Generation of higher harmonics in laser plasma formed on the surface of a silver target

The results of investigation of the higher harmonics (from the 21st to the 61st order) of radiation of a femtosecond laser (793 nm, 48 fs) that are generated in silver plasma are presented. The changes in the shape and spectra of harmonics for different chirps of the laser radiation are studied. It is found that the wavelengths of harmonics generated in the region of the plateaulike distribution of the converted radiation intensity can be tuned. It is shown that the conditions of phase matching between harmonics and laser radiation are different for different modulations of the femtosecond pulse spectrum. The tuning range of the spectrum of the converted radiation in the region of lower harmonics, which lie in the beginning region of the plateau, is shown to amount to 0.8 nm.     

Homotopy perturbation method for a limit case Stefan problem governed by fractional diffusion equation

The work presents a mathematical model describing the time fractional anomalous-diffusion process of a generalized Stefan problem which is a limit case of a shoreline problem. In this model, the governing equations include a fractional time derivative of order 0 < α ? 1 and variable latent heat. The approximate solution of the problem is obtained by homotopy perturbation method. The results thus obtained are compared graphically with the exact solutions. A brief sensitivity study is also performed.     

A novel catalyst-free synthesis of vertically aligned silicon nanowire-carbon nanotube heterojunction arrays for high performance electron field emitters

A novel, catalyst-free strategy for the direct synthesis of vertically aligned silicon nanowire-carbon nanotube (SiNW-CNT) heterojunction arrays is presented. Such a heterojunction with the junction area in the nanoscale displays enhanced field emission characteristics at low turn-on field, with a nearly three times increase in the field enhancement factor.     

Benzotriazole-Mediated Facile Synthesis of Novel Glycosyl Tetrazole

A facile, simple, and high-yielding synthetic protocol for novel glycosyl tetrazoles has been devised from different carbohydrate-containing amides using benzotriazole methodology under mild reaction condition.     

Solid-state thermal degradation behaviour of 1-D coordination polymers of Ni(II) and Cu(II) bridged by conjugated ligand

Monometallic complexes [Cudadb·yH₂O]_n (2) and [Nidadb·yH₂O]_n (3) and heterobimetallic complex [Cu_0.5Ni_0.5dadb·yH₂O]_n (4) {where dadbH₂ = 2,5-Diamino-3,6-dichloro-1,4-benzoquinone (1); y = 2–4; n = degree of polymerization} were characterized by elemental analysis, atomic absorption spectroscopy, infrared spectroscopy (FTIR) and powder X-ray diffraction. The thermal behaviour of the complexes was studied by thermal analysis (TG/DTA) under air as well as under helium atmospheres. The released gaseous products were investigated by evolved gas analysis performed by an online coupled mass spectrometer (TG/DTA-MS). Thermal degradation of 2 under helium atmosphere is distributed over five steps, whereas 3 and 4 exhibited only four degradation steps due to overlap of second and third degradation steps of into one major step. All the complexes exhibit three steps degradation under air. The complex 2 loses NH group in the second and HCl/Cl₂, CO groups simultaneously in third steps of decomposition under helium, whereas it loses NH and CO groups simultaneously in low temperature region of second step of degradation under air atmosphere as the loss of CO group is facilitated by air. EGA-MS under air and helium atmospheres shows that HCl, CO/CO₂ and (CN)₂ fragments are lost simultaneously at multiple steps, and not successively as predicted earlier. Rate of evolution of most evolved gases exhibits several maxima as a consequence of degradation followed by recombination reactions. Final residues under air and helium atmospheres correspond to the metal oxides and metals along with some carbonaceous matter.     

Fluorogenic dual click derived bis-glycoconjugated triazolocoumarins for selective recognition of Cu(II) ion

Carbohydrate based fluorescent sensors S1 and S2 have been developed by fluorogenic dual click chemistry and are characterized by various spectroscopic techniques. Both the fluorescent probes displayed highly selective detection of Cu²⁺ ions by means of fluorescence quenching. The job plot experiment suggested 1:1 complexation of probes S1 and S2 with Cu²⁺ ions having detection limit of 6.99 μM and 7.30 μM, respectively. The binding constants for S1-Cu²⁺ and S2-Cu²⁺ complexation were evaluated to be 3.34 × 10³ M⁻¹ and 5.93 × 10³ M⁻¹, respectively.     

Thermodynamic and kinetic investigations of uranium adsorption on soil

In order to understand the mobility of uranium it is very important to know about its sorption kinetics and the thermodynamics behind the sorption process on soil. In the present study the sorption kinetics of uranium was studied in soil and the influence parameters to the sorption process, such as initial uranium concentration, pH, contact time and temperature were investigated. Distribution coefficient of uranium on soil was measured by laboratory batch method. Experimental isotherms evaluated from the distribution coefficients were fit to Langmuir, Freundlich and Dubinin?CRadushkevich (D?CR) models. The sorption energy for uranium from the D?CR adsorption isotherm was calculated to be 7.07?kJ?mol^?1.The values of ??H and ??S were calculated to be 37.33?kJ?mol^?1 and 162?J?K^?1?mol^?1, respectively. ??G at 30?°C was estimated to be ?11.76?kJ?mol^?1. From sorption kinetics of uranium the reaction rate was calculated to be 1.6?×?10^?3?min^?1.     

Stability of the normal, zwitterionic neutral and anionic forms of aspartic acid in gas phase and aqueous media

Aspartic acid has a place of special importance among amino acids in view of its property to racemize from the - to the -form in living and nonliving systems which can be used to determine age. Molecular geometries of two isomeric normal neutral forms (called A and B forms), isomeric zwitterionic neutral forms (called A(Z) and B(Z) forms) and anions of these forms of aspartic acid were optimized at the RHF/6-31+G^* level. The geometries of hydrogen bonded complexes of each of the above species with one, two and three water molecules were also optimized at the same level. All these systems were solvated in bulk water using the polarized continuum model (PCM) of the self-consistent reaction field (SCRF) theory at the RHF/6-31+G^* level using the gas phase optimized geometries. It is found that in gas phase, the normal neutral A and B forms of aspartic acid would coexist while the zwitterionic A(Z) and B(Z) forms of the same would be absent. On the other hand, in bulk aqueous media, the normal neutral A and B forms of aspartic acid would not occur while the zwitterionic A(Z) and B(Z) forms would be present. Further, the abundance of the A(Z) form would be much more than that of the B(Z) form in bulk water. If the solution pH is adjusted appropriately so that a monoanion is formed, the anion of aspartic acid obtained from the neutral zwitterionic form by deprotonating O₈ would occur dominantly.