7,759 research outputs found
BCS-BEC Crossover in Atomic Fermi Gases with a Narrow Resonance
We determine the effects on the BCS-BEC crossover of the energy dependence of
the effective two-body interaction, which at low energies is determined by the
effective range. To describe interactions with an effective range of either
sign, we consider a single-channel model with a two-body interaction having an
attractive square well and a repulsive square barrier. We investigate the
two-body scattering properties of the model, and then solve the Eagles-Leggett
equations for the zero temperature crossover, determining the momentum
dependent gap and the chemical potential self-consistently. From this we
investigate the dependence of the crossover on the effective range of the
interaction.Comment: 12 pages, 14 figure
Flux creep in type-II superconductors: self-organized criticality approach
We consider the current density distribution function of a flux creep regime
in type-II superconductors by mapping the flux creep process to the dynamics of
a model with a self-organized criticality. We use an extremal Robin Hood type
model which evolves to Been's type critical state to treat magnetic flux
penetration into a superconductor and derive an analog of the current-voltage
characteristics in the flux creep region.Comment: 7 pages, 7 figure
Effects of increasing the affinity of CarD for RNA polymerase on Mycobacterium tuberculosis growth, rRNA transcription, and virulence
CarD is an essential RNA polymerase (RNAP) interacting protein in Mycobacterium tuberculosis that stimulates formation of RNAP-promoter open complexes. CarD plays a complex role in M. tuberculosis growth and virulence that is not fully understood. Therefore, to gain further insight into the role of CarD in M. tuberculosis growth and virulence, we determined the effect of increasing the affinity of CarD for RNAP. Using site-directed mutagenesis guided by crystal structures of CarD bound to RNAP, we identified amino acid substitutions that increase the affinity of CarD for RNAP. Using these substitutions, we show that increasing the affinity of CarD for RNAP increases the stability of the CarD protein in M. tuberculosis. In addition, we show that increasing the affinity of CarD for RNAP increases the growth rate in M. tuberculosis without affecting 16S rRNA levels. We further show that increasing the affinity of CarD for RNAP reduces M. tuberculosis virulence in a mouse model of infection despite the improved growth rate in vitro. Our findings suggest that the CarD-RNAP interaction protects CarD from proteolytic degradation in M. tuberculosis, establish that growth rate and rRNA levels can be uncoupled in M. tuberculosis and demonstrate that the strength of the CarD-RNAP interaction has been finely tuned to optimize virulence. IMPORTANCE Mycobacterium tuberculosis, the causative agent of tuberculosis, remains a major global health problem. In order to develop new strategies to battle this pathogen, we must gain a better understanding of the molecular processes involved in its survival and pathogenesis. We have previously identified CarD as an essential transcriptional regulator in mycobacteria. In this study, we detail the effects of increasing the affinity of CarD for RNAP on transcriptional regulation, CarD protein stability, and virulence. These studies expand our understanding of the global transcription regulator CarD, provide insight into how CarD activity is regulated, and broaden our understanding of prokaryotic transcription
Lack of Mutual Respect in Relationship The Endangered Partner
Violence in a relationship and in a family setting has been
an issue of concern to various interest groups and professional organizations.
Of particular interest in this article is violence against women
in a relationship. While there is an abundance of knowledge on violence
against women in general, intimate or partner femicide seems to have
received less attention. Unfortunately, the incidence of violence against
women, and intimate femicide in particular, has been an issue of concern
in the African setting.
This article examines the trends of intimate femicide in an African setting
in general, and in Botswana in particular. The increase in intimate
femicide is an issue of concern, which calls for collective effort to address.
This article also examines trends offemicide in Botswana, and the
antecedents and the precipitating factors. Some studies have implicated
societal and cultural dynamics as playing significant roles in intimate
femicide in the African setting. It is believed that the patriarchal nature
of most African settings and the ideology of male supremacy have relegated
women to a subordinate role. Consequently, respect for women
in any relationship with men is lopsided in favor of men and has led to
abuse of women, including intimate femicide. Other militating factors in
intimate femicide ,are examined and the implications for counseling to
assist the endangered female partner are discussed
Are Damage Spreading Transitions Generically in the Universality Class of Directed Percolation?
We present numerical evidence for the fact that the damage spreading
transition in the Domany-Kinzel automaton found by Martins {\it et al.} is in
the same universality class as directed percolation. We conjecture that also
other damage spreading transitions should be in this universality class, unless
they coincide with other transitions (as in the Ising model with Glauber
dynamics) and provided the probability for a locally damaged state to become
healed is not zero.Comment: 10 pages, LATE
Patenting and licensing of university research: promoting innovation or undermining academic values?
Since the 1980s in the US and the 1990s in Europe, patenting and licensing activities by universities have massively increased. This is strongly encouraged by governments throughout the Western world. Many regard academic patenting as essential to achieve 'knowledge transfer' from academia to industry. This trend has far-reaching consequences for access to the fruits of academic research and so the question arises whether the current policies are indeed promoting innovation or whether they are instead a symptom of a pro-intellectual property (IP) culture which is blind to adverse effects. Addressing this question requires both empirical analysis (how real is the link between academic patenting and licensing and 'development' of academic research by industry?) and normative assessment (which justifications are given for the current policies and to what extent do they threaten important academic values?). After illustrating the major rise of academic patenting and licensing in the US and Europe and commenting on the increasing trend of 'upstream' patenting and the focus on exclusive as opposed to non-exclusive licences, this paper will discuss five negative effects of these trends. Subsequently, the question as to why policymakers seem to ignore these adverse effects will be addressed. Finally, a number of proposals for improving university policies will be made
Piecewise Linear Models for the Quasiperiodic Transition to Chaos
We formulate and study analytically and computationally two families of
piecewise linear degree one circle maps. These families offer the rare
advantage of being non-trivial but essentially solvable models for the
phenomenon of mode-locking and the quasi-periodic transition to chaos. For
instance, for these families, we obtain complete solutions to several questions
still largely unanswered for families of smooth circle maps. Our main results
describe (1) the sets of maps in these families having some prescribed rotation
interval; (2) the boundaries between zero and positive topological entropy and
between zero length and non-zero length rotation interval; and (3) the
structure and bifurcations of the attractors in one of these families. We
discuss the interpretation of these maps as low-order spline approximations to
the classic ``sine-circle'' map and examine more generally the implications of
our results for the case of smooth circle maps. We also mention a possible
connection to recent experiments on models of a driven Josephson junction.Comment: 75 pages, plain TeX, 47 figures (available on request
Opportunities for mesoscopics in thermometry and refrigeration: Physics and applications
This review presents an overview of the thermal properties of mesoscopic
structures. The discussion is based on the concept of electron energy
distribution, and, in particular, on controlling and probing it. The
temperature of an electron gas is determined by this distribution:
refrigeration is equivalent to narrowing it, and thermometry is probing its
convolution with a function characterizing the measuring device. Temperature
exists, strictly speaking, only in quasiequilibrium in which the distribution
follows the Fermi-Dirac form. Interesting nonequilibrium deviations can occur
due to slow relaxation rates of the electrons, e.g., among themselves or with
lattice phonons. Observation and applications of nonequilibrium phenomena are
also discussed. The focus in this paper is at low temperatures, primarily below
4 K, where physical phenomena on mesoscopic scales and hybrid combinations of
various types of materials, e.g., superconductors, normal metals, insulators,
and doped semiconductors, open up a rich variety of device concepts. This
review starts with an introduction to theoretical concepts and experimental
results on thermal properties of mesoscopic structures. Then thermometry and
refrigeration are examined with an emphasis on experiments. An immediate
application of solid-state refrigeration and thermometry is in ultrasensitive
radiation detection, which is discussed in depth. This review concludes with a
summary of pertinent fabrication methods of presented devices.Comment: Close to the version published in RMP; 59 pages, 35 figure
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