290 research outputs found
Photoexcitation in thin films deposited on silicon substrates by reactive pulsed laser ablation
Reactive pulsed laser ablation is a very interesting method to deposit thin films of several materials and compounds such as oxides, nitrides, semiconductors and superconductors. This technique relies on photoablation of pure elements, or a mixture of materials, with simultaneous exposure to a reactive atmosphere. In the case of oxides, reactions between the laser vaporized metals and oxygen lead to the formation of intermediate complexes and finally to oxide thin films. The reactivity of the plume has been already studied by our group in other oxides and nitrides productions and ascertained by Time of Flight Mass Spectrometry measurements [1].Thin films of semiconducting oxides such asIn2O3,SnO2, and multilayers of these two compounds have been deposited by Reactive Pulsed Laser Ablation, with the aim to evaluate the behaviour of such films under variable halogen lamp illumination.Deposition of these thin films has been carried out by a frequency doubled Nd-YAG laser (wavelength = 532 nm) on Silicon (100) substrates. A comparison, among indium oxide, tin oxide, and multilayers of indium and tin oxides, has been performed. The influence of physical parameters, such as substrate temperature and oxygen pressure in the deposition chamber, has been investigated. The deposited films have been characterized by Electric Resistance measurements
Efeito da granulometria do milho sobre a digestibilidade das dietas para suínos em crescimento e terminação.
bitstream/item/58534/1/CUsersPiazzonDocuments223.pd
NMR and biochemical studies
RNA‐containing vesicles, recovered from the supernatant of high‐density cell samples of human colon carcinoma, produce a high‐resolution 1H NMR spectrum of lipids characterized by isotropic tumbling; these vesicles contain large amounts of triglycerides and cholesterol esters. Both findings have strict analogies to what is displayed by the proteolipid complexes isolated from the sera of tumor‐bearing patients [(1985) Proc. Natl. Acad. Sci. USA 82, 3455–3459; (1986) FEBS Lett. 203, 164–168]. Lipid analysis and enzymatic tests indicate that these vesicles are selected micromaps of plasma membranes, analogous to those that can be recovered from culture media in which tumor cells are grown [(1985) Dev. Biol. 3, 33–57]. Peculiar lipids, an acylated oligopeptide and a modified phospholipid, are also present in the vesicles
Fornecimento de água dentro do comedouro e efeitos no desempenho, carcaça e efluentes da produção de suínos.
bitstream/CNPSA/8520/1/cot231.pd
Ultracold Bosonic Atoms in Disordered Optical Superlattices
The influence of disorder on ultracold atomic Bose gases in quasiperiodic
optical lattices is discussed in the framework of the one-dimensional
Bose-Hubbard model. It is shown that simple periodic modulations of the well
depths generate a rich phase diagram consisting of superfluid, Mott insulator,
Bose-glass and Anderson localized phases. The detailed evolution of mean
occupation numbers and number fluctuations as function of modulation amplitude
and interaction strength is discussed. Finally, the signatures of the different
phases, especially of the Bose-glass phase, in matter-wave interference
experiments are investigated.Comment: 4 pages, 4 figures, using REVTEX
Discovery of a Nearby Low-Surface-Brightness Spiral Galaxy
During the course of a search for compact, isolated gas clouds moving with
anomalous velocities in or near our own Galaxy (Braun and Burton 1998 A&A, in
press), we have discovered, in the data of the Leiden/Dwingeloo survey
(Hartmann and Burton 1997, Atlas of Galactic Neutral Hydrogen, CUP) of Galactic
hydrogen, the HI signature of a large galaxy, moving at a recession velocity of
282 km/s, with respect to our Galaxy. Deep multicolor and spectroscopic optical
observations show the presence of star formation in scattered HII regions;
radio HI synthesis interferometry confirms that the galaxy is rich in HI and
has the rotation signature of a spiral galaxy; a submillimeter observation
failed to detect the CO molecule. The radio and optical evidence combined
suggest its classification as a low-surface-brightness spiral galaxy. It is
located in close spatial and kinematic proximity to the galaxy NGC 6946. The
newly-discovered galaxy, which we call Cepheus 1, is at a distance of about 6
Mpc. It is probably to be numbered amongst the nearest few LSB spirals.Comment: 13 page LaTeX, requires aastex, 4 GIF figures. Accepted for
publication in the AJ, January 199
Spin liquid ground state in a two dimensional non-frustrated spin model
We consider an exchange model describing two isotropic spin-1/2 Heisenberg
antiferromagnets coupled by a quartic term on the square lattice. The model is
relevant for systems with orbital degeneracy and strong electron-vibron
coupling in the large Hubbard repulsion limit, and is known to show a
spin-Peierls-like dimerization in one dimension. In two dimensions we calculate
energy gaps, susceptibilities, and correlation functions with a Green's
Function Monte Carlo. We find a finite spin gap and no evidence of any kind of
order. We conclude that the ground state is, most likely, a spin liquid of
resonating valence bonds.Comment: 4 pages, 4 figures, Revte
Solvent free interactions in contact pairs of molecules of biological interest: Laser spectroscopic and electrospray mass spectrometric studies
A laser spectroscopic and mass spectrometric study of ionic and molecular clusters of biological interest is reported. The molecules of interest and their aggregates were generated in a supersonic beam and analyzed by mass resolved resonant two photon absorption and ionization (R2PI) and by collision induced mass spectrometry (CID-MS). The absence of the solvent allows to study these systems in the isolated state free of undesired solvent effects which may level off the differences in their properties. The gas phase results have been compared to theoretical estimates of the structure and stability of the systems under investigation
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