7,362 research outputs found
Enhanced conversion efficiency for harmonic generation with double resonance
Conversion efficiency for cw harmonic generation is calculated for the situation in which both fundamental and harmonic waves are resonant. Compared with the situation of a singly resonant cavity at the fundamental, the doubly resonant geometry can lead to an increase of the effective nonlinear coefficient. High conversion efficiency can thus be achieved with nonlinear crystals of relatively low nonlinear coefficient. and with modest pump power for the fundamental input
Spin correlated interferometry for polarized and unpolarized photons on a beam splitter
Spin interferometry of the 4th order for independent polarized as well as
unpolarized photons arriving simultaneously at a beam splitter and exhibiting
spin correlation while leaving it, is formulated and discussed in the quantum
approach. Beam splitter is recognized as a source of genuine singlet photon
states. Also, typical nonclassical beating between photons taking part in the
interference of the 4th order is given a polarization dependent explanation.Comment: RevTeX, 19 pages, 1 ps figure, author web page at
http://m3k.grad.hr/pavici
85% efficiency for cw frequency doubling from 1.08 to 0.54 μm
Conversion efficiency of 85% has been achieved in cw second-harmonic generation from 1.08 to 0.54 μm with a potassium titanyl phosphate crystal inside an external ring cavity. An absolute comparison between the experimental data and a simple theory is made and shows good agreement
Spheres and Prolate and Oblate Ellipsoids from an Analytical Solution of Spontaneous Curvature Fluid Membrane Model
An analytic solution for Helfrich spontaneous curvature membrane model (H.
Naito, M.Okuda and Ou-Yang Zhong-Can, Phys. Rev. E {\bf 48}, 2304 (1993); {\bf
54}, 2816 (1996)), which has a conspicuous feature of representing the circular
biconcave shape, is studied. Results show that the solution in fact describes a
family of shapes, which can be classified as: i) the flat plane (trivial case),
ii) the sphere, iii) the prolate ellipsoid, iv) the capped cylinder, v) the
oblate ellipsoid, vi) the circular biconcave shape, vii) the self-intersecting
inverted circular biconcave shape, and viii) the self-intersecting nodoidlike
cylinder. Among the closed shapes (ii)-(vii), a circular biconcave shape is the
one with the minimum of local curvature energy.Comment: 11 pages, 11 figures. Phys. Rev. E (to appear in Sept. 1999
Mode-Locked Two-Photon States
The concept of mode locking in laser is applied to a two-photon state with
frequency entanglement. Cavity enhanced parametric down-conversion is found to
produce exactly such a state. The mode-locked two-photon state exhibits a
comb-like correlation function. An unbalanced Hong-Ou-Mandel type
interferometer is used to measure the correlation function. A revival of the
typical interference dip is observed. We will discuss schemes for engineering
of quantum states in time domain.Comment: 4 pages, 5 figure
Large deformation of spherical vesicle studied by perturbation theory and Surface evolver
With tangent angle perturbation approach the axial symmetry deformation of a
spherical vesicle in large under the pressure changes is studied by the
elasticity theory of Helfrich spontaneous curvature model.Three main results in
axial symmetry shape: biconcave shape, peanut shape, and one type of myelin are
obtained. These axial symmetry morphology deformations are in agreement with
those observed in lipsome experiments by dark-field light microscopy [Hotani,
J. Mol. Biol. 178, (1984) 113] and in the red blood cell with two thin
filaments (myelin) observed in living state (see, Bessis, Living Blood Cells
and Their Ultrastructure, Springer-Verlag, 1973). Furthermore, the biconcave
shape and peanut shape can be simulated with the help of a powerful software,
Surface Evolver [Brakke, Exp. Math. 1, 141 (1992) 141], in which the
spontaneous curvature can be easy taken into account.Comment: 16 pages, 6 EPS figures and 2 PS figure
Patients attitudes to vaginal examination and use of chaperones at a public hospital in South Africa
Background: Obstetrics and gynecology units in public hospitals in South Africa (SA) are often overloaded with patients. Most physical examinations/consultations in these units involve vaginal examination (VE) and often because of the rapid turnover of patients the pelvic examination may be performed hurriedly without due consideration being given to the psychosocial aspects of such procedures.Objective: This study surveyed the attitudes of patients to VE and the use of chaperones.Methods: A descriptive cross.sectional survey of patients attending obstetrics and gynecology clinics at a public hospital in SA was carried out. A structured questionnaire was used to collect sociodemographic data such as age, ethnic group, gravidity, feelings toward VE, and preferences about the gender of the examining doctor, as well as the presence of a chaperone.Results: Most women (68%) were aged between 20 and 35 years. The respondents stated that the most intimate examination was VE in 48.3% and abdominal in 25% of cases; 19.0% and 1.5% of respondents felt that breast and rectal examinations, respectively, was the most intimate. On the response to the statement gthere is no need for chaperone during VE;h 54% of the participants were in support of chaperone while 45.1% were against chaperone. Women aged 20.35 years, preferred a nurse as their chaperone; younger women, aged .19 years preferred their mother as a chaperone.Conclusion: In an SA public hospital, women are more likely to regard VE as the most intimate examination. Women are equivocal on the use of a chaperone and if it was necessary; nurses are their preferred choice except for teenagers, who preferred their mothers.Key words: Intimate examinations, patient.physician relationship, use of chaperone, vaginal examination
A model for the force stretching double-stranded chain molecules
We modify and extend the recently developed statistical mechanical model for
predicting the thermodynamic properties of chain molecules having noncovalent
double-stranded conformations, as in RNA or ssDNA, and sheets in
protein, by including the constant force stretching at one end of molecules as
in a typical single-molecule experiment. The conformations of double-stranded
regions of the chain are calculated based on polymer graph-theoretic approach
[S-J. Chen and K. A. Dill, J. Chem. Phys. {\bf109}, 4602(1998)], while the
unpaired single-stranded regions are treated as self-avoiding walks. Sequence
dependence and excluded volume interaction are taken into account explicitly.
Two classes of conformations, hairpin and RNA secondary structure are explored.
For the hairpin conformations, all possible end-to-end distances corresponding
to the different types of double-stranded regions are enumerated exactly. For
the RNA secondary structure conformations, a new recursive formula
incorporating the secondary structure and end-to-end distribution has been
derived. Using the model, we investigate the extension-force curves, contact
and population distributions and re-entering phenomena, respectively. we find
that the force stretching homogeneous chains of hairpin and secondary structure
conformations are very different: the unfolding of hairpins is two-state, while
unfolding the latter is one-state. In addition, re-entering transitions only
present in hairpin conformations, but are not observed in secondary structure
conformations.Comment: 19 pages, 28 figure
Reversible Embedding to Covers Full of Boundaries
In reversible data embedding, to avoid overflow and underflow problem, before
data embedding, boundary pixels are recorded as side information, which may be
losslessly compressed. The existing algorithms often assume that a natural
image has little boundary pixels so that the size of side information is small.
Accordingly, a relatively high pure payload could be achieved. However, there
actually may exist a lot of boundary pixels in a natural image, implying that,
the size of side information could be very large. Therefore, when to directly
use the existing algorithms, the pure embedding capacity may be not sufficient.
In order to address this problem, in this paper, we present a new and efficient
framework to reversible data embedding in images that have lots of boundary
pixels. The core idea is to losslessly preprocess boundary pixels so that it
can significantly reduce the side information. Experimental results have shown
the superiority and applicability of our work
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