12,864 research outputs found
Neutrino fluence after r-process freeze-out and abundances of Te isotopes in presolar diamonds
Using the data of Richter et al. (1998) on Te isotopes in diamond grains from
a meteorite, we derive bounds on the neutrino fluence and the decay timescale
of the neutrino flux relevant for the supernova r-process. Our new bound on the
neutrino fluence F after freeze-out of the r-process peak at mass number A =
130 is more stringent than the previous bound F < 0.045 (in units of 10**37
erg/cm**2) of Qian et al. (1997) and Haxton et al. (1997) if the neutrino flux
decays on a timescale tau > 0.65 s. In particular, it requires that a fluence
of F = 0.031 be provided by a neutrino flux with tau < 0.84 s. Such a fluence
may be responsible for the production of the solar r-process abundances at A =
124-126 (Qian et al. 1997; Haxton et al. 1997). Our results are based on the
assumption that only the stable nuclei implanted into the diamonds are retained
while the radioactive ones are lost from the diamonds upon decay after
implantation (Ott 1996). We consider that the nanodiamonds are condensed in an
environment with C/O > 1 in the expanding supernova debris or from the exterior
H envelope. The implantation of nuclei would have occurred 10**4-10**6 s after
r-process freeze-out. This time interval may be marginally sufficient to permit
adequate cooling upon expansion for the formation of diamond grains. The
mechanisms of preferential retention/loss of the implanted nuclei are not well
understood.Comment: AASTeX, 11 pages, 3 Postscript figure
Measurement of charm and bottom production in p+p collisions at = 200 GeV at RHIC-PHENIX
RHIC-PHENIX has observed a large suppression pattern and azimuthal anisotropy
of non-photonic electron at mid-rapidity () in Au+Au
collisions at GeV. To understand these results and the
interaction of heavy quarks in the hot and dense medium, experimental
determination of production ratio of charm over bottom is one of the most
important topics, since the behavior of bottom may differ from charm in the
medium. We measured the ratio of charm over bottom and total cross section of
bottom via partial reconstruction of De K decay in p+p
collisions at GeV. Total cross sections of charm and bottom
were also measured via di-electron continuum in p+p collisions at GeV.Comment: 4pages, 4figures,coferenc
Wilson chains are not thermal reservoirs
Wilson chains, based on a logarithmic discretization of a continuous
spectrum, are widely used to model an electronic (or bosonic) bath for Kondo
spins and other quantum impurities within the numerical renormalization group
method and other numerical approaches. In this short note we point out that
Wilson chains can not serve as thermal reservoirs as their temperature changes
by a number of order Delta E when a finite amount of energy Delta E is added.
This proves that for a large class of non-equilibrium problems they cannot be
used to predict the long-time behavior.Comment: 2 page
Properties of Resonating-Valence-Bond Spin Liquids and Critical Dimer Models
We use Monte Carlo simulations to study properties of Anderson's
resonating-valence-bond (RVB) spin-liquid state on the square lattice (i.e.,
the equal superposition of all pairing of spins into nearest-neighbor singlet
pairs) and compare with the classical dimer model (CDM). The latter system also
corresponds to the ground state of the Rokhsar-Kivelson quantum dimer model at
its critical point. We find that although spin-spin correlations decay
exponentially in the RVB, four-spin valence-bond-solid (VBS) correlations are
critical, qualitatively like the well-known dimer-dimer correlations of the
CDM, but decaying more slowly (as with , compared with
for the CDM). We also compute the distribution of monomer (defect) pair
separations, which decay by a larger exponent in the RVB than in the CDM. We
further study both models in their different winding number sectors and
evaluate the relative weights of different sectors. Like the CDM, all the
observed RVB behaviors can be understood in the framework of a mapping to a
"height" model characterized by a gradient-squared stiffness constant . Four
independent measurements consistently show a value , with the same kinds of numerical evaluations of give
results in agreement with the rigorously known value . The
background of a nonzero winding number gradient introduces spatial
anisotropies and an increase in the effective K, both of which can be
understood as a consequence of anharmonic terms in the height-model free
energy, which are of relevance to the recently proposed scenario of "Cantor
deconfinement" in extended quantum dimer models. We also study ensembles in
which fourth-neighbor (bipartite) bonds are allowed, at a density controlled by
a tunable fugacity, resulting (as expected) in a smooth reduction of K.Comment: 26 pages, 21 figures. v3: final versio
Redshifted emission lines and radiative recombination continuum from the Wolf-Rayet binary theta Muscae: evidence for a triplet system?
We present XMM-Newton observations of the WC binary Theta Muscae (WR 48), the
second brightest Wolf-Rayet binary in optical wavelengths. The system consists
of a short-period (19.1375 days) WC5/WC6 + O6/O7V binary and possibly has an
additional O supergiant companion (O9.5/B0Iab) which is optically identified at
a separation of ~46 mas. Strong emission lines from highly ionized ions of C,
O, Ne, Mg, Si, S, Ar, Ca and Fe are detected. The spectra are fitted by a
multi-temperature thin-thermal plasma model with an interstellar absorption N_H
= 2--3*10**21 cm**-2. Lack of nitrogen line indicates that the abundance of
carbon is at least an order of magnitude larger than that of nitrogen. A
Doppler shift of ~630 km/s is detected for the OVIII line, while similar shifts
are obtained from the other lines. The reddening strongly suggests that the
emission lines originated from the wind-wind shock zone, where the average
velocity is ~600 km/s. The red-shift motion is inconsistent with a scenario in
which the X-rays originate from the wind-wind collision zone in the
short-period binary, and would be evidence supporting the widely separated O
supergiant as a companion. This may make up the collision zone be lying behind
the short-period binary. In addition to the emission lines, we also detected
the RRC (radiative recombination continuum) structure from carbon around 0.49
keV. This implies the existence of additional cooler plasma.Comment: 6 pages, 4 figures, accepted to A&
Sustainability Research of the Secure Wireless Communication System with Channel Reservation
The paper presents the research of the stability of the system with redundancy of communication channels. For this, two prototypes have been developed that are built (1) according to the classical circuit-switched scheme and (2) with aggregation of several virtual channels. Prototyping, installation on various vehicles and measurements of the stability of the entire system as a whole were carried out. The paper also presents structural diagrams, hardware, and a list of problems and difficulties that the authors encountered during the practical implementation and implementation of these systems. In the future, it is planned to expand the study of these systems when working with high-level channel virtualization and the search for methods to accelerate its work
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