1,366 research outputs found
Electron Population Aging Models for Wide-Angle Tails
Color-color diagrams have been useful in studying the spectral shapes in
radio galaxies. At the workshop we presented color-color diagrams for two
wide-angle tails, 1231+674 and 1433+553, and found that the standard aging
models do not adequately represent the observed data. Although the JP and KP
models can explain some of the observed points in the color-color diagram, they
do not account for those found near the power-law line. This difficulty may be
attributable to several causes. Spectral tomography has been previously used to
discern two separate electron populations in these sources. The combination
spectra from two such overlying components can easily resemble a range of
power-laws. In addition, any non-uniformity in the magnetic field strength can
also create a power-law-like spectrum. We will also discuss the effects that
angular resolution has on the shape of the spectrum.Comment: 4 pages, 1 figure, proceedings from 1999 'Life Cycles of Radio
Galaxies' workshop at STScI in Baltimore, M
The Semileptonic Decays and from QCD Sum Rules
We investigate the semileptonic decays of B and D mesons into and
mesons, respectively, by means of QCD sum rules. We find that for the
vector formfactors involved the pole dominance hypothesis is valid to good
accuracy with pole masses in the expected range. Pole dominance, however, does
not apply to the axial formfactors which results in specific predictions for
the predominant polarization of the meson and the shape of the lepton
spectrum. For the total decay rates we find , , and .Comment: 23 pages, 12 figures included as uu-encoded file, needs REVTEX,
TUM--T31--39/9
Strong Effects of Weak Localization in Charge Density Wave/Normal Metal Hybrids
Collective transport through a multichannel disordered conductor in contact
with charge-density-wave electrodes is theoretically investigated. The
statistical distribution function of the threshold potential for charge-density
wave sliding is calculated by random matrix theory. In the diffusive regime
weak localization has a strong effect on the sliding motion.Comment: To be published in Physical Review
Educational Virtual Reality Visualisations of Heritage Sites.
This paper discusses the use of games engines to create virtual heritage applications. The use of 3D software for cultural or heritage applications is discussed with reference to the capabilities and potential of games engines. The contribution of students from Bournemouth University to the New Forest Heritage Mapping project through the creation of interactive virtual reality visualisations of historic landscapes is described. The creation and evaluation of three different applications representing three alternative interaction styles are discussed. The first does not indicate where information can be found, the second uses visible cues and the third implements an objective marker system
Selection of touch gestures for children’s applications
The touch-screen revolution is not restricted to adults only. Parents find games and educational applications running on touch-screen devices and purchase them for their children. Therefore, very young children are playing with and exploring these touch-screen devices. For any one device there can be hundreds of applications for the parents to choose from, so it is likely that the selection of applications is based on advertisements and recommendations. There is a large range of gestures available on multi-touch devices and there is very little known about the relationship between the age of a child and the gestures that they can master. This research focuses on the iPad device and children aged between 2 to 4 years old and investigate which gestures the children in that age group can manage. The results of the research, therefore, could be used to form guidelines for the design of gesture-based software for very young children
Noise and Measurement Efficiency of a Partially Coherent Mesoscopic Detector
We study the noise properties and efficiency of a mesoscopic resonant-level
conductor which is used as a quantum detector, in the regime where transport
through the level is only partially phase coherent. We contrast models in which
detector incoherence arises from escape to a voltage probe, versus those in
which it arises from a random time-dependent potential. Particular attention is
paid to the back-action charge noise of the system. While the average detector
current is similar in all models, we find that its noise properties and
measurement efficiency are sensitive both to the degree of coherence and to the
nature of the dephasing source. Detector incoherence prevents quantum limited
detection, except in the non-generic case where the source of dephasing is not
associated with extra unobserved information. This latter case can be realized
in a version of the voltage probe model.Comment: 15 pages, 5 figures; revised dicussion of voltage probe model
Selection of touch gestures for children’s applications: repeated experiment to increase reliability
This paper discusses the selection of touch gestures for children’s applications. This research investigates the gestures that children aged between 2 to 4 years old can manage on the iPad device. Two experiments were conducted for this research. The first experiment was carried out in United Kingdom. The second experiment was carried out in Malaysia. The two similar experiments were carried out to increase the reliability and refine the result. This study shows that children aged 4 years have no problem using the 7 common gestures found in iPad applications. Some children aged 3 years have problem with two of the gestures. A high percentage of children aged 2 years struggled with the free rotate, drag & drop, pinch and spread gestures. This paper also discusses the Additional Criteria for the use of Gestures, Interface Design Components and Research on Children using iPad and Applications
Low-Luminosity Accretion in Black Hole X-ray Binaries and Active Galactic Nuclei
At luminosities below a few percent of Eddington, accreting black holes
switch to a hard spectral state which is very different from the soft
blackbody-like spectral state that is found at higher luminosities. The hard
state is well-described by a two-temperature, optically thin, geometrically
thick, advection-dominated accretion flow (ADAF) in which the ions are
extremely hot (up to K near the black hole), the electrons are also
hot ( K), and thermal Comptonization dominates the X-ray
emission. The radiative efficiency of an ADAF decreases rapidly with decreasing
mass accretion rate, becoming extremely low when a source reaches quiescence.
ADAFs are expected to have strong outflows, which may explain why relativistic
jets are often inferred from the radio emission of these sources. It has been
suggested that most of the X-ray emission also comes from a jet, but this is
less well established.Comment: To appear in "From X-ray Binaries to Quasars: Black Hole Accretion on
All Mass Scales" edited by T. Maccarone, R. Fender, L. Ho, to be published as
a special edition of "Astrophysics and Space Science" by Kluwe
Resistive and magnetized accretion flows with convection
We considered the effects of convection on the radiatively inefficient
accretion flows (RIAF) in the presence of resistivity and toroidal magnetic
field. We discussed the effects of convection on transports of angular momentum
and energy. We established two cases for the resistive and magnetized RIAFs
with convection: assuming the convection parameter as a free parameter and
using mixing-length theory to calculate convection parameter. A self-similar
method was used to solve the integrated equations that govern the behavior of
the presented model. The solutions showed that the accretion and rotational
velocities decrease by adding the convection parameter, while the sound speed
increases. Moreover, by using mixing-length theory to calculate convection
parameter, we found that the convection can be important in RIAFs with magnetic
field and resistivity.Comment: 7 pages, 3 figures, accepted by Ap&S
Aspects of Magnetic Field Configurations in Planar Nonlinear Electrodynamics
In the framework of three-dimensional Born-Infeld Electrodynamics, we pursue
an investigation of the consequences of the space-time dimensionality on the
existence of magnetostatic fields generated by electric charges at rest in an
inertial frame, which are present in its four-dimensional version. Our analysis
reveals interesting features of the model. In fact, a magnetostatic field
associated with an electric charge at rest does not appear in this case.
Interestingly, the addition of the topological term (Chern-Simons) to
Born-Infeld Electrodynamics yields the appearance of the magnetostatic field.
We also contemplate the fields associated to the would-be-magnetic monopole in
three dimensions.Comment: 8 page
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