Biomedical subjects

L Santos

Publications and source records attributed to L Santos.

At least 37 records · Page 2Linked to original sources

PubMed2004

Atomic Bose-Fermi mixtures in an optical lattice.

A mixture of ultracold bosons and fermions placed in an optical lattice constitutes a novel kind of quantum gas, and leads to phenomena, which so far has been discussed neither in atomic physics, nor in condensed matter physics. We discuss the phase diagram at low temperatures, and in the limit of strong atom-atom interactions, and predict the existence of quantum phases that involve pairing of fermions with one or more bosons, or, respectively, bosonic holes. The resulting composite fermions may form, depending on the system parameters, a normal Fermi liquid, a density wave, a superfluid liquid, or an insulator with fermionic domains. We discuss the feasibility for observing such phases in current experiments.

Journal Article↗

PubMed2004

Comparison between RFLP-PCR and antigenemia for pp65 antigen for diagnosis of cytomegalovirus disease after kidney transplantation.

Cytomegalovirus (CMV) infection is the single most frequent infectious complication in renal transplant recipients. The purpose of this study was to analyze the diagnostic efficacy of PCR-RFLP compared to antigenemia for CMV disease (CMVD) in kidney transplant recipients. From November 2001 to February 2002, 19 renal adult transplant recipients were followed with weekly measurements of CMV pp65 antigen to monitor the activity of CMV from the week 4 to 12 posttransplantation. Only 4 (21.1%) patients did not develop viremia during the first 12 posttransplantation weeks. Active infection was observed in 15 patients (78.9%): asymptomatic viremia in 6 (31.6%) and CMVD in 9 (47%). All patients who developed CMVD showed positivity in both methods during the observation period. The number of positive cells ranged from 11 to 292 cells in patients with CMVD and one to eight cells among those with asymptomatic viremia. Both methods revealed 100% sensitivity for CMVD diagnosis. The specificity was 60% for antigenemia and 70% for PCR, with positive predictive values of 60% and 75%, respectively.

Acute Disease↗

PubMed2004

Study on quality control parameters of a TLD system for individual monitoring.

This work intends to identify and follow up quality control parameters important for the general improvement of our thermoluminescence dosemeter (TLD) system for Individual Monitoring that is currently preparing its accreditation according to the EN ISO/IEC 17025 Standard. A retrospective analysis of the readers' start-up tests revealed an eventual variation of parameters, like the high voltage, which may affect the light collecting system, and hence the TL dose results. This was investigated and although the high voltage requires a careful look, the stability and reproducibility of the TLD system was ascertained by the results of quality control procedures. As a consequence of this work, the start-up procedure was modified and the warning levels used for the start-up daily tests of the readers were derived from a more realistic approach.

Accreditation↗

PubMed2004

Thermoluminescence dosimetry of a thermal neutron field and comparison with Monte Carlo calculations.

The characteristics of thermoluminescence dosemeters (TLDs) regarding the determination of photon and neutron absorbed doses were investigated in a thermal neutron beam. Harshaw TLD-100 (LiF:Mg,Ti) and TLD-700 (7LiF:Mg,Ti) were compared with similar materials from Solid Dosimetric Detector and Method Laboratory (People's Republic of China). Harshaw TLD-700H (7LiF:Mg,Cu,P) and aluminium oxide (Al2O3:Mg,Y) from Hungary were also considered for photon dose measurement. The neutron sensitivity of the investigated materials was measured and found to be consistent with values reported by other authors. A comparison was made between the TL dose measurements and results obtained via conventional methods. An agreement within 20% was obtained, which demonstrates the ability of TLD for measuring neutron and photon doses in a mixed field, using careful calibration procedures and determining the neutron sensitivity for the usage conditions.

Aluminum Oxide↗

PubMed2003

Three-dimensional quasi-Tonks gas in a harmonic trap.

We analyze the macroscopic dynamics of a Bose gas in a harmonic trap with a superimposed two-dimensional optical lattice, assuming a weak coupling between different lattice sites. We consider the situation in which the local chemical potential at each lattice site can be considered as that provided by the Lieb-Liniger solution. Because of the weak coupling between sites and the form of the chemical potential, the three-dimensional ground-state density profile and the excitation spectrum acquire remarkable properties different from both 1D and 3D gases. We call this system a quasi-Tonks gas. We discuss the range of applicability of this regime, as well as realistic experimental situations where it can be observed.

Journal Article↗

PubMed2003

Atomic Bose and Anderson glasses in optical lattices.

An ultracold atomic Bose gas in an optical lattice is shown to provide an ideal system for the controlled analysis of disordered Bose lattice gases. This goal may be easily achieved under the current experimental conditions by introducing a pseudorandom potential created by a second additional lattice or, alternatively, by placing a speckle pattern on the main lattice. We show that, for a noncommensurable filling factor, in the strong-interaction limit, a controlled growing of the disorder drives a dynamical transition from superfluid to Bose-glass phase. Similarly, in the weak interaction limit, a dynamical transition from superfluid to Anderson-glass phase may be observed. In both regimes, we show that even very low-intensity disorder-inducing lasers cause large modifications of the superfluid fraction of the system.

Journal Article↗

PubMed2003

Roton-maxon spectrum and stability of trapped dipolar Bose-Einstein condensates.

We find that pancake dipolar condensates can exhibit a roton-maxon character of the excitation spectrum, so far observed only in superfluid helium. We also obtain a condition for the dynamical stability of these condensates. The spectrum and the border of instability are tunable by varying the particle density and/or the confining potential. This opens wide possibilities for manipulating the superfluid properties of dipolar condensates.

Journal Article↗

PubMed2003

Creation of a dipolar superfluid in optical lattices.

We show that, by loading a Bose-Einstein condensate of two different atomic species into an optical lattice, it is possible to achieve a Mott-insulator phase with exactly one atom of each species per lattice site. A subsequent photoassociation leads to the formation of one heteronuclear molecule with a large electric dipole moment, at each lattice site. The melting of such a dipolar Mott insulator creates a dipolar superfluid, and eventually a dipolar molecular condensate.

Journal Article↗

PubMed2003

Liver transplantation for fulminant and subfulminant hepatic failure.

AIMS: The aim of this study was to assess the long-term course and outcome after liver transplantation (LTX) for fulminant/subfulminant hepatic failure (FSHF) to determine which factors relate to outcome. PATIENTS AND METHODS: Between April 1990 and October 2002, 30 adult patients with FSHF underwent LTX. King's College criteria were used to decide which patients needed LTX. Pretransplantation parameters (age, sex, degree of hepatic encephalopathy, etiology, and time between onset of symptoms and LTX) were examined as risk factors for LTX outcome. RESULTS: Mean age at LTX was 40.4+/-13.9 years and 46.7% were men. The most frequent causes of FSHF were virus B in 23.3%, autoimmune hepatitis in 23.3%, and cryptogenic in 20%. Fifty percent of the patients with a survival longer than 15 days suffered episodes of acute rejection; chronic rejection occurred in 25%. One- and five-year patient and allograft survival rates for FSHF were 56.3% and 54.7%, respectively. Autoimmune hepatitis was the only factor associated with better posttransplantation outcome, although there were no differences in posttransplant course. Patient survival rates increased during the study period. During the first 5 years (1990-1995) the survival rates were 53.3% (1-year and 5-year), whereas they were 60% at 1 and 5 years in the second interval (1996-2002). CONCLUSIONS: The mortality rate of FSHF is high during the first year post-LTX. LTX for FSHF of autoimmune etiology showed better outcomes with increasing patient survival rates during the study period.

Adolescent↗

PubMed2003

Neovascularisation is a prognostic factor of early recurrence in T1/G2 urothelial bladder tumours.

BACKGROUND: Of patients with superficial bladder cancer, a group are still at risk of disease recurrence, progression and death from their cancer after curative treatment. Angiogenesis is a crucial pathogenic mechanism for this type of urothelial cell carcinoma (UCC), and is a potential therapeutic target. However, the selection of the appropriate patients remains a dilemma. PATIENTS AND METHODS: Vascular endothelial growth factor (VEGF) expression and the presence of angiogenesis and occurrence of CD31, CD34, endoglin and factor VIII immunoexpression, were evaluated in 66 superficial papillary UCCs of the bladder and were correlated with classical histopathological factors and disease outcome. RESULTS: VEGF immunoreactivity was observed in 100% of cases, and more intensely in the luminal surface. The presence of microvessel clusters independently of a fibrovascular core was observed in 22.7% of cases. Of these, the T1/G2 subgroup had an independent and significantly lower recurrence-free survival (P = 0.0002). CONCLUSIONS: These results indicate that the presence of angiogenesis in tumour urothelium is a potential prognostic factor in superficial UCC, particularly in T1/G2 tumours, and may be used to select patients for anti-angiogenic treatments.

Antigens, CD↗

PubMed2002

Dynamical transition from a quasi-one-dimensional Bose-Einstein condensate to a Tonks-Girardeau gas.

We analyze in detail the expansion of a 1D Bose gas after removing the axial confinement. We show that during its one-dimensional expansion the density of the Bose gas does not follow a self-similar solution. Our analysis is based on a nonlinear Schrödinger equation with variable nonlinearity whose validity is discussed for the expansion problem, by comparing with an exact Bose-Fermi mapping for the case of an initial Tonks-Girardeau gas. For this case, the gas is shown to expand self-similarly, with a different scaling law compared to the one-dimensional Thomas-Fermi condensate.

Journal Article↗

PubMed2002

Direct determination of chlorophenols in landfill leachates by solid-phase micro-extraction-gas chromatography-mass spectrometry.

Landfill leachates represent a serious environmental concern with regard to trace priority pollutants introduced into the aquatic environment. From the analytical point of view, they constitute complex matrices because of their high organic matter content and competition with the trace analytes in the extraction procedure. Although the use of SPME to extract chlorophenols in leachates has already been described in several publications, the limited number of chlorophenols restricts this analysis field of application. This paper presents a new analytical methodology to determine 13 chlorophenols and phenol by SPME-GC-MS in landfill leachates. The overall analysis was performed in 90 min and the detection limits range from 0.005 microg/l (pentachlorophenol) to 2.5 microg/l (phenol). Reproducibility, expressed by the coefficient of variation of repeated extractions at different concentration levels of the analytes, was on average inferior to 10%. Recovery, evaluated by standard addition to leachates, was 86.2% on average. Pentachlorophenol, 2,3,4,5-tetrachlorophenol and 2,3,4,6-tetrachlorophenol were the sole analytes detected at nanogram level in the landfill leachates analysed.

Chlorophenols↗

PubMed2002

Quantum phases of dipolar bosons in optical lattices.

The ground state of dipolar bosons placed in an optical lattice is analyzed. We show that the modification of experimentally accessible parameters can lead to the realization and control of different quantum phases, including superfluid, supersolid, Mott insulator, checkerboard, and collapse phases.

Journal Article↗

PubMed2002

A reinvestigation of the molecular structures, vibrations and rotation of methyl group in o-methylaniline in S0 and S1 states studied by laser induced fluorescence spectroscopy and ab initio calculations.

The UV fluorescence excitation and dispersed fluorescence spectra of a jet-cooled o-methylaniline have been obtained for the S1 <-- S0 transition, in which some of the bands have been observed and assigned for the first time. The origin of the electronic transition appears at 34,328.4 cm(-1). It was found that the spectra exhibit an important feature corresponding to the internal rotation of the methyl group in the electronic ground and excited states. Ab initio calculations at MP2/6-31 + G* and CIS/6-31 + G* show that the optimised structure of o-methylaniline in the ground state is not planar with the amino group having sp3 hybridation-like character due to the existence of lone paired electrons on the N atom. Upon electronic excitation, the C-N bond exhibits a partial double character, as in the case of other aniline derivatives.

Algorithms↗

PubMed2002

Reproducibility of TL measurements in a mixed field of thermal neutrons and photons.

The reproducibility of measurements performed with GR-100 (LiF:Mg,Ti) from the Solid Dosimetric Detector and Method Laboratory (DML) China, GR-107 (7LiF:Mg,Ti, DML), TLD-700H (7LiF:Mg.Cu,P, Harshaw) and Al2O3:Mg,Y (Hungary) in photon and mixed photon-neutron fields was investigated. Mixed-field irradiations were performed in a thermal neutron field generated at a nuclear reactor. GR-100 sensitivity decreased after mixed-field irradiations, while no significant change was found for the other materials. Using GR-100 for the dosimetry of mixed and high-intensity fields requires careful procedures.

Aluminum Oxide↗

PubMed2001

Observation of phase fluctuations in elongated Bose-Einstein condensates.

The occurrence of phase fluctuations due to thermal excitations in Bose-Einstein condensates (BECs) is studied for a variety of temperatures and trap geometries. We observe the statistical nature of the appearance of phase fluctuations and characterize the dependence of their average value on temperature, number of particles, and the trapping potential. We find pronounced phase fluctuations for condensates in very elongated traps in a broad temperature range. The results are of great importance for the realization of BEC in quasi-1D geometries, for matter wave interferometry with BECs, as well as for coherence properties of guided atom laser beams.

Journal Article↗

PubMed2001

Dark solitons in a two-component Bose-Einstein condensate.

The creation and interaction of dark solitons in a two-component Bose-Einstein condensate is investigated. For a miscible case, the interaction of dark solitons in different components is studied. Various possible scenarios are presented, including the formation of a soliton-soliton bound pair. We also analyze the soliton propagation in the presence of domains, and show that a dark soliton can be transferred from one component to the other at the domain wall when it exceeds a critical velocity. For lower velocities multiple reflections within the domain are observed, where the soliton is evaporated and accelerated after each reflection until it finally escapes from the domain.

Journal Article↗

PubMed2001

The Gab1 docking protein links the b cell antigen receptor to the phosphatidylinositol 3-kinase/Akt signaling pathway and to the SHP2 tyrosine phosphatase.

B cell antigen receptor (BCR) signaling causes tyrosine phosphorylation of the Gab1 docking protein. This allows phosphatidylinositol 3-kinase (PI3K) and the SHP2 tyrosine phosphatase to bind to Gab1. In this report, we tested the hypothesis that Gab1 acts as an amplifier of PI3K- and SHP2-dependent signaling in B lymphocytes. By overexpressing Gab1 in the WEHI-231 B cell line, we found that Gab1 can potentiate BCR-induced phosphorylation of Akt, a PI3K-dependent response. Gab1 expression also increased BCR-induced tyrosine phosphorylation of SHP2 as well as the binding of Grb2 to SHP2. We show that the pleckstrin homology (PH) domain of Gab1 is required for BCR-induced phosphorylation of Gab1 and for Gab1 participation in BCR signaling. Moreover, using confocal microscopy, we show that BCR ligation can induce the translocation of Gab1 from the cytosol to the plasma membrane and that this requires the Gab1 PH domain as well as PI3K activity. These findings are consistent with a model in which the binding of the Gab1 PH domain to PI3K-derived lipids brings Gab1 to the plasma membrane, where it can be tyrosine-phosphorylated and then act as an amplifier of BCR signaling.

B-Lymphocytes↗