Gas‐Sensing Properties of Needle‐Shaped Ni‐Doped SnO2 Nanocrystals Prepared by a Simple Sol–Gel Chemical Precipitation Method

The preparation of needle‐shaped SnO₂ nanocrystals doped with different concentration of nickel by a simple sol–gel chemical precipitation method is demonstrated. By varying the Ni‐dopant concentration from 0 to 5 wt %, the phase purity and morphology of the SnO₂ nanocrystals are significantly changed. Powder XRD results reveal that the SnO₂ doped with a nickel concentration of up to 1 wt % shows a single crystalline tetragonal rutile phase, whereas a slight change in the crystallite structure is observed for samples with nickel above 1 wt %. High resolution scanning electron microscopy (HRSEM) results reveal the change in morphology of the materials from spherical, for SnO₂, to very fine needle‐like nanocrystals, for Ni‐doped SnO₂, annealed at different temperatures. The gas sensing properties of the SnO₂ nanocrystals are significantly enhanced after the nickel doping.     

Development of core‐shell structure aided by SiC‐coated MWNT in ABS/LCP blend

Agglomeration is an issue of major concern for unmodified multi‐walled carbon nanotubes (MWNTs)‐aided polymeric composites. To overcome the above‐mentioned problem, multi‐walled carbon nanotubes (MWNTs) are modified by polycarbosilane (PCS)‐derived Silicone carbide (SiC). Acrylonitrile Butadiene Styrene (ABS)/Liquid Crystalline polymer (LCP)/MWCNT nanocomposites are prepared through melt blending in a twin screw extruder. X‐Ray Diffraction (XRD) studies authenticate the creation of ß‐SiC particles. Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) studies reveal the formation of core–shell morphology involving MWNT as the core and SiC‐coated MWNT as the shell. The degree of dispersion of MWNT is far better when it has been coated with SiC. As viewed from Thermo‐gravimetric analysis (TGA), the thermal stability is substantially increased in SiC‐aided nanocomposite in comparison to ABS/LCP/unmodified CNT blend. Glass transition temperature as well as mechanical properties are improved significantly (in the presence of SiC‐coated MWNT) as a result of homogeneous dispersion exhibited by MWNT. Copyright © 2009 John Wiley & Sons, Ltd.     

Role of sugar in controlling reaction pattern: A comparative study with adenine and 2′-deoxyadenosine

Interaction between 2-methyl-1,4-naphthoquinone (MQ) and adenine (A) and 2′-deoxyadenosine (dA) reveals interesting differences with respect to electron transfer (ET) and hydrogen abstraction (HA). In our case A and dA exhibited ET from different sites, which has been associated to the presence of a sugar unit in dA. Sugar unit has also reduced the rate of ET from dA. We have utilized an external magnetic field in conjunction with our laser flash photolysis set-up to establish our data. In a polar MeCN/H₂O medium A and dA are found to promote ET but HA from dA is seen to be insignificant. However shifting to a heterogeneous micellar medium has been found to have a marked effect in increasing the HA rate for dA only. Separate experiments with 2′-deoxyribose sugar have revealed sugar moiety to be more susceptible to HA in SDS medium.     

L1 regression estimate and its bootstrap

We study the asymptotic distribution of the L ₁ regression estimator under general conditions with matrix norming and possibly non i.i.d. errors. We then introduce an appropriate bootstrap procedure to estimate the distribution of this estimator and study its asymptotic properties. It is shown that this bootstrap is consistent under suitable conditions and in other situations the bootstrap limit is a random distribution. This work was supported by J.C. Bose National Fellowship, Government of India     

Optimal predictive densities and fractional moments

The maximum entropy approach used together with fractional moments has proven to be a flexible and powerful tool for density approximation of a positive random variable. In this paper we consider an optimality criterion based on the Kullback–Leibler distance in order to select appropriate fractional moments. We discuss the properties of the proposed procedure when all the available information comes from a sample of observations. The method is applied to the size distribution of the U.S. family income. Copyright © 2008 John Wiley & Sons, Ltd.     

An optimization based approach for deployment of roadway incident response vehicles with reliability constraints

In recent years transportation agencies have introduced patrol based response programs to remove roadway incidents rapidly. With the evolution of technology incident detection and notification from remote traffic operation centers is possible and patrols to detect incidents are not necessary. Instead, the response units can be placed at various depots in urban areas and dispatched to incident sites upon notification. In this paper, we propose a reliability based mixed integer programming model to find best locations of incidence response depots and assign response vehicles to these depots so that incidents can be cleared efficiently at a minimum cost. The approach is unique as it considers fixed and variable costs of vehicles and depots, occurrences of major and minor incidents, and reliability of response service in the same model. Numerical results are generated for an example problem and sensitivity analysis is conducted to explore the relationships between parameters of the problem.     

Water-in-trichloroethylene emulsions stabilized by uniform carbon microspheres

Uniform hard carbon spheres (HCS), synthesized by the hydrothermal decomposition of sucrose followed by pyrolysis, are effective at stabilizing water-in-trichloroethylene (TCE) emulsions. The irreversible adsorption of carbon particles at the TCE-water interface resulting in the formation of a monolayer around the water droplet in the emulsion phase is identified as the key reason for emulsion stability. Cryogenic scanning electron microscopy was used to image the assembly of carbon particles clearly at the TCE-water interface and the formation of bilayers in regions of droplet-droplet contact. The results of this study have potential implications to the subsurface injection of carbon submicrometer particles containing zero-valent iron nanoparticles to treat pools of chlorinated hydrocarbons that are sequestered in fractured bedrock.     

A Series of Amino Acid Functionalized Tripodal Hexaamide Anion Receptors: Ion‐Pair‐Assisted Capped‐Cleft Formation by a Pentafluorophenyl‐Functionalized Amide

A new series of tris(2‐aminoethyl)amine (tren)‐based L ‐alanine amino acid backboned tripodal hexaamide receptors (L1–L5) with various attached moieties based on electron‐withdrawing fluoro groups and lipophilicity have been synthesized and characterized. Detailed binding studies of L1–L5 with different anions, such as halides (F^?, Cl^?, Br^?, and I^?) and oxyanions (AcO^?, BzO^? (Bz=benzoyl), NO₃^?, H₂PO₄^?, and HSO₄^?), have been carried out by isothermal titration calorimetric (ITC) experiments in acetonitrile/dimethylsulfoxide (99.5:0.5 v/v) at 298 K. ITC titration experiments have clearly shown that receptors L1–L4 invariably form 1:1 complexes with Cl^?, AcO^?, BzO^?, and HSO₄^?, whereas L5 forms a 1:1 complex only with AcO^?. In the case of Br^?, I^?, and NO₃^?, no appreciable heat change is observed owing to weak interactions between these anions and receptors; this is further confirmed by ¹H NMR spectroscopy. The ITC binding studies of F^? and H₂PO₄^? do not fit well for a 1:1 binding model. Furthermore, ITC binding studies also revealed slightly higher selectivity of this series of receptors towards AcO^? over Cl^?, BzO^?, and HSO₄^?. Solid‐state structural evidence for the recognition of Cl^? by this new category of receptor was confirmed by single‐crystal X‐ray structural analysis of the complex of tetrabutylammonium chloride (TBACl) and L1. Single‐crystal X‐ray diffraction clearly showed that the pentafluorophenyl‐functionalized amide receptor (L1) encapsulated Cl^? in its cavity by hydrogen bonds from amides, and the cavity of L1 was capped with a TBA cation through hydrogen bonding and ion‐pair interactions to form a capped‐cleft orientation. To understand the role of the cationic counterpart in solution‐state Cl^? binding processes with this series of receptors (L1–L4), a detailed Cl^? binding study was carried out with three different tetraalkylammonium (Me₄N⁺, Et₄N⁺, and Bu₄N⁺) salts of Cl^?. The binding affinities of these receptors with different tetralkylammonium salts of Cl^? gave binding constants with the TBA cation in the following order: butyl>ethyl>methyl. This study further supports the role of the TBA countercation in ion‐pair recognition by this series of receptors.