8,282 research outputs found
Competing bounds on the present-day time variation of fundamental constants
We compare the sensitivity of a recent bound on time variation of the fine
structure constant from optical clocks with bounds on time varying fundamental
constants from atomic clocks sensitive to the electron-to-proton mass ratio,
from radioactive decay rates in meteorites, and from the Oklo natural reactor.
Tests of the Weak Equivalence Principle also lead to comparable bounds on
present variations of constants. The "winner in sensitivity" depends on what
relations exist between the variations of different couplings in the standard
model of particle physics, which may arise from the unification of gauge
interactions. WEP tests are currently the most sensitive within unified
scenarios. A detection of time variation in atomic clocks would favour
dynamical dark energy and put strong constraints on the dynamics of a
cosmological scalar field.Comment: ~4 Phys Rev page
Shape Representation in Primate Visual Area 4 and Inferotemporal Cortex
The representation of contour shape is an essential component of object recognition, but the cortical mechanisms underlying it are incompletely understood, leaving it a fundamental open question in neuroscience. Such an understanding would be useful theoretically as well as in developing computer vision and Brain-Computer Interface applications. We ask two fundamental questions: “How is contour shape represented in cortex and how can neural models and computer vision algorithms more closely approximate this?” We begin by analyzing the statistics of contour curvature variation and develop a measure of salience based upon the arc length over which it remains within a constrained range. We create a population of V4-like cells – responsive to a particular local contour conformation located at a specific position on an object’s boundary – and demonstrate high recognition accuracies classifying handwritten digits in the MNIST database and objects in the MPEG-7 Shape Silhouette database. We compare the performance of the cells to the “shape-context” representation (Belongie et al., 2002) and achieve roughly comparable recognition accuracies using a small test set. We analyze the relative contributions of various feature sensitivities to recognition accuracy and robustness to noise. Local curvature appears to be the most informative for shape recognition. We create a population of IT-like cells, which integrate specific information about the 2-D boundary shapes of multiple contour fragments, and evaluate its performance on a set of real images as a function of the V4 cell inputs. We determine the sub-population of cells that are most effective at identifying a particular category. We classify based upon cell population response and obtain very good results. We use the Morris-Lecar neuronal model to more realistically illustrate the previously explored shape representation pathway in V4 – IT. We demonstrate recognition using spatiotemporal patterns within a winnerless competition network with FitzHugh-Nagumo model neurons. Finally, we use the Izhikevich neuronal model to produce an enhanced response in IT, correlated with recognition, via gamma synchronization in V4. Our results support the hypothesis that the response properties of V4 and IT cells, as well as our computer models of them, function as robust shape descriptors in the object recognition process
Enhancing The Seeking Safety Group Intervention With Trauma Sensitive Yoga Practice: A Program Evaluation
Seeking Safety is an evidence-based manualized group counseling intervention designed to address the intersection of trauma and addiction. Trauma-sensitive yoga practice has been shown to be effective as an adjunct treatment in addictions. This qualitative utilization-focused program evaluation analyzed the effectiveness of enhancing Seeking Safety with a trauma-sensitive yoga practice integrated into the Seeking Safety group intervention. The author utilized archival interviews, focus groups and documents collected from a community mental health agency. Data included client interviews, key informant interviews, and demographics. Data were analyzed using narrative analysis of transcripts and documents to assess the efficacy of Seeking Safety with the yoga enhanced intervention. Implications and recommendations for further research on the use of trauma-sensitive yoga with Seeking Safety are discussed
Symmetries, Cluster Synchronization, and Isolated Desynchronization in Complex Networks
Synchronization is of central importance in power distribution,
telecommunication, neuronal, and biological networks. Many networks are
observed to produce patterns of synchronized clusters, but it has been
difficult to predict these clusters or understand the conditions under which
they form, except for in the simplest of networks. In this article, we shed
light on the intimate connection between network symmetry and cluster
synchronization. We introduce general techniques that use network symmetries to
reveal the patterns of synchronized clusters and determine the conditions under
which they persist. The connection between symmetry and cluster synchronization
is experimentally explored using an electro-optic network. We experimentally
observe and theoretically predict a surprising phenomenon in which some
clusters lose synchrony while leaving others synchronized. The results could
guide the design of new power grid systems or lead to new understanding of the
dynamical behavior of networks ranging from neural to social
Complete Characterization of Stability of Cluster Synchronization in Complex Dynamical Networks
Synchronization is an important and prevalent phenomenon in natural and
engineered systems. In many dynamical networks, the coupling is balanced or
adjusted in order to admit global synchronization, a condition called Laplacian
coupling. Many networks exhibit incomplete synchronization, where two or more
clusters of synchronization persist, and computational group theory has
recently proved to be valuable in discovering these cluster states based upon
the topology of the network. In the important case of Laplacian coupling,
additional synchronization patterns can exist that would not be predicted from
the group theory analysis alone. The understanding of how and when clusters
form, merge, and persist is essential for understanding collective dynamics,
synchronization, and failure mechanisms of complex networks such as electric
power grids, distributed control networks, and autonomous swarming vehicles. We
describe here a method to find and analyze all of the possible cluster
synchronization patterns in a Laplacian-coupled network, by applying methods of
computational group theory to dynamically-equivalent networks. We present a
general technique to evaluate the stability of each of the dynamically valid
cluster synchronization patterns. Our results are validated in an electro-optic
experiment on a 5 node network that confirms the synchronization patterns
predicted by the theory.Comment: 6 figure
Primordial nucleosynthesis as a probe of fundamental physics parameters
We analyze the effect of variation of fundamental couplings and mass scales
on primordial nucleosynthesis in a systematic way. The first step establishes
the response of primordial element abundances to the variation of a large
number of nuclear physics parameters, including nuclear binding energies. We
find a strong influence of the n-p mass difference (for the 4He abundance), of
the nucleon mass (for deuterium) and of A=3,4,7 binding energies (for 3He, 6Li
and 7Li). A second step relates the nuclear parameters to the parameters of the
Standard Model of particle physics. The deuterium, and, above all, 7Li
abundances depend strongly on the average light quark mass hat{m} \equiv
(m_u+m_d)/2. We calculate the behaviour of abundances when variations of
fundamental parameters obey relations arising from grand unification. We also
discuss the possibility of a substantial shift in the lithium abundance while
the deuterium and 4He abundances are only weakly affected.Comment: v2: 34 pages, 2 figures, typo in last GUT scenario corrected, added
discussion and graph of nonlinear behaviour in GUT scenarios, added short
section discussing binding of dineutron and 8Be, refs added, conclusions
unaltered. Accepted for publication, Phys. Rev.
Gender, guns, and legislating: An analysis of state legislative policy preferences
Author's manuscript made available in accordance with the publisher's policy.Extant research suggests that gender affects the policy preferences of state legislators, particularly on women's issues. Fewer studies, however, have examined whether gender affects state legislators' policy preferences on other issues such as gun control. The current study uses 2000 National Political Awareness Test (NPAT) data to examine whether gender affects the preferences of state legislators regarding gun control policies. Results suggest that net of individual and constituency characteristics, female legislators are more likely to indicate support for gun control policies than their male counterparts
Big bang nucleosynthesis as a probe of fundamental "constants"
Big Bang nucleosynthesis (BBN) is the earliest sensitive probe of the values
of many fundamental particle physics parameters. We have found the leading
linear dependences of primordial abundances on all relevant parameters of the
standard BBN code, including binding energies and nuclear reaction rates. This
enables us to set limits on possible variations of fundamental parameters. We
find that 7Li is expected to be significantly more sensitive than other species
to many fundamental parameters, a result which also holds for variations of
coupling strengths in grand unified (GUT) models. Our work also indicates which
areas of nuclear theory need further development if the values of ``constants''
are to be more accurately probed.Comment: Refereed article to be published in Nuclear Physics in Astrophysics
III Proceedings, J. Phys. G. Special Issue. Based on work in collaboration
with C. Wetterich (Heidelberg). 6 page
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