521 research outputs found
The Measurement Calculus
Measurement-based quantum computation has emerged from the physics community
as a new approach to quantum computation where the notion of measurement is the
main driving force of computation. This is in contrast with the more
traditional circuit model which is based on unitary operations. Among
measurement-based quantum computation methods, the recently introduced one-way
quantum computer stands out as fundamental.
We develop a rigorous mathematical model underlying the one-way quantum
computer and present a concrete syntax and operational semantics for programs,
which we call patterns, and an algebra of these patterns derived from a
denotational semantics. More importantly, we present a calculus for reasoning
locally and compositionally about these patterns.
We present a rewrite theory and prove a general standardization theorem which
allows all patterns to be put in a semantically equivalent standard form.
Standardization has far-reaching consequences: a new physical architecture
based on performing all the entanglement in the beginning, parallelization by
exposing the dependency structure of measurements and expressiveness theorems.
Furthermore we formalize several other measurement-based models:
Teleportation, Phase and Pauli models and present compositional embeddings of
them into and from the one-way model. This allows us to transfer all the theory
we develop for the one-way model to these models. This shows that the framework
we have developed has a general impact on measurement-based computation and is
not just particular to the one-way quantum computer.Comment: 46 pages, 2 figures, Replacement of quant-ph/0412135v1, the new
version also include formalization of several other measurement-based models:
Teleportation, Phase and Pauli models and present compositional embeddings of
them into and from the one-way model. To appear in Journal of AC
Theory of Chiral Order in Random Copolymers
Recent experiments have found that polyisocyanates composed of a mixture of
opposite enantiomers follow a chiral ``majority rule:'' the chiral order of the
copolymer, measured by optical activity, is dominated by whichever enantiomer
is in the majority. We explain this majority rule theoretically by mapping the
random copolymer onto the random-field Ising model. Using this model, we
predict the chiral order as a function of enantiomer concentration, in
quantitative agreement with the experiments, and show how the sharpness of the
majority-rule curve can be controlled.Comment: 13 pages, including 4 postscript figures, uses REVTeX 3.0 and
epsf.st
Isotropic-Nematic Transition in Liquid-Crystalline Elastomers
In liquid-crystalline elastomers, the nematic order parameter and the induced
strain vary smoothly across the isotropic-nematic transition, without the
expected first-order discontinuity. To investigate this smooth variation, we
measure the strain as a function of temperature over a range of applied stress,
for elastomers crosslinked in the nematic and isotropic phases, and analyze the
results using a variation on Landau theory. This analysis shows that the smooth
variation arises from quenched disorder in the elastomer, combined with the
effects of applied stress and internal stress.Comment: 4 pages, including 4 postscript figures, uses REVTeX
Order and Frustration in Chiral Liquid Crystals
This paper reviews the complex ordered structures induced by chirality in
liquid crystals. In general, chirality favors a twist in the orientation of
liquid-crystal molecules. In some cases, as in the cholesteric phase, this
favored twist can be achieved without any defects. More often, the favored
twist competes with applied electric or magnetic fields or with geometric
constraints, leading to frustration. In response to this frustration, the
system develops ordered structures with periodic arrays of defects. The
simplest example of such a structure is the lattice of domains and domain walls
in a cholesteric phase under a magnetic field. More complex examples include
defect structures formed in two-dimensional films of chiral liquid crystals.
The same considerations of chirality and defects apply to three-dimensional
structures, such as the twist-grain-boundary and moire phases.Comment: 39 pages, RevTeX, 14 included eps figure
The Role of Bilayer Tilt Difference in Equilibrium Membrane Shapes
Lipid bilayer membranes below their main transition have two tilt order
parameters, corresponding to the two monolayers. These two tilts may be
strongly coupled to membrane shape but only weakly coupled to each other. We
discuss some implications of this observation for rippled and saddle phases,
bilayer tubules, and bicontinuous phases. Tilt difference introduces a length
scale into the elastic theory of tilted fluid membranes. It can drive an
instability of the flat phase; it also provides a simple mechanism for the
spontaneous breaking of inversion symmetry seen in some recent experiments.Comment: Latex file; .ps available at
http://dept.physics.upenn.edu/~nelson/saddle.p
Picturing classical and quantum Bayesian inference
We introduce a graphical framework for Bayesian inference that is
sufficiently general to accommodate not just the standard case but also recent
proposals for a theory of quantum Bayesian inference wherein one considers
density operators rather than probability distributions as representative of
degrees of belief. The diagrammatic framework is stated in the graphical
language of symmetric monoidal categories and of compact structures and
Frobenius structures therein, in which Bayesian inversion boils down to
transposition with respect to an appropriate compact structure. We characterize
classical Bayesian inference in terms of a graphical property and demonstrate
that our approach eliminates some purely conventional elements that appear in
common representations thereof, such as whether degrees of belief are
represented by probabilities or entropic quantities. We also introduce a
quantum-like calculus wherein the Frobenius structure is noncommutative and
show that it can accommodate Leifer's calculus of `conditional density
operators'. The notion of conditional independence is also generalized to our
graphical setting and we make some preliminary connections to the theory of
Bayesian networks. Finally, we demonstrate how to construct a graphical
Bayesian calculus within any dagger compact category.Comment: 38 pages, lots of picture
Anomalous Elasticity of Polymer Cholesterics
We show that polymer cholesterics have much longer pitches than comparable
short molecule cholesterics, due to their anomalous elasticity. The pitch
of a chiral mixture with concentration near the racemic (non-chiral)
concentration diverges like with (for short molecule cholesterics ). The short molecule law is
recovered for polymers of finite molecular length once the pitch is
longer than a length that diverges like with . Our predictions could be tested by measurements of the pitch in DNA.Comment: 12 pages, Plain TeX, (1 postscript figure, compressed, uuencoded and
appended to paper), minor corrections, IASSNS-HEP-94/4
Non-therapeutic administration of a model antimicrobial growth promoter modulates intestinal immune responses
<p>Abstract</p> <p>Background</p> <p>The development of efficacious alternatives to antimicrobial growth promoters (AGP) in livestock production is an urgent issue, but is hampered by a lack of knowledge regarding the mode of action of AGP. The belief that AGP modulate the intestinal microbiota has become prominent in the literature; however, there is a lack of experimental evidence to support this hypothesis. Using a chlortetracycline-murine-<it>Citrobacter rodentium </it>model, the ability of AGP to modulate the intestinal immune system in mammals was investigated.</p> <p>Results</p> <p><it>C. rodentium </it>was transformed with the tetracycline resistance gene, <it>tet</it>O, and continuous oral administration of a non-therapeutic dose of chlortetracycline to mice did not affect densities of <it>C. rodentium </it>CFU in feces throughout the experiment or associated with mucosal surfaces in the colon (i.e. at peak and late infection). However, chlortetracycline regulated transcription levels of Th1 and Th17 inflammatory cytokines in a temporal manner in <it>C. rodentium</it>-inoculated mice, and ameliorated weight loss associated with infection. In mice inoculated with <it>C. rodentium</it>, those that received chlortetracycline had less pathologic changes in the distal colon than mice not administered CTC (i.e. relative to untreated mice). Furthermore, chlortetracycline administration at a non-therapeutic dose did not impart either prominent or consistent effects on the colonic microbiota.</p> <p>Conclusion</p> <p>Data support the hypothesis that AGP function by modulating the intestinal immune system in mammals. This finding may facilitate the development of biorationale-based and efficacious alternatives to AGP.</p
Raman spectroscopy investigation of the H content of heated hard amorphous carbon layers
We revisit here how Raman spectroscopy can be used to estimate the H content
in hard hydrogenated amorphous carbon layers. The H content was varied from 2
at.% to 30 at.%, using heat treatments of a a-C:H, from room temperature to
1300 K and was determined independently using ion beam analysis. We examine the
correlation of various Raman parameters and the consistency of their thermal
evolution with thermo-desorption results. We identify a weak band at 860 cm-1
attributed to H bonded to C(sp2). We show that the HD/HG parameter (Height
ratio between the D and G bands) is quasi-linear in the full range of H content
and can thus be used to estimate the H content. Conversely, we show that the
m/HG parameter (ratio between the photoluminescence background, m, and the
height of the G band), often used to estimate the H content, should be used
with care, first because it is sensitive to various photoluminescence quenching
processes and second because it is not sensitive to H bonded to C(sp2)
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