Nanofluidic channels by anodic bonding of amorphous silicon to glass to study ion-accumulation and ion-depletion effect

A unique phenomenon, ion-enrichment and ion-depletion effect, exists in nanofluidic channels and is observed in amorphous silicon (α-Si) nanochannels as shallow as 50 nm. As a voltage is applied across a nanochannel, ions are rapidly enriched at one end and depleted at the other end of the nanochannel. α-Si is deposited on glass by plasma enhanced chemical vapor deposition and is selectively etched to form nanochannels. The depth of nanochannels is defined by the thickness of the α-Si layer. Low temperature anodic bonding of α-Si to glass was used to seal the channel with a second glass wafer. The strength of the anodic bond was optimized by the introduction of a silicon nitride adhesion promoting layer and double-sided bonding resulting from the electric field reversal. Completed channels, 50 nm in depth, 5 micron wide, and 1 mm long were completely and reliably sealed. Structures based on nanochannels 50-300 nm deep were successfully incorporated into nanofluidic devices to investigate ionic accumulation and depletion effect due to overlapping of electric double layer.     

Convergence of linear functions of Pfeifer records

The probabilistic behaviour of partial sums of upper and lower records has been studied in the literature. In this article, we take a broader view and study partial sums of record like sequences. We show that such sequences converge in distribution to normal and lognormal distribution. In particular our results apply to Pfeifer records. We also show the strong convergence of partial sums of lower Pfeifer records under suitable assumptions.     

Kinetics and mechanism of formation of tetrachloropalladate(II) in the reactions of bis(oxalato)- and bis(malonato) palladate(II) with chloride in acid media

Summary Kinetics of formation of [PdCl₄]^2– from [Pd(ox)₂]^2– and [Pd(mal)₂]^2– has been studies in aqueous acid media in the presence of an excess of chloride ion by stopped-flow spectrophotometry. Both the complexes undergo the transformation in two well separated consecutive steps. In 0.02–0.05 M acid with 0.2 M Cl^–, Pd(AA)^2– dissociates leading to the formation of [Pd(AA)Cl₂]^2– (where AA =ox^2– or mal^2–), which in 0.1–0.6 M acid and 1 M Cl^– forms [PdCl₄]^2– in a relatively slow step. For both steps k_abs=k₀+k₂[H⁺][Cl^–]. Activation parameters corresponding to k₀ and k₂ have been determined. Results indicate that [Pd(mal)₂]^2– is much more labile to substitution than [Pd(ox)₂]^2– and for both the lability is far greater than that of [Pd(bigH)₂]²⁺ and [Pt(ox)₂]^2– reported earlier.     

Exploring rheological properties of aqueous polyaniline‐PVP dispersion

Stable aqueous dispersion of polyaniline (PAn) stabilized by a hydrophilic polymer poly(vinyl pyrrolidone) (PVP) exhibits interesting rheological properties different from its components. Shear thinning observed for both PVP and PAn–PVP colloid (PP) indicates partially entangled nature of the later. Linear viscoelastic response of PVP solution exhibit strong frequency dependence of elastic (G′) and viscous (G″) modulus over the whole frequency range (0.1–100 ras/s) where G′ never exceeds G″ indicating the applicability of the Rouse‐Zimm model to this system. On the other hand, there is a crossover of G′ and G″ in the rheological profile of PP dispersion so that a single relaxation time model can be applicable. Therefore, PVP presents an entangled polymeric system and supposed to have a spectrum of relaxation times, whereas PP resembles to a physically crosslinked system with a single relaxation time. Increasing the extent of hydrogen bonding within the system (by raising the fraction of PAn or by leaving the solution undisturbed for long) relaxation time also becomes longer. The large difference in values of steady and complex shear viscosity (η and η*) within LVE regime reflects that original Cox‐Merz rule is obviously inapplicable to these systems. But at larger strain amplitude, η and η* are satisfactorily coincident that indicates a broader applicability of the modified Cox‐Merz rule. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2443–2455, 2008     

A note on random coin tossing

Harris and Keane [Probab. Theory Related Fields 109 (1997) 27-37] studied absolute continuity/singularity of two probabilities on the coin-tossing space, one representing independent tosses of a fair coin, while in the other a biased coin is tossed at renewal times of an independent renewal process and a fair coin is tossed at all other times. We extend their results by allowing possibly different biases at the different renewal times. We also investigate the contiguity and asymptotic separation properties in this kind of set-up and obtain some sufficient conditions.Keywords:renewal process, absolute continuity, singularity, contiguity, asymptotic separation, martingale convergence theorem     

First x-ray scattering studies on electrostatically levitated metallic liquids: demonstrated influence of local icosahedral order on the nucleation barrier

To explain the unusual stability of undercooled liquids against crystallization, Frank hypothesized that the local structures of undercooled liquids contain a significant degree of icosahedral short-range order, which is incompatible with long-range periodicity. We present here the first direct experimental demonstration of Frank's complete hypothesis, showing a correlation between the nucleation barrier and a growing icosahedral short-range order with decreasing temperature in a Ti39.5Zr39.5Ni21 liquid. A new experimental facility, BESL (Beamline Electrostatic Levitation), was developed to enable the synchrotron x-ray structural studies on deeply undercooled, reactive liquids.     

Levels in doubly odd 138Pr

The band structures of the doubly odd ¹³⁸Pr nucleus have been investigated using the ¹²⁸Te(¹⁴N, 4n)¹³⁸Pr reaction at a beam energy of 55-65 MeV. Altogether six distinct structures have been established, of which the lower part of the yrast band and two side bands were known from earlier works. The observed level properties of the members of the yrast band have been compared with theoretical calculations performed within the Particle Rotor Model (PRM) with axially symmetric core. The experimental branching ratios and B(M1)/B(E2) values when compared with the theoretical results of the PRM, suggest an oblate core.     

Complexation of uranium(VI) by salicylate and substituted salicylates: A kinetic study

Summary Kinetic studies on the complexation of uranium(VI) by salicylate and various substituted salicylates have been carried out using the stopped-flow spectrophotometric technique at pH 7.0–8.5 (NH₄OH+NH₄NO₃ buffer). Results are in conformity with a mechanism involving binding of UO₂OH⁺ species through the carboxylate group of the salicylate to form an inner-sphere species in a fast equilibrium (equilibrium constant=K) followed by a slow rate-determining ring closure (rate constant=k) involving loss of a molecule of water between the OH group bound to uranium(VI) and the phenolic group of the salicylate. The value of the equilibrium constant (K) obtained from the kinetic data in the case of 5-sulphosalicylate (log K=3.21 at 25 °C, I=1 M) is compatible with the literature thermodynamic value (log K = 3.89 at 25 °C, I=0.015 M). Increase in pH retards the reaction due to the equilibrium, UO₂OH⁺ + OH^– UO₂(OH)₂, the UO₂(OH)₂ being unreactive. The average value of K (log K=8.58 at 25°C, I=1M) obtained kinetically from the results of investigation with different ligands is also in good agreement with the literature thermodynamic value (log K= 8.8 at 25°C, I=0.1M). Both K and k are sensitive to the nature of the substituent in the benzene ring, decreasing with increasing acidity of the -CO₂H group of the salicyclic acid; the substituent effect is well demonstrated by the plot of log kversus _L (where ), which is linear. H^# and S^# values corresponding to k have been evaluated in each case. S^# values are all negative in conformity with ring closure in the rate-determining step.