15,875 research outputs found
Crowding effects in vehicular traffic
While the impact of crowding on the diffusive transport of molecules within a
cell is widely studied in biology, it has thus far been neglected in traffic
systems where bulk behavior is the main concern. Here, we study the effects of
crowding due to car density and driving fluctuations on the transport of
vehicles. Using a microscopic model for traffic, we found that crowding can
push car movement from a superballistic down to a subdiffusive state. The
transition is also associated with a change in the shape of the probability
distribution of positions from negatively-skewed normal to an exponential
distribution. Moreover, crowding broadens the distribution of cars' trap times
and cluster sizes. At steady state, the subdiffusive state persists only when
there is a large variability in car speeds. We further relate our work to prior
findings from random walk models of transport in cellular systems.Comment: 23 pages, 11 figures, accepted for publication in PLoS ON
Non-Equilibrium Dynamics of Correlated Electron Transfer in Molecular Chains
The relaxation dynamics of correlated electron transport (ET) along molecular
chains is studied based on a substantially improved numerically exact path
integral Monte Carlo (PIMC) approach. As archetypical model we consider a
Hubbard chain containing two interacting electrons coupled to a bosonic bath.
For this generalization of the ubiquitous spin-boson model, the intricate
interdependence of correlations and dissipation leads to non-Boltzmann thermal
equilibrium distributions for many-body states. By mapping the multi-particle
dynamics onto an isomorphic single particle motion this phenomenon is shown to
be sensitive to the particle statistics and due to its robustness allows for
new control schemes in designed quantum aggregates.Comment: 5 pages, 4 figure
Symptomatic Social Science: Reflexivity, Recognition and Redistribution in the GBCS
The article examines methodological and theoretical issues related to the GBCS.
It acknowledges its importance for the public profile of sociology, whilst arguing
that it needs to develop a better sense of what it stands for not only in terms of
understanding societal changes, but contributing to human betterment. To achieve
this it discusses the role of reflexivity in the GBCS with reference to position and
disposition and accounts of its process. It then moves on to examine its normative
basis in terms of an ‘existential analytics’ and suggests a series of ways in which it
might advance its insights as the work develops
The Electron Spectral Function in Two-Dimensional Fractionalized Phases
We study the electron spectral function of various zero-temperature
spin-charge separated phases in two dimensions. In these phases, the electron
is not a fundamental excitation of the system, but rather ``decays'' into a
spin-1/2 chargeless fermion (the spinon) and a spinless charge e boson (the
chargon). Using low-energy effective theories for the spinons (d-wave pairing
plus possible N\'{e}el order), and the chargons (condensed or quantum
disordered bosons), we explore three phases of possible relevance to the
cuprate superconductors: 1) AF*, a fractionalized antiferromagnet where the
spinons are paired into a state with long-ranged N\'{e}el order and the
chargons are 1/2-filled and (Mott) insulating, 2) the nodal liquid, a
fractionalized insulator where the spinons are d-wave paired and the chargons
are uncondensed, and 3) the d-wave superconductor, where the chargons are
condensed and the spinons retain a d-wave gap. Working within the gauge
theory of such fractionalized phases, our results should be valid at scales
below the vison gap. However, on a phenomenological level, our results should
apply to any spin-charge separated system where the excitations have these
low-energy effective forms. Comparison with ARPES data in the undoped,
pseudogapped, and superconducting regions is made.Comment: 10 page
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Low density molecular gas in the galaxy
The distributions and physical conditions in molecular gas in the interstellar medium have been investigated in both the Galaxy and towards external galaxies. For example, Galactic plane surveys in the CO J =1-0 line with the Columbia 1.2-m telescope and with the Five College Radio Astronomy Observatory (FCRAO) 14-m telescopes have been able to trace spiral arms more clearly than HI surveys have been able to reveal, and indicate that most of molecular mass is contained in Giant Molecular Clouds (GMCs). Extensive maps of the whole Milky Way showed two prominent features, the 4-kpc molecular ring and the Galactic center. The physical conditions in the Galaxy have been studied by comparing the intensity of CO J =1-0 line with those of other lines, e.g., 13CO J =1-0, higher J transitions of CO, and dense gas tracers such as HCO+, CS, and HCN.
Previous studies were however strongly biased towards regions where CO emission was known to be intense. The radial distribution of molecular hydrogen shows that most of the H2 gas which is indirectly traced by observations of its associated CO emission, originates from the inner Galaxy (Dame 1993). Extending outwards from a galacto-centric distance of ~7 kpc, the H2 mass surface density decreases dramatically, and HI dominates over H2 in the outer Galaxy. What are physical conditions of molecular gas where the CO emission is relatively weak, and can we really trace all of the molecular gas through obervations of CO? These kinds of problems have not been solved yet, but are addressed in our study
Construction of the Soudan 2 detector
Progress in the construction of the Soudan 2 nucleon decay detector which is being built at the Soudan iron mine in Minnesota is discussed. The expected event rate and characteristics of low energy neutrino events, muon events, multiple muon events, and other cosmic ray phenomena are discussed
From theory to 'measurement' in complex interventions: methodological lessons from the development of an e-health normalisation instrument
<b>Background</b> Although empirical and theoretical understanding of processes of implementation in health care is advancing, translation of theory into structured measures that capture the complex interplay between interventions, individuals and context remain limited. This paper aimed to (1) describe the process and outcome of a project to develop a theory-based instrument for measuring implementation processes relating to e-health interventions; and (2) identify key issues and methodological challenges for advancing work in this field.<p></p>
<b>Methods</b> A 30-item instrument (Technology Adoption Readiness Scale (TARS)) for measuring normalisation processes in the context of e-health service interventions was developed on the basis on Normalization Process Theory (NPT). NPT focuses on how new practices become routinely embedded within social contexts. The instrument was pre-tested in two health care settings in which e-health (electronic facilitation of healthcare decision-making and practice) was used by health care professionals.<p></p>
<b>Results</b> The developed instrument was pre-tested in two professional samples (N = 46; N = 231). Ratings of items representing normalisation 'processes' were significantly related to staff members' perceptions of whether or not e-health had become 'routine'. Key methodological challenges are discussed in relation to: translating multi-component theoretical constructs into simple questions; developing and choosing appropriate outcome measures; conducting multiple-stakeholder assessments; instrument and question framing; and more general issues for instrument development in practice contexts.<p></p>
<b>Conclusions</b> To develop theory-derived measures of implementation process for progressing research in this field, four key recommendations are made relating to (1) greater attention to underlying theoretical assumptions and extent of translation work required; (2) the need for appropriate but flexible approaches to outcomes measurement; (3) representation of multiple perspectives and collaborative nature of work; and (4) emphasis on generic measurement approaches that can be flexibly tailored to particular contexts of study
An Evaluation of the Effects of Flexibility on Wing Strains in Rough Air for a Large Swept-wing Airplane by Means of Experimentally Determined Frequency-response Functions with an Assessment of Random-process Techniques Employed
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