2,429 research outputs found
Real time image subtraction and "exclusive or" operation using a self-pumped phase conjugate mirror
Real time "exclusive or" operation with an interferometer using a self-pumped phase conjugate mirror is reported. Also, results of image subtraction and intensity inversion are shown
Self-excited Threshold Poisson Autoregression
This paper studies theory and inference of an observation-driven model for
time series of counts. It is assumed that the observations follow a Poisson
distribution conditioned on an accompanying intensity process, which is
equipped with a two-regime structure according to the magnitude of the lagged
observations. The model remedies one of the drawbacks of the Poisson
autoregression model by allowing possibly negative correlation in the
observations. Classical Markov chain theory and Lyapunov's method are utilized
to derive the conditions under which the process has a unique invariant
probability measure and to show a strong law of large numbers of the intensity
process. Moreover the asymptotic theory of the maximum likelihood estimates of
the parameters is established. A simulation study and a real data application
are considered, where the model is applied to the number of major earthquakes
in the world
Comment on ``A new efficient method for calculating perturbative energies using functions which are not square integrable'': regularization and justification
The method recently proposed by Skala and Cizek for calculating perturbation
energies in a strict sense is ambiguous because it is expressed as a ratio of
two quantities which are separately divergent. Even though this ratio comes out
finite and gives the correct perturbation energies, the calculational process
must be regularized to be justified. We examine one possible method of
regularization and show that the proposed method gives traditional quantum
mechanics results.Comment: 6 pages in REVTeX, no figure
Factors influencing adolescent girls' decision in initiation for human papillomavirus vaccination: A cross-sectional study in Hong Kong
Background: Cervical cancer is one of the common cancers among women worldwide. Despite HPV vaccination being one of the effective preventive measures, it is not included in government vaccination programme in Hong Kong. This study aimed to assess the knowledge of and attitude towards cervical cancer prevention among Chinese adolescent girls in Hong Kong, and to identify factors influencing the initiation of HPV vaccination. Methods: This was a cross-sectional study conducted in Hong Kong during the period of October 2010 to November 2010. A self-administered questionnaire was used, with 1,416 girls from 8 secondary schools completing the questionnaire. Knowledge scores were composited and initiation of HPV vaccination was staged based on stage of change. Analyses were conducted to identify the association of initiation of HPV vaccination with participant's personal and family factors as well as their knowledge and attitude towards cervical cancer prevention. Results: The uptake rate of HPV vaccination was low (7%) with 58% respondents in pre-contemplation and contemplation stage. The survey identified a significant gap in knowledge on cervical cancer prevention. The main channels of information were from media and very few from schools or parents. However, 70% expressed their wishes to have more information on cancer prevention, and 78% stated that they were willing to change their lifestyles if they knew the ways of prevention. Multivariate analysis identified three independent significant factors for initiation of vaccination (action and intention): perceived cancer as terrifying disease, school should provide more information on cancer prevention, and comments from relatives and friends having received the vaccine. The cost of vaccination and socio-economic background were not found to be significant. Conclusions: Public education on cervical cancer needs to be well penetrated into the community for more sharing among friends and relatives. School as setting to provide source of information would facilitate uptake rate of HPV vaccine as students have expressed their wishes that school should provide more information on prevention of cancer. School and community education on cancer prevention would help adolescents to have better understanding of the seriousness of cancer. © 2014 Lee et al.; licensee BioMed Central Ltd.link_to_subscribed_fulltex
Real-Time Image Processing Using A Self-Pumped Phase Conjugate Mirror
Real-time 'exclusive or' operation obtained with an interferometer using a self-pumped phase conjugate mirror is reported. Also, results of image subtraction, intensity inversion and image differentiation are shown. Methods of extending the operation to higher order differentiation and of obtaining the Laplacian are discussed
New Eaxactly Solvable Hamiltonians: Shape Invariance and Self-Similarity
We discuss in some detail the self-similar potentials of Shabat and
Spiridonov which are reflectionless and have an infinite number of bound
states. We demonstrate that these self-similar potentials are in fact shape
invariant potentials within the formalism of supersymmetric quantum mechanics.
In particular, using a scaling ansatz for the change of parameters, we obtain a
large class of new, reflectionless, shape invariant potentials of which the
Shabat-Spiridonov ones are a special case. These new potentials can be viewed
as q-deformations of the single soliton solution corresponding to the
Rosen-Morse potential. Explicit expressions for the energy eigenvalues,
eigenfunctions and transmission coefficients for these potentials are obtained.
We show that these potentials can also be obtained numerically. Included as an
intriguing case is a shape invariant double well potential whose supersymmetric
partner potential is only a single well. Our class of exactly solvable
Hamiltonians is further enlarged by examining two new directions: (i) changes
of parameters which are different from the previously studied cases of
translation and scaling; (ii) extending the usual concept of shape invariance
in one step to a multi-step situation. These extensions can be viewed as
q-deformations of the harmonic oscillator or multi-soliton solutions
corresponding to the Rosen-Morse potential.Comment: 26 pages, plain tex, request figures by e-mai
Design and fabrication of a long-life Stirling cycle cooler for space application. Phase 3: Prototype model
A second-generation, Stirling-cycle cryocooler (cryogenic refrigerator) for space applications, with a cooling capacity of 5 watts at 65 K, was recently completed. The refrigerator, called the Prototype Model, was designed with a goal of 5 year life with no degradation in cooling performance. The free displacer and free piston of the refrigerator are driven directly by moving-magnet linear motors with the moving elements supported by active magnetic bearings. The use of clearance seals and the absence of outgassing material in the working volume of the refrigerator enable long-life operation with no deterioration in performance. Fiber-optic sensors detect the radial position of the shafts and provide a control signal for the magnetic bearings. The frequency, phase, stroke, and offset of the compressor and expander are controlled by signals from precision linear position sensors (LVDTs). The vibration generated by the compressor and expander is cancelled by an active counter balance which also uses a moving-magnet linear motor and magnetic bearings. The driving signal for the counter balance is derived from the compressor and expander position sensors which have wide bandwidth for suppression of harmonic vibrations. The efficiency of the three active members, which operate in a resonant mode, is enhanced by a magnetic spring in the expander and by gas springs in the compressor and counterbalance. The cooling was achieved with a total motor input power of 139 watts. The magnetic-bearing stiffness was significantly increased from the first-generation cooler to accommodate shuttle launch vibrations
Relativistic Effects in S-Wave Quarkonium Decay
The decay widths of S-wave quarkonia (\etc,\etb\to \gg{~~and~~}
\J,\U\to\ee) are calculated on the basis of a quasipotential approach. The
nontrivial dependence on relative quark motion of decay amplitude is taken into
consideration via quarkonium wave function. It is shown that relativistic
corrections may be large (10-50 %) and comparable with QCD corrections.Comment: 10 pages, no figure
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