Dielectric studies on sulphonated novolacs

The dielectric constants of novalac type of phenolic resins and their sulphonated derivatives were studied as a function of frequency, temperature and extent of sulphonation. The effect of moisture on the dielectric constant has also been reported. Introduction of —SO₃H groups into the polymer matrix increases the dielectric constant by several orders, while the resin continues to exhibit low losses.     

Facilitated transport in spherical shells: application of the combined damköhler number technique

In cell membranes, double emulsion drops, or other particles with spherical shell geometry, reversible carriers may be present which serve to facilitate transport of solutes into the particles. The physical phenomena taking place are both diffusion and chemical reaction. When the reaction deviates from chemical equilibrium, the solution of the conservation equations becomes difficult because the equations are non-linear. The combined Damköhler technique, recently devised by Hoofd and Kreuzer, is a simple analytical method to accurately predict facilitated mass transfer in the presence of non-equilibrium chemical reaction. The application of the combined Damköhler technique to spherical shell geometry gives accurate predictions of the facilitated flux over the full range of Damköhler numbers, when compared to results from a numerical analysis technique. The non-equilibrium facilitated flux depends on the sphericity of the spherical shell.     

Cloning, expression, and sequence analysis of diaminopropionate ammonia lyase gene from a nonvirulentsalmonella typhimurium PU011

Background: Seeds ofLathyrus sativus, a legume plant, contain 3-oxalyl and 2,3-dioxalyl DAP (O-DAP), neurotoxins which when consumed causes Neurolathyrism or Osteolathyrism, in humans, affecting nervous system and bone formation respectively. Some microorganisms viz virulent and non-virulentSalmonella typhimurium, Salmonella typhi and Pseudomonad have been shown to detoxifyL-α,β-diaminopropionate (DAP), the immediate precursor of O-DAP. Result: The gene coding for diaminopropionate ammonia lyase (DAPAL) which detoxifies DAP was cloned from nonvirulentS. typhimurium PU011 intoEscherichia coli DH5α and the nucleotides sequenced (1212 bp). Whereas the specific enzyme activity of DAPAL obtained from recombinantE. coli PU018 was 0.346 U/mg, the specific activity of the enzyme from nonvirulentS. typhimurium PU011 was 0.351 U/mg. The DAPAL corresponding to 43 kDa protein was found both in nonvirulentS. typhimurium PU011 andE. coli PU018. The Km value was found to be 0.740 mM and 0.680 mM forS. typhimurium PU011 and 0.741 mM and 0.683 mM forE. coli PU018 when grown in minimal medium (MM+DAP) andL. sativus seed extracts respectively, indicating that both of them were capable of utilizing the neurotoxins present inL. sativus seeds. The biomass, enzyme production and the effect of pH and temperature on DAPAL enzyme activity from both non-virulentS. typhimurium PU011 andE. coli PU018 were found to be similar. Conclusion: The recombinantE. coli PU018 as well as non-virulentS. typhimurium PU011 are as good as pathogenicS. typhimurium in detoxifying DAP, the immediate precursor of O-DAP present inL. sativus seeds.     

Synthesis of spiropyrazolines

Synthesis of a series of novel 1,3,2′-triphenyl-4-aryl spiropyrazolines [5.4′]-2′-butenolides has been accomplished in good yield by regioselective 1,3-dipolar cycloaddition of diphenylnitrilimine with (E)-3-arylidenebutenolides. X-ray crystal structure analysis of one of the products 4a confirms the structure of the product and the regiochemistry of cycloaddition. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:517–522, 1998     

Design theory and some forbidden configurations

In this paper we relate $t$‐designs to a forbidden configuration problem in extremal set theory. Let ${\mathbf{1}}_t{\mathbf{0}}_{?}$ denote a column of $t$ 1's on top of $?$ 0's. Let $q?{\mathbf{1}}_t{\mathbf{0}}_{?}$ denote the $\left(t+?\right)\times q$ matrix consisting of $t$ rows of $q$ 1's and $?$ rows of $q$ 0's. We consider extremal problems for matrices avoiding certain submatrices. Let $A$ be a (0, 1)‐matrix forbidding any $\left(t+?\right)\times \left(\lambda +2\right)$ submatrix $\left(\lambda +2\right)?{\mathbf{1}}_t{\mathbf{0}}_{?}$. Assume $A$ is $m$‐rowed and only columns of sum $t+1,t+2,\text{…},m??$ are allowed to be repeated. Assume that $A$ has the maximum number of columns subject to the given restrictions. Assume $m$ is sufficiently large. Then $A$ has each column of sum $0,1,\text{…},t$ and $m??+1,m??+2,\text{…},m$ exactly once and, given the appropriate divisibility condition, the columns of sum $t+1$ correspond to a $t$‐design with block size $t+1$ and parameter $\lambda$. The proof derives a basic upper bound on the number of columns of $A$ by a pigeonhole argument and then a careful argument, for large m, reduces the bound by a substantial amount down to the value given by design‐based constructions. We extend in a few directions.     

Laser-assisted cleaning: Dominant role of surface

Pulsed laser-assisted removal of particulates from substrates has decided advantages over the conventional methods of cleaning. Experiments conducted with loose contamination on metal and transparent dielectric surfaces proved conclusively the dominant role played by the absorption of the incident radiation by the surface towards the generation of the cleaning force as against the absorption in the particulates alone. Further, the presence of transparent/semi-transparent particulates on a metal surface was found to result in an increased absorption of the incident radiation by the substrate. This effect, identified as field-enhanced surface absorption was found to increase with reduction in the average particulate size.     

Ramanujan summation and the exponential generating function \sum_{k=0}^{\infty}\frac{z^{k}}{k!}\zeta^{\prime}(-k)

In the sixth chapter of his notebooks, Ramanujan introduced a method of summing divergent series which assigns to the series the value of the associated Euler-MacLaurin constant that arises by applying the Euler-MacLaurin summation formula to the partial sums of the series. This method is now called the Ramanujan summation process. In this paper we calculate the Ramanujan sum of the exponential generating functions ∑ _n≥1log?n e ^nz and $\sum_{n\geq 1}H_{n}^{(j)}~e^{-nz}$ where $H_{n}^{(j)}=\sum_{m=1}^{n}\frac{1}{m^{j}}$ . We find a surprising relation between the two sums when j=1 from which follows a formula that connects the derivatives of the Riemann zeta-function at the negative integers to the Ramanujan sum of the divergent Euler sums ∑ _n≥1 n ^k H _n , k ≥ 0, where $H_{n}=H_{n}^{(1)}$ . Further, we express our results on the Ramanujan summation in terms of the classical summation process called the Borel sum.     

The Discrete Logarithm Problem Over Prime Fields: The Safe Prime Case. The Smart Attack,Non-Canonical Lifts and Logarithmic Derivatives

We connect the discrete logarithm problem over prime fields in the safe prime case to the logarithmic derivative.     

Supramolecular light harvesting antennas to enhance absorption cross-section in dye-sensitized solar cells

Doping a zinc porphyrin based-sensitizer with antenna molecules, axially held by metallo-supramolecular interactions, enhances the light-harvesting efficiency and the overall photo-conversion efficiency of the solar cells by about 30%.     

Side-chain-grafted random copolymer brushes as neutral surfaces for controlling the orientation of block copolymer microdomains in thin films

Random copolymers of P(S-r-MMA-r-HEMA)s with a distribution of surface reactive hydroxyl groups were synthesized to formulate neutral surface layers on a SiO2 substrate. The layers were designed to drive vertical orientation of lamellar microdomains in a top P(S-b-MMA) thin film. Copolymers with a styrene weight fraction (f(St)) of 0.58 and a HEMA fraction (f(HEMA)) ranging from 0.01 to 0.03, with a corresponding MMA fraction (f(MMA)) ranging from 0.41 to 0.39, in the P(S-r-MMA-r-HEMA) copolymer showed neutral surface characteristics. The morphology of block copolymer thin films was studied by scanning electron microscopy (SEM). P(S-r-MMA-r-HEMA) copolymers prepared by both living and classical free-radical polymerizations were equally effective in demonstrating the neutrality of the surface. These side-chain-grafted random copolymer brushes showed faster grafting kinetics than the end-chain-grafted P(S-r-MMA) because of multipoint attachment to the surface. The modified surfaces had a very thin layer of random copolymer brush (5-7 nm), which is desirable for effective pattern transfer. Furthermore, neutral surfaces could be obtained even when the grafting time was reduced to 3 h. These results indicate that the composition of the random copolymer brush, rather than its PDI or molecular weights, is the most important factor in controlling the neutrality of the surface. These results also demonstrate the feasibility of using a third comonomer (C) in the random copolymer brush P(A-r-B-r-C) to alter the interfacial and surface energies of a diblock copolymer (A-b-B).