4,394 research outputs found
Elementary analysis of the special relativistic combination of velocities, Wigner rotation, and Thomas precession
The purpose of this paper is to provide an elementary introduction to the
qualitative and quantitative results of velocity combination in special
relativity, including the Wigner rotation and Thomas precession. We utilize
only the most familiar tools of special relativity, in arguments presented at
three differing levels: (1) utterly elementary, which will suit a first course
in relativity; (2) intermediate, to suit a second course; and (3) advanced, to
suit higher level students. We then give a summary of useful results, and
suggest further reading in this often obscure field.Comment: V1: 25 pages, 6 figures; V2: 22 pages, 5 figures. The revised version
is shortened and the arguments streamlined. Minor changes in notation and
figures. This version matches the published versio
Quantum matchgate computations and linear threshold gates
The theory of matchgates is of interest in various areas in physics and
computer science. Matchgates occur in e.g. the study of fermions and spin
chains, in the theory of holographic algorithms and in several recent works in
quantum computation. In this paper we completely characterize the class of
boolean functions computable by unitary two-qubit matchgate circuits with some
probability of success. We show that this class precisely coincides with that
of the linear threshold gates. The latter is a fundamental family which appears
in several fields, such as the study of neural networks. Using the above
characterization, we further show that the power of matchgate circuits is
surprisingly trivial in those cases where the computation is to succeed with
high probability. In particular, the only functions that are
matchgate-computable with success probability greater than 3/4 are functions
depending on only a single bit of the input
Distributed Drug Discovery, Part 2: Global Rehearsal of Alkylating Agents for the Synthesis of Resin-Bound Unnatural Amino Acids and Virtual D3 Catalog Construction
Non-Statistical Effects in Neutron Capture
There have been many reports of non-statistical effects in neutron-capture
measurements. However, reports of deviations of reduced-neutron-width
distributions from the expected Porter-Thomas (PT) shape largely have been
ignored. Most of these deviations have been reported for odd-A nuclides.
Because reliable spin (J) assignments have been absent for most resonances for
such nuclides, it is possible that reported deviations from PT might be due to
incorrect J assignments. We recently developed a new method for measuring spins
of neutron resonances by using the DANCE detector at LANSCE. Measurements made
with a 147Sm sample allowed us to determine spins of almost all known
resonances below 1 keV. Furthermore, analysis of these data revealed that the
reduced-neutron-width distribution was in good agreement with PT for resonances
below 350 eV, but in disagreement with PT for resonances between 350 and 700
eV. Our previous (n,alpha) measurements had revealed that the alpha strength
function also changes abruptly at this energy. There currently is no known
explanation for these two non-statistical effects. Recently, we have developed
another new method for determining the spins of neutron resonances. To
implement this technique required a small change (to record pulse-height
information for coincidence events) to a much simpler apparatus: A pair of C6D6
gamma-ray detectors which we have employed for many years to measure
neutron-capture cross sections at ORELA. Measurements with a 95Mo sample
revealed that not only does the method work very well for determining spins,
but it also makes possible parity assignments. Taken together, these new
techniques at LANSCE and ORELA could be very useful for further elucidation of
non-statistical effects.Comment: 8 pages, 3 figures, for proceedings of CGS1
Thermodynamic metrics and optimal paths
A fundamental problem in modern thermodynamics is how a molecular-scale
machine performs useful work, while operating away from thermal equilibrium
without excessive dissipation. To this end, we derive a friction tensor that
induces a Riemannian manifold on the space of thermodynamic states. Within the
linear-response regime, this metric structure controls the dissipation of
finite-time transformations, and bestows optimal protocols with many useful
properties. We discuss the connection to the existing thermodynamic length
formalism, and demonstrate the utility of this metric by solving for optimal
control parameter protocols in a simple nonequilibrium model.Comment: 5 page
Distributed Drug Discovery, Part 3: Using D3 Methodology to Synthesize Analogs of an Anti-Melanoma Compound
Neutrinoless Double Beta Decay and CP Violation
We study the relation between the Majorana neutrino mass matrices and the
neutrinoless double beta decay when CP is not conserved. We give an explicit
form of the decay rate in terms of a rephasing invariant quantity and
demonstrate that in the presence of CP violation it is impossible to have
vanishing neutrinoless double beta decay in the case of two neutrino
generations (or when the third generation leptons do not mix with other leptons
and hence decouple).Comment: 9 pages, UTPT-93-1
Chronic locked anterior shoulder dislocation with impaction of the humeral head onto the coracoid: a case report
The glenohumeral joint is one of the most commonly dislocated joints. When dislocated, the humeral head typically moves anteriorly and medially within the soft tissues adjacent to the glenoid. We present a case of a 64-year-old female who presented with a locked anterior shoulder dislocation with impaction of the humeral head onto the coracoid. To our knowledge, this is the first reported instance of humeral head impaction onto the coracoid causing the shoulder dislocation to be irreducible by closed means. Complications of this dislocation can include humeral head deformity, pseudoparalysis, brachial plexus injury, and significant pain. Level of evidence V
B -> K^* gamma from D -> K^* l nu
The B -> K^* gamma branching fraction is predicted using heavy quark spin
symmetry at large recoil to relate the tensor and (axial-)vector form factors,
using heavy quark flavor symmetry to relate the B decay form factors to the
measured D -> K^* l nu form form factors, and extrapolating the semileptonic B
decay form factors to large recoil assuming nearest pole dominance. This
prediction agrees with data surprisingly well, and we comment on its
implications for the extraction of |Vub| from B -> rho l nu.Comment: 10 page
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