Noise reduction with perforated three-duct muffler components

This paper describes the authors’ distributed parameter approach for derivation of closed-form expressions for the four-pole parameters of the perforated three-duct muffler components. In this method, three simultaneous second-order partial differential equations are first reduced to a set of six first-order ordinary differential equations. These equations are then uncoupled by means of a modal matrix. The resulting 6 × 6 matrix is reduced to the 2 × 2 transfer matrix using the relevant boundary conditions. This is combined with transfer matrices of other elements (upstream and downstream of this perforated element) to predict muffler performance like noise reduction, which is also measured. The correlation between experimental and theoretical values of noise reduction is shown to be satisfactory.

Crystal packing and melting temperatures of small oxalate esters: the role of C-H center dot center dot center dot O hydrogen bonding

The simple dialkyl oxalates are generally liquids at room temperature except for dimethyl and di-tert-butyl oxalate which melt at 327 and 343 K. The crystal structures of diethyl, di-iso-propyl, di-n-butyl, di-tert-butyl and methyl ethyl oxalates were determined. The liquid esters were crystallized using the cryocrystallization technique. A comparison of the intermolecular interactions and packing features in these crystal structures was carried out. The crystal structure of dimethyl oxalate was redetermined at various temperatures. The other compounds were also studied at several temperatures in order to assess the attractive nature of the hydrogen bonds therein. A number of moderate to well defined C-H center dot center dot center dot O interactions account for the higher melting points of the two solid esters. Additionally, a diminished entropic contribution Delta S(m) in di-tert-butyl oxalate possibly increases the melting point of this compound further.

Extending the Supramolecular Synthon Based Fragment Approach (SBFA) for Transferability of Multipole Charge Density Parameters to Monofluorobenzoic Acids and their Cocrystals with Isonicotinamide: Importance of C-H center dot center dot center dot O, C-H center dot center dot center dot F, and F center dot center dot center dot F Intermolecular Regions

An extension of the supramolecular synthon-based fragment approach (SBFA) method for transferability of multipole charge density parameters to include weak supramolecular synthons is proposed. In particular, the SBFA method is applied to C-H center dot center dot center dot O, C-H center dot center dot center dot F, and F center dot center dot center dot F containing synthons. A high resolution charge density study has been performed on 4-fluorobenzoic acid to build a synthon library for C-H center dot center dot center dot F infinite chain interactions. Libraries for C-H center dot center dot center dot O and F center dot center dot center dot F synthons were taken from earlier work. The SBFA methodology was applied successfully to 2- and 3-fluorobenzoic acids, data sets for which were collected in a routine manner at 100 K, and the modularity of the synthons was demonstrated. Cocrystals of isonicotinamide with all three fluorobenzoic acids were also studied with the SBFA method. The topological analysis of inter- and intramolecular interaction regions was performed using Bader's AIM approach. This study shows that the SBFA method is generally applicable to generate charge density maps using information from multiple intermolecular regions.

Large reduction of leakage current by graded-layer La doping in (Ba0.5, Sr0.5)TiO3 thin films

A large reduction in the leakage current behavior in (Ba, Sr)TiO3 (BST) thin films was observed by graded-layer donor doping. The graded doping was achieved by introducing La-doped BST layers in the grown BST films. The films showed a large decrease (about six orders of magnitude) in the leakage current in comparison to undoped films at an electric field of 100 kV/cm. The large decrease in leakage current was attributed to the formation of highly resistive layers, originating from compensating defect chemistry involved for La-doped films grown in oxidizing environment. Temperature-dependent leakage-current behavior was studied to investigate the conduction mechanism and explanations of the results were sought from Poole–Frenkel conduction mechanism.

Dioxomolybdenum reagents in organic synthesis: utility of redox capability to design reduction and oxidation

The usefulness of dioxomolybdenum reagents in oxo-transfer reactions have been reviewed. The redox ability of dioxomolybdenum reagent has been utilized in designing several synthetic methods, which are useful in organic synthesis. Several reactions such as oxidation of alcohols, sulfides, amines, azides olefins etc are accomplished by using dioxomolybdenum reagents. Similarly, it is also demonstrated that dioxomolybdenum complex is useful in performing reduction of aldehydes, ketones, esters, azides etc. A fine tuning of reaction conditions provides suitable conditions to perform either oxidation or reduction by using catalytic amount of reagents. The oxidation reactions are further simplified by employing the polymer supported molybdenum reagents.

Sensitivity of terrestrial water and energy budgets to CO(2)-physiological forcing: an investigation using an offline land model

Increasing concentrations of atmospheric carbon dioxide (CO(2)) influence climate by suppressing canopy transpiration in addition to its well- known greenhouse gas effect. The decrease in plant transpiration is due to changes in plant physiology (reduced opening of plant stomata). Here, we quantify such changes in water flux for various levels of CO(2) concentrations using the National Center for Atmospheric Research's (NCAR) Community Land Model. We find that photosynthesis saturates after 800 ppmv (parts per million, by volume) in this model. However, unlike photosynthesis, canopy transpiration continues to decline at about 5.1% per 100 ppmv increase in CO(2) levels. We also find that the associated reduction in latent heat flux is primarily compensated by increased sensible heat flux. The continued decline in canopy transpiration and subsequent increase in sensible heat flux at elevated CO(2) levels implies that incremental warming associated with the physiological effect of CO(2) will not abate at higher CO(2) concentrations, indicating important consequences for the global water and carbon cycles from anthropogenic CO(2) emissions.

Hypersonic wave drag reduction in re-entry capsules using concentrated energy deposition

Experiments are carried out in a shock tunnel at a nominal Mach number of 5.75 in order to study the effect of concentrated energy deposition on the drag force experienced by a 120° blunt cone. Electrical energy was deposited along the stagnation streamline of the model using a high voltage DC discharge circuit (1.5 – 3.5KW) and the drag force was measured by a single component accelerometer balance. Numerical simulations were also carried complimenting the experiments. These simulations showed a substantial drag reduction (20% ~ 65%) whereas the experiments show no appreciable reduction in drag

Pulsed plasma treatment for NOx reduction from filtered/unfiltered stationary diesel engine exhaust

A detailed study on the removal of oxides of nitrogen (NOx) from the filtered/unfiltered exhaust of a stationary diesel engine was carried out using non-thermal plasma (pulsed electrical discharge plasma) process and cascaded processes namely plasma- adsorbent and plasma-catalyst processes. The superior performance of discharge plasma with regard to NOx removal, energy consumption and formation of by-products in unfiltered exhaust environment is identified. In the cascaded plasma-adsorbent process, the plasma was cascaded with adsorbents (MS13X/Activated alumina/Activated charcoal). The cascaded process treating unfiltered exhaust exhibits a very high NOx removal compared to the individual processes and further, the cascaded process gives almost the same NOx removal efficiency irrespective of type of adsorbent used. In the cascaded plasma- catalyst process, the plasma was cascaded with activated alumina catalyst at high temperature. The synergy effect and improved performance of the cascaded process are explained. Further, experiments were conducted at room temperature as well as at higher temperatures.

Corona treatment for NOx reduction from stationary diesel engine exhaust: Impact of nature of energization and exhaust composition

A detailed study on the removal of oxides of nitrogen (NOx) from the exhaust of a stationary diesel engine was carried out using non-thermal plasma (dielectric barrier discharge) process. The objective of the study was to explore the effect of different voltage energizations and exhaust composition on the NOx removal process. Three types of voltage energizations, namely AC, DC and Pulse were examined. Due to the ease of generation of high voltage AC/DC electrical discharges from automobile/Vehicular battery supply for possible retrofitting in exhaust cleaning circuit, it was found relevant to investigate individual energisation cases in detail for NOx removal. AC and Pulse energisations exhibit a superior NOx removal efficiency compared to DC energisation. However,Pulse energisation is found to be more energy efficient. Experiments were further carried out with filtered/ unfiltered (raw) exhaust under pulse energisations. The results were discussed with regard to NOx removal, energy consumption and formation of by-products.

Evidence for the ``Amphoteric'' Nature of Fluorine in Halogen Bonds: An Instance of Cl center dot center dot center dot F Contact

This study presents unambiguous experimental evidence in support of the highly debated ``halogen bond donor'' character of organic fluorine. Two examples of intermolecular Cl center dot center dot center dot F contacts, with F-atom as halogen bond acceptor and donor, have been analyzed by in situ cryocrystallography and theoretical charge density studies.

Dilithium phthalocyanine as a catalyst for oxygen reduction in non-aqueous Li-O-2 cells

The electrochemical performance of Li-O-2 cells depends mainly on the kinetics of the cathode reaction, namely, oxygen reduction reaction in non-aqueous electrolytes. The catalyst plays an important role on the kinetics of the reaction. In the present work, dilithium phthalocyanine is used as the catalyst in the cathode of Li-O-2 cells. Dual-layer O-2 electrodes are fabricated employing a high surface area microporous carbon with Ni gauge current collector present between the two layers. Discharge capacity of Li-O-2 cell measured at 0.2 mA.cm(-2) is about 30 mAh.cm(-2). Phthalocyanine ring is considered to interact with O-2 producing Li2Pc+delta - O-2(-delta) as a reaction intermediate, which facilitates the electron-transfer reaction.

Guanidine catalyzed aerobic reduction: a selective aerobic hydrogenation of olefins using aqueous hydrazine

An efficient aerobic reduction of olefins, internal as well as terminal, is developed using guanidine as an organocatalyst. A remarkable chemoselectivity in reduction has been demonstrated in the presence of a variety of functional groups and protective groups and a selective reduction of a terminal olefin in the presence of an internal olefin is revealed.

Reduction of aromatic nitro compounds to amines using zinc and aqueous chelating ethers: Mild and efficient method for zinc activation

A mild, environmentally friendly method for reduction of aromatic nitro group to amine is reported, using zinc powder in aqueous solutions of chelating ethers. The donor ether acts as a ligand and also serves as a co-solvent. Water is the proton source. This procedure is also a new method for the activation of zinc for electron transfer reduction of aromatic nitro compounds. The reduction is accomplished in a neutral medium and other reducing groups remained unaffected. The ethers used are dioxolane, 1,4-dioxane, ethoxymethoxyethane, dimethoxymethane, 1,2-dimethoxyethane, and diglyme.

Surrogate based design optimisation of composite aerofoil cross-section for helicopter vibration reduction

Design optimisation of a helicopter rotor blade is performed. The objective is to reduce helicopter vibration and constraints are put on frequencies and aeroelastic stability. The ply angles of the D-spar and skin of the composite rotor blade with NACA 0015 aerofoil section are considered as design variables. Polynomial response surfaces and space filling experimental designs are used to generate surrogate models of the objective function with respect to cross-section properties. The stacking sequence corresponding to the optimal cross-section is found using a real-coded genetic algorithm. Ply angle discretisation of 1 degrees, 15 degrees, 30 degrees and 45 degrees are used. The mean value of the objective function is used to find the optimal blade designs and the resulting designs are tested for variance. The optimal designs show a vibration reduction of 26% to 33% from the baseline design. A substantial reduction in vibration and an aeroelastically stable blade is obtained even after accounting for composite material uncertainty.