reciprocal mean intervortex distance. This behavior was predicted by the L'vov-Nazarenko-Rudenko bottleneck model of gradual eddy-wave crossover [J. Low Temp. Phys. 153, 140-161 (2008)], further developed in the paper.Comment: (re)submitted to PRB: 5.5 pages, 4 figure

STAPHYLOCOCCAL INFECTION IN DOGS (DIAGNOSIS, TREATMENT AND PREVENTION)

The paper provides characteristics of diagnostic methods, treatment and preventive measures for staphylococcal infection in dogs. Staphylococcal infection in dogs is an infectious disease caused primarily by staphylococcus virulent strains, characterized by various clinical forms, and it affects the dogs having defects in their immune system. Staphylococci produce a great number of pathogenicity factors (including toxins able to act independently). Therefore, it is rather difficult to apply tools of specific protection and prophylaxis. Skin and mucosa inflammation is the most common pathological condition observed in dogs. Clinical signs include: chronic septic condition with internal abscesses, different skin lesions accompanied by conjunctivitis, otitis, vulvitis, posthitis, rhinitis, sinusitis, cystitis, phlegmon, abscesses, pyometra, wound abscess, polyarthritis, gingivitis. In addition to the pathological agent, the following extra factors are needed for the disease clinical manifestation: immune deficiency, metabolic disorder, parasitic disease, manipulations resulting in damage to the skin and mucosa integrity. The fact that domestic animals can be a source of infection for people can be another reason behind an increasing interest in staphylococcal infection. A comprehensive approach is required to diagnose this disease. In addition to clinical examination, the following tests are needed biochemical blood test, bacteriological tests of biomaterials from animals, isolation of pure agent cultures and determination of sensitivity to antibacterial preparations in every particular case. Bacteriological tests are mandatory to make the final diagnosis. Treatment of dogs also requires a comprehensive approach including specific immunotherapy (active, with the use of anatoxins and antigens and passive with antistaphylococcal hyperimmune sera). Timely prevention and new approaches to treatment are crucial elements

Geophysical studies with laser-beam detectors of gravitational waves

The existing high technology laser-beam detectors of gravitational waves may find very useful applications in an unexpected area - geophysics. To make possible the detection of weak gravitational waves in the region of high frequencies of astrophysical interest, ~ 30 - 10^3 Hz, control systems of laser interferometers must permanently monitor, record and compensate much larger external interventions that take place in the region of low frequencies of geophysical interest, ~ 10^{-5} - 3 X 10^{-3} Hz. Such phenomena as tidal perturbations of land and gravity, normal mode oscillations of Earth, oscillations of the inner core of Earth, etc. will inevitably affect the performance of the interferometers and, therefore, the information about them will be stored in the data of control systems. We specifically identify the low-frequency information contained in distances between the interferometer mirrors (deformation of Earth) and angles between the mirrors' suspensions (deviations of local gravity vectors and plumb lines). We show that the access to the angular information may require some modest amendments to the optical scheme of the interferometers, and we suggest the ways of doing that. The detailed evaluation of environmental and instrumental noises indicates that they will not prevent, even if only marginally, the detection of interesting geophysical phenomena. Gravitational-wave instruments seem to be capable of reaching, as a by-product of their continuous operation, very ambitious geophysical goals, such as observation of the Earth's inner core oscillations.Comment: 29 pages including 8 figures, modifications and clarifications in response to referees' comments, to be published in Class. Quant. Gra