2,612 research outputs found
Gravitational quantum states of neutrons in a rough waveguide
A theory of gravitational quantum states of ultracold neutrons in waveguides
with absorbing/scattering walls is presented. The theory covers recent
experiments in which the ultracold neutrons were beamed between a mirror and a
rough scatterer/absorber. The analysis is based on a recently developed theory
of quantum transport along random rough walls which is modified in order to
include leaky (absorbing) interfaces and, more importantly, the low-amplitude
high-aperture roughness. The calculations are focused on a regime when the
direct transitions into the continuous spectrum above the absorption threshold
dominate the depletion of neutrons from the gravitational states and are more
efficient than the processes involving the intermediate states. The theoretical
results for the neutron count are sensitive to the correlation radius (lateral
size) of surface inhomogeneities and to the ratio of the particle energy to the
absorption threshold in a weak roughness limit. The main impediment for
observation of the higher gravitational states is the "overhang" of the
particle wave functions which can be overcome only by use scatterers with
strong roughness. In general, the strong roughness with high amplitude is
preferable if one wants just to detect the individual gravitational states,
while the strong roughness experiments with small amplitude and high aperture
are preferable for the quantitative analysis of the data. We also discuss the
ways to further improve the accuracy of calculations and to optimize the
experimental regime.Comment: 48 pages, 14 figure
Predicting the movements of permanently installed electrodes on an active landslide using time-lapse geoelectrical resistivity data only
If electrodes move during geoelectrical resistivity monitoring and their new positions are not incorporated in the inversion, then the resulting tomographic images exhibit artefacts that can obscure genuine time-lapse resistivity changes in the subsurface. The effects of electrode movements on time-lapse resistivity tomography are investigated using a simple analytical model and real data. The correspondence between the model and the data is sufficiently good to be able to predict the effects of electrode movements with reasonable accuracy. For the linear electrode arrays and 2D inversions under consideration, the data are much more sensitive to longitudinal than transverse or vertical movements. Consequently the model can be used to invert the longitudinal offsets of the electrodes from their known baseline positions using only the time-lapse ratios of the apparent resistivity data. The example datasets are taken from a permanently installed electrode array on an active lobe of a landslide. Using two sets with different levels of noise and subsurface resistivity changes, it is found that the electrode positions can be recovered to an accuracy of 4 % of the baseline electrode spacing. This is sufficient to correct the artefacts in the resistivity images, and provides for the possibility of monitoring the movement of the landslide and its internal hydraulic processes simultaneously using electrical resistivity tomography only
Mode Coupling in Quantized High Quality Films
The effect of coupling of quantized modes on transport and localization in
ultrathin films with quantum size effect (QSE) is discussed. The emphasis is on
comparison of films with Gaussian, exponential, and power-law long-range
behavior of the correlation function of surface, thickness, or bulk
fluctuations. For small-size inhomogeneities, the mode coupling is the same for
inhomogeneities of all types and the transport coefficients behave in the same
way. The mode coupling becomes extremely sensitive to the correlators for
large-size inhomogeneities leading to the drastically distinct behavior of the
transport coefficients. In high-quality films there is a noticeable difference
between the QSE patterns for films with bulk and surface inhomogeneities which
explains why the recently predicted new type of QSE with large oscillations of
the transport coefficients can be observed mostly in films with surface-driven
relaxation. In such films with surface-dominated scattering the higher modes
contribute to the transport only as a result of opening of the corresponding
mode coupling channels and appear one by one. Mode coupling also explains a
much higher transport contribution from the higher modes than it is commonly
believed. Possible correlations between the inhomogeneities from the opposite
walls provide, because of their oscillating response to the mode quantum
numbers, a unique insight into the mode coupling. The presence of
inhomogeneities of several sizes leads not to a mechanical mixture of QSE
patterns, but to the overall shifting and smoothing of the oscillations. The
results can lead to new, non-destructive ways of analysis of the buried
interfaces and to study of inhomogeneities on the scales which are inaccessible
for scanning techniques
The Effect of Random Surface Inhomogeneities on Microresonator Spectral Properties: Theory and Modeling at Millimeter Wave Range
The influence of random surface inhomogeneities on spectral properties of
open microresonators is studied both theoretically and experimentally. To solve
the equations governing the dynamics of electromagnetic fields the method of
eigen-mode separation is applied previously developed with reference to
inhomogeneous systems subject to arbitrary external static potential. We prove
theoretically that it is the gradient mechanism of wave-surface scattering
which is the highly responsible for non-dissipative loss in the resonator. The
influence of side-boundary inhomogeneities on the resonator spectrum is shown
to be described in terms of effective renormalization of mode wave numbers
jointly with azimuth indices in the characteristic equation. To study
experimentally the effect of inhomogeneities on the resonator spectrum, the
method of modeling in the millimeter wave range is applied. As a model object
we use dielectric disc resonator (DDR) fitted with external inhomogeneities
randomly arranged at its side boundary. Experimental results show good
agreement with theoretical predictions as regards the predominance of the
gradient scattering mechanism. It is shown theoretically and confirmed in the
experiment that TM oscillations in the DDR are less affected by surface
inhomogeneities than TE oscillations with the same azimuth indices. The DDR
model chosen for our study as well as characteristic equations obtained
thereupon enable one to calculate both the eigen-frequencies and the Q-factors
of resonance spectral lines to fairly good accuracy. The results of
calculations agree well with obtained experimental data.Comment: 17+ pages, 5 figure
Characterising sand and gravel deposits using electrical resistivity tomography (ERT) : case histories from England and Wales
Electrical Resistivity Tomography (ERT) is a rapidly developing geophysical imaging technique that is now widely
used to visualise subsurface geological structure, groundwater and lithological variations. It is being increasingly used
in environmental and engineering site investigations, but despite its suitability and potential benefits, ERT has yet to
be routinely applied by the minerals industry to sand and gravel deposit assessment and quarry planning. The
principal advantages of ERT for this application are that it is a cost-effective non-invasive method, which can provide
2D or 3D spatial models of the subsurface throughout the full region of interest. This complements intrusive sampling
methods, which typically provide information only at discrete locations. Provided that suitable resistivity contrasts are
present, ERT has the potential to reveal mineral and overburden thickness and quality variations within the body of
the deposit.
Here we present a number of case studies from the UK illustrating the use of 2D and 3D ERT for sand and gravel
deposit investigation in a variety of geological settings. We use these case studies to evaluate the performance of ERT,
and to illustrate good practice in the application of ERT to deposit investigation. We propose an integrated approach
to site investigation and quarry planning incorporating both conventional intrusive methods and ERT
Brittleness index of machinable dental materials and its relation to the marginal chipping factor
OBJECTIVES:
The machinability of a material can be measured with the calculation of its brittleness index (BI). It is possible that different materials with different BI could produce restorations with varied marginal integrity. The degree of marginal chipping of a milled restoration can be estimated by the calculation of the marginal chipping factor (CF). The aim of this study is to investigate any possible correlation between the BI of machinable dental materials and the CF of the final restorations.
METHODS:
The CERECTM system was used to mill a wide range of materials used with that system; namely the Paradigm MZ100TM (3M/ESPE), Vita Mark II (VITA), ProCAD (Ivoclar-Vivadent) and IPS e.max CAD (Ivoclar-Vivadent). A Vickers hardness Tester was used for the calculation of BI, while for the calculation of CF the percentage of marginal chipping of crowns prepared with bevelled marginal angulations was estimated.
RESULTS:
The results of this study showed that Paradigm MZ100 had the lowest BI and CF, while IPS e.max CAD demonstrated the highest BI and CF. Vita Mark II and ProCAD had similar BI and CF and were lying between the above materials. Statistical analysis of the results showed that there is a perfect positive correlation between BI and CF for all the materials.
CONCLUSIONS:
The BI and CF could be both regarded as indicators of a material’s machinability. Within the limitations of this study it was shown that as the BI increases so does the potential for marginal chipping, indicating that the BI of a material can be used as a predictor of the CF
A model of the reflection distribution in the vacuum ultra violet region
A reflection model with three components, a specular spike, a specular lobe
and a diffuse lobe is discussed. This model was successfully applied to
describe reflection of xenon scintillation light (175 nm) by PTFE and other
fluoropolymers and can be used for Monte Carlo simulation and analysis of
scintillation detectors. The measured data favors a Trowbridge-Reitz
distribution function of ellipsoidal micro-surfaces. The intensity of the
coherent reflection increases with increasing angle of incidence, as expected,
since the surface appears smoother at grazing angles. The total reflectance
obtained for PTFE is about 70% for VUV light at normal incidence in vacuum and
estimated to be up to 100% in contact with liquid xenon
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Intra-arterial Onyx Embolization of Vertebral Body Lesions
While Onyx embolization of cerebrospinal arteriovenous shunts is well-established, clinical researchers continue to broaden applications to other vascular lesions of the neuraxis. This report illustrates the application of Onyx (eV3, Plymouth, MN) embolization to vertebral body lesions, specifically, a vertebral hemangioma and renal cell carcinoma vertebral body metastatic lesion
Eye-Safe Solid-State Quasi-CW Raman Laser with Millisecond Pulse Duration
We demonstrate the first quasi-CW (ms-long pulses, pump duty cycle of 10%)
end-diode pumped solid state laser generating eye-safe radiation via
intracavity Raman conversion. The output power at the first Stokes wavelength
(1524 nm) was 250 mW. A theoretical model was applied to analyze the laser
system and provide routes for optimization. The possibility of true CW
operation was discussed.Comment: Preprint accepted for publication in Optics Communications on Feb 6,
201
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