The variety generated by order algebras

Every ordered set can be considered as an algebra in a natural way. We investigate the variety generated by order algebras. We prove, among other things, that this variety is not finitely based and, although locally finite, it is not contained in any finitely generated variety; we describe the bottom of the lattice of its subvarieties

Excluding Light Asymmetric Bosonic Dark Matter

We argue that current neutron star observations exclude asymmetric bosonic non-interacting dark matter in the range from 2 keV to 16 GeV, including the 5-15 GeV range favored by DAMA and CoGeNT. If bosonic WIMPs are composite of fermions, the same limits apply provided the compositeness scale is higher than ~10^12 GeV (for WIMP mass ~1 GeV). In case of repulsive self-interactions, we exclude large range of WIMP masses and interaction cross sections which complements the constraints imposed by observations of the Bullet Cluster.Comment: published versio

Imaging the charge transport in arrays of CdSe nanocrystals

A novel method to image charge is used to measure the diffusion coefficient of electrons in films of CdSe nanocrystals at room temperature. This method makes possible the study of charge transport in films exhibiting high resistances or very small diffusion coefficients.Comment: 4 pages, 4 jpg figure

Efikasno premeštanje push-pull 5-supstituisanih 4-oksotiazolidina indukovano piridinijum-hidrobromid-perbromidom pod homogenim reakcionim uslovima

Pyridinium hydrobromide perbromide (PHBP) is a highly efficient reagent for the conversion of 5-substituted-2-alkylidene-4-oxothiazolidine derivatives to the corresponding thiazolidines with two fully delocalized exocyclic double bonds at the C(2) and C(5) positions. This conversion as a two-step bromination-rearrangement process occurs in acetonitrile under homogeneous reaction conditions.Piridinijum-hidrobromid-perbromid (PHBP) je veoma efikasan reagens za konverziju 5-supstituisanih-2-alkiliden-4-oksotiazolidinskih derivata u odgovarajuće tiazolidine sa dve potpuno delokalizovane egzociklične dvogube veze u položajima C(2) i C(5). Ova konverzija je dvofazni proces bromovanja i premeštanja koji se odvija u acetonitrilu pod homogenim reakcionim uslovima

Droop vs. virtual inertia: Comparison from the perspective of converter operation mode

Virtual Inertia Emulation (VIE) and traditional Active Power Droop Control (APDC) are among the most common approaches for regulating the active power output of inverter-based generators. Furthermore, it has been shown that, under certain conditions, these two methods can be equivalent. However, neither those studies, nor the analyses comparing the two control schemes with respect to their dynamical properties, have investigated the impact of the converter operation mode. This paper explores the subject by investigating the two control approaches under such conditions, and determining when this assumption does not hold. Using time-domain simulations with a detailed Voltage Source Converter model, we compare VIE and APDC qualitatively and reformulate the respective conditions for equivalence

Las actitudes de los padres sobre la adaptación de los niños a la institución preescolar

The aim of this research study is to examine parents´ attitudes towards the process of children´s adjustment to a pre-school institution, as well as towards separation difficulties which are encountered when a child starts attending kindergarten. Research results provide answers to whether parents are familiar with the problems manifested in the children´s adjustment process, as well as with the possibilities of successfully overcoming such issues. The research included 763 parents of pre-school children in the territory of Serbia. The differences in parents´ attitudes have been analysed relative to their sex, education and age. In the course of research the authors resorted to a five-point Likert scale composed of 16 items grouped into the following categories: factors which influence the process of adjustment, indicators of a successfully completed adjustment process and methods for overcoming the issues raised in the process of children´s adjustment to a pre-school institution. Parents believe that children´s satisfaction when they attend kindergarten is a more significant indicator of a successfully completed adjustment process relative to the absence of crying and deprecation, as well as that for the purposes of overcoming the difficulties which occur when children start attending a pre-school institution parents most frequently introduce preschool teachers to their child´s habits and traits, and later talk with the child about events in the kindergarten. Research results indicate the presence of statistically significant differences in parents´ attitudes relative to their sex, i.e. they indicate that the adjustment period is more stressful for mothers than for fathers.El objetivo de la investigación es examinar las actitudes de los padres sobre el proceso de adaptación de los niños a la institución preescolar, y también las dificultades de separación que ocurren con el ingreso del niño en jardín de infantes. Los resultados del estudio proponen respuestas a las preguntas si los padres están familiarizados con los problemas que se manifiestan en el proceso de adaptación de los niños a la institución preescolar, y también preguntas sobre las posibilidades de su superación exitosa. El estudio involucró a 763 padres de niños en edad preescolar de Serbia. Se analizan las diferencias en las actitudes de los padres en relación con el género, el nivel de educación y la edad. En la investigación fue utilizada una escala de evaluación de Likert de cinco pasos, compuesta por 16 ítems agrupados en las siguientes categorías: factores que intervienen en el proceso de adaptación, indicadores de una adaptación exitosa y métodos para superar los problemas que surgen en el proceso de adaptación de los niños a la institución preescolar. Los padres lo consideran que la satisfacción de los niños cuando van al jardín de infantes representa un indicador muy importante de la finalización exitosa del proceso de adaptación en relación a la ausencia de llanto y resentimiento, y de que los padres, para superar las dificultades que ocurren cuando niños empiezan a ir en el jardín de infantes, a menudo se reúnen con maestros para familiarizarlos con los costumbres y las características de sus hijos, y luego hablan con sus hijos sobre los acontecimientos en el jardín de infancia. Los resultados del estudio indican que existen unas diferencias estadísticamente significativas en las actitudes de los padres con respecto al género, es decir, el período de adaptación es más estresante para las madres que para los padres

Gravitational Collapse with a Cosmological Constant

We consider the effect of a positive cosmological constant on spherical gravitational collapse to a black hole for a few simple, analytic cases. We construct the complete Oppenheimer-Snyder-deSitter (OSdS) spacetime, the generalization of the Oppenheimer-Snyder solution for collapse from rest of a homogeneous dust ball in an exterior vacuum. In OSdS collapse, the cosmological constant may affect the onset of collapse and decelerate the implosion initially, but it plays a diminishing role as the collapse proceeds. We also construct spacetimes in which a collapsing dust ball can bounce, or hover in unstable equilibrium, due to the repulsive force of the cosmological constant. We explore the causal structure of the different spacetimes and identify any cosmological and black hole event horizons which may be present.Comment: 7 pages, 10 figures; To appear in Phys. Rev.

Thionation of N-Methyl- and N-Unsubstituted Thiazolidine Enaminones

The potential of the directional non-bonded 1,5-type S···O interactions to initiate an incipient stage of an in situ rearrangement of N-unsubstituted thiazolidine enaminones to the functionalized 1,2-dithioles has been demonstrated. Spectral characteristics, as well as an X-ray structural analysis of the selected rearranged product, indicate that a dynamic interconversion occurs in a solution between the 1,2-dithiole and 3,3aλ⁴,4-trithia-1-azapentalene bicylic form. The lack of the rearrangement in the case of the N-methyl substituted enaminone precursor is attributed to an unfavorable methyl migration in the last reaction step

Gravitational Collapse of Inhomogeneous Dust in (2+1) Dimensions

We examine the gravitational collapse of spherically symmetric inhomogeneous dust in (2+1) dimensions, with cosmological constant. We obtain the analytical expressions for the interior metric. We match the solution to a vacuum exterior. We discuss the nature of the singularity formed by analyzing the outgoing radial null geodesics. We examine the formation of trapped surfaces during the collapse.Comment: Accepted for publication in CQ