52,155 research outputs found
Constructive counterexamples to additivity of minimum output R\'enyi entropy of quantum channels for all p>2
We present a constructive example of violation of additivity of minimum
output R\'enyi entropy for each p>2. The example is provided by antisymmetric
subspace of a suitable dimension. We discuss possibility of extension of the
result to go beyond p>2 and obtain additivity for p=0 for a class of
entanglement breaking channels.Comment: 4 pages; a reference adde
Anomalously slow spin dynamics and short-range correlations in the quantum spin ice systems Yb2Ti2O7 and Yb2Sn2O7
We report a positive muon spin relaxation and rotation (\muSR) study of the
quantum spin ice materials Yb2Ti2O7 and Yb2Sn2O7 focusing on the low field
response. In agreement with earlier reports, data recorded in small
longitudinal fields evidence anomalously slow spin dynamics in the microsecond
range below the temperature T_c at which the specific heat displays an intense
peak, namely T_c = 0.24 K and 0.15 K, respectively, for the two systems. We
found that slow dynamics extends above T_c up to at least 0.7 K for both
compounds. The conventional dynamical Gaussian Kubo-Toyabe model describes the
\muSR spectra recorded above T_c. At lower temperatures a published analytical
extension of the Gaussian Kubo-Toyabe model provides a good description,
consistent with the existence of short-range magnetic correlations. While the
physical response of the two systems is qualitatively the same, Yb2Ti2O7
exhibits a much larger local magnetic susceptibility than Yb2Sn2O7 below T_c.
Considering previously reported ac susceptibility, neutron scattering and \muSR
results, we suggest the existence of anomalously slow spin dynamics to be a
common physical property of pyrochlore magnetic materials. The possibility of
molecular spin substructures to be associated to the slow dynamics and
therefore the short-range correlations is mentioned. The slow spin dynamics
observed under field does not exclude the presence of much faster dynamics
detected in extremely low or zero field.Comment: 11 pages, 10 figure
Design of a monitor and simulation terminal (master) for space station telerobotics and telescience
Based on Space Station and planetary spacecraft communication time delays and bandwidth limitations, it will be necessary to develop an intelligent, general purpose ground monitor terminal capable of sophisticated data display and control of on-orbit facilities and remote spacecraft. The basic elements that make up a Monitor and Simulation Terminal (MASTER) include computer overlay video, data compression, forward simulation, mission resource optimization and high level robotic control. Hardware and software elements of a MASTER are being assembled for testbed use. Applications of Neural Networks (NNs) to some key functions of a MASTER are also discussed. These functions are overlay graphics adjustment, object correlation and kinematic-dynamic characterization of the manipulator
Instability of human societies as a result of conformity
We introduce a new model that mimics the strong and sudden effects induced by
conformity in tightly interacting human societies. Such effects range from mere
crowd phenomena to dramatic political turmoil. The model is a modified version
of the Ising Hamiltonian. We have studied the properties of this Hamiltonian
using both a Metropolis simulation and analytical derivations. Our study shows
that increasing the value of the conformity parameter, results in a first order
phase transition. As a result a majority of people begin honestly to support
the idea that may contradict the moral principles of a normal human beings
though each individual would support the moral principle without tight
interaction with the society. Thus, above some critical level of conformity our
society occurs to be instable with respect to ideas that might be doubtful. Our
model includes, in a simplified way, human diversity with respect to loyalty to
the moral principles.Comment: 5 pages, 5 figures, accepted in Int. journ of modern physics section
Age structure, dispersion and diet of a population of stoats (Mustela erminea) in southern Fiordland during the decline phase of the beechmast cycle
The dispersion, age structure and diet of stoats (Mustela erminea) in beech forest in the Borland and Grebe Valleys, Fiordland National Park, were examined during December and January 2000/01, 20 months after a heavy seed-fall in 1999. Thirty trap stations were set along a 38-km transect through almost continuous beech forest, at least 1 km apart. Mice were very scarce (nights, C/100TN) along two standard index lines placed at either end of the transect, compared with November 1999 (>60/100TN), but mice were detected (from footprints in stoat tunnels) along an 8 km central section of the transect (stations 14-22). Live trapping with one trap per station (total 317.5 trap nights) in December 2000 caught 2 female and 23 male stoats, of which 10 (including both females) were radio collared. The minimum range lengths of the two females along the transect represented by the trap line were 2.2 and 6.0 km; those of eight radio-tracked males averaged 2.9 ± 1.7 km. Stations 14-22 tended to be visited more often, by more marked individual stoats, than the other 21 stations.
Fenn trapping at the same 30 sites, but with multiple traps per station (1333.5 trap nights), in late January 2001 collected carcasses of 35 males and 28 females (including 12 of the marked live-trapped ones). Another two marked males were recovered dead. The stoat population showed no sign of chronic nutritional stress (average fat reserve index = 2.8 on a scale of 1-4 where 4 = highest fat content); and only one of 63 guts analysed was empty. Nevertheless, all 76 stoats handled were adults with 1-3 cementum annuli in their teeth, showing that reproduction had failed that season. Prey categories recorded in descending frequency of occurrence were birds, carabid beetle (ground beetle), weta, possum, rat, and mouse. The frequencies of occurrence of mice and birds in the diet of these stoats (10% and 48%, respectively) were quite different from those in stoats collected in Pig Creek, a tributary of the Borland River (87%, 5%), 12 months previously when mice were still abundant. Five of the six stoat guts containing mice were collected within 1 km of stations 14-22
Self-awareness of driving impairment in patients with cataract or glaucoma
This study compared the driving performance of individuals with the eye diseases cataracts or glaucoma with age-matched controls, as well as the individual’s own perceptions of driving. Participants included drivers over the age of 50 years who had been diagnosed with glaucoma (n=29) or cataracts (n=33) and a control group with no ocular pathology (n=13). Driving performance was measured on a closed road circuit using a range of standardised measures of vehicle control and hazard recognition and avoidance, while visual performance was measured with a battery of tests including visual acuity, contrast sensitivity and visual fields. Perceptions of vision and driving were assessed using the Activities of Daily Vision Scale, Driver Behaviour Questionnaire and a driving exposure questionnaire. Driving performance was significantly poorer (p<0.05) for each of the ocular disease groups compared to the control group. Impaired contrast sensitivity and the higher disease severity scores (for the glaucoma group only) correlated most strongly with poorer driving performance. While participants with cataracts rated their vision significantly more poorly than those in the glaucoma and control groups, there were no significant differences between the participant groups rating of their own driving performance. These findings suggest that there is no direct relationship between self-rated driving ability and actual vision and driving performance. This has serious road safety implications
Retrograde Accretion and Merging Supermassive Black Holes
We investigate whether a circumbinary gas disc can coalesce a supermassive
black hole binary system in the centre of a galaxy. This is known to be
problematic for a prograde disc. We show that in contrast, interaction with a
retrograde circumbinary disc is considerably more effective in shrinking the
binary because there are no orbital resonances. The binary directly absorbs
negative angular momentum from the circumbinary disc by capturing gas into a
disc around the secondary black hole, or discs around both holes if the binary
mass ratio is close to unity. In many cases the binary orbit becomes eccentric,
shortening the pericentre distance as the eccentricity grows. In all cases the
binary coalesces once it has absorbed the angular momentum of a gas mass
comparable to that of the secondary black hole. Importantly, this conclusion is
unaffected even if the gas inflow rate through the disc is formally
super--Eddington for either hole. The coalescence timescale is therefore always
, where is the secondary black hole mass and
the inflow rate through the circumbinary disc.Comment: 8 pages, 4 figures. Accepted for publication in MNRAS. Movies of the
simulations can be found at:
http://www.astro.le.ac.uk/users/cjn12/RetroBinaryMovies.htm
Hopf algebras and characters of classical groups
Schur functions provide an integral basis of the ring of symmetric functions.
It is shown that this ring has a natural Hopf algebra structure by identifying
the appropriate product, coproduct, unit, counit and antipode, and their
properties. Characters of covariant tensor irreducible representations of the
classical groups GL(n), O(n) and Sp(n) are then expressed in terms of Schur
functions, and the Hopf algebra is exploited in the determination of
group-subgroup branching rules and the decomposition of tensor products. The
analysis is carried out in terms of n-independent universal characters. The
corresponding rings, CharGL, CharO and CharSp, of universal characters each
have their own natural Hopf algebra structure. The appropriate product,
coproduct, unit, counit and antipode are identified in each case.Comment: 9 pages. Uses jpconf.cls and jpconf11.clo. Presented by RCK at
SSPCM'07, Myczkowce, Poland, Sept 200
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