84,350 research outputs found
PSR B1828-11: a precession pulsar torqued by a quark planet?
The pulsar PSR B1828-11 has long-term, highly periodic and correlated
variations in both pulse shape and the rate of slow-down. This phenomenon may
provide evidence for precession of the pulsar as suggested previously within
the framework of free precession as well as forced one. On a presumption of
forced precession, we propose a quark planet model to this precession henomenon
instead, in which the pulsar is torqued by a quark planet. We construct this
model by constraining mass of the pulsar (), mass of the planet
() and orbital radius of the planet (). Five aspects
are considered: derived relation between and ,
movement of the pulsar around the center of mass, ratio of and
, gravitational wave radiation timescale of the planetary system,
and death-line criterion. We also calculate the range of precession period
derivative and gravitational wave strength (at earth) permitted by the model.
Under reasonable parameters, the observed phenomenon can be understood by a
pulsar () with a quark planet
() orbiting it. According to the calculations
presented, the pulsar would be a quark star because of its low mass, which
might eject a lump of quark matter (to become a planet around) during its
birth.Comment: 6 pages, 3 figures, accepted by MNRAS (Letters
Visualizing urban microclimate and quantifying its impact on building energy use in San Francisco
Weather data at nearby airports are usually used in building energy simulation to estimate energy use in buildings or evaluate building design or retrofit options. However, due to urbanization and geography characteristics, local weather conditions can differ significantly from those at airports. This study presents the visualization of 10-year hourly weather data measured at 27 sites in San Francisco, aiming to provide insights into the urban microclimate and urban heat island effect in San Francisco and how they evolve during the recent decade. The 10-year weather data are used in building energy simulations to investigate its influence on energy use and electrical peak demand, which informs the city's policy making on building energy efficiency and resilience. The visualization feature is implemented in CityBES, an open web-based data and computing platform for urban building energy research
Asymptotic Matrix Theory of Bragg Fibers
We developed a matrix theory that applies to any cylindrically symmetric fiber surrounded with Bragg cladding, which includes both the Bragg fibers and the recently proposed dielectric coaxial fibers. In this formalism,an arbitrary number of inner dielectric layers are treated exactly and the outside cladding structure is approximated in the asymptotic limit. An estimate of the radiation loss of such fibers is given. We compare the asymptotic results with those obtained from the finite difference time domain (FDTD) calculations and find excellent agreement between the two approaches
On effects of regular S=1 dilution of S=1/2 antiferromagnetic Heisenberg chains by a quantum Monte Carlo simulation
The effects of regular S=1 dilution of S=1/2 isotropic antiferromagnetic
chain are investigated by the quantum Monte Carlo loop/cluster algorithm. Our
numerical results show that there are two kinds of ground-state phases which
alternate with the variation of concentration. When the effective spin
of a unit cell is half-integer, the ground state is ferrimagnetic with gapless
energy spectrum and the magnetism becomes weaker with decreasing of the
concentration . While it is integer, a non-magnetic ground state
with gaped spectrum emerges and the gap gradually becomes narrowed as fitted by
a relation of .Comment: 6 pages, 9 figure
Enhanced spin-orbit torques in MnAl/Ta films with improving chemical ordering
We report the enhancement of spin-orbit torques in MnAl/Ta films with
improving chemical ordering through annealing. The switching current density is
increased due to enhanced saturation magnetization MS and effective anisotropy
field HK after annealing. Both damplinglike effective field HD and fieldlike
effective field HF have been increased in the temperature range of 50 to 300 K.
HD varies inversely with MS in both of the films, while the HF becomes liner
dependent on 1/MS in the annealed film. We infer that the improved chemical
ordering has enhanced the interfacial spin transparency and the transmitting of
the spin current in MnAl layer
Analysis of excited quark propagator effects on neutron charge form factor
The charge form factor and charge radius of neutron are investigated in the
perturbative chiral quark model (PCQM) with considering both the ground and
excited states in the quark propagator. A Cornell-like potential is extracted
in accordance with the predetermined ground state quark wavefunction, and the
excited quark states are derived by solving the Dirac equation with the
extracted PCQM potential numerically. The study reveals that the contributions
of the excited quark states are considerably influential in the charge form
factor and charge radius of neutron as expected, and the total results are
significantly improved and increased by nearly four times by including the
excited states in the quark propagator. The theoretical PCQM results are found,
including the ground and excited quark propagators, in good agreement with the
recent lattice QCD values at pion mass of about 130 MeV.Comment: 8 pages, 8 figure
Quantising Higher-spin String Theories
In this paper, we examine the conditions under which a higher-spin string
theory can be quantised. The quantisability is crucially dependent on the way
in which the matter currents are realised at the classical level. In
particular, we construct classical realisations for the algebra,
which is generated by a primary spin- current in addition to the
energy-momentum tensor, and discuss the quantisation for . From these
examples we see that quantum BRST operators can exist even when there is no
quantum generalisation of the classical algebra. Moreover, we find
that there can be several inequivalent ways of quantising a given classical
theory, leading to different BRST operators with inequivalent cohomologies. We
discuss their relation to certain minimal models. We also consider the
hierarchical embeddings of string theories proposed recently by Berkovits and
Vafa, and show how the already-known strings provide examples of this
phenomenon. Attempts to find higher-spin fermionic generalisations lead us to
examine the whether classical BRST operators for ( odd)
algebras can exist. We find that even though such fermionic algebras close up
to null fields, one cannot build nilpotent BRST operators, at least of the
standard form.Comment: CTP TAMU-24/94, KUL-TF-94/11, SISSA-135/94/E
Analytical models for quark stars
We find two new classes of exact solutions to the Einstein-Maxwell system of
equations. The matter content satisfies a linear equation of state consistent
with quark matter; a particular form of one of the gravitational potentials is
specified to generate solutions. The exact solutions can be written in terms of
elementary functions, and these can be related to quark matter in the presence
of an electromagnetic field. The first class of solutions generalises the Mak
and Harko model. The second class of solutions does not admit any singularities
in the matter and gravitational potentials at the centre.Comment: 10 pages, To appear in Int. J. Mod. Phys.
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