16,747 research outputs found
Conservation laws in the quantum Hall Liouvillian theory and its generalizations
It is known that the localization length scaling of noninteracting electrons
near the quantum Hall plateau transition can be described in a theory of the
bosonic density operators, with no reference to the underlying fermions. The
resulting ``Liouvillian'' theory has a global supersymmetry as well as
a hierarchy of geometric conservation laws related to the noncommutative
geometry of the lowest Landau level (LLL). Approximations to the Liouvillian
theory contain quite different physics from standard approximations to the
underlying fermionic theory. Mean-field and large-N generalizations of the
Liouvillian are shown to describe problems of noninteracting bosons that
enlarge the supersymmetry to or .
These noninteracting bosonic problems are studied numerically for by Monte Carlo simulation and compared to the original N=1 Liouvillian
theory. The generalizations preserve the first two of the hierarchy of
geometric conservation laws, leading to logarithmic corrections at order 1/N to
the diffusive large-N limit, but do not preserve the remaining conservation
laws. The emergence of nontrivial scaling at the plateau transition, in the
Liouvillian approach, is shown to depend sensitively on the unusual geometry of
Landau levels.Comment: 13 page
Power spectral analysis of voltage-gated channels in neurons
This article develops a fundamental insight into the behavior of neuronal
membranes, focusing on their responses to stimuli measured with power spectra
in the frequency domain. It explores the use of linear and nonlinear (quadratic
sinusoidal analysis) approaches to characterize neuronal function. It further
delves into the random theory of internal noise of biological neurons and the
use of stochastic Markov models to investigate these fluctuations. The text
also discusses the origin of conductance noise and compares different power
spectra for interpreting this noise. Importantly, it introduces a novel
sequential chemical state model, named p2, which is more general than the
Hodgkin-Huxley formulation, so that the probability for an ion channel to be
open does not imply exponentiation. In particular, it is demonstrated that the
p2 (without exponentiation) and n4 (with exponentiation) models can produce
similar neuronal responses. A striking relationship is also shown between
fluctuation and quadratic power spectra, suggesting that voltage-dependent
random mechanisms can have a significant impact on deterministic nonlinear
responses, themselves known to have a crucial role in the generation of action
potentials in biological neural networks
Dyon condensation in topological Mott insulators
We consider quantum phase transitions out of topological Mott insulators in
which the ground state of the fractionalized excitations (fermionic spinons) is
topologically non-trivial. The spinons in topological Mott insulators are
coupled to an emergent compact U(1) gauge field with a so-called "axion" term.
We study the confinement transitions from the topological Mott insulator to
broken symmetry phases, which may occur via the condensation of dyons. Dyons
carry both "electric" and "magnetic" charges, and arise naturally in this
system because the monopoles of the emergent U(1) gauge theory acquires gauge
charge due to the axion term. It is shown that the dyon condensate, in general,
induces simultaneous current and bond orders. To demonstrate this, we study the
confined phase of the topological Mott insulator on the cubic lattice. When the
magnetic transition is driven by dyon condensation, we identify the bond order
as valence bond solid order and the current order as scalar spin chirality
order. Hence, the confined phase of the topological Mott insulator is an exotic
phase where the scalar spin chirality and the valence bond order coexist and
appear via a single transition. We discuss implications of our results for
generic models of topological Mott insulators.Comment: 14 pages, accepted to the New Journal of Physic
Trigonometric vehicle guidance assembly which aligns the three perpendicular axes of two three-axes systems Patent
Electrical and electromechanical trigonometric computation assembly and space vehicle guidance system for aligning perpendicular axes of two sets of three-axes coordinate reference
Surviving the big chill: overwintering strategies of aquatic and terrestrial insects.
The purpose of this paper is to describe the cold-hardiness of aquatic insects and to use the literature to compare physiological and behavioral strategies that aquatic and terrestrial insects use to cope with minimum winter temperatures. In sharp contrast to terrestrial insects, aquatic insects from seven different orders had limited ability to supercool and did so to temperatures of only −3 to −7°C. Inability to supercool may be due to inoculative freezing—the penetration of external ice crystals through pores or orifices of the insect's cuticle. Furthermore, our results suggest that terrestrial adult stages of aquatic insects may have greater capacity to supercool than aquatic stages of the same taxon. Our results and others' suggested that few aquatic species are freeze tolerant, and those that are appear to be restricted to the order Diptera. Consequently, behavioral avoidance of ice or the capacity to remain unfrozen while encased in ice may be particularly important for overwintering aquatic insects. Ecological implications of insect coldhardiness at the individual, population, and community level are discussed for both terrestrial and aquatic insects
Keypad mobile phones are associated with a significant increased risk of microbial contamination compared to touch screen phones
The use of mobile phones in the clinical environment by healthcare workers has become widespread. Despite evidence that these devices can harbour pathogenic micro-organisms there is little guidance on how to reduce contamination. Recently touchscreen phones with a single flat surface have been introduced. We hypothesise that bacterial contamination of phones used in hospitals will be lower on touchscreen devices compared to keypad devices. Sixty seven mobile phones belonging to health care workers were sampled. The median colony count for touchscreen phones and keypad devices was 0·09 colony forming units (cfu)/cm2 (interquartile range (IQR) 0.05–0·14) and 0·77 cfu/cm2 (IQR range 0·45–3.52) respectively. Colony counts were significantly higher on the keypad phones (Fisher’s exact test p<0.001). Multivariate analysis showed the type of phone (keypad vs. touch screen) was associated with increased colony counts (F-statistic 14.13: p<0.001). Overall, nine (13%) phones grew either meticillin resistant Staphylococcus aureus or vancomycin resistant enterococci. Eight (24%) keypad phones were contaminated with these organisms compared with one touch screen phone (3%). Our data indicate that touchscreen mobile phones are less contaminated than their keypad counterparts, and they are less likely to harbour pathogenic bacteria in the clinical setting
Surviving the Big Chill: Overwintering Strategies of Aquatic and Terrestrial Insects
The purpose of this paper is to describe the cold-hardiness of aquatic insects and to use the literature to compare physiological and behavioral strategies that aquatic and terrestrial insects use to cope with minimum winter temperatures. In sharp contrast to terrestrial insects, aquatic insects from seven different orders had limited ability to supercool and did so to temperatures of only −3 to −7°C. Inability to supercool may be due to inoculative freezing—the penetration of external ice crystals through pores or orifices of the insect\u27s cuticle. Furthermore, our results suggest that terrestrial adult stages of aquatic insects may have greater capacity to supercool than aquatic stages of the same taxon. Our results and others\u27 suggested that few aquatic species are freeze tolerant, and those that are appear to be restricted to the order Diptera. Consequently, behavioral avoidance of ice or the capacity to remain unfrozen while encased in ice may be particularly important for overwintering aquatic insects. Ecological implications of insect coldhardiness at the individual, population, and community level are discussed for both terrestrial and aquatic insects
Leading Groups To Create Healthy Culture Through Accomplishing Tasks Aligned To Strategy
This study examined the link between the consistency of self-evaluation versus peer-evaluation of managers’ skills and the level of relational stress in an organization and was based on two models: (a) the Competing Values Framework (CVF), which measures different management skills of individuals in an organization, and (b) the Healthy versus Toxic Organization Model, which focuses on the stress level in partnerships. The researchers hypothesized that the lower the stress in the organization, the more consistent the results will be between self-evaluation and peer-evaluation. In an empirical analysis, the researchers found that the relationship was most visible in the area of managers’ facilitator skills. With strong facilitator skills, managers can lead their organizations effectively and stay focused on maintaining strategic alignment. The study also examined how management skills could be most effective in developing a healthy work culture
City Best Practices to Improve Transit Operations and Safety
Public, fixed-route transit services most commonly operate on public streets. In addition, transit passengers must use sidewalks to access transit stops and stations. However, streets and sidewalks are under the jurisdiction of municipalities, not transit agencies. Various municipal policies, practices, and decisions affect transit operations, rider convenience, and passenger safety. Thus, these government entities have an important influence over the quality, safety, and convenience of transit services in their jurisdictions. This research identified municipal policies and practices that affect public transport providers’ ability to deliver transit services. They were found from a comprehensive literature review, interviews and discussions with five local transit agencies in the U.S., five public transportation experts and staff from five California cities. The city policies and practices identified fall into the following five categories: Infrastructure for buses, including bus lanes, signal treatments, curbside access; Infrastructure for pedestrians walking and bicycling to, and waiting at, transit stops and stations; Internal transportation planning policies and practices; Land development review policies; Regional and metropolitan planning organization (MPO) issues. The understanding, acknowledgment, and implementation of policies and practices identified in this report can help municipalities proactively work with local transit providers to more efficiently and effectively operate transit service and improve passenger comfort and safety on city streets
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