152,235 research outputs found
Debye length dependence of the anomalous dynamics of ionic double layers in a parallel plate capacitor
No full textThe electrical impedance spectrum of simple ionic solutions is measured in a parallel plate capacitor at small applied ac voltage. The influence of the ionic strength is investigated using several electrolytes at different concentrations in solvents of different dielectric constants. The electric double layers that appear at the electrodes at low frequencies are not perfectly capacitive. At moderate ionic strength, ion transport agrees with a model based on the Poisson-Nernst-Planck (PNP) equations. At low ionic strength, double layer dynamics deviate from the PNP model, and the deviation is well described by an empirical function with only one fit parameter. This deviation from the PNP equations increases systematically with increasing Debye length, possibly caused by the long-range Coulomb interaction
Instabilities in free-surface electroosmotic flows
No full textThis paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.With the recent development of novel microfluidic devices electroosmotic flows with fluid/fluid interfaces have emerged as very important subjects of investigation. Two immiscible fluids may need to be
transported in a microchannel, or one side of a channel may be open to air for various purposes, including adsorption of airborne molecules to liquid for high-sensitivity substance detection. The liquid/liquid or
liquid/gas interface in these cases can deform, resulting in significant corrugations followed sometimes by incipient rupture of liquid layers. For electroosmotic flow the rupture, leading to shortcircuit, can cause overall failure of the device. It is thus imperative to know the conditions for the rupture as well as the initial interfacial instability. Studies based on the Debye-Huckle approximation reveal that all free-surface electroosmotic flows of thickness larger than the Debye screening length are unstable and selectively lead to
rupture. Layers of the order of Debye screening length, however, are not properly described by the Debye-Huckle approximation. Even for micro-scale layers, the rupture phenomenon can make local layer
thickness to be nanoscale. A fully coupled system of hydrodynamics, electric field, and ionic distribution need to be analyzed. In this paper linear instability and subsequent nonlinear developments of a nanoscale free-surface electroosmotic flow are reported.This study is sponsored by the Ministry of Education, Science and Technology of Korea through the World Class University Grant
Scattering under the Rayleigh-Debye-Gans condition for transparent glass ceramics
No full textWe review the various theoretical relations that quantify light scattering under the Rayleigh-Debye-Gans (RDG) approximation and apply these relations to the calculation of scattering within Transparent Glass Ceramics (TGCs) composed of large nanocrystals within a glass matrix. For a more realistic picture of scattering, we include within these models material dispersion of the crystals and glasses across the transparency range of these materials by way of the Sellmeier equation. We first select a number of crystal-glass sets that are near index matched in the visible and near infrared in order to fulfill one of the RDG criterions. We find that the various forms of scattering under the RDG approximation differ significantly across the visible and near infrared. We also find that the inclusion of material dispersion changes significantly the trends in the calculated scattering cross section across the studied wavelength range. Overall, we find that the calculation of the scattering cross section is highly dependent on the chosen theoretical relation and that the inclusion of material dispersion is vital in order to achieve a clear picture of scattering loss of this new class of optical material
A Novel Piecewise Linear Recursive Convolution Approach for Dispersive Media Using the Finite-Difference Time-Domain Method
No full textTwo novel methods for implementing recursively the convolution betweenthe electric field and a time dependent electric susceptibility function inthe finite-difference time domain (FDTD) method are presented. Both resultingalgorithms are straightforward to implement and employ an inclusive susceptibilityfunction which holds as special cases the Lorentz, Debye, and Drude mediarelaxations. The accuracy of the new proposed algorithms is found to be systematicallyimproved when compared to existing standard piecewise linear recursive convolution(PLRC) approaches, it is conjectured that the reason for this improvementis that the new proposed algorithms do not make any assumptions about thetime variation of the polarization density in each time interval; no finitedifference or semi-implicit schemes are used for the calculation of the polarizationdensity. The only assumption that these two new methods make is that the firsttime derivative of the electric field is constant within each FDTD time interval
Ion plasma waves induced by frustrated Debye shielding
No full textThe oscillation of electrons, in a sufficiently intense pump wave, frustrates Debye shielding in the direction of the oscillation. One finds that such oscillating electrons cannot shield charge fluctuations over distances smaller than the distance they sample in a plasma period. One consequence is that the frequency of ion waves can be increased from the ion acoustic frequency to the ion plasma frequency in the presence of large enough oscillations. This may explain a number of observations in laser experiments. More generally, any phenomenon involving Debye shielding will be altered by an intense pump wave. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69595/2/PHPAEN-9-1-267-1.pd
Development of oilseed crops for biodiesel production under Colorado limited irrigation conditions: final report to the Colorado Water Institute
No full textApril 2009.Financed in part by the U.S. Department of the Interior, Geological Survey, through the Colorado Water Institute
(Fourth) Report on Meteorological Activities at the DGAI (8-1-36)(Weather Bureau Copy)
No full textThis report is on the investigations of frontal phenomena at the Daniel Guggenheim Airship Institute in Akron, Ohio from January 1, 1935 through August 1, 1936. The investigation was carried out with the cooperation of the U.S. Bureau of Aeronautics, the U.S. Weather Bureau, the California Institute of Technology, and the Guggenheim Airship Institute. Mr. R.C. Robinson of the Weather Bureau cooperated with the author in carrying out the investigation. The object of the investigation was to determine the intensity of the atmospheric disturbances (i.e. rapidity of wind shift and gustiness) accompanying the passage of cold fronts, along with a study of the characteristics of the air masses involved and other features which might affect the intensity of the disturbance. The report treated thirty cold fronts which passed the station during 1935 to 1936
Infrared to near-infrared and visible upconversion mechanisms in LiYF 4: Yb3+, Ho3+
No full textUpconversion materials have regained interest in recent years due to their potential to enhance the efficiency of solar cells. The research has focused on lanthanide based upconverters, especially Er3+- and Yb 3+-doped materials. In this paper we report Ho3+ and Yb3+ upconversion after excitation into the 5I6 Ho3+ state in LiYF4. Infrared excitation into the 5I6 Ho3+ level at 1150 nm induces both visible 5F5→5I8 Ho3+ and near-infrared 2F5/2→2F7/2 Yb3+ upconversion luminescence, around 650 nm and 1000 nm, respectively. The concentration dependence was investigated and the most efficient Ho3+ upconversion was found for LiYF4: 2%Yb 3+, 20%Ho3+. Time-resolved spectroscopy as well as temperature dependent measurements were used to unravel the mechanism underlying the upconversion processes. Experimental results and rate equation modeling provides evidence for infrared to near-infrared/visible upconversion mechanisms that are different from those previously reported in the literature
Routes toward Long-Term Stability of Mixed-Halide Perovskites
No full textIn the recent anniversary issue of Trends in Chemistry, Brennan et al. review halide segregation in mixed-halide perovskites, discussing multiple perspectives on the underlying origins and reported routes to retard halide segregation. Here, we argue that only slowing down the segregation may be insufficient to achieve long-term stability
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