9,436 research outputs found

    Transient shear banding in the nematic dumbbell model of liquid crystalline polymers

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    In the shear flow of liquid crystalline polymers (LCPs) the nematic director orientation can align with the flow direction for some materials, but continuously tumble in others. The nematic dumbbell (ND) model was originally developed to describe the rheology of flow-aligning semi-flexible LCPs, and flow-aligning LCPs are the focus in this paper. In the shear flow of monodomain LCPs it is usually assumed that the spatial distribution of the velocity is uniform. This is in contrast to polymer solutions, where highly non-uniform spatial velocity profiles have been observed in experiments. We analyse the ND model, with an additional gradient term in the constitutive model, using a linear stability analysis. We investigate the separate cases of constant applied shear stress, and constant applied shear rate. We find that the ND model has a transient flow instability to the formation of a spatially inhomogeneous flow velocity for certain starting orientations of the director. We calculate the spatially resolved flow profile in both constant applied stress and constant applied shear rate in start up from rest, using a model with one spatial dimension to illustrate the flow behaviour of the fluid. For low shear rates flow reversal can be seen as the director realigns with the flow direction, whereas for high shear rates the director reorientation occurs simultaneously across the gap. Experimentally, this inhomogeneous flow is predicted to be observed in flow reversal experiments in LCPs.Comment: 16 pages, 15 figure

    Hawking-Page transition in holographic massive gravity

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    We study the Hawking-Page transition in a holographic model of field theories with momentum dissipation. We find that the deconfinement temperature strictly decreases as momentum dissipation is increased. For sufficiently strong momentum dissipation, the critical temperature goes to zero, indicating a zero-temperature deconfinement transition in the dual field theory.Comment: 17 pages, 1 figure, uncomment \newcommand*{\ShowCalculations}{} in the tex file for additional details. Journal version (PRD). Presentation clarified, reference added, and line spacing and title update

    International collaboration clusters in Africa

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    Recent discussion about the increase in international research collaboration suggests a comprehensive global network centred around a group of core countries and driven by generic socio-economic factors where the global system influences all national and institutional outcomes. In counterpoint, we demonstrate that the collaboration pattern for countries in Africa is far from universal. Instead, it exhibits layers of internal clusters and external links that are explained not by monotypic global influences but by regional geography and, perhaps even more strongly, by history, culture and language. Analysis of these bottom-up, subjective, human factors is required in order to provide the fuller explanation useful for policy and management purposes.Comment: 12 pp, 5 Figs including map links to viewe

    Relationships of Job and Family Involvement, Family Social Support, and Work–Family Conflict with Job and Life Satisfaction

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    A model of the relationship between work and family that incorporates variables from both the work-family conflict and social support literatures was developed and empirically tested. This model related bidirectional work-family conflict, family instrumental and emotional social support, and job and family involvement to job and life satisfaction. Data came from 163 workers who were living with at least 1 family member. Results suggested that relationships between work and family can have an important effect on job and life satisfaction and that the level of involvement the worker assigns to work and family roles is associated with this relationship. The results also suggested that the relationship between work and family can be simultaneously characterized by conflict and support. Higher levels of work interfering with family predicted lower levels of family emotional and instrumental support. Higher levels of family emotional and instrumental support were associated with lower levels of family interfering with work. (PsycINFO Database Record (c) 2013 APA, all rights reserved)

    Cumulonimbus Computing Concerns: Information Security in Public, Private, and Hybrid Cloud Computing

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    Companies of all sizes operating in all markets are moving toward cloud computing for greater flexibility, efficiency, and cost savings. The decision of how to adopt the cloud is a question of major security concern due to the fact that control is relinquished over certain portions of the IT ecosystem. This thesis presents the position that the main security decision in moving to cloud computing is choosing which type of cloud to employ for each portion of the network – the hybrid cloud approach. Vulnerabilities that exist on a public cloud will be explored, and recommendations on decision factors will be made for which specific types of systems to harbor inside a private cloud. Picking the best location for each system allows risk to be managed and sensitive information to be protected while at the same time providing a cost effective option

    Computational efficiency of staggered Wilson fermions: A first look

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    Results on the computational efficiency of 2-flavor staggered Wilson fermions compared to usual Wilson fermions in a quenched lattice QCD simulation on 163×3216^3\times32 lattice at β=6\beta=6 are reported. We compare the cost of inverting the Dirac matrix on a source by the conjugate gradient (CG) method for both of these fermion formulations, at the same pion masses, and without preconditioning. We find that the number of CG iterations required for convergence, averaged over the ensemble, is less by a factor of almost 2 for staggered Wilson fermions, with only a mild dependence on the pion mass. We also compute the condition number of the fermion matrix and find that it is less by a factor of 4 for staggered Wilson fermions. The cost per CG iteration, dominated by the cost of matrix-vector multiplication for the Dirac matrix, is known from previous work to be less by a factor 2-3 for staggered Wilson compared to usual Wilson fermions. Thus we conclude that staggered Wilson fermions are 4-6 times cheaper for inverting the Dirac matrix on a source in the quenched backgrounds of our study.Comment: v2: Major correction and revisions: we had overlooked a factor 1/4 in the cost estimate for matrix-vector multiplication with the staggered Wilson Dirac matrix. This gives an increased speed-up by a factor 4 for the overall computation cost. 7 pages, 3 figures, presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German

    Factors associated with antler size of white-tailed deer in Iowa

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    Antler size of an individual cervid is a result of age, genetic, and environmental factors. Antlers are physiologically costly to produce and dependent upon condition, as nutritional requirements for body maintenance and growth take precedence over antler growth, indicating only individuals with access to adequate nutrition and in good health can afford to allocate resources for maximum antler growth. Therefore, biologists and managers are interested in antlers as possible indicators of condition of individuals and populations. To date, most studies of relationships between environmental factors and antler size have been conducted in the Southeastern U.S., but findings from these studies may not be generalizable to deer elsewhere in North America where environmental conditions are different. In order to identify associations between antler size and environmental factors in the Midwest U.S., I sampled hunter-harvested white-tailed deer in the row-crop dominated state of Iowa. I collected antler measurements, age, and location for 1,575 deer harvested between 2012–2018 to identify relationships between environmental factors and antler size. The first component of this thesis was an evaluation of methods for aging white-tailed deer. Because of the close relationship between antler size and age, controlling for the influence of age is important when attempting to identify environmental factors associated with antler size. I examined the congruence of age estimates obtained from two different methods for aging white-tailed deer: tooth replacement-and-wear (TRW) and counting cementum annuli (CA). I also examined the precision of the CA method using paired CA age estimates from two incisors from the same deer. Congruence rates of CA and TRW ages differed among age classes (80% congruence in yearling TRW age classification, 65% with 2-year-olds, 78% with ≥ 3-year-olds) and the precision of CA aging was influenced by the level of certainty assigned to the age estimate as well as the batch in which the teeth were aged. These findings suggest managers are best served by using TRW to age adult deer as yearlings or ≥ 2-years-old, as the TRW method does not accurately age deer ≥ 2-years-old to a single age. If additional ages are required, CA aging is likely to be more, but not perfectly, accurate. The second component of this thesis was to, after controlling for age, identify environmental factors associated with antler size of Iowa white-tailed deer and quantify variation in antler size across Iowa. Age was the most important factor explaining variation in antler size of white-tailed deer in Iowa. The amount of agricultural area in the area (typically ≈ 23.3 km2) the deer was harvested and the average summer temperature the year the deer was born both had a positive influence on antler size, while the amount of forested area and the winter severity while the deer was in utero both had a negative influence. I observed regional differences in antler size among older age classes where, generally, deer from the southwestern part of Iowa had larger antler sizes than deer from the northern regions of Iowa. Environmental influences and aging error were among the possible explanations for these differences. However, the magnitude of the differences was smaller than previously observed in other studies examining differences in antler size metrics between physiographic regions (e.g., \u3c 1–13% differences between landform regions in Iowa compared to 3–31% for deer sampled in Mississippi). Through the sampling of harvested deer, I identified that the primary factor responsible for the antler size of an individual white-tailed deer in Iowa is age, with small, but statistically significant, influence from environmental factors. These environmental factors may partially explain regional differences in antler size across Iowa. The third component of this thesis was an analysis of spatial and temporal trends in the Iowa Department of Natural Resources’ Iowa Trophy Deer record book that included entries from 1939–2017. While I did not identify any temporal trends within the records, negative latitudinal trends were observed within a category of the records. These trends are similar to the regional differences in antler size from my contemporary sample. Although I observed some interesting trends from the record book data, biases associated with record books, such as their reliance on self-reporting by hunters, lack of age information for the submitted specimen, and focus on larger deer, may limit their usefulness for making inferences about a population. Monitoring a more representative sample of a population may better serve managers looking to observe trends in antler attributes of a population. Overall, the environmental factors I identified influenced antler size of white-tailed deer in Iowa. However, antler size, when controlling for age, did not vary as greatly across the state compared to previous studies conducted outside of the Midwest. These findings suggest the Iowa landscape offers deer adequate nutritional resources for antler growth, such that age is the primary factor explaining antler size in Iowa white-tailed deer

    Gulf

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    In Ernest Hemingway\u27s novel The Old Man and the Sea, the narrator speaks of the healing power of the Gulf in a literal manner: the waters of the Gulf of Mexico heal the wounded hands of the fisherman. The seventeen stories in the following collection examine Hemingway\u27s concept on other levels, focusing on the human ability--or lack thereof--to bridge psychological gulfs, and to find emotional healing. Three major currents run through the lives of the characters in Gulf: difficulties in relationships, struggles with identity, and a sense of being haunted by the unexplained. As the stories progress, the healing waters of the Gulf move the characters away from chaos and toward contentment. In early stories, characters are often appalled by the discovery of their true identities; the later stories feature heroes who\u27ve found happiness and peace. Scattered throughout the book are the haunted stories, those that question the boundaries between what is real and what is imagined, what is known and what can never be understood. Gulf is informed by the landscape of the south, yet some stories venture around the world, from the Gulf of Mexico to the heather-dotted hills of Scotland, exploring themes as dark and mysterious as the Gulf itself
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