21,171 research outputs found
Initial experiments concerning quantum information processing in rare-earth-ion doped crystals
In this paper initial experiments towards constructing simple quantum gates
in a solid state material are presented. Instead of using specially tailored
materials, the aim is to select a subset of randomly distributed ions in the
material, which have the interaction necessary to control each other and
therefore can be used to do quantum logic operations. The experimental results
demonstrate that part of an inhomogeneously broadened absorption line can be
selected as a qubit and that a subset of ions in the material can control the
resonance frequency of other ions. This opens the way for the construction of
quantum gates in rare-earth-ion doped crystals.Comment: 24 pages, including 12 figure
On Making Good Games - Using Player Virtue Ethics and Gameplay Design Patterns to Identify Generally Desirable Gameplay Features
This paper uses a framework of player virtues to perform a
theoretical exploration of what is required to make a game
good. The choice of player virtues is based upon the view
that games can be seen as implements, and that these are
good if they support an intended use, and the intended use
of games is to support people to be good players. A collection of gameplay design patterns, identified through
their relation to the virtues, is presented to provide specific starting points for considering design options for this type of good games. 24 patterns are identified supporting the virtues, including RISK/REWARD, DYNAMIC ALLIANCES, GAME MASTERS, and PLAYER DECIDED RESULTS, as are 7 countering three or more virtues, including ANALYSIS
PARALYSIS, EARLY ELIMINATION, and GRINDING. The paper concludes by identifying limitations of the approach as well as by showing how it can be applied using other views of what are preferable features in games
Electronic structure of GaAs1-xNx alloy by soft-X-ray absorption and emission: Origin of the reduced optical efficiency
The local electronic structure of N atoms in a diluted GaAs1-xNx (x=3%)
alloy, in view of applications in optoelectronics, is determined for the first
time using soft-X-ray absorption (SXA) and emission (SXE). Deviations from
crystalline GaN, in particular in the conduction band, are dramatic. Employing
the orbital character and elemental specificity of the SXE/SXA spectroscopies,
we identify a charge transfer from the N atoms at the valence band maximum,
reducing the overlap with the wavefunction in conduction band minimum, as the
main factor limiting the optical efficiency of GaAs1-xNx alloys. Moreover, a
k-conserving process of resonant inelastic x-ray scattering involving the L1
derived valence and conduction states is discovered.Comment: 3 pages, physica status solidi (Rapid Research Notes), in pres
Timelike self-similar spherically symmetric perfect-fluid models
Einstein's field equations for timelike self-similar spherically symmetric
perfect-fluid models are investigated. The field equations are rewritten as a
first-order system of autonomous differential equations. Dimensionless
variables are chosen in such a way that the number of equations in the coupled
system is reduced as far as possible and so that the reduced phase space
becomes compact and regular. The system is subsequently analysed qualitatively
using the theory of dynamical systems.Comment: 23 pages, 6 eps-figure
The planet search programme at the ESO CES and HARPS. IV. The search for Jupiter analogues around solar-like stars
In 1992 we began a precision radial velocity (RV) survey for planets around
solar-like stars with the Coude Echelle Spectrograph and the Long Camera (CES
LC) at the 1.4 m telescope in La Silla (Chile). We have continued the survey
with the upgraded CES Very Long Camera (VLC) and HARPS, both at the 3.6 m
telescope, until 2007. The observations for 31 stars cover a time span of up to
15 years and the RV precision permit a search for Jupiter analogues. We perform
a joint analysis for variability, trends, periodicities, and Keplerian orbits
and compute detection limits. Moreover, the HARPS RVs are analysed for
correlations with activity indicators (CaII H&K and CCF shape). We achieve a
long-term RV precision of 15 m/s (CES+LC, 1992-1998), 9 m/s (CES+VLC,
1999-2006), and 2.8 m/s (HARPS, 2003-2009, including archive data), resp. This
enables us to confirm the known planets around Iota Hor, HR 506, and HR 3259. A
steady RV trend for Eps Ind A can be explained by a planetary companion. On the
other hand, we find previously reported trends to be smaller for Beta Hyi and
not present for Alp Men. The candidate planet Eps Eri b was not detected
despite our better precision. Also the planet announced for HR 4523 cannot be
confirmed. Long-term trends in several of our stars are compatible with known
stellar companions. We provide a spectroscopic orbital solution for the binary
HR 2400 and refined solutions for the planets around HR 506 and Iota Hor. For
some other stars the variations could be attributed to stellar activity. The
occurrence of two Jupiter-mass planets in our sample is in line with the
estimate of 10% for the frequency of giant planets with periods smaller than 10
yr around solar-like stars. We have not detected a Jupiter analogue, while the
detections limits for circular orbits indicate at 5 AU a sensitivity for
minimum mass of at least 1 M_Jup (2 M_Jup) for 13% (61%) of the stars.Comment: 63 pages, 24 figures (+33 online figures), 13 Tables, accepted for
publication in A&A (2012-11-13
Relativistic Compact Objects in Isotropic Coordinates
We present a matrix method for obtaining new classes of exact solutions for
Einstein's equations representing static perfect fluid spheres. By means of a
matrix transformation, we reduce Einstein's equations to two independent
Riccati type differential equations for which three classes of solutions are
obtained. One class of the solutions corresponding to the linear barotropic
type fluid with an equation of state is discussed in detail.Comment: 9 pages, no figures, accepted for publication in Pramana-Journal of
Physic
Recommended from our members
Dielectric spectroscopy study of thermally-aged extruded model power cables
“Model” extruded power cables, having a much reduced geometry but using the same extrusion techniques and materials as full-sized cables, have been examined using dielectric spectroscopy techniques to study their thermal ageing effects. Cables insulated with homo-polymer XLPE and co-polymer of XLPE with micron-sized ethylene-butyl-acrylate (EBA) islands were studied by both frequency-domain and time-domain dielectric spectroscopy techniques after accelerated thermal ageing under 135°C for 60 days. In the frequency domain, a frequency response analyzer (FRA) was used to measure the frequency range from 10-4Hz to 1Hz at temperatures from 20°C to 80°C. In the time domain, a special charging/discharging current measurement system was developed to measure the frequencies from 10-1Hz to 102Hz. These techniques were chosen to cope with the extremely low dielectric losses of the model cables. The results are compared with those from new model power cables that were degassed at 80°C for 5 days. Thermal ageing was found to increase the low-frequency conductivity, permittivity and the discharging current. Both homo- and co-polymer cables have substantial increase of dielectric loss after ageing
- …