111 research outputs found
Nitrofurantoin and fosfomycin for resistant urinary tract infections: old drugs for emerging problems
Uncomplicated urinary tract infection is one of the most common indications for antibiotic use in
the community. However, the Gram-negative organisms that can cause the infection are becoming
more resistant to antibiotics.
Many multidrug resistant organisms retain susceptibility to two old antibiotics, nitrofurantoin
and fosfomycin. Advantages over newer drugs include their high urinary concentrations and
minimal toxicity.
Fosfomycin is a potential treatment option for patients with uncomplicated urinary tract infection
due to resistant organisms. Nitrofu
Phase space theory of Bose-Einstein condensates and time-dependent modes
A phase space theory approach for treating dynamical behaviour of
Bose-Einstein condensates applicable to situations such as interferometry with
BEC in time-dependent double well potentials is presented. Time-dependent mode
functions are used, chosen so that one, two,.. highly occupied modes describe
well the physics of interacting condensate bosons in time dependent potentials
at well below the transition temperature. Time dependent mode annihilation,
creation operators are represented by time dependent phase variables, but time
independent total field annihilation, creation operators are represented by
time independent field functions. Two situations are treated, one (mode theory)
is where specific mode annihilation, creation operators and their related phase
variables and distribution functions are dealt with, the other (field theory)
is where only field creation, annihilation operators and their related field
functions and distribution functionals are involved. The paper focuses on the
hybrid approach, where the modes are divided up between condensate (highly
occupied) modes and non-condensate (sparsely occupied) modes. It is found that
there are extra terms in the Ito stochastic equations both for the stochastic
phases and stochastic fields, involving coupling coefficients defined via
overlap integrals between mode functions and their time derivatives. For the
hybrid approach both the Fokker-Planck and functional Fokker-Planck equations
differ from those derived via the correspondence rules, the drift vectors are
unchanged but the diffusion matrices contain additional terms involving the
coupling coefficients. Results are also presented for the combined approach
where all the modes are treated as one set.Comment: 83 pages. 0 figures. Version 3. Details to Appendices, typos
corrected, field theory treatment highlighted. To be published in Annals of
Physic
Grassmann Variables and the Jaynes-Cummings Model
This paper shows that phase space methods using a positive P type
distribution function involving both c-number variables (for the cavity mode)
and Grassmann variables (for the two level atom) can be used to treat the
Jaynes-Cummings model. Although it is a Grassmann function, the distribution
function is equivalent to six c-number functions of the two bosonic variables.
Experimental quantities are given as bosonic phase space integrals involving
the six functions. A Fokker-Planck equation involving both left and right
Grassmann differentiation can be obtained for the distribution function, and is
equivalent to six coupled equations for the six c-number functions.
The approach used involves choosing the canonical form of the (non-unique)
positive P distribution function, where the correspondence rules for bosonic
operators are non-standard and hence the Fokker-Planck equation is also
unusual. Initial conditions, such as for initially uncorrelated states, are
used to determine the initial distribution function. Transformations to new
bosonic variables rotating at the cavity frequency enables the six coupled
equations for the new c-number functions (also equivalent to the canonical
Grassmann distribution function) to be solved analytically, based on an ansatz
from a 1980 paper by Stenholm. It is then shown that the distribution function
is the same as that determined from the well-known solution based on coupled
equations for state vector amplitudes of atomic and n-photon product states.
The treatment of the simple two fermion mode Jaynes-Cummings model is a
useful test case for the future development of phase space Grassmann
distribution functional methods for multi-mode fermionic applications in
quantum-atom optics.Comment: 57 pages, 0 figures. Version
Decoherence effects in Bose-Einstein condensate interferometry. I General Theory
The present paper outlines a basic theoretical treatment of decoherence and
dephasing effects in interferometry based on single component BEC in double
potential wells, where two condensate modes may be involved. Results for both
two mode condensates and the simpler single mode condensate case are presented.
A hybrid phase space distribution functional method is used where the
condensate modes are described via a truncated Wigner representation, and the
basically unoccupied non-condensate modes are described via a positive P
representation. The Hamiltonian for the system is described in terms of quantum
field operators for the condensate and non-condensate modes. The functional
Fokker-Planck equation for the double phase space distribution functional is
derived. Equivalent Ito stochastic equations for the condensate and
non-condensate fields that replace the field operators are obtained, and
stochastic averages of products of these fields give the quantum correlation
functions used to interpret interferometry experiments. The stochastic field
equations are the sum of a deterministic term obtained from the drift vector in
the functional Fokker-Planck equation, and a noise field whose stochastic
properties are determined from the diffusion matrix in the functional
Fokker-Planck equation. The noise field stochastic properties are similar to
those for Gaussian-Markov processes in that the stochastic averages of odd
numbers of noise fields are zero and those for even numbers of noise field
terms are sums of products of stochastic averages associated with pairs of
noise fields. However each pair is represented by an element of the diffusion
matrix rather than products of the noise fields themselves. The treatment
starts from a generalised mean field theory for two condensate mode. The
generalized mean field theory solutions are needed for calculations using the
Ito stochastic field equations.Comment: To be published in Annals of Physics. Full version of paper,
including all Appendices. Journal version only includes Appendix A.
Appendices are in online supplementary material. Cross references to material
in Appendices improved in Version 2 (5 July 2010). Minor amendments made in
Version 3 (23 Nov 2010), including reference to Takagi factorisation of
complex symmetric matrice
Noise-free scattering of the quantized electromagnetic field from a dispersive linear dielectric
We study the scattering of the quantized electromagnetic field from a linear,
dispersive dielectric using the scattering formalism for quantum fields. The
medium is modeled as a collection of harmonic oscillators with a number of
distinct resonance frequencies. This model corresponds to the Sellmeir
expansion, which is widely used to describe experimental data for real
dispersive media. The integral equation for the interpolating field in terms of
the in field is solved and the solution used to find the out field. The
relation between the in and out creation and annihilation operators is found
which allows one to calculate the S-matrix for this system. In this model, we
find that there are absorption bands, but the input-output relations are
completely unitary. No additional quantum noise terms are required.Comment: Revtex, submitted to Physical Review
Stochastic processes with finite correlation time: modeling and application to the generalized Langevin equation
The kangaroo process (KP) is characterized by various forms of the covariance
and can serve as a useful model of random noises. We discuss properties of that
process for the exponential, stretched exponential and algebraic (power-law)
covariances. Then we apply the KP as a model of noise in the generalized
Langevin equation and simulate solutions by a Monte Carlo method. Some results
appear to be incompatible with requirements of the fluctuation-dissipation
theorem because probability distributions change when the process is inserted
into the equation. We demonstrate how one can construct a model of noise free
of that difficulty. This form of the KP is especially suitable for physical
applications.Comment: 22 pages (RevTeX) and 4 figure
Anomalous diffusion and the first passage time problem
We study the distribution of first passage time (FPT) in Levy type of
anomalous diffusion. Using recently formulated fractional Fokker-Planck
equation we obtain three results. (1) We derive an explicit expression for the
FPT distribution in terms of Fox or H-functions when the diffusion has zero
drift. (2) For the nonzero drift case we obtain an analytical expression for
the Laplace transform of the FPT distribution. (3) We express the FPT
distribution in terms of a power series for the case of two absorbing barriers.
The known results for ordinary diffusion (Brownian motion) are obtained as
special cases of our more general results.Comment: 25 pages, 4 figure
Quantum Computing and Quantum Simulation with Group-II Atoms
Recent experimental progress in controlling neutral group-II atoms for
optical clocks, and in the production of degenerate gases with group-II atoms
has given rise to novel opportunities to address challenges in quantum
computing and quantum simulation. In these systems, it is possible to encode
qubits in nuclear spin states, which are decoupled from the electronic state in
the S ground state and the long-lived P metastable state on the
clock transition. This leads to quantum computing scenarios where qubits are
stored in long lived nuclear spin states, while electronic states can be
accessed independently, for cooling of the atoms, as well as manipulation and
readout of the qubits. The high nuclear spin in some fermionic isotopes also
offers opportunities for the encoding of multiple qubits on a single atom, as
well as providing an opportunity for studying many-body physics in systems with
a high spin symmetry. Here we review recent experimental and theoretical
progress in these areas, and summarise the advantages and challenges for
quantum computing and quantum simulation with group-II atoms.Comment: 11 pages, 7 figures, review for special issue of "Quantum Information
Processing" on "Quantum Information with Neutral Particles
Use of SMS texts for facilitating access to online alcohol interventions: a feasibility study
A41 Use of SMS texts for facilitating access to online alcohol interventions: a feasibility study
In: Addiction Science & Clinical Practice 2017, 12(Suppl 1): A4
Epidemiologia, sinais clínicos e distribuição das lesões encefálicas em bovinos afetados por meningoencefalite por herpesvírus bovino-5
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