Resources and student achievement – evidence from a Swedish policy reform

This paper utilizes a policy change to estimate the effect of teacher density on student performance. We find that an increase in teacher density has a positive effect on student achievement. The baseline estimate – obtained by using the grade point average as the outcome variable – implies that resource increases corresponding to the class-size reduction in the STAR-experiment (i.e., a reduction of 7 students) improves performance by 2.6 percentile ranks (or 0.08 standard deviations). When we use test score data for men, potentially a more objective measure of student performance, the effect of resources appears to be twice the size of the baseline estimate.Student performance; teacher/student ratio; policy reform; differences-in-differences

Numerical Study of Structural Phase Transitions in a Vertically Confined Plasma Crystal

Dusty plasmas consists of an ionized gas containing small (usually negatively charged) particles. Dusty plasmas are of interest in both astrophysics and space physics as well as in research in plasma processing and nanofabrication. In this work, the formation of plasma crystals confined in an external one-dimensional parabolic potential well is simulated for a normal experimental environment employing a computer code called BOX_TREE. Such crystals are layered systems, with each layer a two dimensional lattice composed of grain particles. The number of layers is dependent upon the external potential parameter. For constant layer number, the intralayer structure transits from a square lattice to a hexagonal (triangular) lattice as the confining potential decreases. For hexagonal lattices, both hcp and fcc characteristics were found but hcp structures dominate. The relative thickness of the system was also examined. The results were compared with previous experimental and theoretical results and found to agree

Could bacterial associations determine the success of weevil species?

The weevil superfamily Curculionoidea is the largest insect group and so the largest animal group on earth. This taxon includes species which represent an important threat to many economically important crops and, therefore, pose a risk to agriculture and food security. Insect–bacteria associations have been recognised to provide the insect host with many benefits, such as ensuring the acquisition of essential nutrients or protecting the host from natural enemies. The role of bacteria associations within the weevil superfamily remains nonetheless understudied in comparison with other insect taxa. This review draws together existing knowledge on the influence of bacteria associated with weevils known to be agricultural pest species. The implications of these weevil–bacterial associations in determining pest status and their relevance to targeted pest management interventions are discussed. Specific consideration is given to the role of bacteria in cuticle formation, flight activity, reproduction manipulation and adaptation to different environments and food sources

Categorification of persistent homology

We redevelop persistent homology (topological persistence) from a categorical point of view. The main objects of study are diagrams, indexed by the poset of real numbers, in some target category. The set of such diagrams has an interleaving distance, which we show generalizes the previously-studied bottleneck distance. To illustrate the utility of this approach, we greatly generalize previous stability results for persistence, extended persistence, and kernel, image and cokernel persistence. We give a natural construction of a category of interleavings of these diagrams, and show that if the target category is abelian, so is this category of interleavings.Comment: 27 pages, v3: minor changes, to appear in Discrete & Computational Geometr

Оценивание устойчивого развития окружающей среды на субнациональном уровне в Украине

Рассмотрены существующие методы оценивания устойчивого развития окружающей среды (самостоятельные индикаторы, а также их системы и индексы). Предложен индекс устойчивого развития окружающей среды для оценивания взаимоотношений с окружающей средой на уровне регионов Украины, учитывающий национальные приоритеты в экологической политике. По предложенному региональному индексу получены экологические профили и рейтинг областей Украины.Розглянуто існуючі методи оцінювання сталого розвитку довкілля (самостійні індикатори, а також їх системи та індекси). Запропоновано індекс сталого розвитку довкілля для оцінювання взаємовідносин із навколишнім середовищем на рівні регіонів України, який враховує національні пріоритети в екологічній політиці. За запропонованим регіональним індексом отримано екологічні профілі і рейтинг областей України.The existing methods for assessment of the environment sustainable development (independent indicators, their systems and indices) are considered. The environment sustainability index for assessment of relations with the environment at a regional level for Ukraine is proposed, which takes into account the national priorities in ecological policy. Ecological profiles and rating of the Ukrainian regions are obtained according to the proposed regional index

Geographic origin may not influence vine weevil Otiorhynchus sulcatus (Fabricius) susceptibility to the entomopathogenic fungus Metarhizium brunneum (Petch)

Otiorhynchus sulcatus, known as the vine weevil, is a polyphagous pest that causes economically important damage to horticultural crops worldwide. The entomopathogenic fungus Metarhizium brunneum is widely used to control this pest. Little research has investigated variation in susceptibility to this pathogen between vine weevil populations at different locations. This study addresses this knowledge gap by comparing survival rates of larvae from adults collected in two UK areas when treated with M. brunneum. Larvae from these locations did not differ in their susceptibility, suggesting that location per se may not affect the efficacy of M. brunneum against vine weevil larvae

Facility for studying the effects of elevated carbon dioxide concentration and increased temperature on crops

The requirements for the experimental study of the effects of global climate change conditions on plants are outlined. A semi-controlled plant growth facility is described which allows the study of elevated CO2 and temperature, and their interaction on the growth of plants under radiation and temperature conditions similar to the field. During an experiment on winter wheat (cv. Mercia), which ran from December 1990 through to August 1991, the facility maintained mean daytime CO2 concentrations of 363 and 692 cm3 m-3 for targets of 350 and 700 cm3 m-3 respectively. Temperatures were set to follow outside ambient or outside ambient +4-degrees-C, and hourly means were within 0.5-degrees-C of the target for 92% of the time for target temperatures greater than 6-degrees-C. Total photosynthetically active radiation incident on the crop (solar radiation supplemented by artifical light with natural photoperiod) was 2% greater than the total measured outside over the same period

Influence of dietyl ether on the mixture of biodiesel B50

Biodiesel is generally defined as monoalkyl esters of plant oils and animal fats. Oils derived from plants and animal fats and their derivatives have the possibility as a substitute for diesel fuel. This biodiesel is then mixed with diesel with a composition of 50% biodiesel and 50% diesel to make B50. In this study, B50 was then mixed with diethyl ether. The results of this study, obtained a mixture of B50+0% diethyl ether, B50+2% diethyl ether, B50+4% diethyl ether, B50+6% diethyl ether, B50+8% diethyl ether, B50+10% diethyl ether with kinematic viscosity (6.5 mm2/s, 6 mm2/s, 5.4 mm2/s, 5 mm2/s, 4.3 mm2/s, and 3.6 mm2/s), flash point (183 oC, 179 oC, 177 oC, 175 oC, 171 oC, and 167 oC), pour point (7 oC, 6 oC, 5 oC, 4 oC, 2 oC, and 1 oC), caloric value (10051,66 cal/m3, 10097,1322 cal/gram, 10128,13 cal/gram, 10170,38 cal/gram, 10235,37 cal/gram, and 10306,84 cal/gram), and density 15 oC (841.1 Kg/m3, 839.5 Kg/m3, 838.2 Kg/m3, 837 Kg/m3, 836.2 Kg/m3, dan 835.1 Kg/m3

Amorphization threshold in Si-implanted strained SiGe alloy layers

The authors have examined the damage produced by Si-ion implantation into strained Si{sub 1{minus}x}Ge{sub x} epilayers. Damage accumulation in the implanted layers was monitored in situ by time-resolved reflectivity and measured by ion channeling techniques to determine the amorphization threshold in strained Si{sub 1{minus}x}Ge{sub x} (x = 0.16 and 0.29) over the temperature range 30--110 C. The results are compared with previously reported measurements on unstrained Si{sub 1{minus}x}Ge{sub x}, and with the simple model used to describe those results. They report here data which lend support to this model and which indicate that pre-existing strain does not enhance damage accumulation in the alloy layer

Amorphization Threshold in Si-Implanted Strained Sige Alloy Layers

The authors have examined the damage produced by Si-ion implantation into strained Si{sub 1{minus}x}Ge{sub x} epilayers. Damage accumulation in the implanted layers was monitored in situ by time-resolved reflectivity and measured by ion channeling techniques to determine the amorphization threshold in strained Si{sub 1{minus}x}Ge{sub x} (x = 0.16 and 0.29) over the temperature range 30--110 C. The results are compared with previously reported measurements on unstrained Si{sub 1{minus}x}Ge{sub x}, and with the simple model used to describe those results. They report here data which lend support to this model and which indicate that pre-existing strain does not enhance damage accumulation in the alloy layer