|
| ||
|
|
||
Certain Threshold (certain + threshold)
Selected AbstractsA simple procedure to approximate slip displacement of freestanding rigid body subjected to earthquake motionsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2007Tomoyo Taniguchi Abstract A simple calculation procedure for estimating absolute maximum slip displacement of a freestanding rigid body placed on the ground or floor of linear/nonlinear multi-storey building during an earthquake is developed. The proposed procedure uses the displacement induced by the horizontal sinusoidal acceleration to approximate the absolute maximum slip displacement, i.e. the basic slip displacement. The amplitude of this horizontal sinusoidal acceleration is identical to either the peak horizontal ground acceleration or peak horizontal floor response acceleration. Its period meets the predominant period of the horizontal acceleration employed. The effects of vertical acceleration are considered to reduce the friction force monotonously. The root mean square value of the vertical acceleration at the peak horizontal acceleration is used. A mathematical solution of the basic slip displacement is presented. Employing over one hundred accelerograms, the absolute maximum slip displacements are computed and compared with the corresponding basic slip displacements. Their discrepancies are modelled by the logarithmic normal distribution regardless of the analytical conditions. The modification factor to the basic slip displacement is quantified based on the probability of the non-exceedence of a certain threshold. Therefore, the product of the modification factor and the basic slip displacement gives the design slip displacement of the body as the maximum expected value. Since the place of the body and linear/nonlinear state of building make the modification factor slightly vary, ensuring it to suit the problem is essential to secure prediction accuracy. Copyright © 2006 John Wiley & Sons, Ltd. [source] FISCAL READJUSTMENTS IN THE UNITED STATES: A NONLINEAR TIME-SERIES ANALYSISECONOMIC INQUIRY, Issue 1 2009ANDREA CIPOLLINI We analyze the fiscal adjustment process in the United States using a multivariate threshold vector error regression model. The shift from single-equation to multivariate setting adds value both in terms of our economic understanding of the fiscal adjustment process and the forecasting performance of nonlinear models. We find evidence that fiscal authorities intervene to reduce real per capita deficit only when it reaches a certain threshold and that fiscal adjustment takes place primarily by cutting government expenditure. The results of out-of-sample density forecast and probability forecasts suggest that a shift from a univariate autoregressive model to a multivariate model improves forecast performance. (JEL C32, C53, E62) [source] Simulating the spatial distribution of clay layer occurrence depth in alluvial soils with a Markov chain geostatistical approachENVIRONMETRICS, Issue 1 2010Weidong Li Abstract The spatial distribution information of clay layer occurrence depth (CLOD), particularly the spatial distribution maps of occurrence of clay layers at depths less than a certain threshold, in alluvial soils is crucial to designing appropriate plans and measures for precision agriculture and environmental management in alluvial plains. Markov chain geostatistics (MCG), which was proposed recently for simulating categorical spatial variables, can objectively decrease spatial uncertainty and consequently increase prediction accuracy in simulated results by using nonlinear estimators and incorporating various interclass relationships. In this paper, a MCG method was suggested to simulate the CLOD in a meso-scale alluvial soil area by encoding the continuous variable with several threshold values into binary variables (for single thresholds) or a multi-class variable (for all thresholds being considered together). Related optimal prediction maps, realization maps, and occurrence probability maps for all of these indicator-coded variables were generated. The simulated results displayed the spatial distribution characteristics of CLOD within different soil depths in the study area, which are not only helpful to understanding the spatial heterogeneity of clay layers in alluvial soils but also providing valuable quantitative information for precision agricultural management and environmental study. The study indicated that MCG could be a powerful method for simulating discretized continuous spatial variables. Copyright © 2009 John Wiley & Sons, Ltd. [source] The medullary dorsal reticular nucleus enhances the responsiveness of spinal nociceptive neurons to peripheral stimulation in the ratEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2003Christophe Dugast Abstract Single-unit spinal recordings combined with application of glutamate into the medullary dorsal reticular nucleus were used to assess the action of this nucleus upon deep dorsal horn neurons in rats. Injection of high glutamate concentrations (10 and 100 mm) induced a dramatic and long-lasting increase of the responses of wide-dynamic range neurons to electrical stimulation of the sciatic nerve in the noxious range, without affecting ongoing discharges. Post-stimulus time histograms revealed that this increase concerned the post-discharge, but not A- or C-fibre-mediated responses, which remained unchanged independently of the stimulation frequency applied. The onset of the glutamate-induced response enhancement occurred with a concentration-dependent time delay and developed slowly until its maximum. These data indicate that the medullary dorsal reticular nucleus exerts a facilitating action upon deep dorsal horn wide-dynamic range neurons by enhancing their capacity to respond to peripheral stimulation through prolongation of their discharge. This action is accompanied by the strengthening of wind-up of deep dorsal horn wide-dynamic range neurons, hence providing a plausible substrate for chronic pain states. These results are in agreement with previous behavioural studies suggesting a pronociceptive role for the dorsal reticular nucleus [Almeida et al. (1996) Brain Res. Bull., 39, 7,15; Almeida et al. (1999) Eur. J. Neurosci., 11, 110,122], and support the involvement of a reverberating circuit, previously described in morphological studies [Almeida et al. (1993) Neuroscience, 55, 1093,1106; Almeida et al. (2000) Eur. J. Pain, 4, 373,387], which probably operates only at a certain threshold of activation. [source] Short-term scheduling of a wind generation and hydrogen storage in the electricity marketEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 5 2010G. Tina Abstract Intermittent renewable energy sources (RES) are promising to be the future of electricity generation. In particular wind generation, owing to its stochastic behaviour, has to be carefully managed. Its lack of sufficient predictability decreases the energy value in the current framework of electrical markets, therefore, beyond a certain threshold; this kind of generation into the electrical system represents a problem for the transmission system operator (TSO) during its despatching service. The coupling of wind energy conversion system (WECS) with a storage medium (i.e. hydrogen) could improve the programmability of such generation plants in electrical markets. In this paper, an economical optimization tool has been developed in order to find the short-term scheduling so as to maximize the economic revenues in the day-ahead electricity market of a storage plant coupled with a wind farm. This tool needs as input the forecasts of both wind generation power and market prices, obtained with the adoption of pre-processing input data algorithm based on different methods that involve both statistical and probabilistic approaches. Copyright © 2009 John Wiley & Sons, Ltd. [source] CONSTANCY OF THE G MATRIX IN ECOLOGICAL TIMEEVOLUTION, Issue 6 2004Mats BjÖrklund Abstract The constancy of the genetic variance-covariance matrix (G matrix) across environments and populations has been discussed and tested empirically over the years but no consensus has so far been reached. In this paper, I present a model in which morphological traits develop hierarchically, and individuals differ in their resource allocation and acquisition patterns. If the variance in resource acquisition is many times larger than the variance in resource allocation then strong genetic correlations are expected, and with almost isometric relations among traits. As the variation in resource acquisition decreases below a certain threshold, the correlations decrease overall and the relations among traits become a function of the allocation patterns, and in particular reflecting the basal division of allocation. A strong bottleneck can break a pattern of strong genetic correlation, but this effect diminishes rapidly with increasing bottleneck size. This model helps to understand why some populations change their genetic correlations in different environments, whereas others do not, since the key factor is the relation between the variances in resource acquisition and allocation. If a change in environment does not lead to a change in this ratio, no change can be expected, whereas if the ratio is changed substantially then major changes can be expected. This model can also help to understand the constancy of morphological patterns within larger taxa as a function of constancy in resource acquisition patterns over time and environments. When this pattern breaks, for example on islands, larger changes can be expected. [source] Regulation of cerebral blood flow in mammals during chronic hypoxia: a matter of balanceEXPERIMENTAL PHYSIOLOGY, Issue 2 2010Philip N. Ainslie Respiratory-induced changes in the partial pressures of arterial carbon dioxide and oxygen play a major role in cerebral blood flow (CBF) regulation. Elevations in (hypercapnia) lead to vasodilatation and increases in CBF, whereas reductions in (hypocapnia) lead to vasoconstriction and decreases in CBF. A fall in (hypoxia) below a certain threshold (<40,45 mmHg) also produces cerebral vasodilatation. Upon initial exposure to hypoxia, CBF is elevated via a greater relative degree of hypoxia compared with hypocapnia. At this point, hypoxia-induced elevations in blood pressure and loss of cerebral autoregulation, stimulation of neuronal pathways, angiogenesis, release of adenosine, endothelium-derived NO and a variety of autocoids and cytokines are additional factors acting to increase CBF. Following 2,3 days, however, the process of ventilatory acclimatization results in a progressive rise in ventilation, which increases and reduces , collectively acting to attenuate the initial rise in CBF. Other factors acting to lower CBF include elevations in haematocrit, sympathetic nerve activity and local and endothelium-derived vasoconstrictors. Hypoxia-induced alterations of cerebrovascular reactivity, autoregulation and pulmonary vascular tone may also affect CBF. Thus, the extent of change in CBF during exposure to hypoxia is dependent on the balance between the myriad of vasodilators and constrictors derived from the endothelium, neuronal innervations and perfusion pressure. This review examines the extent and mechanisms by which hypoxia regulates CBF. Particular focus will be given to the marked influence of hypoxia associated with exposure to high altitude and chronic lung disease. The associated implications of these hypoxia-induced integrative alterations for the regulation of CBF are discussed, and future avenues for research are proposed. [source] Functional dissection of transformation by c-Src and v-SrcGENES TO CELLS, Issue 1 2008Chitose Oneyama The c-src proto-oncogene product, c-Src, is frequently over-expressed and activated in various human malignant cancers, implicating a role for c-Src in cancer progression. To verify the role of c-Src, we analyzed the transforming ability of c-Src in mouse embryonic fibroblasts that lack Csk, a negative regulator of Src family kinases. Although Csk deficiency is not sufficient for cell transformation, c-Src over-expression induced characteristic transformed phenotypes including anchorage-independent growth and tumorigenecity. These phenotypes were dose-dependently inhibited by the re-expression of Csk, indicating that there is a certain threshold for c-Src transformation, which is determined by the c-Src : Csk ratio. In contrast to v-Src, c-Src induced the phosphorylation of a limited number of cellular proteins and elicited a restricted change in gene expression profiles. The activation of some critical targets for v-Src transformation, such as STAT3, was not significantly induced by c-Src transformation. Several genes that are involved in cancer progression, that is, cyclin D1 and HIF-1,, were induced by v-Src, but not by c-Src. Furthermore, v-Src tumors exhibited aggressive growth and extensive angiogenesis, while c-Src tumors grew more slowly accompanied by the induction of hematomas. These findings demonstrate that c-Src has the potential to induce cell transformation, but it requires coordination with an additional pathway(s) to promote tumor progression in vivo. [source] True and false positive peaks in genomewide scans: The long and the short of itGENETIC EPIDEMIOLOGY, Issue 4 2001Peter Visscher Abstract When performing a genome scan in linkage or linkage disequilibrium studies to detect loci underlying complex or quantitative traits, it is important to attempt to distinguish between true and false positives using the appropriate statistical methods. There has been some controversy in the literature regarding the use of the length of a positive peak, i.e., the length of a chromosome region displaying identity-by-descent in linkage studies among affected individuals or the length of a continuous chromosome region for which the test statistic is above a certain threshold. We show in this study, by reasoning and by simulation studies, that conditional on the strength of evidence for a locus affecting a trait of interest, i.e., conditional on the peak height of a test statistic, there is no information in the length of the peak. Our finding has implications for linkage and association studies. Genet. Epidemiol. 20:409,414, 2001. © 2001 Wiley-Liss, Inc. [source] Relationship between cribra orbitalia and enamel hypoplasia in the early medieval Slavic population at Borovce, SlovakiaINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 3 2008Z. Obertová Abstract Cribra orbitalia and enamel hypoplasia were examined in an early medieval (8th to beginning of 12th century AD) skeletal sample of 451 individuals from Borovce, Slovakia. More than 40% of these individuals died before reaching 20 years of age. The relationship between the occurrence of orbital and enamel lesions was analysed by focusing on the age-specific distribution, and on its influence on demographic parameters. Both features were found in 11.2% of the observed skulls. The presence of orbital and dental lesions showed a considerable impact on mortality as well as the life expectancy. Generally, the highest mortality was observed among 0,4 year old individuals. The greatest discrepancy in the demographic parameters, however, appeared between the affected and unaffected individuals aged 10,14 and 15,19 years. In these two age groups the co-occurrence of both lesions was most frequently recorded. These individuals obviously had a history of sickness, and thus could not cope with further bouts of disease and with the increased physiological demands of pubertal growth. The missing correlation in younger age categories can be largely explained by the difficulty of macroscopically examining the permanent dentition, since an interrelationship between the age at hypoplasia development and the occurrence of cribra orbitalia was detected. Several differences between the individuals with enamel defects and both conditions were observed in the distribution of age at hypoplasia formation. According to these results, several factors, such as impaired health status, growth demands and diet, influence the development of enamel hypoplasia and cribra orbitalia in a particular population. It is possible that after reaching a certain threshold, the underlying factors act synergistically in a kind of vicious cycle as the balance between the immune system, metabolism, and exogenous factors such as pathogens and nutrition, is disturbed. Copyright © 2007 John Wiley & Sons, Ltd. [source] Is Leptin the Link Between Fat and Bone Mass?,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 9 2002Thierry Thomas Ph.D. Abstract Recently, leptin has emerged as a potential candidate responsible for protective effects of fat on bone tissue. However, it remains difficult to draw a clear picture of leptin effects on bone metabolism because published data are sometimes conflicting or apparently contradictory. Beyond differences in models or experimental procedures, it is tempting to hypothesize that leptin exerts dual effects depending on bone tissue, skeletal maturity, and/or signaling pathway. Early in life, leptin could stimulate bone growth and bone size through direct angiogenic and osteogenic effects on stromal precursor cells. Later, it may decrease bone remodeling in the mature skeleton, when trabecular bone turnover is high, by stimulating osteoprotegerin (OPG) expression. Leptin negative effects on bone formation effected through central nervous system pathway could counterbalance these peripheral and positive effects, the latter being predominant when the blood-brain barrier permeability decreases or the serum leptin level rises above a certain threshold. Thus, the sex-dependent specificity of the relationship between leptin and bone mineral density (BMD) in human studies could be, at least in part, caused by serum leptin levels that are two- to threefold higher in women than in men, independent of adiposity. Although these hypotheses remain highly speculative and require further investigations, existing studies consistently support the role of leptin as a link between fat and bone. [source] Modelling fault-proneness statistically over a sequence of releases: a case studyJOURNAL OF SOFTWARE MAINTENANCE AND EVOLUTION: RESEARCH AND PRACTICE, Issue 3 2001Magnus C. Ohlsson Abstract Many of today's software systems evolve through a series of releases that add new functionality and features, in addition to the results of corrective maintenance. As the systems evolve over time it is necessary to keep track of and manage their problematic components. Our focus is to track system evolution and to react before the systems become difficult to maintain. To do the tracking, we use a method based on a selection of statistical techniques. In the case study we report here that had historical data available primarily on corrective maintenance, we apply the method to four releases of a system consisting of 130 components. In each release, components are classified as fault-prone if the number of defect reports written against them are above a certain threshold. The outcome from the case study shows stabilizing principal components over the releases, and classification trees with lower thresholds in their decision nodes. Also, the variables used in the classification trees' decision nodes are related to changes in the same files. The discriminant functions use more variables than the classification trees and are more difficult to interpret. Box plots highlight the findings from the other analyses. The results show that for a context of corrective maintenance, principal components analysis together with classification trees are good descriptors for tracking software evolution. Copyright © 2001 John Wiley & Sons, Ltd. [source] Interpenetrating Polymer Networks with Spatially Graded Morphology Controllable by UV-Radiation CuringMACROMOLECULAR SYMPOSIA, Issue 1 2006Hideyuki Nakanishi Abstract Interpenetrating Polymer Networks (IPNs) composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA) were synthesized from a precursor mixture by using dissimilar photo-cross-link reactions. When the reation yields exceeded a certain threshold, the mixture was quenched from one-phase region into two-phase region, leading to phase separation. Upon irradiation with strong UV-light, an intensity gradient was formed along the propagating direction of the exciting light, generating a gradient of quench depth via the spatial inhomogeneity of the cross-link reactions. As a consequence, a gradient of the characteristic length scales was continuously generated from the top to the bottom of the mixture. The resulting three-dimensional (3-D) morphology was in-situ observed at different depths of the mixture by using a laser-scanning confocal microscope (LSCM). From this 3-D observation, it was found that phase separation was accelerated at the bottom of the mixture and proceeded in an autocatalytic fashion. The mechanism for the formation of the graded morphology was discussed in conjunction with the kinetics of the autocatalytic phase separation. [source] The effect of crowd density on the expected number of casualties in a suicide attackNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 1 2005Moshe Kress Abstract Utilizing elementary geometric and probability considerations, we estimate the effect of crowd blocking in suicide bombing events. It is shown that the effect is quite significant. Beyond a certain threshold, the expected number of casualties decreases with the number of people in the arena. The numerical results of our model are consistent with casualty data from suicide bombing events in Israel. Some operational insights are discussed. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2005. [source] Threshold optimization for weighted voting classifiersNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 4 2003G. Levitin Abstract Weighted voting classifiers considered in this paper consist of N units each providing individual classification decisions. The entire system output is based on tallying the weighted votes for each decision and choosing the one which has total support weight exceeding a certain threshold. Each individual unit may abstain from voting. The entire system may also abstain from voting if no decision support weight exceeds the threshold. Existing methods of evaluating the reliability of weighted voting systems can be applied to limited special cases of these systems and impose some restrictions on their parameters. In this paper a universal generating function method is suggested which allows the reliability of weighted voting classifiers to be exactly evaluated without imposing constraints on unit weights. Based on this method, the classifier reliability is determined as a function of a threshold factor, and a procedure is suggested for finding the threshold which minimizes the cost of damage caused by classifier failures (misclassification and abstention may have different price.) Dynamic and static threshold voting rules are considered and compared. A method of analyzing the influence of units' availability on the entire classifier reliability is suggested, and illustrative examples are presented. © 2003 Wiley Periodicals, Inc. Naval Research Logistics 50: 322,344, 2003. [source] When Less is More: Distinguishing Between Entrepreneurial Choice and PerformanceOXFORD BULLETIN OF ECONOMICS & STATISTICS, Issue 5 2000Andrew E. Burke This paper uses NCDS data on individual characteristics to distinguish determinants of entrepreneurial choice, income and job generation. A new model of utility from self-employment shows that relaxing liquidity constraints could inhibit performance. Empirically, we find that a range of inheritance enhances the performance of the self-employed and increases self-employment; while higher education also increases self-employment income and job creation, but reduces the probability of self-employment. Combining these choice and performance effects, we find that education has a positive net effect on job creation, as does inheritance up to a certain threshold. [source] The relationship between changes in the cell wall, lipid peroxidation, proliferation, senescence and cell deathPHYSIOLOGIA PLANTARUM, Issue 1 2003Gerhard Spiteller Plants and mammals contain polyunsaturated fatty acids (PUFAs) in their membranes. PUFAs belong to the most oxygen sensitive molecules encountered in nature. It would seem that nature has selected this property of PUFAs for signalling purposes: PUFAs are stored in the surface of cells and organelles not in free form but conjugated to phospho- and galactolipids. Any change in membrane structure apparently activates membrane-bound phospholipases, which cleave the conjugates. The obtained free PUFAs are substrates for lipoxygenases (LOX). These transform PUFAs to lipidhydroperoxides (LOOHs). LOOHs are converted to a great variety of secondary products. These lipid-peroxidation (LPO) products and the resulting generated products thereof represent biological signals, which do not require a preceding activation of genes. They are produced as a non-specific response to a large variety of external or internal impacts, which therefore do not need interaction with specific receptors. When, due to an external impact, e.g. attack of a microorganism, or to a change in temperature, the amount of liberated free PUFAs exceeds a certain threshold, LOX commit suicide. Thus iron ions, located in the active centre of LOX, are liberated. Iron ions react with LOOHs in the close surroundings by generating alkoxy radicals (LO.). These induce a non-enzymatic LPO. A fraction of the LO. radicals generated from linoleic acid (LPO products derived from linoleic acid play a dominant role in signalling which was previously overlooked) is converted to 2,4-dienals which induce the programmed cell death (PCD) and the hypersensitive reaction (HR). While peroxyl radicals (LOO.) generated as intermediates in the course of an enzymatic LPO are transformed within the enzyme complex to corresponding anions (LOO,), and thus lose their reactivity, peroxyl radicals generated in non-enzymatic reactions are not deactivated. They not only react by abstraction of hydrogen atoms from activated X-H bonds of molecules in their close vicinity, but also by epoxidation of double bonds and oxidation of a variety of biological molecules, causing a dramatic change in molecular structure which finally leads to cell death. As long as reducing agents, like glutathione, or compounds with free phenolic groups are available, the amount of LOOHs is kept low. Cell death is induced in a defined way by apoptosis. But when the reducing agents have been consumed, PCD seems to switch to necrotic processes. Thus proliferation is induced by minor changes at the cell membrane, while slow changes at cell membranes are linked with apoptosis (e.g. response to attack of microorganisms or drought) and necrosis (severe wounding), depending only on the amount, but not on the type, of applied stimulus. [source] Cadaveric and Engineering Analysis of the Septal L-Strut,THE LARYNGOSCOPE, Issue 11 2007Ted Mau MD Abstract Objectives: To identify patterns of failure of the L-strut, to identify elements of the nasal framework that support the L-strut, and to investigate the effect of altering L-strut design on its stability. Study Design: Laboratory study with human cadaveric heads and computational modeling. Methods: Directional forces were applied to cadaveric L-struts and patterns of failure with incremental force were noted. Computational modeling using the finite element method (FEM) was employed to determine quantitatively the effect of various modifications on the stability of the L-strut. Results: The L-strut was found to respond to frontal force initially by buckling. This buckling was reversible until the force exceeded a certain threshold when the L-strut broke at the bony-cartilaginous junction. The threshold force varied depending on the length of the overlap with the bony vault. Intact mucoperichondrium provided significant stability. Modeling with FEM showed that the preservation of a triangular piece of cartilage at the dorsal anchor of a narrowed L-strut can offset some of the loss in mechanical stability. Conclusions: Intrinsic elasticity of the septal cartilage, the mucoperichondrial flap, and overlap with the bony vault all contribute to the stability of the L-strut, which is enhanced by preserving a small segment of cartilage at the bony-cartilaginous junction of the dorsal L-strut. [source] A Quantitative Study of the Medial Surface Dynamics of an In Vivo Canine Vocal Fold during Phonation,THE LARYNGOSCOPE, Issue 9 2005Michael Doellinger PhD Abstract Objectives/Hypothesis: The purpose of this study was to measure the medial surface dynamics of a canine vocal fold during phonation. In particular, displacements, velocities, accelerations, and relative phase velocities of vocal fold fleshpoints were reported across the entire medial surface. Although the medial surface dynamics have a profound influence on voice production, such data are rare because of the inaccessibility of the vocal folds. Study Design: Medial surface dynamics were investigated during both normal and fry-like phonation as a function of innervation to the recurrent laryngeal nerve for conditions of constant glottal airflow. Methods: An in vivo canine model was used. The larynx was dissected similar to methods described in previous excised hemilarynx experiments. Phonation was induced with artificial airflow and innervation to the recurrent laryngeal nerve. The recordings were obtained using a high-speed digital imaging system. Three dimensional coordinates were computed for fleshpoints along the entire medial surface. The trajectories of the fleshpoints were preprocessed using the method of Empirical Eigenfunctions. Results: Although considerable variability existed within the data, in general, the medial-lateral displacements and vertical displacements of the vocal fold fleshpoints were large compared with anterior-posterior displacements. For both normal and fry-like phonation, the largest displacements and velocities were concentrated in the upper medial portion. During normal phonation, the mucosal wave propagated primarily in a vertical direction. Above a certain threshold of subglottal pressure (or stimulation to the recurrent laryngeal nerve), an abrupt transition from chest-like to fry-like phonation was observed. Conclusions: The study reports unique, quantitative data regarding the medial surface dynamics of an in vivo canine vocal fold during phonation, capturing both chest-like and fry-like vibration patterns. These data quantify a complex set of dynamics. The mathematical modeling of such complexity is still in its infancy and requires quantitative data of this nature for development, validation, and testing. [source] On a cumulative damage process and resulting first passages timesAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 1 2004Waltraud Kahle Abstract The reliability of a product is often affected by a damage process. In this paper we consider a shock model where at random times a shock causes a random damage. The cumulative damage process is assumed to be generated by a position-dependent marking of a doubly stochastic Poisson process. Some characteristics of this process are described. For general and special cases the probability that the damage process does not cross a certain threshold before a time t is calculated. Copyright © 2004 John Wiley & Sons, Ltd. [source] Dispersal abilities and spatial patterns in fragmented landscapesBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2010CONCEPCIÓN L. ALADOS Recent theoretical studies suggest that the distribution of species in space has important implications for the conservation of communities in fragmented landscapes. Facilitation and dispersal are the primary mechanisms responsible for the formation of spatial patterns. Furthermore, disruptions in the formation of patterns arise after degradation, which can serve as an early indicator of stress in plant communities. Spatial dispersal ability and pattern formation were evaluated in 53 linear transects of 500 m in length within 14 fragments of natural vegetation within a matrix of abandoned crop fields in Cabo de Gata National Park, Almería, Spain. Fragments were classified into three size classes (< 300, 300,900, and > 900 ha). Fragment connectivity was quantified using the distances between fragments. Spatial dispersal ability was quantified for the 187 species recorded in the study. Species with restricted dispersal had the highest degree of long-range spatial autocorrelation and, species that disperse by biotic vectors (e.g. vertebrates), the lowest. In addition, species most susceptible to fragmentation are vertebrate-dispersed shrubs, which declined in abundance and was associated with loss of spatial organization in the smallest fragments. It is postulated that the positive feedback between abundance of recruitment and vertebrate visits influences the colonization and persistence of vertebrate-dispersed shrubs, explaining its abundance in large fragments. Indeed, fragments lower than a certain threshold reduced spatial organization not only in shrubs with biotic dispersal, but also in species with abiotic dispersal (mainly wind) and with restricted dispersal. Fragments lower than a certain threshold may be vulnerable to a cascade of species loss because of reduced recruitment, establishment and patch biomass as a result of natural senescence, finally breaking up facilitative plant interactions. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 935,947. [source] Export Credit Guarantees, Moral Hazard and Exports QualityBULLETIN OF ECONOMIC RESEARCH, Issue 4 2004María del Carmen García-Alonso F12; H56; L10 Abstract We analyse the role played by export credit guarantees (ECGs) in encouraging exports to developing countries. The existence of moral hazard on the side of the firm is introduced. We show that the inability of the exporter's government to verify the actual quality of the product will limit its ability to encourage trade through ECGs, once the coverage provided goes beyond a certain threshold. This result provides a rationale behind the limited coverage on ECGs. [source] Influence of forces on peri-implant boneCLINICAL ORAL IMPLANTS RESEARCH, Issue S2 2006Flemming Isidor Abstract: Occlusal forces affect an oral implant and the surrounding bone. According to bone physiology theories, bones carrying mechanical loads adapt their strength to the load applied on it by bone modeling/remodeling. This also applies to bone surrounding an oral implant. The response to an increased mechanical stress below a certain threshold will be a strengthening of the bone by increasing the bone density or apposition of bone. On the other hand, fatigue micro-damage resulting in bone resorption may be the result of mechanical stress beyond this threshold. In the present paper literature dealing with the relationship between forces on oral implants and the surrounding bone is reviewed. Randomized controlled as well as prospective cohorts studies were not found. Although the results are conflicting, animal experimental studies have shown that occlusal load might result in marginal bone loss around oral implants or complete loss of osseointegration. In clinical studies an association between the loading conditions and marginal bone loss around oral implants or complete loss of osseointegration has been stated, but a causative relationship has not been shown. [source] Financial integration, capital mobility, and income convergenceECONOMIC POLICY, Issue 58 2009Abdul Abiad Summary Recent studies have found that capital moves ,uphill' from poor to rich countries, and brings little or no growth dividend when it does flow into poor economies. We show that Europe does not conform to this paradigm. In the European experience of financial integration, capital has flown from rich to poor countries, and such inflows have been associated with significant acceleration of income convergence. Analysing broader samples of countries, we find that ,downhill' capital flows tend to be observed above certain thresholds in institutional quality and financial integration. But Europe remains different even when allowing for such threshold effects, and its experience is similar to that of interstate flows within the United States. Our findings are consistent with the notion that financial diversification reduces countries' incentives to save in order to self-insure against specific shocks. ,Abdul Abiad, Daniel Leigh and Ashoka Mody [source] Bootstrap simulations for evaluating the uncertainty associated with peaks-over-threshold estimates of extreme wind velocityENVIRONMETRICS, Issue 1 2003M. D. Pandey Abstract In the peaks-over-threshold (POT) method of extreme quantile estimation, the selection of a suitable threshold is critical to estimation accuracy. In practical applications, however, the threshold selection is not so obvious due to erratic variation of quantile estimates with minor changes in threshold. To address this issue, the article investigates the variation of quantile uncertainty (bias and variance) as a function of threshold using a semi-parametric bootstrap algorithm. Furthermore, the article compares the performance of L-moment and de Haan methods that are used for fitting the Pareto distribution to peak data. The analysis of simulated and actual U.S. wind speed data illustrates that the L-moment method can lead to almost unbiased quantile estimates for certain thresholds. A threshold corresponding to minimum standard error appears to provide reasonable estimates of wind speed extremes. It is concluded that the quantification of uncertainty associated with a quantile estimate is necessary for selecting a suitable threshold and estimating the design wind speed. For this purpose, semi-parametric bootstrap method has proved to be a simple, practical and effective tool. Copyright © 2003 John Wiley & Sons, Ltd. [source] Semiparametric variance-component models for linkage and association analyses of censored trait dataGENETIC EPIDEMIOLOGY, Issue 7 2006G. Diao Abstract Variance-component (VC) models are widely used for linkage and association mapping of quantitative trait loci in general human pedigrees. Traditional VC methods assume that the trait values within a family follow a multivariate normal distribution and are fully observed. These assumptions are violated if the trait data contain censored observations. When the trait pertains to age at onset of disease, censoring is inevitable because of loss to follow-up and limited study duration. Censoring also arises when the trait assay cannot detect values below (or above) certain thresholds. The latent trait values tend to have a complex distribution. Applying traditional VC methods to censored trait data would inflate type I error and reduce power. We present valid and powerful methods for the linkage and association analyses of censored trait data. Our methods are based on a novel class of semiparametric VC models, which allows an arbitrary distribution for the latent trait values. We construct appropriate likelihood for the observed data, which may contain left or right censored observations. The maximum likelihood estimators are approximately unbiased, normally distributed, and statistically efficient. We develop stable and efficient numerical algorithms to implement the corresponding inference procedures. Extensive simulation studies demonstrate that the proposed methods outperform the existing ones in practical situations. We provide an application to the age at onset of alcohol dependence data from the Collaborative Study on the Genetics of Alcoholism. A computer program is freely available. Genet. Epidemiol. 2006. © 2006 Wiley-Liss, Inc. [source] | |||||||||||||||||||||||||