Discretization of electronic states in large InAsP/InP multilevel quantum dots probed by scanning tunneling spectroscopy.

The topography and the electronic structure of InAsP/InP quantum dots are probed by cross-sectional scanning tunneling microscopy and spectroscopy. The study of the local density of states in such large quantum dots confirms the discrete nature of the electronic levels whose wave functions are measured by differential conductivity mapping. Because of their large dimensions, the energy separation between the discrete electronic levels is low, allowing for quantization in both the lateral and growth directions as well as the observation of the harmonicity of the dot lateral potential.

A novel method for sampling alpha-helical protein backbones.

We present a novel technique of sampling the configurations of helical proteins. Assuming knowledge of native secondary structure, we employ assembly rules gathered from a database of existing structures to enumerate the geometrically possible three-dimensional arrangements of the constituent helices. We produce a library of possible folds for 25 helical protein cores. In each case, our method finds significant numbers of conformations close to the native structure. In addition, we assign coordinates to all atoms for four of the 25 proteins and show that this has a small effect on the number of near-native conformations. In the context of database driven exhaustive enumeration our method performs extremely well, yielding significant percentages of conformations (between 0.02% and 82%) within 6 A of the native structure. The method's speed and efficiency make it a valuable tool for predicting protein structure.

Prevalencia de eschericia coli enterohemorrágico en una zona ganadera de Argentina: caracterización genotípica de las cepas de origen animal / Animal reservoir and genotipic characterization of enterohemorrhagic escherichia coli in Argentina

Background: There is a high prevalence of infection by Enterohemorrhagic Escherichia coli (EHEC) and patients with hemolytic uremic syndrome (HUS) in Argentina. Aim: To study cattle and pigs as a possible reservoir of EHEC in Argentina. Material and methods: One hundred two healthy animals (68 cattles and 31 pigs) from a livestock in Argentina, were studied. Stool samples were obtained with a rectal swab. The strains were identified by DNA hybridization with specific gene probes detecting Shiga-like toxin 1 and 2 (Stx1, Stx2), and hly gen related to fimbrial adhesin-associated plasmid. EHEC strains were serogrouped using comercial antisera. Results: EHEC was isolated from 30 out of 68 bovines cultures (44.1 percent) and from 25 out of 31 pigs (58.1 percent). Isolates carrying genes codifying both Stx1 and Sxt2, were observed in 50 percent of cattle and 63.9 percent of pigs. The gene which codifies for hemolysin (associated to fimbrial adhesin) was observed in about 41 percent of EHEC isolates. Strains belonging to serogroups O26, O111, and O157 were isolated from cattle, and O111, and O157 from pigs. Conclusions: The high percentage of EHEC in both cattle and pigs and the presence of human infection-associated serogroups, suggests that these animals are a reservoir of EHEC associated with disease in humans

Conformations of closed DNA.

We examine the conformations of a model for a short segment of closed DNA. The molecule is represented as a cylindrically symmetric elastic rod with a constraint corresponding to a specification of the linking number. We obtain analytic expressions leading to the spatial configuration of a family of solutions representing distortions that interpolate between the circular form of DNA and a figure-eight form that represents the onset of interwinding. We are also able to generate knotted loops. We suggest ways to use our approach to produce other configurations relevant to studies of DNA structure. The stability of the distorted configurations is assessed, along with the effects of fluctuations on the free energy of the various configurations.

[Tension activity of pulmonary surfactant: adsorption of liposomes of model phospholipids]. / Tensioactivié du surfactant pulmonaire: adsorption de liposomes de phospholipides modèles.

One peculiarity of pulmonary surfactant, which is the tensioactive material physiologically present at the surface of alveoli, lies in its very quick localization at in the air-water interface. This being one of the limiting factors of artificial exogenous surfactants for the treatment of patients suffering of respiratory distress syndromes, we have studied the mechanisms which are intervening in the adsorption kinetics of a pure liquid--phase phospholipid, the dioleylphosphatidylcholine (DOPC), and of mixtures of dipalmitoylphosphatidylcholine (DPPC) and phosphatidic acid (PA) in presence of divalent cations (Ca++ and Mg++). The adsorption kinetics of liposomal suspensions of DOPC, which were studied by the Wilhelmy plate method, are determined by the existence of a barrier potential which height depends on the temperature and medium osmolarity, and on the deformability of vesicules. The study of PA-DPPC liposomes was performed with the help of a pulsating bubble surfactometer, a physicochemical instrumentation which mimics the pulmonary alveoli. To obtain performant responses with this model, high concentrations of PA and of divalent cations Ca++ and Mg++ are needed. These results, which are similar to those observed during the study of liposomal fusion, allow to propose a model, according to which adsorption of liposomes at the air-water interface is comparable to liposomal fusion and may be related to the presence of a thin aqueous film.

Exophytic renal angiomyolipoma. A case report.

A case of a large exophytic renal angiomyolipoma is presented. Despite the features on excretory urography suggestive of an extrarenal mass, computed tomography provided information concerning the origin and pathological nature of the lesion.

Eye metastases in carcinoma of the cervix. A case report.

Eye metastases in carcinoma of the cervix are very rare, although not an uncommon presentation of carcinomas in general. A patient with eye symptoms secondary to retro-ocular metastatic carcinoma of the cervix is presented.

Adult tethered cord syndrome. A case report.

A patient with adult onset of the tethered cord syndrome is described. The significance of the clinical presentation and the myelographic and computed tomographic findings are discussed.