Role of confinements on the melting of Wigner molecules in quantum dots

We explore the stability of a Wigner molecule (WM) formed in confinements with differentgeometries emulating the role of disorder and analyze the melting (or crossover) of such asystem. Building on a recent calculation [D. Bhattacharya, A. Ghosal, Eur. Phys. J.B 86, 499 (2013)] that discussed the effects of irregularities on thethermal crossover in classical systems, we expand our studies in the untested territory byincluding both the effects of quantum fluctuations and ofdisorder. Our results, using classical and quantum (path integral)Monte Carlo techniques, unfold complementary mechanisms that drive the quantum and thermalcrossovers in a WM and show that the symmetry of the confinement plays no significant rolein determining the quantum crossover scale n_X. This is because thezero-point motion screens the boundary effects within short distances. The phase diagramas a function of thermal and quantum fluctuations determined from independent criteria isunique, and shows “melting” from the WM to both the classical and quantum “liquids”. Anintriguing signature of weakening liquidity with increasing temperature, T, is found in the extreme quantum regime. The crossover is associated with production of defects. However, thesedefects appear to play distinct roles in driving the quantum and thermal “melting”. Ouranalyses carry serious implications for a variety of experiments on many-particle systems? semiconductor heterostructure quantum dots, trapped ions, nanoclusters, colloids and complex plasma.     

Zwitterionic imidazolium salt: An efficient organocatalyst for tetrahydropyranylation of alcohols

An aprotic imidazole based zwitterionic-salt, 4-(3-methylimidazolium)-butane sulfonate has been found to be an efficient organocatalyst for tetrahydropyranylation by the reaction of 3,4-dihydro-2H-pyran (DHP) and different aliphatic alcohols as well as various phenolic compounds. The notable advantages of the present method are general applicability to various alcohols, clean reaction, production of no hazardous waste, open air reaction conditions and high yields. The catalyst can be reused without the loss of significant catalytic activity.     

A method for characterizing adsorption of flowing solutes to microfluidic device surfaces

We present a method for characterizing the adsorption of solutes in microfluidic devices that is sensitive to both long-lived and transient adsorption and can be applied to a variety of realistic device materials, designs, fabrication methods, and operational parameters. We have characterized the adsorption of two highly adsorbing molecules (FITC-labeled bovine serum albumin (BSA) and rhodamine B) and compared these results to two low adsorbing species of similar molecular weights (FITC-labeled dextran and fluorescein). We have also validated our method by demonstrating that two well-known non-fouling strategies [deposition of the polyethylene oxide (PEO)-like surface coating created by radio-frequency glow discharge plasma deposition (RF-GDPD) of tetraethylene glycol dimethyl ether (tetraglyme, CH(3)O(CH(2)CH(2)O)(4)CH(3)), and blocking with unlabeled BSA] eliminate the characteristic BSA adsorption behavior observed otherwise.     

Diffusion thermopower of the two-dimensional electron gas in GaN single quantum wells

Diffusion thermopower ($S_d$) of the two-dimensional (2D) electron gas in GaN single quantum wells is calculated in the temperature range 1 K–12 K using the Fermi–Dirac distribution function. Scattering of carriers through acoustic phonons via deformation potential and piezoelectric couplings, and through background and remote ionized impurities is included. $S_d$ is found to decrease with temperature and the 2D electron concentration, and is primarily controlled by deformation potential acoustic scattering. The dependence of $S_d$ on the well width and the ionized impurity concentration is found to be quite weak.     

Stereoselective total synthesis of Jaspine B (Pachastrissamine) utilizing iodocyclization and an investigation of its cytotoxic activity

The stereoselective synthesis of Jaspine B has been achieved from easily available (S)-Garner’s aldehyde. The trisubstituted tetrahydrofuran core of Jaspine B was constructed by utilizing a diastereoselective iodocyclization as the key step. Deiodination and debenzylation were performed in a single step by using n-Bu₃SnH and ABCN as a conjugate catalyst system. The in vitro cytotoxicity of compounds 1 and 1a against 3 human cancer cell lines-A549 (lung), MCF7 (breast), and KB (oral); and a non-cancer cell line (NIH3T3) was determined by sulphorhodamine B based assay.     

Dithioannulation of Alkynes

A direct method for the preparation of 2,3-diphenyl-1,4-dithiins has been developed. The process involves treating alkynes with nickel bisdiphenyl-dithiolene in refluxing chlorobenzene in the presence of pyridine. Pyridine appears to be essential in order to avoid further transformation of 1,4-dithiins to thiophenes.     

On Bayesian Adaptation

We show that Bayes estimators of an unknown density can adapt to unknown smoothness of the density. We combine prior distributions on each element of a list of log spline density models of different levels of regularity with a prior on the regularity levels to obtain a prior on the union of the models in the list. If the true density of the observations belongs to the model with a given regularity, then the posterior distribution concentrates near this true density at the rate corresponding to this regularity.     

In situ study of water-induced segregation of bromide in bromide-doped sodium chloride by scanning polarization force microscopy

The adsorption of water on Br-doped NaCl crystals has been studied in situ using scanning polarization force microscopy, a noncontact electrostatic atomic force microscopy operation mode. Both topography and contact potential images were acquired as a function of relative humidity at room temperature, from 0% to more than 55%. It was found that the surface of the freshly cleaved crystal has an inhomogeneous electrical surface potential distribution with the steps more negative than the terraces below 40% relative humidity. This difference disappears when the humidity reaches 40% and higher. Below 40% the step morphology experiences only small changes due to water adsorption; however, above 40% major changes take place due to solvation, segregation, and redistribution of lattice ions. Bromide-rich islands and crystallites segregate to the surface above 40% relative humidity followed by drying. These islands and crystallites have a negative surface potential relative to the rest of the surface. These effects are attributed to the preferential solvation and segregation of Br- ions.