Biomedical subjects
Publications and source records attributed to L E González.
First-principles molecular-dynamics simulations have been performed for the liquid-vapor interfaces of liquid Li, Mg, Al, and Si. We analyze the oscillatory ionic and valence electronic density profiles obtained, their wavelengths, and the mechanisms behind their relative phase shift.
We report the results of an ab initio molecular dynamics simulation of the liquid-vapor interface of two binary liquid alloys, Na(0.3)K(0.7) and Li(0.4)Na(0.6), whose bulk behavior exhibits rather differing ordering tendencies. The study has been performed using samples of 2000 and 3000 particles, respectively, in a slab geometry with periodic boundary conditions. In both cases, the total ionic density distributions along the normal to the interface display some layering with a virtually pure monolayer of the lower surface tension component located outermost at the interface. However, the two systems behave very differently below the interface which can be accounted for by their different ordering tendencies in the bulk.
Trypanosoma vivax is the principal etiological agent of bovine trypanosomosis, a widely disseminated disease in tropical and subtropical regions. Here, we present a simple and reproducible method for the purification of T. vivax from experimentally infected and immunosuppressed sheep, using an isopycnic Percoll gradient, followed by DEAE-cellulose chromatography, with an estimated yield of 11-15%. This method could be used for the purification of T. vivax geographical isolates from various locations and from different natural hosts.
This paper presents the viscoelastic model for the Ashcroft-Langreth dynamic structure factors of liquid binary mixtures. We also provide expressions for the Bhatia-Thornton dynamic structure factors and, within these expressions, show how the model reproduces both the dynamic and the self-dynamic structure factors corresponding to a one-component system in the appropriate limits (pseudobinary system or zero concentration of one component). In particular we analyze the behavior of the concentration-concentration dynamic structure factor and longitudinal current, and their corresponding counterparts in the one-component limit, namely, the self-dynamic structure factor and self-longitudinal current. The results for several lithium alloys with different ordering tendencies are compared with computer simulation data, leading to a good qualitative agreement, and showing the natural appearance in the model of the fast sound phenomenon.
We present results for several structural and dynamical properties of the liquid Li(1-x)Na(x) alloy. The study has been carried out by means of the orbital-free ab initio molecular dynamics method, combined with local ionic pseudopotentials constructed within the same framework. We obtain good agreement with the available experimental data, reproducing accurately, the strong homocoordinating tendencies exhibited by this alloy. The calculated partial dynamic structure factors exhibit clear side peaks whose frequencies, for q<or=0.25 A(-1), correspond to the hydrodynamic sound dispersion of the binary alloy, whereas for larger q values fast and slow sound modes are identified. The mass ratio in this system, m(Na)/m(Li) approximately 3, is the smallest one so far for which the fast mode is observed.
Molecular dynamics simulations of the liquid-vapor interfaces of liquid metals have been performed using first principles methods. Results are presented for liquid lithium and sodium near their respective triple points, for samples of 2000 particles in a slab geometry. The atomic density profiles show a pronounced stratification extending several atomic diameters into the bulk, which is similar to that already experimentally observed in liquid K, Ga, In, and Hg.
Stars that explode as supernovae come in two main classes. A type Ia supernova is recognized by the absence of hydrogen and the presence of elements such as silicon and sulphur in its spectrum; this class of supernova is thought to produce the majority of iron-peak elements in the Universe. They are also used as precise 'standard candles' to measure the distances to galaxies. While there is general agreement that a type Ia supernova is produced by an exploding white dwarf star, no progenitor system has ever been directly observed. Significant effort has gone into searching for circumstellar material to help discriminate between the possible kinds of progenitor systems, but no such material has hitherto been found associated with a type Ia supernova. Here we report the presence of strong hydrogen emission associated with the type Ia supernova SN2002ic, indicating the presence of large amounts of circumstellar material. We infer from this that the progenitor system contained a massive asymptotic-giant-branch star that lost several solar masses of hydrogen-rich gas before the supernova explosion.
We present results for several structural and dynamical properties of the liquid Na-Cs alloy. The study has been carried out by means of the orbital-free ab initio molecular dynamics method, combined with local ionic pseudopotentials constructed within the same framework. The results show good agreement with the available experimental data, reproducing the homocoordinating tendency exhibited by this alloy.
After analyzing how facial tissues are affected during the aging process, 36 rhytidoplasties were performed by plicating the superficial musculoaponeurotic system (SMAS)-platysma complex. Also, additional procedures were performed to improve the aesthetic result. Patients were followed for 3 to 33 months (median, 13 months); their ages ranged from 42 to 72 years (median, 53 years). Because the facial soft tissues present specific anatomic particularities and the force-vector determinants for facial ptosis are many and varied, specific plications were combined to obtain the desired results during a rhytidoplasty. Combinations of six different types of plications are described; some of them are used individually by various authors to manage the SMAS-platysma complex. Major complications did not occur, despite extensive cutaneous undermining, and morbidity was similar to that of other techniques that handle the SMAS. The results were satisfactory for all patients, and clinical improvement was noted in all cases. On the basis of these results, using combined plication to manage the SMAS-platysma complex during a rhytidoplasty is recommended. The opposing vectors should be considered when planning the combination of plications.
We have carried out a prospective study of the sympathetic skin response (SSR) in 21 patients with lateral medullary syndrome (LMS), with the aim of identifying the most common pattern of SSR abnormalities and its possible correlation with clinical and radiological findings. The amplitude of the SSR recorded in the ipsilateral hand to the infarct was abnormally reduced in the patients as a group. However, using different stimulation and recording sites, and considering only the presence or absence of the response, we identified 5 different patterns of SSR abnormalities: 1. Normal responses; 2. Bilaterally absent responses to stimulation of the ipsilateral supraorbital nerve but not to other stimulation sites; 3. Absent responses in the side ipsilateral to the stroke, with normal responses in the contralateral side; 4. A combination of patterns 2 and 3; and 5. Absent responses to all stimuli. All patients with ipsilateral facial sensory loss had absent SSR to ipsilateral supraorbital nerve stimulation, while there was only a positive correlation between abnormal contralateral facial sensation and preservation of the SSR (Fisher's exact test P=0.003). No correlation was found between the pattern of SSR abnormalities and the infarct topography, assessed with the MRI. Our findings suggest that the damage to the SSR circuits of patients with LMS is not uniform, and follows an heterogeneous distribution independent from the MRI findings, and poorly related to the clinical sensory manifestations.
Patients with neurogenic claudication do not usually exhibit symptoms at rest. The diagnosis is uncertain when there are no signs of lumbar radiculopathy. However, the functional deficiary could show up during a brief time at presentation of the symptoms if appropriate electrophysiological techniques are used to measure nerve conduction at the radicular segment. In 8 patients with neurogenic claudication, we examined the curve of recruitment of the soleus H reflex and in four of them the chronodispersion of the F wave of the posterior tibial nerve, before and after walking was also examined. Both studies showed normal results before walking in all patients. The H wave showed a transient diminution of excitability in 6 patients after walking, which lasted for a mean period of 7 min. Only one of these patients also showed an increase in the chronodispersion of the F wave. Our data suggest that conduction is transiently blocked in large myelinated fibers at a radicular level in patients with neurogenic claudication after walking. This could partially explain the symptoms of neurogenic claudication.
Forty-two female patients underwent liposuction of large volumes and extensive abdominoplasty during an 18-month period, with an average follow-up period of 9 months. Fifty-two percent of the patients underwent a third surgical procedure, which was basically aesthetic. The average age was 40 years; weight varied between 51 kg and 113 kg, with only 11 percent of the patients at their ideal weight. The tumescent technique was used for performing liposuction, which was done on the loins, trochanters, lumbar, upper scapular, and upper lateral abdominal regions, avoiding liposuction of the abdominal flap in all cases except for one. The abdominoplasty was extensive with detachment to the xiphoid process without detaching liposuctioned areas. Volumes of 1600 ml to 11,200 ml were obtained through liposuction, with an average of 4230 cc, and minimal blood loss. Fatty dermal tissue was removed through abdominoplasty and it varied between 400 g and 5000 g with an average of 1300 g. Only the two heaviest patients required an autologous blood unit, because they underwent breast reduction at the same time. All the other patients were managed exclusively with intravenous crystalloids solutions. No major complications arose, and only five patients had minor complications. Based on these results, we consider it to be feasible to combine the liposuctioning of large volumes with abdominoplasty to improve body shape, even with the addition of a third surgical procedure. Nevertheless, it is essential to use the tumescent technique for liposuction to reduce bleeding to a minimum and to allow us to perform other procedures.
In spite of the general clinical uniformity of Wallenberg's syndrome (WS), individual patients present with a slightly different clinical picture, and detailed studies with magnetic resonance imaging (MRI) show differences in the topography of the brain stem lesion. Neurophysiological characterization of the lesion in WS has been known for a long time, but there are no studies on the possible correlation between lesion topography and neurophysiological deficit. Assuming that afferents from the three branches of the trigeminal nerve reach different parts of the trigeminal nuclei, we examined the possible correlation between the lesion topography assessed by the MRI and the neurophysiological deficit, assessed by studying the brain stem reflexes in patients with WS within 2 weeks after stroke. Neurophysiological abnormalities were always located in the afferent branch of the reflexes examined, but not all patients exhibited abnormalities in all responses. The ophthalmic branch was involved in 92.8% of patients, and the mandibular branch in 57.1% of patients. The patients with MRI lesions located in the lower medulla had normal responses with infraorbital or mental nerve stimulation. The results of this neurophysiological study confirm the heterogeneity of WS. Whether the neurophysiological identification of different subgoups of patients is relevant for clinical outcome needs further studies.
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