Porous, catalytically active palladium nanostructures by tuning nanoparticle interactions in an organic medium

We present a simple template-free method for the synthesis of interconnected hierarchical porous palladium nanostructures by controlling the aggregation of nanoparticles in organic media. The interaction between the nanoparticles is tuned by varying the dielectric constant of the medium consistent with DLVO calculations. The reaction products range from discrete nanoparticles to compact porous clusters with large specific surface areas. The nanoclusters exhibit hierarchical porosity and are found to exhibit excellent activity towards the reduction of 4-nitrophenol into 4-aminophenol and hydrogen oxidation. The method opens up possibilities for synthesizing porous clusters of other functional inorganics in organic media.

Self-assembled composite nano-materials exploiting a thermo reversible n-acene fibrillar scaffold and organic-capped ZnO nanoparticles

An organic-inorganic composite material is obtained by self-assembly of 2,3-didecyloxy-anthracene (DDOA), an organogelator of butanol, and organic-capped ZnO nanoparticles (NPs). The ligand 3, 2,3-di(6-oxy-n-hexanoic acid)-anthracene, designed to cap ZnO and interact with the DDOA nanofibers by structural similarity, improves the dispersion of the NPs into the organogel. The composite material displays mechanical properties similar to those of the pristine DDOA organogel, but gelates at a lower critical concentration and emits significantly less, even in the presence of very small amounts of ZnO NPs. The ligand 3 could also act as a relay to promote the photo-induced quenching process.

Second harmonic generation in poled molecularly doped polymer films : Push-pull butadienes in poly(methyl methacrylate) and polystyrene

We report second harmonic generation in a new class of organic materials, namely donor-acceptor substituted all-trans butadienes doped in poly(methyl methacrylate) or polystyrene and oriented by corona poling at elevated temperatures. Second harmonic measurements were made at room temperature. The observed d33 coefficients are greater than those of potassium dihydrogen phosphate or 4-dimethylamino-4'-nitrostilbene doped in similar polymer matrices. Rotational diffusion coefficients estimated from the decay characteristics of the second harmonic intensity in the polymer films indicate that the polymer matrix plays a major role in stabilizing the dopants in a nonlinear optics conducive environment.

Heterogeneous nucleation of pb particles embedded in a Zn matrix

Zinc-10 and 20 wt pct Pb alloys have been rapidly solidified by melt spinning to obtain a very fine scale dispersion of nanometer-sized Pb particles embedded in Zn matrix. The microstructure and crystallography of the Pb particles have been studied using transmission electron microscopy (TEM). Each embedded Pb particle is a single crystal, with a truncated hexagonal biprism shape with the 6/mmm Zn matrix point group symmetry surrounded by and { 0001 á },\text { \text10[`\text1] \text0 },\text and { \text10[`\text1] \text1 }0001 1010 and 1011 facets. The Pb particles solidify with a well-defined orientation relationship with the Zn matrix of ( 0001 )Zn ||(111)Pb\text and\text [ \text11[`\text2] \text0 ]Zn| ||[ 1[`1] 0 ]Pb 0001Zn(111)Pb and 1120Zn110Pb . The melting and solidification behavior of the Pb particle have been studied using differential scanning calorimetry (DSC). The Pb particles solidify with an undercooling of approximately 30 K, by heterogeneous nucleation on the {0001} facets of the surrounding Zn matrix, with an apparent contact angle of 23 deg.

Characteristics of superplasticity domain in the processing map for hot working of an Al alloy 2014---20vol.%Al2O3 metal matrix composite

The processing map for hot working of Al alloy 2014-20vol.%Al2O3 particulate-reinforced cast-plus-extruded composite material has been generated covering the temperature range 300-500 degrees C and the strain rate range 0.001-10 s(-1) based on the dynamic materials model. The efficiency eta of power dissipation given by 2m/(m + 1), where m is the strain rate sensitivity, is plotted as a function of temperature and strain rate to obtain a processing map. A domain of superplasticity has been identified, with a peak efficiency of 62% occurring at 500 degrees C and 0.001 s(-1). The characteristics of this domain have been studied with the help of microstructural evaluation and hot-ductility measurements. Microstructural instability is predicted at higher strain rates above (ls(-1)) and lower temperatures (less than 350 degrees C).

Concise row-pruning algorithm to invert a matrix

Presented here, in a vector formulation, is an O(mn2) direct concise algorithm that prunes/identifies the linearly dependent (ld) rows of an arbitrary m X n matrix A and computes its reflexive type minimum norm inverse A(mr)-, which will be the true inverse A-1 if A is nonsingular and the Moore-Penrose inverse A+ if A is full row-rank. The algorithm, without any additional computation, produces the projection operator P = (I - A(mr)- A) that provides a means to compute any of the solutions of the consistent linear equation Ax = b since the general solution may be expressed as x = A(mr)+b + Pz, where z is an arbitrary vector. The rank r of A will also be produced in the process. Some of the salient features of this algorithm are that (i) the algorithm is concise, (ii) the minimum norm least squares solution for consistent/inconsistent equations is readily computable when A is full row-rank (else, a minimum norm solution for consistent equations is obtainable), (iii) the algorithm identifies ld rows, if any, and reduces concerned computation and improves accuracy of the result, (iv) error-bounds for the inverse as well as the solution x for Ax = b are readily computable, (v) error-free computation of the inverse, solution vector, rank, and projection operator and its inherent parallel implementation are straightforward, (vi) it is suitable for vector (pipeline) machines, and (vii) the inverse produced by the algorithm can be used to solve under-/overdetermined linear systems.

Utility of microbes in organic-synthesis - selective transformations of acyclic isoprenoids by aspergillus-niger

Bioconversion of acyclic isoprenoids using a strain of Aspergillus niger results in hydroxylated metabolites with regio- and stereoselectivity. The organism carries out oxidation of the terminal allylic methyl group and the remote double bond in all the compounds tested (I-VII). However, these two activities seem to have preferential structural requirements. When an acyclic isoprenoid with a ketone functionality such as geranylacetone is used as the substrate, the organism also carries out the asymmetric reduction of the keto group. All the metabolites formed have been purified and characterized by conventional spectroscopic methods and quantification has been made by gas chromatographic analyses.

Matrix method for eigenstructure assignment - The multi-input case with application

The eigenvalue and eigenstructure assignment procedure has found application in a wide variety of control problems. In this paper a method for assigning eigenstructure to a linear time invariant multi-input system is proposed. The algorithm determines a matrix that has eigenvalues and eigenvectors at the desired locations. It is obtained from the knowledge of the open-loop system and the desired eigenstructure. Solution of the matrix equation, involving unknown controller gams, open-loop system matrices, and desired eigenvalues and eigenvectors, results hi the state feedback controller. The proposed algorithm requires the closed-loop eigenvalues to be different from those of the open-loop case. This apparent constraint can easily be overcome by a negligible shift in the values. Application of the procedure is illustrated through the offset control of a satellite supported, from an orbiting platform, by a flexible tether.

Matrix method for eigenvalue assignment: The single input case

The eigenvalue assignment/pole placement procedure has found application in a wide variety of control problems. The associated literature is rather extensive with a number of techniques discussed to that end. In this paper a method for assigning eigenvalues to a Linear Time Invariant (LTI) single input system is proposed. The algorithm determines a matrix, which has eigenvalues at the desired locations. It is obtained from the knowledge of the open-loop system and the desired eigenvalues. Solution of the matrix equation, involving unknown controller gains, open-loop system matrices and desired eigenvalues, results in the state feedback controller. The proposed algorithm requires the closed-loop eigenvalues to be different from those of the open-loop case. This apparent constraint is easily overcome by a negligible shift in the values. Two examples are considered to verify the proposed algorithm. The first one pertains to the in-plane libration of a Tethered Satellite System (TSS) while the second is concerned with control of the short period dynamics of a flexible airplane. Finally, the method is extended to determine the Controllability Grammian, corresponding to the specified closed-loop eigenvalues, without computing the controller gains.

Matrix method for eigenstructure assignment - The multi-input case with application

The eigenvalue and eigenstructure assignment procedure has found application in a wide variety of control problems. In this paper a method for assigning eigenstructure to a Linear time invariant multi-input system is proposed. The algorithm determines a matrix that has eigenvalues and eigenvectors at the desired locations. It is obtained from the knowledge of the open-loop system and the desired eigenstructure. solution of the matrix equation, involving unknown controller gains, open-loop system matrices, and desired eigenvalues and eigenvectors, results in the state feedback controller. The proposed algorithm requires the closed-loop eigenvalues to be different from those of the open-loop case. This apparent constraint can easily be overcome by a negligible shift in the values. Application of the procedure is illustrated through the offset control of a satellite supported, from an orbiting platform, by a flexible tether,

Matrix method for eigenvalue assignment: The single input case

The eigenvalue assignment/pole placement procedure has found application in a wide variety of control problems. The associated literature is rather extensive with a number of techniques discussed to that end. In this paper a method for assigning eigenvalues to a Linear Time Invariant (LTI) single input system is proposed. The algorithm determines a matrix, which has eigenvalues at the desired locations. It is obtained from the knowledge of the open-loop system and the desired eigenvalues. Solution of the matrix equation, involving unknown controller gains, open-loop system matrices and desired eigenvalues, results in the state feedback controller. The proposed algorithm requires the closed-loop eigenvalues to be different from those of the open-loop case. This apparent constraint is easily overcome by a negligible shift in the values. Two examples are considered to verify the proposed algorithm. The first one pertains to the in-plane libration of a Tethered Satellite System (TSS) while the second is concerned with control of the short period dynamics of a flexible airplane. Finally, the method is extended to determine the Controllability Grammian, corresponding to the specified closed-loop eigenvalues, without computing the controller gains.

Physical characterization of the organic nonlinear optical crystal � 3-methoxy 4-hydroxy benzaldehyde

We highlight our recent experimental work on an efficient molecular nonlinear optical crystal, 3-methoxy 4-hydroxy benzaldehyde (MHBA). Optical quality single crystals of MHBA were grown from mixtures of solvents and from melt. The overall absorption and transparency window were improved by growing them in a mixture of chloroform and acetone. The grown crystals were characterized for their optical transmission, mechanical hardness and laser damage. We have observed a strong correlation between mechanical properties and laser induced damage.

A study of microstructure and wear behaviour of TiB2/Al metal matrix composites

The present paper deals with the study of microstructure and wear characteristics of TiB2 reinforced aluminium metal matrix composites (MMCs). Matrix alloys with 5, 10 and 15% of TiB2 were made using stir casting technique. Effect of sliding velocity on the wear behaviour and tribo-chemistry of the worn surfaces of both matrix and composites sliding against a EN24 steel disc has been investigated under dry conditions. A pin-on-disc wear testing machine was used to find the wear rate, in which EN24 steel disc was used as the counter face, loads of 10-60N in steps of 10N and speeds of 100, 200, 300, 400 and 500 rpm were employed. The results showed that the wear rate was increased with an increase in load and sliding speed for both the materials. However, a lower wear rate was obtained for MMCs when compared to the matrix alloys. The wear transition from slight to severe was presented at the critical applied loads. The transition loads for the MMCs were much higher than that of the matrix alloy. The transition loads were increased with increase in TiB2 and the same was decreased with the increase of sliding speeds. The SEM and EDS analyses were undertaken to demonstrate the effect of TiB2 particles on the wear mechanism for each conditions.

Role of organic fluorine in crystal engineering

The design of compounds with novel and improved physico-chemical properties as advanced functional materials with a specific application spectrum requires the knowledge about possible supramolecular packing motifs and their experimental control in crystalline lattice. Besides the structure of the individual molecule, non-covalent interactions play a significant role in the determination of molecular conformation, along with the formation of three-dimensional supramolecular architecture in a crystal as a requirement for molecular recognition processes, and the related bioactivity. Involvement of functional groups will contribute to the formation of a predefined packing motif due to their well-defined interactions. The strength and directionality of these interactions create characteristic packing motifs, which can be used for the design of supramolecular arrangements by the development of appropriate strategies for the precise control of their topology. Most relevant of these non-covalent interactions are stacking interactions and hydrogen bonds, which have been subjects of extensive study in the last two decades. In recent literature, substantial efforts have been put in by various researchers towards the understanding of interactions involving organic fluorine and the role they play in generating different packing motifs which guides assembling of molecules in the crystal lattice.

Use of L matrix to obtain reliable ab initio force constants of polyatomic molecules: ethylene as a test system

Direct use of experimental eigenvalues of the vibrational secular equation on to the ab initio predicted eigenvector space is suggested as a means of obtaining a reliable set of intramolecular force constants. This method which we have termed RECOVES (recovery in the eigenvector space) is computationally simple and free from arbitrariness. The RECOVES force constants, by definition, reproduce the experimental vibrational frequencies of the parent molecule exactly. The ab initio calculations were carried out for ethylene as a test molecule and the force constants obtained by the present procedure also correctly predict the vibrational frequencies of the deuterated species. The RECOVES force constants for ethylene are compared with those obtained by using the SQM procedure.