5,160 research outputs found
Quantum Layers over Surfaces Ruled Outside a Compact Set
In this paper, we proved the quantum layer over a surface which is ruled
outside a compact set, asymptotically flat but not totally geodesic admits
ground states
Polymer Maximum Drag Reduction: A Unique Transitional State
The upper bound of polymer drag reduction is identified as a unique
transitional state between laminar and turbulent flow corresponding to the
onset of the nonlinear breakdown of flow instabilities
Jet substructure and probes of CP violation in Vh production
We analyse the hVV (V = W, Z) vertex in a model independent way using Vh
production. To that end, we consider possible corrections to the Standard Model
Higgs Lagrangian, in the form of higher dimensional operators which parametrise
the effects of new physics. In our analysis, we pay special attention to linear
observables that can be used to probe CP violation in the same. By considering
the associated production of a Higgs boson with a vector boson (W or Z), we use
jet substructure methods to define angular observables which are sensitive to
new physics effects, including an asymmetry which is linearly sensitive to the
presence of CP odd effects. We demonstrate how to use these observables to
place bounds on the presence of higher dimensional operators, and quantify
these statements using a log likelihood analysis. Our approach allows one to
probe separately the hZZ and hWW vertices, involving arbitrary combinations of
BSM operators, at the Large Hadron Collider.Comment: 37 pages, 17 figures; v3 matches published versio
Wind-Fed GRMHD Simulations of Sagittarius A*: Tilt and Alignment of Jets and Accretion Discs, Electron Thermodynamics, and Multi-Scale Modeling of the Rotation Measure
Wind-fed models offer a unique way to form predictive models of the accretion
flow surrounding Sagittarius A*. We present 3D, wind-fed MHD and GRMHD
simulations spanning the entire dynamic range of accretion from parsec scales
to the event horizon. We expand on previous work by including nonzero black
hole spin and dynamically evolved electron thermodynamics. Initial conditions
for these simulations are generated from simulations of the observed Wolf-Rayet
stellar winds in the Galactic Centre. The resulting flow tends to be highly
magnetized () with an density profile
independent of the strength of magnetic fields in the winds. Our simulations
reach the MAD state for some, but not all cases. In tilted flows, SANE jets
tend to align with the angular momentum of the gas at large scales, even if
that direction is perpendicular to the black hole spin axis. Conversely, MAD
jets tend to align with the black hole spin axis. The gas angular momentum
shows similar behavior: SANE flows tend to only partially align while MAD flows
tend to fully align. With a limited number of dynamical free parameters, our
models can produce accretion rates, 230 GHz flux, and unresolved linear
polarization fractions roughly consistent with observations for several choices
of electron heating fraction. Absent another source of large-scale magnetic
field, winds with a higher degree of magnetization (e.g., where the magnetic
pressure is 1/100 of the ram pressure in the winds) may be required to get a
sufficiently large RM with consistent sign.Comment: Accepted by MNRAS. Animations for several figures in the paper are
available at
https://www.youtube.com/playlist?list=PL3pLmTeUPcqSd4jVBnRubYQpa-Dma25i
On-board processing for future satellite communications systems: Satellite-Routed FDMA
A frequency division multiple access (FDMA) 30/20 GHz satellite communications architecture without on-board baseband processing is investigated. Conceptual system designs are suggested for domestic traffic models totaling 4 Gb/s of customer premises service (CPS) traffic and 6 Gb/s of trunking traffic. Emphasis is given to the CPS portion of the system which includes thousands of earth terminals with digital traffic ranging from a single 64 kb/s voice channel to hundreds of channels of voice, data, and video with an aggregate data rate of 33 Mb/s. A unique regional design concept that effectively smooths the non-uniform traffic distribution and greatly simplifies the satellite design is employed. The satellite antenna system forms thirty-two 0.33 deg beam on both the uplinks and the downlinks in one design. In another design matched to a traffic model with more dispersed users, there are twenty-four 0.33 deg beams and twenty-one 0.7 deg beams. Detailed system design techniques show that a single satellite producing approximately 5 kW of dc power is capable of handling at least 75% of the postulated traffic. A detailed cost model of the ground segment and estimated system costs based on current information from manufacturers are presented
Dark-Matter Decays and Self-Gravitating Halos
We consider models in which a dark-matter particle decays to a slightly less
massive daughter particle and a noninteracting massless particle. The decay
gives the daughter particle a small velocity kick. Self-gravitating dark-matter
halos that have a virial velocity smaller than this velocity kick may be
disrupted by these particle decays, while those with larger virial velocities
will be heated. We use numerical simulations to follow the detailed evolution
of the total mass and density profile of self-gravitating systems composed of
particles that undergo such velocity kicks as a function of the kick speed
(relative to the virial velocity) and the decay time (relative to the dynamical
time). We show how these decays will affect the halo mass-concentration
relation and mass function. Using measurements of the halo mass-concentration
relation and galaxy-cluster mass function to constrain the
lifetime--kick-velocity parameter space for decaying dark matter, we find
roughly that the observations rule out the combination of kick velocities
greater than 100 km/s and decay times less than a few times the age of the
Universe.Comment: 17 pages, 10 figures, replaced with published versio
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