Fixed Effect Estimation of Large T Panel Data Models

This article reviews recent advances in fixed effect estimation of panel data models for long panels, where the number of time periods is relatively large. We focus on semiparametric models with unobserved individual and time effects, where the distribution of the outcome variable conditional on covariates and unobserved effects is specified parametrically, while the distribution of the unobserved effects is left unrestricted. Compared to existing reviews on long panels (Arellano and Hahn 2007; a section in Arellano and Bonhomme 2011) we discuss models with both individual and time effects, split-panel Jackknife bias corrections, unbalanced panels, distribution and quantile effects, and other extensions. Understanding and correcting the incidental parameter bias caused by the estimation of many fixed effects is our main focus, and the unifying theme is that the order of this bias is given by the simple formula p/n for all models discussed, with p the number of estimated parameters and n the total sample size.Comment: 40 pages, 1 tabl

First-egg date and air temperature affect nest construction in Blue Tits Cyanistes caeruleus, but not in Great Tits Parus major

Capsule For nest construction by Blue Tits, but not Great Tits, first-egg date (FED) and air temperature significantly affected the mass of the nest as a whole and some of its component parts. Aims To test the hypothesis that use of nest materials is influenced by prevailing climatic conditions during nest construction. Methods Nests used in the study were built by Blue Tits Cyanistes caeruleus and Great Tits Parus major in nestboxes at a site in Lincolnshire, England during the 2008 and 2009 breeding seasons. Nests were dissected into their component parts and then weighed. Results Stepwise discriminant analysis showed that the asses of grasses, feathers and bark were significantly affected by species (all higher in Blue Tits) and year significantly affected the mass of wool and dust in the nests. ANOVA showed that total mass of the nest was not significantly affected by year of construction or species. By contrast, species, but not year, did significantly influence the masses of animal- and plant-derived materials in the nest. In Blue Tit nests there were significant correlations between FED and the mass of animal-derived material in 2008, but with plant-derived material in 2009. There were significant correlations between mean air temperature recorded during the seven days up to FED and the mass of the nests and their plant-derived materials. No significant correlations were observed between FED and nest components for Great Tits. Conclusion Nest construction is potentially affected by a variety of environmental factors, which may impact upon how nests function. A better understanding of how nest variability affects its function may allow better assessment of how climate change may impact upon the reproductive performance of bird

Estimation of Steam Turbine Shafts Fatigue Damage Caused by Torsional Vibrations

В Україні 74 енергоблоки потужністю 150-800 МВт теплових електростанцій із 102 перебувають на межі перевищення паркового ресурсу (220 тис. Годин). З них 17 енергоблоків наближаються до кінця ресурсу парку, а 11 енергоблоків досягли передбачуваного ресурсу (100 тис. Годин). Статистика аварій на електростанціях у різних країнах показує, що більшість з них спричинені тривалим накопиченням збитків від втоми. Серед основних причин пошкодження втоми - пульсація високотемпературних потоків пари в циліндрах турбіни, поперечні та крутильні коливання валів при тривалій експлуатації тощо. Це обумовлює розробку обчислювальних та експериментальних методів визначення втомних пошкоджень вали турбінних установок при динамічних навантаженнях. Оцінка втомних пошкоджень вала парової турбіни К-200-130 базується на 3D-моделі кінцевих елементів. Розрахунки враховують експериментально визначені втомні властивості роторної сталі. Розраховано втомну пошкодження в результаті крутильних коливань валу турбіни, спричинених аномальною роботою турбінного генератора. Зони концентрації напружень в обертових елементах парової турбіни типу К-200-130 встановлені для різних режимів роботи. Запропоновано процедуру прогнозування впливу втоми від пошкоджень на розрахунковий ресурс турбінного агрегату.In Ukraine, 74 power units with a capacity of 150-800 MW of thermal power plants out of 102 are on the verge of exceeding the park resource (220 thousand hours). Of these, 17 power units are close to the end the park resource, and 11 units have reached their estimated resource (100 thousand hours). Statistics of power plants accidents in different countries indicates that most of them are caused by the long term accumulation of fatigue damage. Among the main causes of fatigue damage are the pulsating of high-temperature steam flows in the turbine cylinders, transverse and torsional vibrations of shafts during long-term operation etc. This causes the development of computational and experimental methods for the determination of fatigue damage of turbine units’ shafts under dynamic loads. The evaluation of fatigue damage of steam turbine K-200-130 shaft is based on the 3D finite element model. The calculations take into account experimentally determined fatigue properties of rotor steel. The fatigue damage as a result of torsional vibrations of turbine shaft caused by the abnormal operation of turbine generator is calculated. Zones of stress concentration in the rotating elements of the steam turbine type K-200-130 are established for various operating modes. The procedure to predict the effect of fatigue damage on the estimated resource of turbine unit is proposed.В Украине 74 энергоблока мощностью 150-800 МВт тепловых электростанций из 102 находятся на грани превышения ресурса парка (220 тыс. Часов). Из них 17 энергоблоков близки к исчерпанию ресурса парка, а 11 энергоблоков вышли на расчетный ресурс (100 тыс. Часов). Статистика аварий на электростанциях в разных странах показывает, что большинство из них вызвано длительным накоплением усталостных повреждений. Среди основных причин усталостных повреждений - пульсации высокотемпературных потоков пара в цилиндрах турбины, поперечные и крутильные колебания валов при длительной эксплуатации и т. Д. Это вызывает развитие расчетных и экспериментальных методов определения усталостных повреждений. валы турбоагрегатов при динамических нагрузках. Оценка усталостных повреждений вала паровой турбины К-200-130 проводится на основе трехмерной конечно-элементной модели. В расчетах учтены экспериментально определенные усталостные свойства роторной стали. Рассчитано усталостное повреждение в результате крутильных колебаний вала турбины, вызванных ненормальной работой турбогенератора. Установлены зоны концентрации напряжений во вращающихся элементах паровой турбины типа К-200-130 для различных режимов работы. Предложена методика прогнозирования влияния усталостных повреждений на расчетный ресурс турбоагрегата

HLA-A Confers an HLA-DRB1 Independent Influence on the Risk of Multiple Sclerosis

A recent high-density linkage screen confirmed that the HLA complex contains the strongest genetic factor for the risk of multiple sclerosis (MS). In parallel, a linkage disequilibrium analysis using 650 single nucleotide polymorphisms (SNP) markers of the HLA complex mapped the entire genetic effect to the HLA-DR-DQ subregion, reflected by the well-established risk haplotype HLA-DRB1*15,DQB1*06. Contrary to this, in a cohort of 1,084 MS patients and 1,347 controls, we show that the HLA-A gene confers an HLA-DRB1 independent influence on the risk of MS (P = 8.4×10−10). This supports the opposing view, that genes in the HLA class I region indeed exert an additional influence on the risk of MS, and confirms that the class I allele HLA-A*02 is negatively associated with the risk of MS (OR = 0.63, P = 7×10−12) not explained by linkage disequilibrium with class II. The combination of HLA-A and HLA-DRB1 alleles, as represented by HLA-A*02 and HLA-DRB1*15, was found to influence the risk of MS 23-fold. These findings imply complex autoimmune mechanisms involving both the regulatory and the effector arms of the immune system in the triggering of MS

On the relations between historical epistemology and students’ conceptual developments in mathematics

There is an ongoing discussion within the research field of mathematics education regarding the utilization of the history of mathematics within mathematics education. In this paper we consider problems that may emerge when the historical epistemology of mathematics is paralleled to students’ conceptual developments in mathematics. We problematize this attempt to link the two fields on the basis of Grattan-Guinness’ distinction between “history” and “heritage”. We argue that when parallelism claims are made, history and heritage are often mixed up, which is problematic since historical mathematical definitions must be interpreted in its proper historical context and conceptual framework. Furthermore, we argue that cultural and local ideas vary at different time periods, influencing conceptual developments in different directions regardless of whether historical or individual developments are considered, and thus it may be problematic to uncritically assume a platonic perspective. Also, we have to take into consideration that an average student of today and great mathematicians of the past are at different cognitive levels

A functional calcium-transporting ATPase encoded by chlorella viruses

Calcium-transporting ATPases (Ca2+ pumps) are major players in maintaining calcium homeostasis in the cell and have been detected in all cellular organisms. Here, we report the identification of two putative Ca2+ pumps, M535L and C785L, encoded by chlorella viruses MT325 and AR158, respectively, and the functional characterization of M535L. Phylogenetic and sequence analyses place the viral proteins in group IIB of P-type ATPases even though they lack a typical feature of this class, a calmodulin-binding domain. A Ca2+ pump gene is present in 45 of 47 viruses tested and is transcribed during virus infection. Complementation analysis of the triple yeast mutant K616 confirmed that M535L transports calcium ions and, unusually for group IIB pumps, also manganese ions. In vitro assays show basal ATPase activity. This activity is inhibited by vanadate, but, unlike that of other Ca2+ pumps, is not significantly stimulated by either calcium or manganese. The enzyme forms a 32P-phosphorylated intermediate, which is inhibited by vanadate and not stimulated by the transported substrate Ca2+, thus confirming the peculiar properties of this viral pump. To our knowledge this is the first report of a functional P-type Ca2+-transporting ATPase encoded by a virus

Harmonising and linking biomedical and clinical data across disparate data archives to enable integrative cross-biobank research

A wealth of biospecimen samples are stored in modern globally distributed biobanks. Biomedical researchers worldwide need to be able to combine the available resources to improve the power of large-scale studies. A prerequisite for this effort is to be able to search and access phenotypic, clinical and other information about samples that are currently stored at biobanks in an integrated manner. However, privacy issues together with heterogeneous information systems and the lack of agreed-upon vocabularies have made specimen searching across multiple biobanks extremely challenging. We describe three case studies where we have linked samples and sample descriptions in order to facilitate global searching of available samples for research. The use cases include the ENGAGE (European Network for Genetic and Genomic Epidemiology) consortium comprising at least 39 cohorts, the SUMMIT (surrogate markers for micro- and macro-vascular hard endpoints for innovative diabetes tools) consortium and a pilot for data integration between a Swedish clinical health registry and a biobank. We used the Sample avAILability (SAIL) method for data linking: first, created harmonised variables and then annotated and made searchable information on the number of specimens available in individual biobanks for various phenotypic categories. By operating on this categorised availability data we sidestep many obstacles related to privacy that arise when handling real values and show that harmonised and annotated records about data availability across disparate biomedical archives provide a key methodological advance in pre-analysis exchange of information between biobanks, that is, during the project planning phase

Calcium Uptake and Proton Transport by Acidocalcisomes of Toxoplasma gondii

Acidocalcisomes are acidic calcium stores found in diverse organisms, being conserved from bacteria to humans. They possess an acidic matrix that contains several cations bound to phosphates, which are mainly present in the form of short and long polyphosphate chains. Their matrix is acidified through the action of proton pumps such as a vacuolar proton ATPase and a vacuolar proton pyrophosphatase. Calcium uptake occurs through a Ca2+/H+ countertransporting ATPase located in the membrane of the organelle. Acidocalcisomes have been identified in a variety of microorganisms, including Apicomplexan parasites such as Plasmodium and Eimeria species, and in Toxoplasma gondii. We report the purification and characterization of an acidocalcisome fraction from T. gondii tachyzoites after subcellular fractionation and further discontinuous iodixanol gradient purification. Proton and calcium transport activities in the fraction were characterized by fluorescence microscopy and spectrophotometric methods using acridine orange and arsenazo III, respectively. This work will facilitate the understanding of the function of acidocalcisomes in Apicomplexan parasites, as we can now isolate highly purified fractions that could be used for proteomic analysis to find proteins that may clarify the biogenesis of these organelles