A quasi-time-dependent radiative transfer model of OH104.9+2.4

We investigate the pulsation-phase dependent properties of the circumstellar dust shell (CDS) of the OH/IR star OH104.9+2.4 based on radiative transfer modeling (RTM) using the code DUSTY. Our previous study concerning simultaneous modeling of the spectral energy distribution (SED) and near-infrared (NIR) visibilities (Riechers et al. 2004) has now been extended by means of a more detailed analysis of the pulsation-phase dependence of the model parameters of OH104.9+2.4. In order to investigate the temporal variation in the spatial structure of the CDS, additional NIR speckle interferometric observations in the K' band were carried out with the 6 m telescope of the Special Astrophysical Observatory (SAO). At a wavelength of 2.12 micron the diffraction-limited resolution of 74 mas was attained. Several key parameters of our previous best-fitting model had to be adjusted in order to be consistent with the newly extended amount of observational data. It was found that a simple rescaling of the bolometric flux F_bol is not sufficient to take the variability of the source into account, as the change in optical depth over a full pulsation cycle is rather high. On the other hand, the impact of a change in effective temperature T_eff on SED and visibility is rather small. However, observations, as well as models for other AGB stars, show the necessity of including a variation of T_eff with pulsation phase in the radiative transfer models. Therefore, our new best-fitting model accounts for these changes.Comment: 7 pages, including 5 postscript figures and 3 tables. Published in Astronomy and Astrophysics. (v1: accepted version; v2: published version, minor grammatical changes

Chesapeake Bay wave climate : Thimble Shoal light wave station, report and summary of wave observations, October 8, 1990 through August 22, 1991 and Chesapeake light tower - VIMS Star gage test measurements and evaluation, July, August, October 1991

This report also presents a description of a directional wave gaging system, known as a Star gage, that is designed for long-term, low-maintenance operation both within and immediately outside the Chesapeake Bay entrance area. This development was prompted by our dependence to date on the single-point, PUV-type directional wave gage described below. While ideally suited for short-term investigative studies at different sites, the PUV directional wave gage requires field service visits at monthly intervals to maintain adequate performance and uninterrupted operation. A prototype Star gage system was constructed and field tested to evaluate its potential use as a long-term and eventual real-time wave gage for the Virginia coastal environment. A test deployment of the VIMS Star gage, a 4-element pressure sensor array utilizing a star configuration (Goda, 1985) was conducted at the Chesapeake Light Tower (CLT, Fig. 1) located approximately 14 nautical miles east of the bay entrance. Results of these tests are reported in Section VII

Chesapeake Bay wave climate : Thimble Shoals wave station, report and summary of wave observations, September 27, 1988 through October 17, 1989

The Virginia Institute of Marine Science, in cooperation with the Virginia Department of Conservation and Recreation, Division of Soil and Water Conservation, has identified as one of its major goals the systematic study of hydrodynamic processes that affect recreational, shoreline and benthic resources in the coastal zone of the Commonwealth. In pursuit of that goal, a long-term study of the wave climate in the Virginia portion of Chesapeake Bay was initiated in 1988 with support from the National Oceanographic and Atmospheric Administration through the Coastal Zone Management Program administered by the Virginia Council on the Environment (Grant Ho. HA88AA-D-CZ092). Past knowledge of wave properties in the Chesapeake Bay region has been conspicuous in its lack of an observational basis. Although inner shelf and deep water wave measurements have been made outside the Chesapeake Bay entrance, none of these have produced reliable directional information (Seymour et al., 1985). Therefore, before addressing certain long-term wave monitoring objectives, it was deemed essential to develop a basis for them by obtaining a representative (year-long) series of wave observations at one or more selected locations. The first of these has recently been completed for a station designated as VIMS BAY! located near Thimble Shoals to the west of the Chesapeake Bay entrance (Fig. 1). This report contains a summary of data for the initial year of continuous directional wave measurements made at the Thimble Shoals station

An Over-Massive Black Hole in a Typical Star-Forming Galaxy, 2 Billion Years After the Big Bang

Supermassive black holes (SMBHs) and their host galaxies are generally thought to coevolve, so that the SMBH achieves up to about 0.2 to 0.5% of the host galaxy mass in the present day. The radiation emitted from the growing SMBH is expected to affect star formation throughout the host galaxy. The relevance of this scenario at early cosmic epochs is not yet established. We present spectroscopic observations of a galaxy at redshift z = 3.328, which hosts an actively accreting, extremely massive BH, in its final stages of growth. The SMBH mass is roughly one-tenth the mass of the entire host galaxy, suggesting that it has grown much more efficiently than the host, contrary to models of synchronized coevolution. The host galaxy is forming stars at an intense rate, despite the presence of a SMBH-driven gas outflow.Comment: Author's version, including the main paper and the Supplementary Materials (16+21 pages, 3+3 figures

P2P assisted streaming for low popularity VoD contents

The Video on Demand (VoD) service is becoming a dominant service in the telecommunication market due to the great convenience regarding the choice of content items and their independent viewing time. However, due to its high traffic demand nature, the VoD streaming systems are faced with the problem of huge amounts of traffic generated in the core of the network, especially for serving the requests for content items that are not in the top popularity range. Therefore, we propose a peer assisted VoD model that takes advantage of the clients unused uplink and storage capacity to serve requests for less popular items with the objective to keep the traffic on the periphery of the network, reduce the transport cost in the core of the network and make the system more scalable

Speckle-visibility spectroscopy: A tool to study time-varying dynamics

We describe a multispeckle dynamic light scattering technique capable of resolving the motion of scattering sites in cases that this motion changes systematically with time. The method is based on the visibility of the speckle pattern formed by the scattered light as detected by a single exposure of a digital camera. Whereas previous multispeckle methods rely on correlations between images, here the connection with scattering site dynamics is made more simply in terms of the variance of intensity among the pixels of the camera for the specified exposure duration. The essence is that the speckle pattern is more visible, i.e. the variance of detected intensity levels is greater, when the dynamics of the scattering site motion is slow compared to the exposure time of the camera. The theory for analyzing the moments of the spatial intensity distribution in terms of the electric field autocorrelation is presented. It is demonstrated for two well-understood samples, a colloidal suspension of Brownian particles and a coarsening foam, where the dynamics can be treated as stationary. However, the method is particularly appropriate for samples in which the dynamics vary with time, either slowly or rapidly, limited only by the exposure time fidelity of the camera. Potential applications range from soft-glassy materials, to granular avalanches, to flowmetry of living tissue.Comment: review - theory and experimen

Interplay between carrier and impurity concentrations in annealed Ga1−x_{1-x}Mnx_{x}As intrinsic anomalous Hall Effect

Investigating the scaling behavior of annealed Ga$_{1-x}$Mn$_{x}$As anomalous Hall coefficients, we note a universal crossover regime where the scaling behavior changes from quadratic to linear, attributed to the anomalous Hall Effect intrinsic and extrinsic origins, respectively. Furthermore, measured anomalous Hall conductivities when properly scaled by carrier concentration remain constant, equal to theoretically predicated values, spanning nearly a decade in conductivity as well as over 100 K in T$_{C}$. Both the qualitative and quantitative agreement confirms the validity of new equations of motion including the Berry phase contributions as well as tunablility of the intrinsic anomalous Hall Effect.Comment: 4 pages, 5 figure

Study of the neutron star structure in strong magnetic fields including the anomalous magnetic moments

We study the effects of strong magnetic fields on the neutron star structure. If the interior field of a star is on the same order of the surface field currently observed, the influences of the magnetic field on the star mass and radius are negligible. If one assumes that the internal magnetic field can be as large as that estimated from the scalar virial theorem, considerable effects can be induced. The maximum mass of stars is arisen substantially while the central density is largely suppressed. For two equal-mass stars the radius of the magnetic star can be larger by about 10% $\sim$ 20% than the nonmagnetic star.Comment: 26 pages, 5 postscript figures; replaced by the revised version, Chin. J. Astron. Astrophys., accepte