Effects of drop and film viscosity on drop impacts onto thin films

While drop-film impacts have been studied extensively in the past, little thought has been given towards separating the effects of the drop fluid properties from those of the film. Distinguishing between the behaviors resulting from characteristics of each independently could provide insight into the underlying physical phenomena with a clarity that is unavailable when the drop and the film consist of identical liquids. In this study, the viscosity is the central parameter varied in both drop and film liquid. Using water, aqueous glycerol mixtures, and Fluoroinert FC-72, a range of kinematic viscosity covering 3 orders of magnitude (4 × 10-7 - 6.5 × 10 -4 m2/s) is examined; a smaller range of surface tension (0.024-0.072 N/m) is covered, as well. Drop impacts occur over a range of Weber numbers from 20 to 3000 and Reynolds numbers from 20 to 14000. Impact outcomes categorized are both formation of a crown and splashing from the crown. Criteria for each impact outcome are presented in light of both film and drop properties; certain outcomes are found to depend more strongly on either the properties of the drop or the film individually. Crown formation appears to relate more strongly to the film's properties, whereas crown splashing has some dependence on the drop properties. Existing splashing correlations are examined in light of the separation of properties. © 2013 by Begell House, Inc

Indirect determination of the Kugo-Ojima function from lattice data

We study the structure and non-perturbative properties of a special Green's function, u(q), whose infrared behavior has traditionally served as the standard criterion for the realization of the Kugo-Ojima confinement mechanism. It turns out that, in the Landau gauge, u(q) can be determined from a dynamical equation, whose main ingredients are the gluon propagator and the ghost dressing function, integrated over all physical momenta. Using as input for these two (infrared finite) quantities recent lattice data, we obtain an indirect determination of u(q). The results of this mixed procedure are in excellent agreement with those found previously on the lattice, through a direct simulation of this function. Most importantly, in the deep infrared the function deviates considerably from the value associated with the realization of the aforementioned confinement scenario. In addition, the dependence of u(q), and especially of its value at the origin, on the renormalization point is clearly established. Some of the possible implications of these results are briefly discussed.Comment: 25 pages, 10 figures; v2: typos corrected, expanded version that matches the published articl

Stability of Ca-montmorillonite hydrates: A computer simulation study

Classic simulations are used to study interlayer structure, swelling curves, and stability of Ca-montmorillonite hydrates. For this purpose, NPzzT$ and MuPzzT ensembles are sampled for ground level and given burial conditions. For ground level conditions, a double layer hydrate having 15.0 A of basal spacing is the predominant state for relative vapor pressures (p/po) ranging in 0.6-1.0. A triple hydrate counting on 17.9 A of interlaminar distance was also found stable for p/po=1.0. For low vapor pressures, the system may produce a less hydrated but still double layer state with 13.5 A or even a single layer hydrate with 12.2 A of interlaminar distance. This depends on the established initial conditions. On the other hand, the effect of burial conditions is two sided. It was found that it enhances dehydration for all vapor pressures except for saturation, where swelling is promoted.Comment: 8 pages, 9 figure

Electromagnons in multiferroic YMn2O5 and TbMn2O5

Based on temperature dependent far infrared transmission spectra of YMn2O5 and TbMn2O5 single crystals, we report the observation of electric dipole-active magnetic excitations, or electromagnons, in these multiferroics. Electromagnons are found to be directly responsible for the step-like anomaly of the static dielectric constant at the commensurate--incommensurate magnetic transition and are the origin of the colossal magneto-dielectric effect reported in these multiferroics.Comment: 4 pages, 4 figures, submitte

Spin phonon coupling in frustrated magnet CdCr2_2O4_4

The infrared phonon spectrum of the spinel CdCr2O4 is measured as a function temperature from 6 K to 300K. The triply degenerate Cr phonons soften in the paramagnetic phase as temperature is lowered below 100 K and then split into a singlet and doublet in the low T antiferromagnetic phase which is tetragonally distorted to relieve the geometric frustration in the pyrochlore lattice of Cr$^{3+}$ ions. The phonon splitting is inconsistent with the simple increase (decrease) in the force constants due to deceasing (increasing) bond lengths in the tetragonal phase. Rather they correspond to changes in the force constants due to the magnetic order in the antiferromagnetic state. The phonon splitting in this system is opposite of that observed earlier in ZnCr2O4 as predicted by theory. The magnitude of the splitting gives a measure of the spin phonon coupling strength which is smaller than in the case of ZnCr2O4.Comment: 4.2 pages, 4 figures, 1 reference added, submmite

Comparison of PI Controllers Designed for the Delay Model of TCP/AQM Networks

Cataloged from PDF version of article.One of the major problems of communication networks is congestion. In order to address this problem in TCP/IP networks, Active Queue Management (AQM) scheme is recommended. AQM aims to minimize the congestion by regulating the average queue size at the routers. To improve upon AQM, recently, several feedback control approaches were proposed. Among these approaches, PI controllers are gaining attention because of their simplicity and ease of implementation. In this paper, by utilizing the fluid-flow model of TCP networks, we study the PI controllers designed for TCP/AQM. We compare these controllers by first analyzing their robustness and fragility. Then, we implement these controllers in ns-2 platform and conduct simulation experiments to compare their performances in terms of queue length. Taken together, our results provide a guideline for choosing a PI controller for AQM given specific performance requirements. (C) 2013 Elsevier B.V. All rights reserved