713 research outputs found
Equation of State for Parallel Rigid Spherocylinders
The pair distribution function of monodisperse rigid spherocylinders is
calculated by Shinomoto's method, which was originally proposed for hard
spheres. The equation of state is derived by two different routes: Shinomoto's
original route, in which a hard wall is introduced to estimate the pressure
exerted on it, and the virial route. The pressure from Shinomoto's original
route is valid only when the length-to-width ratio is less than or equal to
0.25 (i.e., when the spherocylinders are nearly spherical). The virial equation
of state is shown to agree very well with the results of numerical simulations
of spherocylinders with length-to-width ratio greater than or equal to 2
On the Relation between Solar Activity and Clear-Sky Terrestrial Irradiance
The Mauna Loa Observatory record of direct-beam solar irradiance measurements
for the years 1958-2010 is analysed to investigate the variation of clear-sky
terrestrial insolation with solar activity over more than four solar cycles.
The raw irradiance data exhibit a marked seasonal cycle, extended periods of
lower irradiance due to emissions of volcanic aerosols, and a long-term
decrease in atmospheric transmission independent of solar activity. After
correcting for these effects, it is found that clear-sky terrestrial irradiance
typically varies by about 0.2 +/- 0.1% over the course of the solar cycle, a
change of the same order of magnitude as the variations of the total solar
irradiance above the atmosphere. An investigation of changes in the clear-sky
atmospheric transmission fails to find a significant trend with sunspot number.
Hence there is no evidence for a yet unknown effect amplifying variations of
clear-sky irradiance with solar activity.Comment: 16 pages, 7 figures, in press at Solar Physics; minor changes to the
text to match final published versio
Existence and uniqueness for Legendre curves
We give a moving frame of a Legendre curve (or, a frontal) in the unite tangent bundle and define a pair of smooth functions of a Legendre curve like as the curvature of a regular plane curve. The existence and uniqueness for Legendre curves are holded like as regular plane curves. It is quite useful to analyse the Legendre curves. As applications, we consider contact between Legendre curves and the arc-length parameter of Legendre immersions in the unite tangent bundle.
Subcritical and supercritical granular flow around an obstacle on a rough inclined plane
A blunt obstacle in the path of a rapid granular avalanche generates a bow shock (a jump in the avalanche thickness and velocity), a region of static grains upstream of the obstacle, and a grain-free region downstream. Here, it is shown that this interaction is qualitatively altered if the incline on which the avalanche is flowing is changed from smooth to rough. On a rough incline, the friction between the grains and the incline depends on the flow thickness and speed, which allows both rapid (supercritical) and slow (subcritical) steady uniform avalanches. For supercritical experimental flows, the material is diverted around a blunt obstacle by the formation of a bow shock and a static dead zone upstream of the obstacle. Downslope, a grain-free vacuum region forms, but, in contrast to flows on smooth beds, static levees form at the boundary between the vacuum region and the flow. In slower, subcritical, flows the flow is diverted smoothly around the dead zone and the obstacle without forming a bow shock. After the avalanche stops, signatures of the dead zone, levees and (in subcritical flows) a deeper region upslope of the obstacle are frozen into the deposit. To capture this behaviour, numerical simulations are performed with a depth-averaged avalanche model that includes frictional hysteresis and depth-averaged viscous terms, which are needed to accurately model the flowing and deposited regions. These results may be directly relevant to geophysical mass flows and snow avalanches, which flow over rough terrain and may impact barriers or other infrastructure
Depth-Resolved Composition and Electronic Structure of Buried Layers and Interfaces in a LaNiO/SrTiO Superlattice from Soft- and Hard- X-ray Standing-Wave Angle-Resolved Photoemission
LaNiO (LNO) is an intriguing member of the rare-earth nickelates in
exhibiting a metal-insulator transition for a critical film thickness of about
4 unit cells [Son et al., Appl. Phys. Lett. 96, 062114 (2010)]; however, such
thin films also show a transition to a metallic state in superlattices with
SrTiO (STO) [Son et al., Appl. Phys. Lett. 97, 202109 (2010)]. In order to
better understand this transition, we have studied a strained LNO/STO
superlattice with 10 repeats of [4 unit-cell LNO/3 unit-cell STO] grown on an
(LaAlO)(SrAlTaO) substrate using soft x-ray
standing-wave-excited angle-resolved photoemission (SWARPES), together with
soft- and hard- x-ray photoemission measurements of core levels and
densities-of-states valence spectra. The experimental results are compared with
state-of-the-art density functional theory (DFT) calculations of band
structures and densities of states. Using core-level rocking curves and x-ray
optical modeling to assess the position of the standing wave, SWARPES
measurements are carried out for various incidence angles and used to determine
interface-specific changes in momentum-resolved electronic structure. We
further show that the momentum-resolved behavior of the Ni 3d eg and t2g states
near the Fermi level, as well as those at the bottom of the valence bands, is
very similar to recently published SWARPES results for a related
LaSrMnO/SrTiO superlattice that was studied using the
same technique (Gray et al., Europhysics Letters 104, 17004 (2013)), which
further validates this experimental approach and our conclusions. Our
conclusions are also supported in several ways by comparison to DFT
calculations for the parent materials and the superlattice, including
layer-resolved density-of-states results
Dynamics of the Tippe Top via Routhian Reduction
We consider a tippe top modeled as an eccentric sphere, spinning on a
horizontal table and subject to a sliding friction. Ignoring translational
effects, we show that the system is reducible using a Routhian reduction
technique. The reduced system is a two dimensional system of second order
differential equations, that allows an elegant and compact way to retrieve the
classification of tippe tops in six groups as proposed in [1] according to the
existence and stability type of the steady states.Comment: 16 pages, 7 figures, added reference. Typos corrected and a forgotten
term in de linearized system is adde
Backreacted T-folds and non-geometric regions in configuration space
We provide the backreaction of the T-fold doubly T-dual to a background with
NSNS three-form flux on a three-torus. We extend the backreacted T-fold to
include cases with a flux localized in one out of three directions. We analyze
the resulting monodromy domain walls and vortices. In these backgrounds, we
give an analysis of the action of T-duality on observables like charges and
Wilson surfaces. We analyze arguments for the existence of regions in the
configuration space of second quantized string theory that cannot be reduced to
geometry. Finally, by allowing for space-dependent moduli, we find a
supergravity solution which is a T-fold with hyperbolic monodromies.Comment: 25 pages, 4 figures; v2: minor changes, reference adde
Neutron scattering and molecular correlations in a supercooled liquid
We show that the intermediate scattering function for neutron
scattering (ns) can be expanded naturely with respect to a set of molecular
correlation functions that give a complete description of the translational and
orientational two-point correlations in the liquid. The general properties of
this expansion are discussed with special focus on the -dependence and hints
for a (partial) determination of the molecular correlation functions from
neutron scattering results are given. The resulting representation of the
static structure factor is studied in detail for a model system using
data from a molecular dynamics simulation of a supercooled liquid of rigid
diatomic molecules. The comparison between the exact result for and
different approximations that result from a truncation of the series
representation demonstrates its good convergence for the given model system. On
the other hand it shows explicitly that the coupling between translational
(TDOF) and orientational degrees of freedom (ODOF) of each molecule and
rotational motion of different molecules can not be neglected in the
supercooled regime.Further we report the existence of a prepeak in the
ns-static structure factor of the examined fragile glassformer, demonstrating
that prepeaks can occur even in the most simple molecular liquids. Besides
examining the dependence of the prepeak on the scattering length and the
temperature we use the expansion of into molecular correlation
functions to point out intermediate range orientational order as its principle
origin.Comment: 13 pages, 7 figure
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