Possible role of 3He impurities in solid 4He

We use a quantum lattice gas model to describe essential aspects of the motion of 4He atoms and of 3He impurities in solid 4He. This study suggests that 3He impurities bind to defects and promote 4He atoms to interstitial sites which can turn the bosonic quantum disordered crystal into a metastable supersolid. It is suggested that defects and interstitial atoms are produced during the solid 4He nucleation process where the role of 3He impurities (in addition to the cooling rate) is known to be important even at very small (1 ppm) impurity concentration. It is also proposed that such defects can form a glass phase during the 4He solid growth by rapid cooling.Comment: 4 two-column Revtex pages, 4 figures. Europhysics Letters (in Press

Metastability in Spin-Polarized Fermi Gases

We study the role of particle transport and evaporation on the phase separation of an ultracold, spin-polarized atomic Fermi gas. We show that the previously observed deformation of the superfluid paired core is a result of evaporative depolarization of the superfluid due to a combination of enhanced evaporation at the center of the trap and the inhibition of spin transport at the normal-superfluid phase boundary. These factors contribute to a nonequilibrium jump in the chemical potentials at the phase boundary. Once formed, the deformed state is highly metastable, persisting for times of up to 2 s.Comment: 4 pages, 6 figure

Giant Coulomb broadening and Raman lasing on ionic transitions

CW generation of anti-Stokes Raman laser on a number of blue-green argon-ion lines (4p-4s, 4p-3d) has been demonstrated with optical pumping from metastable levels 3d'^2G, 3d^4F. It is found, that the population transfer rate is increased by a factor of 3-5 (and hence, the output power of such Raman laser) owing to Coulomb diffusion in the velocity space. Measured are the excitation and relaxation rates for the metastable level. The Bennett hole on the metastable level has been recorded using the probe field technique. It has been shown that the Coulomb diffusion changes shape of the contour to exponential cusp profile while its width becomes 100 times the Lorentzian one and reaches values close to the Doppler width. Such a giant broadening is also confirmed by the shape of the absorption saturation curve.Comment: RevTex 18 pages, 5 figure

Web-based Platform For Collaborative Medical Imaging Research

Medical imaging research depends basically on the availability of large image collections, image processing and analysis algorithms, hardware and a multidisciplinary research team. It has to be reproducible, free of errors, fast, accessible through a large variety of devices spread around research centers and conducted simultaneously by a multidisciplinary team. Therefore, we propose a collaborative research environment, named Adessowiki, where tools and datasets are integrated and readily available in the Internet through a web browser. Moreover, processing history and all intermediate results are stored and displayed in automatic generated web pages for each object in the research project or clinical study. It requires no installation or configuration from the client side and offers centralized tools and specialized hardware resources, since processing takes place in the cloud.941

Conformational analysis of 2,2-difluoroethylamine hydrochloride: double gauche effect

The gauche effect in fluorinated alkylammonium salts is well known and attributed either to an intramolecular hydrogen bond or to an electrostatic attraction between the positively charged nitrogen and the vicinal electronegative fluorine atom. This work reports the effect of adding a fluorine atom in 2-fluoroethylamine hydrochloride on the conformational isomerism of the resulting 2,2-difluoroethylamine chloride (2). The analysis was carried out using NMR coupling constants in D2O solution, in order to mimic the equilibrium conditions in a physiological medium, in the gas phase and in implicit water through theoretical calculations. Despite the presence of sigma(CH)->sigma(*)(CF) and sigma(CH)->sigma(*)(CN) interactions, which usually rule the hyperconjugative gauche effect in 1,2-disubstituted ethanes, the most important forces leading to the double gauche effect (+NH3 in the gauche relationship with both fluorine atoms) in 2 are the Lewis-type ones. Particularly, electrostatic interactions are operative even in water solution, where they should be significantly attenuated, whereas hyperconjugation and hydrogen bond have secondary importance10877882CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIGFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPsem informaçãosem informação2012/03933-5; 2011/11098-6; 2011/01170-

Structure of the archaeal chemotaxis protein CheY in a domain-swapped dimeric conformation

Archaea are motile by the rotation of the archaellum. The archaellum switches between clockwise and counterclockwise rotation, and movement along a chemical gradient is possible by modulation of the switching frequency. This modulation involves the response regulator CheY and the archaellum adaptor protein CheF. In this study, two new crystal forms and protein structures of CheY are reported. In both crystal forms, CheY is arranged in a domain-swapped conformation. CheF, the protein bridging the chemotaxis signal transduction system and the motility apparatus, was recombinantly expressed, purified and subjected to X-ray data collection

Structure of the archaeal chemotaxis protein CheY in a domain-swapped dimeric conformation

Archaea are motile by the rotation of the archaellum. The archaellum switches between clockwise and counterclockwise rotation, and movement along a chemical gradient is possible by modulation of the switching frequency. This modulation involves the response regulator CheY and the archaellum adaptor protein CheF. In this study, two new crystal forms and protein structures of CheY are reported. In both crystal forms, CheY is arranged in a domain-swapped conformation. CheF, the protein bridging the chemotaxis signal transduction system and the motility apparatus, was recombinantly expressed, purified and subjected to X-ray data collection

Thermal History of Solid 4He Under Oscillation

We have studied the thermal history of the resonant frequency of a torsional oscillator containing solid 4He. We find that the magnitude of the frequency shift that occurs below 100 mK is multivalued in the low temperature limit, with the exact value depending on how the state is prepared. This result can be qualitatively explained in terms of the motion and pinning of quantized vortices within the sample. Several aspects of the data are also consistent with the response of dislocation lines to oscillating stress fields imposed on the solid.Comment: 7 pages, 6 figure

Zero-point vacancies in quantum solids

A Jastrow wave function (JWF) and a shadow wave function (SWF) describe a quantum solid with Bose--Einstein condensate; i.e. a supersolid. It is known that both JWF and SWF describe a quantum solid with also a finite equilibrium concentration of vacancies x_v. We outline a route for estimating x_v by exploiting the existing formal equivalence between the absolute square of the ground state wave function and the Boltzmann weight of a classical solid. We compute x_v for the quantum solids described by JWF and SWF employing very accurate numerical techniques. For JWF we find a very small value for the zero point vacancy concentration, x_v=(1.4\pm0.1) x 10^-6. For SWF, which presently gives the best variational description of solid 4He, we find the significantly larger value x_v=(1.4\pm0.1) x 10^-3 at a density close to melting. We also study two and three vacancies. We find that there is a strong short range attraction but the vacancies do not form a bound state.Comment: 19 pages, submitted to J. Low Temp. Phy