3,247 research outputs found
Weak inter-band coupling in MgB: a specific heat analysis
The superconducting state of MgB is investigated by specific
heat measurements in detail. The specific heat in the normal state is analyzed
using a recently developed computer code. This allows for an extraction of the
electronic specific heat in the superconducting state with high accuracy and a
fair determination of the main lattice features. One of the two investigated
samples shows a hump in the specific heat at low temperatures within the
superconducting state, accompanied by an unusual low value of the small gap,
, pointing to a very weak inter-band coupling. This
sample allows for a detailed analysis of the contribution from the -band
to the electronic specific heat in the superconducting state. Therefore the
usual analysis method is modified, to include the individual conservation of
entropy of both bands. From analyzing the deviation function of
MgB, the theoretically predicted weak inter-band coupling scenario is
confirmed.Comment: major revision
Towards the Development of a Risk Model for Unmanned Vessels Design and Operations
An unmanned merchant vessel seems to be escaping from the stage of idea exploration. Once the concept proofs its safety, it may become a part of maritime reality. Although the safety aspect of such a ship has been addressed by a handful of scholars, the problem remains open. This is mainly due to lack of knowledge regarding actual operational circumstances and design of unmanned ships, which are yet to be developed. In the attempt of bridging this gap, the risk analysis associated with unmanned ships needs to be carried out, where all relevant hazards and consequences are assessed and quantified in systematic manner. In this paper we present the results of a first step of such analysis, namely the hazard analysis associated with the unmanned ships. The list of hazards covers various aspects of unmanned shipping originating from both design and operational phases of vessel’s life. Subsequently the hazards and related consequences are organized in a casual manner, resulting in the development of a structure of a risk model
Spitzer Observations of Cold Dust Galaxies
We combine new Spitzer Space Telescope observations in the mid- and
far-infrared with SCUBA 850 micron observations to improve the measurement of
dust temperatures, masses and luminosities for 11 galaxies of the SCUBA Local
Universe Galaxy Survey (SLUGS). By fitting dust models we measure typical dust
masses of 10E7.9 M_sol and dust luminosities of ~ 10E10 L_sol, for galaxies
with modest star formation rates. The data presented in this paper combined
with previous observations show that cold dust is present in all types of
spiral galaxies and is a major contributor to their total luminosity. Because
of the lower dust temperature of the SCUBA sources measured in this paper, they
have flatter Far-IR nu F_nu(160um)/nu F_nu(850um) slopes than the larger
Spitzer Nearby Galaxies Survey (SINGS), the sample that provides the best
measurements of the dust properties of galaxies in the nearby universe. The new
data presented here added to SINGS extend the parameter space that is well
covered by local galaxies, providing a comprehensive set of templates that can
be used to interpret the observations of nearby and distant galaxies.Comment: Accepted by A.J. 16 pages, 10 figures, 7 tables. High resolution
version at http://mips.as.arizona.edu/~cnaw/slugs_hires.pd
Mapping with Skysat Images
The very high-resolution space imagery now competes with some functions that were previously solved with aerial images. Several very high-resolution optical satellites with a ground sampling distance (GSD) of 1 m and smaller are currently active. Not all of these satellites take images worldwide. Nevertheless, it is not a problem to obtain up-to-date satellite images with a very high resolution. Mapping projects not only need to consider access and quality, but also cost-effectiveness. Of course, the economic framework conditions are decisive for the decision as to whether space images or very high-resolution satellite images should be used. With a total 21 SkySat satellites, low-cost satellites with very high resolution have changed the economic conditions. To keep costs and weights down, the Skysat satellites were not designed to offer the best direct geo-referencing performance, but this problem can be solved by automatic orientation in relation to existing orthoimages.In North Rhine-Westphalia, the cadastral maps must be checked at regular intervals to ensure that the buildings are complete. A test project examined whether this is possible with SkySat images. The geometric conditions and the image quality with the effective ground resolutions are investigated. Experiences from earlier publications could not be used. First the specific problem had to be solved, the resolution of the SkySat images was improved by lowering the satellite orbit altitude from 500 km to 450 km and by a better super resolution with 0.50 m ground sampling distance for the SkySat Collect orthoimages and in addition Planet improved their generation of Collect images. The required standard deviation of the object details of 4 m was achieved clearly as the effective ground resolution of 0.5 m if the angle of incidence is below 20°
A disrupted circumstellar torus inside eta Carinae's Homunculus Nebula
We present thermal infrared images of the bipolar nebula surrounding eta
Carinae at six wavelengths from 4.8 to 24.5 microns. These were obtained with
the MIRAC3 camera system at the Magellan Observatory. Our images reveal new
intricate structure in the bright core of the nebula, allowing us to
re-evaluate interpretations of morphology seen in images with lower resolution.
Complex structures in the core might not arise from a pair of overlapping rings
or a cool (110 K) and very massive dust torus, as has been suggested recently.
Instead, it seems more likely that the arcs and compact knots comprise a warm
(350 K) disrupted torus at the intersection of the larger polar lobes. Some of
the arcs appear to break out of the inner core region, and may be associated
with equatorial features seen in optical images. The torus could have been
disrupted by a post-eruption stellar wind, or by ejecta from the Great Eruption
itself if the torus existed before that event. Kinematic data are required to
rule out either possibility.Comment: 8 pages, 3 figures (Fig. 1 in color); to appear in ApJ Letter
Concept to analyze the displacement time series of individual persistent scatterers
Persistent Scatterer Interferometry (PSInSAR) exploits a time series of Synthetic Aperture Radar (SAR) images to estimate the mean velocity with which the surface of the earth is deforming. However, most PSInSAR algorithms estimate the mean velocities using a linear regression model. Since some deformation phenomena can exhibit a more complex behavior over time, using a linear regression model leads to potentially wrong estimations for the mean velocity. For example, the velocity of a landslide moving down a steep slope can change depending on the water content of the material of the landslide, or an inactive landslide can reactivate due to an earthquake. Both scenarios would not result in a time series with a constant linear slope but in a piecewise linear time series.
This paper presents a Matlab-based tool to analyze an individual Persistent Scatterer (PS) time series. The Persistent Scatterer Deformation Pattern Analysis Tool (PSDefoPAT) aims to build a mathematical model that sufficiently describes the time series trend and seasonal and noise components. The trend component is estimated using polynomial regression and piecewise linear models, while a sine function approximates the seasonal component. The goal is to identify the best fitting model for the displacement time series of a PS. PSDefoPAT is introduced by examine the time series of three different PS located in the region surrounding Patras, Greece. Based on the derived models, we discuss the nature of their deformation patterns
- …