Flicker noise in degenerately doped Si single crystals near the metal-insulator transition

In this paper we report some of the important results of experimental investigations of the flicker noise near the metal-insulator (MI) transition in doped silicon single crystals. This is the first comprehensive work to study low-frequency noise in heavily doped Si over an extensive temperature range (2 K<T<500 K). The measurements of conductance fluctuations (flicker noise) were carried out in the frequency range 10⁻²<f<4 × 10¹ Hz in single crystalline Si across the MI transition by doping with phosphorous and boron. The magnitude of noise in heavily doped Si is much larger than that seen in lightly doped Si over the whole temperature range. The extensive temperature range covered allowed us to detect two distinct noise mechanisms. At low temperatures (T<100 K) universal conductance fluctuations (UCF) dominate and the spectral dependence of the noise is determined by dephasing the electron from defects with two-levels (TLS). At higher temperatures (T>200 K) the noise arises from activated defect dynamics. As the MI transition is approached, the 1/f spectral power, typical of the metallic regime, gets modified by the presence of discrete Lorentzians which arise from generation-recombination process which is the characteristic of a semiconductor.     

Two-warehouse production model for deteriorating inventory items with stock-dependent demand under inflation over a random planning horizon

This paper develops a production-inventory model for a deteriorating item with stock-dependent demand under two storage facilities over a random planning horizon, which is assumed to follow exponential distribution with known parameter. The effects of learning in set-up, production, selling and reduced selling is incorporated. Different inflation rates for various inventory costs and time value of money are also considered. A hybrid genetic algorithm is designed to solve the optimization problem which is hard to solve with existing algorithms due to the complexity of the decision variable. To illustrate the model and to show the effectiveness of the proposed approach a numerical example is provided. A sensitivity analysis of the optimal solution with respect to the parameters of the system is carried out.     

Essential Amino Acid–Enabled Lead Bromide Perovskite Nanocrystals with High Stability

This work reports the first synthesis of MAPbBr₃ perovskite nanocrystals (PNCs) using amino acids as the ligand with excellent optical properties. A variety of amino acids are used to optimize the luminescence properties. A mechanochemical approach has taken lead over conventional colloidal chemistry during synthesis. All morphological and optical studies are performed to characterize the synthesized perovskite nanoparticles. Later, stability studies are investigated through thermogravimetric analysis, temperature‐dependent photoluminescence, time‐dependent X‐ray diffraction, as well as X‐ray photoelectron spectroscopy. In an application, interestingly, these perovskites show high luminescence upon scratching on flexible conducting plates and on plain paper surface. These results suggest that the amino acid–ligated perovskite nanocrystals can be potential materials for optoelectronic application including light‐emitting diodes and imaging.     

Equivalent operator preconditioning for elliptic problems

The numerical solution of linear elliptic partial differential equations most often involves a finite element or finite difference discretization. To preserve sparsity, the arising system is normally solved using an iterative solution method, commonly a preconditioned conjugate gradient method. Preconditioning is a crucial part of such a solution process. In order to enable the solution of very large-scale systems, it is desirable that the total computational cost will be of optimal order, i.e. proportional to the degrees of freedom of the approximation used, which also induces mesh independent convergence of the iteration. This paper surveys the equivalent operator approach, which has proven to provide an efficient general framework to construct such preconditioners. Hereby one first approximates the given differential operator by some simpler differential operator, and then chooses as preconditioner the discretization of this operator for the same mesh. In this survey we give a uniform presentation of this approach, including theoretical foundation and several practically important applications for both symmetric and nonsymmetric equations and systems, and some nonlinear examples in the context of Newton linearization. Dedicated to the memory of Gene Golub for his friendly manner and for his broad interest and significant impact on numerical analysis.     

Harmonic averages, exact difference schemes and local Green’s functions in variable coefficient PDE problems

A brief survey is given to show that harmonic averages enter in a natural way in the numerical solution of various variable coefficient problems, such as in elliptic and transport equations, also of singular perturbation types. Local Green’s functions used as test functions in the Petrov-Galerkin finite element method combined with harmonic averages can be very efficient and are related to exact difference schemes.     

On further application of r as a metric for validation of QSAR models

Validation is a crucial aspect for quantitative structure–activity relationship (QSAR) model development. External validation is considered, in general, as the most conclusive proof of predictive capacity of a QSAR model. In the absence of truly external data set, external validation is usually performed on test set compounds, which are members of the original data set but not used in model development exercise. In the case of small data sets, QSAR researchers experience problem in model development due to the fact that the developed models may be less reliable on account of the small number of training set compounds and such models may also show poor external predictability because the models may not have captured all necessary features required for the particular structure–activity relationships. The present paper attempts to show that ‘true r_(LOO)’ statistic calculated based on the model derived from the undivided data set with application of variable selection strategy at each cycle of leave‐one‐out (LOO) validation may reflect external validation characteristics of the developed model thus obviating the requirement of splitting of the data set into training and test sets. This approach may be helpful in the case of small data sets as it uses all available data for model development and validation thus making the resulting model more reliable. Copyright © 2009 John Wiley & Sons, Ltd.     

Reactivity of triazolyl Schiff bases with Ru(II)-2,2′-bipyridyl: Synthesis,spectroscopic characterization of isomers and their photo-physical properties

The condensation of 3-amino-1H-1,2,4-triazole with benzaldehyde and terephthalaldehyde provides the bidentate and tetradentate Schiff bases 1,2,4-triazolo-3-imino-benzene L¹H and 1,4-bis(1,2,4-triazolo-3-imino)benzene L²H₂, respectively. The well characterized Schiff bases were allowed to react with cis-Ru(bpy)₂Cl₂ · 2H₂O. Isomers of the mononuclear complexes Ru(bpy)₂L¹]PF₆ · NH₄PF₆ (1a, N4) and [Ru(bpy)₂L¹]PF₆ · 0.5NH₄PF₆ (1b, N2), and the dinuclear Ru(II) complexes [Ru(bpy)₂L²Ru(bpy)₂](PF₆)₂ · NH₄PF₆ (2a, N4N4), [Ru(bpy)₂L²Ru(bpy)₂](PF₆)₂ · NH₄PF₆ · 2H₂O (2b, N2N2) and [Ru(bpy)₂L²Ru(bpy)₂](PF₆)₃ · NH₄PF₆ (2c, Ru(II)-Ru(III)) were separated by column chromatography and characterized by their elemental analysis, FAB mass and spectral (IR, NMR, UV–Vis) data. The data obtained suggest that the ligands are bound to the metal centre via the N4 and N2 atoms of the triazole moiety along with the N (imine) atom. The complexes display metal-to-ligand charge-transfer (MLCT) transitions in the visible region from the dπ(Ru^II) → π^∗L transition. Highly intense ligand-based π→π^∗ transitions are observed in the UV region. A dual emission occurs from the N2 and N2N2 isomers.     

Synthesis of naturally occurring bioactive butyrolactones: maculalactones A-C and nostoclide I

Starting from citraconic anhydride (13), a simple multistep (9-10 steps) synthesis of naturally occurring butyrolactones maculalactone A (3), maculalactone B (1), maculalactone C (2) and nostoclide I (4) have been described with good overall yields via dibenzylmaleic anhydride (20) and benzylisopropylmaleic anhydride (27). The two anhydrides 20 and 27 were prepared by S_N2′ coupling reactions of appropriate Grignard reagents with dimethyl bromomethylfumarate (14), LiOH-induced hydrolysis of esters to acids, bromination of carbon-carbon double bond, in situ dehydration followed by dehydrobromination and chemoselective allylic substitution of bromoatom in disubstituted anhydrides 19 and 26 with appropriate Grignard reagents. The NaBH₄ reduction of these anhydrides 20 and 27 furnished the desired lactones 21 and 29, respectively. The lactone 21 on Knoevenagel condensation with benzaldehyde, furnished maculalactone B (1), which on isomerization gave maculalactone C (2). Selective catalytic hydrogenation of 1 gave maculalactone A (3). The conversion of lactone 29 to nostoclide I (4) is known.     

Quantitative evaluation of benzene, toluene, and xylene in the larvae of Drosophila melanogaster by solid-phase microextraction/gas chromatography/mass spectrometry for potential use in toxicological studies

A simple, rapid, and solvent-free method for quantitative determination of benzene, toluene, and Xylene in exposed Drosophila larvae was developed using headspace solid-phase microextraction (HS-SPME) coupled to GC/MS. Larvae fed on standard Drosophila food mixed with benzene, toluene, and Xylene for 48 h were homogenized in Milli-Q water. Extraction of benzene, toluene, and Xylene was performed at 65 degrees C for 30 min on the SPME fiber (silica-fused). Subsequently, the fiber was desorbed in the GC injection port, followed by GC/MS analysis in the selected-ion monitoring mode. An external calibration curve was used for the quantification of benzene, toluene, and Xylene in the exposed organism. Recoveries were in the range of 78-82% (intraday) and 76-81% (interday) in larvae, and 91-96% (intraday) and 87-92% (interday) in the diet. LOD with an S/N of 3:1 and LOQ with an S/N of 10:1 were in the range of 0.01-0.023 and 0.034-0.077 microg/L, respectively. Percent RSD values for benzene, toluene, and Xylene were in the range of 0.50-0.81 (intraday) and 0.89-1.23 (interday) for retention time, and 2.16--3.85 (intraday) and 2.99-4.95 (interday) for peak concentration, showing good repeatability. This method was sensitive enough to quantitate benzene, toluene, and Xylene in small exposed organisms like Drosophila larvae. The SPME/GC/MS method developed may have wider applications in various in vivo toxicological studies.