16,528 research outputs found
Localized structures in Kagome lattices
We investigate the existence and stability of gap vortices and multi-pole gap
solitons in a Kagome lattice with a defocusing nonlinearity both in a discrete
case and in a continuum one with periodic external modulation. In particular,
predictions are made based on expansion around a simple and analytically
tractable anti-continuum (zero coupling) limit. These predictions are then
confirmed for a continuum model of an optically-induced Kagome lattice in a
photorefractive crystal obtained by a continuous transformation of a honeycomb
lattice
Distribution of Manganese, Iron, Copper, Lead and Zinc in Water and Sediment of Kelang Estuary
A study was conducted on the distrubution of manganese, iron, copper, lead and zinc in the
water and sediment of Kelang estuary in 1981. The mean total levels of manganese, iron, copper, lead
and zinc in the estuarine water were 27.1 pgl1,106.5 gil, '10.0 pgl1, 4.1 Ilg/l and 17.9 Ilg11
respectively. For the dissolved copper, lead and zinc, the values were 4.3 pg/l, 1.6 Ilg/l and 3.9
pgI l respectively. In the estuarine sediment, the copper, lead and zinc contents were 1.92, 0.48 and
5.43 ppm wet sediment respectively. The levels of these heavy metalized water and sediment were
comparable to the values reported for other estuarise. The copper and zinc levels were similar to those
found in the world oceans, The results indicate that Kelang estuary is polluted with lead, manganese
and iron. However, levels of these heavy, metals may still be considered safe for aquaculture, if the
farm is located at least 10 km away from the Rivers mouth
Thinking beyond the hybrid:“actually-existing” cities “after neoliberalism” in Boyle <i>et al.</i>
In their article, ‘The spatialities of actually existing neoliberalism in Glasgow, 1977 to present’, Mark Boyle, Christopher McWilliams and Gareth Rice (2008) usefully problematise our current understanding of neoliberal urbanism. Our response is aimed at developing a sympathetic but critical approach to Boyle et al's understanding of neoliberal urbanism as illustrated by the Glasgow example. In particular, the counterposing by Boyle et al of a 'hybrid, mutant' model to a 'pure' model of neoliberalism for us misrepresents existing models of neoliberalism as a perfectly finished object rather than a roughly mottled process. That they do not identify any ‘pure’ model leads them to create a straw construct against which they can claim a more sophisticated, refined approach to the messiness of neoliberal urbanism. In contrast, we view neoliberalism as a contested and unstable response to accumulation crises at various scales of analysis
A Constraint on the Organization of the Galactic Center Magnetic Field Using Faraday Rotation
We present new 6 and 20 cm Very Large Array (VLA) observations of polarized
continuum emission of roughly 0.5 square degrees of the Galactic center (GC)
region. The 6 cm observations detect diffuse linearly-polarized emission
throughout the region with a brightness of roughly 1 mJy per 15"x10" beam. The
Faraday rotation measure (RM) toward this polarized emission has structure on
degree size scales and ranges from roughly +330 rad/m2 east of the dynamical
center (Sgr A) to -880 rad/m2 west of the dynamical center. This RM structure
is also seen toward several nonthermal radio filaments, which implies that they
have a similar magnetic field orientation and constrains models for their
origin. Modeling shows that the RM and its change with Galactic longitude are
best explained by the high electron density and strong magnetic field of the GC
region. Considering the emissivity of the GC plasma shows that while the
absolute RM values are indirect measures of the GC magnetic field, the RM
longitude structure directly traces the magnetic field in the central
kiloparsec of the Galaxy. Combining this result with previous work reveals a
larger RM structure covering the central ~2 degrees of the Galaxy. This RM
structure is similar to that proposed by Novak and coworkers, but is shifted
roughly 50 pc west of the dynamical center of the Galaxy. If this RM structure
originates in the GC region, it shows that the GC magnetic field is organized
on ~300 pc size scales. The pattern is consistent with a predominantly poloidal
field geometry, pointing from south to north, that is perturbed by the motion
of gas in the Galactic disk.Comment: Accepted to ApJ. emulateapj style, 14 pages, 15 figure
Natural orbits of atomic Cooper pairs in a nonuniform Fermi gas
We examine the basic mode structure of atomic Cooper pairs in an
inhomogeneous Fermi gas. Based on the properties of Bogoliubov quasi-particle
vacuum, the single particle density matrix and the anomalous density matrix
share the same set of eigenfunctions. These eigenfunctions correspond to
natural pairing orbits associated with the BCS ground state. We investigate
these orbits for a Fermi gas in a spherical harmonic trap, and construct the
wave function of a Cooper pair in the form of Schmidt decomposition. The issue
of spatial quantum entanglement between constituent atoms in a pair is
addressed.Comment: 14 pages, 4 figures, submitted to Phys. Rev.
The golden circle: A way of arguing and acting about technology in the London ambulance service
This paper analyses the way in which the London Ambulance Service recovered from the events of October 1992, when it implemented a computer-aided despatch system (LASCAD) that remained in service for less than two weeks. It examines the enactment of a programme of long-term organizational change, focusing on the implementation of an alternative computer system in 1996. The analysis in this paper is informed by actor-network theory, both by an early statement of this approach developed by Callon in the sociology of translation, and also by concepts and ideas from Latour’s more recent restatement of his own position. The paper examines how alternative interests emerged and were stabilized over time, in a way of arguing and acting among key players in the change programme, christened the Golden Circle. The story traces four years in the history of the London Ambulance Service, from the aftermath of October 1992 through the birth of the Golden Circle to the achievement of National Health Service (NHS) trust status. LASCAD was the beginning of the story, this is the middle, an end lies in the future, when the remaining elements of the change programme are enacted beyond the Golden Circle
Production of photons by the parametric resonance in the dynamical Casimir effect
We calculate the number of photons produced by the parametric resonance in a
cavity with vibrating walls. We consider the case that the frequency of
vibrating wall is which is a generalization of other
works considering only , where is the fundamental-mode
frequency of the electromagnetic field in the cavity. For the calculation of
time-evolution of quantum fields, we introduce a new method which is borrowed
from the time-dependent perturbation theory of the usual quantum mechanics.
This perturbation method makes it possible to calculate the photon number for
any and to observe clearly the effect of the parametric resonance.Comment: 15 pages, RevTeX, no figure
The High-Order-Multiplicity of Unusually Wide M-dwarf Binaries: Eleven New Triple and Quadruple Systems
M-dwarfs in extremely wide binary systems are very rare, and may thus have
different formation processes from those found as single stars or close
binaries in the field. In this paper we search for close companions to a new
sample of 36 extremely wide M-dwarf binaries, covering a spectral type range of
M1 to M5 and a separation range of 600 - 6500 AU. We discover 10 new triple
systems and one new quadruple system. We carefully account for selection
effects including proper motion, magnitude limits, the detection of close
binaries in the SDSS, and other sample biases. The bias-corrected total
high-order-multiple fraction is 45% (+18%/-16%) and the bias-corrected
incidence of quadruple systems is < 5%, both statistically compatible with that
found for the more common close M-dwarf multiple systems. Almost all the
detected companions have similar masses to their primaries, although two very
low mass companions, including a candidate brown dwarf, are found at relatively
large separations. We find that the close-binary separation distribution is
strongly peaked towards < 30AU separations. There is marginally significant
evidence for a change in high-order M-dwarf multiplicity with binding energy
and total mass. We also find 2-sigma evidence of an unexpected increased
high-order-multiple fraction for the widest targets in our survey, with a
high-order-multiple fraction of 21% (+17%/-7%) for systems with separations up
to 2000AU, compared to 77% (+9%/-22%) for systems with separations > 4000AU.
These results suggest that the very widest M-dwarf binary systems need higher
masses to form or to survive.Comment: 11 pages, 14 figures, accepted for publication in Ap
Dynamic and Energetic Stabilization of Persistent Currents in Bose-Einstein Condensates
We study conditions under which vortices in a highly oblate harmonically
trapped Bose-Einstein condensate (BEC) can be stabilized due to pinning by a
blue-detuned Gaussian laser beam, with particular emphasis on the potentially
destabilizing effects of laser beam positioning within the BEC. Our approach
involves theoretical and numerical exploration of dynamically and energetically
stable pinning of vortices with winding number up to , in correspondence
with experimental observations. Stable pinning is quantified theoretically via
Bogoliubov-de Gennes excitation spectrum computations and confirmed via direct
numerical simulations for a range of conditions similar to those of
experimental observations. The theoretical and numerical results indicate that
the pinned winding number, or equivalently the winding number of the superfluid
current about the laser beam, decays as a laser beam of fixed intensity moves
away from the BEC center. Our theoretical analysis helps explain previous
experimental observations, and helps define limits of stable vortex pinning for
future experiments involving vortex manipulation by laser beams.Comment: 8 pages 5 figure
- …