14,355 research outputs found
Jaynes' MaxEnt, Steady State Flow Systems and the Maximum Entropy Production Principle
Jaynes' maximum entropy (MaxEnt) principle was recently used to give a
conditional, local derivation of the ``maximum entropy production'' (MEP)
principle, which states that a flow system with fixed flow(s) or gradient(s)
will converge to a steady state of maximum production of thermodynamic entropy
(R.K. Niven, Phys. Rev. E, in press). The analysis provides a steady state
analog of the MaxEnt formulation of equilibrium thermodynamics, applicable to
many complex flow systems at steady state. The present study examines the
classification of physical systems, with emphasis on the choice of constraints
in MaxEnt. The discussion clarifies the distinction between equilibrium, fluid
flow, source/sink, flow/reactive and other systems, leading into an appraisal
of the application of MaxEnt to steady state flow and reactive systems.Comment: 6 pages; paper for MaxEnt0
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The septin cytoskeleton facilitates membrane retraction during motility and blebbing.
Increasing evidence supports a critical role for the septin cytoskeleton at the plasma membrane during physiological processes including motility, formation of dendritic spines or cilia, and phagocytosis. We sought to determine how septins regulate the plasma membrane, focusing on this cytoskeletal element's role during effective amoeboid motility. Surprisingly, septins play a reactive rather than proactive role, as demonstrated during the response to increasing hydrostatic pressure and subsequent regulatory volume decrease. In these settings, septins were required for rapid cortical contraction, and SEPT6-GFP was recruited into filaments and circular patches during global cortical contraction and also specifically during actin filament depletion. Recruitment of septins was also evident during excessive blebbing initiated by blocking membrane trafficking with a dynamin inhibitor, providing further evidence that septins are recruited to facilitate retraction of membranes during dynamic shape change. This function of septins in assembling on an unstable cortex and retracting aberrantly protruding membranes explains the excessive blebbing and protrusion observed in septin-deficient T cells
Limiting two-Higgs-doublet models
We update the constraints on two-Higgs-doublet models (2HDMs) focusing on the
parameter space relevant to explain the present muon anomaly, , in four different types of models, type I, II, "lepton specific" (or
X) and "flipped" (or Y). We show that the strong constraints provided by the
electroweak precision data on the mass of the pseudoscalar Higgs, whose
contribution may account for , are evaded in regions where the
charged scalar is degenerate with the heavy neutral one and the mixing angles
and satisfy the Standard Model limit . We combine theoretical constraints from vacuum stability and
perturbativity with direct and indirect bounds arising from collider and
~physics. Possible future constraints from the electron are also
considered. If the 126 GeV resonance discovered at the LHC is interpreted as
the light CP-even Higgs boson of the 2HDM, we find that only models of type X
can satisfy all the considered theoretical and experimental constraints.Comment: 18 pages, 3 figure
Lateral shift of the transmitted light beam through a left-handed slab
It is reported that when a light beam travels through a slab of left-handed
medium in the air, the lateral shift of the transmitted beam can be negative as
well as positive. The necessary condition for the lateral shift to be positive
is given. The validity of the stationary-phase approach is demonstrated by
numerical simulations for a Gaussian-shaped beam. A restriction to the slab's
thickness is provided that is necessary for the beam to retain its profile in
the traveling. It is shown that the lateral shift of the reflected beam is
equal to that of the transmitted beam in the symmetric configuration.Comment: 14 pages, 4 figure
Lymphoscintigraphy and triangulated body marking for morbidity reduction during sentinel node biopsy in breast cancer
Current trends in patient care include the desire for minimizing invasiveness of procedures and interventions. This aim is reflected in the increasing utilization of sentinel lymph node biopsy, which results in a lower level of morbidity in breast cancer staging, in comparison to extensive conventional axillary dissection. Optimized lymphoscintigraphy with triangulated body marking is a clinical option that can further reduce morbidity, more than when a hand held gamma probe alone is utilized. Unfortunately it is often either overlooked or not fully understood, and thus not utilized. This results in the unnecessary loss of an opportunity to further reduce morbidity. Optimized lymphoscintigraphy and triangulated body marking provides a detailed 3 dimensional map of the number and location of the sentinel nodes, available before the first incision is made. The number, location, relevance based on time/sequence of appearance of the nodes, all can influence 1) where the incision is made, 2) how extensive the dissection is, and 3) how many nodes are removed. In addition, complex patterns can arise from injections. These include prominent lymphatic channels, pseudo-sentinel nodes, echelon and reverse echelon nodes and even contamination, which are much more difficult to access with the probe only. With the detailed information provided by optimized lymphoscintigraphy and triangulated body marking, the surgeon can approach the axilla in a more enlightened fashion, in contrast to when the less informed probe only method is used. This allows for better planning, resulting in the best cosmetic effect and less trauma to the tissues, further reducing morbidity while maintaining adequate sampling of the sentinel node(s)
Investigation into the cause of pneumatic actuator failure on the HypoSurface
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (leaf 11).An investigation into the failure of pneumatic actuators on the HypoSurface was conducted to provide information on the current HypoSurface prototype. Using a systematic approach throughout testing, piston components were found to have been subjected to fatigue-failure, causing pressure leaks from the piston. Through further analysis, the increase in wear on the piston gaskets was caused by exceeding the recommended loads during operation of the HypoSurface with its skin. Furthermore, vibrations from piston actuation may be the cause of loose electrical connections in the control panel, resulting in voltage problems in the solenoids.by Darren M.K. Chun.S.B
High Resolution X-Ray Imaging of the Center of IC342
We presented the result of a high resolution (FWHM~0.5'') 12 ks Chandra HRC-I
observation of the starburst galaxy IC342 taken on 2 April 2006. We identified
23 X-ray sources within the central 30' x 30' region of IC342. Our HRC-I
observation resolved the historical Ultraluminous X-ray sources (ULX), X3, near
the nucleus into 2 sources, namely C12 and C13, for the first time. The
brighter source C12, with L(0.08-10keV)=(6.66\pm0.45)\times10^{38}ergs^-1, was
spatially extended (~82 pc x 127 pc). From the astrometric registration of the
X-ray image, C12 was at R.A.=03h:46m:48.43s, decl.=+68d05m47.45s, and was
closer to the nucleus than C13. Thus we concluded that source was not an ULX
and must instead be associated with the nucleus. The fainter source C13, with
L(0.08-10keV)=(5.1\pm1.4) x 10^{37}ergs^-1 was consistent with a point source
and located $6.51'' at P.A. 240 degree of C12.
We also analyzed astrometrically corrected optical Hubble Space Telescope and
radio Very Large Array images, a comparison with the X-ray image showed
similarities in their morphologies. Regions of star formation within the
central region of IC342 were clearly visible in HST H alpha image and this was
the region where 3 optical star clusters and correspondingly our detected X-ray
source C12 were observed. We found that a predicted X-ray emission from
starburst was very close to the observed X-ray luminosity of C12, suggesting
that nuclear X-ray emission in IC342 was dominated by starburst. Furthermore,
we discussed the possibility of AGN in the nucleus of IC342. Although our data
was not enough to give a firm existence of an AGN, it could not be discarded.Comment: 29 page, 8 figures, accepted by Ap
Neutrino Oscillations and Collider Test of the R-parity Violating Minimal Supergravity Model
We study the R-parity violating minimal supergravity models accounting for
the observed neutrino masses and mixing, which can be tested in future collider
experiments. The bi-large mixing can be explained by allowing five dominant
tri-linear couplings and . The desired ratio
of the atmospheric and solar neutrino mass-squared differences can be obtained
in a very limited parameter space where the tree-level contribution is tuned to
be suppressed. In this allowed region, we quantify the correlation between the
three neutrino mixing angles and the tri-linear R-parity violating couplings.
Qualitatively, the relations , and are required by the large
atmospheric neutrino mixing angle and the small angle
, and the large solar neutrino mixing angle ,
respectively. Such a prediction on the couplings can be tested in the next
linear colliders by observing the branching ratios of the lightest
supersymmetric particle (LSP). For the stau or the neutralino LSP, the ratio
can be measured
by establishing or , respectively. The
information on the couplings can be drawn by measuring if the neutralino LSP is heavier than the top
quark.Comment: RevTex, 25 pages, 8 eps figure
Understanding mechanisms of genetic risk for adolescent internalizing and externalizing problems: The mediating role of parenting and personality
Genetic predispositions play an important role in the development of internalizing and externalizing behaviors. Understanding the mechanisms through which genetic risk unfolds to influence these developmental outcomes is critical for developing prevention and intervention efforts, capturing key elements of Irv's research agenda and scientific legacy. In this study, we examined the role of parenting and personality in mediating the effect of genetic risk on adolescents' major depressive disorder and conduct disorder symptoms. Longitudinal data were drawn from a sample of 709 European American adolescents and their mothers from the Collaborative Studies on Genetics of Alcoholism. Results from multivariate path analysis indicated that adolescents' depressive symptoms genome-wide polygenic scores (DS_GPS) predicted lower parental knowledge, which in turn was associated with more subsequent major depressive disorder and conduct disorder symptoms. Adolescents' DS_GPS also had indirect effects on these outcomes via personality, with a mediating effect via agreeableness but not via other dimensions of personality. Findings revealed that the pattern of associations was similar across adolescent gender. Our findings emphasize the important role of evocative gene-environment correlation processes and intermediate phenotypes in the pathways of risk from genetic predispositions to complex adolescent outcomes
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