11,915 research outputs found
Vibrational assignments and line shapes in inelastic tunnelling spectroscopy: H on Cu(100)
We have carried out a computational study of the inelastic electron tunneling
spectrum (IETS) of the two vibrational modes of a single hydrogen atom on a
Cu(100) surface in a scanning tunneling microscopy (STM) junction. This study
addresses key issues about vibrational assignment and line shape of observed
peaks in IETS within the framework of density functional theory calculations
and the Lorente-Persson theory for STM-IETS. We argue that the observation of
only a single, broad peak in the STM-IETS [L.J. Lauhon and W. Ho, Phys. Rev.
Lett. 85, 4566 (2000)] is not caused by any symmetry restrictions or any
cancellation between inelastic and elastic vibrational contributions for one of
the two modes but is due to strongly overlapping superposition of the
contributions from the two modes caused by the rather large instrumental
broadening and the narrow vibrational energy separation between the modes. In
particular, we find that this broadening and the large asymmetry of the
vibrational line shapes gives rise to substantial apparent vibrational energy
shifts of the two modes and decrease their apparent energy separation
The luminosity function of the brightest galaxies in the IRAS survey
Results from a study of the far infrared properties of the brightest galaxies in the IRAS survey are described. There is a correlation between the infrared luminosity and the infrared to optical luminosity ratio and between the infrared luminosity and the far infrared color temperature in these galaxies. The infrared bright galaxies represent a significant component of extragalactic objects in the local universe, being comparable in space density to the Seyferts, optically identified starburst galaxies, and more numerous than quasars at the same bolometric luminosity. The far infrared luminosity in the local universe is approximately 25% of the starlight output in the same volume
Influence of seating styles on head and pelvic vertical movement symmetry in horses ridden at trot
Detailed knowledge of how a rider’s seating style and riding on a circle influences the movement symmetry of the horse’s head and pelvis may aid rider and trainer in an early recognition of low grade lameness. Such knowledge is also important during both subjective and objective lameness evaluations in the ridden horse in a clinical setting. In this study, inertial sensors were used to assess how different rider seating styles may influence head and pelvic movement symmetry in horses trotting in a straight line and on the circle in both directions. A total of 26 horses were subjected to 15 different conditions at trot: three unridden conditions and 12 ridden conditions where the rider performed three different seating styles (rising trot, sitting trot and two point seat). Rising trot induced systematic changes in movement symmetry of the horses. The most prominent effect was decreased pelvic rise that occurred as the rider was actively rising up in the stirrups, thus creating a downward momentum counteracting the horses push off. This mimics a push off lameness in the hindlimb that is in stance when the rider sits down in the saddle during the rising trot. On the circle, the asymmetries induced by rising trot on the correct diagonal counteracted the circle induced asymmetries, rendering the horse more symmetrical. This finding offers an explanation to the equestrian tradition of rising on the ‘correct diagonal.’ In horses with small pre-existing movement asymmetries, the asymmetry induced by rising trot, as well as the circular track, attenuated or reduced the horse’s baseline asymmetry, depending on the sitting diagonal and direction on the circle. A push off hindlimb lameness would be expected to increase when the rider sits during the lame hindlimb stance whereas an impact hindlimb lameness would be expected to decrease. These findings suggest that the rising trot may be useful for identifying the type of lameness during subjective lameness assessment of hindlimb lameness. This theory needs to be studied further in clinically lame horses
Photon generation in an electromagnetic cavity with a time-dependent boundary
We report the observation of photon generation in a microwave cavity with a
time-dependent boundary condition. Our system is a microfabricated quarter-wave
coplanar waveguide cavity. The electrical length of the cavity is varied using
the tunable inductance of a superconducting quantum interference device. It is
measured in the quantum regime, where the temperature is significantly less
than the resonance frequency (~ 5 GHz). When the length is modulated at
approximately twice the static resonance frequency, spontaneous oscillations of
the cavity field are observed. Time-resolved measurements of the dynamical
state of the cavity show multiple stable states. The behavior is well described
by theory. Connections to the dynamical Casimir effect are discussed.Comment: 5 pages, 3 Figure
Dynamical transitions and sliding friction in the two-dimensional Frenkel-Kontorova model
The nonlinear response of an adsorbed layer on a periodic substrate to an
external force is studied via a two dimensional uniaxial Frenkel-Kontorova
model. The nonequlibrium properties of the model are simulated by Brownian
molecular dynamics. Dynamical phase transitions between pinned solid, sliding
commensurate and incommensurate solids and hysteresis effects are found that
are qualitatively similar to the results for a Lennard-Jones model, thus
demonstrating the universal nature of these features.Comment: 11 pages, 12 figures, to appear in Phys. Rev.
On the distribution of sequences of the form
We study the distribution of sequences of the form ,
where is some increasing sequence of integers. In
particular, we study the Lebesgue measure and find bounds on the Hausdorff
dimension of the set of points which are well approximated
by points in the sequence . The bounds on Hausdorff
dimension are valid for almost every in the support of a measure of
positive Fourier dimension. When the required rate of approximation is very
good or if our sequence is sufficiently rapidly growing, our dimension bounds
are sharp. If the measure of positive Fourier dimension is itself Lebesgue
measure, our measure bounds are also sharp for a very large class of sequences.
We also give an application to inhomogeneous Littlewood type problems.Comment: 15 pages. Niclas Technau pointed out to us that Theorems 1 and 2 in
the original version were in fact consequences of arXiv:2307.14871 . In this
revised version, we have strengthened both theorems to cover a wider class of
sequence
Nitrogen hydrides in interstellar gas: Herschel/HIFI observations towards G10.6-0.4 (W31C)
The HIFI instrument on board the Herschel Space Observatory has been used to observe interstellar nitrogen hydrides along the sight-line towards
G10.6−0.4 in order to improve our understanding of the interstellar chemistry of nitrogen. We report observations of absorption in NH N = 1 ← 0,
J = 2 ← 1 and ortho-NH_2 1_(1,1) ← 0_(0,0). We also observed ortho-NH_3 1_0 ← 0_0, and 2_0 ← 1_0, para-NH_3 2_1 ← 1_1, and searched unsuccessfully for
NH^+. All detections show emission and absorption associated directly with the hot-core source itself as well as absorption by foreground material
over a wide range of velocities. All spectra show similar, non-saturated, absorption features, which we attribute to diffuse molecular gas. Total
column densities over the velocity range 11−54 km s^(−1) are estimated. The similar profiles suggest fairly uniform abundances relative to hydrogen,
approximately 6 × 10^(−9), 3 × 10^(−9), and 3 × 10^(−9) for NH, NH_2, and NH_3, respectively. These abundances are discussed with reference to models of
gas-phase and surface chemistry
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