Showing papers by "University of Buenos Aires published in 1999"

Culture specific and cross-culturally generalizable implicit leadership theories: Are attributes of charismatic/transformational leadership universally endorsed?

Abstract: This study focuses on culturally endorsed implicit theories of leadership (CLTs). Although cross-cultural research emphasizes that different cultural groups likely have different conceptions of what leadership should entail, a controversial position is argued here: namely that attributes associated with charismatic/transformational leadership will be universally endorsed as contributing to outstanding leadership. This hypothesis was tested in 62 cultures as part of the Global Leadership and Organizational Behavior Effectiveness (GLOBE) Research Program. Universally endorsed leader attributes, as well as attributes that are universally seen as impediments to outstanding leadership and culturally contingent attributes are presented here. The results support the hypothesis that specific aspects of charismatic/transformational leadership are strongly and universally endorsed across cultures.

Interim Report and Recommendations of the World Health Organization Task-Force for Osteoporosis

Abstract: Harry K. Genant (Chairman) , Cyrus Cooper (Rapporteur) , Gyula Poor (Rapporteur) , Ian Reid (Rapporteur) , George Ehrlich (Editor), J. Kanis (Editor), B. E. Christopher Nordin (Editor), Elizabet h Barrett-Connor , Dennis Black, J.-P. Bonjour, Bess Dawson-Hughes , Pierre D. Delmas, J. Dequeker , Sergio Ragi Eis, Carlo Gennari , Olaf Johnell , C. Conrad Johnston, Jr, Edith M. C. Lau, Uri A. Liberman, Robert Lindsay, Thomas John Martin, Basel Masri, Carlos A. Mautalen, Pierre J. Meunier, Paul D. Miller , Ambrish Mithal, Hirotoshi Morii , Socrates Papapoul os, Anthony Woolf, Wei Yu and Nikolai Khaltaev (WHO Secretariat) 30

Patch structure, dynamics and implications for the functioning of arid ecosystems

Abstract: Arid ecosystems present a two-phase mosaic structure of high- and low-cover patches. Vegetation patches differ among ecosystems in size and shape. However, recent studies indicate striking similarities in patch dynamics and in mechanisms explaining their origin and maintenance. Two major types of system, banded and spotted vegetation, which are characterized by patch shape, both originate from common mechanisms, although each is dominated by a different driver. Banded vegetation occurs when water is the dominant driver of the redistribution of materials and propagules, whereas spotted vegetation results when wind is the major redistribution driver. Model analysis indicates that patchy vegetation structure enhances primary production.

Large N limit of non-commutative gauge theories

Abstract: Using the correspondence between gauge theories and string theory in curved backgrounds, we investigate aspects of the large-N limit of non-commutative gauge theories by considering gravity solutions with B fields. We argue that the total number of physical degrees of freedom at any given scale coincides with the commutative case. We then compute a two-point correlation function involving momentum components in the directions of the B-field. In the infrared regime it reproduces the usual behavior of the commutative gauge theory (i.e. of the form k4log k2). In the UV regime, we find that the two-point function decays exponentially with the momentum. A calculation of Wilson lines suggests that strings cannot be localized near the boundary. We also find string configurations that are localized in a finite region of the radial direction. These are worldsheet instantons.

Robust principal component analysis for functional data

Abstract: A method for exploring the structure of populations of complex objects, such as images, is considered. The objects are summarized by feature vectors. The statistical backbone is Principal Component Analysis in the space of feature vectors. Visual insights come from representing the results in the original data space. In an ophthalmological example, endemic outliers motivate the development of a bounded influence approach to PCA.

Grassland Precipitation-Use Efficiency Varies Across a Resource Gradient

Abstract: Aboveground net primary production (ANPP) is positively related to mean annual precipitation, an estimate of water availability. This relationship is fundamental to our understanding and management of grassland ecosystems. However, the slope of the relationship between ANPP and precipitation (precipitation-use efficiency, PUE) has been shown to be different for temporal compared with spatial precipitation series. When ANPP and precipitation are averaged over a number of years for different sites, PUE is similar for grasslands all over the world. Studies for two US Long Term Ecological Research Sites have shown that PUE derived from a long-term dataset (temporal model) has a significantly lower slope than the value derived for sites distributed across the US central grassland region (spatial model). PUE differences between the temporal model and the spatial model may be associated with both vegetational and biogeochemical constraints. Here we use two independent datasets, one derived from field estimates of ANPP and the other from remote sensing, to show that the PUE is low at both the dry end and the wet end of the annual precipitation gradient typical of grassland areas (200–1200 mm), and peaks around 475 mm. The intermediate peak may be related to relatively low levels of both vegetational and biogeochemical constraints at this level of resource availability.

Partitioning of soil water among tree species in a Brazilian Cerrado ecosystem.

Abstract: Source water used by woody perennials in a Brazilian savanna (Cerrado) was determined by comparing the stable hydrogen isotope composition (deltaD) of xylem sap and soil water at different depths during two consecutive dry seasons (1995 and 1996). Plant water status and rates of water use were also determined and compared with xylem water deltaD values. Overall, soil water deltaD decreased with increasing depth in the soil profile. Mean deltaD values were -35 per thousand for the upper 170 cm of soil and -55 per thousand between 230 and 400 cm depth at the end of the 1995 dry season. Soil water content increased with depth, from 18% near the surface to about 28% at 400 cm. A similar pattern of decreasing soil water deltaD with increasing depth was observed at the end of the 1996 dry season. Patterns consistent with hydraulic lift were observed in soil profiles sampled in 1995 and 1997. Concurrent analyses of xylem and soil water deltaD values indicated a distinct partitioning of water resources among 10 representative woody species (five deciduous and five evergreen). Among these species, four evergreen and one deciduous species acquired water primarily in the upper soil layers (above 200 cm), whereas three deciduous and one evergreen species tapped deep sources of soil water (below 200 cm). One deciduous species exhibited intermediate behavior. Total daily sap flow was negatively correlated with xylem sap deltaD values indicating that species with higher rates of water use during the dry season tended to rely on deeper soil water sources. Among evergreen species, minimum leaf water potentials were also negatively correlated with xylem water deltaD values, suggesting that access to more readily available water at greater depth permitted maintenance of a more favorable plant water status. No significant relationship between xylem water deltaD and plant size was observed in two evergreen species, suggesting a strong selective pressure for small plants to rapidly develop a deep root system. The degree of variation in soil water partitioning, leaf phenology and leaf longevity was consistent with the high diversity of woody species in the Cerrado.

Dopamine D2 Receptor‐Deficient Mice Exhibit Decreased Dopamine Transporter Function but No Changes in Dopamine Release in Dorsal Striatum

Abstract: Presynaptic D2 dopamine (DA) autoreceptors, which are well known to modulate DA release, have recently been shown to regulate DA transporter (DAT) activity. To examine the effects of D2 DA receptor deficiency on DA release and DAT activity in dorsal striatum, we used mice genetically engineered to have two (D2+/+), one (D2+/-), or no (D2-/-) functional copies of the gene coding for the D2 DA receptor. In vivo microdialysis studies demonstrated that basal and K+-evoked extracellular DA concentrations were similar in all three genotypes. However, using in vivo electrochemistry, the D2-/- mice were found to have decreased DAT function, i.e., clearance of locally applied DA was decreased by 50% relative to that in D2+/+ mice. In D2+/+ mice, but not D2-/- mice, local application of the D2-like receptor antagonist raclopride increased DA signal amplitude, indicating decreased DA clearance. Binding assays with the cocaine analogue [3H]WIN 35,428 showed no genotypic differences in either density or affinity of DAT binding sites in striatum or substantia nigra, indicating that the differences seen in DAT activity were not a result of decreased DAT expression. These results further strengthen the idea that the D2 DA receptor subtype modulates activity of the striatal DAT.

Drought and watering-dependent oxidative stress: effect on antioxidant content in Triticum aestivum L. leaves

Abstract: The purpose of the present work was to evaluate both oxidative stress and the antioxidant response system in leaves from wheat (Triticum aestivum cv. Buck Poncho) subjected sequentially to drought and watering. Drought was imposed by withholding water until soil water potential reached - 2.0 MPa and maintained under those conditions for 24 h. DCFDA oxidation by wheat leaves was not significantly affected by drought, but watering led to an approximately 2-fold increase in DCFDA oxidation rate. However, no significant effect either on lipid radical content or on hydroperoxide content was measured after drought and drought followed by watering. Microsomes isolated from leaves exposed to drought, and from leaves exposed to drought followed by watering, generated a significantly higher amount of hydroxyl radical as compared to microsomes isolated from control leaves, suggesting a higher production of hydroxyl radical in the cellular water-soluble phase, after drought and watering as compared to control values. The content of α-tocopherol in wheat leaves was increased 2.4-fold after drought and β-carotene content was increased by 2.6-fold after drought. Hydration lowered lipid-soluble antioxidant content to control values. Total thiol content was increased by 70% after drought, and watering did not significantly alter the enhanced values. Drought decreased by 28.5% the content of reduced ascorbic acid. Taken as a whole, active species formed at wheat membranes after exposure to moderate water stress, are efficiently removed upon rehydration by reaction with an increased content of α-tocopherol and β-carotene. Moreover, a co-ordinated response involving glutathione reductase activity, thiols and ascorbic acid is triggered to limit free radical dependent effects.

Atmospheric and hydraulic limitations on transpiration in Brazilian cerrado woody species

Abstract: 1. Seasonal regulation of transpiration was studied in four evergreen woody species growing in a Brazilian cerrado (savanna) site with a 5 month dry season. 2. Both seasonal and interspecifc variation in leaf water potential (ΨL) were relatively small. Predawn ΨL was about 0·1–0·25 MPa more negative in the dry season than in the wet season. 3. The dependence of maximum whole-plant sap flow rates on sapwood area was similar among all four species during both the wet and dry seasons. When total daily sap flow on a leaf area basis was normalized by the daily average air saturation deficit (ASD), only one of the four species showed significantly greater water use during the wet season. 4. Although seasonal differences in regulation of transpiration were not pronounced, strong stomatal limitation of both maximum daily transpiration rates and total daily transpiration was evident during both the wet and dry seasons. Sap flow typically increased sharply in the morning, briefly attained a maximum value by about 09.30–10.30 h, then decreased sharply, despite steadily increasing solar radiation and atmospheric evaporative demand. 5. The total leaf area-specific apparent hydraulic conductance of the soil/leaf pathway (Gt) varied among plants and diurnally. The identical linear dependence of transpiration and stomatal conductance (gs) on Gt among the four study species suggested that stomatal adjustment to variation in Gt limited transpiration over the entire range of Gt observed. 6. When gs was normalized for daily variation in Gt, about 80% of the remaining variation in gs was associated with variation in ASD. The results suggested that transpiration in these species was not limited by soil water availability per se, but by high atmospheric evaporative demand and hydraulic constraints possibly arising from their deep rooting habit.

Deregulation of the signaling pathways controlling urokinase production

Abstract: We review the evidence in support of the notion that, upon experimental oncogenic transformation or in spontaneous human cancers, mitogenesis and expression of urokinase (uPA) and its receptor (uPAR) are activated through common signaling complexes and pathways. It is well documented that uPA, uPAR or metalloproteinases (MMPs) are overexpressed in tumor cells of mesenchymal or epithelial origin and these molecules are required for tumor invasion and metastasis. Furthermore, oncogenic stimuli, which may render the transformed cells tumorigenic and metastatic in vivo, activate, in a constitutive fashion, the extracellular-regulated kinases (Erk 1 and 2) classical mitogenic pathway and others such as the NH2-Jun-kinase (Jnk). Cells from human tumors or oncogene-transformed cells overexpress uPA and uPAR, and also show a sustained activation of the above-mentioned signaling modules. In this paper we show that the classical mitogenic pathway involving Ras-Erk, PKC-Erk or Rac-JNK, among others, is activated by growth factors or endogenously by oncogenes, and constitutively activates uPA and uPAR expression. All the data obtained from human tumors or experimental systems, incorporated into a general model, indicate that oncogenic stimuli lead to the constitutive activation of mitogenesis and uPA and its receptor expression, through the activation of the same classical and nonclassical signaling complexes and pathways that regulate cell proliferation. We also discuss contrasting points of view. For instance, what governs the differential regulation of mitogenesis and the signal that leads to protease overexpression in a way that allows normal cells during physiological events to respond to growth factors, and proliferate without overexpressing extracellular matrix (ECM) proteases? Or how can cells remodel their microenvironment without proliferating? What restrains benign tumors from overexpressing tumor-associated proteases when they certainly have the mitogenic signal fully activated? This may occur by the differential regulation of transcriptional programs and recent reports reviewed in this paper may provide an insight into how this occurs at the signaling and transcriptional levels.

The Dopamine D2, but not D3 or D4, Receptor Subtype is Essential for the Disruption of Prepulse Inhibition Produced by Amphetamine in Mice

Abstract: Brain dopamine (DA) systems are involved in the modulation of the sensorimotor gating phenomenon known as prepulse inhibition (PPI). The class of D2-like receptors, including the D2, D3, and D4 receptor subtypes, have all been implicated in the control of PPI via studies of DA agonists and antagonists in rats. Nevertheless, the functional relevance of each receptor subtype remains unclear because these ligands are not specific. To determine the relevance of each receptor subtype, we used genetically altered strains of "knock-out" mice lacking the DA D2, D3, or D4 receptors. We tested the effects of each knock-out on both the phenotypic expression of PPI and the disruption of PPI produced by the indirect DA agonist d-amphetamine (AMPH). No phenotypic differences in PPI were observed at baseline. AMPH significantly disrupted PPI in the D2 (+/+) mice but had no effect in the D2 (-/-) mice. After AMPH treatment, both DA D3 and D4 receptor (+/+) and (-/-) mice had significant disruptions in PPI. These findings indicate that the AMPH-induced disruption of PPI is mediated via the DA D2 receptor and not the D3 or D4 receptor subtypes. Uncovering the neural mechanisms involved in PPI will further our understanding of the substrates of sensorimotor gating and could lead to better therapeutics to treat gating disorders, such as schizophrenia.

The effects of solar ultraviolet-B radiation on the growth and yield of barley are accompanied by increased DNA damage and antioxidant responses

Abstract: There is limited information on the impacts of present-day solar ultraviolet-B radiation (UV-B) on biomass and grain yield of field crops and on the mechanisms that confer tolerance to UV-B radiation under field conditions. We investigated the effects of solar UV-B on aspects of the biochemistry, growth and yield of barley crops using replicated field plots and two barley strains, a catalase (CAT)-deficient mutant (RPr 79/4) and its wild-type mother line (Maris Mink). Solar UV-B reduced biomass accumulation and grain yield in both strains. The effects on crop biomass accumulation tended to be more severe in RPr 79/4 (≈ 32% reduction) than in the mother line (≈ 20% reduction). Solar UV-B caused measurable DNA damage in leaf tissue, in spite of inducing a significant increase in UV-absorbing sunscreens in the two lines. Maris Mink responded to solar UV-B with increased CAT and ascorbate peroxidase (APx) activity. No effects of UV-B on total superoxide dismutase (SOD) activity were detected. Compared with the wild type, RPr 79/4 had lower CAT activity, as expected, but higher APx activity. Neither of these activities increased in response to UV-B in RPr 79/4. These results suggest that growth inhibition by solar UV-B involves DNA damage and oxidative stress, and that constitutive and UV-B-induced antioxidant capacity may play an important role in UV-B tolerance.

Endogenous peroxynitrite mediates mitochondrial dysfunction in rat diaphragm during endotoxemia

Abstract: It has been shown that nitric oxide (NO), synthesized by the inducible NO synthase (iNOS) expressed in the diaphragm during endotoxemia, participates in the development of muscular contractile failure. The aim of the present study was to investigate whether this deleterious action of NO was related to its effects on cellular oxidative pathways. Rats were inoculated with E. coli lipopolysaccharide (LPS) or sterile saline solution (controls) and studied at 3 and 6 h after inoculation. iNOS protein and activity could be detected in the rat diaphragm as early as 3 h after LPS, with a sustained steady-state concentration of 0.5 μM NO in the muscle associated with increased detection of hydrogen peroxide (H2O2). In vitro, the same NO concentration produced a marked increase in H2O2 production by isolated control diaphragm mitochondria, thus reflecting a higher intramitochondrial concentration of nondiffusible superoxide anion (O2−·). In a similar way, whole diaphragmatic muscle and diaphragm mitochondria from e...

Soccer players under regular training show oxidative stress but an improved plasma antioxidant status

Abstract: Physical activity is known to induce oxidative stress in individuals subjected to intense exercise. In this study, we investigated the lipoprotein profile and the plasma antioxidant status in a group of soccer players engaged in a regular training programme. As was expected for aerobic exercise, high-density lipoprotein-cholesterol (HDL-C) and HDL3-C levels were significantly increased in the sportsmen (P<0.05). Total plasma antioxidant capacity was 25% higher in sportsmen than in controls (P<0.005). Accordingly, plasma hydrosoluble antioxidant levels (ascorbic acid and uric acid) were found to be significantly elevated in the soccer players (P<0.005). In addition, these subjects showed high concentrations of alpha-tocopherol in plasma compared with controls (P<0.005). Furthermore, an increase in plasma superoxide dismutase activity was also observed in relation to exercise (P<0.01). The elevation in plasma activities of antioxidant enzymes and the higher levels of free radical scavengers of low molecular mass may compensate the oxidative stress caused by physical activity. High levels of high-density lipoprotein in plasma may offer additional protection by inhibiting low-density lipoprotein oxidation and thus liposoluble antioxidant consumption. Therefore, soccer players under regular training show an improved plasma antioxidant status in comparison to sedentary controls.

Globalización y dualización en la Región Metropolitana de Buenos Aires: Grandes inversiones y reestructuración socioterritorial en los años noventa

Abstract: Las transformaciones estructurales de fin de siglo tienden a concentrarse particularmente en los grandes espacios metropolitanos, convirtiendolos en escenarios protagonicos de la pugna entre las ascendentes tendencias globalizantes y la revitalizacion de las identidades locales. En los anos noventa, en el marco de los procesos de privatizacion, desregulacion y apertura economica, la reestructuracion de dichos espacios constituye un fenomeno donde los factores externos a la metropolis y al pais en que esta se asienta, tienden a avanzar sobre los factores internos, pudiendo ocasionar una considerable perdida de control sobre los procesos economicos, sociales y territoriales que se desenvuelven en estos espacios urbanos. Este trabajo analiza los principales cambios inducidos por una decada de crecimiento de las inversiones extranjeras directas en la Region Metropolitana de Buenos Aires. Asimismo, espera contribuir a la reflexion y debate sobre la dualidad y contradicciones de dichos procesos, con tendencias hacia la modernizacion y globalizacion, y a la vez, hacia la profundizacion de la exclusion social.

Pituitary adenylate cyclase activating peptide phase shifts circadian rhythms in a manner similar to light.

Abstract: The endogenous circadian pacemaker in mammals is located in the suprachiasmatic nuclei (SCN) of the hypothalamus. Various cues can reset circadian rhythm phase, thereby entraining the internal rhythm to the environmental cycle, and these effects can be investigated using anin vitro method to measure phase shifts of the SCN. Although pituitary adenylate cyclase activating peptide (PACAP) is localized in retinal inputs to the SCN, it has been reported to alter clock phase only during the subjective day (Hannibal et al., 1997), whereas light alters phase only in the subjective night. In this study we show that PACAP can reset the clock in the photic pattern during the subjective night when applied in 10 pm to 1 nmdoses. This appears to be mediated via a glutamatergic mechanism, possibly by potentiation of NMDA currents as is seen at 10–100 pm. Given at higher doses (>10 nm), PACAP shifts in the subjective day, apparently via activation of adenylate cyclase and increased intracellular cAMP. These results indicate dose and phase specificity of the effects of PACAP, and a new role as a transmitter in the retinohypothalamic tract.

Effect of temperature and carpel size during pre-anthesis on potential grain weight in wheat

Abstract: The effect of environmental conditions immediately before anthesis on potential grain weight was investigated in wheat at the experimental field of the Faculty of Agronomy (University of Buenos Aires, Argentina) during 1995 and 1996. Plants of two cultivars of wheat were grown in two environments (two contrasting sowing dates) to provide different background temperature conditions. In these environments, transparent boxes were installed covering the spikes in order to increase spike temperature for a short period (c. 6 days) immediately before anthesis, i.e. between ear emergence and anthesis. In both environments, transparent boxes increased mean temperatures by at least 3n8 mC. These increases were almost entirely due to the changes in maximum temperatures because minimum temperatures were little affected. Final grain weight was significantly reduced by higher temperature during the ear emergence–anthesis period. It is possible that this reduction could be mediated by the effect of the heat treatment on carpel weight at anthesis because a curvilinear association between final grain weight and carpel weight at anthesis was found. This curvilinear association may also indicate a threshold carpel weight for maximizing grain weight.