Reentrant Adhesion Behavior in Nanocluster Deposition

We simulate the collision of atomic clusters with a weakly attractive surface using molecular dynamics in a regime between soft-landing and fragmentation, where the cluster undergoes large deformation but remains intact. As a function of incident kinetic energy, we find a transition from adhesion to reflection at low kinetic energies. We also identify a second adhesive regime at intermediate kinetic energies, where strong deformation of the cluster leads to an increase in contact area and adhesive energy.Comment: 7 pages, 6 figure

Biochemical composition of promising leaves genotypes of buckwheat grown in Himachal Pradesh

Buckwheat originated from China and being cultivated all over the world, and has become a prominent pseudocereal. Among the pseudocereals (amaranthus, buckwheat and quinoa), buckwheat plant is economically important primarily due to their carbohydrate and protein rich grains, short growth span; besides foliage being used as a green vegetable and commercial source of the glycoside rutin used in medicine. In the present study, an attempt was made to evaluate the biochemical constituents of nutritional and nutraceutical significance of fourteen promising leaves genotypes of common buckwheat grown in Sangla region by following standard procedures. Wide variations in moisture content, crude protein, fat, ash, crude fiber, carbohydrates, ascorbic acid, oxalate and in vitro protein digestibility were observed to range from 87.4 to 92.2 %, 22.4 to 30.4 %, 1.8 to 3.7 %, 10.6 to 15.4 %, 12.0 to 13.9 %, 34.8 to 42.4 %, 25.0 to 29.2 mg/100g, 1375 to 1390 mg/100g and 53.4 to 65.1 % in that order. The content of minerals such as potassium, phosphorus, calcium, magnesium, zinc, manganese and copper varied from 1767.5 to 2035.0 mg/100g, 808 to 910 mg/100g, 394 to 409 mg/100g, 232.0 to 248.2 mg/100g, 3.1 to 6.1 mg/100g, 20.4 to 29.8 mg/100g and 0.2 to 1.4 mg/100g respectively. Based on cumulative grading done in respect of nutritionally desirable quality i.e., protein, ash, crude fiber, carbohydrates, ascorbic acid, in vitro protein digestibility, calcium, phosphorus, iron and oxalate content, the genotype IC-323731 followed by Kullugangetri and VL-27 emerged out to be overall superior versatile cultivars for cultivation under dry temperate climate

Molecular dynamics simulations of reflection and adhesion behavior in Lennard-Jones cluster deposition

We conduct molecular dynamics simulations of the collision of atomic clusters with a weakly-attractive surface. We focus on an intermediate regime, between soft-landing and fragmentation, where the cluster undergoes deformation on impact but remains largely intact, and will either adhere to the surface (and possibly slide), or be reflected. We find that the outcome of the collision is determined by the Weber number, We i.e. the ratio of the kinetic energy to the adhesion energy, with a transition between adhesion and reflection occurring as We passes through unity. We also identify two distinct collision regimes: in one regime the collision is largely elastic and deformation of the cluster is relatively small but in the second regime the deformation is large and the adhesion energy starts to depend on the kinetic energy. If the transition between these two regimes occurs at a similar kinetic energy to that of the transition between reflection and adhesion, then we find that the probability of adhesion for a cluster can be bimodal. In addition we investigate the effects of the angle of incidence on adhesion and reflection. Finally we compare our findings both with recent experimental results and with macroscopic theories of particle collisions.Comment: 18 pages, 13 figure

Solvent-induced β-hairpin to helix conformational transition in a designed peptide

An octapeptide containing a central Aib-Gly- segment capable of adopting β-turn conformations compatible with both hairpin (βII' or βI′) and helical (βI) structures has been designed. The effect of solvent on the conformation of the peptide Boc-Leu-Val-Val-Aib-Gly-Leu-Val-Val-OMe (VIII; Boc: t-butyloxycarbonyl; OMe: methyl ester) has been investigated by NMR and CD spectroscopy. Peptide VIII adopts a well-defined β-hairpin conformation in solvents capable of hydrogen bonding like (CD3)2SO and CD3OH. In solvents that have a lower tendency to interact with backbone peptide groups, like CDCl3 and CD3CN, helical conformations predominate. Nuclear Overhauser effects between the backbone protons and solvent shielding of NH groups involved in cross-strand hydrogen bonding, backbone chemical shifts, and vicinal coupling constants provide further support for the conformational assignments in different solvents. Truncated peptides Boc-Val-Val-Aib-Gly-Leu-Val-Val-OMe (VII), Boc-Val-Val-Aib-Gly-Leu-Val-OMe (VI), and Boc-Val-Aib-Gly-Leu-OMe (IV) were studied in CDCl3 and (CD3)2SO by 500 MHz 1H-NMR spectroscopy. Peptides IV and VI show no evidence for hairpin conformation in both the solvents. The three truncated peptides show a well-defined helical conformation in CDCl3. In (CD3)2SO, peptide VII adopts a β-hairpin conformation. The results establish that peptides may be designed, which are poised to undergo a dramatic conformational transition

Multi-wavelength Diagnostics of the Precursor and Main phases of an M1.8 Flare on 2011 April 22

We study the temporal, spatial and spectral evolution of the M1.8 flare, which occurred in NOAA AR 11195 (S17E31) on 22 April 2011, and explore the underlying physical processes during the precursors and their relation to the main phase. The study of the source morphology using the composite images in 131 {\deg}A wavelength observed by the SDO/AIA and 6-14 keV revealed a multiloop system that destabilized systematically during the precursor and main phases. In contrast, HXR emission (20-50 keV) was absent during the precursor phase, appearing only from the onset of the impulsive phase in the form of foot-points of emitting loop/s. This study has also revealed the heated loop-top prior to the loop emission, although no accompanying foot-point sources were observed during the precursor phase. We estimate the flare plasma parameters viz. T, EM, power-law index, and photon turn-over energy by forward fitting RHESSI spectral observations. The energy released in the precursor phase was thermal and constituted ~1 per cent of the total energy released during the flare. The study of morphological evolution of the filament in conjunction with synthesized T and EM maps has been carried out which reveals (a) Partial filament eruption prior to the onset of the precursor emission, (b) Heated dense plasma over the polarity inversion line and in the vicinity of the slowly rising filament during the precursor phase. Based on the implications from multi-wavelength observations, we propose a scheme to unify the energy release during the precursor and main phase emissions in which, the precursor phase emission has been originated via conduction front formed due to the partial filament eruption. Next, the heated leftover S-shaped filament has undergone slow rise and heating due to magnetic reconnection and finally erupted to produce emission during the impulsive and gradual phases.Comment: 16 Pages, 11 Figures, Accepted for Publication in MNRAS Main Journa

Effects of weak disorder on stress-wave anisotropy in centered square nonlinear granular crystals

The present study describes wave propagation characteristics in a weakly disordered two-dimensional granular media composed of a square array of spheres accommodating interstitial cylindrical intruders. Previous investigations, performed experimentally as well as numerically, emphasized that wave-front shapes in similar systems are tunable via choice of material combinations. Here, we investigate the effects of statistical variation in the particle diameters and compare the effects of the resulting disorder in experiments and numerical simulations, finding good agreement

Theoretical study of the thermal behavior of free and alumina-supported Fe-C nanoparticles

The thermal behavior of free and alumina-supported iron-carbon nanoparticles is investigated via molecular dynamics simulations, in which the effect of the substrate is treated with a simple Morse potential fitted to ab initio data. We observe that the presence of the substrate raises the melting temperature of medium and large $Fe_{1-x}C_x$ nanoparticles ($x$ = 0-0.16, $N$ = 80-1000, non- magic numbers) by 40-60 K; it also plays an important role in defining the ground state of smaller Fe nanoparticles ($N$ = 50-80). The main focus of our study is the investigation of Fe-C phase diagrams as a function of the nanoparticle size. We find that as the cluster size decreases in the 1.1-1.6-nm-diameter range the eutectic point shifts significantly not only toward lower temperatures, as expected from the Gibbs-Thomson law, but also toward lower concentrations of C. The strong dependence of the maximum C solubility on the Fe-C cluster size may have important implications for the catalytic growth of carbon nanotubes by chemical vapor deposition.Comment: 13 pages, 11 figures, higher quality figures can be seen in article 9 at http://alpha.mems.duke.edu/wahyu

Baculovirus vector-mediated expression of heterologous genes in insect cells

The baculovirus expression system employing Autagrapha californica nuclear polyhidrosis virus and Spodoptera frugiperda insect cells in culture has proved very popular for high level expression of heterologous genes: In this system, transcription of the foreign gene is usually driven by the hyperactive and temporally regulated polyhedrin gene promoter. Replacement of the polyhedrin gene, which encodes a 29-kDa occlusion protein (non-essential for viral replication), with a gene of interest leads to an occlusion negative phenotype which serves as a visual marker to select for recombinant viruses. Simultaneous expression of multiple genes can also be achieved. The heterologous proteins synthesized in this system are antigenically, immunologically and functionally identical in most respects to their native counterparts. This mini-review will aim at summarizing the potentials and utility of the baculovirus expression vector system and will address some important questions relating to the biology of this system