794 research outputs found
On modeling of growth processes driven by velocity fluctuations
In the classical theory of diffusion limited growth, it is assumed that the concentration field of solution is described by the standard diffusion equation. It means that particles of the solution undergo a random walk
described by the Wiener process. In turn, it means that the velocity of particles is a stochastic process being Gaussian white noise. In consequence, the velocity–velocity correlation function is the Dirac -function and velocity correlation time is zero. In many cases such modeling is insufficient and one should consider models in which velocity is correlated in space and/or time. The question is whether correlations of velocity can change the kinetics of growth, in particular, whether the long-time asymptotics of the growth kinetics displays the power-law time dependence with the classical exponent 1/2. How to model such processes is a subject of this paper
Economic Consequences of the Wolf Comeback in the Western United States
Gray wolves were eradicated from most of the United States in the 1940’s but have made a comeback in parts of their historic range over the last two decades. First reintroduced into the Greater Yellowstone Ecosystem and central Idaho in the mid-1990’s, wolves have subsequently dispersed into at least 7 western states. Coloradoans became the latest state to take interest in bolstering wolf populations, as residents passed a ballot initiative in November 2020 to reintroduce a self-sustaining population of gray wolves by the end of 2023. Conflicts between people in rural areas that might incur costs (such as livestock loss) and people in urban areas geographically removed from direct contact with wolves suggest that the distribution of benefits may not align uniformly with the distribution of costs. Given that Colorado will imminently make many policy decisions that have an impact on costs and benefits, we review available literature to better understand the magnitude of gainers and losers from wolf reintroduction in western states. Although no single study has included all possible economic values, the magnitude of impacts can be inferred by assembling a broad range of estimates for different types of values into a single space. Our review of existing valuation literature from western states indicates that the magnitude of economic benefits of wolves is many times higher than what it costs to manage wolves and to reduce or compensate for losses to livestock producers and others
Willingness to pay for reintroducing wolves in a divided voting base
Wolves will soon be reintroduced in Colorado based on a statewide ballot initiative that narrowly passed in November 2020. Using an economic choice experiment, we estimate the benefits that wolf introduction might bring to Colorado. We calculated willingness to pay (WTP) for a sustainable wolf population by considering six program attributes: 1) state wolf population, 2) compensation for livestock-related losses, 3) cost-sharing for conflict reduction, 4) number of livestock killed statewide, 5) lethal government control of wolves, and 6) wolf hunting. Respondents who reported they voted yes on the ballot initiative had a positive WTP for a population of 200 wolves, referred to as the minimum sustainable population in the survey, but WTP diminished for larger populations. Preferences for a population of 200 wolves amounts to an annual WTP of approximately 115 million statewide among yes-voting households. We estimated a 1 benefit-cost ratio for a sustainable wolf population. However, benefits and costs are not evenly distributed across urban and rural residents, which suggests that mechanisms to transfer resources from those willing to pay to those that incur costs would be needed to balance that distribution
Magnetic field generation in a jet-sheath plasma via the kinetic Kelvin-Helmholtz instability
We have investigated generation of magnetic fields associated with velocity
shear between an unmagnetized relativistic jet and an unmagnetized sheath
plasma. We have examined the strong magnetic fields generated by kinetic shear
(Kelvin-Helmholtz) instabilities. Compared to the previous studies using
counter-streaming performed by Alves et al. (2012), the structure of KKHI of
our jet-sheath configuration is slightly different even for the global
evolution of the strong transverse magnetic field. In our simulations the major
components of growing modes are the electric field and the magnetic
field . After the component is excited, an induced
electric field becomes significant. However, other field components
remain small. We find that the structure and growth rate of KKHI with mass
ratios and are similar.
In our simulations saturation in the nonlinear stage is not as clear as in
counter-streaming cases. The growth rate for a mildly-relativistic jet case
() is larger than for a relativistic jet case
().Comment: 6 pages, 6 figures, presented at Dynamical processes in space plasmas
II, Isradinamic 2012, in press, ANGEO. arXiv admin note: text overlap with
arXiv:1303.256
Radiation from accelerated particles in relativistic jets with shocks, shear-flow, and reconnection
We have investigated particle acceleration and shock structure associated
with an unmagnetized relativistic jet propagating into an unmagnetized plasma.
Strong magnetic fields generated in the trailing jet shock lead to transverse
deflection and acceleration of the electrons. We have self-consistently
calculated the radiation from the electrons accelerated in the turbulent
magnetic fields. We find that the synthetic spectra depend on the bulk Lorentz
factor of the jet, the jet temperature, and the strength of the magnetic fields
generated in the shock. We have also begun study of electron acceleration in
the strong magnetic fields generated by kinetic shear (Kelvin-Helmholtz)
instabilities. Our calculated spectra should lead to a better understanding of
the complex time evolution and/or spectral structure from gamma-ray bursts,
relativistic jets, and supernova remnants.Comment: 6 pages, 4 figures, 2012 Fermi Symposium proceedings - eConf C12102
Mixed quark-nucleon phase in neutron stars and nuclear symmetry energy
The influence of the nuclear symmetry energy on the formation of a mixed
quark-nucleon phase in neutron star cores is studied. We use simple
parametrizations of the nuclear matter equation of state, and the bag model for
the quark phase. The behavior of nucleon matter isobars, which is responsible
for the existence of the mixed phase, is investigated. The role of the nuclear
symmetry energy changes with the value of the bag constant B. For lower values
of B the properties of the mixed phase do not depend strongly on the symmetry
energy. For larger B we find that a critical pressure for the first quark
droplets to form is strongly dependent on the nuclear symmetry energy, but the
pressure at which last nucleons disappear is independent of it.Comment: 12 pages, 16 figures, Phys. Rev. C in pres
The upstream magnetic field of collisionless GRB shocks: constraint by Fermi-LAT observations
Long-lived >100 MeV emission has been a common feature of most Fermi-LAT
detected gamma-ray bursts (GRBs), e.g., detected up to ~10^3s in long GRBs
080916C and 090902B and ~10^2s in short GRB 090510. This emission is consistent
with being produced by synchrotron emission of electrons accelerated to high
energy by the relativistic collisionless shock propagating into the weakly
magnetized medium. Here we show that this high-energy afterglow emission
constrains the preshock magnetic field to satisfy 1(n/1cc)^{9/8}
mG<B<10^2(n/1cc)^{3/8}mG, where n is the preshock density, more stringent than
the previous constraint by X-ray afterglow observations on day scale. This
suggests that the preshock magnetic field is strongly amplified, most likely by
the streaming of high energy shock accelerated particles.Comment: 9 pages, JCAP accepte
Photonic Sorting of Aligned, Crystalline Carbon Nanotube Textiles
Floating catalyst chemical vapor deposition uniquely generates aligned carbon nanotube (CNT) textiles with individual CNT lengths magnitudes longer than competing processes, though hindered by impurities and intrinsic/extrinsic defects. We present a photonic-based post-process, particularly suited for these textiles, that selectively removes defective CNTs and other carbons not forming a threshold thermal pathway. In this method, a large diameter laser beam rasters across the surface of a partly aligned CNT textile in air, suspended from its ends. This results in brilliant, localized oxidation, where remaining material is an optically transparent film comprised of few-walled CNTs with profound and unique improvement in microstructure alignment and crystallinity. Raman spectroscopy shows substantial D peak suppression while preserving radial breathing modes. This increases the undoped, specific electrical conductivity at least an order of magnitude to beyond that of single-crystal graphite. Cryogenic conductivity measurements indicate intrinsic transport enhancement, opposed to simply removing nonconductive carbons/residual catalyst
Radiation from Shock-Accelerated Particles
Plasma instabilities excited in collisionless shocks are responsible for particle acceleration, generation of magnetic fields , and associated radiation. We have investigated the particle acceleration and shock structure associated with an unmagnetized relativistic jet propagating into an unmagnetized plasma. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic-like shock structure. The shock structure depends on the composition of the jet and ambient plasma (electron-positron or electron-ions). Strong electromagnetic fields are generated in the reverse , jet shock and provide an emission site. These magnetic fields contribute to the electron's transverse deflection behind the shock. We have calculated, self-consistently, the radiation from electrons accelerated in the turbulent magnetic fields. We found that the synthetic spectra depend on the Lorentz factor of the jet, its thermal temperature and strength of the generated magnetic fields. The detailed properties of the radiation are important for understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jet shocks, and supernova remnant
Radiation from Accelerated Particles in Shocks and Reconnections
Plasma instabilities are responsible not only for the onset and mediation of collisionless shocks but also for the associated acceleration of particles. We have investigated particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic-like shock structure. In the leading shock, electron density increases by a factor of about 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. These magnetic fields contribute to the electrons transverse deflection and, more generally, relativistic acceleration behind the shock. We have calculated, self-consistently, the radiation from electrons accelerated in the turbulent magnetic fields. We found that the synthetic spectra depend on the Lorentz factor of the jet, its thermal temperature and strength of the generated magnetic fields. Our initial results of a jet-ambient interaction with anti-parallelmagnetic fields show pile-up of magnetic fields at the colliding shock, which may lead to reconnection and associated particle acceleration. We will investigate the radiation in a transient stage as a possible generation mechanism of precursors of prompt emission. In our simulations we calculate the radiation from electrons in the shock region. The detailed properties of this radiation are important for understanding the complex time evolution and spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants
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