8,484 research outputs found
Super- and subradiant emission of two-level systems in the near-Dicke limit
We analyze the stability of super- and subradiant states in a system of
identical two-level atoms in the near-Dicke limit, i.e., when the atoms are
very close to each other compared to the wavelength of resonant light. The
dynamics of the system are studied using a renormalized master equation, both
with multipolar and minimal-coupling interaction schemes. We show that both
models lead to the same result and, in contrast to unrenormalized models,
predict that the relative orientation of the (co-aligned) dipoles is
unimportant in the Dicke limit. Our master equation is of relevance to any
system of dipole-coupled two-level atoms, and gives bounds on the strength of
the dipole-dipole interaction for closely spaced atoms. Exact calculations for
small atom systems in the near-Dicke limit show the increased emission times
resulting from the evolution generated by the strong dipole-dipole interaction.
However, for large numbers of atoms in the near-Dicke limit, it is shown that
as the number of atoms increases, the effect of the dipole-dipole interaction
on collective emission is reduced.Comment: 14 pages, 6 figures, published versio
Peer Rejection and Friendships in Children with Attention-Deficit/Hyperactivity Disorder: Contributions to Long-Term Outcomes
Even after evidence-based treatment, Attention- Deficit/Hyperactivity Disorder (ADHD) is associated with poor long-term outcomes. These outcomes may be partly explained by difficulties in peer functioning, which are common among children with ADHD and which do not respond optimally to standard ADHD treatments. We examined whether peer rejection and lack of dyadic friendships experienced by children with ADHD after treatment contribute to long-term emotional and behavioral problems and global impairment, and whether having a reciprocal friend buffers the negative effects of peer rejection. Children with Combined type ADHD (N0300) enrolled in the Multimodal Treatment Study of Children with ADHD (MTA) were followed for 8 years. Peer rejection and dyadic friendships were measured with sociometric assessments after the active treatment period (14 or 24 months after baseline; M ages 9.7 and 10.5 years, respectively). Outcomes included delinquency, depression, anxiety, substance use, and general impairment at 6 and 8 years after baseline (Mean ages 14.9 and 16.8 years, respectively). With inclusion of key covariates, including demographics, symptoms ofADHD, ODD, and CD, and level of the outcome variable at 24 months, peer rejection predicted cigarette smoking, delinquency, anxiety, and global impairment at 6 years and global impairment at 8 years after baseline. Having a reciprocal friend was not, however, uniquely predictive of any outcomes and did not reduce the negative effects of peer rejection. Evaluating and addressing peer rejection in treatment planning may be necessary to improve long-term outcomes in children with ADHD
The primary cosmic ray spectrum above 10 to the 19th power eV
Progress on a re-evaluation of the spectrum of cosmic rays determined with the Haverah Park shower array is described. Particular attention is paid to the reality of some giant showers
History Dependent Phenomena in the Transverse Ising Ferroglass: the Free Energy Landscape
In this paper we investigate the relationship between glassy and
ferromagnetic phases in disordered Ising ferromagnets in the presence of
transverse magnetic fields, . Iterative mean field simulations probe
the free energy landscape and suggest the existence of a glass transition as a
function of which is distinct from the Curie temperature. New
experimental field-cooled and zero-field-cooled data on LiHoYF
provide support for our theoretical picture.Comment: 4 pages RevTex; 5 figure
A new array for the study of ultra high energy gamma-ray sources
The design and operation of a 32 x 1 10 to the 15th power sq m array of scintillation detectors for the detection of 10 to the 15th power eV cosmic rays is described with an expected angular resolution of 1 deg, thus improving the present signal/background ratio for gamma ray sources. Data are recorded on a hybrid CAMAC, an in-house system which uses a laser and Pockel-Cell arrangement to routinely calibrate the timing stability of the detectors
Panchromatic observations and modeling of the HV Tau C edge-on disk
We present new high spatial resolution (<~ 0.1") 1-5 micron adaptive optics
images, interferometric 1.3 mm continuum and 12CO 2-1 maps, and 350 micron, 2.8
and 3.3 mm fluxes measurements of the HV Tau system. Our adaptive optics images
reveal an unusually slow orbital motion within the tight HV Tau AB pair that
suggests a highly eccentric orbit and/or a large deprojected physical
separation. Scattered light images of the HV Tau C edge-on protoplanetary disk
suggest that the anisotropy of the dust scattering phase function is almost
independent of wavelength from 0.8 to 5 micron, whereas the dust opacity
decreases significantly over the same range. The images further reveal a marked
lateral asymmetry in the disk that does not vary over a timescale of 2 years.
We further detect a radial velocity gradient in the disk in our 12CO map that
lies along the same position angle as the elongation of the continuum emission,
which is consistent with Keplerian rotation around an 0.5-1 Msun central star,
suggesting that it could be the most massive component in the triple system. We
use a powerful radiative transfer model to compute synthetic disk observations
and use a Bayesian inference method to extract constraints on the disk
properties. Each individual image, as well as the spectral energy distribution,
of HV Tau C can be well reproduced by our models with fully mixed dust provided
grain growth has already produced larger-than-interstellar dust grains.
However, no single model can satisfactorily simultaneously account for all
observations. We suggest that future attempts to model this source include more
complex dust properties and possibly vertical stratification. (Abridged)Comment: 26 pages, 11 figures, editorially accepted for publication in Ap
Perspectives: Quantum Mechanics on Phase Space
The basic ideas in the theory of quantum mechanics on phase space are
illustrated through an introduction of generalities, which seem to underlie
most if not all such formulations and follow with examples taken primarily from
kinematical particle model descriptions exhibiting either Galileian or
Lorentzian symmetry. The structures of fundamental importance are the relevant
(Lie) groups of symmetries and their homogeneous (and associated) spaces that,
in the situations of interest, also possess Hamiltonian structures. Comments
are made on the relation between the theory outlined and a recent paper by
Carmeli, Cassinelli, Toigo, and Vacchini.Comment: "Quantum Structures 2004" - Meeting of the International Quantum
Structures Association; Denver, Colorado; 17-22 July, 200
Separate GABA Afferents to Dopamine Neurons Mediate Acute Action of Opioids, Development of Tolerance, and Expression of Withdrawal
SummaryGABA release from interneurons in VTA, projections from the nucleus accumbens (NAc), and rostromedial tegmental nucleus (RMTg) was selectively activated in rat brain slices. The inhibition induced by μ-opioid agonists was pathway dependent. Morphine induced a 46% inhibition of IPSCs evoked from the RMTg, 18% from NAc, and IPSCs evoked from VTA interneurons were almost insensitive (11% inhibition). In vivo morphine treatment resulted in tolerance to the inhibition of RMTg, but not local interneurons or NAc, inputs. One common sign of opioid withdrawal is an increase in adenosine-dependent inhibition. IPSCs evoked from the NAc were potently inhibited by activation of presynaptic adenosine receptors, whereas IPSCs evoked from RMTg were not changed. Blockade of adenosine receptors selectively increased IPSCs evoked from the NAc during morphine withdrawal. Thus, the acute action of opioids, the development of tolerance, and the expression of withdrawal are mediated by separate GABA afferents to dopamine neurons
First results on the performance of the CMS global calorimeter trigger
The CMS Global Calorimeter Trigger (GCT) uses data from the CMS calorimeters to compute a number kinematical quantities which characterize the LHC event. The GTC output is used by the Global Trigger (GT) along with data from the Global Muon Trigger (GMT) to produce the Level-1 Accept (L1A) decision. The design for the current GCT system commenced early in 2006. After a rapid development phase all the different GCT components have been produced and a large fraction of them have been installed at the CMS electronics cavern (USC-55). There the GCT system has been under test since March 2007. This paper reports results from tests which took place at the USC-55. Initial tests aimed to test the integrity of the GCT data and establish that the proper synchronization had been achieved both internally within GCT as well as with the Regional Calorimeter Trigger (RCT) which provides the GCT input data and with GT which receives the GCT results. After synchronization and data integrity had been established, Monte Carlo Events with electrons in the final state were injected at the GCT inputs and were propagated to the GCT outputs. The GCT output was compared with the predictions of the GCT emulator model in the CMS Monte Carlo and were found to be identical
Residual Energies after Slow Quantum Annealing
Features of the residual energy after the quantum annealing are investigated.
The quantum annealing method exploits quantum fluctuations to search the ground
state of classical disordered Hamiltonian. If the quantum fluctuation is
reduced sufficiently slowly and linearly by the time, the residual energy after
the quantum annealing falls as the inverse square of the annealing time. We
show this feature of the residual energy by numerical calculations for
small-sized systems and derive it on the basis of the quantum adiabatic
theorem.Comment: 4 pages, 2 figure
- …