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R^2 Dark Matter
There is a non-trivial four-derivative extension of the gravitational
spectrum that is free of ghosts and phenomenologically viable. It is the so
called -gravity since it is defined by the only addition of a term
proportional to the square of the scalar curvature. Just the presence of this
term does not improve the ultraviolet behaviour of Einstein gravity but
introduces one additional scalar degree of freedom that can account for the
dark matter of our Universe.Comment: 6 pages, 1 figure, to appear in the Proceedings of the sixth
International Workshop on the Dark Side of the Universe (DSU2010) Leon,
Guanajuato, Mexico 1-6 June 201
General purpose computer programs for numerically analyzing linear ac electrical and electronic circuits for steady-state conditions
Digital computer programs determine steady-state performance characteristics of active and passive linear circuits. The ac analysis program solves the basic circuit parameters. The compiler program solves these circuit parameters and in addition provides a more versatile program by allowing the user to perform mathematical and logical operations
An approach to nonstandard quantum mechanics
We use nonstandard analysis to formulate quantum mechanics in
hyperfinite-dimensional spaces. Self-adjoint operators on
hyperfinite-dimensional spaces have complete eigensets, and bound states and
continuum states of a Hamiltonian can thus be treated on an equal footing. We
show that the formalism extends the standard formulation of quantum mechanics.
To this end we develop the Loeb-function calculus in nonstandard hulls. The
idea is to perform calculations in a hyperfinite-dimensional space, but to
interpret expectation values in the corresponding nonstandard hull. We further
apply the framework to non-relativistic quantum scattering theory. For
time-dependent scattering theory, we identify the starting time and the
finishing time of a scattering experiment, and we obtain a natural separation
of time scales on which the preparation process, the interaction process, and
the detection process take place. For time-independent scattering theory, we
derive rigorously explicit formulas for the M{\o}ller wave operators and the
S-Matrix
Collisionless reconnection: Mechanism of self-ignition in thin current sheets
The spontaneous onset of magnetic reconnection in thin collisionless current
sheets is shown to result from a thermal-anisotropy driven magnetic
Weibel-mode, generating seed-magnetic field {\sf X}-points in the centre of the
current layer.Comment: 8 pages, 6 figures, prepared for Annales Geophysica
Particle motion around magnetized black holes: Preston-Poisson space-time
We analyze motion of massless and massive particles around black holes
immersed in an asymptotically uniform magnetic field and surrounded by some
mechanical structure, which provides the magnetic field. The space-time is
described by Preston-Poisson metric, which is the generalization of the
well-known Ernst metric with a new parameter, tidal force, characterizing the
surrounding structure. The Hamilton-Jacobi equations allow separation of
variables in the equatorial plane. The presence of tidal force from
surroundings considerably changes parameters of the test particle motion: it
increases the radius of circular orbits of particles, increases the binding
energy of massive particles going from a given circular orbits to the innermost
stable orbit near black hole. In addition, it increases the distance of minimal
approach, time delay and bending angle for a ray of light propagating near
black hole.Comment: 6 pages, RevTex, the version accepted for publication in Phys. Rev.
Nflation: multi-field inflationary dynamics and perturbations
We carry out numerical investigations of the dynamics and perturbations in
the Nflation model of Dimopoulos et al. (2005). This model features large
numbers of scalar fields with different masses, which can cooperate to drive
inflation according to the assisted inflation mechanism. We extend previous
work to include random initial conditions for the scalar fields, and explore
the predictions for density perturbations and the tensor-to-scalar ratio. The
tensor-to-scalar ratio depends only on the number of e-foldings and is
independent of the number of fields, their masses, and their initial
conditions. It therefore always has the same value as for a single massive
field. By contrast, the scalar spectral index has significant dependence on
model parameters. While normally multi-field inflation models make predictions
for observable quantities which depend also on the unknown field initial
conditions, we find evidence of a `thermodynamic' regime whereby the predicted
spectral index becomes independent of initial conditions if there are enough
fields. Only in parts of parameter space where the mass spectrum of the fields
is extremely densely packed is the model capable of satisfying the tight
observational constraints from WMAP3 observations.Comment: 6 pages RevTeX4, 4 figures included. Updated to match PRD accepted
version. Analysis and conclusions unchanged. New references, especially
astro-ph/0510441 which was first to give the general r=8/N resul
Evaluation of Antimicrobial Efficacy Against E. Coli Isolates of Different Serogroups Obtained From Diarrhoeic Neonates of Calves, Kids, and Lambs
Fourteen antimicrobials were evaluated their efficacy against 115 Escherichia coli isolates recovered from faecal samples collected from neonatal diarrhoeic calves (66), kids (25) and lambs (24). Of these isolates 37 were nontypeable, four were of rough type and 74 isolates were typeable for 'O' antigen belonging to 19 different serogroups (O2, O3, O5, O17, O21, O22, O25, O41, O45, O55, O60, O65, O70, O76, O114, O116, O147, O152, and O158). Evaluation of antimicrobial efficacy by disc diffusion method revealed that the most effective antibiotics were ciprofloxacin, sparfloxacin and triple sulpha followed by co-trimoxazole, chloramphenicol, nitrofurantoin, gentamicin, nalidixic acid, polymixin-B and amoxyclav in decreasing order of their efficacy while ampicillin and cephotaxime were found totally ineffective against these isolates. All the isolates showed multiple drug resistance to various antibiotics ranging from two to ten antibiotics. The resistance patterns were independent of serogroups of isolates and the animal species from which isolates were obtained. However, there was a variation in resistance pattern for same antibiotic vis-a vis locations of their isolation
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The Potential of Freeform Construction Processes
The level of automation technology and processes control found in modern day construction
lags significantly behind other industries such as automotive and aerospace. The construction
industry has health and safety issues and still uses traditional methods of procurement. These
problems are compounded by diminishing skills in the labour force. Methods of production
must change if these issues are to be resolved and Freeform Construction is a collection of
processes that could have potential impact. This paper outlines some of the major issues
facing construction and sets a context with examples of digital fabrication in construction.
Freeform Construction is defined and potential applications are presented and related to
application scale. The viability of two potential applications are investigated in terms of cost.Mechanical Engineerin
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