24,730 research outputs found
Surface brightness measurements for APM galaxies
This paper considers some simple surface brightness (SB) estimates for
galaxies in the Automated Plate Measuring Machine (APM) catalogue in order to
derive homogeneous SB data for a very large sample of faint galaxies. The
isophotal magnitude and area are used to estimate the central surface
brightness and total magnitude based on the assumption of an exponential SB
profile. The surface brightness measurements are corrected for field effects on
each UK Schmidt plate and the zero-point of each plate is adjusted to give a
uniform sample of SB and total magnitude estimates over the whole survey.
Results are obtained for 2.4 million galaxies with blue photographic magnitudes
brighter than b_J = 20.5 covering 4300 deg^2 in the region of the south
galactic cap. Almost all galaxies in our sample have central surface brightness
in the range 20 to 24 b_J mag per arcsec^2. The SB measurements we obtain are
compared to previous SB measurements and we find an acceptable level of error
of +/- 0.2 b_J mag per arcsec^2. The distribution of SB profiles is considered
for different galaxy morphologies for the bright APM galaxies. We find that
early-type galaxies have more centrally concentrated profiles.Comment: 14 pages, 17 figures, accepted for publication in MNRA
Microwave Slow-Wave Structure and Phase-Compensation Technique for Microwave Power Divider
In this paper, T-shaped electromagnetic bandgap is loaded on a coupled transmission line itself and its electric performance is studied. Results show that microwave slow-wave effect can be enhanced and therefore, size reduction of a transmission-line-based circuit is possible. However, the transmission-line-based circuits characterize varied phase responses against frequency, which becomes a disadvantage where constant phase response is required. Consequently, a phase-compensation technique is further presented and studied. For demonstration purpose, an 8-way coupled-line power divider with 22.5 degree phase shifts between adjacent output ports, based on the studied slow-wave structure and phase-compensation technique, is developed. Results show both compact circuit architecture and improved phase imbalance are realized, confirming the investigated circuit structures and analyzing methodologies
Gisin's Theorem for Arbitrary Dimensional Multipartite States
We present a set of Bell inequalities which are sufficient and necessary for
separability of general pure multipartite quantum states in arbitrary
dimensions. The relations between Bell inequalities and distillability are also
studied. We show that any quantum states that violate one of these Bell
inequalities are distillable.Comment: 5 page
Helicity Entanglement of Moving Bodies
We investigate the Lorentz transformation of the reduced helicity density
matrix for a pair of massive spin 1/2 particles. The corresponding Wootters
concurrence shows no invariant meaning, which implies that we can generate
helicity entanglement simply by the transformation from one reference frame to
another. The difference between the helicity and spin case is also discussed.Comment: 3 pages, 1 figure, version to appear in Int. J. Quant. In
Diffraction Analysis of 2-D Pupil Mapping for High-Contrast Imaging
Pupil-mapping is a technique whereby a uniformly-illuminated input pupil,
such as from starlight, can be mapped into a non-uniformly illuminated exit
pupil, such that the image formed from this pupil will have suppressed
sidelobes, many orders of magnitude weaker than classical Airy ring
intensities. Pupil mapping is therefore a candidate technique for coronagraphic
imaging of extrasolar planets around nearby stars. Unlike most other
high-contrast imaging techniques, pupil mapping is lossless and preserves the
full angular resolution of the collecting telescope. So, it could possibly give
the highest signal-to-noise ratio of any proposed single-telescope system for
detecting extrasolar planets. Prior analyses based on pupil-to-pupil
ray-tracing indicate that a planet fainter than 10^{-10} times its parent star,
and as close as about 2 lambda/D, should be detectable. In this paper, we
describe the results of careful diffraction analysis of pupil mapping systems.
These results reveal a serious unresolved issue. Namely, high-contrast pupil
mappings distribute light from very near the edge of the first pupil to a broad
area of the second pupil and this dramatically amplifies diffraction-based edge
effects resulting in a limiting attainable contrast of about 10^{-5}. We hope
that by identifying this problem others will provide a solution.Comment: 23 pages, 13 figures, also posted to
http://www.orfe.princeton.edu/~rvdb/tex/piaaFresnel/ms.pd
Bringing closure to microlensing mass measurement
Interferometers offer multiple methods for studying microlensing events and
determining the properties of the lenses. We investigate the study of
microlensing events with optical interferometers, focusing on narrow-angle
astrometry, visibility, and closure phase. After introducing the basics of
microlensing and interferometry, we derive expressions for the signals in each
of these three channels. For various forecasts of the instrumental performance,
we discuss which method provides the best means of measuring the lens angular
Einstein radius theta_E, a prerequisite for determining the lens mass. If the
upcoming generation of large-aperture, AO-corrected long baseline
interferometers (e.g. VLTI, Keck, OHANA) perform as well as expected, theta_E
may be determined with signal-to-noise greater than 10 for all bright events.
We estimate that roughly a dozen events per year will be sufficiciently bright
and have long enough durations to allow the measurement of the lens mass and
distance from the ground. We also consider the prospects for a VLTI survey of
all bright lensing events using a Fisher matrix analysis, and find that even
without individual masses, interesting constraints may be placed on the bulge
mass function, although large numbers of events would be required.Comment: 23 pages, aastex, submitted to Ap
On the VLSI design of a pipeline Reed-Solomon decoder using systolic arrays
A new very large scale integration (VLSI) design of a pipeline Reed-Solomon decoder is presented. The transform decoding technique used in a previous article is replaced by a time domain algorithm through a detailed comparison of their VLSI implementations. A new architecture that implements the time domain algorithm permits efficient pipeline processing with reduced circuitry. Erasure correction capability is also incorporated with little additional complexity. By using a multiplexing technique, a new implementation of Euclid's algorithm maintains the throughput rate with less circuitry. Such improvements result in both enhanced capability and significant reduction in silicon area
Numerical Study on Indoor Wideband Channel Characteristics with Different Internal Wall
Effects of material and configuration of the internal wall on the performance of wideband channel are investigated by using the Finite Difference Time-Domain (FDTD) method. The indoor wideband channel characteristics, such as the path-loss, Root-Mean-Square (RMS) delay spread and number of the multipath components (MPCs), are presented. The simulated results demonstrate that the path-loss and MPCs are affected by the permittivity, dielectric loss tangent and thickness of the internal wall, while the RMS delay spread is almost not relevant with the dielectric permittivity. Furthermore, the comparison of simulated result with the measured one in a simple scenario has validated the simulation study
Numerical investigation of fire in the cavity of naturally ventilated double skin façade with venetian blinds
Double skin façades (DSFs), offer great views, architectural aesthetics, and energy savings. Yet, in a fire event the glass façade breaks leading to risks to human life and firefighting difficulties. Shading devices incorporated to prevent unfavourable heat gains to reduce cooling load though offer energy savings potentially present other challenges in firefighting and occupants’ evacuation. In this study, Fire Dynamic Simulator (FDS) was used to numerically investigate the spread of a 5 MW HRR polyurethane GM27 fire in a multi-storey double skin façade building with Venetian blinds placed in its cavity. The blinds were positioned 0.4 m away from the internal glazing, middle of the cavity and 0.4 m away from the external glazing respectively. In each blind position the slat angle was opened at 0°, 45°, 90° and 135° respectively. The results show peak inner glazing surface temperature ranged between 283°C to 840°C depending on the thermocouple position, the Venetian blind position and slat opening angle. Without Venetian blinds, peak inner glazing surface temperatures ranged between 468°C to 614°C. In all cases except when the slat angle was 0° and the blind was positioned closer to the outer glazing, the inner glazing surface temperature from the closest thermocouple (TC 14) above the fire room exceeded 600°C, the glass breakage temperature threshold. Overall, the Venetian blind position and slat opening angle influenced the spread of fire. Venetian blind combustibility and flammability were not considered and therefore recommended for future studies
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