3,089 research outputs found
Gravitational couplings of charged leptons in a medium
We calculate the leading order matter-induced corrections to the
gravitational interactions of charged leptons and their antiparticles in a
medium that contains electrons but not the other charged leptons, such as
normal matter. The gravitational coupling, which is universal at the tree
level, is found to be flavor-dependent, and also different for the
corresponding antiparticles, when the corrections of are taken into
account. General expressions are obtained for the matter-induced corrections to
the gravitational mass in a generic matter background, and explicit formulas
for those corrections are given in terms of the macroscopic parameters of the
medium for particular conditions of the background gases.Comment: Latex, axodraw, 39 pages. Added a few stylistic corrections and
clarifying statements in the treatment of the photon tadpole diagra
Inequalities for means of chords, with application to isoperimetric problems
We consider a pair of isoperimetric problems arising in physics. The first
concerns a Schr\"odinger operator in with an attractive
interaction supported on a closed curve , formally given by
; we ask which curve of a given length
maximizes the ground state energy. In the second problem we have a loop-shaped
thread in , homogeneously charged but not conducting,
and we ask about the (renormalized) potential-energy minimizer. Both problems
reduce to purely geometric questions about inequalities for mean values of
chords of . We prove an isoperimetric theorem for -means of chords
of curves when , which implies in particular that the global extrema
for the physical problems are always attained when is a circle. The
article finishes with a discussion of the --means of chords when .Comment: LaTeX2e, 11 page
Self-interference fluorescence microscopy: three dimensional fluorescence imaging without depth scanning
We present a new method for high-resolution, three-dimensional fluorescence imaging. In contrast to beam-scanning confocal microscopy, where the laser focus must be scanned both laterally and axially to collect a volume, we obtain depth information without the necessity of depth scanning. In this method, the emitted fluorescence is collected in the backward direction and is sent through a phase plate that encodes the depth information into the phase of a spectrally resolved interference pattern. We demonstrate that decoding this phase information allows for depth localization accuracy better than 4 Όm over a 500 Όm depth-of-field. In a high numerical aperture configuration with a much smaller depth of field, a localization accuracy of tens of nanometers can be achieved. This approach is ideally suited for miniature endoscopes, where space limitations at the endoscope tip render depth scanning difficult. We illustrate the potential for 3D visualization of complex biological samples by constructing a threedimensional volume of the microvasculature of ex vivo murine heart tissue from a single 2D scan. © 2012 Optical Society of America
A model for the atomic-scale structure of a dense, nonequilibrium fluid: the homogeneous cooling state of granular fluids
It is shown that the equilibrium Generalized Mean Spherical Model of fluid
structure may be extended to nonequilibrium states with equation of state
information used in equilibrium replaced by an exact condition on the two-body
distribution function. The model is applied to the homogeneous cooling state of
granular fluids and upon comparison to molecular dynamics simulations is found
to provide an accurate picture of the pair distribution function.Comment: 29 pages, 11 figures Revision corrects formatting of the figure
Smaller Cortisol Awakening Responses Are Associated with Greater Visual Dependence in Postural Control
There are known links between the hypothalamicâpituitaryâadrenal (HPA) axis and systems responsible for regulating posture. Our aim was to explore directly, for the first time, whether an aspect of circadian HPA axis activity (the cortisol awakening response: CAR) was associated with greater visual dependency in postural control. For measurement of the CAR, electronically monitored saliva samples were collected by participants following morning awakening in their home environment. On the afternoons of the same days, postural sway was measured in the laboratory by exposing participants to static (control) and moving visual stimuli whilst standing still and upright on a force platform. Visual dependence was assessed as the increase in postural sway (path length) during exposure to the moving compared with the static condition. The 44 measurement days were derived from four days for each of eleven healthy participants (mean ± SD age: 51.18 ± 3.3 years). As expected, postural sway was greater when exposed to moving versus static cues. Mixed regression modelling showed that participants with smaller four day average CARs had greater deterioration in postural sway when presented with moving stimuli. These data are the first to document associations between the CAR and visual dependency in postural sway
Collider phenomenology of Higgs bosons in Left-Right symmetric Randall-Sundrum models
We investigate the collider phenomenology of a left-right symmetric
Randall-Sundrum model with fermions and gauge bosons in the bulk. We find that
the model is allowed by precision electroweak data as long as the ratio of the
(unwarped) Higgs vev to the curvature scale is . In that region
there can be substantial modifications to the Higgs properties. In particular,
the couplings to and are reduced, the coupling to gluons is enhanced,
and the coupling to can receive shifts in either direction. The
Higgs mass bound from LEP II data can potentially be relaxed to GeV.Comment: 21 pages, 11 figures. Minor changes to numerics; replaced with
published versio
Improving averted loss estimates for better biodiversity outcomes from offset exchanges
Biodiversity offsetting aims to achieve at least âno net lossâ of biodiversity by fully compensating for residual development-induced biodiversity losses after the mitigation hierarchy (avoid, minimise, remediate) has been applied. Actions used to generate offsets can include securing protection, maintaining condition, or enhancing condition of targeted biodiversity at an offset site. Protection and maintenance actions aim to prevent future loss of biodiversity, so such offsets are referred to as âaverted lossâ offsets. However, the benefits of such approaches can be highly uncertain and opaque, because assumptions about the change in likelihood of loss due to the offset are often implicit. As a result, the gain generated by averting losses can be intentionally or inadvertently overestimated, leading to offset outcomes that are insufficient for achieving no net loss of biodiversity. We present a method and decision tree to guide consistent and credible estimation of the likelihood of loss of a proposed offset site with and without protection, for use when calculating the amount of benefit associated with the âprotectionâ component of averted loss offsets. In circumstances such as when a jurisdictional offset policy applies to most impacts, plausible estimates of averted loss can be very low. Averting further loss of biodiversity is desirable, and averted loss offsets can be a valid approach for generating tangible gains. However, overestimation of averted loss benefits poses a major risk to biodiversity
A Comparative Study on the Solution Techniques for Fiber Orientation in Two-Dimensional Converging and Diverging Flows
The two-dimensional steady flow of both infinite and finite aspect ratio (length to diameter ratio) fibers suspended in a Newtonian fluid is investigated numeri cally. Forty-five-degree convergent and divergent channel geometries are considered for the analysis. Due to symmetry, only half the channel geometry is considered and the ori entation field is assumed to be planar. The analysis is carried out for the creeping flows where the inertia terms are neglected. Numerical grid generation is used to generate the mesh, and the transformed governing equations in terms of the stream function are solved in the computational domain using a finite difference scheme. In this study, several solu tion strategies for solving the orientation field are investigated. The orientation of individ ual fibers are assumed to be governed by Jeffery's equation. The orientation field, which can be expressed in different forms (i.e., a unit vector, tensorial quantities, or an orienta tion distribution function), is specified by solving the orientation equations along particle paths. A tracing technique is implemented to obtain these particle paths for each grid point in the flow domain. The solution of the orientation field is obtained by using two basic techniques. First, a large number of fibers are considered, and by using analytical expres sions developed to describe the orientation state of one fiber, a statistical orientation distri bution function is generated. Second, tensorial quantities (both second- and fourth-order orientation tensors) are employed to solve for the orientation field. In order to overcome the closure problem occurring in the resulting orientation equations, quadratic approxima tions are used. Maximum orientation angles are reported from both the techniques, and their accuracies are investigated. The maximum orientation angles (i.e., preferred orienta tion) obtained from the second- and fourth-order tensorial solutions are observed to be identical. On the other hand, the degree of fiber alignments that are specified by the indi vidual tensor components differ considerably. Comparison of the solution techniques shows that the accuracy of the preferred angle obtained from statistical solution is depen dent on the number of fibers considered. In addition, the calculations for the finite fiber aspect ratio revealed some discrepancies between the statistical and tensorial results at the regions of rapid fiber tumbling.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
Process mapping of laser surface modification of AISI 316L stainless steel for biomedical applications
A 1.5-kW CO2 laser in pulsed mode at 3 kHz was used to investigate the effects of varied laser process parameters and resulting morphology of AISI 316L stainless steel. Irradiance and residence time were varied between 7.9 to 23.6 MW/cm2 and 50 to 167 ”s respectively. A strong correlation between irradiance, residence time, depth of processing and roughness of processed steel was established. The high depth of altered microstructure and increased roughness were linked to higher levels of both irradiance and residence times. Energy fluence and surface temperature models were used to predict levels of melting occurring on the surface through the analysis of roughness and depth of the region processed. Microstructural images captured by the SEM revealed significant grain structure changes at higher irradiances, but due to increased residence times, limited to the laser in use, the hardness values were not improved
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