2,183 research outputs found
Methodology for urban rail and construction technology research and development planning
A series of transit system visits, organized by the American Public Transit Association (APTA), was conducted in which the system operators identified the most pressing development needs. These varied by property and were reformulated into a series of potential projects. To assist in the evaluation, a data base useful for estimating the present capital and operating costs of various transit system elements was generated from published data. An evaluation model was developed which considered the rate of deployment of the research and development project, potential benefits, development time and cost. An outline of an evaluation methodology that considered benefits other than capital and operating cost savings was also presented. During the course of the study, five candidate projects were selected for detailed investigation; (1) air comfort systems; (2) solid state auxiliary power conditioners; (3) door systems; (4) escalators; and (5) fare collection systems. Application of the evaluation model to these five examples showed the usefulness of modeling deployment rates and indicated a need to increase the scope of the model to quantitatively consider reliability impacts
Unfolding cross-linkers as rheology regulators in F-actin networks
We report on the nonlinear mechanical properties of a statistically
homogeneous, isotropic semiflexible network cross-linked by polymers containing
numerous small unfolding domains, such as the ubiquitous F-actin cross-linker
Filamin.
We show that the inclusion of such proteins has a dramatic effect on the
large strain behavior of the network. Beyond a strain threshold, which depends
on network density, the unfolding of protein domains leads to bulk shear
softening. Past this critical strain, the network spontaneously organizes
itself so that an appreciable fraction of the Filamin cross-linkers are at the
threshold of domain unfolding. We discuss via a simple mean-field model the
cause of this network organization and suggest that it may be the source of
power-law relaxation observed in in vitro and in intracellular microrheology
experiments. We present data which fully justifies our model for a simplified
network architecture.Comment: 11 pages, 4 figures. to appear in Physical Review
The mechanical response of semiflexible networks to localized perturbations
Previous research on semiflexible polymers including cytoskeletal networks in
cells has suggested the existence of distinct regimes of elastic response, in
which the strain field is either uniform (affine) or non-uniform (non-affine)
under external stress. Associated with these regimes, it has been further
suggested that a new fundamental length scale emerges, which characterizes the
scale for the crossover from non-affine to affine deformations. Here, we extend
these studies by probing the response to localized forces and force dipoles. We
show that the previously identified nonaffinity length [D.A. Head et al. PRE
68, 061907 (2003).] controls the mesoscopic response to point forces and the
crossover to continuum elastic behavior at large distances.Comment: 16 pages, 18 figures; substantial changes to text and figures to
clarify the crossover to continuum elasticity and the role of finite-size
effect
Causal Consistency of Structural Equation Models
Complex systems can be modelled at various levels of detail. Ideally, causal
models of the same system should be consistent with one another in the sense
that they agree in their predictions of the effects of interventions. We
formalise this notion of consistency in the case of Structural Equation Models
(SEMs) by introducing exact transformations between SEMs. This provides a
general language to consider, for instance, the different levels of description
in the following three scenarios: (a) models with large numbers of variables
versus models in which the `irrelevant' or unobservable variables have been
marginalised out; (b) micro-level models versus macro-level models in which the
macro-variables are aggregate features of the micro-variables; (c) dynamical
time series models versus models of their stationary behaviour. Our analysis
stresses the importance of well specified interventions in the causal modelling
process and sheds light on the interpretation of cyclic SEMs.Comment: equal contribution between Rubenstein and Weichwald; accepted
manuscrip
Comparative Monte Carlo Efficiency by Monte Carlo Analysis
We propose a modified power method for computing the subdominant eigenvalue
of a matrix or continuous operator. Here we focus on defining
simple Monte Carlo methods for its application. The methods presented use
random walkers of mixed signs to represent the subdominant eigenfuction.
Accordingly, the methods must cancel these signs properly in order to sample
this eigenfunction faithfully. We present a simple procedure to solve this sign
problem and then test our Monte Carlo methods by computing the of
various Markov chain transition matrices. We first computed for
several one and two dimensional Ising models, which have a discrete phase
space, and compared the relative efficiencies of the Metropolis and heat-bath
algorithms as a function of temperature and applied magnetic field. Next, we
computed for a model of an interacting gas trapped by a harmonic
potential, which has a mutidimensional continuous phase space, and studied the
efficiency of the Metropolis algorithm as a function of temperature and the
maximum allowable step size . Based on the criterion, we
found for the Ising models that small lattices appear to give an adequate
picture of comparative efficiency and that the heat-bath algorithm is more
efficient than the Metropolis algorithm only at low temperatures where both
algorithms are inefficient. For the harmonic trap problem, we found that the
traditional rule-of-thumb of adjusting so the Metropolis acceptance
rate is around 50% range is often sub-optimal. In general, as a function of
temperature or , for this model displayed trends defining
optimal efficiency that the acceptance ratio does not. The cases studied also
suggested that Monte Carlo simulations for a continuum model are likely more
efficient than those for a discretized version of the model.Comment: 23 pages, 8 figure
Write Night: How a Writing Accountability Group (WAG) supports scholarly work and connection at a community residency program
Purpose: The purpose of this innovative endeavor was to improve scholarly output and collaboration at the Swedish First Hill Family Medicine residency by establishing a Writing Accountability Group (WAG).
Background: While scholarly work during residency training is both required by the ACGME and important for producing physician leaders, many community-based residency programs have no formal structure to support such work and promote collaboration. At our program, faculty worked in functional silos and found it difficult to consistently involve residents in scholarly projects. WAGs have been studied in a variety of settings as a tool to increase scholarly output, improve writing habits, and provide mentorship for junior and senior faculty.
Objectives: We aimed to analyze the effectiveness of a WAG in promoting scholarly work and resident scholarly mentorship in a community-based residency program. By reporting this work, we hope to provide inspiration and a roadmap for other faculty to increase scholarly productivity and joy in their work.
Implementation/Design: After reviewing the literature regarding WAGs, a faculty member at Swedish First Hill Family Medicine invited other faculty to form a WAG at our community-based residency program. Over the next 18 months, a group of 4-6 faculty met every 2-3 weeks for 90-minute sessions to write, provide peer mentorship regarding scholarly pursuits, and collaborate on scholarly projects. Sessions were held on mutually convenient evenings at a faculty member’s home and over Zoom during the COVID-19 pandemic.
Results/Outcomes: To assess the efficacy of the WAG, we measured total scholarly activity in an academic year for the five faculty participants both before (2018-2019) and after (2019-2020) the implementation of the WAG. We used the ACGME template for faculty scholarly activity to identify and categorize different types of activity. The total number of faculty scholarly activities increased from 20 to 44 after the formation of a WAG, representing a 120% increase in our total activity. For scholarly activity that required peer review or conference acceptance, our total number of submissions increased from 14 to 28, yet maintained a similar acceptance rate (79% in 2018-2019, 85% in 2019-2020). While the majority of our scholarly activity consisted of national conference submissions, we also noted increases in publications, podcasts, and other writing submissions. In addition to increased faculty scholarly productivity, our WAG was associated with increases in faculty job satisfaction, faculty collaboration, and resident scholarly activity.
Significance: Creation of a WAG provided a structure for faculty scholarly collaboration and accountability for completion of scholarly projects. The WAG also provided a clear point of contact for other faculty and residents interested in scholarly work. In addition to increasing scholarly output and resident participation, our WAG improved wellness among faculty, providing a sense of collaboration and celebration of our scholarly work, particularly important during the COVID-19 pandemic. We plan to continue to evaluate the impact of the WAG in future years to look for sustained improvement.https://digitalcommons.psjhealth.org/swedish_learning_day_posters/1005/thumbnail.jp
MOST detects variability on tau Bootis possibly induced by its planetary companion
(abridged) There is considerable interest in the possible interaction between
parent stars and giant planetary companions in 51 Peg-type systems. We
demonstrate from MOST satellite photometry and Ca II K line emission that there
has been a persistent, variable region on the surface of tau Boo A which
tracked its giant planetary companion for some 440 planetary revolutions and
lies ~68deg (phi=0.8) in advance of the sub-planetary point. The light curves
are folded on a range of periods centered on the planetary orbital period and
phase dependent variability is quantified by Fourier methods and by the mean
absolute deviation (MAD) of the folded data for both the photometry and the Ca
II K line reversals. The region varies in brightness on the time scale of a
rotation by ~1 mmag. In 2004 it resembled a dark spot of variable depth, while
in 2005 it varied between bright and dark. Over the 123 planetary orbits
spanned by the photometry the variable region detected in 2004 and in 2005 are
synchronised to the planetary orbital period within 0.0015 d. The Ca II K line
in 2001, 2002 and 2003 also shows enhanced K-line variability centered on
phi=0.8, extending coverage to some 440 planetary revolutions. The apparently
constant rotation period of the variable region and its rapid variation make an
explanation in terms of conventional star spots unlikely. The lack of
complementary variability at phi=0.3 and the detection of the variable region
so far in advance of the sub-planetary point excludes tidal excitation, but the
combined photometric and Ca II K line reversal results make a good case for an
active region induced magnetically on the surface of tau Boo A by its planetary
companion.Comment: 7 pages, 7 figures; accepted for publication in A&
Are superflares on solar analogues caused by extra-solar planets?
Stellar flares with times more energy than the largest solar
flare have been detected from 9 normal F and G main sequence stars (Schaefer,
King & Deliyannis 1999). These superflares have durations of hours to days and
are visible from at least x-ray to optical frequencies. The absence of
world-spanning aurorae in historical records and of anomalous extinctions in
the geological record indicate that our Sun likely does not suffer superflares.
In seeking to explain this new phenomenon, we are struck by its similarity to
large stellar flares on RS Canum Venaticorum binary systems, which are caused
by magnetic reconnection events associated with the tangling of magnetic fields
between the two stars. The superflare stars are certainly not of this class,
although we propose a similar flare mechanism. That is, superflares are caused
by magnetic reconnection between fields of the primary star and a close-in
Jovian planet. Thus, by only invoking known planetary properties and
reconnection scenarios, we can explain the energies, durations, and spectra of
superflares, as well as explain why our Sun does not have such events.Comment: 13 pages, Accepted for publication in Ap
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