890 research outputs found
EP-1545: Dosimetric impact of target separation in craniocaudal direction with TomoDirect Dynamic Jaw
Correlation Time-of-flight Spectrometry of Ultracold Neutrons
The fearures of the correlation method used in time-of-flight spectrometry of
ultracold neutrons are analyzed. The time-of-flight spectrometer for the energy
range of ultracold neutrons is described, and results of its testing by
measuring spectra of neutrons passing through interference filters are
presented.Comment: 16 pages, 5 figure
Cost-effectiveness of influenza immunization in adult cancer patients in Taiwan
AbstractThe aim of this study was to investigate the efficacy of the influenza vaccine among cancer patients in Taiwan. We determined the effect of immunization on the following outcomes of disease: hospitalizations, emergency department visits, hospital out-patient visits, physician office visits, and deaths. Cost-effectiveness was analysed from the perspectives of the healthcare system and society. A decision tree was used, with estimates of disease burden and costs based on data from published and unpublished sources. The model followed 34 112 cancer patients aged 20–64 years who were registered by the Taiwan National Cancer Registry in 2002. An influenza immunization programme for the cancer population would prevent 2555 cases of all types of influenza infection, 660 of which would be serious cases involving hospitalization, emergency department visits and death. From the perspective of the healthcare system, the programme would cost US5.4 million. From a societal perspective, the programme would cost US22.3 million. This corresponds to savings of US6338 per case averted, from healthcare and societal perspectives, respectively, as well as 110 lives saved. Lesser disease burden, greater vaccine efficacy and lower cost of hospitalizations increased cost-effectiveness. Influenza immunization for cancer patients is cost-saving and cost-effective from a healthcare and societal perspective in Taiwan. We highly recommend annual influenza vaccinations for this patient group
Unified description of ballistic and diffusive carrier transport in semiconductor structures
A unified theoretical description of ballistic and diffusive carrier
transport in parallel-plane semiconductor structures is developed within the
semiclassical model. The approach is based on the introduction of a
thermo-ballistic current consisting of carriers which move ballistically in the
electric field provided by the band edge potential, and are thermalized at
certain randomly distributed equilibration points by coupling to the background
of impurity atoms and carriers in equilibrium. The sum of the thermo-ballistic
and background currents is conserved, and is identified with the physical
current. The current-voltage characteristic for nondegenerate systems and the
zero-bias conductance for degenerate systems are expressed in terms of a
reduced resistance. For arbitrary mean free path and arbitrary shape of the
band edge potential profile, this quantity is determined from the solution of
an integral equation, which also provides the quasi-Fermi level and the
thermo-ballistic current. To illustrate the formalism, a number of simple
examples are considered explicitly. The present work is compared with previous
attempts towards a unified description of ballistic and diffusive transport.Comment: 23 pages, 10 figures, REVTEX
On the application of radio frequency voltages to ion traps via helical resonators
Ions confined using a Paul trap require a stable, high voltage and low noise
radio frequency (RF) potential. We present a guide for the design and
construction of a helical coil resonator for a desired frequency that maximises
the quality factor for a set of experimental constraints. We provide an
in-depth analysis of the system formed from a shielded helical coil and an ion
trap by treating the system as a lumped element model. This allows us to
predict the resonant frequency and quality factor in terms of the physical
parameters of the resonator and the properties of the ion trap. We also compare
theoretical predictions with experimental data for different resonators, and
predict the voltage applied to the ion trap as a function of the Q-factor,
input power and the properties of the resonant circuit
Relativistic Structure of the Deuteron: 1.Electro-disintegration and y-scaling
Realistic solutions of the spinor-spinor Bethe-Salpeter equation for the
deuteron with realistic interaction kernel including the exchange of pi, sigma,
omega, rho, eta and delta mesons, are used to systematically investigate
relativistic effects in inclusive quasi-elastic electron-deuteron scattering
within the relativistic impulse approximation. Relativistic y-scaling is
considered by generalising the non relativistic scaling function to the
relativistic case, and it is shown that y-scaling does occur in the usual
relativistic scaling variable resulting from the energy conservation in the
instant form of dynamics. The present approach of y-scaling is fully covariant,
with the deuteron being described by eight components, viz. the 3S_1^{++},
3S_1^{--}, 3D_1^{++}, 3D_1^{--}, 3P_1^{+-}, 3P_1^{-+}, 1P_1^{+-}, 1P_1^{-+}
waves. It is demonstrated that if the negative relative energy states 1P_1,
3P_1 are disregarded, the concept of covariant momentum distributions N(p_0,p),
with p_0=M_D/2-\sqrt{p^2+m^2}, can be introduced, and that calculations of
lectro-disintegration cross section in terms of these distributions agree
within few percents with the exact calculations which include the 1P_1, 3P_1
states, provided the nucleon three momentum |p|\<= 1 GeV/c; in this momentum
range, the asymptotic relativistic scaling function is shown to coincide with
the longitudinal covariant momentum distribution.Comment: 32 LaTeX pages, 18 eps-figures. Final version to appear in Phys. Rev.
Quantum Maxwell-Bloch equations for spatially inhomogeneous semiconductor lasers
We present quantum Maxwell-Bloch equations (QMBE) for spatially inhomogeneous
semiconductor laser devices. The QMBE are derived from fully quantum mechanical
operator dynamics describing the interaction of the light field with the
quantum states of the electrons and the holes near the band gap. By taking into
account field-field correlations and field-dipole correlations, the QMBE
include quantum noise effects which cause spontaneous emission and amplified
spontaneous emission. In particular, the source of spontaneous emission is
obtained by factorizing the dipole-dipole correlations into a product of
electron and hole densities. The QMBE are formulated for general devices, for
edge emitting lasers and for vertical cavity surface emitting lasers, providing
a starting point for the detailed analysis of spatial coherence in the near
field and far field patterns of such laser diodes. Analytical expressions are
given for the spectra of gain and spontaneous emission described by the QMBE.
These results are applied to the case of a broad area laser, for which the
frequency and carrier density dependent spontaneous emission factor beta and
the evolution of the far field pattern near threshold are derived.Comment: 22 pages RevTex and 7 figures, submitted to Phys.Rev.A, revisions in
abstract and in the discussion of temporal coherenc
Multifractality of Hamiltonians with power-law transfer terms
Finite-size effects in the generalized fractal dimensions are
investigated numerically. We concentrate on a one-dimensional disordered model
with long-range random hopping amplitudes in both the strong- and the
weak-coupling regime. At the macroscopic limit, a linear dependence of on
is found in both regimes for values of q \alt 4g^{-1}, where is the
coupling constant of the model.Comment: RevTex4, 5 two-column pages, 5 .eps figures, to be published in Phys.
Rev.
Superradiance of low density Frenkel excitons in a crystal slab of three-level atoms: Quantum interference effect
We systematically study the fluorescence of low density Frenkel excitons in a
crystal slab containing V-type three-level atoms. Based on symmetric
quasi-spin realization of SU(3) in large limit, the two-mode exciton
operators are invoked to depict various collective excitations of the
collection of these V-type atoms starting from their ground state. By making
use of the rotating wave approximation, the light intensity of radiation for
the single lattice layer is investigated in detail. As a quantum coherence
effect, the quantum beat phenomenon is discussed in detail for different
initial excitonic states. We also test the above results analytically without
the consideration of the rotating wave approximation and the self-interaction
of radiance field is also included.Comment: 18pages, 17 figures. Resubmit to Phys. Rev.
Effect of chemical composition on luminescence of thiol-stabilized CdTe nanocrystals
Judicious selection of the amount of surfactant during synthesis enables a drastic increase in the photoluminescence efficiency of aqueous CdTe nanocrystals (NCs) stabilized by thioglycolic acid (TGA). Elemental determination of the NCs was undertaken to identify the origin of this effect. The molar ratio of (Te + S) to Cd approached unity when the optimum amount of TGA was used during synthesis, whereas the number of S atoms originating from TGA molecules in one NC (2.6 nm of diameter) remained unchanged at 90 ± 3. This indicates that the core lattice composition at the beginning of synthesis, rather than the surface conditions, affects the photoluminescence efficiency of the NCs even after prolonged refluxing
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