Theoretical and experimental analysis of iron-exchanged X-zeolite catalyst for SI engine emission control

The fuel economy potential of lean-burn gasoline engines can be utilized without any adverse effect on the environment, only if a suitable catalytic system for converting NO_x in an oxidizing atmosphere is available. Selective catalytic reduction of NO_x over metal-exchanged zeolite can be one of the solutions for reducing NO_x in automobile exhaust containing excess oxygen. Iron-exchanged X-zeolite catalyst (Fe–X) has been developed and tested in the exhaust of an actual SI engine over a wide range of air–fuel ratio, space velocity (SV) and catalyst temperature. Maximum conversion efficiencies of 55.8% and 57.4% were recorded for NO_x and CO, respectively. The catalyst also maintains its high performance through a wide range of temperatures. A mathematical model has been developed as well for predicting the performance of the catalytic converter containing Fe–X catalyst and the numerical solutions are presented. The predicted results agree well with the experimental results and are within the experimental uncertainty limits. The absolute average deviations are found to be within 6% and 5% of the predicted conversion efficiencies for NO_x and CO, respectively.     

Sharp depletion of attenuation of 22.235 GHz associated with Nor’wester over Kolkata, India and possible method of forecasting Nor’wester

The sharp depletion of attenuation of 22.235 GHz signal before the onset of Nor’wester over Kolkata, India is observed and possible explanation of such type of variation is presented. It is concluded that this may be taken as one possible method of forecasting severe thunderstorm associated with Nor’wester. Physical explanations based on the formation and dissipation mechanisms of thunderstorm are also presented.     

Defining the membrane proteome of NK cells

The present study was initiated to define the composition of the membrane proteome of the Natural Killer (NK) like cell line YTS. Isolated membranes were treated with reagents that have been reported to remove peripheral membrane proteins. Additional steps involving trifluoroethanol (TFE) were introduced in an effort to remove remaining nonintegral membrane proteins. This treatment resulted in the release of a subset of proteins without any apparent disruption of membrane integrity. The membranes were solubilized and digested with trypsin in 25% TFE. The resulting peptides were separated using an off‐line two‐dimensional reversed phase LC technique at alkaline and acidic pHs. Mass spectrometric analysis identified 1843 proteins with high confidence scores. On the basis of the presence of transmembrane regions or evidence of posttranslational modifications and prediction algorithms, approximately 40% of the identified proteins were predicted as plausible membrane proteins. The remaining species were largely involved in cellular processes and molecular functions that could be predicted to be transiently associated with membranes. The analytical approaches presented in this study offer robust generic methods for the identification and characterization of membrane proteins. These observations highlight the fact that the membrane is a dynamic entity that is composed of integral and stably associated proteins. Copyright © 2009 John Wiley & Sons, Ltd.     

Structural, electronic and magnetic properties of Cr-doped Cd12S12 clusters: A density functional investigation

We have carried out first-principles density functional investigation of Cd₁₂S₁₂ cluster doped with one (monodoped) and two (bidoped) Cr-atoms, to explore the manifestation of novel magnetism in this family of stable II-VI semiconducting clusters. Different types of possible configurations of the dopant e.g. substitutional, exohedral, endohedral and substitutional-exohedral have been considered. Both for monodoped and bidoped clusters, substitutional doping corresponds to the ground state. In case of bidoped clusters, the coupling is found to be short-ranged, that depends on the Cr-Cr separation and the local environment. The main competing factors stabilizing ferromagnetic (FM) state in this class of doped nanoclusters are: (a) the FM interaction between two Cr atoms via S atom due to strong p-d hybridization and (b) the short range Cr-Cr direct antiferromagnetic (AFM) interaction. When additional hole is introduced in the system by substituting S with P, in substitutional bidoped clusters, FM state is found to be the ground sate.     

Role of positional isomers on receptor-anion binding and evidence for resonance energy transfer

New urea-based sensors show a strong affinity for F⁻, CH₃COO⁻, and H₂PO₄⁻ with an appreciable color change in the presence of excess F⁻. The position of the nitro group in the urea derivative influences the relative affinity toward anionic analytes. Spectral and ab initio studies showed the difference in the deprotonation sites for the ortho- and meta/para-isomers in these cases. Photophysical studies confirmed the resonance energy transfer in the case of the ortho-isomer. The ortho-isomer can act as a dual emission probe for F⁻.     

Deep level transient spectroscopy of cyanide treated polycrystalline p-Cu2O/n-ZnO solar cell

Deep levels in polycrystalline p-Cu₂O/i-ZnO/n-ZnO/glass photovoltaic structures were studied by deep level transient spectroscopy (DLTS). Post-deposition crown-ether cyanide (CN) treatments of the samples were performed with the variation of time. DLTS spectra for all samples showed the presence of two traps localized at 0.2 eV and 0.5 eV from the top of the valence band. Effects of defect passivation and improvement of cell performance were demonstrated with the cyanide treated samples. Optimum time of cyanide treatment was found to be 3 min. Cell performance was increased from 0.4% to 0.7% for the samples undergoing the optimum post-deposition cyanide treatment.     

Determination of carbidic carbon in steels

An attempt has been made to develop a simple analytical technique that can readily be used in an industrial laboratory to isolate and quantify the precipitated carbides in steel samples. Attempt has also been made to correlate this value with the thermodynamically predicted values. There is good agreement between the predicted and experimental results. More work is in progress to develop this technique for the preparation of Certifed Reference Materials with dissolved and precipitated carbon in steels.     

Inhibition of phosphatase activity by positively-charged cyclodextrins

[formula: see text] Aminocyclodextrins are known to bind phosphate esters such as phosphotyrosine and p-nitrophenyl phosphate. This paper describes the inhibition of phosphate ester hydrolysis, as catalyzed by lambda-protein phosphatase and acid phosphatase, that is caused by such binding interactions. ROESY studies provide structural information about the cyclodextrin-aryl phosphate complexes. In addition, these experiments are used to generate approximations of the rates of dissociation of the noncovalent complexes.     

A Study on Hall Voltage and Electrical Resistivity of Doped Conducting Polyaniline

We report the electrical resistivity of HCl doped polyaniline in the temperature range 77 T 300 K. A maximum is obtained in the conductivity versus concentration of HCl curve at 3(N) HCl. The resistivity of the sample has been observed to show a decreasing trend with increase in temperature. The resistivity obeys the Mott variable range hopping theory. The Mott characteristic temperature (T _Mott) is very low in this sample compared to other studies. The Hall voltages have been found to be negative. The Hall coefficient, carrier concentration, and density of states have been determined from Hall measurement. From the conductivity versus temperature plot, different physical quantities such as localisation length and molecular vibrational frequency have been determined.