17,610 research outputs found
Transmission phase of a quantum dot: Testing the role of population switching
We propose a controlled experiment to clarify the physical mechanism causing
phase lapses of the amplitude for electron transmission through nanoscale
devices. Such lapses are generically observed in valleys between adjacent
Coulomb--blockade peaks. The experiment involves two quantum dots embedded in
the same arm of an Aharonov--Bohm interferometer. It offers a decisive test of
"population switching", one of the leading contenders for an explanation of the
phenomenon.Comment: 4 pages, 4 figure
Modelling human factors in perceptual multimedia quality: On the role of personality and culture
Perception of multimedia quality is shaped by a rich interplay between system, context, and human factors. While system and context factors are widely researched, few studies in this area consider human factors as sources of systematic variance. This paper presents an analysis on the influence of personality (Five-Factor Model) and cultural traits (Hofstede Model) on the perception of multimedia quality. A set of 144 video sequences (from 12 short movie excerpts) were rated by 114 participants from a cross-cultural population, producing 1232 ratings. On this data, three models are compared: a baseline model that only considers system factors; an extended model that includes personality and culture as human factors; and an optimistic model in which each participant is modeled as a random effect. An analysis shows that personality and cultural traits represent 9.3% of the variance attributable to human factors while human factors overall predict an equal or higher proportion of variance compared to system factors. In addition, the quality-enjoyment correlation varied across the movie excerpts. This suggests that human factors play an important role in perceptual multimedia quality, but further research to explore moderation effects and a broader range of human factors is warranted
Galactic Spiral Structure
We describe the structure and composition of six major stellar streams in a
population of 20 574 local stars in the New Hipparcos Reduction with known
radial velocities. We find that, once fast moving stars are excluded, almost
all stars belong to one of these streams. The results of our investigation have
lead us to re-examine the hydrogen maps of the Milky Way, from which we
identify the possibility of a symmetric two-armed spiral with half the
conventionally accepted pitch angle. We describe a model of spiral arm motions
which matches the observed velocities and composition of the six major streams,
as well as the observed velocities of the Hyades and Praesepe clusters at the
extreme of the Hyades stream. We model stellar orbits as perturbed ellipses
aligned at a focus in coordinates rotating at the rate of precession of
apocentre. Stars join a spiral arm just before apocentre, follow the arm for
more than half an orbit, and leave the arm soon after pericentre. Spiral
pattern speed equals the mean rate of precession of apocentre. Spiral arms are
shown to be stable configurations of stellar orbits, up to the formation of a
bar and/or ring. Pitch angle is directly related to the distribution of orbital
eccentricities in a given spiral galaxy. We show how spiral galaxies can evolve
to form bars and rings. We show that orbits of gas clouds are stable only in
bisymmetric spirals. We conclude that spiral galaxies evolve toward grand
design two-armed spirals. We infer from the velocity distributions that the
Milky Way evolved into this form about 9 Gyrs ago.Comment: Published in Proc Roy Soc A. A high resolution version of this file
can be downloaded from http://papers.rqgravity.net/SpiralStructure.pdf. A
simplified account with animations begins at
http://rqgravity.net/SpiralStructur
Dimensional analysis and Rutherford Scattering
Dimensional analysis, and in particular the Buckingham theorem is
widely used in fluid mechanics. In this article we obtain an expression for the
impact parameter from Buckingham's theorem and we compare our result with
Rutherford's original discovery found in the early twentieth century
From the Birkhoff-Gustavson normalization to the Bertrand-Darboux integrability condition
The Bertrand-Darboux integrability condition for a certain class of perturbed
harmonic oscillators is studied from the viewpoint of the
Birkhoff-Gustavson(BG)-normalization: By solving an inverse problem of the
BG-normalization on computer algebra, it is shown that if the perturbed
harmonic oscillators with a homogeneous-{\it cubic} polynomial potential and
with a homogeneous-{\it quartic} polynomial potentials admit the same
BG-normalization up to degree-4 then both oscillators satisfy the
Bertrand-Darboux integrability condition.Comment: 23 pages, LaTeX (iop.sty), typos and Appendix adde
The language of Einstein spoken by optical instruments
Einstein had to learn the mathematics of Lorentz transformations in order to
complete his covariant formulation of Maxwell's equations. The mathematics of
Lorentz transformations, called the Lorentz group, continues playing its
important role in optical sciences. It is the basic mathematical language for
coherent and squeezed states. It is noted that the six-parameter Lorentz group
can be represented by two-by-two matrices. Since the beam transfer matrices in
ray optics is largely based on two-by-two matrices or matrices, the
Lorentz group is bound to be the basic language for ray optics, including
polarization optics, interferometers, lens optics, multilayer optics, and the
Poincar\'e sphere. Because the group of Lorentz transformations and ray optics
are based on the same two-by-two matrix formalism, ray optics can perform
mathematical operations which correspond to transformations in special
relativity. It is shown, in particular, that one-lens optics provides a
mathematical basis for unifying the internal space-time symmetries of massive
and massless particles in the Lorentz-covariant world.Comment: LaTex 8 pages, presented at the 10th International Conference on
Quantum Optics (Minsk, Belarus, May-June 2004), to be published in the
proceeding
Covariant Uniform Acceleration
We show that standard Relativistic Dynamics Equation F=dp/d\tau is only
partially covariant. To achieve full Lorentz covariance, we replace the
four-force F by a rank 2 antisymmetric tensor acting on the four-velocity. By
taking this tensor to be constant, we obtain a covariant definition of
uniformly accelerated motion. We compute explicit solutions for uniformly
accelerated motion which are divided into four types: null, linear, rotational,
and general. For null acceleration, the worldline is cubic in the time. Linear
acceleration covariantly extends 1D hyperbolic motion, while rotational
acceleration covariantly extends pure rotational motion.
We use Generalized Fermi-Walker transport to construct a uniformly
accelerated family of inertial frames which are instantaneously comoving to a
uniformly accelerated observer. We explain the connection between our approach
and that of Mashhoon. We show that our solutions of uniformly accelerated
motion have constant acceleration in the comoving frame. Assuming the Weak
Hypothesis of Locality, we obtain local spacetime transformations from a
uniformly accelerated frame K' to an inertial frame K. The spacetime
transformations between two uniformly accelerated frames with the same
acceleration are Lorentz. We compute the metric at an arbitrary point of a
uniformly accelerated frame.
We obtain velocity and acceleration transformations from a uniformly
accelerated system K' to an inertial frame K. We derive the general formula for
the time dilation between accelerated clocks. We obtain a formula for the
angular velocity of a uniformly accelerated object. Every rest point of K' is
uniformly accelerated, and its acceleration is a function of the observer's
acceleration and its position. We obtain an interpretation of the
Lorentz-Abraham-Dirac equation as an acceleration transformation from K' to K.Comment: 36 page
Theory of four-wave mixing of matter waves from a Bose-Einstein condensate
A recent experiment [Deng et al., Nature 398, 218(1999)] demonstrated
four-wave mixing of matter wavepackets created from a Bose-Einstein condensate.
The experiment utilized light pulses to create two high-momentum wavepackets
via Bragg diffraction from a stationary Bose-Einstein condensate. The
high-momentum components and the initial low momentum condensate interact to
form a new momentum component due to the nonlinear self-interaction of the
bosonic atoms. We develop a three-dimensional quantum mechanical description,
based on the slowly-varying-envelope approximation, for four-wave mixing in
Bose-Einstein condensates using the time-dependent Gross-Pitaevskii equation.
We apply this description to describe the experimental observations and to make
predictions. We examine the role of phase-modulation, momentum and energy
conservation (i.e., phase-matching), and particle number conservation in
four-wave mixing of matter waves, and develop simple models for understanding
our numerical results.Comment: 18 pages Revtex preprint form, 13 eps figure
Scaling of the electron dissipation range of solar wind turbulence
Electron scale solar wind turbulence has attracted great interest in recent
years. Clear evidences have been given from the Cluster data that turbulence is
not fully dissipated near the proton scale but continues cascading down to the
electron scales. However, the scaling of the energy spectra as well as the
nature of the plasma modes involved at those small scales are still not fully
determined. Here we survey 10 years of the Cluster search-coil magnetometer
(SCM) waveforms measured in the solar wind and perform a statistical study of
the magnetic energy spectra in the frequency range []Hz. We show that a
large fraction of the spectra exhibit clear breakpoints near the electon
gyroscale , followed by steeper power-law like spectra. We show that
the scaling below the electron breakpoint cannot be determined unambiguously
due to instrumental limitations that will be discussed in detail. We compare
our results to recent ones reported in other studies and discuss their
implication on the physical mechanisms and the theoretical modeling of energy
dissipation in the SW.Comment: 10 pages, submitte
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