2,859 research outputs found
Vibration-induced climbing of drops
We report an experimental study of liquid drops moving against gravity, when
placed on a vertically vibrating inclined plate, which is partially wetted by
the drop. The frequency of vibrations ranges from 30 to 200 Hz, and, above a
threshold in vibration acceleration, drops experience an upward motion. We
attribute this surprising motion to the deformations of the drop, as a
consequence of an up or down symmetry breaking induced by the presence of the
substrate. We relate the direction of motion to contact angle measurements.
This phenomenon can be used to move a drop along an arbitrary path in a plane,
without special surface treatments or localized forcing.Comment: 4 pages, 7 figure
Coalescence of Liquid Drops
When two drops of radius touch, surface tension drives an initially
singular motion which joins them into a bigger drop with smaller surface area.
This motion is always viscously dominated at early times. We focus on the
early-time behavior of the radius \rmn of the small bridge between the two
drops. The flow is driven by a highly curved meniscus of length 2\pi \rmn and
width \Delta\ll\rmn around the bridge, from which we conclude that the
leading-order problem is asymptotically equivalent to its two-dimensional
counterpart. An exact two-dimensional solution for the case of inviscid
surroundings [Hopper, J. Fluid Mech. , 349 (1990)] shows that
\Delta \propto \rmn^3 and \rmn \sim (t\gamma/\pi\eta)\ln [t\gamma/(\eta
R)]; and thus the same is true in three dimensions. The case of coalescence
with an external viscous fluid is also studied in detail both analytically and
numerically. A significantly different structure is found in which the outer
fluid forms a toroidal bubble of radius \Delta \propto \rmn^{3/2} at the
meniscus and \rmn \sim (t\gamma/4\pi\eta) \ln [t\gamma/(\eta R)]. This basic
difference is due to the presence of the outer fluid viscosity, however small.
With lengths scaled by a full description of the asymptotic flow for
\rmn(t)\ll1 involves matching of lengthscales of order \rmn^2, \rmn^{3/2},
\rmn\rmn^{7/4}$.Comment: 36 pages, including 9 figure
One-Dimensional Approximation of Viscous Flows
Attention has been paid to the similarity and duality between the
Gregory-Laflamme instability of black strings and the Rayleigh-Plateau
instability of extended fluids. In this paper, we derive a set of simple
(1+1)-dimensional equations from the Navier-Stokes equations describing thin
flows of (non-relativistic and incompressible) viscous fluids. This
formulation, a generalization of the theory of drop formation by Eggers and his
collaborators, would make it possible to examine the final fate of
Rayleigh-Plateau instability, its dimensional dependence, and possible
self-similar behaviors before and after the drop formation, in the context of
fluid/gravity correspondence.Comment: 17 pages, 3 figures; v2: refs & comments adde
Rapid deconvolution of low-resolution time-of-flight data using Bayesian inference
The deconvolution of low-resolution time-of-flight data has numerous advantages, including the ability to extract additional information from the experimental data. We augment the well-known Lucy-Richardson deconvolution algorithm using various Bayesian prior distributions and show that a prior of second-differences of the signal outperforms the standard Lucy-Richardson algorithm, accelerating the rate of convergence by more than a factor of four, while preserving the peak amplitude ratios of a similar fraction of the total peaks. A novel stopping criterion and boosting mechanism are implemented to ensure that these methods converge to a similar final entropy and local minima are avoided. Improvement by a factor of two in mass resolution allows more accurate quantification of the spectra. The general method is demonstrated in this paper through the deconvolution of fragmentation peaks of the 2,5-dihydroxybenzoic acid matrix and the benzyltriphenylphosphonium thermometer ion, following femtosecond ultraviolet laser desorption
Planetary explorer liquid propulsion study
An analytical evaluation of several candidate monopropellant hydrazine propulsion system approaches is conducted in order to define the most suitable configuration for the combined velocity and attitude control system for the Planetary Explorer spacecraft. Both orbiter and probe-type missions to the planet Venus are considered. The spacecraft concept is that of a Delta launched spin-stabilized vehicle. Velocity control is obtained through preprogrammed pulse-mode firing of the thrusters in synchronism with the spacecraft spin rate. Configuration selection is found to be strongly influenced by the possible error torques induced by uncertainties in thruster operation and installation. The propulsion systems defined are based on maximum use of existing, qualified components. Ground support equipment requirements are defined and system development testing outlined
Monoamine activity reflected in urine of young patients with obsessive compulsive disorder, psychosis with and without reality distortion and healthy subjects: an explorative analysis
Introduction: Positive psychotic symptoms are reported to be associated with high dopamine (DA), negative symptoms with low DA activity and serotonin (5-HT) activity may be altered in obsessive-compulsive disorder (OCD).
Method: We analysed 24h urine samples in groups of patients with OCD, paranoid and non-paranoid schizophrenia and in healthy controls for supportive evidence.
Results: Young unmedicated OCD subjects excreted more adrenaline (AD) and homovanillic acid (HVA) and showed a higher HVA/MHPG metabolite ratio and metabolic rate than healthy controls. Independent of general metabolic rate OCD patients showed higher HVA concentrations which suggests that the relative activity of catecholamine systems in OCD (HVA/MHPG) is due more to high DA than to low noradrenergic (NA) activity. Concentrations of 5-HT were also high in OCD patients. In psychotic patients low levels of DA, HVA, NA and MHPG probably resulted from neuroleptic medication.
Conclusions: 1. Patients diagnosed with paranoid psychosis showed higher DA utilization than controls and those with few paranoid symptoms showed high 5-HT utilization. 2. These results support studies suggesting that paranoid psychosis is associated more with increased DA activity (discussed in the context of neuroleptic reactivity), that non-paranoid forms are associated more with increased 5-HT activity and that OCD patients are unusually aroused with high levels of Adrenaline, 5-HT and HVA
Stochastic energy-cascade model for 1+1 dimensional fully developed turbulence
Geometrical random multiplicative cascade processes are often used to model
positive-valued multifractal fields such as the energy dissipation in fully
developed turbulence. We propose a dynamical generalization describing the
energy dissipation in terms of a continuous and homogeneous stochastic field in
one space and one time dimension. In the model, correlations originate in the
overlap of the respective spacetime histories of field amplitudes. The
theoretical two- and three-point correlation functions are found to be in good
agreement with their equal-time counterparts extracted from wind tunnel
turbulent shear flow data
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