Showing papers by "Autonomous University of Barcelona published in 1991"

Interpolated variational transition-state theory: Practical methods for estimating variational transition-state properties and tunneling contributions to chemical reaction rates from electronic structure calculations

Abstract: In many cases, variational transition states for a chemical reaction are significantly displaced from a saddle point because of zero‐point and entropic effects that depend on the reaction coordinate Such displacements are often controlled by the competition between the potential energy along the minimum‐energy reaction path and the energy requirements of one or more vibrational modes whose frequencies show a large variation along the reaction path In calculating reaction rates from potential‐energy functions we need to take account of these factors and—especially at lower temperatures—to include tunneling contributions, which also depend on the variation of vibrational frequencies along a reaction path To include these effects requires more information about the activated complex region of the potential‐energy surface than is required for conventional transition‐state theory In the present article we show how the vibrational and entropic effects of variational transition‐state theory and the effective potentials and effective masses needed to calculate tunneling probabilities can be estimated with a minimum of electronic structure information, thereby allowing their computation at a higher level of theory than would otherwise be possible As examples, we consider the reactions OH+H2, CH3+H2, and Cl+CH4 and some of their isotopic analogs We find for Cl+CH4→HCl+CH3 that the reaction rate is greatly enhanced by tunneling under conditions of interest for atmospheric chemistry

Occult cancer in patients with deep venous thrombosis. A systematic approach.

Abstract: The authors prospectively studied 113 consecutive patients with deep venous thrombosis of the lower extremities to determine the most appropriate workup study for searching for a hidden cancer. After a careful physical examination, the following routine tests were performed: erythrocyte sedimentation rate (ESR), whole blood counts, biochemistry, carcinoembryonic antigen (CEA) levels, chest radiograph, upper gastrointestinal endoscopy, abdominal ultrasound and computed tomography (CT) scan. If a malignant lesion was suspected, further appropriate studies were performed. After discharge, periodic follow-up was performed on all patients in the outpatient clinic. A malignant neoplasm was detected in 12 patients. Of these 12 patients, six were asymptomatic with the exception of experiencing thrombophlebitis. Cancer was found more commonly in patients with idiopathic deep vein thrombosis (DVT) (7 of 31 versus 5 of 82 patients with secondary DVT; P = 0.012), and in those patients with abnormal lactic dehydrogenase (LDH) levels (6 of 23 versus 6 of 90; P = 0.007). Abnormal CEA levels allowed diagnosis of two cases of colonic cancer (on colonoscopy). Both ultrasound and CT scan of the abdomen showed two cases of urinary bladder carcinoma at a very early stage. Furthermore, two cases of adenomatous polyps in colon were found, a condition considered by most authors to be a colorectal cancer precursor. In addition, there were five patients with large benign pelvic tumors, and two patients with absent inferior vena cava. The most striking finding was that some cases of cancer were at a very early stage. It was concluded that blood cell counts, LDH, CEA, chest radiograph, and abdominal ultrasonography (or CT scan) should be routinely performed on all patients with deep venous thrombosis (particularly those with idiopathic DVT). Malignancy would not have been recognized in some patients if these tests had not been performed.

Primary ciliary dyskinesia

Abstract: A seven-year old patient with Kartagener syndrome and clinical manifestations at birth that characterize the primary effects of ciliary motility such as neonatal respiratory distress, rhinosinusitis, otitis and chronic bronchitis, atelectasis and recurrent pneumonia. It was underlined that this disease has autosomal recessive inheritance, the possible occurrence of symptoms or malformations in other apparatuses or systems, in the child or his/her relatives. Since the early diagnosis has a significant impact on the quality of life of the individual and this is a difficult-todiagnose disease, emphasis was made on the need of clinically suspecting the

An Alternative Paradigm to Evaluate the Acquisition of the Van Hiele Levels.

Abstract: This article presents an alternative way of analyzing the van Hiele level of students’ geometrical reasoning. We evaluate the students’ answers, taking into account the van Hiele level they reflect and their mathematical accuracy. This gives us a description of how accomplished the students are in applying the procedures associated with each of the van Hiele levels and allows us to determine the students’ degree of acquisition of the van Hiele levels. In this way we obtain a clearer picture of the students’ geometrical reasoning than with the traditional assignment of one van Hiele level to the learners. An example of the application of this method is provided: We describe a test that evaluated students’ ability to reason in three-dimensi onal geometry, some responses of students (9 eighth-grade pupils and 41 future primary school teachers), and the classification of their responses using our method. Approximately 25 years ago, the van Hieles proposed a model of the development of geometric thinking that identified five differentiated levels of thinking, ordered so that the students moved sequentially from one level of thinking to the next as their capability increased (van Hiele, 1957, 1986; van Hiele-Geldof, 1957). In the last 10 years there has been a growing interest in the van Hieles’ model of the development of geometric thinking (Fuys, Geddes, & Tischler, 1988; Gutierrez & Jaime, 1989; Hoffer, 1983; Senk, 1985). An important focus of research has been on ways to determine students’ level of thinking. The main goal of this article is to present an alternative method to evaluate the students’ van Hiele level of reasoning, thus offering a way of identifying those students who are in transition between levels. The way the student’s level of reasoning is ascertained plays an important role in research related to the van Hiele model. Most researchers have determined a student’s van Hiele level for a topic following assessment criteria based on the number of right answers to a written test (Gutierrez & Jaime, 1987; Mayberry, 1983; Usiskin, 1982) or on the thinking level shown by the student in each activity during an interview (Burger & Shaughnessy, 1986; Fuys et al., 1988). In both cases, the respective criteria have assigned each student to one van Hiele level. Although most students show a dominant level of thinking when answering open-ended questions, a large number of them clearly reflect in their answers the presence of other levels, and there are some students whose answers show two consecutive dominant levels of reasoning simultaneously (Usiskin, 1982; Burger & Shaughnessy, 1986; Fuys et al., 1988). Burger and Shaughnessy and Fuys et al. suggested that these students were in transition between two levels, but their approaches to the problem have been different. Burger and Shaughnessy sought a consensus in the evaluators’ opinions; Fuys et al. assigned a student to Level 1-2 to indicate that the student clearly used both Levels 1 and 2 of reasoning for an activity.

Rotation vectors and entropy for homeomorphisms of the torus isotopic to the identity

Abstract: We show that if a homeomorphism f of the torus, isotopic to the identity, has three or more periodic orbits with non-collinear rotation vectors, then it has positive topological entropy. Furthermore, for each point ρ of the convex hull Δ of their rotation vectors, there is an orbit of rotation vector ρ, for each rational point p/q, p ∈ ℤ2, q ∈ ℕ, in the interior of Δ, there is a periodic orbit of rotation vector p / q, and for every compact connected subset C of Δ there is an orbit whose rotation set is C. Finally, we prove that f has ‘toroidal chaos’.

Parton distributions from a global QCD analysis of deep inelastic scattering and lepton pair production

Abstract: Parton distribution functions consistent with neutrino and muon deep inelastic scattering as well as Drell-Yan pair production results have been extracted. This analysis incorporates experimental systematic errors which are the dominant errors in recent deep inelastic scattering experiments. The dependence of the results on factors such as kinematic cuts in the data, heavy target corrections, and choice of initial functional form are also explored. The form adopted is motivated by perturbative QCD and particularly useful in exploring the small-x extrapolation of the distributions. This is crucial for studying the range of predictions for Collider, HERA, and SSC/LHC cross sections. Representative distribution function sets are presented in a very compact parametrized form both in the DIS and MS-bar renormalization schemes.

Evaluation of practical chromatographic procedures for identification of clinical isolates of mycobacteria.

Abstract: After experimental conditions were established, 366 strains of mycobacteria belonging to 23 different species were studied for fatty acids, secondary alcohols, and mycolic acid cleavage products by capillary gas-liquid chromatography. Additionally, the mycolic acid pattern was studied by thin-layer chromatography. Capillary gas-liquid chromatography allowed direct identification of the following Mycobacterium spp.: M. kansasii, M. marinum, M. szulgai, M. xenopi, M. malmoense, and M. gordonae. The patterns of mycolic acid methyl esters recorded for the test strains of M. chelonae and M. agri may be of value in the identification of these species. Moreover, the combined use of the two chromatographic techniques provided precise identification of the M. tuberculosis complex, M. simiae, M. fallax, M. triviale, and M. chelonae-like organisms. A minimal set of biochemical tests is usually required to obtain identification to the species level when chromatographic procedures alone are not sufficient. Under the reported experimental conditions, thin-layer chromatography and capillary gas-liquid chromatography are rapid and very useful techniques for the identification of mycobacteria.

Influence of various acute stressors on the activity of adult male rats in a holeboard and in the forced swim test.

Abstract: The effects of various acute stressors on the activity of adult male rats in a holeboard and in the forced swim test were studied. When tested immediately or 24 h after 1 h exposure to noise, restraint in tubes or tail shock, no changes in either defecation rate or activity in the holeboard were observed. In contrast, immediately after 1 h immobilization in wood-boards, a reduction of the number of areas crossed and the number of head-dips was found. The inhibitory effect of immobilization on head-dips persisted 24 h later. The behavior of the rats in the forced swim test was classified into three categories: struggling, mild swim and immobility. The changes in the behavior were critically dependent on the type of stressor, and more specifically on its intensity, that was evaluated with three different physiological parameters (serum prolactin, corticosterone and glucose levels). Thus, if tested immediately after stress, noise did not alter the response of the rats, restraint in tubes and tail shock-reduced immobility, and the latter stressor increased mild swim. In the second experiment, immobilization in wood-boards reduced struggling. Twenty-four hours after stress, noise, restraint in tubes or tail shock were without effect, but immobilized rats showed increased immobility and reduced mild swim activity. The present data clearly indicate that behavior of rats in a holeboard and in a forced swim situation are not related, and that acute stress could have a differential effect on the various categories of behavior in a forced swim situation.

Ecology and the Poor: A Neglected Dimension of Latin American History

Abstract: This Commentary addresses the issue of ecological perception and ecological politics among poor populations, rural and urban. Some social struggles by poor people (and some national struggles by poor countries) can be understood also as ecological struggles. This approach reveals the ecological content, both hidden and explicit, of social movements from the past or present, which have been geared to defend access to natural resources against the advance of the generalised market system, and that have contributed to the conservation of resources to the extent that the market undervalues externalities. Examples are taken mainly from the history of highland and coastal Peru, but this approach is relevant also for the Amazonian region. Some comparisons are made with other countries in Latin America and also with India.

Influence of "diagnostic delay" upon cancer survival: an analysis of five tumour sites.

Abstract: STUDY OBJECTIVE--The aim was to assess the relationship between survival, tumour stage, and the interval from first symptom to diagnosis (SDI, or duration of symptoms). DESIGN--This was a retrospective follow up study of a cohort of patients registered in the tumour registry of the Hospital del Mar (Barcelona). SETTING--Hospital based tumour registry, with patients derived mainly from the City of Barcelona. PARTICIPANTS--1247 cases of lung, breast, stomach, colon, or rectal cancer were analysed using survival curves and Cox proportional hazards regression. Subjects (mean age 63.6 years) were followed for a median length of 12.9 months after diagnosis. At the time of diagnosis one fourth of patients had disseminated disease. MEASUREMENTS AND MAIN RESULTS--Based on clinical records, a physician registered the onset time of the first symptom attributable to cancer (from which the SDI is computed), as well as the tumour stage at diagnosis. Other measurements followed standard tumour registry procedures. Overall, the crude mean SDI was 5.15 months (SD 8.03, median 2.03); only 24.5% of cases had an SDI less than a month. Crude mean SDIs by anatomical site were as follows: lung cancer 3.07 months; breast 7.44; stomach 5.34; colon 5.74; rectum 5.03. Tumour extension did not appear to be significantly influenced by SDI, only breast cancer showing a distinct pattern of increased extension with increasing SDI. As expected, the probability of survival decreased monotonically with increasing stage in all sites. Tumour site was also a significant predictor of survival, which at one year ranged from 93% for breast cancer to 28% for lung cancer. However, a longer SDI tended sometimes to be associated with a better chance of survival, a fact that was most apparent in colon cancer. All Cox proportional hazards models showed a consistent picture: SDI was not a significant predictor of survival (age and sex adjusted hazard ratios ranging from 0.97 to 1.01), neither was sex; age did predict survival, and so did site and stage. CONCLUSIONS--The results provide further evidence of a very weak relationship between SDI and tumour stage at diagnosis (except for breast cancer), and between SDI and survival, thus emphasising some limitations within which early clinical detection operates. They also suggest that in addition to reflecting patient and physician behaviour, as well as the functioning of the health system, SDI may be influenced by the biological behaviour of the tumour.

Chromium III‐iron interaction in Fe‐deficient and Fe‐sufficient bean plants. I. Growth and nutrient content

Abstract: The influence of low Cr III concentrations (0, 0.25, 0.5, and 1.0 μM as CrCl3–6H2O) on growth, chlorophyll and carotenoid content, the concentration of selected mineral nutrients (Fe, Mn, P), and Cr content was determined in both Fe‐control (10 μM Fe as Fe‐EDTA) and Fe‐deficient (no Fe supply) bush bean (Phaseolus vulgaris L.) plants grown hydroponically. Chromium significantly enhanced growth of both Fe‐control and Fe‐deficient plants. In Fe‐deficient plants, Cr significantly reduced chlorosis in young leaves, increasing the concentration of chlorophyll and carotenoids. This beneficial effect of low Cr concentrations was neither correlated to changes of Mn, P, or Fe tissue concentrations nor to Cr‐induced alterations of the Fe/Mn and P/Fe ratios. As total Fe was analyzed, the effect of Cr on the subcellular Fe distribution or on the Fe2+/Fe3+ ratio can not be excluded.

Genetic variance for body size in a natural population of Drosophila buzzatii.

Abstract: Previous work has shown thorax length to be under directional selection in the Drosophila buzzatii population of Carboneras. In order to predict the genetic consequences of natural selection, genetic variation for this trait was investigated in two ways. First, narrow sense heritability was estimated in the laboratory F2 generation of a sample of wild flies by means of the offspring-parent regression. A relatively high value, 0.59, was obtained. Because the phenotypic variance of wild flies was 7-9 times that of the flies raised in the laboratory, "natural" heritability may be estimated as one-seventh to one-ninth that value. Second, the contribution of the second and fourth chromosomes, which are polymorphic for paracentric inversions, to the genetic variance of thorax length was estimated in the field and in the laboratory. This was done with the assistance of a simple genetic model which shows that the variance among chromosome arrangements and the variance among karyotypes provide minimum estimates of the chromosome's contribution to the additive and genetic variances of the trait, respectively. In males raised under optimal conditions in the laboratory, the variance among second-chromosome karyotypes accounted for 11.43% of the total phenotypic variance and most of this variance was additive; by contrast, the contribution of the fourth chromosome was nonsignificant. The variance among second-chromosome karyotypes accounted for 1.56-1.78% of the total phenotypic variance in wild males and was nonsignificant in wild females. The variance among fourth chromosome karyotypes accounted for 0.14-3.48% of the total phenotypic variance in wild flies. At both chromosomes, the proportion of additive variance was higher in mating flies than in nonmating flies.

Resprouting vigour of two mediterranean shrub species after experimental fire treatments

Abstract: Experimental fire treatments were carried out by applying a propane torch flame to individual stumps ofArbutus unedo andErica arborea, two dominant ericaceous shrubs living in relatively moist maquis of the western Mediterranean Basin. No mortality was observed in either species. Individual plant size, measured as the individual stump area, was the most important factor determining both number and biomass of resprouts for all fire treatments. The number of resprouts at 3 months was less at the higher temperature, but no difference could not be detected at 18 months. Duration of flame application had no effect on resprouting success. This effect was not statistically significant 18 months after treatments were applied. Biomass of resprouts was not clearly affected by different fire treatments either 3 months or 18 months after the start of the resprouting process.

A double staining technique for simultaneous demonstration of astrocytes and microglia in brain sections and astroglial cell cultures

Abstract: We developed a double staining technique for simultaneous demonstration of astrocytes and microglial cells in histological brain sections and cell cultures. The procedure included a histochemical stain specific for microglial cells and an immunocytochemical stain specific for astroglial cells, with postponement of the final visualization of the staining products until both reactions had been performed. First, microglial cells were specifically but invisibly labeled by histochemical reaction for nucleoside diphosphatase (NDPase). Then the astroglial cells were labeled by performing the first parts of the immunocytochemical reaction for glial fibrillary acidic protein (GFAP). Finally, in a series of intervening steps, the NDPase reaction product was visualized and stabilized by treatment with ammonium sulfide and silver nitrate, while the 1-naphthol basic dye method was used to visualize the GFAP immunoreactive product. As an end product, the NDPase-positive microglial cells were brown and the GFAP-reactive astroglial cells blue. The two types of glial cells were clearly distinguishable in vibratome sections of rat brain tissue and in primary astroglial cell cultures, and we never observed cells that stained for both NDPase and GFAP. When the GFAP antibody was replaced by the OX-42 antibody, which recognizes microglial cells and macrophages, double staining of microglial cells was observed. The staining protocol has wide applications in studies of the functional interactions between microglial and astroglial cells in the normal brain and in different pathological states with neuronal or axonal degeneration, just as it can be used for experimental studies in cell cultures.