Detrapping and retrapping of free carriers in nominally pure single crystal GaP, GaAs and 4H-SiC semiconductors under light illumination at cryogenic temperatures

We report on extremely sensitive measurements of changes in the microwave properties of high purity non-intentionally-doped single-crystal semiconductor samples of gallium phosphide, gallium arsenide and 4H-silicon carbide when illuminated with light of different wavelengths at cryogenic temperatures. Whispering gallery modes were excited in the semiconductors whilst they were cooled on the coldfinger of a single-stage cryocooler and their frequencies and Q-factors measured under light and dark conditions. With these materials, the whispering gallery mode technique is able to resolve changes of a few parts per million in the permittivity and the microwave losses as compared with those measured in darkness. A phenomenological model is proposed to explain the observed changes, which result not from direct valence to conduction band transitions but from detrapping and retrapping of carriers from impurity/defect sites with ionization energies that lay in the semiconductor band gap. Detrapping and retrapping relaxation times have been evaluated from comparison with measured data.Comment: 7 pages, 6 figure

Modified permittivity observed in bulk Gallium Arsenide and Gallium Phosphide samples at 50 K using the Whispering Gallery mode method

Whispering Gallery modes in bulk cylindrical Gallium Arsenide and Gallium Phosphide samples have been examined both in darkness and under white light at 50 K. In both samples we observed change in permittivity under light and dark conditions. This results from a change in the polarization state of the semiconductor, which is consistent with a free electron-hole creation/recombination process. The permittivity of the semiconductor is modified by free photocarriers in the surface layers of the sample which is the region sampled by Whispering Gallery modes.Comment: 8 pages, 3 figure

Creating traveling waves from standing waves from the gyrotropic paramagnetic properties of Fe3+^{3+} ions in a high-Q whispering gallery mode sapphire resonator

We report observations of the gyrotropic change in magnetic susceptibility of the Fe$^{3+}$ electron paramagnetic resonance at 12.037GHz (between spin states $|1/2>$ and $|3/2>$) in sapphire with respect to applied magnetic field. Measurements were made by observing the response of the high-Q Whispering Gallery doublet (WGH$_{\pm17,0,0}$) in a Hemex sapphire resonator cooled to 5 K. The doublets initially existed as standing waves at zero field and were transformed to traveling waves due to the gyrotropic response.Comment: Accepted for publication in Phys. Rev.

Multigap Superconductivity in Y2_2C3_3: A 13^{13}C-NMR Study

We report on the superconducting (SC) properties of Y$_2$C$_3$ with a relatively high transition temperature $T_{\rm c}=15.7$ K investigated by $^{13}$C nuclear-magnetic-resonance (NMR) measurements under a magnetic field. The $^{13}$C Knight shift has revealed a significant decrease below $T_{\rm c}$, suggesting a spin-singlet superconductivity. From an analysis of the temperature dependence of the nuclear spin-lattice relaxation rate $1/T_1$ in the SC state, Y$_2$C$_3$ is demonstrated to be a multigap superconductor that exhibits a large gap $2\Delta/k_{\rm B}T_{\rm c}=5$ at the main band and a small gap $2\Delta/k_{\rm B}T_{\rm c}=2$ at other bands. These results have revealed that Y$_2$C$_3$ is a unique multigap s-wave superconductor similar to MgB$_2$.Comment: 4 pages, 5 figure

ТРАНСФОРМАЦІЯ НАПРЯМІВ ВЗАЄМОДІЇ ПОДАТКОВИХ ОРГАНІВ ТА ПІДПРИЄМСТВ У ПРОЦЕСІ РЕАЛІЗАЦІЇ ПОДАТКОВОГО КОНТРОЛЮ

The focus of tax reforms in Ukraine, the development of partnerships between payers and supervisors requires new approaches to tax control. The current state of the functioning of the tax control system in Ukraine shows the necessity and at the same time its unpreparedness to transition to more advanced forms, including horizontal monitoring. The purpose of the article is to substantiate the need for effective interaction between taxpayers and controlling bodies in the context of improving the quality of tax control. The methodological basis of the study, in particular the theoretical positions, is the methods of scientific abstraction, induction, deduction, logical method, etc. For analytical research mathematical methods were used, in particular correlation-regression analysis, methods of comparison and grouping, synthesis, tabular and graphical methods. As a result of the research, it was found that the main factors hindering the implementation of horizontal monitoring in Ukraine are the lack of compliance with the legislative framework, the insecurity of the confidentiality of information on the activities of taxpayers, corruption in the DFS, large amounts of shadow economy in the country, etc. At the same time, the high level of inconsistency of the assessed tax liabilities and a considerable number of disputes as a result of this also confirm the low level of trust and cooperation between the DFS authorities and the payers. The analysis of the state of tax audits and the dynamics of tax debt — the calculation of correlation relationships between these indicators (R2 = -0,92) and the forecast of tax debt — showed that preventive tax control measures do not discipline payers to pay them tax arrears, the conducted tax inspections have a positive effect on the repayment of the tax debt by the payers. Such research results indicate that there are problems in establishing trusting relationships between payers and supervisors and the need to find ways to adjust them in the context of the development of progressive forms of tax control.Спрямованість податкових реформ в Україні, розвиток партнерських взаємовідносин між платниками та органами контролю вимагає нових підходів до проведення податкового контролю. Сучасний стан функціонування системи податкового контролю в Україні свідчить про необхідність та одночасно неготовність її до переходу на нові прогресивніші форми, зокрема горизонтальний моніторинг. Метою статті є обґрунтування необхідності налагодження ефективної взаємодії платників та органів контролю в контексті підвищення якості податкового контролю. Методологічною базою дослідження, зокрема теоретичних положень, є методи наукової абстракції, індукції, дедукції, логічний метод тощо. Для аналітичного дослідження використано математичні методи, зокрема кореляційно-регресійний аналіз, методи порівняння та групування, синтезу, табличний і графічний методи. У результаті дослідження з’ясовано, що основними чинниками, які перешкоджають запровадженню горизонтального моніторингу в Україні, є невідповідність законодавчої бази, незахищеність конфіденційності інформації про діяльність платників податків, корупція в органах ДФС, великі обсяги тіньової економіки в країні тощо. Поряд з цим високий рівень неузгодженості донарахованих податкових зобов’язань і значна кількість спорів унаслідок цього також підтверджують низький рівень довіри та співпраці між органами ДФС і платниками. Проведений аналіз стану податкових перевірок та динаміки податкового боргу — розрахунок кореляційних взаємозв’язків між цими показниками (R2 = -0,92) і прогноз податкового боргу — показав, що превентивні заходи податкового контролю не дисциплінують платників щодо погашення ними податкової заборгованості, натомість кількість фактично проведених податкових перевірок позитивно впливають на погашення податкового боргу платниками. Такі результати дослідження свідчать про наявність проблем у налагодженні довірливих взаємин між платниками та органами контролю і необхідність пошуку шляхів їх налагодження в контексті розвитку прогресивних форм податкового контролю

Influence of roughness on ZDDP tribofilm formation in boundary lubricated fretting

Influence of initial surface topography on tribofilm formation in ZDDP lubricated contact was analysed. A small displacement fretting tests with sinusoidal motion were carried out in classical sphere/plane configuration. A range of surfaces with different initial roughness were prepared by milling and grinding processes. Tests were carried out using variable displacement method where amplitude of imposed displacement was gradually increased after every 1000 cycles from 2 to 30 µm. The surfaces after tribological tests were measured by interferometric profiler. Main findings confirm that initial roughness has a significant influence on antiwear tribofilm formation in boundary lubricated contact. Tribofilm form faster and require less energy to activate in case of rough surface obtained by milling process than in case of smooth grinded surface. However, in contact lubricated by ZDDP additive a significant transfer of material occurred from plane to sphere specimen

Symmetries in Classical Field Theory

The multisymplectic description of Classical Field Theories is revisited, including its relation with the presymplectic formalism on the space of Cauchy data. Both descriptions allow us to give a complete scheme of classification of infinitesimal symmetries, and to obtain the corresponding conservation laws.Comment: 70S05; 70H33; 55R10; 58A2

Synthesis and non-resonant nonlinear optical properties of push-pull side-chain azobenzene polymers

In this work, we report preliminary results obtained for methacrylic polymers incorporating azobenzene side-group as nonlinear optical (NLO) active molecule. The trans-cis isomerization properties are discussed. The third-order non-resonant nonlinear refractive index (n2) and nonlinear absorption coefficient (β) are measured using the Z-scan technique at 1064 nm in the picosecond regime. The influence of different electron-acceptor groups in azobenzene moieties on the nonlinear properties is investigated