The effect of pressure on statics, dynamics and stability of multielectron bubbles

The effect of pressure and negative pressure on the modes of oscillation of a multi-electron bubble in liquid helium is calculated. Already at low pressures of the order of 10-100 mbar, these effects are found to significantly modify the frequencies of oscillation of the bubble. Stabilization of the bubble is shown to occur in the presence of a small negative pressure, which expands the bubble radius. Above a threshold negative pressure, the bubble is unstable.Comment: 4 pages, 2 figures, accepted for publication in Physical Review Letter

Cold Collision Frequency Shift in Two-Dimensional Atomic Hydrogen

We report a measurement of the cold collision frequency shift in atomic hydrogen gas adsorbed on the surface of superfluid 4He at T<=90 mK. Using two-photon electron and nuclear magnetic resonance in 4.6 T field we separate the resonance line shifts due to the dipolar and exchange interactions, both proportional to surface density sigma. We find the clock shift Delta v_c = -1.0(1)x10^-7 Hz cm^-2 x sigma, which is about 100 times smaller than the value predicted by the mean field theory and known scattering lengths in the 3D case.Comment: 4 pages, 3 figure

Vortices on a superconducting nanoshell: phase diagram and dynamics

In superconductors, the search for special vortex states such as giant vortices focuses on laterally confined or nanopatterned thin superconducting films, disks, rings, or polygons. We examine the possibility to realize giant vortex states and states with non-uniform vorticity on a superconducting spherical nanoshell, due to the interplay of the topology and the applied magnetic field. We derive the phase diagram and identify where, as a function of the applied magnetic field, the shell thickness and the shell radius, these different vortex phases occur. Moreover, the curved geometry allows these states (or a vortex lattice) to coexist with a Meissner state, on the same curved film. We have examined the dynamics of the decay of giant vortices or states with non-uniform vorticity into a vortex lattice, when the magnetic field is adapted so that a phase boundary is crossed.Comment: 21 pages, 9 figure

Síndrome de TAR y estado de heterocigosis para anemia falciforme

Resumen Presentación de un paciente con el cuadro clínico del síndrome de TAR, quien presenta además un estado de heterocigosis para anemia falciforme. El síndrome de TAR, descrito por primera vez en 1959 por Shaw y Oliver, es un trastorno genético no común que ocurre con una prevalencia aproximada de 1: 500.000 a 1: 1.000.000 de nacidos vivos. En 1969 Hall y col. delinearon los criterios diagnósticos de este síndrome que incluyen ausencia bilateral del radio con presencia de ambos pulgares y trombocitopenia. Otras anomalías descritas en menor frecuencia son: Alteraciones óseas del húmero y cúbito, en los casos severos, focomelia, mal- formaciones de expresión variable en extremidades inferiores, malformaciones cardiacas e intolerancia a la leche de vaca (1, 2). Los hallazgos encontrados en este caso se comparan con los de la literatura y se discute su posible etiología, además de resaltar la importancia de realizar un diagnóstico y tratamiento precoz y preciso especialmente de la trombocitopenia. Palabras clave: Malformaciones congénitas, aplasia, hipoplasia, trombocitopenia, anemia falciforme. Abstract This paper shows a patient with clinical features of the TAR syndrome, who presents heterozigosis state for sickle cell anemia. The TAR syndrome was described by Shaw and Oliver in 1959, it is a rare genetic disease, occurring with an approximate prevalence of 1 case in 500.000 to 1 million births. Hall et al. described the current diagnostic criteria for TAR syndrome in 1969. These include bilateral absence of the radii in the presence of both thumbs and trombocytopenia. Other anomalies described included ulnar or humeral defects and the most severe cases phocomelia, lower limb involvement is variable, cadiac anomalies and cow’s milk intolerance (1,2) In this paper, we compare the findings of the literature review, discuss the ethiology and the importance of a diagnostic and treatment specially for trombocytopenia Key words: Congenital malformations, aplasia, hypoplasia, trombocytopenia, sickle cell anemia

Atomic Deuterium Adsorbed on the Surface of Liquid Helium

We investigate deuterium atoms adsorbed on the surface of liquid helium in equilibrium with a vapor of atoms of the same species. These atoms are studied by a sensitive optical method based on spectroscopy at a wavelength of 122 nm, exciting the 1S-2P transition. We present a direct measurement of the adsorption energy of deuterium atoms on helium and show evidence for the existence of resonantly enhanced recombination of atoms residing on the surface to molecules.Comment: 6 pages 4 figure

Variational Monte Carlo study of the ground state properties and vacancy formation energy of solid para-H2 using a shadow wave function

A Shadow Wave Function (SWF) is employed along with Variational Monte Carlo techniques to describe the ground state properties of solid molecular para-hydrogen. The study has been extended to densities below the equilibrium value, to obtain a parameterization of the SWF useful for the description of inhomogeneous phases. We also present an estimate of the vacancy formation energy as a function of the density, and discuss the importance of relaxation effects near the vacant site

Static Properties of Trapped Bose-Fermi Mixed Condensate of Alkali Atoms

Static properties of a bose-fermi mixture of trapped potassium atoms are studied in terms of coupled Gross-Pitaevskii and Thomas-Fermi equations for both repulsive and attractive bose-fermi interatomic potentials. Qualitative estimates are given for solutions of the coupled equations, and the parameter regions are obtained analytically for the boson-density profile change and for the boson/fermion phase separation. Especially, the parameter ratio $R_{int}$ is found that discriminates the region of the large boson-profile change. These estimates are applied for numerical results for the potassium atoms and checked their consistency. It is suggested that a small fraction of fermions could be trapped without an external potential for the system with an attractive boson-fermion interaction.Comment: 8 pages,5 figure

Evaluation of the visibility distance with the Istram program on third-class roads with a high accident rate

In Peru there are many roads where accidents occur due to their inadequate geometric design. The traffic accidents with the most incidents are of the side collision or collision type with a percentage of 42.73%, and distraction with 20.19% [1]. This shows that it is necessary to carry out a redesign on this road that seeks to reduce the percentage of accidents in the area. For the case study, a section of a 3km highway located in Santiago de Chuco, north of the city of Lima, was used. Thanks to the photogrammetric record of the current state of the road, sectors with geometric deficiencies were identified, such as visibility distance and safety in terms of precariousness in the use of signaling. Likewise, the evaluation carried out in the stopping and overtaking visibility distance concludes that with a constant speed of 30 km/h there are stretchs or sections that do not meet the necessary distance for its route.Academia Mexicana de Ciencia