956 resultados para Milieu ambient
Resumo:
The present study examined the relative importance of outcome expectancies and self-efficacy [1] in the prediction of alcohol dependence [2] and alcohol consumption in a sample of young adult drinkers drawn from a milieu previously reported as supportive of risky drinking. In predicting alcohol dependence, outcome expectancies were found to mediate self-efficacy and the same pattern was found for both males and females. This suggests that male and female drinkers may become more similar as they progress along the drinking continuum from risky drinking to dependent drinking. However, in women, in comparison to men, a greater array of expectancies and self-efficacy scales were found to predict heavy drinking, as measured by quantity and frequency. These results suggest that heavy drinking women are particularly at risk of developing drinking related complications and that preventative education needs to take into account gender differences.
Resumo:
Pulse-amplitude-modulation chlorophyll fluorometry was used to examine changes in dark-adapted F-v/F-m of endosymbiotic dinoflagellate microalgae within the tissues of the temperate coral Plesiastrea versipora exposed to elevated seawater temperature. The F-v/F-m was markedly reduced following exposure of corals to 28 degrees C for 48 h. When corals were returned to ambient (24 degrees C) conditions, F-v/F-m increased in an initial rapid and then secondary slower phase. Tissue discolouration (coral bleaching), caused by a significant decrease in the density of algae, was observed during the first 2-3 days of the recovery period. After 14 days, F-v/F-m was still significantly lower than in control corals. The recovery of F-v/F-m is discussed in terms of repair processes within the symbiotic algae, division of healthy algae and also the selective removal of photo-damaged dinoflagellates. Under field conditions, bleached corals sampled at Heron Island Reef during a bleaching event had significantly lower F-v/F-m than non-bleached colonies; four months after the bleaching event, there were no differences in F-v/F-m or algal density in corals marked as having bleached or having shown no signs of colour loss. The results of this laboratory and field study are consistent with the hypothesis that an impairment of photosynthesis occurs during heat-stress, and is the underlying cause of coral bleaching.
Resumo:
Pepper (Capsicum annuum L.) plants were grown aeroponically in a Singapore greenhouse under natural diurnally fluctuating ambient shoot temperatures, but at two different root-zone temperatures (RZTs): a constant 20 +/- 2 degrees C RZT and a diurnally fluctuating ambient (A) (25-40 degrees C) RZT, Plants grown at 20-RZT had more leaves, greater leaf area and dry weight than A-RZT plants. Reciprocal transfer experiments were conducted between RZTs to investigate the effect on plant growth, stomatal conductance (g(s)) and water relations. Transfer of plants from A-RZT to 20-RZT increased plant dry weight, leaf area, number of leaves, shoot water potential (Psi(shoot)), and g(s); while transfer of plants from 20-RZT to A-RZT decreased these parameters. Root hydraulic conductivity was measured in the latter transfer and decreased by 80% after 23 d at A-RZT. Transfer of plants from 20-RZT to A-RZT had no effect on xylem ABA concentration or xylem nitrate concentration, but reduced xylem sap pH by 0.2 units. At both RZTs, g(s) measured in the youngest fully expanded leaves increased with plant development. In plants with the same number of leaves, A-RZT plants had a higher g(s) than 20-RZT plants, but only under high atmospheric vapour pressure deficit. The roles of chemical signals and hydraulic factors in controlling g(s) of aeroponically grown Capsicum plants at different RZTs are discussed.
Resumo:
In a case-control study in three Australian states that included 794 women with epithelial ovarian cancer and 853 community controls for whom we had adequate contraceptive and reproductive histories, Re examined the effects of oral contraceptive use after controlling for estimated number of ovulatory cycles. Other covariates included in the multiple logistic regression analysis were parity, smoking, and history of pelvic surgery. The protective effect of duration of oral contraceptive use appeared to be multiplicative, with a 7% decrease in relative risk per year [95% confidence interval (CI) = 4-9%], persisting beyond 15 years of exposure. Use for up to 1 year may have a greater effect than predicted (odds ratio = 0.57; 95% CI = 0.40-0.82), whereas use before the first pregnancy may be additionally beneficial (odds ratio = 0.95; 95% CI = 0.87-1.03, adjusted for overall duration of use). Better control for ovulatory life might attenuate these estimates somewhat. There was little evidence of waning protection with time since last exposure or of extra benefit with early commencement of oral contraceptive use. We found no convincing evidence of effect modification in any factor examined or differences in effect among the three main histologic cancer types or between borderline and malignant tumors. Oral contraceptives may act by both suppressing ovulation and altering the tumor-promoting milieu.
Resumo:
The crystal structures of the Tutton salts (NH4)(2)[Cu(H2O)(6)](SO4)(2), diammonium hexaaquacopper disulfate, formed with normal water and isotopically substituted (H2O)-O-18, have been determined by X-ray diffraction at 9.5 K and are very similar, with Cu-O(7) the longest of the Cu-O bonds of the Jahn-Teller distorted octahedral [Cu(H2O)(6)](2+) complex. It is known that structural differences accompany deuteration of (NH4)(2)[Cu(H2O)(6)](SO4)(2), the most dramatic of which is a switch to Cu-O(8) as the longest such bond. The present result suggests that the structural differences are associated with hydrogen-bonding effects rather than with increased mass of the water ligands affecting the Jahn-Teller coupling. The Jahn-Teller distortions and hydrogen-bonding contacts in the compounds are compared with those reported for other Tutton salts at ambient and high pressure.
Resumo:
Many layered metals such as quasi-two-dimensional organic molecular crystals show properties consistent with a Fermi-liquid description at low temperatures. The effective masses extracted from the temperature dependence of the magnetic oscillations observed in these materials are in the range, m(c)*/m(e) similar to 1 - 7, suggesting that these systems are strongly correlated. However, the ratio m(c)*/m(e) contains both the renormalization due to the electron-electron interaction and the periodic potential of the lattice. We show that for any quasi-two-dimensional band structure, the cyclotron mass is proportional to the density-of-states at the Fermi energy. Due to Luttinger's theorem, this result is also valid in the presence of interactions. We then evaluate m(c) for several model band structures for the beta, kappa, and theta families of (BEDT-TTF)(2)X, where BEDT-TTF is bis-(ethylenedithia-tetrathiafulvalene) and X is an anion. We find that for kappa-(BEDT-TTF)(2)X, the cyclotron mass of the beta orbit, m(c)*(beta) is close to 2 m(c)*(alpha), where m(c)*(alpha) is the effective mass of the alpha orbit. This result is fairly insensitive to the band-structure details. For a wide range of materials we compare values of the cyclotron mass deduced from band-structure calculations to values deduced from measurements of magnetic oscillations and the specific-heat coefficient gamma.
Resumo:
A heterogeneous copper catalyst supported on mesoporous MCM-41 was developed. The parent MCM-41 has a large pore area of over 1400 m(2)/g. Copper was chosen as the active element of catalyst and loaded into MCM-41 by adsorption at ambient temperature. The prepared catalysts were evaluated in the catalytic wet oxidation of phenol solution with an initial concentration of 1,300 ppm at 150 and 200 degreesC. The catalyst was found to be of high catalytic activity. It is also shown that the catalyst with a higher copper loading exhibits higher ability of accelerating the catalytic reaction to certain extent but reaches its constant level afterwards. (C) 2001 Elsevier Science B.V. All rights reserved.
Resumo:
Polybia scutellaris constructs huge nests characterized by numerous spinal projections on the surface. We investigated the thermal characteristics of P scutellaris nests in order to determine whether their nest temperature is homeothermically maintained and whether the spines play a role in the thermoregulation of the nests. In order to examine these hypotheses, we measured the nest temperature in a active nest and in an abandoned nest. The temperature in the active nest was almost stable at 27 degrees C, whereas that of the abandoned nest varied with changes in the ambient temperature, suggesting that nest temperature was maintained by the thermogenesis of colony individuals. In order to predict the thermal properties of the spines, a numerical simulation was employed. To construct a 3D-model of a P scutellaris nest, the nest architecture was simplified into an outer envelope and the surface spines, for both of which the initial temperature was set at 27 degrees C. The physical properties of the simulated nest were regarded to be those of wood since the nest of this species is constructed from plant materials. When the model was exposed to cool air (12 degrees C), the temperature was lower in the models with more spines. On the other hand, when the nest was heated (42 degrees C), the temperature increase was smaller in models with more spines. It is suggested that the spines act as a heat radiator, not as an insulator, against the changes in ambient temperature.
Thermal Characteristics of the Mud Nests of the Social Wasp Polybia spinifex (Hymenoptera; Vespidae)
Resumo:
The thermal characteristics of mud nests of Polybia spinifex were investigated by measuring internal and surface temperatures of the nests. The nests had a layer of mud envelope and consisted of mud with fine sand particles. The envelope had a vertically long slit-like entrance hole. The mud nests had high thermal conductivities (0.51-0.67 W/(m degrees C)) comparable to brick, rather than insulation materials of wasps` nests such as paper and wood. It was revealed that the long entrance radiated more heat from the thereto-image. The rate of thermal radiation (emissivity) of the nest surface was 0.80, and the value was similar to that of sand. The internal temperatures of the nests were high from top (T(n1), temperature difference between ambient temperature (T(a)) was 10 degrees C) to bottom (T(n3), difference, 5 degrees C) at noon. On the other hand, the temperature distributions were reversed during the night. Temperature T(n1) was lower by 1 degrees C than T(a), possibly from nightly dew on the top surface, whereas, at the middle point (T(n2),) and T(n3), temperatures were higher by 1 degrees C compared to T(a). Temperature fluctuations (ranges between maximum and minimum temperature) at T(n2) and T(n3) were similar to that of T(a), whereas the values at T(n1) and T(s) were higher than that of T(a).
Resumo:
We evaluate hemolymph osmotic and ionic regulatory abilities and characterize a posterior gill microsomal (Na(+), K(+))-ATPase from the marine swimming crab, Callinectes ornatus, acclimated to 21 parts per thousand or 33 parts per thousand salinity. C ornatus is isosmotic after acclimation to 21 parts per thousand but is hyposmotic at 33 parts per thousand salinity; hemolymph ions do not recover initial levels on acclimation to 21 parts per thousand salinity but are anisoionic compared to ambient concentrations, revealing modest regulatory ability. NH(4)(+) modulates enzyme affinity for K(+), which increases 187-fold in crabs acclimated to 33%. salinity. The (Na(+), K(+))-ATPase redistributes into membrane fractions of different densities, suggesting that altered membrane composition results from salinity acclimation. ATP was hydrolyzed at maximum rates of 182.6 +/- 7.1 nmol Pi min(-1) mg(-1) (21 parts per thousand) and 76.2 +/- 3.5 nmol Pi min(-1) mg(-1) (33 parts per thousand), with little change in K(M) values (approximate to 50 mu mol L(-1)). K(+) together with NH(4)(+) synergistically stimulated activity to maximum rates of approximate to 240 nmol Pi min(-1) mg(-1). K, values for ouabain inhibition (approximate to 110 mu mol L(-1)) decreased to 44.9 +/- 1.0 mu mol L(-1) (21 parts per thousand) and 28.8 +/- 1.3 mu mol L(-1) (33 parts per thousand) in the presence of both K(+) and NH(4)(+). Assays employing various inhibitors suggest the presence of mitochondrial F(0)F(1)- and K(+)- and V-ATPase activities in the gill microsomes. (C) 2009 Elsevier Inc. All rights reserved.
Resumo:
Although stingless bees are capable of maintaining their nest temperature within certain limits, brood production of several species declines or even completely stops during periods of low ambient temperature. In the present study, we investigated whether the brood production of the meliponine species Nannotrigona testaceicornis can be artificially increased through heating the colonies during the cold season. For this, we monitored the rate of brood cell production of seven hives in intervals of 24 hours under two different experimental conditions: 1. without; and 2. with heating. Each treatment (first with and subsequently without heating) lasted for nine consecutive days. The ambient temperature (TA) during both experimental periods was very similar (TA(WITH) = 16.1 degrees C; TA(WITHOUT) = 16.3 degrees C). On average, the colonies built 3.6 brood cells per day without and 15.8 brood cells per day with artificial heating (Wilcoxon Rank Sum test: T = 10, Z = 4, P < 0.001). In both treatments, the rate of brood cell production increased with increasing environmental temperature (Spearman Rank Correlation: R(WITH) = 0.71, P = 0.02; R(WITHOUT) = 0.66, P = 0.05). We concluded that artificial heating during cold periods increased the brood cell production in N. testaceicornis Our results indicate that the use of heaters for stingless bee hives during periods of low ambient temperature may be helpful for stingless beekeeping.
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An experimental white cast iron with the unprecedented fracture tough ness of 40 MPa m(1/2) is currently being studied to determine the mechanisms of toughening. This paper reports the investigation of the role of strain-induced martensitic (SIM) transformation. The dendritic microconstituent in the toughened alloy consists primarily of retained austenite, with precipitated M(7)C(3) carbides and some martensite. Refrigeration experiments and differential scanning calorimetry (DSC) were used to demonstrate, firstly, that this retained austenite has an ''effective'' sub-ambient M(S) temperature and, secondly, that SIM transformation can occur at ambient temperatures. Comparison between room temperature and elevated temperature K-Ic tests showed that the observed SIM produces a transformation toughening response in the alloy, contributing to, but not fully accounting for, its high tough ness. SIM as a mechanism for transformation toughening has not previously been reported for white cast irons. Microhardness traverses on crack paths and X-ray diffraction (XRD) on fracture surfaces confirmed the interpretation of the K-Ic experiments. Further DSC and quantitative XRD showed that, as heat-treatment temperature is varied, there is a correlation between fracture toughness and the volume fraction of unstable retained austenite.
Resumo:
Background: Urban air pollutants are associated with cardiovascular events. Traffic controllers are at high risk for pollution exposure during outdoor work shifts. Objective: The purpose of this study was to evaluate the relationship between air pollution and systemic blood pressure in traffic controllers during their work shifts. Methods: This cross-sectional study enrolled 19 male traffic controllers from Santo Andre city (Sao Paulo, Brazil) who were 30-60 years old and exposed to ambient air during outdoor work shifts. Systolic and diastolic blood pressure readings were measured every 15 min by an Ambulatory Arterial Blood Pressure Monitoring device. Hourly measurements (lags of 0-5 h) and the moving averages (2-5 h) of particulate matter (PM(10)), ozone (O(3)) ambient concentrations and the acquired daily minimum temperature and humidity means from the Sao Paulo State Environmental Agency were correlated with both systolic and diastolic blood pressures. Statistical methods included descriptive analysis and linear mixed effect models adjusted for temperature, humidity, work periods and time of day. Results: Interquartile increases of PM(10) (33 mu g/m(3)) and O(3) (49 mu g/m(3)) levels were associated with increases in all arterial pressure parameters, ranging from 1.06 to 2.53 mmHg. PM(10) concentration was associated with early effects (lag 0), mainly on systolic blood pressure. However, O(3) was weakly associated most consistently with diastolic blood pressure and with late cumulative effects. Conclusions: Santo Andre traffic controllers presented higher blood pressure readings while working their outdoor shifts during periods of exposure to ambient pollutant fluctuations. However, PM(10) and O(3) induced cardiovascular effects demonstrated different time courses and end-point behaviors and probably acted through different mechanisms. (C) 2011 Elsevier Inc. All rights reserved.
Resumo:
Signal transduction through the surface molecule CD40 is critical for cellular activation in immunoinflammatory states such as sepsis. The mechanisms regulating this pathway are not completely understood. Because CD40 displays potentially regulatory cysteine residues and CD40 is probably exposed to NO in the inflammatory milieu, we hypothesized that S-nitrosylation, the interaction of NO with cysteines residues, acts as a post-translational modification on CD40, coregulating the signaling activity and, therefore, the level of cellular activation. As assessed by the biotin switch and the reduction/chemiluminescence S-nitrosylation detection techniques, CD40 was found to be S-nitrosylated endogenously and upon exposure to NO donors in both human and murine macrophages. S-nitrosylation of CD40 was associated with milder activation by its ligand (CD40L), leading to reduced in vitro cytokine (IL-1 beta, IL-12, and TNF-alpha) production, which was reversed in the presence of inhibitors of NO synthesis. S-nitrosylated CD40 was found in resting RAW 246.7 macrophages and BALB/c mice peritoneal macrophages, turning into the denitrosylated state upon in vitro or systemic exposure, respectively, to LPS. Moreover, monocytes from patients with sepsis displayed denitrosylated CD40 in contrast to the CD40 S-nitrosylation measured in healthy individuals. Finally, in an attempt to explain how S-nitrosylation regulates CD40 activation, we demonstrate that NO affects the redistribution of CD40 on the cell surface, which is a requirement for optimal signal transduction. Our results support a novel post-translational regulatory mechanism in which the CD40 signal may be, at least in part, dependent on cellular activation-induced receptor denitrosylation.
Resumo:
Samples of dermal and epidermal tissues of epaulette sharks Hemiscyllium ocellatum were examined histologically to assess damage caused by tagging. Tissues from around tag sites were removed at time intervals ranging from 100 min to 284 days post-tagging. These samples showed acute and chronic responses to tagging. Acute responses consisted of localized tissue breakdown and haemorrhaging, and occurred within the first few hours after tag insertion. At 10 h post-tagging, an intermediate response was apparent. This phase was characterized by further haemorrhaging and red and white blood cell movement into the wound area. The chronic response observed in the 10-284-day post-tagging samples was characterized by fibrous tissue formation to sequester the tag. This tissue presumably protects the adjacent musculature from further trauma produced by movement of the tag and provides a continuous barrier between the internal and external milieu. Tissue repair appeared to progress consistently in all specimens and no secondary infections at the tag site were seen. Tagging produced only localized tissue disruption and did not appear to be detrimental to the long term health of individual sharks. Our findings show that spaghetti style dart tagging is an acceptable method for marking individuals (40-75+ cm total length) of this species. (C) 1997 The Fisheries Society of the British Isles.