2,604 research outputs found
Mean curvature flow in a Ricci flow background
Following work of Ecker, we consider a weighted Gibbons-Hawking-York
functional on a Riemannian manifold-with-boundary. We compute its variational
properties and its time derivative under Perelman's modified Ricci flow. The
answer has a boundary term which involves an extension of Hamilton's Harnack
expression for the mean curvature flow in Euclidean space. We also derive the
evolution equations for the second fundamental form and the mean curvature,
under a mean curvature flow in a Ricci flow background. In the case of a
gradient Ricci soliton background, we discuss mean curvature solitons and
Huisken monotonicity.Comment: final versio
Space shuttle launch vehicle performance trajectory, exchange ratios, and dispersion analysis
A baseline space shuttle performance trajectory for Mission 3A launched from WTR has been generated. Design constraints of maximum dynamic pressure, longitudinal acceleration, and delivered payload were satisfied. Payload exchange ratios are presented with explanation on use. Design envelopes of dynamic pressure, SRB staging point, aerodynamic heating and flight performance reserves are calculated and included
Fermi-LAT Observations of the 2014 May-July outburst from 3C 454.3
A prominent outburst of the flat spectrum radio quasar 3C~454.3 was observed
in 2014 June with the \emph{Fermi} Large Area Telescope. This outburst was
characterized by a three-stage light-curve pattern---plateau, flare and
post-flare---that occurred from 2014 May to July, in a similar pattern as
observed during the exceptional outburst in 2010 November. The highest flux of
the outburst reported in this paper occurred during 2014 June 7--29, showing a
multiple-peak structure in the light-curves. The average flux in these 22 days
was found to be ~ph~cm~s, with a spectral index, for a simple power law,
of . That made this outburst the first -ray
high state of 3C~454.3 ever to be detected by \emph{Fermi} with such a hard
spectrum over several days. The highest flux was recorded on 2014 June 15, in a
3 hr bin, at MJD 56823.5625, at a level of ~ph~cm~s. The rise time of one of the short
subflares was found to be ~s at MJD = 56827, when the flux
increased from 4 to 12 ~ph~cm~s. Several photons
above 20 GeV were collected during this outburst, including one at 45 GeV on
MJD 56827, constraining the -ray emission region to be located close to
the outer boundary of the broad-line region, leading to fast flux variability.Comment: Accepted for publication in {\sc the astrophysical journal}: 2016
July 12}; 15 pages, 7 figures, 6 table
Analytic Torsion on Hyperbolic Manifolds and the Semiclassical Approximation for Chern-Simons Theory
The invariant integration method for Chern-Simons theory for gauge group
SU(2) and manifold \Gamma\H^3 is verified in the semiclassical approximation.
The semiclassical limit for the partition function associated with a connected
sum of hyperbolic 3-manifolds is presented. We discuss briefly L^2 - analytical
and topological torsions of a manifold with boundary.Comment: 12 pages, LaTeX fil
Journal Club: Glymphatic System in Neurodegenerative Diseases
Neurodegenerative diseases such as Alzheimer\u27s Disease impact a multitude of individuals worldwide. The neural Glymphatic system is a relatively newly discovered cellular transport pathway within the brain that has been implicated in neurodegenerative diseases. This article serves to provide a journal club review of current literature on the Glymphatic system to raise awareness of this system and its potential for future treatment and prevention of neurodegenerative conditions
Retardation of Particle Evaporation from Excited Nuclear Systems Due to Thermal Expansion
Particle evaporation rates from excited nuclear systems at equilibrium matter
density are studied within the Harmonic-Interaction Fermi Gas Model (HIFGM)
combined with Weisskopf's detailed balance approach. It is found that thermal
expansion of a hot nucleus, as described quantitatively by HIFGM, leads to a
significant retardation of particle emission, greatly extending the validity of
Weisskopf's approach. The decay of such highly excited nuclei is strongly
influenced by surface instabilities
Prey localization in spider orb webs using modal vibration analysis
Spider webs are finely tuned multifunctional structures, widely studied for their prey capture functionalities such as impact strength and stickiness. However, they are also sophisticated sensing tools that enable the spider to precisely determine the location of impact and capture the prey before it escapes. In this paper, we suggest a new mechanism for this detection process, based on potential modal analysis capabilities of the spider, using its legs as distinct distributed point sensors. To do this, we consider a numerical model of the web structure, including asymmetry in the design, prestress, and geometrical nonlinearity effects. We show how vibration signals deriving from impacts can be decomposed into web eigenmode components, through which the spider can efficiently trace the source location. Based on this numerical analysis, we discuss the role of the web structure, asymmetry, and prestress in the imaging mechanism, confirming the role of the latter in tuning the web response to achieve an efficient prey detection instrument. The results can be relevant for efficient distributed impact sensing applications
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