26,010 research outputs found
Coherent Amplification of Optical Pulses in Metamaterials
In this paper we theoretically study propagation of steady state ultrashort
pulse in dissipative medium. We considered two cases (i) medium consists of
lossy metallic nanostructures embedded into a gain material and (ii) the gain
material is embedded directly into the nanostructures. We found the shape and
velocity of an optical pulse coupled with the polarization wave.Comment: 9 pages, 5 figures, submitted to IEEE Tran
Development and preliminary evaluation of a clinical guidance programme for the decision about prophylactic oophorectomy in women undergoing a hysterectomy
Objectives: To develop a decision analysis based and computerised clinical guidance programme
(CGP) that provides patient specific guidance on the decision whether or not to undergo a prophylactic
oophorectomy to reduce the risk of subsequent ovarian cancer and to undertake a preliminary pilot
and evaluation.
Subjects: Women who had already agreed to have a hysterectomy who otherwise had no ovarian
pathology.
Setting: Oophorectomy decision consultation at the outpatient or pre-admission clinic.
Methods: A CGP was developed with advice from gynaecologists and patient groups, incorporating
a set of Markov models within a decision analytical framework to evaluate the benefits of undergoing
a prophylactic oophorectomy or not on the basis of quality adjusted life expectancy, life expectancy,
and for varying durations of hormone replacement therapy. Sensitivity analysis and preliminary testing
of the CGP were undertaken to compare its overall performance with established guidelines and practice.
A small convenience sample of women invited to use the CGP were interviewed, the interviews
were taped and transcribed, and a thematic analysis was undertaken.
Results: The run time of the programme was 20 minutes, depending on the use of opt outs to default
values. The CGP functioned well in preliminary testing. Women were able to use the programme and
expressed overall satisfaction with it. Some had reservations about the computerised format and some
were surprised at the specificity of the guidance given.
Conclusions: A CGP can be developed for a complex healthcare decision. It can give evidence-based
health guidance which can be adjusted to account for individual risk factors and reflects a patient’s
own values and preferences concerning health outcomes. Future decision aids and support systems
need to be developed and evaluated in a way which takes account of the variation in patients’ preferences
for inclusion in the decision making process
Study of 42 and 85 GHz coupled cavity traveling-wave tubes for space use
Designs were formulated for four CW, millimeter wavelength traveling-wave tubes having high efficiency and long life. Three of these tubes, in the 42 to 44 GHz frequency region, develop power outputs of 100 to 300 watts with overall efficiencies of typically 45 percent. Another tube, which covers the frequency range of 84 to 86 GHz, provides a power output of 200 watts at 25 percent efficiency. The cathode current density in each design was 1A/sq cm. Each tube includes: metal-ceramic construction, periodic permanent magnet focusing, a two step velocity taper, an electron beam refocusing section, and a radiation cooled three-stage depressed collector. The electrical and mechanical design for each tube type is discussed in detail. The results of thermal and mechanical analyses are presented
Effect of a Spin-1/2 Impurity on the Spin-1 Antiferromagnetic Heisenberg Chain
Low-lying excited states as well as the ground state of the spin-1 antiferro-
magnetic Heisenberg chain with a spin-1/2 impurity are investigated by means of
a variational method and a method of numerical diagonalization. It is shown
that 1) the impurity spin brings about massive modes in the Haldane gap, 2)
when the the impurity-host coupling is sufficiently weak, the phenomenological
Hamiltonian used by Hagiwara {\it et al.} in the analysis of ESR experimental
results for NENP containing a small amount of spin-1/2 Cu impurities is
equivalent to a more realistic Hamiltonian, as far as the energies of the
low-lying states are concerned, 3) the results obtained by the variational
method are in semi-quantitatively good agreement with those obtained by the
numerical diagonalization.Comment: 11 pages, plain TeX (Postscript figures are included), KU-CCS-93-00
Electrotransport in metals electroluminescence in zinc telluride
(i) ELECTROTRANSPORT IN METALS
The effects of an applied electric field on diffusion in metals is
discussed. Frequently, under high current densities, and for
temperatures in the diffusion range, a directed displacement of the
diffusion species results. This mass transport is described by
the term electrotransport. The major theoretical considerations
relevant to the development of this topic are described, with particular
emphasis on derivations which have been applied to the interpretation
of experimental results. Previous experimental investigations
of electrotransport in metals are reviewed.The results of experiments on electrotransport of indium, using a
radioactive isotope technique, are presented. The investigations
are concerned with the electrotransport of the isotope In114m in
solid gold, thin gold films and thin indium films. Electrotransport
phenomena in thin films have not previously been investigated in any
detail. The results are amenable to interpretation in terms of the
interaction of electrons with an activated complex associated with
the diffusing species.(ii) ELECTROLUMINESCENCE IN ZINC TELLURIDE
This section reports on the electroluminescent properties of the
II VI semiconducting compound zinc telluride. Previous investigations
into the preparation of zinc telluride crystals and the optical,
electrical and electroluminescent properties of the material
are reviewed. The results of an experimental programme concerned
with the preparation of zinc telluride crystals and the electroluminescent
properties of devices fabricated from several forms
of the material are presented. Relatively simple contacting and
processing techniques are utilised and the electroluminescence is
primarily associated with metal :semiconductor junctions and contact
barrier regions. Particular emphasis is placed on the observation
of room- temperature electroluminescence in zinc telluride as this
has not been the subject of previous detailed investigation. The
incorporation of oxygen in the crystals results in radiative recombinations
in which temperature quenching of the emission is not pro-
nounced. This results in considerable improvement in room- tempera-
ture emission efficiencies; the associated emission is located in
the red region of the visible spectrum. Other forms of zinc
telluride investigated include nominally undoped and semi -insulating
single crystals and also polycrystalline material. The potential
of electroluminescent devices based on these various forms of zinc
telluride as room -temperature visible emitters is evaluated.
Possible mechanisms of electroluminescence are discussed
Methyl 2-amino-5-isopropyl-1,3-thiazole-4-carboxylate
The title compound, C8H12N2O2S, forms a supramolecular network based on N-HN hydrogen-bonded centrosymmetric dimers that are linked in turn by N-HO contacts
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