20,805 research outputs found
PVLAS experiment, star cooling and BBN constraints: Possible interpretation with temperature dependent gauge symmetry breaking
It is known that the kinetic mixing of photon and another U(1)_ex gauge boson
can introduce millicharged particles. Millicharged particles of mass 0.1 eV
can explain the PVLAS experiment. We suggest a temperature dependent gauge
symmetry breaking of U(1)_ex for this idea to be consistent with astrophysical
and cosmological constraints.Comment: 9 pages, 3 figue
Neutron Star Properties with Hyperons
In the light of the recent discovery of a neutron star with a mass accurately
determined to be almost two solar masses, it has been suggested that hyperons
cannot play a role in the equation of state of dense matter in
-equilibrium. We re-examine this issue in the most recent development of
the quark-meson coupling model. Within a relativistic Hartree-Fock approach and
including the full tensor structure at the vector-meson-baryon vertices, we
find that not only must hyperons appear in matter at the densities relevant to
such a massive star but that the maximum mass predicted is completely
consistent with the observation.Comment: Minor correction
Power System Simulation by Parallel Computation
The concept of parallel processing is applied to power system simulation. The Component Connection Model (CCM) and appropriate numerical methods, such as the Relaxation Algorithm, are established as a conceptual basis for the parallel simulation of small power networks and individual power system components. A commercially available multiprocessing system is introduced for the power system simulator, and the system is adapted to facilitate high-speed parallel simulations. Two separate strategies for controlling the parallel simulation, synchronous and asynchronous relaxation, are introduced, and their performances are evaluated for the parallel simulation of an induction motor drive system. The performances of the parallel methods are also compared to a similar simulation run on a single processor, and the results show that considerable simulation speed-up can be obtained when parallel processing is employed
Hawking radiation, Unruh radiation and the equivalence principle
We compare the response function of an Unruh-DeWitt detector for different
space-times and different vacua and show that there is a {\it detailed}
violation of the equivalence principle. In particular comparing the response of
an accelerating detector to a detector at rest in a Schwarzschild space-time we
find that both detectors register thermal radiation, but for a given,
equivalent acceleration the fixed detector in the Schwarzschild space-time
measures a higher temperature. This allows one to locally distinguish the two
cases. As one approaches the horizon the two temperatures have the same limit
so that the equivalence principle is restored at the horizon.Comment: 9 pages. Added references and added discussion. To be published in
PR
Equation of state for Entanglement in a Fermi gas
Entanglement distance is the maximal separation between two entangled
electrons in a degenerate electron gas. Beyond that distance, all entanglement
disappears. We relate entanglement distance to degeneracy pressure both for
extreme relativistic and non-relativistic systems, and estimate the
entanglement distance in a white dwarf. Treating entanglement as a
thermodynamical quantity, we relate the entropy of formation and concurrence to
relative electron distance, pressure, and temperature, to form a new equation
of state for entanglement.Comment: To appear in Phys. Rev. A., 4 pages, 1 figur
R-matrix calculation of electron collisions with electronically excited O2 molecules
Low-energy electron collisions with O molecules are studied using the
fixed-bond R-matrix method. In addition to the O ground
state, integrated cross sections are calculated for elecron collisions with the
and excited states of O molecules. 13
target electronic states of O are included in the model within a valence
configuration interaction representations of the target states. Elastic cross
sections for the and excited states are
similar to the cross sections for the ground state. As in
case of excitation from the state, the O
resonance makes the dominant contribution to excitation cross sections from the
and states. The magnitude of excitation
cross sections from the state to the
state is about 10 time larger than the corresponding cross sections from the
to the state. For this
transition, our cross section at
4.5 eV agrees well with the available experimental value. These results should
be important for models of plasma discharge chemistry which often requires
cross sections between the excited electronic states of O.Comment: 26 pages, 10 figure
Theory of quantum dot spin-lasers
We formulate a model of a semiconductor Quantum Dot laser with injection of
spin-polarized electrons. As compared to higher-dimensionality structures, the
Quantum-Dot-based active region is known to improve laser properties, including
the spin-related ones. The wetting layer, from which carriers are captured into
the active region, acts as an intermediate level that strongly influences the
lasing operation. The finite capture rate leads to an increase of lasing
thresholds, and to saturation of emitted light at higher injection. In spite of
these issues, the advantageous threshold reduction, resulting from spin
injection, can be preserved. The "spin-filtering" effect, i.e., circularly
polarized emission at even modest spin-polarization of injection, remains
present as well. Our rate-equations description allows to obtain analytical
results and provides transparent guidance for improvement of spin-lasers.Comment: 7 pages, 3 figure
Representing older people: towards meaningful images of the user in design scenarios
Designing for older people requires the consideration of a range of difficult and sometimes highly personal design problems. Issues such as fear, loneliness, dependency, and physical decline may be difficult to observe or discuss in interviews. Pastiche scenarios and pastiche personae are techniques that employ characters to create a space for the discussion of new technological developments and as a means to explore user experience. This paper argues that the use of such characters can help to overcome restrictive notions of older people by disrupting designers' prior assumptions.
In this paper, we reflect on our experiences using pastiche techniques in two separate technology design projects that sought to address the needs of older people. In the first case pastiche scenarios were developed by the designers of the system and used as discussion documents with users. In the second case, pastiche personae were used by groups of users themselves to generate scenarios which were scribed for later use by the design team. We explore how the use of fictional characters and settings can generate new ideas and undermine rhetorical devices within scenarios that attempt to fit characters to the technology, rather than vice versa.
To assist in future development of pastiche techniques in designing for older people, we provide an array of fictional older characters drawn from literary and popular culture.</p
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