Time dependence of effective slip on textured hydrophobic surfaces

In this paper, we present results on water flow past randomly textured hydrophobic surfaces with relatively large surface features of the order of 50 µm. Direct shear stress measurements are made on these surfaces in a channel configuration. The measurements indicate that the flow rates required to maintain a shear stress value vary substantially with water immersion time. At small times after filling the channel with water, the flow rates are up to 30% higher compared with the reference hydrophilic surface. With time, the flow rate gradually decreases and in a few hours reaches a value that is nearly the same as the hydrophilic case. Calculations of the effective slip lengths indicate that it varies from about 50 µm at small times to nearly zero or “no slip” after a few hours. Large effective slip lengths on such hydrophobic surfaces are known to be caused by trapped air pockets in the crevices of the surface. In order to understand the time dependent effective slip length, direct visualization of trapped air pockets is made in stationary water using the principle of total internal reflection of light at the water-air interface of the air pockets. These visualizations indicate that the number of bright spots corresponding to the air pockets decreases with time. This type of gradual disappearance of the trapped air pockets is possibly the reason for the decrease in effective slip length with time in the flow experiments. From the practical point of usage of such surfaces to reduce pressure drop, say, in microchannels, this time scale of the order of 1 h for the reduction in slip length would be very crucial. It would ultimately decide the time over which the surface can usefully provide pressure drop reductions. ©2009 American Institute of Physics

Time dependence of wet oxidized AlGaAs/GaAs distributed Bragg reflectors

The time dependence of wet oxidized AlGaAs/GaAs in a distributed Bragg reflector (DBR) structure has been studied by mean of transmission electron microscopy and Raman spectroscopy. The wet oxidized AlGaAs transforms from an initial amorphous hydroxide phase to the polycrystalline gamma-Al2O3 phase with the extension of oxidation time. The thickness of oxide layers will contract due to the different volume per Al atom in AlGaAs and in the oxides. In the samples oxidized for 10 and 20 min, there are some fissures along the AlGaAs/GaAs interfaces. In the samples oxidized longer, although no such fissures are present along the interfaces, the whole oxidized DBR delaminates from the buffer. (c) 2005 American Vacuum Society.

Guiding of 150 keV O6+ ions through nanocapillaries in an uncoated Al2O3 membrane: special time dependence of the transmission profile width

This paper reports that the transmission of O6+ ions with energy of 150keV through capillaries in an uncoated Al2O3 membrane was measured, and agreements with previously reported results in general angular distribution of the transmitted ions and the transmission fractions as a function of the tilt angle well fitted to Gaussian-like functions were observed. Due to using an uncoated capillary membrane, our c is larger than that using a gold-coated one with a smaller value of E-p/q, which suggests a larger equilibrium charge Q(infinity) in our experiment. The observed special width variation with time and a larger width than that using a smaller E-p/q were qualitatively explained by using mean-field classical transport theory based on a classical-trajectory Monte Carlo simulation.

Time dependence of rotational state populations of excited hydrogen molecules in an RF excited plasma reactor

We report on time-dependent population distributions of excited rotational states of hydrogen in a capacitively coupled RF discharge. The common model to obtain the gas temperature from the rotational distribution is not applicable at all times during the discharge cycle due to the time dependence of the EEDF. The apparent temperature within a cycle assumes values between 350 K and 450 K for the discharge parameters of this experiment. We discuss the optimum time window within the discharge cycle that yields the best approximation to the actual temperature. Erroneous results can be obtained, in principle, with time-integrated measurements; we find, however, that in the present case the systematic error amounts to only approximately 20 K. This is due to the fact that the dominant contribution to the average intensity arises during that time window for which the assumptions underlying the analysis are best fulfilled. A similar analysis can be performed for N+2 rotational bands with a small amount of nitrogen added to the discharge gas. These populations do not exhibit the time variations found in the case of H2.

Time dependence of the spatial coherence of the 23.6- and 23.2-nm radiation from the germanium soft-x-ray laser

The time dependence of the spatial coherence of the combined spectral lines at 23.2 and 23.6 nm from the Ge XXIII collisionally pumped soft-x-ray laser with a double-slab target is examined within a single nanosecond pulse by use of Young's interference fringes and a streak camera. High source intensity is linked with low spatial coherence and vice verse. Calculations of the source intensity, size, and position have also been made; these calculations refer to a single-slab source. Comparison between the observed and calculated intensities, and of the source sizes both calculated and derived from the Young's fringes by interpretation with a Gaussian model of source emission, show good agreement in general trends. (C) 1998 Optical Society of America [S0740-3224(98)01905-5].

Critical slip and time dependence in sea ice friction

Recent research into sea ice friction has focussed on ways to provide a model which maintains much of the clarity and simplicity of Amonton's law, yet also accounts for memory effects. One promising avenue of research has been to adapt the rate- and state- dependent models which are prevalent in rock friction. In such models it is assumed that there is some fixed critical slip displacement, which is effectively a measure of the displacement over which memory effects might be considered important. Here we show experimentally that a fixed critical slip displacement is not a valid assumption in ice friction, whereas a constant critical slip time appears to hold across a range of parameters and scales. As a simple rule of thumb, memory effects persist to a significant level for 10 s. We then discuss the implications of this finding for modelling sea ice friction and for our understanding of friction in general.

Time dependence and energy-transfer mechanisms in Tm3+Ho3+ and Tm3+-Ho3+ co-doped alkali niobium tellurite glasses sensitized by Yb3+

Glass samples with the composition (mol%) 80TeO(2)-10Nb(2)O(5)-5K(2)O-5Li(2)O, stable against crystallization, were prepared containing Yb3+, Tm3+ and Ho3+. The energy transfer and energy back transfer mechanisms in samples containing 5% Yb3+-5% Tm3+ and 5% Yb3+-5% Tm3+-0.5% Ho3+ were estimated by measuring the absorption and fluorescence spectra together with the time dependence of the Yb3+ F-2(5/2) excited state. A good fit for the luminescence time evolution was obtained with the Yokota-Tanimoto's diffusion-limited model. The up-conversion fluorescence was also studied in 5% Yb-5% Tm. 5% Yb-0.5% Ho and 5% Yb-5% Tm-0.5% Ho tellurite glasses under laser excitation at 975 nm. Strong emission was observed from (1)G(4) and F-3(2) Tm3+ energy levels in all samples. The S-5(2) Ho3+ emission was observed only in Yb3+Ho3+ samples being completely quenched in Yb3+/Tm3+/Tm3+ samples. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Time Dependence of Elimination of Different PEth Homologues in Alcoholics in Comparison with Social Drinkers

BACKGROUND: Phosphatidylethanol (PEth) is a direct marker of alcohol consumption, which has been known for almost 30 years. Each PEth molecule carries 2 fatty acids, which differ in chain length and degree of unsaturation. It is formed by means of phospholipase D in the presence of ethanol. Usually, this marker was used by quantification of the PEth homologue 16:0/18:1. The intention of this work was to get more information about the distribution and the quantity of the different PEth homologues. METHODS: Blood samples from 12 alcohol-dependent subjects were collected and analyzed during withdrawal therapy. For comparison, blood from 78 healthy social drinkers was also analyzed. PEth analysis was performed as follows: after liquid-liquid extraction, the homologues were separated on a Luna Phenyl Hexyl column, injected to an HPLC system (1100 system; Agilent) and identified by ESI-MS/MS (QTrap 2000; AB Sciex) using multiple reaction monitoring. RESULTS: PEth 16:0/18:1 is the major homologue comparing the area ratios of PEth homologues in blood samples from alcoholics. Additional prevalent homologues were PEth 16:0/18:2, 18:0/18:2, and 18:0/18:1. The homologues occurring in blood samples from alcoholics as well as from social drinkers were mostly the same, but differences among their distribution pattern were observed. CONCLUSIONS: In addition to the approach to quantitate the PEth homologue 16:0/18:1, this is a new and alternative proceeding for the differentiation between alcoholics and social drinkers using this alcohol consumption marker.

Runup variability due to time dependence and stochasticity in the beach profiles: two extreme cases of the Spanish coast

Equations for extreme runup worked out from several experimental studies are compared. Infragraviatory oscillations dominate the swash in a dissipative state but not in intermediate - reflective states. Therefore two kinds of equation depending on either significant wave height, H-0, or the Iribarren number, xi(0), should be used. Through a sand bed physical model with a uniform sand bed slope, equations are proposed for both beach states, and results are compared with precedent field and physical model experiments. Once the equations are chosen, the time-longshore variability in a medium - long term time scale of the foreshore slope is evaluated in two extreme cases relating to the Spanish coast. The Salinas beach on the North coast (Bay of Biscay) displayed a permanent dissipative beach state with small variations in the beach foreshore slope both along the shore and in time, so foreshore slope deviations in a medium-long term period were irrelevant and extreme runup is predicted with the wave height worked out from the design return period. Peniscola beach on the East coast (Mediterranean sea) displayed an intermediate state. If only time variations are analysed, variations in determining extreme runup are irrelevant. In contrast, significant differences were found when the longshore variations were studied in this Mediterranean beach.

Spin and spatial dynamics in electron-impact scattering off S-wave He using R-matrix with Time-Dependence theory

R-matrix with time-dependence theory is applied to electron-impact ionisation processes for He in the S-wave model. Cross sections for electron-impact excitation, ionisation and ionisation with excitation for impact energies between 25 and 225 eV are in excellent agreement with benchmark cross sections. Ultra-fast dynamics induced by a scattering event is observed through time-dependent signatures associated with autoionisation from doubly excited states. Further insight into dynamics can be obtained through examination of the spin components of the time-dependent wavefunction.

The Dependence of Retention Time on Gate Length in UTBOX FBRAM With Different Source/Drain Junction Engineering

The floating-body-RAM sense margin and retention-time dependence on the gate length is investigated in UTBOX devices using BJT programming combined with a positive back bias (so-called V th feedback). It is shown that the sense margin and the retention time can be kept constant versus the gate length by using a positive back bias. Nevertheless, below a critical L, there is no room for optimization, and the memory performances suddenly drop. The mechanism behind this degradation is attributed to GIDL current amplification by the lateral bipolar transistor with a narrow base. The gate length can be further scaled using underlap junctions.

Electrochemical phase formation. Time-dependent nucleation and growth rates

The theory of phase formation is generalised for any arbitrary time dependence of nucleation and growth rates. Some sources of this time dependence are time-dependent potential inputs, ohmic drop and the ingestion effect. Particular cases, such as potentiostatic and, especially, linear potential sweep, are worked out for the two limiting cases of nucleation, namely instantaneous and progressive. The ohmic drop is discussed and a procedure for this correction is indicated. Recent results of Angerstein-Kozlowska, Conway and Klinger are critically investigated. Several earlier results are deduced as special cases. Evans' overlap formula is generalised for the time-dependent case and the equivalence between Avrami's and Evans' equations established.

Mode coupling theory analysis of electrolyte solutions: Time dependent diffusion, intermediate scattering function, and ion solvation dynamics

A self-consistent mode coupling theory (MCT) with microscopic inputs of equilibrium pair correlation functions is developed to analyze electrolyte dynamics. We apply the theory to calculate concentration dependence of (i) time dependent ion diffusion, (ii) intermediate scattering function of the constituent ions, and (iii) ion solvation dynamics in electrolyte solution. Brownian dynamics with implicit water molecules and molecular dynamics method with explicit water are used to check the theoretical predictions. The time dependence of ionic self-diffusion coefficient and the corresponding intermediate scattering function evaluated from our MCT approach show quantitative agreement with early experimental and present Brownian dynamic simulation results. With increasing concentration, the dispersion of electrolyte friction is found to occur at increasingly higher frequency, due to the faster relaxation of the ion atmosphere. The wave number dependence of intermediate scattering function, F(k, t), exhibits markedly different relaxation dynamics at different length scales. At small wave numbers, we find the emergence of a step-like relaxation, indicating the presence of both fast and slow time scales in the system. Such behavior allows an intriguing analogy with temperature dependent relaxation dynamics of supercooled liquids. We find that solvation dynamics of a tagged ion exhibits a power law decay at long times-the decay can also be fitted to a stretched exponential form. The emergence of the power law in solvation dynamics has been tested by carrying out long Brownian dynamics simulations with varying ionic concentrations. The solvation time correlation and ion-ion intermediate scattering function indeed exhibit highly interesting, non-trivial dynamical behavior at intermediate to longer times that require further experimental and theoretical studies. (c) 2015 AIP Publishing LLC.