Surface-induced magnetic anisotropy for impurity spins in granular AuFe films

The theory of the surface-induced anisotropy is extended to the case of granular films of dilute magnetic alloys. Since the surface-induced blocking of a magnetic-impurity spin appears to be very sensitive to the specific polycrystalline structure, we speculate that the apparent discrepancy between the experimental results of different groups for the size dependence of the Kondo resistivity can be linked to different microstructure of the samples. We apply our model to calculate the magnetization of impurity spins in small AuFe grains and to interpret the experimental data on the anomalous Hall effect in thin Fe doped Au films.Comment: 4 pages, 5 figures, E-mail addresses: [email protected], [email protected], [email protected]

Self-propelled micromotors for cleaning polluted water

We describe the use of catalytically self-propelled microjets (dubbed micromotors) for degrading organic pollutants in water via the Fenton oxidation process. The tubular micromotors are composed of rolled-up functional nanomembranes consisting of Fe/Pt bilayers. The micromotors contain double functionality within their architecture, i.e., the inner Pt for the self-propulsion and the outer Fe for the in situ generation of ferrous ions boosting the remediation of contaminated water.The degradation of organic pollutants takes place in the presence of hydrogen peroxide, which acts as a reagent for the Fenton reaction and as main fuel to propel the micromotors. Factors influencing the efficiency of the Fenton oxidation process, including thickness of the Fe layer, pH, and concentration of hydrogen peroxide, are investigated. The ability of these catalytically self-propelled micromotors to improve intermixing in liquids results in the removal of organic pollutants ca. 12 times faster than when the Fenton oxidation process is carried out without catalytically active micromotors. The enhanced reaction-diffusion provided by micromotors has been theoretically modeled. The synergy between the internal and external functionalities of the micromotors, without the need of further functionalization, results into an enhanced degradation of nonbiodegradable and dangerous organic pollutants at small-scale environments and holds considerable promise for the remediation of contaminated water

Coupled Ripplon-Plasmon Modes in a Multielectron Bubble

In multielectron bubbles, the electrons form an effectively two-dimensional layer at the inner surface of the bubble in helium. The modes of oscillation of the bubble surface (the ripplons) are influenced by the charge redistribution of the electrons along the surface. The dispersion relation for these charge redistribution modes (`longitudinal plasmons') is derived and the coupling of these modes to the ripplons is analysed. We find that the ripplon-plasmon coupling in a multielectron bubble differs markedly from that of electrons a flat helium surface. An equation is presented relating the spherical harmonic components of the charge redistribution to those of the shape deformation of the bubble.Comment: 8 pages, 1 figure, E-mail addresses: [email protected], [email protected], [email protected], [email protected]

Shape of nanosize superconducting grains: Does it influence pairing characteristics?

The Richardson exact solution for the reduced BCS Hamiltonian is applied to examine how sensitive are the pairing characteristics (condensation energy, spectroscopic gap, parity gap) to a specific configuration of single-electron energy levels in nanosize metallic grains. Using single-electron energy spectra in parallelepiped-shaped potential boxes with various volumes and aspect ratios as a model of energy levels in grains, we show that this sensitivity is extremely high. Just due to such an extreme sensitivity, the detailed shape of grains cannot be detected through the pairing characteristics, averaged over an ensemble of grains, even in the case of relatively small size dispersion within this ensemble. We analyse the effect of the pairing interaction on the excited-level spacings in superconducting grains and comment on the influence of shape-dependent fluctuations in single-electron energy spectra on the possibility to reveal this effect through tunnelling measurements.Comment: 13 pages, 5 figures, to be published in Solid State Communications, E-mail addresses: [email protected], [email protected], [email protected]

Vortex states in superconducting rings

The superconducting state of a thin superconducting disk with a hole is studied within the non-linear Ginzburg-Landau theory in which the demagnetization effect is accurately taken into account. We find that the flux through the hole is not quantized, the superconducting state is stabilized with increasing size of the hole for fixed radius of the disk, and a transition to a multi-vortex state is found if the disk is sufficiently large. Breaking the circular summetry through a non central location of the hole in the disk enhances the multi-vortex state.Comment: 11 pages, 23 figures (postscript). To appear in Physical Review B, Vol. 61 (2000

Совершенствование показателей работы автомобильного двигателя с непосредственным впрыскиванием бензина

Here are analyzed the problem questions which are connected with perspective working out of domestic automobile petrol engines of new generation with internal carburetion which stimulates necessity to search the means and the new technical decisions which can be suitable for domestic engine engineering. The method of developing automobile explosion engine performance of the given type has been suggested as an alternative variant, which is based on the use of hydrogen as a chemical reagent.Анализируются вопросы, связанные с перспективой разработки отечественных автомобильных бензиновых двигателей нового поколения с внутренним смесеобразованием, которые стимулируют необходимость поиска средств и новых технических решений, приемлемых для отечественного двигателестроения. В качестве альтернативного варианта предложен метод совершенствования показателей работы двигателя данного типа, основанный на использовании водорода в качестве химического реагента

Influence of the Characteristics of the STM-tip on the Electroluminescence Spectra

We analyze the influence of the characteristics of the STM-tip (applied voltage, tip radius) on the electroluminescence spectra from an STM-tip-induced quantum dot taking into account the many-body effects. We find that positions of electroluminescence peaks, attributed to the electron-hole recombination in the quantum dot, are very sensitive to the shape and size of the confinement potential as determined by the tip radius and the applied voltage. A critical value of the tip radius is found, at which the luminescence peak positions as a function of the tip radius manifest a transition from decreasing behavior for smaller radii to increasing behavior for larger radii. We find that this critical value of the tip radius is related to the confinement in the lateral and normal direction.Comment: 15 pages, 5 figure

Роль водорода как химического реагента в кинетическом механизме углеродообразования в дизеле

Here is discussed the actual problem of modern engine engineering, namely reduction of soot particles emissions in diesel engines. One of the most effective methods of particles emission reduction, which is on based on hydrogen addition to a working body of diesel is considered here. A number of methodically well-founded positions about a hydrogen role as chemical reagent has been suggested in certificates of formation and the soot combustion which reliability is confirmed by results of natural experiment on diesel.Обсуждается актуальная проблема современного двигателестроения - снижение выбросов сажевых частиц дизелями. Рассмотрен один из наиболее эффективных методов снижения эмиссии частиц на основе добавления к рабочему телу дизеля водорода. Предложен ряд методически обоснованных положений о роли водорода как химического реагента в актах образования и сгорания сажи, достоверность которых подтверждена результатами натурного эксперимента на дизеле

Phase diagram of a superconductor / ferromagnet bilayer

The magnetic field (H) - temperature (T) phase diagram of a superconductor is significantly altered when domains are present in an underlying ferromagnet with perpendicular magnetic anisotropy. When the domains have a band-like shape, the critical temperature Tc of the superconductor in zero field is strongly reduced, and the slope of the upper critical field as a function of T is increased by a factor of 2.4 due to the inhomogeneous stray fields of the domains. Field compensation effects can cause an asymmetric phase boundary with respect to H when the ferromagnet contains bubble domains. For a very inhomogeneous domain structure, Tc~H^2 for low H and Tc~H for higher fields, indicating a dimensional crossover from a one-dimensional network-like to a two-dimensional behavior in the nucleation of superconductivity.Comment: 6 pages, 7 figure