Nonlinear metal-dielectric nanoantennas for light switching and routing

We introduce a novel hybrid metal-dielectric nanoantenna composed of dielectric (crystalline silicon) and metal (silver) nanoparticles. A high-permittivity dielectric nanoparticle allows to achieve effective light harvesting, and nonlinearity of a metal nanoparticle controls the radiation direction. We show that the radiation pattern of such a nanoantenna can be switched between the forward and backward directions by varying only the light intensity around the level of 11 MW/cm$^2$, with the characteristic switching time of 260 fs.Comment: 9 pages, 5 figures, submitted to New J. Phy

Digging into Lipid Membrane Permeation for Cardiac Ion Channel Blocker d-Sotalol with All-Atom Simulations.

Interactions of drug molecules with lipid membranes play crucial role in their accessibility of cellular targets and can be an important predictor of their therapeutic and safety profiles. Very little is known about spatial localization of various drugs in the lipid bilayers, their active form (ionization state) or translocation rates and therefore potency to bind to different sites in membrane proteins. All-atom molecular simulations may help to map drug partitioning kinetics and thermodynamics, thus providing in-depth assessment of drug lipophilicity. As a proof of principle, we evaluated extensively lipid membrane partitioning of d-sotalol, well-known blocker of a cardiac potassium channel Kv11.1 encoded by the hERG gene, with reported substantial proclivity for arrhythmogenesis. We developed the positively charged (cationic) and neutral d-sotalol models, compatible with the biomolecular CHARMM force field, and subjected them to all-atom molecular dynamics (MD) simulations of drug partitioning through hydrated lipid membranes, aiming to elucidate thermodynamics and kinetics of their translocation and thus putative propensities for hydrophobic and aqueous hERG access. We found that only a neutral form of d-sotalol accumulates in the membrane interior and can move across the bilayer within millisecond time scale, and can be relevant to a lipophilic channel access. The computed water-membrane partitioning coefficient for this form is in good agreement with experiment. There is a large energetic barrier for a cationic form of the drug, dominant in water, to cross the membrane, resulting in slow membrane translocation kinetics. However, this form of the drug can be important for an aqueous access pathway through the intracellular gate of hERG. This route will likely occur after a neutral form of a drug crosses the membrane and subsequently re-protonates. Our study serves to demonstrate a first step toward a framework for multi-scale in silico safety pharmacology, and identifies some of the challenges that lie therein

Coherent X-ray radiation of a relativistic electron in a bilayer amorphous layer – single crystal target

A theory of coherent X-ray radiation is proposed, which is generated when a relativistic electron is transversing a hybrid target consisting of two parallel plates: amorphous and crystalline. Within a two-wave approximation of the dynamic diffraction theory, expressions describing the spectral-angular density of coherent radiation from this target are obtaine

Diffracted transition radiation of a relativistic electron in a three-layer structure

We develop a theory of coherent X-ray radiation of a relativistic electron crossing a three-layer structure consisting of two amorphous layers and a crystal layer. The particular case when the second amor- phous layer is a vacuum is considered. Expressions describing the spectral and angular distributions of coher-ent radiation in such a structure are derived and analyze

Предварительная оценка энергоэффективности зданий в условиях резко континентального климата

Construction of energy-efficient buildings becomes a top priority for many countries. Yet certain obstacles in achieving internal environment comfort standards remain in regions with extreme continental climate. In addition to engineering and economic challenges, there exist design process issues since design data should closely correspond with resulting performance of the building. This paper focuses on accurate energy demand estimation during design stage. Two types of buildings designed for Ural-Siberian region of Russia and for Kazakhstan are examined: detached and medium-rise apartment buildings. Most influential factors are taken into consideration and general recommendations on improving energy efficiency using effective combination of structural and engineering solutions are given. Adaptation of design procedure in terms of extreme continental climate made by means of simplified but precise Passive House planning tool is demonstrated.Строительство энергоэффективных зданий является приоритетным направлением для многих стран. Однако в регионах с суровым климатом часто возникают проблемы достижения нормативных показателей комфорта внутренней среды. В идеале проектные значения потребностей в электроэнергии на отопление и кондиционирование здания должны точно соответствовать итоговым показателям. В этой статье рассматриваются методики точного прогнозирования энергопотребления на стадии проектирования. Исследовано два типа зданий, проектируемых для Урало-Сибирского региона России и Казахстана: индивидуальный дом и многоквартирный дом средней этажности. Даны рекомендации по снижению энергопотребления зданий путем эффективного сочетания конструктивных и инженерных решений. Показан учет основных факторов, влияющих на энергетический баланс зданий. На примере Пакета проектирования пассивного дома 2007 приведен пример адаптации упрощенной, но достаточно точной методики расчета к резко континентальным климатическим условиям

Resolving the mystery of milliwatt-threshold opto-mechanical self-oscillation in dual-nanoweb fiber

It is interesting to pose the question: How best to design an optomechanical device, with no electronics, optical cavity, or laser gain, that will self-oscillate when pumped in a single pass with only a few mW of single-frequency laser power? One might begin with a mechanically resonant and highly compliant system offering very high optomechanical gain. Such a system, when pumped by single-frequency light, might self-oscillate at its resonant frequency. It is well-known, however, that this will occur only if the group velocity dispersion of the light is high enough so that phonons causing pump-to-Stokes conversion are sufficiently dissimilar to those causing pump-to-anti-Stokes conversion. Recently it was reported that two light-guiding membranes 20 μm wide, ∼500 nm thick and spaced by ∼500 nm, suspended inside a glass fiber capillary, oscillated spontaneously at its mechanical resonant frequency (∼6 MHz) when pumped with only a few mW of single-frequency light. This was surprising, since perfect Raman gain suppression would be expected. In detailed measurements, using an interferometric side-probing technique capable of resolving nanoweb movements as small as 10 pm, we map out the vibrations along the fiber and show that stimulated intermodal scattering to a higher-order optical mode frustrates gain suppression, permitting the structure to self-oscillate. A detailed theoretical analysis confirms this picture. This novel mechanism makes possible the design of single-pass optomechanical oscillators that require only a few mW of optical power, no electronics nor any optical resonator. The design could also be implemented in silicon or any other suitable material

Coherent control of flexural vibrations in dual-nanoweb fibers using phase-modulated two-frequency light

Coherent control of the resonant response in spatially extended optomechanical structures is complicated by the fact that the optical drive is affected by the back-action from the generated phonons. Here we report a new approach to coherent control based on stimulated Raman-like scattering, in which the optical pressure can remain unaffected by the induced vibrations even in the regime of strong optomechanical interactions. We demonstrate experimentally coherent control of flexural vibrations simultaneously along the whole length of a dual-nanoweb fiber, by imprinting steps in the relative phase between the components of a two-frequency pump signal,the beat frequency being chosen to match a flexural resonance. Furthermore, sequential switching of the relative phase at time intervals shorter than the lifetime of the vibrations reduces their amplitude to a constant value that is fully adjustable by tuning the phase-modulation depth and switching rate. The results may trigger new developments in silicon photonics, since such coherent control uniquely decouples the amplitude of optomechanical oscillations from power-dependent thermal effects and nonlinear optical loss.Comment: This 11 pages-long document includes the main text with 8 figures and an appendix with one figur

Hydrobionts of a freshwater oil-polluted northern lake: bioaccumulation of heavy metals in fish and the rate of ecosystem recovery

The response of phytoplankton, zooplankton, benthic and fish community structure to one of the biggest oil spill in history of Komi Republic (north-west part of Russia) was investigated using data from a long-term survey off the polluted lake. The characteristics of aquatic freshwater communities observed in the study area 10, 11 and 22 years after the spill (1994) were compared to find out the rate of natural recovery of the ecosystem after oil decontamination of bottom sediments. The concentrations of fifteen trace metals (Al, Cr, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Sb, Pb, U, Bi, Th) were analyzed in the tissues (muscle) of three fish species. The concentrations of Al (3-309 mg/kg), Cr (0,1-3,71 mg/kg), Fe (8,6-317 mg/kg), and Cu (0,09-99 mg/kg) in fishes from polluted lake resulted in most cases higher than reference thresholds. Quantitative and qualitative indicators of aquatic invertebrates from polluted lake reach those one of unpolluted lake but do not fully recover 22 years after the spill, despite that oil concentration in water column and in bottom sediments was lower than reference tresholds. We conclude that natural recovery rate of aquatic freshwater ecosystems in northern regions after oil pollution is extremely low. The purification of water and bottom sediments of oil-polluted northern water bodies is necessary for stimulation of ecosystem restoration