Surface response of spherical core-shell structured nanoparticle by optically induced elastic oscillations of soft shell against hard core

The optically induced oscillatory response of a spherical two-component, shell-core structured, nanoparticle by nodeless elastic vibrations of soft peripheral shell against hard and dynamically immobile inner core is considered. The eigenfrequencies of the even-parity, spheroidal and odd-parity torsional vibrational modes trapped in the finite-depth shell are obtained which are of practical interest for modal specification of individual resonances in spectra of resonant scattering of long wavelength electromagnetic waves by ultrafine particles.Comment: Surface Review and Letters (World Scientific) Year: 2009 Vol: 16 Issue: 1 (February 2009) Page: 5 - 1

Internet Communication of Volunteers and its Features

The purpose of the article is to analyze the practice of using concepts related to volunteering on the Internet. Particular attention is paid to the reasons for the existence of a conceptual set and the breadth of volunteer activity in the virtual space. Turning to Internet resources allows volunteers not only to transmit information in a high-quality manner, but also to solve specific problems mobilely.Целью статьи является анализ практики использования концепций, связанных с волонтерством в Интернете. Особое внимание уделено причинам существования концептуального набора и широте волонтерской деятельности в виртуальном пространстве. Обращение к ресурсам Интернета позволяет организаторам волонтерства не только качественно передать информацию, но и мобильно решить конкретные задачи

Self-gravitating astrophysical mass with singular central density vibrating in fundamental mode

The fluid-dynamical model of a self-gravitating mass of viscous liquid with singular density at the center vibrating in fundamental mode is considered in juxtaposition with that for Kelvin fundamental mode in a homogeneous heavy mass of incompressible inviscid liquid. Particular attention is given to the difference between spectral formulae for the frequency and lifetime of $f$-mode in the singular and homogeneous models. The newly obtained results are discussed in the context of theoretical asteroseismology of pre-white dwarf stage of red giants and stellar cocoons -- spherical gas-dust clouds with dense star-forming core at the center.Comment: Mod. Phys. Lett. A, Vol. 24, No. 40 (2009) pp. 3257-327

Elasticity of nuclear medium as a principal macrodynamical promoter of electric dipole pygmy resonance

Motivated by arguments of the nuclear core-layer model formulated in [S.I. Bastrukov, J.A. Maruhn, Z.Phys. A 335 (1990) 139], the macroscopic excitation mechanism of electric pygmy dipole resonance (PDR) is considered as owing its origin to perturbation-induced effective decomposition of nucleus into two spherical domains - undisturbed inner region treated as static core and dynamical layer undergoing elastic shear vibrations. The focus is placed on the imprinted in the core-layer model mechanism of emergence of the low-energy dipole electric resonant excitation as Goldstone soft mode of translation layer-against-core oscillations. To accentuate this attitude we regain the obtained in the above paper spectral equation for the frequency of spheroidal elastic vibrations trapped in the finite-depth layer, but by working from canonical equation of elastic dynamics of continuous medium. The obtained analytic equations for the frequency of dipole vibrational state in question and its excitation strength exhibit fundamental character of this soft dipole mode of nuclear resonant response.Comment: Accepted in Phys.Lett.

Torsional nodeless vibrations of quaking neutron star restored by combined forces of shear elastic and magnetic field stresses

Within the framework of Newtonian magneto-solid-mechanics, relying on equations appropriate for a perfectly conducting elastic continuous medium threaded by a uniform magnetic field, the asteroseismic model of a neutron star undergoing axisymmetric global torsional nodeless vibrations under the combined action of Hooke's elastic and Lorentz magnetic forces is considered with emphasis on a toroidal Alfv\'en mode of differentially rotational vibrations about the dipole magnetic moment axis of the star. The obtained spectral equation for frequency is applied to $\ell$-pole identification of quasi-periodic oscillations (QPOs) of X-ray flux during the giant flares of SGR 1806-20 and SGR 1900+14. Our calculations suggest that detected QPOs can be consistently interpreted, within the framework of this model, as produced by global torsional nodeless vibrations of quaking magnetar if they are considered to be restored by the joint action of bulk forces of shear elastic and magnetic field stresses.Comment: 18 pages, 5 figures; accepted in Ap

Swarmodroid 1.0: A Modular Bristle-Bot Platform for Robotic Active Matter Studies

Large swarms of extremely simple robots (i.e., capable just of basic motion activities, like propelling forward or self-rotating) are widely applied to study collective task performance based on self-organization or local algorithms instead of sophisticated programming and global swarm coordination. Moreover, they represent a versatile yet affordable platform for experimental studies in physics, particularly in active matter - non-equilibrium assemblies of particles converting their energy to a directed motion. However, a large set of robotics platforms is being used in different studies, while the universal design is still lacking. Despite such platforms possess advantages in certain application scenarios, their large number sufficiently limits further development of results in the field, as advancing some study requires to buy or manually produce the corresponding robots. To address this issue, we develop an open-source Swarmodroid 1.0 platform based on bristle-bots with reconfigurable 3D-printed bodies, external control of motion velocity, and basic capabilities of velocity profile programming. In addition, we introduce AMPy software package in Python featuring OpenCV-based extraction of robotic swarm kinematics accompanied by the evaluation of key physical quantities describing the collective dynamics. We perform a detailed analysis of individual Swarmodroids' motion characteristics and address their use cases with two examples: a cargo transport performed by self-rotating robots and a velocity-dependent jam formation in a bottleneck by self-propelling robots. Finally, we provide a comparison of existing centimeter-scale robotic platforms, a review of key quantities describing collective dynamics of many-particle systems, and a comprehensive outlook considering potential applications as well as further directions for fundamental studies and Swarmodroid 1.0 platform development.Comment: 18 pages, 7 figures, 1 table + Supplementary Information. Comments are welcom

Systematic study of niobium thermal treatments for superconducting radio frequency cavities employing x ray photoelectron spectroscopy

The structural and chemical composition of the surface layer 100 140 nm of niobium radiofrequency cavities operating at cryogenic temperature has enormous impact on their superconducting characteristics. During the last years, cavities treated with a new thermal processing recipe, so called nitrogen infusion, have demonstrated an increased efficiency and high accelerating gradients. The role and importance of nitrogen gas has been a topic of many debates. In the present work we employ variable energy synchrotron x ray photoelectron spectroscopy XPS , to study the niobium surface subjected to the following treatments vacuum annealing at 800 C, nitrogen infusion, and vacuum heat treatment as for the infusion process but without nitrogen supply. Careful analysis of XPS energy distribution curves revealed a slightly increased thickness of the native oxide Nb2O5 for the infused samples amp; 8764;3.8 nm as compared to the annealed one amp; 8764;3.5 nm which indicates insignificant oxygen incorporation into niobium during 120 C baking and no effect of nitrogen on the formation of oxides or other niobium phases. By conducting an additional in situ annealing experiment and analyzing the niobium after the failed infusion process, we conclude that the vacuum furnace hygiene particularly during the high temperature stage is the prerequisite for success of any treatment recip

Frequency spectrum of toroidal Alfv\'en mode in a neutron star with Ferraro's form of nonhomogeneous poloidal magnetic field

Using the energy variational method of magneto-solid-mechanical theory of a perfectly conducting elastic medium threaded by magnetic field, the frequency spectrum of Lorentz-force-driven global torsional nodeless vibrations of a neutron star with Ferraro's form of axisymmetric poloidal nonhomogeneous internal and dipole-like external magnetic field is obtained and compared with that for this toroidal Alfv\'en mode in a neutron star with homogeneous internal and dipolar external magnetic field. The relevance of considered asteroseismic models to quasi-periodic oscillations of the X-ray flux during the ultra powerful outbursts of SGR 1806-20 and SGR 1900+14 is discussed.Comment: Accepted for publication in Astrophysics & Space Scienc

Исследование влияния вида обработки на прочность монокристаллических пластин нелегированного антимонида индия

The method of plane-transverse bending was used to measure the strength of thin single-crystal plates of undoped InSb with a crystallographic orientation of (100). It was found that the strength of the plates (thickness ≤ 800 μm) depends on their processing. Using a full processing cycle (grinding and chemical polishing) allows to increase the strength of InSb plates by 2 times (from 3.0 to 6.4 kg/mm2). It is shown that the dependence of strength on processing for wafers with (100) orientation is similar to this dependence for wafers (111), while the strength of wafers (111) is 2 times higher. The contact profilometry method was used to measure the roughness of thin plates, which also passed successive processing steps. It was found that during a full cycle of processing, the roughness of InSb plates decreases (Ra from 0.6 to 0.04 μm), leading to a general smoothing of the surface roughness. The strength and roughness of the (100) InSb and GaAs wafers are compared. It was found that the strength of GaAs cut wafers is 2 times higher than the strength of InSb cut wafers and slightly increases after a full cycle of their processing. It was shown that the roughness of GaAs and InSb plates after a full cycle of surface treatment is significantly reduced: 10 times for InSb due to overall surface leveling and 3 times for GaAs (Rz from 2.4 to 0.8 μm) due to a decrease in the peak component. Conducting a full cycle of processing InSb plates can increase their strength by removing broken layers by sequential operations and reducing the risk of mechanical damage.Методом плоско-поперечного изгиба проведены измерения прочности тонких монокристаллических пластин нелегированного InSb с кристаллографической ориентацией (100). Установлено, что прочность пластин (толщиной ≤ 800 мкм) зависит от их обработки. Использование полного цикла обработки (шлифовки и химической полировки) позволяет увеличить прочность пластин InSb в 2 раза (от 3,0 до 6,4 кг/мм2). Показано, что зависимость прочности от обработки для пластин с ориентацией (100) аналогична этой зависимости для пластин (111), при этом величина прочности пластин (111) в 2 раза выше. Методом контактной профилометрии измерена шероховатость тонких пластин, также прошедших последовательные этапы обработки. Установлено, что при проведении полного цикла обработки шероховатость пластин InSb уменьшается (Ra от 0,6 до 0,04 мкм), приводя к общему выравниванию шероховатости на поверхности. Проведено сравнение прочности и шероховатости пластин (100) InSb и GaAs. Установлено, что прочность резаных пластин GaAs в 2 раза выше прочности резаных пластин InSb и незначительно увеличивается после полного цикла их обработки. Показано, что шероховатость пластин GaAs и InSb после полного цикла обработки поверхности значительно уменьшается: в 10 раз для InSb за счет общего выравнивания поверхности и в 3 раза для GaAs (Rz от 2,4 до 0,8 мкм) за счет снижения пиковой составляющей. Проведение полного цикла обработки пластин InSb позволяет повысить их прочность, удаляя нарушенные слои последовательными операциями и снижая риск развития механических повреждений