ChemInform Abstract: Enantioselective Formal Total Synthesis of (-)-Homogynolide-A

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Simple and Regioselective Reductive Cleavage of Tetrahydropyranyl Ethers to Alcohols

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Slicing the Perovskite Structure into Layers: Synthesis of Novel Three- Dimensional and Layered Perovskite Oxides, ALaSrNb2M(II)O9 (A: Na, Cs)

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Sodium Perborate/Acetic Anhydride: A Convenient Reagent for the Conversion of Cyclic Acetals to Esters

A facile oxidative cleavage of cyclic acetals to their respective esters using an inexpensive reagent system, sodium perborate/acetic anhydride is described.

ChemInform Abstract: Synthesis Based on Cyclohexadienes. Part 16. Synthesis of Methyl 2,7-Dimethyltricyclo (5.2.2.01,5)undec-5-ene-6-carboxylates

Synthesis of methyl 2, 7-dimethyltricyclo{5.2.2.0(1,5}undec-5-en-6-carboxylates, the tricyclic skeleton present in (+)-allo-cedrol (1) is described using the Diels-Alder strategy. Thus, Birch reduction of the aromatic acid 8 gives 5, the methyl ester of which is isomerised with DBU to a 1:1 mixture of the dienes 6 and 4. Cycloaddition of this mixture with 2-chloroacrylonitrile followed by hydrolysis yields the ketone 60 having the tricyclo{5.2.2.0(1.5)}undec-5-ene framework. Similar reaction with methyl vinyl ketone affords the regioisomeric adducts 61 and 62.

Electrical and Optical Properties of Diketopyrrolopyrrole-Based Copolymer Interfaces in Thin Film Devices

Two donor acceptor diketopyrrolopyrrole (DPP)-based copolymers (PDPP-BBT and TDPP-BBT) have been synthesized for their application in organic devices such as metal-insulator semiconductor (MIS) diodes and field-effect transistors (FETs). The semiconductor-dielectric interface was characterized by capacitance-voltage and conductance-voltage methods. These measurements yield an interface trap density of 4.2 x 10(12) eV(-1) cm(-2) in TDPP-BBT and 3.5 x 10(12) eV(-1) cm(-2) in PDPP-BBT at the flat-band voltage. The FETs based on these spincoated DPP copolymers display p-channel behavior with hole mobilities of the order 10(-3) cm(2)/(V s). Light scattering studies from PDPP-BBT FETs show almost no change in the Raman spectrum after the devices are allowed to operate at a gate voltage, indicating that the FETs suffer minimal damage due to the metal-polymer contact or the application of an electric field. As a comparison Raman intensity profile from the channel-Au contact layer in pentacene FETs are presented, which show a distinct change before and after biasing.

ChemInform Abstract: Chemical Design of Solid Inorganic Materials

Newer strategies for the synthesis of inorganic solids have made a great impact on present-day materials chemistry. In this article, typical case studies of synthesis involving new methods and soft chemical routes are discussed besides recent results from nebulized spray pyrolysis and synthesis of nanoscale metal and alloy particles.

Locating and sizing plants for bottling propane in south India

Shri Shakti LPG Ltd. (SSLPG) imports and markets propane (referred to as liquefied petroleum gas (LPG) in India) in south India. It sells LPG in packed (cylinder) form to domestic customers and commercial establishments through a network of dealers. Dealers replenish their stocks of filled cylinders from bottling plants, which in turn receive LPG in bulk from the cheaper of SSLPG's two import-and-storage facilities that are located on the Indian coast. We implemented integer programming to help SSLPG decide on the locations and long-run sizes of its bottling plants. We estimate that our recommended configuration of bottling plants is about $1 million cheaper annually than the one that SSLPG had initially planned.

Studies of interfaces in Al-65 Cu20Fe15

The study of interfaces in quasicrystalline alloys is relatively new. Apart From the change in orientation, symmetry and chemistry which can occur across homophase and heterophase boundaries in crystalline materials, we have the additional, exciting possibility of an interface between quasicrystalline and its rational approximant. High resolution electron microscopy is a powerful technique to study the structural details of such interfaces. We report the results of a HREM study of the interface between the icosahedral phase and the related Al13Fe4 type monoclinic phase in melt spun and annealed Al65Cu20Fe15 alloy.

Studies on age-hardening characteristics of ceramic particle/matrix interfaces in Al-Cu-SiCp composites using ultra low-load-dynamic microhardness measurements

Ultra low-load-dynamic microhardness testing facilitates the hardness measurements in a very low volume of the material and thus is suited for characterization of the interfaces in MMC's. This paper details the studies on age-hardening behavior of the interfaces in Al-Cu-5SiC(p) composites characterized using this technique. Results of hardness studies have been further substantiated by TEM observations. In the solution-treated condition, hardness is maximum at the particle/matrix interface and decreases with increasing distance from the interface. This could be attributed to the presence of maximum dislocation density at the interface which decreases with increasing distance from the interface. In the case of composites subjected to high temperature aging, hardening at the interface is found to be faster than the bulk matrix and the aging kinetics becomes progressively slower with increasing distance from the interface. This is attributed to the dislocation density gradient at the interface, leading to enhanced nucleation and growth of precipitates at the interface compared to the bulk matrix. TEM observations reveal that the sizes of the precipitates decrease with increasing distance from the interface and thus confirms the retardation in aging kinetics with increasing distance from the interface.

X-ray reflectivity study of semiconductor interfaces

The results of an X-ray reflectivity study of thick AlAs-AlGaAs and thin GeSi-Ge multilayers grown using metal-organic vapour-phase epitaxy and ion-beam sputtering deposition techniques, respectively, are presented. Asymmetry in interfaces is observed in both of these semiconductor multilayers. It is also observed that although the Si-on-Ge interface is sharp, an Si0.4Ge0.6 alloy is formed at the Ge-on-Si interface. In the case of the III-V semiconductor, the AlAs-on-AlGaAs interface shows much greater roughness than that observed in the AlGaAs-on-AlAs interface. For thin multilayers it is demonstrated that the compositional profile as a function of depth can be obtained directly from the X-ray reflectivity data.

Phase separation in a simple model with dynamical asymmetry

We perform computer simulations of a Cahn-Hilliard model of phase separation that has dynamical asymmetry between the two coexisting phases. The dynamical asymmetry is incorporated by considering a mobility function that is order parameter dependent. Simulations of this model reveal morphological features similar to those observed in viscoelastic phase separation. In the early stages, the minority phase domains form a percolating structure that shrinks with time, eventually leading to the formation of disconnected regions that are characterized by the presence of random interfaces as well as isolated droplets. The domains grow as L(t)similar to t(1/3) in the very late stages. Although dynamical scaling is violated in the area shrinking regime, it is restored at late times. However, the form of the scaling function is found to depend on the extent of dynamical asymmetry. [S1063-651X(99)12101-9].

On optimal timer-based distributed selection for rate-adaptive multi-user diversity systems

We develop an optimal, distributed, and low feedback timer-based selection scheme to enable next generation rate-adaptive wireless systems to exploit multi-user diversity. In our scheme, each user sets a timer depending on its signal to noise ratio (SNR) and transmits a small packet to identify itself when its timer expires. When the SNR-to-timer mapping is monotone non-decreasing, timers of users with better SNRs expire earlier. Thus, the base station (BS) simply selects the first user whose timer expiry it can detect, and transmits data to it at as high a rate as reliably possible. However, timers that expire too close to one another cannot be detected by the BS due to collisions. We characterize in detail the structure of the SNR-to-timer mapping that optimally handles these collisions to maximize the average data rate. We prove that the optimal timer values take only a discrete set of values, and that the rate adaptation policy strongly influences the optimal scheme's structure. The optimal average rate is very close to that of ideal selection in which the BS always selects highest rate user, and is much higher than that of the popular, but ad hoc, timer schemes considered in the literature.

Modelling, simulation, and graphical user interface for industrial gas carburising process

A mathematical model has been developed for the gas carburising (diffusion) process using finite volume method. The computer simulation has been carried out for an industrial gas carburising process. The model's predictions are in good agreement with industrial experimental data and with data collected from the literature. A study of various mass transfer and diffusion coefficients has been carried out in order to suggest which correlations should be used for the gas carburising process. The model has been interfaced in a Windows environment using a graphical user interface. In this way, the model is extremely user friendly. The sensitivity analysis of various parameters such as initial carbon concentration in the specimen, carbon potential of the atmosphere, temperature of the process, etc. has been carried out using the model.