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F Martín

Publications and source records attributed to F Martín.

At least 37 records · Page 2Linked to original sources
PubMed2004

In-plane and out-of-plane diffraction of H(2) from metal surfaces.

We have measured in-plane and out-of-plane diffraction of H2 and D2 molecular beams scattered by reactive Pd(111) and nonreactive NiAl(110) surfaces at 140-150 meV. A comparison with six-dimensional quantum dynamics and classical trajectory calculations shows for the first time that accurate diffraction patterns can be obtained from state-of-the-art potential energy surfaces based on density functional theory. Our measurements show that, at general incidence conditions, out-of-plane diffraction is much more important than was assumed in previous experiments.

Journal Article↗
PubMed2004

Babinet principle applied to the design of metasurfaces and metamaterials.

The electromagnetic theory of diffraction and the Babinet principle are applied to the design of artificial metasurfaces and metamaterials. A new particle, the complementary split rings resonator, is proposed for the design of metasurfaces with high frequency selectivity and planar metamaterials with a negative dielectric permittivity. Applications in the fields of frequency selective surfaces and polarizers, as well as in microwave antennas and filter design, can be envisaged. The tunability of all these devices by an applied dc voltage is also achievable if these particles are etched on the appropriate substrate.

Journal Article↗
PubMed2004

Fragmentation of highly excited small neutral carbon clusters.

We present a combined experimental and theoretical study of fragmentation of small Cn clusters (n = 5,7,9) produced in charge transfer collisions of fast (nu = 2.6 a.u.) singly charged Cn+ clusters with He. Branching ratios for all possible fragmentation channels have been measured. Comparison with microcanonical Metropolis Monte Carlo simulations based on quantum chemistry calculations allows us to determine the energy distribution of the excited clusters just after the collision.

Journal Article↗
PubMed2004

The Shiga toxin 2 B subunit inhibits net fluid absorption in human colon and elicits fluid accumulation in rat colon loops.

Shiga toxin (Stx)-producing Escherichia coli (STEC) colonizes the large intestine causing a spectrum of disorders, including watery diarrhea, bloody diarrhea (hemorrhagic colitis), and hemolytic-uremic syndrome. It is estimated that hemolytic-uremic syndrome is the most common cause of acute renal failure in infants in Argentina. Stx is a multimeric toxin composed of one A subunit and five B subunits. In this study we demonstrate that the Stx2 B subunit inhibits the water absorption (Jw) across the human and rat colonic mucosa without altering the electrical parameters measured as transepithelial potential difference and short circuit current. The time-course Jw inhibition by 400 ng/ml purified Stx2 B subunit was similar to that obtained using 12 ng/ml Stx2 holotoxin suggesting that both, A and B subunits of Stx2 contributed to inhibit the Jw. Moreover, non-hemorrhagic fluid accumulation was observed in rat colon loops after 16 h of treatment with 3 and 30 ng/ml Stx2 B subunit. These changes indicate that Stx2 B subunit induces fluid accumulation independently of A subunit activity by altering the usual balance of intestinal absorption and secretion toward net secretion. In conclusion, our results suggest that the Stx2 B subunit, which is non-toxic for Vero cells, may contribute to the watery diarrhea observed in STEC infection. Further studies will be necessary to determine whether the toxicity of Stx2 B subunit may have pathogenic consequences when it is used as a component in an acellular STEC vaccine or as a vector in cancer vaccines.

Adult↗
PubMed2004

Theoretical analysis of the relation between H2 dissociation and reflection on Pd surfaces.

We study the scattering of H2 (v=0, J=0) molecules by the Pd(110) surface using classical trajectory methods. We show that the dissociative adsorption probability barely depends on incidence angle (total energy scaling) up to an impact energy of 200 meV. This is the consequence of a "loss of memory" of the initial incidence angle, mostly due to dynamic trapping, which also reflects itself in a cosinelike angular distribution of reflected molecules. Consequently, a cosinelike distribution can be the result of a subpicosecond process that involves neither energy dissipation to the surface nor transient thermal accommodation.

Journal Article↗
PubMed2004

Soil pollution by a pyrite mine spill in Spain: evolution in time.

Soil pollution was studied after the spill of the Aznalcóllar pyrite mine between 1998 and 2001, analyzing As, Zn, Cd, Cu and Pb both in total concentrations as well as in soluble and bioavailable forms. The main remediation measures were: clean-up of the tailings and polluted soils, plus application of amendment materials (liming). The results indicate that, after three years, 50-70% of the acidic soils and 25-30% of the basic soils are still highly polluted in total arsenic. The limit of 0.04 mg kg(-1) for water-soluble arsenic is exceeded in 15-20% of all soils. The EDTA-extractable arsenic (bioavailable) exceeds the limit of 2 mg kg(-1) only in the acidic sectors. After clean-up, the homogenization of the upper 20-25 cm of the soils appears to be the most recommended measure in the reduction of pollution.

Biological Availability↗
PubMed2004

An immunocytochemical mapping of methionine-enkephalin-Arg(6)-Gly(7)-Leu(8) in the human brainstem.

Using an indirect immunoperoxidase technique, we studied the distribution of immunoreactive fibers and cell bodies containing methionine-enkephalin-Arg(6)-Gly(7)-Leu(8) in the adult human brainstem. Immunoreactive cell bodies were found in the reticular formation of the medulla oblongata (in which we observed the highest density of immunoreactive cell bodies) and the pons, the solitary nucleus, the hypoglossal nucleus, the medial and spinal vestibular nuclei, the lateral cuneate nucleus, the nucleus prepositus, the central gray of the pons and mesencephalon, the central and pericentral nuclei of the inferior colliculus, the superior colliculus, ventral to the superior olive and in the midline region of the pons and mesencephalon. The highest density of immunoreactive fibers containing methionine-enkephalin-Arg(6)-Gly(7)-Leu(8) was found in the spinal trigeminal nucleus, the central gray and the reticular formation of the medulla oblongata, pons and mesencephalon, the solitary nucleus, the spinal vestibular nucleus, the dorsal accessory olivary nucleus, the raphe obscurus, the substantia nigra and in the interpeduncular nucleus. The widespread distribution of immunoreactive structures containing methionine-enkephalin-Arg(6)-Gly(7)-Leu(8) in the human brainstem indicates that this neuropeptide might be involved in several physiological mechanisms, acting as a neurotransmitter and/or neuromodulator.

Aged↗
PubMed2004

Efficient lentiviral transduction of Herpesvirus saimiri immortalized T cells as a model for gene therapy in primary immunodeficiencies.

Infection of human T lymphocytes with the Herpesvirus saimiri (HVS) yields immortalized T-cell lines (HVS-T) which retain all the phenotypical and functional characteristics of their parental cells. This represents a new experimental model for studying genetic disorders of T lymphocytes. In spite of the efforts of many laboratories, no satisfactory way has been found so far to modify HVS-T cells genetically. We have analyzed the capacity of oncoretroviral (MLV)- and lentiviral (HIV-1)-based vectors pseudotyped with vesicular stomatitis virus glycoprotein (VSVg) to transduce HVS-T cells. HIV-1-derived vectors efficiently transduced HVS-T cell lines, reaching up to 85% of cells expressing the transgene in a single round of infection. MLV-based vectors, on the other hand, were unable to transduce more than 1% of any of the HVS-T cell lines analyzed. Lentiviral-driven gene expression was maintained constant and stable in HVS-T cells for a minimum of 48 days. We also observed that although the lentiviral transduction efficiency achieved on HVS-T cells is lower than that obtained with tumor or primary endothelial cells, it is nevertheless similar to that found with activated primary T cells.

Adoptive Transfer↗
PubMed2004

[MIBI and parathyroid gland function in secondary hyperparathyroidism].

The role of the double phase parathyroid scintigraphy with MIBI in the primary hyperparathyroidism has been well studied. The present work analyzes the benefit of this image technique in the diagnosis and therapeutic approach to uremia associated hyperparathyroidism. We studied 18 dialysis patients with clinical and analytical data of hyperparathyroidism. All of them were receiving treatment with i.v. vitamin D. We carried out two scintigraphic studies, the first under basal conditions (without changes in treatment) and the second one, a week later after the stimulation of the parathyroid gland through the cessation of the treatment with vitamin D and phosphorus binders, and the use of a low-calcium dialysate. In the basal study, fourteen patients had a positive uptake test in at least one of the four glands. These patients had significantly higher PTHi levels than those with a negative scintigraphic study. After the stimulation test, we found a statistically significative rise in PHTi (644 vs 979 p < 0.001) and phosphorus levels (5.8 vs 7.3; p < 0.01), a slight fall in calcium levels (p = NS) and a statistically significative increment in the score of scintigraphic captation (5.5 +/- 4.5 vs 6.8 +/- 5; p < 0.05). We found a statistically significative correlation between the PTHi level and the score of scintigraphic uptake, in the basal study (r = 0.6, p < 0.01) and after stimulation (r = 0.6, p < 0.01). The only variable associated with the scintigraphic uptake was PTHi, justifying 31.1% of the variance in the first study and 32.7% in the second. In conclusion, the MIBI scintigraphic is a useful exploration in the uremic patient with hyperparathyroidism, as it predicts the functional state of the parathyroid glands according to uptake intensity. The stimulation test could be useful in planning therapy, but some of its characteristics need to be established, such as the precise time to reach the maximum level of parathyroid stimulation.

Acetates↗
PubMed2003

Nicotinamide induces both proliferation and differentiation of embryonic stem cells into insulin-producing cells.

In contrast to the consistent observation that methods that promote proliferation also dedifferentiate insulin-producing cells, useful in vitro differentiation protocols must drive both proliferation and differentiation. We herein describe an strategy in which the combination of nutrient restriction and nicotinamide supplementation results in a consistent increase in the mass of insulin-producing cells.

Cell Differentiation↗
PubMed2003

Tetrofosmin as predictors of tumour response.

Non-invasive imaging methods in the evaluation of chemotherapy response in malignant tumours are currently being explored. Standard Nuclear Medicine procedures seem to offer the clinician a promising tool in the management of those oncologic patients, who might benefit from chemotherapy. Early studies focused on the relationship between radionuclides used in tumour diagnosis and factors associated with multidrug resistance (MDR). The tumour expression of P-glycoprotein (Pgp) and multidrug resistance-related protein-1 expression (MRP) have been suggested as important factors in the failure of chemotherapy. Most studies found an association between Pgp levels and (99m)Tc-sestamibi ((99m)Tc-MIBI) or (99m)Tc-Tetrofosmin uptake ((99m)Tc-TF). Currently investigations in nuclear medicine oncology are focusing on the potential role of radionuclide imaging in the assessment of chemotherapy. Recent papers discuss the usefulness of radionuclides as (99m)Tc-MIBI and (99m)Tc-TF as non-invasive procedures to predict and to monitor therapy response in patients affected by malignant tumours treatable using chemotherapy. This chapter will review the latest development in (99m)Tc-TF, giving an overview of recent investigations carried out using this radiotracer in therapy oncology, with emphasis on its potential role as predictor of tumour response.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2003

Is there a role for (99m)Tc-anti-CEA monoclonal antibody imaging in the diagnosis of recurrent colorectal carcinoma?

AIM: To evaluate the usefulness of immunoscintigraphy with an anti-CEA monoclonal antibody fragment labelled with (99m)Tc for early detection of colorectal recurrence in patients with rising serum CEA levels. METHODS: Fifty-one consecutive patients (27 women, 24 men) with colorectal cancer (mean age 68.9+/-10.2 years) and rising CEA levels (16.2+/-18.2 ng/ml) were prospectively studied. Two immunoscintigraphy studies were performed in 8 patients (n=59). Immunoscintigraphy was performed after i.v. injection of 925 MBq of anti-CEA monoclonal antibody. Planar images of the thorax, abdomen and pelvis, as well as SPECT of the abdomen and pelvis were obtained at 4 and 24 hours after injection. In all cases an abdominal CT scan was previously performed. Findings were validated by histopathological analysis (28 cases) or by imaging and clinical follow-up of at least 6 months following the immunoscintigraphy (31 cases). RESULTS: Forty-one patients did not show recurrence during follow-up. We found 18 cases with confirmed diagnosis of extrahepatic abdominal or pelvic diseases, 11 cases with liver metastases, 9 in the thorax and 2 in the bone. In patients with pelvic and extrahepatic abdominal disease, immunoscintigraphy was positive in 18 cases (14 true positive, 4 false positive). From the 14 true positive only 7 cases had been detected by CT. Immunoscintigraphy was negative in the remaining 41 cases (37 true negative, 4 false negative). Therefore, the sensitivity and specificity for immunoscintigraphy in extrahepatic abdominal and pelvic disease were 78% and 90%, respectively. CT results showed a lower sensitivity of 61% (p<0.05) and specificity of 83%. Liver metastases were detected by CT in 9 cases, but only 2 of these were identified using immunoscintigraphy. CONCLUSION: Scintigraphy with anti-CEA monoclonal antibody fragment labelled with (99m)Tc is superior to CT for the detection of pelvic and extrahepatic abdominal recurrence of colorectal cancer, while CT is more sensitive in the detection of liver and lung metastases. Immunoscintigraphy has a limited usefulness in the detection of distant metastases, but it may be helpful in the diagnosis of suspected colorectal recurrence in patients with non-conclusive CT findings, when FDG-PET is not available.

Aged↗
PubMed2003

An immunocytochemical mapping of somatostatin in the cat auditory cortex.

Using an indirect immunoperoxidase technique, the localization of somatostatin-28 (1-12)-like immunoreactive fibers and cell bodies in the auditory cortex of the cat (anterior, primary, secondary, temporal, ventral, ventroposterior, posterior and dorsoposterior auditory fields) was studied. In general, the distribution of SOM-ir structures is widespread in the auditory cortex of the feline. A high density of immunoreactive fibers as well as a low density of cell bodies containing somatostatin were observed in all the layers of the eight above-mentioned auditory fields. These data indicate that somatostatin-28 (1-12) could act as a neurotransmitter and/or a neuromodulator in the auditory cortex of the cat. The origin of the SOM-ir fibers in the auditory cortex of the cat, as well as the issue of whether the cell bodies containing somatostatin-28 (1-12) are local or projecting neurons is discussed.

Animals↗
PubMed2003

[Retinal shortening: the most severe form of proliferative vitreoretinopathy (PVR)].

PURPOSE: To identify the clinical characteristics of patients developing retinal shortening due to intraretinal PVR. METHODS: Observational and retrospective cohort study on 110 PVR patients operated on between 2000 and 2001. During surgery, after removing epiretinal membranes and ruling out the presence of subretinal membranes, a perfluorocarbon liquid was injected. Those cases in which retinal flattening was not accomplished, were considered intraretinal PVR (group 1). Those in which retinal flattening allowed endolaser application, were taken as the control group (group 2). Clinical features of both groups were compared by chi-square test. RESULTS: 60 cases (54.5%, CI 95%: 40.5-68.5) showed retinal shortening (group 1). In 24 cases (21.8%, CI 95%: 12.9-30.7) complete retinal flattening was accomplished (group 2). In 26 cases (23.6%), evaluation was inconclusive. In 9 out of the 60 cases of group 1 (15%) a retinectomy was necessary to reattach the retina. Differences between both groups were not statistically significant for any of the clinical variables. However, the number of retinal detachments of more than 60 days of evolution was significantly higher in retinectomized eyes (20.7%) than in group 1 (3.7%) (p=0.04). CONCLUSIONS: Retinal shortening is a relatively frequent phenomenon in PVR. Further studies are necessary to characterize this clinical presentation of PVR and its pathogenesis.

Case-Control Studies↗
PubMed2002

Charge transfer and dissociation in collisions of metal clusters with atoms.

We present a combined theoretical and experimental study of charge transfer and dissociation in collisions of slow Li31(2+) clusters with Cs atoms. We provide a direct quantitative comparison between theory and experiment and show that good agreement is found only when the exact experimental time of flight and initial cluster temperature are taken into account in the theoretical modeling. We demonstrate the validity of the simple physical image that consists in explaining evaporation as resulting from a collisional energy deposit due to cluster electronic excitation during charge transfer.

Journal Article↗