Optical properties of Ce–Ti-containing silicate glasses

Silicate glasses doped with ceria and titania have been studied. Such co-doping determines the specific coloration of the glasses with adjustable absorption in the visible spectral region. Based on measurements of optical transmittance and photoluminescence and studies of electron paramagnetic resonance, it was established that the features of their optical properties are due to the formation of chromophore centers incorporating cerium and titanium ions

Plaquette operators used in the rigorous study of ground-states of the Periodic Anderson Model in D=2D = 2 dimensions

The derivation procedure of exact ground-states for the periodic Anderson model (PAM) in restricted regions of the parameter space and D=2 dimensions using plaquette operators is presented in detail. Using this procedure, we are reporting for the first time exact ground-states for PAM in 2D and finite value of the interaction, whose presence do not require the next to nearest neighbor extension terms in the Hamiltonian. In order to do this, a completely new type of plaquette operator is introduced for PAM, based on which a new localized phase is deduced whose physical properties are analyzed in detail. The obtained results provide exact theoretical data which can be used for the understanding of system properties leading to metal-insulator transitions, strongly debated in recent publications in the frame of PAM. In the described case, the lost of the localization character is connected to the break-down of the long-range density-density correlations rather than Kondo physics.Comment: 34 pages, 5 figure

Is diversity good?

Prominent ethical and policy issues such as affirmative action and female enrollment in science and engineering revolve around the idea that diversity is good. However, even though diversity is an ambiguous concept, a precise definition is seldom provided. We show that diversity may be construed as a factual description, a craving for symmetry, an intrinsic good, an instrumental good, a symptom, or a side effect. These acceptions differ vastly in their nature and properties. The first one cannot lead to any action and the second one is mistaken. Diversity as intrinsic good is a mere opinion, which cannot be concretely applied; moreover, the most commonly invoked forms of diversity (sexual and racial) are not intrinsically good. On the other hand, diversity as instrumental good can be evaluated empirically and can give rise to policies, but these may be very weak. Finally, symptoms and side effects are not actually about diversity. We consider the example of female enrollment in science and engineering, interpreting the various arguments found in the literature in light of this polysemy. Keywords: ethics, policy, higher education, female students, minority students, affirmative actionComment: 7 page

Ferromagnetism without flat bands in thin armchair nanoribbons

Describing by a Hubbard type of model a thin armchair graphene ribbon in the armchair hexagon chain limit, one shows in exact terms, that even if the system does not have flat bands at all, at low concentration a mesoscopic sample can have ferromagnetic ground state, being metallic in the same time. The mechanism is connected to a common effect of correlations and confinement.Comment: 37 pages, 12 figures, in press at Eur. Phys. Jour.

The data acquisition system of the CHORUS experiment

In the years 1994-1998 the CHORUS Collaboration has recorded data in the CERN WA95 experiment. Here we describe the data acquisition system that has been used, featuring concurrent hierarchical state machines, a remote operating system, a buffer manager, a dispatcher, a control panel and a supervisor

The data acquisition system of the CHORUS experiment

In the years 1994--1998 the CHORUS Collaboration has recorded data in the CERN WA95 experiment. Here we describe the data acquisition system that has been used, featuring concurrent hierarchical state machines, a remote operating system, a buffer manager, a dispatcher, a control panel and a supervisor

ВЛИЯНИЕ АКТИВНОГО СОПРОТИВЛЕНИЯ ОБМОТОК ИМПУЛЬСНОГО ТРАНСФОРМАТОРА НА ПАРАМЕТРЫ ФОРМИРУЕМЫХ НА ЕМКОСТНОЙ НАГРУЗКЕ ИМПУЛЬСОВ НАПРЯЖЕНИЯ

Goal. Analysis of the influence of the active resistance of the primary and secondary windings of a pulse transformer on the voltage at the load capacitance based on the developed methodology for the analysis of transients caused by the discharge of the storage capacitance in the primary winding. Methodology. A model for calculating transients is developed using the Laplace transform. Transient modeling is carried out in the MATLAB software package. The results of transient calculations are compared with experimental results. Results. A method for calculating transients in test installations with pulse transformers has been developed, which allows taking into account the effect of power losses in the primary and secondary windings on the voltage at the load capacitance. The calculated relations are obtained, allowing to take into account the influence of the active resistance of the primary and secondary windings of the transformer on the voltage at the load capacitance, the currents in the primary and secondary windings of the transformer, as well as on the voltage drop on the inductance of the primary winding of the transformer. Scientific novelty. A mathematical model is developed for calculating transients in the primary and secondary windings of a pulse transformer, taking into account the influence of the active resistance of the windings when it changes over a wide range of possible values. Practical value. Using the proposed technique, it is possible to determine the parameters of the discharge circuit at which test voltage pulses are formed on the load capacitance without distorting the shape of the pulse front. Цель. Анализ влияния активного сопротивления первичной и вторичной обмоток импульсного трансформатора на напряжение на нагрузочной емкости на основании разработанной методики анализа переходных процессов, вызванных разрядом накопительной емкости в первичной обмотке. Методика. Модель для расчета переходных процессов разработана с применением преобразования Лапласа. Моделирование переходных процессов проводилось в программном пакете MATLAB. Результаты расчетов переходных процессов сравнивались с экспериментальными результатами. Результаты. Разработана методика расчета переходных процессов в испытательных установках с импульсными трансформаторами, позволяющая учитывать влияние потерь мощности в первичной и вторичной обмотках на напряжение на нагрузочной емкости. Получены расчетные соотношения, позволяющие учитывать влияние активного сопротивления первичной и вторичной обмоток трансформатора на напряжение на нагрузочной емкости, токи в первичной и вторичной обмотках трансформатора, а также на падение напряжения на индуктивности первичной обмотки трансформатора. Научная новизна. Разработана математическая модель для расчета переходных процессов в первичной и вторичной обмотках импульсного трансформатора с учетом влияния активного сопротивления обмоток при его изменении в широком диапазоне возможных значений. Практическое значение. Использование предложенной методики позволяет определять параметры разрядной цепи, при которых на нагрузочной емкости происходит формирование тестовых импульсов напряжения без искажений формы фронта импульсов.

Structural properties of hard disks in a narrow tube

Positional ordering of a two-dimensional fluid of hard disks is examined in such narrow tubes where only the nearest-neighbor interactions take place. Using the exact transfer-matrix method the transverse and longitudinal pressure components and the correlation function are determined numerically. Fluid-solid phase transition does not occur even in the widest tube, where the method just loses its exactness, but the appearance of the dramatic change in the equation of state and the longitudinal correlation function shows that the system undergoes a structural change from a fluid to a solid-like order. The pressure components show that the collisions are dominantly longitudinal at low densities, while they are transverse in the vicinity of close packing density. The transverse correlation function shows that the size of solid-like domains grows exponentially with increasing pressure and the correlation length diverges at close packing. It is managed to find an analytically solvable model by expanding the contact distance up to first order. The approximate model, which corresponds to the system of hard parallel rhombuses, behaves very similarly to the system of hard disks.Comment: Acceped in Journal of Statistical Mechanics: Theory and Experimen

The CHORUS neutrino oscillation search experiment

The CHORUS experiment has successfully finished run I (320~000 recorded \numu\ CC in 94/95) and performed half of run II (225~000 \numu\ CC in 96). The analysis chain was exercised on a small data sample for the muonic \tdecay\ search using for the first time fully automatic emulsion scanning. This pilot analysis, resulting in a limit \sintth \leq 3 \cdot 10^{-2}, confirms that the CHORUS proposal sensitivity (\sintth \leq 3 \cdot 10^{-4}) is within reach in two years