16,191 research outputs found
Thermoelectric Amplification of Phonons in Graphene
Amplification of acoustic phonons due to an external temperature gredient
() in Graphene was studied theoretically. The threshold temperature
gradient at which absorption switches over to amplification
in Graphene was evaluated at various frequencies and temperatures
. For and frequency , . The calculation was done in the regime at . The
dependence of the normalized () on the frequency
and the temperature gradient are evaluated numerically and
presented graphically. The calculated for Graphene is lower
than that obtained for homogeneous semiconductors () , Superlattices , Cylindrical Quantum Wire . This makes Graphene a much better material for thermoelectric
phonon amplifier.Comment: 12 Pages, 6 figure
A Robust AFPTAS for Online Bin Packing with Polynomial Migration
In this paper we develop general LP and ILP techniques to find an approximate
solution with improved objective value close to an existing solution. The task
of improving an approximate solution is closely related to a classical theorem
of Cook et al. in the sensitivity analysis for LPs and ILPs. This result is
often applied in designing robust algorithms for online problems. We apply our
new techniques to the online bin packing problem, where it is allowed to
reassign a certain number of items, measured by the migration factor. The
migration factor is defined by the total size of reassigned items divided by
the size of the arriving item. We obtain a robust asymptotic fully polynomial
time approximation scheme (AFPTAS) for the online bin packing problem with
migration factor bounded by a polynomial in . This answers
an open question stated by Epstein and Levin in the affirmative. As a byproduct
we prove an approximate variant of the sensitivity theorem by Cook at el. for
linear programs
The Dual Feminisation of HIV/AIDS
This is an Accepted Manuscript of an article published by Taylor & Francis in Globalizations on 2011, available online: http://wwww.tandfonline.com/10.1080/14747731.2010.49302
Dipole matrix elements in helium in the first order shielding approximation
First order shielding approximation used to calculate off-diagonal matrix elements of dipole moment operator for heliu
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Capital Management Techniques In Developing Countries: An Assessment of Experiences from the 1990\u27s and Lessons For the Future
This paper uses the term, capital management techniques, to refer to two complementary (and often overlapping) types of financial policies: policies that govern international private capital flows and those that enforce prudential management of domestic financial institutions. The paper shows that regimes of capital management take diverse forms and are multi-faceted. The paper also shows that capital management techniques can be static or dynamic. Static management techniques are those that authorities do not modify in response to changes in circumstances. Capital management techniques can also be dynamic, meaning that they can be activated or adjusted as circumstances warrant. Three types of circumstances trigger implementation of management techniques or lead authorities to strengthen or adjust existing regulations--changes in the economic environment, the identification of vulnerabilities, and the attempt to close loopholes in existing measures. The paper presents seven case studies of the diverse capital management techniques employed in Chile, Colombia, Taiwan Province of China, India, China, Singapore and Malaysia during the 1990s. The cases reveal that policymakers were able to use capital management techniques to achieve critical macroeconomic objectives. These included the prevention of maturity and locational mismatch; attraction of favored forms of foreign investment; reduction in overall financial fragility, currency risk, and speculative pressures in the economy; insulation from the contagion effects of financial crises; and enhancement of the autonomy of economic and social policy. The paper examines the structural factors that contributed to these achievements, and also weighs the costs associated with these measures against their macroeconomic benefits. The paper concludes by considering the general policy lessons of these seven experiences. The most important of these lessons are as follows. 1.) Capital management techniques can enhance overall financial and currency stability, buttress the autonomy of macro and micro-economic policy, and bias investment toward the long-term. 2.) The efficacy of capital management techniques is highest in the presence of strong macroeconomic fundamentals, though management techniques can also improve fundamentals. 3.) The nimble, dynamic application of capital management techniques is an important component of policy success. 4.) Controls over international capital flows and prudential domestic financial regulation often function as complementary policy tools, and these tools can be useful to policymakers over the long run. 5.) State and administrative capacity play important roles in the success of capital management techniques. 6.) Evidence suggests that the macroeconomic benefits of capital management techniques probably outweigh their microeconomic costs. 7.) Capital management techniques work best when they are coherent and consistent with a national development vision. 8.) There is no single type of capital management technique that works best for all developing countries. Indeed our cases, demonstrate a rather large array of effective techniques. There are sound reasons for cautious optimism regarding the ability of policymakers in the developing world to build upon these lessons. In particular, we are heartened by the growing understanding of the problems with capital account convertibility in developing countries; by the increasing recognition of the achievements of capital management techniques by important figures in academia, the IMF and the business community; and by the potential for some developing countries (such as China, India, Malaysia, Chile, Singapore) to play a lead role in discussions of the feasibility and efficacy of various capital management techniques
The maximum principle and sign changing solutions of the hyperbolic equation with the Higgs potential
In this article we discuss the maximum principle for the linear equation and
the sign changing solutions of the semilinear equation with the Higgs
potential. Numerical simulations indicate that the bubbles for the semilinear
Klein-Gordon equation in the de Sitter spacetime are created and apparently
exist for all times
Theoretical determination of lifetimes of metastable states in Sc III and Y III
Lifetimes of the first two metastable states in Sc^{2+} and Y^{2+} are
determined using the relativistic coupled-cluster theory. There is a
considerable interest in studying the electron correlation effects in these
ions as though their electronic configurations are similar to the neutral
alkali atoms, their structures are very different from the latter. We have made
a comparative study of the correlation trends between the above doubly ionized
systems with their corresponding neutral and singly ionized iso-electronic
systems. The lifetimes of the excited states of these ions are very important
in the field of astrophysics, especially for the study of post-main sequence
evolution of the cool giant stars.Comment: 13 pages, 1 figure and 5 table
Biodigital publics: personal genomes as digital media artifacts
The recent proliferation of personal genomics and direct-to-consumer (DTC) genomics has attracted much attention and publicity. Concern around these developments has mainly focused on issues of biomedical regulation and hinged on questions of how people understand genomic information as biomedical and what meaning they make of it. However, this publicity amplifies genome sequences which are also made as internet
texts and, as such, they generate new reading publics. The practices around the generation, circulation and reading of genome scans do not just raise questions about biomedical regulation, they also provide the focus for an exploration of how contemporary public participation in genomics works. These issues around the public features of DTC genomic testing can be pursued through a close examination of the modes of one of the best known providers—23andMe. In fact, genome sequences circulate as digital artefacts and, hence, people are addressed by them. They are read as texts, annotated and written about in browsers, blogs and wikis. This activity also yields content for media coverage which addresses an indefinite public in line with Michael Warner’s conceptualisation of publics. Digital genomic texts promise empowerment, personalisation and community, but this promise may obscure the compliance and proscription associated with these forms. The kinds of interaction here
can be compared to those analysed by Andrew Barry. Direct-to-consumer genetics companies are part of a network providing an infrastructure for genomic reading publics and this network can be mapped and examined to demonstrate the ways in which this formation both exacerbates inequalities and offers possibilities for participation in biodigital culture
PDE8 controls CD4(+) T cell motility through the PDE8A-Raf-1 kinase signaling complex
The levels of cAMP are regulated by phosphodiesterase enzymes (PDEs), which are targets for the treatment of inflammatory disorders. We have previously shown that PDE8 regulates T cell motility. Here, for the first time, we report that PDE8A exerts part of its control of T cell function through the V-raf-1 murine leukemia viral oncogene homolog 1 (Raf-1) kinase signaling pathway. To examine T cell motility under physiologic conditions, we analyzed T cell interactions with endothelial cells and ligands in flow assays. The highly PDE8-selective enzymatic inhibitor PF-04957325 suppresses adhesion of in vivo myelin oligodendrocyte glycoprotein (MOG) activated inflammatory CD4(+) T effector (Teff) cells to brain endothelial cells under shear stress. Recently, PDE8A was shown to associate with Raf-1 creating a compartment of low cAMP levels around Raf-1 thereby protecting it from protein kinase A (PKA) mediated inhibitory phosphorylation. To test the function of this complex in Teff cells, we used a cell permeable peptide that selectively disrupts the PDE8A-Raf-1 interaction. The disruptor peptide inhibits the Teff-endothelial cell interaction more potently than the enzymatic inhibitor. Furthermore, the LFA-1/ICAM-1 interaction was identified as a target of disruptor peptide mediated reduction of adhesion, spreading and locomotion of Teff cells under flow. Mechanistically, we observed that disruption of the PDE8A-Raf-1 complex profoundly alters Raf-1 signaling in Teff cells. Collectively, our studies demonstrate that PDE8A inhibition by enzymatic inhibitors or PDE8A-Raf-1 kinase complex disruptors decreases Teff cell adhesion and migration under flow, and represents a novel approach to target T cells in inflammation
Frontostriatal Maturation Predicts Cognitive Control Failure to Appetitive Cues in Adolescents
Adolescent risk-taking is a public health issue that increases the odds of poor lifetime outcomes. One factor thought to influence adolescents' propensity for risk-taking is an enhanced sensitivity to appetitive cues, relative to an immature capacity to exert sufficient cognitive control. We tested this hypothesis by characterizing interactions among ventral striatal, dorsal striatal, and prefrontal cortical regions with varying appetitive load using fMRI scanning. Child, teen, and adult participants performed a go/no-go task with appetitive (happy faces) and neutral cues (calm faces). Impulse control to neutral cues showed linear improvement with age, whereas teens showed a nonlinear reduction in impulse control to appetitive cues. This performance decrement in teens was paralleled by enhanced activity in the ventral striatum. Prefrontal cortical recruitment correlated with overall accuracy and showed a linear response with age for no-go versus go trials. Connectivity analyses identified a ventral frontostriatal circuit including the inferior frontal gyrus and dorsal striatum during no-go versus go trials. Examining recruitment developmentally showed that teens had greater between-subject ventral-dorsal striatal coactivation relative to children and adults for happy no-go versus go trials. These findings implicate exaggerated ventral striatal representation of appetitive cues in adolescents relative to an intermediary cognitive control response. Connectivity and coactivity data suggest these systems communicate at the level of the dorsal striatum differentially across development. Biased responding in this system is one possible mechanism underlying heightened risk-taking during adolescence
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