1,432 research outputs found
Reciprocal relativity of noninertial frames and the quaplectic group
Newtonian mechanics has the concept of an absolute inertial rest frame.
Special relativity eliminates the absolute rest frame but continues to require
the absolute inertial frame. General relativity solves this for gravity by
requiring particles to have locally inertial frames on a curved position-time
manifold. The problem of the absolute inertial frame for other forces remains.
We look again at the transformations of frames on an extended phase space with
position, time, energy and momentum degrees of freedom. Under nonrelativistic
assumptions, there is an invariant symplectic metric and a line element dt^2.
Under special relativistic assumptions the symplectic metric continues to be
invariant but the line elements are now -dt^2+dq^2/c^2 and dp^2-de^2/c^2. Max
Born conjectured that the line element should be generalized to the pseudo-
orthogonal metric -dt^2+dq^2/c^2+ (1/b^2)(dp^2-de^2/c^2). The group leaving
these two metrics invariant is the pseudo-unitary group of transformations
between noninertial frames. We show that these transformations eliminate the
need for an absolute inertial frame by making forces relative and bounded by b
and so embodies a relativity that is 'reciprocal' in the sense of Born. The
inhomogeneous version of this group is naturally the semidirect product of the
pseudo-unitary group with the nonabelian Heisenberg group. This is the
quaplectic group. The Heisenberg group itself is the semidirect product of two
translation groups. This provides the noncommutative properties of position and
momentum and also time and energy that are required for the quantum mechanics
that results from considering the unitary representations of the quaplectic
group.Comment: Substantial revision, Publicon LaTe
Unitarily localizable entanglement of Gaussian states
We consider generic -mode bipartitions of continuous variable
systems, and study the associated bisymmetric multimode Gaussian states. They
are defined as -mode Gaussian states invariant under local mode
permutations on the -mode and -mode subsystems. We prove that such states
are equivalent, under local unitary transformations, to the tensor product of a
two-mode state and of uncorrelated single-mode states. The entanglement
between the -mode and the -mode blocks can then be completely
concentrated on a single pair of modes by means of local unitary operations
alone. This result allows to prove that the PPT (positivity of the partial
transpose) condition is necessary and sufficient for the separability of -mode bisymmetric Gaussian states. We determine exactly their negativity and
identify a subset of bisymmetric states whose multimode entanglement of
formation can be computed analytically. We consider explicit examples of pure
and mixed bisymmetric states and study their entanglement scaling with the
number of modes.Comment: 10 pages, 2 figure
Chiral surfaces self-assembling in one-component systems with isotropic interactions
We show that chiral symmetry can be broken spontaneously in one-component
systems with isotropic interactions, i.e. many-particle systems having maximal
a priori symmetry. This is achieved by designing isotropic potentials that lead
to self-assembly of chiral surfaces. We demonstrate the principle on a simple
chiral lattice and on a more complex lattice with chiral super-cells. In
addition we show that the complex lattice has interesting melting behavior with
multiple morphologically distinct phases that we argue can be qualitatively
predicted from the design of the interaction.Comment: 4 pages, 4 figure
Positive mass theorems for asymptotically AdS spacetimes with arbitrary cosmological constant
We formulate and prove the Lorentzian version of the positive mass theorems
with arbitrary negative cosmological constant for asymptotically AdS
spacetimes. This work is the continuation of the second author's recent work on
the positive mass theorem on asymptotically hyperbolic 3-manifolds.Comment: 17 pages, final version, to appear in International Journal of
Mathematic
Localization of quantum wave packets
We study the semiclassical propagation of squeezed Gau{\ss}ian states. We do
so by considering the propagation theorem introduced by Combescure and Robert
\cite{CR97} approximating the evolution generated by the Weyl-quantization of
symbols . We examine the particular case when the Hessian
evaluated at the corresponding solution of
Hamilton's equations of motion is periodic in time. Under this assumption, we
show that the width of the wave packet can remain small up to the Ehrenfest
time. We also determine conditions for ``classical revivals'' in that case.
More generally, we may define recurrences of the initial width. Some of these
results include the case of unbounded classical motion. In the classically
unstable case we recover an exponential spreading of the wave packet as in
\cite{CR97}
Strong and weak semiclassical limits for some rough Hamiltonians
We present several results concerning the semiclassical limit of the time
dependent Schr\"odinger equation with potentials whose regularity doesn't
guarantee the uniqueness of the underlying classical flow. Different topologies
for the limit are considered and the situation where two bicharateristics can
be obtained out of the same initial point is emphasized
The orientation-preserving diffeomorphism group of S^2 deforms to SO(3) smoothly
Smale proved that the orientation-preserving diffeomorphism group of S^2 has
a continuous strong deformation retraction to SO(3). In this paper, we
construct such a strong deformation retraction which is diffeologically smooth.Comment: 16 page
The contribution of muscle hypertrophy to strength changes following resistance training
Purpose
Whilst skeletal muscle hypertrophy is considered an important adaptation to resistance training (RT), it has not previously been found to explain the inter-individual changes in strength after RT. This study investigated the contribution of hypertrophy to individual gains in isometric, isoinertial and explosive strength after 12 weeks of elbow flexor RT.
Methods
Thirty-three previously untrained, healthy men (18–30 years) completed an initial 3-week period of elbow flexor RT (to facilitate neurological responses) followed by 6-week no training, and then 12-week elbow flexor RT. Unilateral elbow flexor muscle strength [isometric maximum voluntary force (iMVF), single repetition maximum (1-RM) and explosive force], muscle volume (V m), muscle fascicle pennation angle (θ p) and normalized agonist, antagonist and stabilizer sEMG were assessed pre and post 12-week RT.
Results
Percentage gains in V m correlated with percentage changes in iMVF (r = 0.527; P = 0.002) and 1-RM (r = 0.482; P = 0.005) but not in explosive force (r ≤ 0.243; P ≥ 0.175). Percentage changes in iMVF, 1-RM, and explosive force did not correlate with percentage changes in agonist, antagonist or stabilizer sEMG (all P > 0.05). Percentage gains in θ p inversely correlated with percentage changes in normalized explosive force at 150 ms after force onset (r = 0.362; P = 0.038).
Conclusions
We have shown for the first time that muscle hypertrophy explains a significant proportion of the inter-individual variability in isometric and isoinertial strength gains following 12-week elbow flexor RT in healthy young men
Tsirelson's problem and Kirchberg's conjecture
Tsirelson's problem asks whether the set of nonlocal quantum correlations
with a tensor product structure for the Hilbert space coincides with the one
where only commutativity between observables located at different sites is
assumed. Here it is shown that Kirchberg's QWEP conjecture on tensor products
of C*-algebras would imply a positive answer to this question for all bipartite
scenarios. This remains true also if one considers not only spatial
correlations, but also spatiotemporal correlations, where each party is allowed
to apply their measurements in temporal succession; we provide an example of a
state together with observables such that ordinary spatial correlations are
local, while the spatiotemporal correlations reveal nonlocality. Moreover, we
find an extended version of Tsirelson's problem which, for each nontrivial Bell
scenario, is equivalent to the QWEP conjecture. This extended version can be
conveniently formulated in terms of steering the system of a third party.
Finally, a comprehensive mathematical appendix offers background material on
complete positivity, tensor products of C*-algebras, group C*-algebras, and
some simple reformulations of the QWEP conjecture.Comment: 57 pages, to appear in Rev. Math. Phy
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