198 research outputs found
Thin films flowing down inverted substrates: Three dimensional flow
We study contact line induced instabilities for a thin film of fluid under
destabilizing gravitational force in three dimensional setting. In the previous
work (Phys. Fluids, {\bf 22}, 052105 (2010)), we considered two dimensional
flow, finding formation of surface waves whose properties within the
implemented long wave model depend on a single parameter,
, where is the capillary number and is
the inclination angle. In the present work we consider fully 3D setting and
discuss the influence of the additional dimension on stability properties of
the flow. In particular, we concentrate on the coupling between the surface
instability and the transverse (fingering) instabilities of the film front. We
furthermore consider these instabilities in the setting where fluid viscosity
varies in the transverse direction. It is found that the flow pattern strongly
depends on the inclination angle and the viscosity gradient
Three-dimensional localized coherent structures of surface turbulence. III Experiment and model validation
The paper continues a series of publications devoted to the 3D nonlinear
localized coherent structures on the surface of vertically falling liquid
films. The work is primarily focussed on experimental investigations. We study:
(i) instabilities and transitions leading to 3D coherent structures; (ii)
characteristics of these structures. Some nonstationary effects are also
studied numerically. Our experimental results, as well as the results of other
investigators, are in a good agreement with our theoretical and numerical
predictions.Comment: 42 pages, 15 figure
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Assessment of evolution and risks of glacier lake outbursts in the Djungarskiy Alatau, Central Asia, using Landsat imagery and glacier bed topography modelling
Changes in the abundance and area of mountain lakes in the Djungarskiy (Jetysu) Alatau between 2002 and 2014 were investigated using Landsat imagery. The number of lakes increased by 6.2 % from 599 to 636 with a growth rate of 0.51 % a−1. The combined areas were 16.26 ± 0.85 to 17.35 ± 0.92 km2 respectively and the overall change was within the uncertainty of measurements. Fifty lakes, whose potential outburst can damage existing infrastructure, were identified. The glacier bed topography version 2 (GlabTop2) model was applied to simulate ice thickness and subglacial topography using glacier outlines for 2000 and SRTM DEM (Shuttle Radar Topography Mission digital elevation model) as input data achieving realistic patterns of ice thickness. A total of 513 overdeepenings in the modelled glacier beds, presenting potential sites for the development of lakes, were identified with a combined area of 14.7 km2. Morphometric parameters of the modelled overdeepenings were close to those of the existing lakes. A comparison of locations of the overdeepenings and newly formed lakes in the areas de-glacierized in 2000–2014 showed that 67 % of the lakes developed at the sites of the overdeepenings. The rates of increase in areas of new lakes correlated with areas of modelled overdeepenings. Locations where hazardous lakes may develop in the future were identified. The GlabTop2 approach is shown to be a useful tool in hazard management providing data on the potential evolution of future lakes
Stochastic stabilization of cosmological photons
The stability of photon trajectories in models of the Universe that have
constant spatial curvature is determined by the sign of the curvature: they are
exponentially unstable if the curvature is negative and stable if it is
positive or zero. We demonstrate that random fluctuations in the curvature
provide an additional stabilizing mechanism. This mechanism is analogous to the
one responsible for stabilizing the stochastic Kapitsa pendulum. When the mean
curvature is negative it is capable of stabilizing the photon trajectories;
when the mean curvature is zero or positive it determines the characteristic
frequency with which neighbouring trajectories oscillate about each other. In
constant negative curvature models of the Universe that have compact topology,
exponential instability implies chaos (e.g. mixing) in the photon dynamics. We
discuss some consequences of stochastic stabilization in this context.Comment: 4 pages, 3 postscript figures in color which are also appropriate for
black and white printers; v2 emphasizes relevance to flat as well as
negatively curved cosmologies; to appear in J. Phys.
Observation of Resonant Diffusive Radiation in Random Multilayered Systems
Diffusive Radiation is a new type of radiation predicted to occur in randomly
inhomogeneous media due to the multiple scattering of pseudophotons. This
theoretical effect is now observed experimentally. The radiation is generated
by the passage of electrons of energy 200KeV-2.2MeV through a random stack of
films in the visible light region. The radiation intensity increases resonantly
provided the Cherenkov condition is satisfied for the average dielectric
constant of the medium. The observed angular dependence and electron resonance
energy are in agreement with the theoretical predictions. These observations
open a road to application of diffusive radiation in particle detection,
astrophysics, soft X-ray generation and etc.. `Comment: 4pages, 4figure
Stable dynamics in forced systems with sufficiently high/low forcing frequency
We consider a class of parametrically forced Hamiltonian systems with
one-and-a-half degrees of freedom and study the stability of the dynamics when
the frequency of the forcing is relatively high or low. We show that, provided
the frequency of the forcing is sufficiently high, KAM theorem may be applied
even when the forcing amplitude is far away from the perturbation regime. A
similar result is obtained for sufficiently low frequency forcing, but in that
case we need the amplitude of the forcing to be not too large; however we are
still able to consider amplitudes of the forcing which are outside of the
perturbation regime. Our results are illustrated by means of numerical
simulations for the system of a forced cubic oscillator. In addition, we find
numerically that the dynamics are stable even when the forcing amplitude is
very large (beyond the range of validity of the analytical results), provided
the frequency of the forcing is taken correspondingly low.Comment: 12 pages, 3 figures, 2 table
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Changes in the mountain river discharge in the northern Tien Shan since the mid-20th Century: Results from the analysis of a homogeneous daily streamflow data set from seven catchments
This study is an assessment of the changes in seasonal and monthly flow in seven catchments draining the northern Tien Shan Mountains in Central Asia over a period from the 1950s to the present day. The purpose is to provide a first assessment of the flow response to climate change in regionally important catchments given their contribution to the water resource. All the catchments have a natural flow regime, and are therefore sensitive to climate change, but differ in area, elevation and glacial extent. Trends in flow were characterised using the Mann-Kendall test for standard meteorological seasons and individual months for mean flow, five flow quantiles and peak-over-threshold series for the period 1974–2013 at all sites and from the 1950s where data were available. The results were related to trends in seasonal temperature and precipitation from the regional high elevation meteorological stations and glacier mass balance, equilibrium line altitude (ELA) and accumulation
area ratio (AAR) records from the Tuyuksu glacier. The results show no reduction in streamflow in any catchment or season in the northern Tien Shan since the 1950s. Positive trends in all flow indicators, including peak over- threshold frequency, were observed in catchments with higher glacierization of over 10% and extensive presence of rock glaciers and permafrost indicating increased melt over the period which is characterised by a long-term increase in temperature. These trends were most evident in autumn and winter. In catchments with low glacierization, variability in summer flow was controlled primarily by precipitation of the preceding cold season. Correlation with glacier mass balance was weak but changes in ELA and AAR indicate that production of liquid runoff at higher elevations contributes to increased streamflow partly compensating for the declining glacier area. The observed changes in streamflow do not suggest any immediate problems with water availability
in the northern Tien Shan. On the contrary, increased autumn and winter flows point at a more prolonged recharge of reservoirs and aquifers though eventually this water source will be exhausted
EFFICIENCY OF MODERNIZATION OF WHEEL-MOTOR BLOCKS (WMB) USING ANTI-FRICTION TRACTION MOTOR SUPPORT BEARINGS (TMSB)
Purpose. The use of anti-friction traction motor support bearings (TMSB) instead of plain friction traction motor support bearings is a priority direction of locomotive development both for newly constructed locomotives and for those in operation. The solution of the set tasks for introduction of wheel-motor blocks (WMB) with anti-friction bearings demanded the search for alternative variants and new technical solutions. The purpose of the article is to determine the feasibility of re-equipping the diesel locomotive wheel-motor blocks with anti-friction bearings through the life cycle calculation (LCC). Methodology. The procedure and criteria for assessing the economic efficiency of project (investment) proposals and investment projects approved by the Cabinet of Ministers of Ukraine envisage that the cost-effectiveness analysis of an investment project is carried out according to the following criteria: net present value, internal rate of return, discounted payback period and profitability index. The use of these criteria of economic efficiency fully corresponds to modern principles, theoretical-methodical approaches and world practice in evaluating the efficiency of investments. The evaluation of the technical and economic efficiency of the modernization of the diesel locomotive wheel-motor block is made on the basis of calculation and comparison of the following criteria: the net present value (NPV) of modernization, the internal rate of return (IRR), the profitability index (PI) and the discount payback period. Findings. The results of the calculations of the values of the main criteria show that the innovative project for the modernization of the locomotive provides a high level of economic efficiency. At the same time, the value of the discounted payback period of investments in modernization indicates that it is expedient to carry out this operation if the residual life of the upgraded locomotive of the M62 series is at least 15 months. Originality. Taking into account the specifics of the type of locomotive work in freight traffic, we developed a method to determine the individual components of the average annual economic effect of modernization of the diesel locomotive wheel-motor block, which includes saving of oil costs, repairing and servicing the diesel locomotive wheel-motor unit, as well as change of TMSB brass and saving fuel costs for traction. Practical value. The results of the work make it possible to determine the expediency of modernization of diesel locomotives taking into account the features and conditions of their operation and the specifics of modernization
Dipolar superfluidity in electron-hole bilayer systems
Bilayer electron-hole systems, where the electrons and holes are created via
doping and confined to separate layers, undergo excitonic condensation when the
distance between the layers is smaller than typical distance between particles
within a layer. We argue that the excitonic condensate is a novel dipolar
superfluid in which the phase of the condensate couples to the {\it gradient}
of the vector potential. We predict the existence of dipolar supercurrent which
can be tuned by an in-plane magnetic field and detected by independent contacts
to the layers. Thus the dipolar superfluid offers an example of excitonic
condensate in which the {\it composite} nature of its constituent excitons is
manifest in the macroscopic superfluid state. We also discuss various
properties of this superfluid including the role of vortices.Comment: 5 pages, 1 figure, minor changes and added few references; final
published versio
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