2,163 research outputs found
Expected neutrino fluence from short Gamma-Ray Burst 170817A and off-axis angle constraints
We compute the expected neutrino fluence from SGRB 170817A, associated with
the gravitational wave event GW 170817, directly based on Fermi observations in
two scenarios: structured jet and off-axis (observed) top-hat jet. While the
expected neutrino fluence for the structured jet case is very small, large
off-axis angles imply high radiation densities in the jet, which can enhance
the neutrino production efficiency. In the most optimistic allowed scenario,
the neutrino fluence can reach only of the sensitivity of the
neutrino telescopes. We furthermore demonstrate that the fact that gamma-rays
can escape limits the baryonic loading (energy in protons versus photons) and
the off-axis angle for the internal shock scenario. In particular, for a
baryonic loading of ten, the off-axis angle is more strongly constrained by the
baryonic loading than by the time delay between the gravitational wave event
and the onset of the gamma-ray emission.Comment: 9 pages, 6 figure
Dynamics of suspensions of hydrodynamically structured particles: Analytic theory and experiment
We present an easy-to-use analytic toolbox for the calculation of short-time
transport properties of concentrated suspensions of spherical colloidal
particles with internal hydrodynamic structure, and direct interactions
described by a hard-core or soft Hertz pair potential. The considered dynamic
properties include self-diffusion and sedimentation coefficients, the
wavenumber-dependent diffusion function determined in dynamic scattering
experiments, and the high-frequency shear viscosity. The toolbox is based on
the hydrodynamic radius model (HRM) wherein the internal particle structure is
mapped on a hydrodynamic radius parameter for unchanged direct interactions,
and on an existing simulation data base for solvent-permeable and spherical
annulus particles. Useful scaling relations for the diffusion function and
self-diffusion coefficient, known to be valid for hard-core interaction, are
shown to apply also for soft pair potentials. We further discuss extensions of
the toolbox to long-time transport properties including the low-shear
zero-frequency viscosity and the long-time self-diffusion coefficient. The
versatility of the toolbox is demonstrated by the analysis of a previous light
scattering study of suspensions of non-ionic PNiPAM microgels [Eckert et al.,
J. Chem. Phys., 2008, 129, 124902] in which a detailed theoretical analysis of
the dynamic data was left as an open task. By the comparison with Hertz
potential based calculations, we show that the experimental data are
consistently and accurately described using the Verlet-Weis corrected
Percus-Yevick structure factor as input, and for a solvent penetration length
equal to three percent of the excluded volume radius. This small solvent
permeability of the microgel particles has a significant dynamic effect at
larger concentrations.Comment: 25 pages, 24 figure
Cosmogenic Neutrinos Challenge the Cosmic Ray Proton Dip Model
The origin and composition of ultra-high-energy cosmic rays (UHECRs) remain a
mystery. The proton dip model describes their spectral shape in the energy
range above GeV by pair production and photohadronic interactions with
the cosmic microwave background. The photohadronic interactions also produce
cosmogenic neutrinos peaking around GeV. We test whether this model is
still viable in light of recent UHECR spectrum measurements from the Telescope
Array experiment, and upper limits on the cosmogenic neutrino flux from
IceCube. While two-parameter fits have been already presented, we perform a
full scan of the three main physical model parameters: source redshift
evolution, injected proton maximal energy, and spectral index. We find
qualitatively different conclusions compared to earlier two-parameter fits in
the literature: a mild preference for a maximal energy cutoff at the sources
instead of the Greisen--Zatsepin--Kuzmin (GZK) cutoff, hard injection spectra,
and strong source evolution. The predicted cosmogenic neutrino flux exceeds the
IceCube limit for any parameter combination. As a result, the proton dip model
is challenged at more than 95\% C.L. This is strong evidence against this model
independent of mass composition measurements.Comment: published in Apj; 15 pages, 12 figure
A new view on Auger data and cosmogenic neutrinos in light of different nuclear disintegration and air-shower models
We study the implications of Ultra-High Energy Cosmic Ray (UHECR) data from
the Pierre Auger Observatory for potential accelerator candidates and
cosmogenic neutrino fluxes for different combinations of nuclear disintegration
and air-shower models. We exploit the most recent spectral and mass composition
data (2017) with a new, computationally very efficient simulation code PriNCe.
We extend the systematic framework originally developed by the Pierre Auger
Collaboration with the cosmological source evolution as an additional free
parameter. In this framework, an ensemble of generalized UHECR accelerators is
characterized by a universal spectral index (equal for all injection species),
a maximal rigidity, and the normalizations for five nuclear element groups. We
find that the 2017 data favor a small but constrained contribution of heavy
elements (iron) at the source. We demonstrate that the results moderately
depend on the nuclear disintegration (PSB, Peanut, or Talys) model, and more
strongly on the air-shower (EPOS-LHC, Sibyll-2.3, or QGSjet-II-04) model.
Variations of these models result in different source evolutions and spectral
indices, limiting the interpretation in terms of a particular class of cosmic
accelerators. Better constrained parameters include the maximal rigidity and
the mass composition at the source. Hence, the cosmogenic neutrino flux can be
robustly predicted, since it originates from interactions with the cosmic
infrared background and peaks at . Depending on the
source evolution at high redshifts the flux is likely out of reach of future
neutrino observatories in most cases, and a minimal cosmogenic neutrino flux
cannot be claimed from data without assuming a cosmological distribution of the
sources.Comment: 21 pages, 11 figures. Accepted for publication in Ap
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Development and Testing of Supercharger Compressor for Cold Climate Air Source Heat Pumps
The on-going development of a compact centrifugal compressor as a first stage or pre-compressor for cold climate operation of heat pumps is described. Positioned in the low pressure vapor portion of the refrigerant loop, this compressor will, on cold days, operate automatically to boost refrigerant pressure, in a manner similar to the way an automotive supercharger pressurizes air. The single stage motor driven centrifugal compressor runs on oil-free bearings. It is being configured to work in concert with a traditional heat pump compressor. The goal of this work is to enable air source heat pumps to efficiently extract heat from even the coldest ambient air without backup heat and without changing refrigerant type or the basic design of the positive displacement style compressors widely used in todayâs heat pumps. Doing so will allow air source heat pumps to operate effectively in virtually all major population centers. To date, a first article supercharger has been designed and built, and its performance mapped. Work to integrate it with a commercially available positive displacement (PD) heat pump compressor is underway
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