17,798 research outputs found
The twistor geometry of three-qubit entanglement
A geometrical description of three qubit entanglement is given. A part of the
transformations corresponding to stochastic local operations and classical
communication on the qubits is regarded as a gauge degree of freedom. Entangled
states can be represented by the points of the Klein quadric a space
known from twistor theory. It is shown that three-qubit invariants are
vanishing on special subspaces of . An invariant vanishing for the
class is proposed. A geometric interpretation of the canonical
decomposition and the inequality for distributed entanglement is also given.Comment: 4 pages RevTeX
A simple explanation of the non-appearance of physical gluons and quarks
We show that the non-appearance of gluons and quarks as physical particles is
a rigorous and automatic result of the full, i.e. nonperturbative, nonabelian
nature of the color interaction in quantum chromodynamics. This makes it in
general impossible to describe the color field as a collection of elementary
quanta (gluons). Neither can a quark be an elementary quantum of the quark
field, as the color field of which it is the source is itself a source, making
isolated noninteracting quarks, crucial for a physical particle interpretation,
impossible. In geometrical language, the impossibility of quarks and gluons as
physical elementary particles arises due to the fact that the color Yang-Mills
space does not have a constant trivial curvature.
In QCD, the particles ``gluons'' and ``quarks'' are merely artifacts of an
approximation method (the perturbative expansion) and are simply absent in the
exact theory. This also coincides with the empirical, experimental evidence.Comment: 8 pages, Latex (to appear in Can.J.Phys.
Social work education, training and standards in the Asia-Pacific region
This article discusses the joint project between the International Association of Schools of Social Work (IASSW) and the International Federation of Social Workers (IFSW) to establish guidelines for the training and standard setting that elucidates what social work represents on a global level. While it is impossible to address all the issues that might be significant in such a large scope, attention is given to the challenges establishing global standards might encounter in a region as diverse as the Asia-Pacific
Topological Aspects of the Non-adiabatic Berry Phase
The topology of the non-adiabatic parameter space bundle is discussed for
evolution of exact cyclic state vectors in Berry's original example of split
angular momentum eigenstates. It turns out that the change in topology occurs
at a critical frequency. The first Chern number that classifies these bundles
is proportional to angular momentum. The non-adiabatic principal bundle over
the parameter space is not well-defined at the critical frequency.Comment: 14 pages, Dep. of Physics, Uni. of Texas at Austin, Austin, Texas
78712, to appear in J. Physics
Run-and-tumble particles with hydrodynamics: sedimentation, trapping and upstream swimming
We simulate by lattice Boltzmann the nonequilibrium steady states of
run-and-tumble particles (inspired by a minimal model of bacteria), interacting
by far-field hydrodynamics, subject to confinement. Under gravity, hydrodynamic
interactions barely perturb the steady state found without them, but for
particles in a harmonic trap such a state is quite changed if the run length is
larger than the confinement length: a self-assembled pump is formed. Particles
likewise confined in a narrow channel show a generic upstream flux in
Poiseuille flow: chiral swimming is not required
Assessment of methods of acquiring analyzing, and reporting crop production statistics, volume 4
There are no author-identified significant results in this report
The gap exponent of XXZ model in a transverse field
We have calculated numerically the gap exponent of the anisotropic Heisenberg
model in the presence of the transverse magnetic field. We have implemented the
modified Lanczos method to obtain the excited states of our model with the same
accuracy of the ground state. The coefficient of the leading term in the
perturbation expansion diverges in the thermodynamic limit (N --> infinity). We
have obtained the relation between this divergence and the scaling behaviour of
the energy gap. We have found that the opening of gap in the presence of
transverse field scales with a critical exponent which depends on the
anisotropy parameter (Delta). Our numerical results are in well agreement with
the field theoretical approach in the whole range of the anisotropy parameter,
-1 < Delta < 1.Comment: 6 pages and 4 figure
Multi-particle Correlations in Quaternionic Quantum Systems
We investigate the outcomes of measurements on correlated, few-body quantum
systems described by a quaternionic quantum mechanics that allows for regions
of quaternionic curvature. We find that a multi-particle interferometry
experiment using a correlated system of four nonrelativistic, spin-half
particles has the potential to detect the presence of quaternionic curvature.
Two-body systems, however, are shown to give predictions identical to those of
standard quantum mechanics when relative angles are used in the construction of
the operators corresponding to measurements of particle spin components.Comment: REVTeX 3.0, 16 pages, no figures, UM-P-94/54, RCHEP-94/1
Quantum Stability of (2+1)-Spacetimes with Non-Trivial Topology
Quantum fields are investigated in the (2+1)-open-universes with non-trivial
topologies by the method of images. The universes are locally de Sitter
spacetime and anti-de Sitter spacetime. In the present article we study
spacetimes whose spatial topologies are a torus with a cusp and a sphere with
three cusps as a step toward the more general case. A quantum energy momentum
tensor is obtained by the point stripping method. Though the cusps are no
singularities, the latter cusps cause the divergence of the quantum field. This
suggests that only the latter cusps are quantum mechanically unstable. Of
course at the singularity of the background spacetime the quantum field
diverges. Also the possibility of the divergence of topological effect by a
negative spatial curvature is discussed. Since the volume of the negatively
curved space is larger than that of the flat space, one see so many images of a
single source by the non-trivial topology. It is confirmed that this divergence
does not appear in our models of topologies. The results will be applicable to
the case of three dimensional multi black hole\cite{BR}.Comment: 17 pages, revtex, 3 uuencoded figures containe
Identifying a sufficient core group for trachoma transmission.
BackgroundIn many infectious diseases, a core group of individuals plays a disproportionate role in transmission. If these individuals were effectively prevented from transmitting infection, for example with a perfect vaccine, then the disease would disappear in the remainder of the community. No vaccine has yet proven effective against the ocular strains of chlamydia that cause trachoma. However, repeated treatment with oral azithromycin may be able to prevent individuals from effectively transmitting trachoma.Methodology/principal findingsHere we assess several methods for identifying a core group for trachoma, assuming varying degrees of knowledge about the transmission process. We determine the minimal core group from a completely specified model, fitted to results from a large Ethiopian trial. We compare this benchmark to a core group that could actually be identified from information available to trachoma programs. For example, determined from the rate of return of infection in a community after mass treatments, or from the equilibrium prevalence of infection.Conclusions/significanceSufficient groups are relatively easy for programs to identify, but will likely be larger than the theoretical minimum
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