Dynamics of Switching Waves in a Nanofluid in a Light Field

The dynamics of the concentration of nanofluids placed in a light field with a Gaussian intensity profile is studied theoretically. The investigation is based on the analytical and numerical solutions of the system of linearized heat conduction and convectiondiffusion equations. The convection-diffusion equation contains terms that correspond both to the Soret effect and to the transfer of nanoparticles, caused by the action of a light field on them (electrostriction). The dependence of the coefficient of thermal conductivity of the medium on the concentration is taken into account. It is shown that under these conditions single travelling waves appear in the medium, the velocity of which depends not only on the thermal physical parameters of the medium, but also on the polarization of the particles. Conditions under which the stratification of the medium is possible are found

Transformation of polarons into magnetopolarons in GaAs quantum well

An experimental study is made of electron tunneling in a resonant-tunneling diode in magnetic fields directed parallel and perpendicular to the planes of the GaAs/Al xGa1-XAs heterostructure layers. In particular, phonon replicas on the current–voltage characteristics of the diode are investigated. In the second current derivatives a fine structure of replicas is found. The transformation of the structure of replicas in a perpendicular magnetic field can be qualitatively understood as a manifestation of the transition of polaron states to magnetopolaronic ones

Стадії гальваностатичного фазоутворення цинку на вольфрамовому електроді із цинкатного розчину

On the basis of the classical theory of galvanostatic nucleation and Vetter’s kinetic conception, formation of zinc nuclei on the tungsten electrode from the zincate electrolyte (0.5 М ZnO, 6 M NaOH) has been investigated. In the region of the current density 200 - 600 mАсm-2 the charge transfer overpotential (100 - 200 mV), the crystallization overpotential (50 - 60 mV), the nucleation work ((2 - 12)×10-20 J), the number of atoms in the nuclei (2 - 10) were determined. It was proved that nucleation take place on reduced sites of the oxidized tungsten surface. Within the range of studied diapason of current densities nucleis are forming on energetically similar electrode centers. The low value of the charge transfer coefficient (α = 0.26) indicates a weak effect of the double layer electrical field on the activation energy of charge transfer.      На основании классической теории гальваностатического фазообразования и кинетической концепции Феттера исследовано фазообразование цинка на вольфрамовом электроде из цинкатного раствора (0.5 М ZnO, 6 M NaOH). В области плотности тока 200-600 мА/см2 определено: перенапряжение перехода (100-200 мВ), перенапряжение кристаллизации (50-60 мВ), работа фазообразования ((2-12) ×10-20 Дж), число атомов в зародыше (2-10). Обосновано предположение, что фазообразование осуществляется на восстановленных участках окисленной поверхности вольфрама. В изученном диапазоне плотности тока зародыши формируются на энергетически однородных центрах электрода. Низкое значение коэффициента переноса (α = 0.26) отражает слабое влияние электрического поля двойного слоя на энергию активации переноса заряда.                На підставі класичної теорії гальваностатичного фазоутворення і кінетичної концепції Феттер досліджено фазоутворення цинку на вольфрамовому електроді з цинкатного розчину (0.5 М ZnO, 6 М NaOH). В області густини струму 200-600 мА/см2 визначено: перенапругу переходу (100-200 мВ), перенапругу кристалізації (50-60 мВ), роботу фазоутворення ((2-12) × 10-20 Дж), кількість атомів у зародку (2-10). Обґрунтовано припущення, що фазоутворення здійснюється на відновлених ділянках окисленої поверхні вольфраму. У вивченому діапазоні густини струму зародки формуються на енергетично однорідних центрах електрода. Низьке значення коефіцієнта переносу (α = 0.26) відображає слабкий вплив електричного поля подвійного шару на енергію активації переносу заряду.    

The stages of galvanostatic nucleation of zinc on the tungsten electrode from a zincate solution

On the basis of the classical theory of galvanostatic nucleation and Vetter’s kinetic conception, formation of zinc nuclei on the tungsten electrode from the zincate electrolyte (0.5 М ZnO, 6 M NaOH) has been investigated. In the region of the current density 200 - 600 mАсm-2 the charge transfer overpotential (100 - 200 mV), the crystallization overpotential (50 - 60 mV), the nucleation work ((2 - 12)×10-20 J), the number of atoms in the nuclei (2 - 10) were determined. It was proved that nucleation take place on reduced sites of the oxidized tungsten surface. Within the range of studied diapason of current densities nucleis are forming on energetically similar electrode centers. The low value of the charge transfer coefficient (α = 0.26) indicates a weak effect of the double layer electrical field on the activation energy of charge transfer.      </div

Experimental Investigation of an Optical Resonator Gyroscope with a Mach–Zehnder Modulator and Its Sensitive Elements

Today, the task of developing microoptical gyroscopes is topical. Usually, tunable lasers with a built-in frequency stabilization system are used in such gyroscopes. They are comparatively bulky, which hinders the real miniaturization of optical gyroscopes. We propose a new approach implemented by using a Mach–Zehnder modulator with a passive ring resonator connected to one of its arms. This makes it possible to obtain a mutual configuration and makes the use of a tunable laser optional. Two ring resonators made of the polarization-maintaining fiber, suitable for use as sensitive elements of a gyroscope, were realized and investigated. Their Q-factor is equal to 14.5 × 106 and 28.9 × 106. The maximum sensitivity of the proposed method when using the described resonators is 3.2 and 1.8 °/h, respectively. The first experimental setup of a resonator gyroscope implementing this approach has been manufactured and analyzed. When measuring the rotation speed by the quasi-harmonic signal span and its phase, the measurement accuracy was approximately 11 and 0.4 °/s, respectively

A Prototype for a Passive Resonant Interferometric Fiber Optic Gyroscope with a 3 × 3 Directional Coupler

Reducing the dimensions of optical gyroscopes is a crucial task and resonant fiber optic gyroscopes are promising candidates for its solution. The paper presents a prototype of a miniature resonant interferometric gyroscope of a strategic accuracy class. Due to the use of passive optical elements in this gyroscope, it has a great potential for miniaturization, alongside a low production cost and ease of implementation, since it does not require many feedback loops. The presented prototype shows results on a zero instability of 20°/h and an angle random walk of 0.16°/√h. A theoretical model explaining the nature of the multipath interference of resonant spectra and establishing the relationship between the resonator parameters and the output parameters of the presented prototype is proposed. The results predicted are in agreement with the experimental data. The prototype gyroscope demonstrates a scale factor instability and a change in the average signal level, which is due to the presence of polarization non-reciprocity, occurring due to the induced birefringence in the single-mode fiber of the contour. This problem requires further investigation to be performed

A Prototype for a Passive Resonant Interferometric Fiber Optic Gyroscope with a 3 &times; 3 Directional Coupler

Reducing the dimensions of optical gyroscopes is a crucial task and resonant fiber optic gyroscopes are promising candidates for its solution. The paper presents a prototype of a miniature resonant interferometric gyroscope of a strategic accuracy class. Due to the use of passive optical elements in this gyroscope, it has a great potential for miniaturization, alongside a low production cost and ease of implementation, since it does not require many feedback loops. The presented prototype shows results on a zero instability of 20&deg;/h and an angle random walk of 0.16&deg;/&radic;h. A theoretical model explaining the nature of the multipath interference of resonant spectra and establishing the relationship between the resonator parameters and the output parameters of the presented prototype is proposed. The results predicted are in agreement with the experimental data. The prototype gyroscope demonstrates a scale factor instability and a change in the average signal level, which is due to the presence of polarization non-reciprocity, occurring due to the induced birefringence in the single-mode fiber of the contour. This problem requires further investigation to be performed