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Search Models (search + models)
Selected AbstractsEquilibrium Search Models and the Transition From School To WorkINTERNATIONAL ECONOMIC REVIEW, Issue 2 2001Audra J. Bowlus This paper applies the Burdett,Mortensen (1998) equilibrium search model to study the school to work transitions of U.S. high school graduates. We consider the case of discrete firm heterogeneity and provide a computational method to obtain the MLE. Our results show that unemployed blacks receive fewer offers than whites and employed blacks are more likely to lose their jobs. Importantly, employed blacks and whites receive job offers at the same rate. Assigning the whites' search parameters to the blacks and re-solving reveals that 75 percent of the observed wage differential is explained by the job destruction rate differences. [source] Movin' On Up: Interpreting The Earnings,Experience ProfileBULLETIN OF ECONOMIC RESEARCH, Issue 4 2000Alan Manning Human capital theory provides the generally accepted interpretation of the relationship between earnings and labour market experience, namely that general human capital tends to increase with experience. However, there are other plausible interpretations. Search models, for example, generally predict that more time in the labour market increases the chance of finding a better match and hence tends to be associated with higher earnings. This paper shows how a simple search model can be used to predict the amount of earnings growth that can be assigned to search with the residual being assigned to the human capital model. A substantial if not the larger part of the rise in earnings over the life-cycle in Britain can be explained by a simple search model, and virtually all the earnings gap between men and women can be explained in this way. Overall, the evidence suggests that we do need to reinterpret the returns to experience in earnings functions. [source] Contiguity Constraints for Single-Region Site Search ProblemsGEOGRAPHICAL ANALYSIS, Issue 4 2000Thomas J. Cova This paper proposes an explicit set of constraints as a general approach to the contiguity problem in site search modeling. Site search models address the challenging problem of identifying the best area in a study region for a particular land use, given that there are no candidate sites. Criteria that commonly arise in a search include a site's area, suitability, cost, shape, and proximity to surrounding geographic features. An unsolved problem in this modeling arena is the identification of a general set of mathematical programming constraints that can guarantee a contiguous solution (site) for any 0,1 integer-programming site search formulation. The constraints proposed herein address this problem, and we evaluate their efficacy and efficiency in the context of a regular and irregular tessellation of geographic space. An especially efficient constraint form is derived from a more general form and similarly evaluated. The results demonstrate that the proposed constraints represent a viable, general approach to the contiguity problem. [source] AN ON-THE-JOB SEARCH MODEL OF CRIME, INEQUALITY, AND UNEMPLOYMENT*INTERNATIONAL ECONOMIC REVIEW, Issue 3 2004Kenneth Burdett We extend simple search models of crime, unemployment, and inequality to incorporate on-the-job search. This is valuable because, although simple models are useful, on-the-job search models are more interesting theoretically and more relevant empirically. We characterize the wage distribution, unemployment rate, and crime rate theoretically, and use quantitative methods to illustrate key results. For example, we find that increasing the unemployment insurance replacement rate from 53 to 65 percent increases unemployment and crime rates from 10 and 2.7 percent to 14 and 5.2 percent. We show multiple equilibria arise for some fairly reasonable parameters; in one case, unemployment can be 6 or 23 percent, and crime 0 or 10 percent, depending on the equilibrium. [source] Job and residential search behaviour of two-earner households,PAPERS IN REGIONAL SCIENCE, Issue 4 2000Jos van Ommeren Two-earner households; job mobility; residential mobility; commuting; search Abstract Even though a large share of the workforce belongs to two-earner households, job search models invariably ignore the interaction between the wage earners of the same household. In this article, job and residential search behaviour of two-earner households are simultaneously analysed. The main finding of the theoretical model is that two-earner households search less intensively in the housing market, and more intensively in the labour market, if the distance between the workplaces of the two wage earners is longer. In the empirical part the latter finding has been analysed based upon a data set for Dutch two-earner households. [source] Web searching model: Integrating multitasking, cognitive coordination and cognitive shiftsPROCEEDINGS OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE & TECHNOLOGY (ELECTRONIC), Issue 1 2008Jia T. Du Web search models are a significant and important area of Web research. This paper outlines dissertation research to develop a Web search model that integrates processes involving multitasking, cognitive coordination and cognitive shifts. Based on previous studies, we present a preliminary conceptual model of Web search interaction incorporating multitasking, cognitive coordination and cognitive shifts. Research questions and research design are also discussed. [source] Molecular replacement with MOLREPACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2010Alexei Vagin MOLREP is an automated program for molecular replacement that utilizes a number of original approaches to rotational and translational search and data preparation. Since the first publication describing the program, MOLREP has acquired a variety of features that include weighting of the X-ray data and search models, multi-copy search, fitting the model into electron density, structural superposition of two models and rigid-body refinement. The program can run in a fully automatic mode using optimized parameters calculated from the input data. [source] Cluster analysis for phasing with molecular replacement: a feasibility studyACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2009Andreas Buehler Molecular replacement can fail to find a solution, namely a unique orientation and position of a search model, even when many search models are tested under various conditions. Simultaneous use of the results of these searches may help in the solution of such difficult structures. A closeness between the peaks of several calculated rotation functions may identify the model orientation. The largest and most compact cluster of such peaks usually corresponds to models which are oriented similarly to the molecule under study. A search for the optimal translation may be more problematic and both individual translation functions and straightforward cluster analysis in the space of geometric parameters such as rotation angles and translation vectors may give no result. An improvement may be obtained by performing cluster analysis of the peaks of several translation functions in phase-set space. In this case, the Fourier maps computed using the observed structure-factor magnitudes and the phases calculated from differently positioned models are compared. Again, as a rule, the largest and the most compact cluster corresponds to the correct solution. The result of the updated procedure is no longer a single search model but an averaged Fourier map. [source] MrBUMP: an automated pipeline for molecular replacementACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2008Ronan M. Keegan A novel automation pipeline for macromolecular structure solution by molecular replacement is described. There is a special emphasis on the discovery and preparation of a large number of search models, all of which can be passed to the core molecular-replacement programs. For routine molecular-replacement problems, the pipeline automates what a crystallographer might do and its value is simply one of convenience. For more difficult cases, the pipeline aims to discover the particular template structure and model edits required to produce a viable search model and may succeed in finding an efficacious combination that would be missed otherwise. An overview of MrBUMP is given and some recent additions to its functionality are highlighted. [source] Automated search-model discovery and preparation for structure solution by molecular replacementACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2007Ronan M. Keegan A novel automation pipeline for macromolecular structure solution by molecular replacement is described. There is a special emphasis on the discovery and preparation of a large number of search models, all of which can be passed to the core molecular-replacement programs. For routine molecular-replacement problems, the pipeline automates what a crystallographer might do and its value is simply one of convenience. For more difficult cases, the pipeline aims to discover the particular template structure and model edits required to produce a viable search model and may succeed in finding an efficacious combination that would be missed otherwise. The pipeline is described in detail and a number of examples are given. The examples are chosen to illustrate successes in real crystallography problems and also particular features of the pipeline. It is concluded that exploring a range of search models automatically can be valuable in many cases. [source] Crystallization and preliminary X-ray diffraction analysis of shikimate kinase from Mycobacterium tuberculosis in complex with MgADPACTA CRYSTALLOGRAPHICA SECTION D, Issue 12 2001Yijun Gu Shikimate kinase (SK) from Mycobacterium tuberculosis (Mt) was overexpressed in Escherichia coli, purified and cocrystallized with MgADP in hanging drops using the vapor-diffusion procedure with PEG 4000 and 2-propanol as precipitants at pH 7.5. The crystal of MtSK,MgADP, which diffracted to 2.2,Å resolution, belonged to space group P3221 or P3121, with unit-cell parameters a = b = 64.01, c = 92.41,Å. There was one MtSK molecule in the asymmetric unit. Molecular-replacement trials with the crystal structure of SK from Erwinia chrysanthemi (PDB code 1shk) and adenylate kinase (PDB code 1ake) as search models were not successful. Heavy-atom derivative screening is in progress. [source] A systematic case study on using NMR models for molecular replacement: p53 tetramerization domain revisitedACTA CRYSTALLOGRAPHICA SECTION D, Issue 12 2000Yu Wai Chen Molecular replacement using search models derived from nuclear magnetic resonance (NMR) spectroscopy has often proved problematic. It has been known for some time that the overall differences in atomic positions (r.m.s.d.) between the crystalline and the solution states of the same protein are of the order of 1,2,Å and approach the limit of molecular replacement. In most cases, this structural difference is a result of calculating the NMR structure with insufficient data, yielding an NMR structure of limited accuracy. A systematic case study was performed to investigate the use of NMR models for molecular replacement on the p53 tetramerization domain: NMR search models of varying degrees of accuracy were employed to solve phases for the 1.5,Å X-ray diffraction data. An approximate correlation was found between the accuracy of the NMR search model and the clarity and quality of the molecular-replacement solution. It was found that ensemble models perform better than single averaged models and have a larger tolerance in model inaccuracy. Also, distance-derived B factors can improve the performance of single models. [source] Preliminary structural characterization of human SOUL, a haem-binding proteinACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 7 2009Filipe Freire Human SOUL (hSOUL) is a 23,kDa haem-binding protein that was first identified as the PP23 protein isolated from human full-term placentas. Here, the overexpression, purification and crystallization of hSOUL are reported. The crystals belonged to space group P6422, with unit-cell parameters a = b = 145, c = 60,Å and one protein molecule in the asymmetric unit. X-ray diffraction data were collected to 3.5,Å resolution at the ESRF. A preliminary model of the three-dimensional structure of hSOUL was obtained by molecular replacement using the structures of murine p22HBP (PDB codes 2gov and 2hva), obtained by solution NMR, as search models. [source] Cloning, purification, crystallization and preliminary X-ray analysis of a chimeric NADPH-cytochrome P450 reductaseACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2009Louise Aigrain NADPH-cytochrome P450 reductase (CPR) is the favoured redox partner of microsomal cytochromes P450. This protein is composed of two flavin-containing domains (FMN and FAD) connected by a structured linker. An active CPR chimera consisting of the yeast FMN and human FAD domains has been produced, purified and crystallized. The crystals belonged to the monoclinic space group C2 and contained one molecule per asymmetric unit. Molecular replacement was performed using the published rat and yeast structures as search models. The initial electron-density maps revealed that the chimeric enzyme had crystallized in a conformation that differed from those of previously solved structures. [source] There is a baby in the bath water: AcrB contamination is a major problem in membrane-protein crystallizationACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 10 2008David Veesler In the course of a crystallographic study of the Methanosarcina mazei CorA transporter, the membrane protein was obtained with at least 95% purity and was submitted to crystallization trials. Small crystals (<100,µm) were grown that diffracted to 3.42,Å resolution and belonged to space group R32, with unit-cell parameters a = b = 145.74, c = 514.0,Å. After molecular-replacement attempts using available CorA structures as search models failed to yield a solution, it was discovered that the crystals consisted of an Escherichia coli contaminating protein, acriflavine resistance protein B (AcrB), that was present at less than 5% in the protein preparations. AcrB contamination is a major problem when expressing membrane proteins in E. coli since it binds naturally to immobilized metal-ion affinity chromatography (IMAC) resins. Here, the structure is compared with previously deposited AcrB structures and strategies are proposed to avoid this contamination. [source] Expression, purification, crystallization and structure determination of two glutathione S -transferase-like proteins from Shewanella oneidensisACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 6 2008Bert Remmerie Genome analysis of Shewanella oneidensis, a Gram-negative bacterium with an unusual repertoire of respiratory and redox capabilities, revealed the presence of six glutathione S -transferase-like genes (sogst1,sogst6). Glutathione S -transferases (GSTs; EC 2.5.1.18) are found in all kingdoms of life and are involved in phase II detoxification processes by catalyzing the nucleophilic attack of reduced glutathione on diverse electrophilic substrates, thereby decreasing their reactivity. Structure,function studies of prokaryotic GST-like proteins are surprisingly underrepresented in the scientific literature when compared with eukaryotic GSTs. Here, the production and purification of recombinant SoGST3 (SO_1576) and SoGST6 (SO_4697), two of the six GST-like proteins in S. oneidensis, are reported and preliminary crystallographic studies of crystals of the recombinant enzymes are presented. SoGST3 was crystallized in two different crystal forms in the presence of GSH and DTT that diffracted to high resolution: a primitive trigonal form in space group P31 that exhibited merohedral twinning with a high twin fraction and a primitive monoclinic form in space group P21. SoGST6 yielded primitive orthorhombic crystals in space group P212121 from which diffraction data could be collected to medium resolution after application of cryo-annealing protocols. Crystal structures of both SoGST3 and SoGST6 have been determined based on marginal search models by maximum-likelihood molecular replacement as implemented in the program Phaser. [source] | ||||||||||||||||