18,905 research outputs found
Compact artificial hand
A relatively simple, compact artificial hand, is described which includes hooks pivotally mounted on first frame to move together and apart. The first frame is rotatably mounted on a second frame to enable "turning at the wrist" movement without limitation. The second frame is pivotally mounted on a third frame to permit 'flexing at the wrist' movement. A hook-driving motor is fixed to the second frame but has a shaft that drives a speed reducer on the first frame which, in turn, drives the hooks. A second motor mounted on the second frame, turns a gear on the first frame to rotate the first frame and the hooks thereon. A third motor mounted on the third frame, turns a gear on a second frame to pivot it
Some Comments on Gravitational Entropy and the Inverse Mean Curvature Flow
The Geroch-Wald-Jang-Huisken-Ilmanen approach to the positive energy problem
to may be extended to give a negative lower bound for the mass of
asymptotically Anti-de-Sitter spacetimes containing horizons with exotic
topologies having ends or infinities of the form , in
terms of the cosmological constant. We also show how the method gives a lower
bound for for the mass of time-symmetric initial data sets for black holes with
vectors and scalars in terms of the mass, of the double extreme
black hole with the same charges. I also give a lower bound for the area of an
apparent horizon, and hence a lower bound for the entropy in terms of the same
function . This shows that the so-called attractor behaviour extends
beyond the static spherically symmetric case. and underscores the general
importance of the function . There are hints that higher dimensional
generalizations may involve the Yamabe conjectures.Comment: 13pp. late
Generalized entropy and Noether charge
We find an expression for the generalized gravitational entropy of Hawking in
terms of Noether charge. As an example, the entropy of the Taub-Bolt spacetime
is calculated.Comment: 6 pages, revtex, reference correcte
Dynamical N-body Equlibrium in Circular Dilaton Gravity
We obtain a new exact equilibrium solution to the N-body problem in a
one-dimensional relativistic self-gravitating system. It corresponds to an
expanding/contracting spacetime of a circle with N bodies at equal proper
separations from one another around the circle. Our methods are
straightforwardly generalizable to other dilatonic theories of gravity, and
provide a new class of solutions to further the study of (relativistic)
one-dimensional self-gravitating systems.Comment: 4 pages, latex, reference added, minor changes in wordin
Alternative experimental evidence for chiral restoration in excited baryons
Given existing empirical spectral patterns of excited hadrons it has been
suggested that chiral symmetry is approximately restored in excited hadrons at
zero temperature/density (effective symmetry restoration). If correct, this
implies that mass generation mechanisms and physics in excited hadrons is very
different as compared to the lowest states. One needs an alternative and
independent experimental information to confirm this conjecture. Using very
general chiral symmetry arguments it is shown that strict chiral restoration in
a given excited nucleon forbids its decay into the N \pi channel. Hence those
excited nucleons which are assumed from the spectroscopic patterns to be in
approximate chiral multiplets must only "weakly" decay into the N \pi channel,
(f_{N^*N\pi}/f_{NN\pi})^2 << 1. However, those baryons which have no chiral
partner must decay strongly with a decay constant comparable with f_{NN\pi}.
Decay constants can be extracted from the existing decay widths and branching
ratios. It turnes out that for all those well established excited nucleons
which can be classified into chiral doublets N_+(1440) - N_-(1535), N_+(1710) -
N_-(1650), N_+(1720) - N_-(1700), N_+(1680) - N_-(1675), N_+(2220) - N_-(2250),
N_+(?) - N_-(2190), N_+(?) - N_-(2600), the ratio is (f_{N^*N\pi}/f_{NN\pi})^2
~ 0.1 or much smaller for the high-spin states. In contrast, the only well
established excited nucleon for which the chiral partner cannot be identified
from the spectroscopic data, N(1520), has a decay constant into the N\pi
channel that is comparable with f_{NN\pi}. This gives an independent
experimental verification of the chiral symmetry restoration scenario.Comment: 4 pp. A new footnote with an alternative proof of impossibility of
parity doublet decay into pi + N is added. To appear in Phys. Rev. Let
Numerical indications of a q-generalised central limit theorem
We provide numerical indications of the -generalised central limit theorem
that has been conjectured (Tsallis 2004) in nonextensive statistical mechanics.
We focus on binary random variables correlated in a {\it scale-invariant}
way. The correlations are introduced by imposing the Leibnitz rule on a
probability set based on the so-called -product with . We show
that, in the large limit (and after appropriate centering, rescaling, and
symmetrisation), the emerging distributions are -Gaussians, i.e., , with , and
with coefficients approaching finite values . The
particular case recovers the celebrated de Moivre-Laplace theorem.Comment: Minor improvements and corrections have been introduced in the new
version. 7 pages including 4 figure
Lexical-Semantic Organization in Bilingually Developing Deaf Children With ASL-Dominant Language Exposure: Evidence From a Repeated Meaning Association Task
This study compared the lexical-semantic organization skills of bilingually developing deaf children in American Sign Language (ASL) and English with those of a monolingual hearing group. A repeated meaning-association paradigm was used to assess retrieval of semantic relations in deaf 6–10-year-olds exposed to ASL from birth by their deaf parents, with responses coded as syntagmatic or paradigmatic. Deaf children's responses in ASL and English were compared at the within-group level, and their ASL was compared to the English responses of age-matched monolingual hearing children. Finally, the two groups were compared on their semantic performance in English. Results showed similar patterns for deaf children's responses in ASL and English to those of hearing monolinguals, but subtle language differences were also revealed. These findings suggest that sign bilinguals’ language development in ASL and English is driven by similar underlying learning mechanisms rooted in the development of semantic frameworks
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