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F Lado

Publications and source records attributed to F Lado.

At least 19 recordsLinked to original sources
PubMed2006

Phase behavior of a hard sphere Maier-Saupe nematogenic system in three dimensions.

We present a detailed computer simulation and integral equation study of the phase behavior of a nematogenic system composed of hard spheres with embedded three-dimensional Maier-Saupe spins. For this well-known system, we map the gas-liquid equilibrium, which is coupled to a first-order isotropic-nematic transition. The anisotropic integral equation theory is found to yield excellent agreement with the simulation data within the fluid regime. Additionally, we determine the fluid-solid equilibrium transition by means of computer simulation.

Journal Article↗
PubMed2005

Simulation study of the phase behavior of a planar Maier-Saupe nematogenic liquid.

Using extensive Monte Carlo simulations and a simple approximation in density functional theory, we study the phase behavior of a fluid of nematogenic molecules with centers of mass constrained to lie in a plane but with axes free to rotate in any direction, both with and without an external disorienting field perpendicular to the plane. We find that simulation predicts the existence of an order-disorder phase transition belonging to the Berezinskii-Kosterlitz-Thouless type, along with a low temperature gas-liquid transition. In contrast to the simulation results, density functional theory predicts a first-order orientational phase transition coupled continuously with a first-order gas-liquid transition. The approximate theoretical approach qualitatively reproduces the field dependence of the order-disorder and gas-liquid transitions but is far from quantitative.

Journal Article↗
PubMed2005

Perianal ulceration: a case of tuberculosis cutis orificialis.

BACKGROUND: Tuberculosis cutis orificialis is an extremely rare variant of cutaneous tuberculosis. Perianal location is a possible site of presentation. METHODS: We describe the management of a young male with a painless non-specific perianal ulcer, who presented an asymptomatic disseminate pulmonary and intestinal tuberculosis. He had a history of pulmonary sarcoidosis and long-term corticosteroid therapy. RESULTS: Healing of the ulcer was achieved after three-drug antituberculous therapy, with an improvement of the radiographic pulmonary alterations. CONCLUSIONS: Tuberculous origin should be considered in persistent perianal ulcers to avoid delays in the treatment of this rare form of tuberculosis.

Adult↗
PubMed2000

The spectrum of neuropsychiatric abnormalities associated with electrical status epilepticus in sleep.

Electrical status epilepticus in sleep (ESES) is an electrographic pattern consisting of an almost continuous presence of spike-wave discharges in slow wave sleep. ESES is frequently encountered in pediatric syndromes associated with epilepsy or cognitive and language dysfunction. It can be present in various evolutionary stages of a spectrum of diseases, the prototypes of which are the 'continuous spikes and waves during slow wave sleep' syndrome (CSWS), the Landau-Kleffner syndrome (LKS), as well as in patients initially presenting as benign childhood epilepsy with centrotemporal spikes (BECTS). The purpose of this article is to review the literature data on the semiology, electrographic findings, prognosis, therapeutic options, as well as the current theories on the pathophysiology of these disorders. The frequent overlap of CSWS, LKS, and BECTS urges an increased level of awareness for the occasional transition from benign conditions such as BECTS to more devastating syndromes such as LKS and CSWS. Identification of atypical signs and symptoms, such as high discharge rates, prolonged duration of ESES, neuropsychiatric and cognitive dysfunction, lack of responsiveness to medications, and pre-existing neurologic conditions is of paramount importance in order to initiate the appropriate diagnostic measures. Prolonged and if needed repetitive sleep electroencephalographs (EEGs) are warranted for proper diagnosis.

Agnosia↗
PubMed2000

Structure and thermodynamics of a ferrofluid monolayer

We model a disordered planar monolayer of paramagnetic spherical particles, or ferrofluid, as a two-dimensional fluid of hard spheres with embedded three-dimensional magnetic point dipoles. This model, in which the orientational degrees of freedom are three dimensional while particle positions are confined to a plane, can be taken as a crude representation of a colloidal suspension of superparamagnetic particles confined in a water/air interface, a system that has recently been studied experimentally. In this paper, we propose an Ornstein-Zernike integral equation approach capable of describing the structure of this highly inhomogeneous fluid, including the effects of an external magnetic field. The method hinges on the use of specially tailored orthogonal polynomials whose weight function is precisely the one-particle distribution function that describes the surface- and field-induced anisotropy. The results obtained for various particle densities and external fields are compared with Monte Carlo simulations, illustrating the capability of the inhomogeneous Ornstein-Zernike equation and the proposed solution scheme to yield a detailed and accurate description of the spatial and orientational structure for this class of systems. For comparison, results from density-functional theory in the modified mean-field approximation are also presented; this latter approach turns out to yield at least qualitatively correct results.

Journal Article↗
PubMed1999

Thermodynamic perturbation theory for polydisperse colloidal suspensions using orthogonal polynomial expansions.

We present a method for calculating the thermodynamic and structural properties of a polydisperse liquid by means of a thermodynamic perturbation theory: the optimized random phase approximation (ORPA). The approach is an extension of a method proposed recently by one of us for an integral equation application [Phys. Rev. E 54, 4411 (1996)]. The method is based on expansions of all sigma-dependent functions in the orthogonal polynomials p(i)(sigma) associated with the weight function f(Sigma)(sigma), where sigma is a random variable (in our case the size of the particles) with distribution f(Sigma)(sigma). As in the one-component or general N-component case, one can show that the solution of the ORPA is equivalent to the minimization of a suitably chosen functional with respect to variations of the direct correlation functions. To illustrate the method, we study a polydisperse system of square-well particles; extension to other hard-core or soft-core systems is straightforward.

Journal Article↗
PubMed1996

Central motor loop oscillations in parkinsonian resting tremor revealed by magnetoencephalography.

A variety of clinical and experimental findings suggest that parkinsonian resting tremor results from the involuntary activation of a central mechanism normally used for the production of rapid voluntary alternating movements. However, such central motor loop oscillations have never been directly demonstrated in parkinsonian patients. Using magnetoencephalography, we recorded synchronized and tremor-related neuromagnetic activity over wide areas of the frontal and parietal cortex. The spatial and temporal organization of this activity was studied in seven patients suffering from early-stage idiopathic Parkinson's disease (PD). Single equivalent current dipole (ECD) analysis and fully three-dimensional distributed source solutions (magnetic field tomography, MFT) were used in this analysis. ECD and MFT solutions were superimposed on high-resolution MRI. The findings indicate that 3 to 6 Hz tremor in PD is accompanied by rhythmic subsequent electrical activation at the diencephalic level and in lateral premotor, somatomotor, and somatosensory cortex. Tremor-evoked magnetic activity can be attributed to source generators that were previously described for voluntary movements. The interference of such slow central motor loop oscillations with voluntary motor activity may therefore constitute a pathophysiologic link between tremor and bradykinesia in PD.

Aged↗
PubMed1994

Neuromagnetic studies of the lip area of primary somatosensory cortex in humans: evidence for an oscillotopic organization.

Magnetic trigeminal somatosensory responses from human subjects were recorded using a 14-channel magnetoencephalographic system. Sensory stimuli comprising a 15-ms vibration at frequencies of 50 Hz, 150 Hz and 250 Hz were given at randomized interstimulus intervals. Using a single dipole model, the neuronal sources of the evoked responses were determined, and mapped onto magnetic resonance images of each subject. Source localization analysis was based on the main peak of the averaged signal (M55). All of the sources were located deep in the anterior bank of the postcentral gyrus, corresponding to area 3b of somatosensory cortex SI. In all cases, the source for the upper lip was significantly higher in the vertical axis (0.6-1.1 cm) than for the lower lip, while the lower lip stimulation produced a larger response than the upper lip. Furthermore, statistically significant differences were found between the locations of the dipoles evoked by different frequency stimulation. The location of the response shifted with change in stimulation frequency, showing a trend among all subjects with medial shift between 150 and 250 Hz for both upper and lower lip. The accuracy of source localization calculated from magnetic fields ranged between +/- 0.9 and +/- 3.0 mm (SEM). These results demonstrate (1) that a large area of the somatosensory cortex is utilized for lip representation and (2) that the spatial displacement of the trigeminal somatosensory response may be related to the discrimination of frequency.

Adult↗
PubMed1992

[Mediastinal tuberculosis as a cause of fever of unknown origin].

Tuberculosis is the most frequent cause of fever from unknown etiology. On the other hand, mediastinal tuberculous adenopathy (TBM), without associated pulmonary affection is a rare form of presentation among adults, generally evolving with sustained fever until a thoracic radiology is performed showing mediastinal enlargement. We present a case which started as fever from unknown etiology (FUE), given that, according to the thoracic radiology performed one month after the onset of fever, no mediastinal affection was observed.

Adult↗
PubMed1991

Magnetic field tomography of coherent thalamocortical 40-Hz oscillations in humans.

This paper introduces the use of magnetic field tomography (MFT), a noninvasive technique based on distributed source analysis of magnetoencephalography data, which makes possible the three-dimensional reconstruction of dynamic brain activity in humans. MFT has a temporal resolution better than 1 msec and a spatial accuracy of 2-5 mm at the cortical level, which deteriorates to 1-3 cm at depths of 6 cm or more. MFT is used here to visualize the origin of a spatiotemporally organized pattern of coherent 40-Hz electrical activity. This coherence, initially observed during auditory input, was proposed to be generated by recurrent corticothalamic oscillation. In support of this hypothesis, we illustrate well-defined 40-Hz coherence between cortical-subcortical sites with a time shift that is consistent with thalamocortical conduction times. Studies on Alzheimer patients indicate that, while a similar activity pattern is present, the cortical component is reduced in these subjects.

Adult↗
PubMed1991

[Starch-induced granulomatous peritonitis].

A case of granulomatous peritonitis produced by starch is presented. This is a rare pathology caused by abdominal contamination with starch from surgical gloves during an operation. The symptoms can be very similar to acute abdomen, therefore, it is sometimes necessary to carry out a second operation in order to confirm the diagnosis. A peritoneal biopsy or cytology of the ascitic liquid usually provides the correct diagnosis as the typical starch granules show up. With non-steroid analgesics, or steroids in some cases, the process can controlled.

Abdomen, Acute↗