Multi-walled microchannels: free-standing porous silicon membranes for use in µTAS

Electrochemically formed porous silicon (PS) can be released from the bulk silicon substrate by underetching at increased current density. Using this technique, two types of channels containing free-standing layers of PS were constructed, which were failed multi-walled microchannels (MW µCs). They can be used in devices like microsieves, microbatteries, and porous electrodes. Two types of MWµC were made: the 'conventional' version, consisting of two or more coaxially constructed microchannels separated by a suspended PS membrane, and the buried variety, where a PS membrane is suspended halfway in an etched cavity surrounded by silicon nitride walls. The latter is more robust. The pore size of the PS was measured using transmission electron microscopy and field emission gun scanning electron microscopy (FEGSEM) and found to be of the order of 7 n

Liquid Transport in Composite Cellulose—Superabsorbent Fiber Networks

Wicking flow of water is examined in composite networks of cellulose and carboxymethyl cellulose (CMC) fibers. The rate of advance of water through paper strips and fluff pads of varying composition is reported, while dynamic electrotensiometry is used to measure the wetting and swelling characteristics of the individual cellulose and CMC fibers. Cellulose fibers swell to a small degree almost instantaneously, while CMC fibers swell to more than twice their original diameter over a period of several minutes.The Lucas-Washburn capillary model adequately describes the imbibition of a nonswelling reference liquid (n-octane) in all of the fiber networks examined. The imbibition of water, however, deviates significantly from Lucas-Washburn kinetics when CMC is present, because of the long-term swelling of the CMC fibers. The net pore restriction effected by fiber swelling is quantified by a "permeability factor," defined as the ratio of the wicking-equivalent radius in the swollen state to that in the unswollen state. A modified capillary model is developed, based on individual fiber swelling characteristics, which describes observed deviations from the Lucas-Washburn model

The Impact of Judicial Decisions: New Dimensions in Supreme Court-Congressional Relations, 1945-1968

This research report is an investigation of Congressional roll call behavior and interest group activity in response to Supreme Court decisions involving civil rights and liberties, and economic, labor and welfare issues. The report is designed to explore the nature and relative stability of those variables which may influence Congressmen when they vote on judiciary-oriented roll calls in the above mentioned issue categories

Threonine Deficiency in Hydrolysates of Zein Prepared by Autoclaving

In a previous paper (Borchers and Berg, 1942) we showed that autoclaving zein with sulfuric acid longer than necessary for complete hydrolysis causes destruction and racemization; either of these might account for the failure of such a hydrolysate to promote growth in young rats when substituted for a hvdrolysate, prepared by refiuxing, in a diet which produced moderate growth. It seemed to us that this deterioration in the dietary protein might well be the result primarily of essential amino acid deficiencies which could be detected and overcome by appropriate supplementation. Because threonine is known to be present in zein in relatively small amount1 and because its 2 asymmetric carbon atoms might render it more susceptible to configurational modification by racemization, a ready production of threonine deficiency was considered likely. This was confirmed; addition of threonine to an autoclave hydrolysate (heated with 10 per cent sulfuric acid for 8 hours at 165°) promoted about as rapid growth as had the reflux hydrolysate which it replaced. Longer heating at higher temperatures produced deficiencies not fully met by threonine alone

Inflation from D3-brane motion in the background of D5-branes

We study inflation arising from the motion of a BPS D3-brane in the background of a stack of k parallel D5-branes. There are two scalar fields in this set up-- (i) the radion field R, a real scalar field, and (ii) a complex tachyonic scalar field chi living on the world volume of the open string stretched between the D3 and D5 branes. We find that inflation is realized by the potential of the radion field, which satisfies observational constraints coming from the Cosmic Microwave Background. After the radion becomes of order the string length scale l_s, the dynamics is governed by the potential of the complex scalar field. Since this field has a standard kinematic term, reheating can be successfully realized by the mechanism of tachyonic preheating with spontaneous symmetry breaking.Comment: 10 pages, 4 figures. Minor clarifications and references added. Version to appear in Phys. Rev.

Shift in critical temperature for random spatial permutations with cycle weights

We examine a phase transition in a model of random spatial permutations which originates in a study of the interacting Bose gas. Permutations are weighted according to point positions; the low-temperature onset of the appearance of arbitrarily long cycles is connected to the phase transition of Bose-Einstein condensates. In our simplified model, point positions are held fixed on the fully occupied cubic lattice and interactions are expressed as Ewens-type weights on cycle lengths of permutations. The critical temperature of the transition to long cycles depends on an interaction-strength parameter $\alpha$. For weak interactions, the shift in critical temperature is expected to be linear in $\alpha$ with constant of linearity $c$. Using Markov chain Monte Carlo methods and finite-size scaling, we find $c = 0.618 \pm 0.086$. This finding matches a similar analytical result of Ueltschi and Betz. We also examine the mean longest cycle length as a fraction of the number of sites in long cycles, recovering an earlier result of Shepp and Lloyd for non-spatial permutations.Comment: v2 incorporated reviewer comments. v3 removed two extraneous figures which appeared at the end of the PDF