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C Díaz

Publications and source records attributed to C Díaz.

At least 19 recordsLinked to original sources
PubMed2006

Reactive and nonreactive scattering of N2 from Ru(0001): a six-dimensional adiabatic study.

We have studied the dissociative chemisorption and scattering of N(2) on and from Ru(0001), using a six-dimensional quasiclassical trajectory method. The potential energy surface, which depends on all the molecular degrees of freedom, has been built applying a modified Shepard interpolation method to a data set of results from density functional theory, employing the RPBE generalized gradient approximation. The frozen surface and Born-Oppenheimer [Ann. Phys. (Leipzig) 84, 457 (1927)] approximations were used, neglecting phonons and electron-hole pair excitations. Dissociative chemisorption probabilities are found to be very small even for translational energies much higher than the minimum reaction barrier, in good agreement with experiment. A comparison to previous low dimensional calculations shows the importance of taking into account the multidimensional effects of N(2) rotation and translation parallel to the surface. The new calculations strongly suggest a much smaller role of nonadiabatic effects than previously assumed on the basis of a comparison between low dimensional results and experiments [J. Chem. Phys. 115, 9028 (2001)]. Also in agreement with experiment, our theoretical results show a strong dependence of reaction on the initial vibrational state. Computed angular scattering distributions and parallel translation energy distributions are in good agreement with experiments on scattering, but the theory overestimates vibrational and rotational excitations in scattering.

Journal Article↗
PubMed2006

Experimental evidence of dynamic trapping in the scattering of H2 from Pd(110).

We have performed H2(D2) diffraction experiments on a Pd(110) surface using two different high-sensitivity set-ups. We have found that, although the total reflectivity of Pd(110) is comparable to that observed in other reactive systems, the corresponding H2(D2) diffraction patterns are quite different: no diffraction peak, including the specular one, is observed on Pd(110). This unexpected result is the consequence of dynamic trapping. Such interpretation is supported by classical dynamics calculations based on accurate ab initio potential energy surfaces.

Journal Article↗
PubMed2006

Multidimensional effects on dissociation of N2 on Ru(0001).

The applicability of the Born-Oppenheimer approximation to molecule-metal surface reactions is presently a topic of intense debate. We have performed classical trajectory calculations on a prototype activated dissociation reaction, of N2 on Ru(0001), using a potential energy surface based on density functional theory. The computed reaction probabilities are in good agreement with molecular beam experiments. Comparison to previous calculations shows that the rotation of N2 and its motion along the surface affect the reactivity of N2 much more than nonadiabatic effects.

Journal Article↗
PubMed2005

Two cases of cystic seroma following mesh incisional hernia repair.

Cystic seromas, or mature fibrous cysts, are rare complications after ventral and incisional hernioplasties employing polypropylene mesh. We analyzed the medical records of patients, whose abdominal-wall hernias were surgically repaired with polypropylene mesh from November 1996 to February 2004 (N=685). Of the 162 patients, who had incisional hernias repaired with the Rives technique (preperitoneal mesh), we detected two patients who developed giant cystic seromas. Both patients underwent surgical resection of the cyst wall. As follow-up care improves for patients undergoing hernioplasties with polypropylene meshes, more cystic seromas are detected, thereby improving our knowledge of the clinical, radiological, and histopathological characteristics of this complication. However, the etiologic factors related to the appearance of this chronic cyst remain uncertain.

Aged↗
PubMed2005

A classical dynamics method for H2 diffraction from metal surfaces.

We present a discretization method that allows one to interpret measurements on diffraction of diatomic molecules from solid surfaces using six-dimensional (6D) classical trajectory calculations. It has been applied to the D2NiAl(110) and H2Pd(111) systems (which are models for activated and nonactivated dissociative chemisorption, respectively) using realistic potential energy surfaces obtained from first principles. Comparisons with experimental results and 6D quantum dynamical calculations show that, in general, the method is able to predict the relative intensity of the most important diffraction peaks. We therefore conclude that classical mechanics can be an efficient guide for experimentalists in the search for the most significant diffraction channels.

Journal Article↗
PubMed2005

Hepatocellular carcinoma in renal transplant patients.

INTRODUCTION: Chronic liver diseases, especially those related to hepatitis B (HBV) and C viruses (HCV), are a common problem in renal transplant patients. Hepatocellular carcinoma (HCC) is a complication of chronic liver diseases, incidence in the renal transplant cohort is higher than in the general population (1.4% to 4% vs 0.005% to 0.015%). METHODS: We retrospectively evaluated the incidence of HCC, its clinical presentation, the treatments, and the relation to chronic viral hepatitis among the population transplanted at our center between January 1980 and December 1998 and followed to August 2003. RESULTS: During the study period, six recipients among 534 renal transplants displayed HCC (incidence 1.12% of the entire population and 2.29% of patients with chronic viral hepatitis). Among the cohort five were men, and all had chronic viral hepatitis: three HBV, one HCV, and 2, a coinfection. HCC was diagnosed 124.1 (range 45 to 244) months after transplantation. All patients presented with abnormal liver function tests and tumors larger than 5 cm. Four had more than three tumors and three had an alpha-fetoprotein level higher than 400 IU/mL. Three patients received no treatment (survivals 1, 1, and 4 months); two patients, chemoembolization (survival 6 and 12 months); and one, surgical ethanol injections (survival 4 months). The overall survival was 4.5 months. CONCLUSION: HCC in renal transplant recipients is a common complication among patients with chronic viral hepatitis. The outcome was poor because HCC was detected at an advanced stage. Screening strategies for early diagnosis must be prospectively evaluated.

Carcinoma, Hepatocellular↗
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

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

Allele-frequency determination of BsmI and FokI polymorphisms of the VDR gene by quantitative real-time PCR (QRT-PCR) in pooled genomic DNA samples.

The vdr gene is a candidate for osteoporosis susceptibility, with conflicting results in association studies. We have designed and optimized an individual allele-specific and DNA pooling PCR-based methodology to quantitate BsmI and FokI polymorphisms of the vdr gene and studied single-nucleotide polymorphisms (SNPs) from pooled DNA samples. The allele frequency in DNA pooling experiments has been analyzed by kinetic PCR: quantitative real-time PCR (QRT-PCR). A Spanish cohort of 225 healthy postmenopausal women was studied. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (DEXA) and quantitative ultrasound calcaneous densitometry. Allele-specific PCR amplification of BsmI and FokI genes showed full concordance with the PCR-RFLP approach. The prevalence of the three BsmI VDR genotypes was 19.1, 44.9 and 36.0% for BB, Bb and bb, respectively. In the case of the FokI locus, the prevalence of genotypes was 40.4, 48.0 and 11.6% for FF, Ff and ff, respectively. No positive correlation was found between polymorphism and BMD. The DNA pooling procedure was validated. No differences were found in allele frequencies and T-score data obtained using the high throughput DNA pooling approach, as compared to known individual frequencies. In our hands, this is a very useful approach to study quantitative (thus polygenic) traits like osteoporosis susceptibility.

Absorptiometry, Photon↗
PubMed2004

Comparing alternative definitions of the contemporary group effect in Avilena Negra Iberica beef cattle using classical and Bayesian criteria.

Data on weaning weight from 12,740 animals were used to compare different definitions of contemporary groups (CG) for the genetic evaluation of the Avilena Negra Iberica beef cattle breed. Six alternative definitions for the CG effect were considered: herd-year-season of calving (HYS), with seasons defined according to the four natural seasons; herd-year-month of calving (HYM); herd clusters of 30 d (HC30-30) or 90 d (HC90-90); and adaptive herd clusters with two time limits, 30 and 90 d (HC30-90), and 30 and 180 d (HC30-180). A minimum of five observations in each CG class was required. This rendered substantial differences in loss of information, ranging from 0.7% of the total number of records for HC30-180 to 14% for HYM. Several classical statistics and Bayesian criteria for statistical model comparison were used. The use of classical criteria, such as the between- and within-CG variation and the accuracy of prediction, can be controversial because of their dependency on the unknown variance components. Residual variance decreased with the decrease in time span associated with the definition of CG. This was expected in this population because environmental conditions are highly variable throughout the year. However, estimates of the additive genetic variance for direct effects, which should not be affected by the definition of CG, were substantially larger for definitions involving larger time periods (HYS, HC90-90). When parameters used in the current evaluation procedure were used with all data sets, CG involving 30 d (HYM and HC30-30) were optimal in terms of providing the lowest/largest within-/between-CG variation. On the other hand, CG involving 90 d (HYS and HC90-90) yielded the poorest within-/between CG variation, with only a slight improvement of accuracy of prediction of direct genetic values over the other definitions. Bayes factors and cross-validation predictive densities allowed for improved discrimination among models. Models including CG spanning 30 d were more plausible and showed better predicting ability than models spanning 90 d. Adaptive CG showed intermediate results. Overall, it seems that average time span rendered by the different definitions had a major effect on the ranking of models. However, from the breeder's point of view, the loss of information associated with definitions involving shorter periods of time, such as HYM or HC30-30, might be unacceptable.

Animals↗
PubMed2004

Correlation of heavy metal concentrations with various factors in canned liver paste products using multivariate statistical strategies.

The content of Cu, Fe, Mn, Zn, Co, Cr, Ni, and Pb were determined in 496 samples of heat-treated canned liver pastes by atomic absorption spectrometry. Canned samples were classified according to the presence or absence of coated varnish on the inner side of the can. For each sample, two subsamples were taken: one from the area in contact with the side of the can, the other from the center of the container. Univariate (correlation, box and whisker) and multivariate (quality control charts, principal component analysis, and factor analysis) statistical techniques were applied to detect the presence of outliers and for exploratory data analysis. No significant differences (P < 0.05) were found between the subsamples considered, presence or absence of coated varnish, the sampling areas, or countries of origin. The multivariate analysis allows for the interpretation of grouping tendencies in samples. Cr, Ni, and Pb were associated with presence or absence of oxide in the can, and the essential metals (Fe, Cu, Zn, and Co) were associated with the kind of can. The samples tended to differentiate according to the type of container.

Analysis of Variance↗
PubMed2003

[Parotid tuberculosis following intravesical BCG instillation: a case report].

First case of parotid gland tuberculosis publicated to date is presented after intravesical instillation of BCG for a superficial bladder cancer. The diagnosis of the parotid gland tuberculosis is difficult because it is usually indistinguishable from a neoplasm. Combined fine-needle aspiration cytology with PCR or LCR amplification of mycobacterial DNA could be a good diagnostic tool avoiding an open biopsy.

Administration, Intravesical↗
PubMed2003

[Surgical management of posterior communicating artery aneurysms based on computed tomographic angiography with three-dimensional reconstruction and without preoperative angiography].

OBJECTIVE: To demonstrate the usefulness of three-dimensional computed tomographic angiography (CT-3D-angiography) in the microsurgical management of aneurysms of the posterior communicating artery (PComA). MATERIALS AND METHODS: A series of 27 patients with aneurysms of the PComA diagnosed by means of CT-3D-angiography and without preoperative angiography (group A) were compared with a series of 34 cases diagnosed by cerebral angiography. The findings of the CT-3D-angiography, angiography, microsurgical exploration and clinical data were evaluated. RESULTS: A total of 75 aneurysms were diagnosed preoperatively in 66 patients and 3 additional lesions were found postoperatively in group A. The sensitivity of the CT-3D-angiography was 91.7% for diagnosis of any aneurysm with an specifity of 100%, being the snsibility of angiography a 100% and its specifity 94.9%. Mortality rate was 4.5% without differences between groups regarding clinical results or complications. Both the preoperative timing and hospitalization time were shorter in group A. CONCLUSION: The study of patients with acute subarachnoid hemorrhage with CT-3D-angiography allows a reliable diagnosis of PComA aneurysms. Moreover, provides usefull information for the microsurgical clipping. When compared with angiography in the diagnosis of PComA aneurysms, CT-3D-angiography allows to improve some health indicators with similar clinical results and complications.

Humans↗
PubMed2003

Selenium and mercury concentrations in sweet and dry bottled wines from the Canary Islands, Spain.

The concentrations of selenium and mercury were determined by atomic absorption spectrophotometry in sweet and dry bottled wines from the Canary Islands, Spain. The concentrations of mercury ranged from 2.6 to 4.9 microg x l(-1) for sweet wines, and from 1.5 to 2.6 microg x l(-1) for dry wines, differences (p < 0.05) being observed according to the island of production and type of wine, but not with respect to vintage. The concentration of selenium varied between 1.0 and 2.0 microg x l(-1) for sweet wines, and between 0.6 and 1.6 microg x l(-1) for dry wines. Differences were found in the mean concentrations according to the type of wine. Dry wines produced in La Palma presented a higher (p < 0.05) mean content than those observed in the wines of El Hierro and Lanzarote.

Food Analysis↗
PubMed2003

Is thiopurine methyltransferase genetic polymorphism a major factor for withdrawal of azathioprine in rheumatoid arthritis patients?

OBJECTIVE: To determine whether the presence of thiopurine methyltransferase (TPMT) alleles associated with reduced or absent activity of thiopurine methyltransferase is a major factor for withdrawal of azathioprine (AZA) in rheumatoid arthritis (RA) patients. METHODS: The TPMT genotype, including the variable number of tandem repeats (VNTR) pattern in the 5' untranslated region, was analysed in 111 patients with long-standing RA. Azathioprine (AZA) therapy was used in 40 patients (36%) as a disease-modifying anti-rheumatic drug. RESULTS: Seven out of 111 RA patients (6.3%) were carriers of a mutant allele, TPMT3A (G(460)-->A, A(719)-->G) being the mutant allele observed most frequently. In the group of 40 AZA-treated patients, therapy was discontinued in six patients because of side-effects and in 26 patients because of lack of efficacy. Three patients presented moderate side-effects and were homozygous for the wild-type TPMT allele, whereas the remaining three patients, who developed gastrointestinal effects with severe nausea and vomiting, were TPMT3A carriers. CONCLUSION: In this observational study, the absence of response, probably due to the low-dose scheme used, was the major cause of AZA withdrawal in our series of RA patients. TPMT genotyping may allow the use of high doses of AZA in patients with normal TPMT alleles to improve the efficacy of this immunosuppressive drug. Our data support the relationship between gastrointestinal intolerance and thiopurine metabolic imbalance.

5' Untranslated Regions↗