6,317 research outputs found
Reciprocal transmittances and reflectances: An elementary proof
We present an elementary proof concerning reciprocal transmittances and
reflectances. The proof is direct, simple, and valid for the diverse objects
that can be absorptive and induce diffraction and scattering, as long as the
objects respond linearly and locally to electromagnetic waves. The proof
enables students who understand the basics of classical electromagnetics to
grasp the physical basis of reciprocal optical responses. In addition, we show
an example to demonstrate reciprocal response numerically and experimentally.Comment: 6 pages, 5 figures. RevTEX4. Improved wording. Physics Educatio
Spin and orbital excitation spectrum in the Kugel-Khomskii model
We discuss spin and orbital ordering in the twofold orbital degenerate
superexchange model in three dimensions relevant to perovskite transition metal
oxides. We focus on the particular point on the classical phase diagram where
orbital degeneracy is lifted by quantum effects exclusively. Dispersion and
damping of the spin and orbital excitations are calculated at this point taking
into account their mutual interaction. Interaction corrections to the
mean-field order parameters are found to be small. We conclude that
quasi-one-dimensional Neel spin order accompanied by the uniform
d_{3z^2-r^2}-type orbital ordering is stable against quantum fluctuations.Comment: 4 pages with 3 PS figures, 1 table, RevTeX, accepted to Phys. Rev. B.
Rapid Communicatio
Applications of the calculus of variations to aircraft performance
Variational calculus used to describe optimum aircraft flight trajectorie
Locomotive and reptation motion induced by internal force and friction
We propose a simple mechanical model of locomotion induced by internal force
and friction. We first construct a system of two elements as an analog of the
bipedal motion. The internal force does not induce a directional motion by
itself because of the action-reaction law, but a directional motion becomes
possible by the control of the frictional force. The efficiency of these model
systems is studied using an analogy to the heat engine. As a modified version
of the two-elements model, we construct a model which exhibits a bipedal motion
similar to kinesin's motion of molecular motor. Next, we propose a linear chain
model and a ladder model as an extension of the original two-element model,. We
find a transition from a straight to a snake-like motion in a ladder model by
changing the strength of the internal force.Comment: 10 pages, 7 figur
The frequency and validity of self-reported diagnosis of Parkinson's Disease in the UK elderly: MRC CFAS cohort
Background: Estimates of the incidence and prevalence of chronic diseases can be made using established cohort studies but these estimates may have lower reliability if based purely on self-reported diagnosis.Methods: The MRC Cognitive Function & Ageing Study ( MRC CFAS) has collected longitudinal data from a population-based random sample of 13004 individuals over the age of 65 years from 5 centres within the UK. Participants were asked at baseline and after a two-year follow-up whether they had received a diagnosis of Parkinson's disease. Our aim was to make estimates of the incidence and prevalence of PD using self-reporting, and then investigate the validity of self-reported diagnosis using other data sources where available, namely death certification and neuropathological examination.Results: The self-reported prevalence of Parkinson's disease ( PD) amongst these individuals increases with age from 0.7% (95% CI 0.5 - 0.9) for 65 - 75, 1.4% ( 95% CI 1.0 - 1.7) for 75 - 85, and 1.6% ( 95% CI 1.0 - 2.3) for 85+ age groups respectively. The overall incidence of self reported PD in this cohort was 200/100,000 per year ( 95% CI 144 - 278). Only 40% of the deceased individuals reporting prevalent PD and 35% of those reporting incident PD had diagnoses of PD recorded on their death certificates. Neuropathological examination of individuals reporting PD also showed typical PD changes in only 40%, with the remainder showing basal ganglia pathologies causing parkinsonism rather than true PD pathology.Conclusion: Self-reporting of PD status may be used as a screening tool to identify patients for epidemiological study, but inevitably identifies a heterogeneous group of movement disorders patients. Within this group, age, male sex, a family history of PD and reduced cigarette smoking appear to act as independent risk factors for self-reported PD
Strings in five-dimensional anti-de Sitter space with a symmetry
The equation of motion of an extended object in spacetime reduces to an
ordinary differential equation in the presence of symmetry. By properly
defining of the symmetry with notion of cohomogeneity, we discuss the method
for classifying all these extended objects. We carry out the classification for
the strings in the five-dimensional anti-de Sitter space by the effective use
of the local isomorphism between \SO(4,2) and \SU(2,2). We present a
general method for solving the trajectory of the Nambu-Goto string and apply to
a case obtained by the classification, thereby find a new solution which has
properties unique to odd-dimensional anti-de Sitter spaces. The geometry of the
solution is analized and found to be a timelike helicoid-like surface
Suppression of growth by multiplicative white noise in a parametric resonant system
The author studied the growth of the amplitude in a Mathieu-like equation
with multiplicative white noise. The approximate value of the exponent at the
extremum on parametric resonance regions was obtained theoretically by
introducing the width of time interval, and the exponents were calculated
numerically by solving the stochastic differential equations by a symplectic
numerical method. The Mathieu-like equation contains a parameter that
is determined by the intensity of noise and the strength of the coupling
between the variable and the noise. The value of was restricted not to
be negative without loss of generality. It was shown that the exponent
decreases with , reaches a minimum and increases after that. It was
also found that the exponent as a function of has only one minimum at
on parametric resonance regions of . This minimum
value is obtained theoretically and numerically. The existence of the minimum
at indicates the suppression of the growth by multiplicative
white noise.Comment: The title and the description in the manuscript are change
Theoretical framework of entangled-photon generation from biexcitons in nano-to-bulk crossover regime with planar geometry
We have constructed a theoretical framework of the biexciton-resonant
hyperparametric scattering for the pursuit of high-power and high-quality
generation of entangled photon pairs. Our framework is applicable to
nano-to-bulk crossover regime where the center-of-mass motion of excitons and
biexcitons is confined. Material surroundings and the polarization correlation
of generated photons can be considered. We have analyzed the entangled-photon
generation from CuCl film, by which ultraviolet entangled-photon pairs are
generated, and from dielectric microcavity embedding a CuCl layer. We have
revealed that in the nano-to-bulk crossover regime we generally get a high
performance from the viewpoint of statistical accuracy, and the generation
efficiency can be enhanced by the optical cavity with maintaining the high
performance. The nano-to-bulk crossover regime has a variety of degrees of
freedom to tune the entangled-photon generation, and the scattering spectra
explicitly reflect quantized exciton-photon coupled modes in the finite
structure.Comment: 18 pages, 10 figure
Phase Transition in Perovskite Manganites with Orbital Degree of Freedom
Roles of orbital degree of freedom of Mn ions in phase transition as a
function of temperature and hole concentration in perovskite manganites are
studied. It is shown that the orbital order-disorder transition is of the first
order in the wide region of hole concentration and the Nel
temperature for the anisotropic spin ordering, such as the layer-type
antiferromagnetic one, is lower than the orbital ordering temperature due to
the anisotropy in the orbital space. The calculated results of the temperature
dependence of the spin and orbital order parameters explain a variety of the
experiments observed in manganites.Comment: 10 pages, 5 figure
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