A broadband silicon quarter-wave retarder for far-infrared spectroscopic circular dichroism

The high brightness, broad spectral coverage and pulsed characteristics of infrared synchrotron radiation enable time-resolved spectroscopy under throughput-limited optical systems, as can occur with the high-field magnet cryostat systems used to study electron dynamics and cyclotron resonance by far-infrared techniques. A natural extension for magnetospectroscopy is to sense circular dichroism, i.e. the difference in a material's optical response for left and right circularly polarized light. A key component for spectroscopic circular dichroism is an achromatic 1/4 wave retarder functioning over the spectral range of interest. We report here the development of an in-line retarder using total internal reflection in high-resistivity silicon. We demonstrate its performance by distinguishing electronic excitations of different handednesses for GaAs in a magnetic field. This 1/4 wave retarder is expected to be useful for far-infrared spectroscopy of circular dichroism in many materials

Acceptor binding energies in GaN and AlN

We employ effective mass theory for degenerate hole-bands to calculate the acceptor binding energies for Be, Mg, Zn, Ca, C and Si substitutional acceptors in GaN and AlN. The calculations are performed through the 6$\times$6 Rashba-Sheka-Pikus and the Luttinger-Kohn matrix Hamiltonians for wurtzite (WZ) and zincblende (ZB) crystal phases, respectively. An analytic representation for the acceptor pseudopotential is used to introduce the specific nature of the impurity atoms. The energy shift due to polaron effects is also considered in this approach. The ionization energy estimates are in very good agreement with those reported experimentally in WZ-GaN. The binding energies for ZB-GaN acceptors are all predicted to be shallower than the corresponding impurities in the WZ phase. The binding energy dependence upon the crystal field splitting in WZ-GaN is analyzed. Ionization levels in AlN are found to have similar `shallow' values to those in GaN, but with some important differences, which depend on the band structure parameterizations, especially the value of crystal field splitting used.Comment: REVTEX file - 1 figur

СТАН ТА ТЕНДЕНЦІЇ МІЖБЮДЖЕТНОГО РЕГУЛЮВАННЯ В УКРАЇНІ В УМОВАХ ФІСКАЛЬНОЇ ДЕЦЕНТРАЛІЗАЦІЇ

A balanced socio-economic development of any country is closely related to the efficiency of the system of intergovernmental relations, which should be aimed at optimizing the process of fiscal decentralization and clear definition of the powers of local government. Interbudgetary regulation in Ukraine reflects processes of the national and political importance and is of great importance in the composition of intergovernmental fiscal relations, which priority is growing in terms of decentralization reforms. Purpose. The main objectives of this study are: to summarize a complex task that is resolved in the process of budgetary control; to analyze the dynamics of revenues of the consolidated budget of Ukraine in 2007-2016 and the proportion of own local revenues in GDP; to distinguish formation features of Ukrainian local budgets by region; to analyze volumes of local budgets per capita in terms of area; to highlight the leverage rate of local budgets; to analyze the share of interbudget transfers in total local budgets. Results. The study is a synthesis of the complex challenges that must be resolved in the process of budgetary control, such as: balancing the budget; foster the interest of local governments in the maximum revenue mobilization; reallocation of existing budgetary resources, taking into account local features. The dynamics of the revenues of the consolidated budget of Ukraine in 2007-2016 was analyzed and concluded that the proportion of own local revenues in GDP tended to decrease with a simultaneous increase in the share of the interbudget transfers from the state budget. Abovementioned resulted in the ensuring of a stable share of local budgets in the GDP structure (at 14-15%). As a result of the intergovernmental fiscal decentralization reform by the results of 2016 the share of own revenues of local budgets Ukraine in GDP rose to 7.2%, or 1.1% compared to 2015 with a simultaneous decrease in the interbudget transfers share from the state budget to 8.2% (0.6% compared to 2015). Analyzed the share interbudget transfers in total local budgets, which for a long period tended to increase (from 47.2% in 2007 to 53.4% in 2016), which is contrary to the basic principles of fiscal decentralization. Conclusion. Grounded features of Ukrainian local budget revenues by region and proved that the unevenness of income between regions of Ukraine are often equivalent to the level of industrial production. Analyzed volumes of local budgets per capita in terms of area. Presented the list of influence instruments on local budgets indexes of incomes, including the increase in the minimum wage, inflation, continuing reform of the budget system in the direction of fiscal decentralization and transfer volumes.Представлен комплекс задач, который должен решаться в процессе межбюджетного регулирования, проанализирована динамика доходной части сводного бюджета Украины в 2007-2016 гг. и удельный вес собственных доходов местных бюджетов в структуре ВВП, выделены особенности формирования доходов местных бюджетов Украины по регионам. Проанализированы объемы доходов местных бюджетов на душу населения в разрезе территорий, освещены рычаги влияния на показатель доходов местных бюджетов, проведен анализ удельного веса межбюджетных трансфертов в общей структуре местных бюджетов.Узагальнено комплекс завдань, що має вирішуватись у процесі міжбюджетного регулювання, проаналізовано динаміку дохідної частини зведеного бюджету України у 2007–2016 рр. та питому вагу власних доходів місцевих бюджетів в структурі ВВП, виокремлено особливості формування доходів місцевих бюджетів України за регіонами. Проаналізовано обсяги доходів місцевих бюджетів на душу населення у розрізі територій, висвітлено важелі впливу на показник доходів місцевих бюджетів, здійснено аналіз питомої ваги міжбюджетних трансфертів у загальній структурі місцевих бюджетів

Negative Electron-electron Drag Between Narrow Quantum Hall Channels

Momentum transfer due to Coulomb interaction between two parallel, two-dimensional, narrow, and spatially separated layers, when a current I_{drive} is driven through one layer, is studied in the presence of a perpendicular magnetic field B. The current induced in the drag layer, I_{drag}, is evaluated self-consistently with I_{drive} as a parameter. I_{drag} can be positive or negative depending on the value of the filling factor \nu of the highest occupied bulk Landau level (LL). For a fully occupied LL, I_{drag} is negative, i.e., it flows opposite to I_{drive}, whereas it is positive for a half-filled LL. When the circuit is opened in the drag layer, a voltage \Delta V_{drag} develops in it; it is negative for a half-filled LL and positive for a fully occupied LL. This positive \Delta V_{drag}, expressing a negative Coulomb drag, results from energetically favored near-edge inter-LL transitions that occur when the highest occupied bulk LL and the LL just above it become degenerate.Comment: Text file in Latex/Revtex/preprint format, 7 separate PS figures, Physical Review B, in pres

Bifurcations observed in the spectra of coupled electron-phonon modes in multiferroic PrFe3(BO3)4PrFe_3(BO_3)_4 subjected to a magnetic field

We report on bifurcations effect mediated by the electron-phonon coupling in a concentrated rare-earth-containing antiferromagnet, observed in the spectra of coupled $4f$-electron-phonon modes under the influence of an external magnetic field. The effect was observed in the low-temperature far-infrared (terahertz) reflection spectra of a multiferroic easy-axis antiferromagnet $PrFe_3(BO_3)_4$ in magnetic fields $\textbf{B}_{ext}||c$. Both paramagnetic and magnetically ordered phases (including a spin-flop one) were studied in magnetic fields up to 30 T. We show that the field behavior of the coupled modes can be successfully explained and modeled on the base of the equation derived in the frame of the theory of coupled electron-phonon modes, with the same field-independent electron-phonon interaction constant $|W| = 14.8 cm^{-1}$.Comment: 5 pages, 4 figure

Electronic states and optical properties of GaAs/AlAs and GaAs/vacuum superlattices by the linear combination of bulk bands method

The linear combination of bulk bands method recently introduced by Wang, Franceschetti and Zunger [Phys. Rev. Lett.78, 2819 (1997)] is applied to a calculation of energy bands and optical constants of (GaAs)$_n$/(AlAs)$_n$ and (GaAs)$_n$/(vacuum)$_n$ (001) superlattices with n ranging from 4 to 20. Empirical pseudopotentials are used for the calculation of the bulk energy bands. Quantum-confined induced shifts of critical point energies are calculated and are found to be larger for the GaAs/vacuum system. The $E_1$ peak in the absorption spectra has a blue shift and splits into two peaks for decreasing superlattice period; the $E_2$ transition instead is found to be split for large-period GaAs/AlAs superlattices. The band contribution to linear birefringence of GaAs/AlAs superlattices is calculated and compared with recent experimental results of Sirenko et al. [Phys. Rev. B 60, 8253 (1999)]. The frequency-dependent part reproduces the observed increase with decreasing superlattice period, while the calculated zero-frequency birefringence does not account for the experimental results and points to the importance of local-field effects.Comment: 10 pages, 11 .eps figures, 1 tabl

Image informatics strategies for deciphering neuronal network connectivity

Brain function relies on an intricate network of highly dynamic neuronal connections that rewires dramatically under the impulse of various external cues and pathological conditions. Among the neuronal structures that show morphologi- cal plasticity are neurites, synapses, dendritic spines and even nuclei. This structural remodelling is directly connected with functional changes such as intercellular com- munication and the associated calcium-bursting behaviour. In vitro cultured neu- ronal networks are valuable models for studying these morpho-functional changes. Owing to the automation and standardisation of both image acquisition and image analysis, it has become possible to extract statistically relevant readout from such networks. Here, we focus on the current state-of-the-art in image informatics that enables quantitative microscopic interrogation of neuronal networks. We describe the major correlates of neuronal connectivity and present workflows for analysing them. Finally, we provide an outlook on the challenges that remain to be addressed, and discuss how imaging algorithms can be extended beyond in vitro imaging studies

Binding Energy of Charged Excitons in ZnSe-based Quantum Wells

Excitons and charged excitons (trions) are investigated in ZnSe-based quantum well structures with (Zn,Be,Mg)Se and (Zn,Mg)(S,Se) barriers by means of magneto-optical spectroscopy. Binding energies of negatively () and positively (X+) charged excitons are measured as functions of quantum well width, free carrier density and in external magnetic fields up to 47 T. The binding energy of shows a strong increase from 1.4 to 8.9 meV with decreasing quantum well width from 190 to 29 A. The binding energies of X+ are about 25% smaller than the binding energy in the same structures. The magnetic field behavior of and X+ binding energies differ qualitatively. With growing magnetic field strength, increases its binding energy by 35-150%, while for X+ it decreases by 25%. Zeeman spin splittings and oscillator strengths of excitons and trions are measured and discussed