Wind and wave regime over the Bombay high area under the influence of cyclonic storms

Temporal distributions of wind and wave over Bombay High Area (BHA) during cyclone period have been studied. Ten years’ (1990-99) data of BHA during cyclone period have been used. It is found that under the influence of cyclonic storms strong southwesterly winds prevail over the BHA in pre-monsoon and weaker east to southeasterly winds during post-monsoon. Southwesterly wave with heights exceeding 20 feet are encountered in BHA during pre-monsoon and south easterlies with wave height reaching up to 12 feet in post monsoon. Analysis of situations with different storm locations also yielded similar results. Relationships between wind speeds and wave height as well as the distance of the storm centre over BHA have been established.

Fast and numerically stable Mie solution of EM near field and absorption for stratified spheres

Purpose The purpose of this paper is the development of an analytic computational model for electromagnetic (EM) wave scattering from spherical objects. The main application field is the modeling of electrically large objects, where the standard numerical techniques require huge computational resources. An example is full-wave modeling of the human head in the millimeter-wave regime. Hence, an approximate model or analytical approach is used. Design/methodology/approach The Mie–Debye theorem is used for calculating the EM scattering from a layered dielectric sphere. The evaluation of the analytical expressions involved in the infinite sum has several numerical instabilities, which makes the precise calculation a challenge. The model is validated through an application example with comparing results to numerical calculations (finite element method). The human head model is used with the approximation of a two-layer sphere, where the brain tissues and the cranial bones are represented by homogeneous materials. Findings A significant improvement is introduced for the stable calculation of the Mie coefficients of a core–shell stratified sphere illuminated by a linearly polarized EM plane wave. Using this technique, a semi-analytical expression is derived for the power loss in the sphere resulting in quick and accurate calculations. Originality/value Two methods are introduced in this work with the main objective of estimating the final precision of the results. This is an important aspect for potentially unstable calculations, and the existing implementations have not included this feature so far.

Extraordinary optical transmission from a thin microcavity by macroscopic quantum effect

The macroscopic quantum effect is revealed to elaborate the extraordinary optical transmission (EOT) from a subwavelength thin microcavity based on the uncertainty property of the transmitted electromagnetic fields after the aperture. A critical radius is found in the thin microcavity under a certain incident electromagnetic wavelength. With the aperture radius varying, the transmitted field can be divided into three regimes: I. the macroscopic quantum regime when the aperture radius is less than the critical radius, in which the field edge effect occurs and EOT phenomenon is perfectly manifested; II. The wave-particle duality regime in the vicinity of the critical radius, in which the edge effect and diffraction phenomenon exist simultaneously; III. The wave regime when the aperture radius is greater than the critical radius, in which the near-field diffraction emerges. In addition, the influences of incident wavelength and microcavity thickness on EOT are also investigated. Our research have potential applications in advanced optical devices, such as light switch and optical manipulations.

An Entropy Paradox Free Fractional Diffusion Equation

A new look at the fractional diffusion equation was done. Using the unified fractional derivative, a new formulation was proposed, and the equation was solved for three different order cases: neutral, dominant time, and dominant space. The solutions were expressed by generalizations of classic formulae used for the stable distributions. The entropy paradox problem was studied and clarified through the Rényi entropy: in the extreme wave regime the entropy is −∞. In passing, Tsallis and Rényi entropies for stable distributions are introduced and exemplified.

Optical heating of doped semiconductor nanocylinders supporting quasi-BIC modes

In the recent years, semiconductor and dielectric nanophotonic structures attracted a lot of attention for their resonant optical properties finding applications in thermal tuning and optical heating. Exciting high quality optical modes of both electric and magnetic nature in nanoresonators of high-index materials, one can effectively enhance optical absorption in such structures. Another big advantage of semiconductor materials is the ability to finely control the level of optical losses in visible and near infrared (near-IR) range through varying the doping level. In this work, we show theoretically that by moderate carrier doping of silicon via donors from group V materials one can achieve effective heating of nanoresonators. We show that by tuning the doping level of crystalline silicon supporting high quality non-radiative modes based on quasi bound states in the continuum one can achieve strong heating in near-IR under continuous wave regime illumination. We believe that our finding will pave the way for an efficient semiconductor near-IR all-optical sensors and nanoheaters.

SONOCHEMICAL PROCESSING INDUSTRIAL AND BIOLOGICAL МАТЕRIALS

Проанализированы технологически значимые факторы, обеспечивающие возможности управления сонохимическими процессами. Выявлены качественные и количественные закономерности влияния акустических воздействий на химические процессы в гомогенных и в гетерогенных реакционных системах. Показано, что сонохимический эффект может быть не только положительным (инициирование химической реакции), но и отрицательным (подавление реакции). Соответственно, в экстремальном случае возможен сонохимический резонанс (максимум эффективности акустического воздействия) либо сонохимический антирезонанс (минимум эффективности акустического воздействия). Акустическая обработка конденсированных сред в режиме стоячей волны позволяет контролировать характерный размер частиц плотных фракций: укрупнять частицы кристаллического осадка (соноиндуцированный эффект Тананаева) либо, наоборот, измельчать плотную фазу без использования мелющих тел. The paper deals with technologically essential factors governing sonochemical processes. Qualitative and quantitative characteristic features of sonoinduced chemical processes in homogeneous and heterogeneous reaction systems are revealed and discussed. A sonochemical effect can be either positive (promoting a reaction) or negative (suppressing a reaction). In an extreme case a sonochemical resonance or a sonochemical antiresonance can occur. Ultrasonic processing condensed media in a standing-wave regime enables to control the grain size of dense fractions. Namely, the sediment grain size can be enhanced (Tananayev sonoinduced effect) or, vice versa, a dense phase can be comminuted without grinding.

SESAM Mode-Locked Yb:Ca3Gd2(BO3)4 Femtosecond Laser

We report on the first passively mode-locked femtosecond-laser operation of a disordered Yb:Ca3Gd2(BO3)4 crystal using a SEmiconductor Saturable Absorber Mirror (SESAM). Pumping with a single-transverse mode fiber-coupled laser diode at 976 nm, nearly Fourier-transform-limited pulses as short as 96 fs are generated at 1045 nm with an average output power of 205 mW and a pulse repetition rate of ~67.3 MHz. In the continuous-wave regime, high slope efficiency up to 59.2% and low laser thresholds down to 25 mW are obtained. Continuous wavelength tuning between 1006–1074 nm (a tuning range of 68 nm) is demonstrated. Yb:Ca3Gd2(BO3)4 crystals are promising for the development of ultrafast lasers at ~1 μm.

THE ENERGY POTENTIAL OF BLACK SEA IN ROMANIAN SEASIDE AREA

The Black Sea is considered a relatively calm sea, the optimal choice for the capture process is influenced by the wave regime and its peculiarities. This sea is characterized by winds that blow towards land with greater intensity in January causing the sea to be more agitated and with less power in May, June and July, when the sea was the calmest of the year. It should be noted that the frequency of strong winds is 38%, and of those of low speed of 1m/s of only 1.5%. For the collection of oceanographic and meteorological information, data provided by the Gloria platform located in front of Romania’s coast were is used, as well as records from the three offshore buoys anchored in the Romanian seaside area and which are part of the EMSO EUXINUS research infrastructure managed by National Institute for Research and Development on Marine Geology and Geoecology - GeoEcoMar. In addition, free data such as those provided by the site of the research institute Grigore Antipa were easily accessed. Presently there are three fixed platforms in the Black Sea. Wave energy is underexploited, both worldwide and in the Black Sea. The potential of this type of energy is huge, and the environmental impact is low compared to other renewable energy technologies.

Numerical Study on the Hydrodynamic Characteristics of a Double-Row Floating Breakwater Composed of a Pontoon and an Airbag

By adding a cylindrical airbag on the leeward side of a cuboid pontoon, a new-type double-row floating breakwater is designed to improve the wave attenuation performance, and its hydrodynamic characteristics are studied through numerical simulations. First, based on the smoothed particle hydrodynamics (SPH) method, a numerical model used to simulate the interaction between waves and moored floating bodies is built. The fluid motion is governed by the Navier–Stokes equations. The motion of the floating body is computed according to Newton’s second law. The modified dynamic boundary condition is employed to treat the solid boundary. The lumped-mass method is adopted to implement the mooring system. Then, two physical model experiments on waves interaction with cuboid and dual cylindrical floating pontoons are reproduced. By comparing the experimental and numerical wave transmission coefficients, wave reflection coefficients, response amplitude operators and mooring force, the reliability of the numerical model is validated. Finally, the validated numerical model is applied to study the influence of separation distance and wave parameters on the hydrodynamic characteristics of the double-row floating breakwater. The results indicate that the optimal separation distance between pontoon and airbag is 0.75 times the wavelength. At such separation distance and within the concerned 1–4 m wave heights and 4–7 s wave periods, the pontoon-airbag system presents better wave attenuation performance than a single pontoon. This improvement weakens as wave height increases while it strengthens as the wave period increases. In addition, the double-row floating breakwater is more effective in a high-wave regime than in a low-wave regime. In the case of short waves, attention should be paid to the stability and mooring reliability of the seaward pontoon, while in the case of long waves, care needs to be taken of the leeward airbag.