Nano-enabled microtechnology: polysulfone nanocomposites incorporating cellulose nanocrystals

Microchannel devices hold the potential to transform many separation processes. This preliminary study investigated the feasibility of incorporating cellulose nanocrystals (CNXLs) into polysulfone, a commonly used ultrafiltration membrane polymer. Incorporating CNXLs into non-water soluble polymers without aggregation has been problematic. A solvent exchange process was developed that successfully transferred an aqueous CNXL dispersion into the organic solvent N-methylpyrrolidone (NMP), which is a solvent for polysulfone (PSf). Films were prepared from the solution of PSf in NMP with dispersed CNXLs by a phase inversion process. Films were then examined by scanning electron microscopy and tested for their transport and mechanical properties. The interaction between the polymer matrix and the CNXL filler was studied by means of thermogravimetric analysis (TGA), which suggested a close interaction between the polymer and filler at the 2% filler loading. The tensile modulus showed a large increase beyond 1% filler loading, which could be due to a percolation effect. The water vapor transport rate increased with increase in filler loading. Agglomeration of the CNXLs seemed to be taking place at filler loadings >7%.     

Titration of vanadium(IV) with cerium(IV) sulphate, with ferroin as indicator, in aqueous acetone as facile reaction medium An analytical and mechanistic study

A new procedure for the titration of vanadium(IV) with cerium(IV) sulphate, with ferroin as indicator, in aqueous acetone medium is reported. A differential determination of iron(II) and vanadium(IV) is also possible. A probable mechanism for the fast ferriin-vanadium(IV) reaction in acetone medium is given.     

Perovskites-like composites for CO2 photoreduction into hydrocarbon fuels

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Acid–base polyimide blends for the application as electrolyte membranes for fuel cells

The synthesis and characterization of new acid–base polymer blend membranes for the use in polymer electrolyte membrane fuel cell is presented in this paper. A novel polymeric base is synthesized from 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2-bis [4-(4-aminophenoxy)phenyl] hexafluoropropane and diaminoacrydine hemisulfate where the diaminoacrydine hemisulfate contribute the tertiary nitrogen groups to the polyimide backbone. This base polyimide is blended with a polyimide having sulfonic acid group in the main chain. The sulfonated polyimide is synthesized from 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTDA), 4,4′-diaminobiphenyl 2,2′-disulfonic acid (BDSA), 2-bis [4-(4-aminophenoxy)phenyl] hexafluoropropane (HFBAPP). Various polyimide blends having different molar ratio of sulfonic acid group and acrydine group are synthesized and they are characterized for thermal stability, ion exchange capacity, water uptake, hydrolytic stability and proton conductivity. All the sulfonated polyimides have good thermal stability and exhibited three-step degradation pattern. With the increase in polymeric base content, IEC decreased as AB-0% (2.0640) > AB-10% (2.0058) > AB-20% (1.8792) > AB-30% (1.5686) > AB-40% (1.2670) > AB-50% (1.1690) > AB-75% (0.9098) and water uptake decreased as AB-0% (34.06%) > AB-10% (32.82%) > AB-20% (24.01%) > AB-30% (20.31%) > AB-40% (12.86%) > AB-50% (9.25%) > AB-75% (8.37%). Proton conductivity of the acid–base polyimide blends at 90 °C are AB-0% (0.197) > AB-10% (0.124) > AB-20% (0.122) > AB-30% (0.088) > AB-40% (0.080) > AB-50% (0.034) > AB-75% (0.025). Polyimide blends showed higher hydrolytic stability than the pure acid polyimide. Between the polyimide blends the hydrolytic stability increased with increase in the base polymer content which is attributed to the increase in ionic crosslink density which reduces the polymer swelling and hence the mechanical stability of the membrane increases.     

Photomagnetism and photoluminescence (PL) of (Pb-Fe-e(-)) complex in lead magnesium niobate-lead titanate (PMN-PT) crystals containing beta-PbO nanoclusters

We present electron paramagnetic resonance (EPR)--evidence of photomagnetism under the conditions of in situ green laser illumination (photo-EPR) in lead magnesium niobate-lead titanate, Pb(Mg,Nb)O3-PbTiO3 (PMN-PT), containing nanoparticles/wires of orthorhombic beta-PbO as identified by Raman spectroscopy. Photo-EPR studies of the sample containing beta-PbO, brownish red in color, have shown intense line at g=2.00, and its yield increased when produced in the presence of 7.5 kG external magnetic field suggesting the formation of magnetic polaron. This was identified as due to interaction between Fe3+, photoinduced Pb3+ and unpaired electron trapped at oxygen vacancies. The photoinduced growth and decay of magnetic polaron has shown a non-exponential behavior. Photoluminescence (PL) studies were conducted with excitation at 308 nm (XeCl laser) and also at 454.5, 488 and 514.5 nm using Ar+ laser. The excitation with 308 nm gave broad PL centered at 500 and 710 nm the latter being quite prominent in beta-PbO containing crystals, along with cooperative luminescence at 350 nm involving two emitting centers. The excitation with Ar+ laser lines, close to the electronic absorption in samples containing beta-PbO gave richer and sharp PL emission in red region from the constituents of the magnetic polaron and also intense anti-Stokes emission on excitation with 514.5 nm radiation. This appears to be due to phototransfer optically stimulated luminescence (PT-OSL) involving electron-hole recombination at photoinduced magnetic polaron site.     

Fq-linear Cyclic Codes over $$ F{_q^m}$$ : D FT Approach

Codes over that are closed under addition, and multiplication with elements from F_q are called F_q-linear codes over . For m 1, this class of codes is a subclass of nonlinear codes. Among F_q-linear codes, we consider only cyclic codes and call them F_q-linear cyclic codes (F_q LC codes) over The class of F_q LC codes includes as special cases (i) group cyclic codes over elementary abelian groups (q=p, a prime), (ii) subspace subcodes of Reed–Solomon codes (n=q^m–1) studied by Hattori, McEliece and Solomon, (iii) linear cyclic codes over F_q (m=1) and (iv) twisted BCH codes. Moreover, with respect to any particular F_q-basis of , any F_qLC code over can be viewed as an m-quasi-cyclic code of length mn over F_q. In this correspondence, we obtain transform domain characterization of F_q LC codes, using Discrete Fourier Transform (DFT) over an extension field of The characterization is in terms of any decomposition of the code into certain subcodes and linearized polynomials over . We show how one can use this transform domain characterization to obtain a minimum distance bound for the corresponding quasi-cyclic code. We also prove nonexistence of self dual F_q LC codes and self dual quasi-cyclic codes of certain parameters using the transform domain characterization.AMS classification 94B05     

Spectroscopic studies of transition metal ions in spessartine garnet

From optical absorption studies at room and liquid air temperatures and from Mössbauer spectrum, the absorption bands of spessartine garnet are attributed to Mn²⁺ and Fe²⁺ ions. The energy matrices ofd ⁵ andd ⁶ configurations are solved and the experimental data of Mn²⁺ and Fe²⁺ bands are fitted with the calculated values to solve for the Racah and crystal field parameters.     

On the deque conjecture for the splay algorithm

Splay is a simple, efficient algorithm for searching binary search trees, devised by Sleator and Tarjan, that reorganizes the tree after each search by means of rotations. An open conjecture of Sleator and Tarjan states that Splay is, in essence, the fastest algorithm for processing any sequence of search operations on a binary search tree, using only rotations to reorganize the tree. Tarjan proved a basic special case of this conjecture, called theScanning Theorem, and conjectured a more general special case, called theDeque Conjecture. The Deque Conjecture states that Splay requires linear time to process sequences of deque operations on a binary tree. We prove the following results:

1. Almost tight lower and upper bounds on the maximum numbers of occurrences of various types of right rotations in a sequence of right rotations performed on a binary tree. In particular, the lower bound for right 2-turns refutes Sleator's Right Turn Conjecture.
2. A linear times inverse Ackerman upper bound for the Deque Conjecture. This bound is derived using the above upper bounds.
3. Two new proofs of the Scanning Theorem, one, a simple potential-based proof that solves Tarjan's problem of finding a potential-based proof for the theorem, the other, an inductive proof that generalizes the theorem.

     

Law of the iterated logarithm for solutions of stochastic differential equations

We prove the law of the iterated logarithm for solutions of Stochastic Differential Equations (SDEs) driven by continuous semiraartingales, under suitable conditions. This extends a result of Kulinich for classical diffusions to solutions of SDEs which are not necessarily Markov