221 research outputs found
Phase measurements with weak reference pulses
Quantum state discrimination for two coherent states with opposite phases as
measured relative to a reference pulse is analyzed as functions of the
intensities of both the signal states and of the reference pulse. This problem
is relevant for Quantum Key Distribution with phase encoding. We consider both
the optimum measurements and simple measurements that require only
beamsplitters and photodetectors.Comment: 5 pages, 5 figures. I apologize for this boring pape
Anti-de Sitter Supersymmetry
We give a pedagogical introduction to certain aspects of supersymmetric field
theories in anti-de Sitter space. Among them are the presence of masslike terms
in massless wave equations, irreducible unitary representations and the
phenomenon of multiplet shortening.Comment: Lectures presented by B. de Wit at the Winter School of Theoretical
Physics, Polanica, Poland, February 1999. 23 pp., LateX file, requires
packages latexsym, amsfonts, cl2emult.cl
Wheat straw availability for bioenergy in England
In an effort to meet energy demands while reducing carbon emissions, crop residues, such as wheat straw, have been investigated for their use as feedstock for biofuel production. In order to identify the feasibility of utilising crop residues as bioenergy feedstock, a postal survey was conducted to determine current farm business wheat straw use, destination and potential future supply. The survey responses showed a bias towards larger, more commercially-minded farms, therefore capturing a large area of straw production. Results demonstrated a wide range of responses to both current straw use and potential for the supply of straw to different markets in the future. Interestingly, even for a very generous payment for straw, 28.5% of straw currently chopped and incorporated would not be sold, suggesting that straw supply for bioenergy feedstock is likely to be more limited than previously assumed. However, higher prices for straw would encourage farmers to explore ways of increasing straw yield
AdS and pp-wave D-particle superalgebras
We derive anticommutators of supercharges with a brane charge for a
D-particle in AdS(2) x S(2) and pp-wave backgrounds. A coset GL(2|2)/(GL(1))^4
and its Penrose limit are used with the supermatrix-valued coordinates for the
AdS and the pp-wave spaces respectively. The brane charges have position
dependence, and can be absorbed into bosonic generators by shift of momenta
which results in closure of the superalgebras.Comment: 15 page
Biofilm formation on enteral feeding tubes by Cronobacter sakazakii, Salmonella serovars and other Enterobacteriaceae
WHO (2007) recommended that to reduce microbial risks, powdered infant formula should be reconstituted with water at temperatures >70 °C, and that such feeds should be used within 2 h of preparation. However, this recommendation does not consider the use of enteral feeding tubes which can be in place for more than 48 h and can be loci for bacterial attachment. This study determined the extent to which 29 strains of Cronobacter sakazakii, Salmonella serovars, other Enterobacteriaceae and Acinetobacter spp. can adhere and grow on enteral feeding tubes composed of polyvinyl chloride and polyurethane. The study also included silver-impregnated tubing which was expected to have antibacterial activity. Bacterial biofilm formation by members of the Enterobacteriaceae was ca. 105-106 cfu/cm after 24 h. Negligible biofilm was detected for Acinetobacter gensp. 13; ca. 10 cfu/cm, whereas Cr. sakazakii strain ATCC 12868 had the highest biofilm cell density of 107 cfu/cm. Biofilm formation did not correlate with capsule production, and was not inhibited on silver-impregnated tubing. Bacteria grew in the tube lumen to cell densities of 107 cfu/ml within 8 h, and 109 cfu/ml within 24 h. It is plausible that in vivo the biofilm will both inoculate subsequent routine feeds and as the biofilm ages, clumps of cells will be shed which may survive passage through the neonate's stomach. Therefore biofilm formation on enteral feeding tubes constitutes a risk factor for susceptible neonates
Electronic structure of periodic curved surfaces -- topological band structure
Electronic band structure for electrons bound on periodic minimal surfaces is
differential-geometrically formulated and numerically calculated. We focus on
minimal surfaces because they are not only mathematically elegant (with the
surface characterized completely in terms of "navels") but represent the
topology of real systems such as zeolites and negative-curvature fullerene. The
band structure turns out to be primarily determined by the topology of the
surface, i.e., how the wavefunction interferes on a multiply-connected surface,
so that the bands are little affected by the way in which we confine the
electrons on the surface (thin-slab limit or zero thickness from the outset).
Another curiosity is that different minimal surfaces connected by the Bonnet
transformation (such as Schwarz's P- and D-surfaces) possess one-to-one
correspondence in their band energies at Brillouin zone boundaries.Comment: 6 pages, 8 figures, eps files will be sent on request to
[email protected]
Ion-implanted Nd:MgO:LiNbO<sub>3</sub> planar waveguide laser
Laser oscillation in an ion-implanted planar Nd:MgO:LiNbO3 waveguide is demonstrated for the first time to our knowledge. Details of the waveguide structure, spectroscopic properties, photorefractive effects. and laser performance are given. A simple calculation of the absorbed power threshold gives ~8mW, in fair agreement with the experimental value of ~17mW
Energetics and stability of nanostructured amorphous carbon
Monte Carlo simulations, supplemented by ab initio calculations, shed light
into the energetics and thermodynamic stability of nanostructured amorphous
carbon. The interaction of the embedded nanocrystals with the host amorphous
matrix is shown to determine in a large degree the stability and the relative
energy differences among carbon phases. Diamonds are stable structures in
matrices with sp^3 fraction over 60%. Schwarzites are stable in low-coordinated
networks. Other sp^2-bonded structures are metastable.Comment: 11 pages, 7 figure
Superparticle Models with Tensorial Central Charges
A generalization of the Ferber-Shirafuji formulation of superparticle
mechanics is considered. The generalized model describes the dynamics of a
superparticle in a superspace extended by tensorial central charge coordinates
and commuting twistor-like spinor variables. The D=4 model contains a
continuous real parameter and at a=0 reduces to the SU(2,2|1)
supertwistor Ferber-Shirafuji model, while at a=1 one gets an OSp(1|8)
supertwistor model of ref. [1] (hep-th/9811022) which describes BPS states with
all but one unbroken target space supersymmetries. When 0<a<1 the model admits
an OSp(2|8) supertwistor description, and when a>1 the supertwistor group
becomes OSp(1,1|8). We quantize the model and find that its quantum spectrum
consists of massless states of an arbitrary (half)integer helicity. The
independent discrete central charge coordinate describes the helicity spectrum.
We also outline the generalization of the a=1 model to higher space-time
dimensions and demonstrate that in D=3,4,6 and 10, where the quantum states are
massless, the extra degrees of freedom (with respect to those of the standard
superparticle) parametrize compact manifolds. These compact manifolds can be
associated with higher-dimensional helicity states. In particular, in D=10 the
additional ``helicity'' manifold is isomorphic to the seven-sphere.Comment: 32 pages, LATEX, no figure
General Brane Geometries from Scalar Potentials: Gauged Supergravities and Accelerating Universes
We find broad classes of solutions to the field equations for d-dimensional
gravity coupled to an antisymmetric tensor of arbitrary rank and a scalar field
with non-vanishing potential. Our construction generates these configurations
from the solution of a single nonlinear ordinary differential equation, whose
form depends on the scalar potential. For an exponential potential we find
solutions corresponding to brane geometries, generalizing the black p-branes
and S-branes known for the case of vanishing potential. These geometries are
singular at the origin with up to two (regular) horizons. Their asymptotic
behaviour depends on the parameters of the model. When the singularity has
negative tension or the cosmological constant is positive we find
time-dependent configurations describing accelerating universes. Special cases
give explicit brane geometries for (compact and non-compact) gauged
supergravities in various dimensions, as well as for massive 10D supergravity,
and we discuss their interrelation. Some examples lift to give new solutions to
10D supergravity. Limiting cases with a domain wall structure preserve part of
the supersymmetries of the vacuum. We also consider more general potentials,
including sums of exponentials. Exact solutions are found for these with up to
three horizons, having potentially interesting cosmological interpretation. We
give several additional examples which illustrate the power of our techniques.Comment: 54 pages, 6 figures. Uses JHEP3. Published versio
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