Phase formation and impurity effects in Ar+ ion irradiated Mo/Si thin film bilayer system

We report a dose‐dependent phase evolution in Mo/Si bilayer system upon Ar⁺ ion beam irradiation and subsequent flash annealing at 800 °C for 60 s. Micro‐structural characterization with Grazing Incidence X‐ray Diffraction and Raman scattering reveals a dose‐dependent nucleation of polymorphic phases occurring at the amorphized interface region. The ion beam mixing process has been investigated by Secondary Ion Mass Spectrometry and Rutherford Backscattering Spectrometry. While low ion doses favour nucleation of only metastable MoSi₂ phase, co‐existence of polymorphic phases are observed at high ion doses. The persistence of such polymorphic phases even after a high‐temperature anneal for high dose implanted specimen is indicative of phase retardation. The phase retardation of h‐MoSi₂ to t‐MoSi₂ is accounted in terms of nucleation and growth process. Copyright © 2012 John Wiley & Sons, Ltd.     

On the formation of hydrogen peroxide in water microdroplets

Recent reports on the formation of hydrogen peroxide (H₂O₂) in water microdroplets produced via pneumatic spraying or capillary condensation have garnered significant attention. How covalent bonds in water could break under such mild conditions challenges our textbook understanding of physical chemistry and water. While there is no definitive answer, it has been speculated that ultrahigh electric fields at the air–water interface are responsible for this chemical transformation. Here, we report on our comprehensive experimental investigation of H₂O₂ formation in (i) water microdroplets sprayed over a range of liquid flow-rates, (shearing) air flow rates, and air composition, and (ii) water microdroplets condensed on hydrophobic substrates formed via hot water or humidifier under controlled air composition. Specifically, we assessed the contributions of the evaporative concentration and shock waves in sprays and the effects of trace O₃(g) on the H₂O₂ formation. Glovebox experiments revealed that the H₂O₂ formation in water microdroplets was most sensitive to the air–borne ozone (O₃) concentration. In the absence of O₃(g), we could not detect H₂O₂(aq) in sprays or condensates (detection limit ≥250 nM). In contrast, microdroplets exposed to atmospherically relevant O₃(g) concentration (10–100 ppb) formed 2–30 µM H₂O₂(aq), increasing with the gas–liquid surface area, mixing, and contact duration. Thus, the water surface area facilitates the O₃(g) mass transfer, which is followed by the chemical transformation of O₃(aq) into H₂O₂(aq). These findings should also help us understand the implications of this chemistry in natural and applied contexts.

A. Gallo Jr, H. Mishra et al., pinpoint the origins of the spontaneous H₂O₂ formation in water microdroplets formed via spraying or condensation, i.e., without the addition of electrical energy, catalyst, or co-solvent.     

A lower bound on the error in dimensionality reduction resulting from projection onto a restricted subspace

We obtain the lower bound on a variant of the common problem of dimensionality reduction. In this version, the dataset is projected on to a k dimensional subspace with the property that the first k-1 basis vectors are fixed, leaving a single degree of freedom in terms of basis vectors.     

Pollen from Glycine species survive cryogenic exposure

Pollen of 12 genotypes of the annual soybean and its wild perennial relatives were stored without pre-desiccation at low temperatures (-20 C and -196 C) and tested for their viability in vitro. The influence of cryopreserved pollen on pod set and seed production was also investigated. Cryopreserved pollen of all the genotypes showed germination in vitro. Pollen of annual soybean stored at -20 C retained their viability for 4 months, however, pollen of its wild perennial relatives at same storage conditions failed to germinate in vitro. Flowers pollinated with cryopreserved pollen had similar pod set and number of seeds/pod as those pollinated with fresh pollen. Results of this study suggest that cryopreservation of pollen can be used successfully for soybean breeding, and also offers the possibility of conserving the haploid gene pool of soybean and wild perennial species in a cryobank facility.     

Potts ferromagnets on coexpressed gene networks: identifying maximally stable partitions

Clustering gene expression data by exploiting phase transitions in granular ferromagnets requires transforming the data to a granular substrate. We present a method using the recently introduced homogeneity order parameter Lambda [H. Agrawal, Phys. Rev. Lett. 89, 268702 (2002)]] for optimizing the parameter controlling the "granularity" and thus the stability of partitions. The model substrates obtained for gene expression data have a highly granular structure. We explore properties of phase transition in high q ferromagnetic Potts models on these substrates and show that the maximum of the width of superparamagnetic domain, corresponding to maximally stable partitions, coincides with the minimum of Lambda.     

Photophysical characterization of pyrromethene 597 laser dye in silicon-containing organic matrices

Samples of dipyrromethene-BF₂ dye PM597 incorporated in copolymers of 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) with methyl methacrylate (MMA) and 2-hydroxyethylmethacrylate (HEMA), and in terpolymers of MMA, HEMA and TMSPMA are characterized. The absorption cross-section spectra, stimulated emission cross-section spectra, and the excited-state absorption cross-section at 527 nm are determined. The fluorescence quantum distributions and fluorescence lifetimes are measured. The photo-degradation is studied under cw laser excitation conditions and quantum yields of photo-degradation are extracted. PM597 solid state samples are compared with PM597 in liquid ethyl acetate solution. The fluorescence quantum yield of PM597 is higher in doped samples (around 70%) compared to PM597 in ethyl acetate (43%). The excited-state absorption cross-section was found to be negligibly small. The photo-stability is considerably larger in the polymeric samples compared to the liquid solutions. PACS 42.55.-f; 78.45.+h; 78.55.-m; 78.40.Me     

Rapid breakdown anodization technique for the synthesis of high aspect ratio and high surface area anatase TiO2 nanotube powders

Clusters of high aspect ratio, high surface area anatase-TiO₂ nanotubes with a typical nanotube outer diameter of about 18 nm, wall thickness of approximately 5 nm and length of 5-10 μm were synthesized, in powder form, by breakdown anodization of Ti foils in 0.1 M perchloric acid, at 10 V (299 K) and 20 V (∼275 and 299 K). The surface area, morphology, structure and band gap were determined from Brunauer Emmet Teller method, field emmission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman, photoluminescence and diffuse reflectance spectroscopic studies. The tubular morphology and anatase phase were found to be stable up to 773 K and above 773 K anatase phase gradually transformed to rutile phase with disintegration of tubular morphology. At 973 K, complete transformation to rutile phase and disintegration of tubular morphology were observed. The band gap of the as prepared and the annealed samples varied from 3.07 to 2.95 eV with increase in annealing temperature as inferred from photoluminescence and diffuse reflectance studies.     

Surface pattern recording in amorphous chalcogenide layers

Investigations of light-induced volume expansion and surface pattern recording in amorphous chalcogenide layers and nano-layered structures (NLS) were extended to direct electron-beam recording on Se/As₂S₃ and Sb/As₂S₃ NLS. Light as well as e-beam induced bleaching occurs in all NLS, while volume expansion occurs only in chalcogenide–chalcogenide NLS and in homogeneous Se or As₂S₃ layers. Comparison of these two phenomena revealed the possible role of purely electronic and thermal processes in the interdiffusion and relief formation. The latter is supposed to be connected with radiation-induced defect creation, free volume increase under the increased fluidity conditions as well as with the possible additional influence of electrostatic forces and stress.     

Rapid and accurate estimation of protein–ligand relative binding affinities using site-identification by ligand competitive saturation

Predicting relative protein–ligand binding affinities is a central pillar of lead optimization efforts in structure-based drug design. The site identification by ligand competitive saturation (SILCS) methodology is based on functional group affinity patterns in the form of free energy maps that may be used to compute protein–ligand binding poses and affinities. Presented are results obtained from the SILCS methodology for a set of eight target proteins as reported originally in Wang et al. (J. Am. Chem. Soc., 2015, 137, 2695–2703) using free energy perturbation (FEP) methods in conjunction with enhanced sampling and cycle closure corrections. These eight targets have been subsequently studied by many other authors to compare the efficacy of their method while comparing with the outcomes of Wang et al. In this work, we present results for a total of 407 ligands on the eight targets and include specific analysis on the subset of 199 ligands considered previously. Using the SILCS methodology we can achieve an average accuracy of up to 77% and 74% when considering the eight targets with their 199 and 407 ligands, respectively, for rank-ordering ligand affinities as calculated by the percent correct metric. This accuracy increases to 82% and 80%, respectively, when the SILCS atomic free energy contributions are optimized using a Bayesian Markov-chain Monte Carlo approach. We also report other metrics including Pearson''s correlation coefficient, Pearlman''s predictive index, mean unsigned error, and root mean square error for both sets of ligands. The results obtained for the 199 ligands are compared with the outcomes of Wang et al. and other published works. Overall, the SILCS methodology yields similar or better-quality predictions without a priori need for known ligand orientations in terms of the different metrics when compared to current FEP approaches with significant computational savings while additionally offering quantitative estimates of individual atomic contributions to binding free energies. These results further validate the SILCS methodology as an accurate, computationally efficient tool to support lead optimization and drug discovery.

Predicting relative protein–ligand binding affinities is a central pillar of lead optimization efforts in structure-based drug design.     

A cylindrically symmetric inhomogeneous cosmological model with electromagnetic field

A cylindrically symmetric inhomogeneous cosmological model with electromagnetic field for perfect fluid distributions is obtained. To get a determinate solution, a supplementary conditionA=(BC) ⁿ between metric potentials is used whereA, B, andC are functions of bothx andt andn is a constant. Some physical and geometrical properties of the model and behavior of electromagnetic field tensors are also discussed.