9,524 research outputs found
Optimal Computation of Avoided Words
The deviation of the observed frequency of a word from its expected
frequency in a given sequence is used to determine whether or not the word
is avoided. This concept is particularly useful in DNA linguistic analysis. The
value of the standard deviation of , denoted by , effectively
characterises the extent of a word by its edge contrast in the context in which
it occurs. A word of length is a -avoided word in if
, for a given threshold . Notice that such a word
may be completely absent from . Hence computing all such words na\"{\i}vely
can be a very time-consuming procedure, in particular for large . In this
article, we propose an -time and -space algorithm to compute all
-avoided words of length in a given sequence of length over a
fixed-sized alphabet. We also present a time-optimal -time and
-space algorithm to compute all -avoided words (of any
length) in a sequence of length over an alphabet of size .
Furthermore, we provide a tight asymptotic upper bound for the number of
-avoided words and the expected length of the longest one. We make
available an open-source implementation of our algorithm. Experimental results,
using both real and synthetic data, show the efficiency of our implementation
A cohort study of influences, health outcomes and costs of patients' health-seeking behaviour for minor ailments from primary and emergency care settings
To compare health-related and cost-related outcomes of consultations for symptoms suggestive of minor ailments in emergency departments (EDs), general practices and community pharmacies
Metronidazole vaginal gel 0.75% (MetroGel-Vaginal): a brief review.
OBJECTIVE: A retrospective review of appendectomies performed at the University of Kansas Medical Center between January 1, 1989, and January 1, 1994, was conducted. In addition, the literature evaluating effectiveness of incidental appendectomy in preventing future operation and morbidity from appendicitis was reviewed. The results of the two reviews were analyzed to formulate guidelines for the appropriateness of performing incidental appendectomy in association with other operative procedures. METHOD: A retrospective review of results of appendectomies performed in 460 patients at the University of Kansas Medical Center with analysis of operative findings, pathology of the removed appendix and operative complications was performed. These results were compared with those of a systematic review of the literature utilizing a Medline search relating to the subject of incidental appendix removal. RESULTS: Two hundred sixty-one incidental appendectomies were performed in this study of 460 patients (60%). The procedure was most commonly performed with total abdominal hysterectomy (56%), followed by oophorectomy (15%) and exploratory laparotomy (11%). Morbidity was minimal at all ages. Microscopic pathology was found in 25% of the cases. CONCLUSION: The data from the current survey and literature review support incidental removal of the appendix in the young patient (< 35 years old). In patients 35-50 years old the literature is controversial, and the patient's clinical condition and judgment of the operating surgeon should determine whether incidental appendectomy should be performed. However, routine incidental appendectomy cannot be justified in patients greater than age 50
Stress Tensor Correlators in the Schwinger-Keldysh Formalism
We express stress tensor correlators using the Schwinger-Keldysh formalism.
The absence of off-diagonal counterterms in this formalism ensures that the +-
and -+ correlators are free of primitive divergences. We use dimensional
regularization in position space to explicitly check this at one loop order for
a massless scalar on a flat space background. We use the same procedure to show
that the ++ correlator contains the divergences first computed by `t Hooft and
Veltman for the scalar contribution to the graviton self-energy.Comment: 14 pages, LaTeX 2epsilon, no figures, revised for publicatio
Estimating the burden of minor ailment consultations in general practices and emergency departments through retrospective review of routine data in North East Scotland
Minor ailment attendances in general practices and emergency departments (EDs) place significant burden on health care resources
Photon creation from vacuum and interactions engineering in nonstationary circuit QED
We study theoretically the nonstationary circuit QED system in which the
artificial atom transition frequency, or the atom-cavity coupling, have a small
periodic time modulation, prescribed externally. The system formed by the atom
coupled to a single cavity mode is described by the Rabi Hamiltonian. We show
that, in the dispersive regime, when the modulation periodicity is tuned to the
`resonances', the system dynamics presents the dynamical Casimir effect,
resonant Jaynes-Cummings or resonant Anti-Jaynes-Cummings behaviors, and it can
be described by the corresponding effective Hamiltonians. In the resonant
atom-cavity regime and under the resonant modulation, the dynamics is similar
to the one occurring for a stationary two-level atom in a vibrating cavity, and
an entangled state with two photons can be created from vacuum. Moreover, we
consider the situation in which the atom-cavity coupling, the atomic frequency,
or both have a small nonperiodic time modulation, and show that photons can be
created from vacuum in the dispersive regime. Therefore, an analog of the
dynamical Casimir effect can be simulated in circuit QED, and several photons,
as well as entangled states, can be generated from vacuum due to the
anti-rotating term in the Rabi Hamiltonian.Comment: 14 pages, 6 figures. Talk presented at the International Workshop "60
Years of Casimir Effect", 23 - 27 June, 2008, Brasili
Quantum radiation in a plane cavity with moving mirrors
We consider the electromagnetic vacuum field inside a perfect plane cavity
with moving mirrors, in the nonrelativistic approximation. We show that low
frequency photons are generated in pairs that satisfy simple properties
associated to the plane geometry. We calculate the photon generation rates for
each polarization as functions of the mechanical frequency by two independent
methods: on one hand from the analysis of the boundary conditions for moving
mirrors and with the aid of Green functions; and on the other hand by an
effective Hamiltonian approach. The angular and frequency spectra are discrete,
and emission rates for each allowed angular direction are obtained. We discuss
the dependence of the generation rates on the cavity length and show that the
effect is enhanced for short cavity lengths. We also compute the dissipative
force on the moving mirrors and show that it is related to the total radiated
energy as predicted by energy conservation.Comment: 17 pages, 1 figure, published in Physical Review
QED vacuum between an unusual pair of plates
We consider the photon field between an unusual configuration of infinite
parallel plates: a perfectly conducting plate and an
infinitely permeable one . After quantizing the vector potential
in the Coulomb gauge, we obtain explicit expressions for the vacuum expectation
values of field operators of the form and . These field correlators allow us to reobtain the Casimir
effect for this set up and to discuss the light velocity shift caused by the
presence of plates (Scharnhorst effect \cite{Scharnhorst,Barton,BarScharn}) for
both scalar and spinor QED.Comment: Latex, 16 pages, no figure
Radiative Corrections to the Casimir Energy
The lowest radiative correction to the Casimir energy density between two
parallel plates is calculated using effective field theory. Since the
correlators of the electromagnetic field diverge near the plates, the
regularized energy density is also divergent. However, the regularized integral
of the energy density is finite and varies with the plate separation L as
1/L^7. This apparently paradoxical situation is analyzed in an equivalent, but
more transparent theory of a massless scalar field in 1+1 dimensions confined
to a line element of length L and satisfying Dirichlet boundary conditions.Comment: 7 pages, Late
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