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At least 127 records · Page 7Linked to original sources
PubMed1995

Seasonal availability of Fasciola hepatica metacercariae in a temperate Mediterranean area (Madrid, Spain).

In this experiment, conducted over a 3-year period (1988-1990), the seasonal availability of Fasciola hepatica metacercariae in a temperate Mediterranean area (Madrid, central Spain) was analysed according to the rhythms of snail infection, the periods of cercarial emission, and the resistance of metacercariae. In this area, snails could be infected from late April to early November. Cercarial emission by spring infection started at the beginning of summer and terminated 3-4 weeks later. Mid-summer temperatures led to the extinction of shedding populations and of the metacercariae emitted by them, but were well tolerated by the snails with undeveloped infections. No aestivation was observed and summer infection led to a progressive shedding wave from August to late December, when it was interrupted. These populations became extinguished in the colder winter of 1988, but overwintered in the mild and belated winter of 1989. Only the snails infected from late summer onwards resumed activity and shed cercariae in spring, from the second half of March to late June. Risk of infection for grazing animals during winter will depend on survival of metacercariae. With a mean mortality of 23% during December and January, and of 38% during the following 2 months, no more than 30% of metacercariae reach the spring alive. Accordingly, risk of infection for grazing animals in spring will depend on overwintering infection of snails. These results indicate that temperature more than humidity could be responsible for different transmission patterns from year to year as winter thermic profiles could be the key for the transmission of fasciolosis during spring.

Animals↗
PubMed1975

The performance of piezoelectric crystal sensors used to determine aerosol mass concentrations.

Aerosol mass concentration determination using piezoelectric crystal sensors was investigated. Five areas of influence were studied: temperature, humidity, particle collection characteristics, response linearity, and mass sensitivity. A theoretical review is included. Neither air stream temperature nor humidity fluctuations were compensated by the use of a reference crystal. The temperature induced error was satisfactorily reduced by minimizing the inlet temperature change rate. The humidity induced error resulted principally from moisture absorption and desorption by the aerosol deposit. The observed linear response limits ranged from 0.2 to 6 mug/mm2 for various aerosols and instrument designs. No relationship between the linearity limit and the point of complete saturation was apparent. The mass sensitivity was a function of the deposit size and location. Energy trapping theory helped to predict the mass sensitivity distribution. The mass sensing ability decreased for particle sizes beginning at approximately 2 mum diameter, reaching essentially zero at 20 mum. The use of viscous crystal coatings appeared to improve the sensing ability in the 2 to 20 mum size range.

Aerosols↗
PubMed2004

Humidity sensitive properties of alkoxysilane-crosslinked polyelectrolyte using sol-gel process.

New trialkoxysilyl group-containing copolymers for humidity-sensitive polyelectrolytes were prepared by copolymerization of [2-(methacryloyloxy)ethyl]trimethyl ammonium chloride (METAC), 3-(trimethoxysilyl)propyl methacrylate (TSPM) and 2-ethylhexyl acrylate (2-EHA). They were self-crosslinkable copolymers composed of different contents of METAC/TSPM/2-EHA = 4/1/5 and 4/2/4. The resistance varied from 10(7) to 10(3)[capital Omega] between 20% RH and 95% RH, which was required for a humidity sensor operating at ambient humidity. Temperature dependence, hysteresis, response time, water durability and long-term stability at high temperature and humidity were also measured and estimated.

Journal Article↗
PubMed1981

Two types of ventilated porometers compared on broadleaf and coniferous species.

Two ventilated porometers (diffusion and steady-state) were compared on four broadleaf and five coniferous species. The diffusion porometer gave consistently lower conductance values for both types of species, reflecting a direct stomatal response to low chamber humidity. At high conductance values, the porometers produced a linear and nearly equal response, but the diffusion porometer was less sensitive at low conductance values. This was due to lower air flow (20% of the velocity in the steady-state porometer) and water vapor sorption (by its acrylic plastic chamber). The broadleaf species had less variation (R(2) = 0.81) than did the coniferous species (R(2) = 0.61), but, with the latter, there was better correspondence between the two porometers, possibly due to sampling technique. Conductance values were clustered by species.

Journal Article↗
PubMed1975

Stomatal Response to Environment with Sesamum indicum. L.

Leaf resistance of Sesamum indicum L. increased when the humidity gradient between leaf and air was increased, at moderate temperatures, even though calculated carbon dioxide concentrations within the leaf decreased slightly. Mesophyll resistance remained relatively constant when humidity gradients were changed, indicating that the increases in leaf resistance were mainly caused by reductions in stomatal aperture and that nonstomatal aspects of photosynthesis and respiration were not affected. Low carbon dioxide concentrations inside the leaf decreased but did not eliminate resistance response to the humidity gradient. Internal carbon dioxide concentrations had little effect on resistance in humid air but had moderate effects on resistance with large humidity gradients between leaf and air. Stomatal response to humidity was not present at high leaf temperatures. Effects of humidity gradients on photosynthetic and stomatal responses to temperature suggested that large humidity gradients may contribute to mid-day closure of stomata and depressions in photosynthesis.

Journal Article↗
PubMed1997

Acute and adaptive responses in humans to exercise in a warm, humid environment.

Acute and repeated exposure for 8-13 consecutive days to exercise in humid heat was studied. Twelve fit subjects exercised at 150 W [45% of maximum O2 uptake (V.O2,max)] in ambient conditions of 35 degrees C and 87% relative humidity which resulted in exhaustion after 45 min. Average core temperature reached 39.9 +/- 0.1 degrees C, mean skin temperature (T-sk) was 37.9 +/- 0.1 degrees C and heart rate (HR) 152 +/- 6 beats min-1 at this stage. No effect of the increasing core temperature was seen on cardiac output and leg blood flow (LBF) during acute heat stress. LBF was 5.2 +/- 0.3 l min-1 at 10 min and 5.3 +/- 0.4 l min-1 at exhaustion (n = 6). After acclimation the subjects reached exhaustion after 52 min with a core temperature of 39.9 +/- 0.1 degrees C, T-sk 37.7 +/- 0.2 degrees C, HR 146 +/- 4 beats min-1. Acclimation induced physiological adaptations, as shown by an increased resting plasma volume (3918 +/- 168 to 4256 +/- 270 ml), the lower exercise heart rate at exhaustion, a 26% increase in sweating rate, lower sweat sodium concentration and a 6% reduction in exercise V.O2. Neither in acute exposure nor after acclimation did the rise of core temperature to near 40 degrees C affect metabolism and substrate utilization. The physiological adaptations were similar to those induced by dry heat acclimation. However, in humid heat the effect of acclimation on performance was small due to physical limitations for evaporative heat loss.

Adaptation, Physiological↗
PubMed1995

Improvement of field sampling methods for adult Karoo paralysis ticks, Ixodes rubicundus (Acari: Ixodidae), through addition of host odour.

The responsiveness of Ixodes rubicundus ticks on questing substrates and the success of their attachment to non-living substrates were investigated. The purpose of this study was to relate responsiveness to conditions of temperature and humidity, to compare the efficacy of flagging and dragging methods to estimate the size of populations of adult I. rubicundus in the field, and to determine the possible influence of host odour on the efficacy of these methods. Responsiveness was tested under varying conditions of temperature and humidity under field conditions, and the same ticks were used to determine the duration of attachment to a flannel cloth, either impregnated with host odour from sheep wool or without it. Flagging and dragging methods were compared under laboratory conditions with cloths either treated with host odour or not. Within the range of ambient temperatures recorded during this study (7-25 degrees C) most of the ticks (86%) were responsive. No obvious relationship between temperature, relative humidity and responsiveness of ticks was evident. Ticks remained on average 32.9 seconds (n = 64) on cloth treated with host odour compared to 9.1 seconds (n = 54) on untreated cloth. Flagging was 1.5-1.7 times as effective as dragging and treatment of the cloths with host odour increased the efficacy 2.4 (dragging) to 2.8 (flagging) times. The reactions of ticks to external stimuli should, therefore, be taken into account to maximize field sampling success.

Animals↗
PubMed1993

Positive correlation between the blood pressure and heart rate response to the cold pressor test and the environmental temperature in older hypertensives.

The aims of our study were to evaluate whether there is any relationship between the environmental temperature and the response to the cold pressor test and if this relationship is different in younger and older hypertensive patients. We studied 100 mild-to-moderate hypertensives, aged 21 to 75 years. In the > or = 45 years group (46 patients) a significant positive correlation between the environmental temperature and the heart rate and blood pressure response to the cold pressor test was found. The relative humidity was not correlated with the response to the cold pressor test, but multiplying the mean temperature and the mean relative humidity enhanced the correlations of the environmental temperature. An increase in the mean temperature for the 20 days before the cold pressor test (the best correlated period) by 10 degrees C correlated with increases in the systolic blood pressure response by 10.5 mm Hg (P = .0195), the diastolic blood pressure response by 8 mmHg (P = .0079), the mean blood pressure by 9 mmHg (P = .0058), and the heart rate response by 3.8 beats/min (P = .0134). In < 45 years patients no environmental relationship of the response to cold pressor test was found. A chronic exposure to low temperatures is correlated with higher blood pressure levels--as previously reported--and, in contrast (but only in elderly), with a lower blood pressure response to acute cold stress. Our findings confirm the higher meteorological dependence of hemodynamics in the elderly, and suggest that the research protocols using the cold pressor test should adjust the response for the previous environmental temperature.

Adult↗
PubMed1996

Race-Specific Elicitors of Cladosporium fulvum Induce Changes in Cell Morphology and the Synthesis of Ethylene and Salicylic Acid in Tomato Plants Carrying the Corresponding Cf Disease Resistance Gene.

Defense responses mediated by the genetically unlinked Cf-9 and Cf-2 genes were compared with those involving no Cf gene (Cf0). Compatible tomato (Lycopersicon esculentum)-Cladosporium fulvum intercellular washing fluids were injected into tomato cotyledons, and the kinetics of responses was monitored under conditions of 70 and 98% relative humidity. The latter conditions suppressed the normal macroscopic responses. For the Cf-9-Avr9 interaction, stomatal opening was induced within 3 to 4 h and after 9 h mesophyll cell death commenced. A burst of ethylene production occurred between 9 and 12.5 h and remained elevated. Free salicylic acid levels increased after 12 h, peaked at 24 h, and thereafter declined. For the Cf-2-Avr2 interaction, stomata became plugged after 8 h, and salicylic acid and ethylene levels increased by 12 and 18 h, respectively, and thereafter declined. Host cell death commenced around vascular tissue by 24 h. Cell death in both incompatible interactions was frequently preceded by cell enlargement. For Cf0-injected plants, no significant responses were detected. High humidity delayed and reduced the Cf-Avr-gene-dependent cell death and ethylene synthesis, whereas induced salicylic acid levels were unaffected for Cf-2-Avr2 and reduced in magnitude only for Cf-9-Avr9.

Journal Article↗
PubMed2003

Use of ISO-NOP200 for measurement of NO in the gas phase under controlled humidity conditions.

A technique has been developed to measure nitric oxide (NO) in the gas phase using the ISO-NOP200 NO-specific probe, which was designed to only measure NO in solution. It was found that probe output was responsive to the relative humidity (RH) of the atmosphere. Increasing sensitivity of probe output to NO was observed with increasing RH but the time to achieve a stable output was also increased. The recommended method to give high sensitivity but an acceptable time between analyses was to hold the probe at a constant temperature (20 degrees C) in a sealed 20 ml glass vial containing 4 ml of a saturated solution of NaCl, which provides a constant RH of 75%. NO standards and samples were injected directly into the vial and provided good baseline stability and a limit of detection of 0.18 microl/L in the vial. The limit of detection of the analytical sample will depend on the volume of gas injected into the vial. Up to 4 ml could be injected without disturbing probe stability and this equates to a detection limit of 0.75 microl/L NO. However, analysis of the internal atmosphere of banana fruit could only consistently extract 1 ml of gas, which gave a detection limit of 3 microl/L NO.

Electrochemistry↗
PubMed2002

Sweating responses to a sustained static exercise is dependent on thermal load in humans.

The purpose of this project was to test the hypothesis that internal temperature modulates the sweating response to sustained handgrip exercise. Ten healthy male subjects immersed their legs in 43 degrees C water for 30-40 min at an ambient temperatures of 30 degrees C and a relative humidity of 50%. Sweating responses to 50% maximal voluntary contraction isometric handgrip exercise (IH) were measured following the onset of sweating (i.e. following slight increases in internal temperature), and after more pronounced increases in internal temperature. Oesophageal temperature (Tes) was significantly lower during the first bout of exercise (37.54 +/- 0.07 degrees C) relative to the second bout (37.84 +/- 0.12 degrees C; P < 0.05). However, the increase in mean sweating rate (SR) from both the chest and forearm (non-glabrous skin) was significantly greater during the first IH bout relative to the second bout (P < 0.05). Increases in mean arterial blood pressure and palm SR (glabrous skin) did not differ significantly between exercise bouts, while heart rate and rating of perceived effort were significantly greater during the second bout of IH. As Tes and mean skin temperature did not change during either bout of exercise, the changes in SR from non-glabrous skin between the bouts of IH were likely because of non-thermal factors. These data suggest that sweating responses from non-glabrous skin during IH vary depending on the magnitude of thermal input as indicated by differing internal temperatures between bouts of IH. Moreover, these data suggest that the contribution of non-thermal factors in governing sweating from non-glabrous skin may be greatest when internal temperature is moderate (37.54 degrees C), but has less of an effect after greater elevations in internal temperature (i.e. 37.84 degrees C).

Adult↗
PubMed1985

Biphasic (early and late) asthmatic responses to exercise in children with severe asthma, resident at high altitude.

Twenty-three children with severe asthma who had been resident at high altitude for at least 3 months, considerably reduced their requirement for regular anti-asthma therapy. On a standard exercise challenge in low humidity, ten had no response, seven had isolated immediate bronchospasm and six had biphasic responses with immediate bronchospasm followed 4-10 h later by a late reaction sustained for at least 2 h. The existence of biphasic responses after exercise, similar to those observed after antigen challenge, supports the concept of mast cell involvement in exercise-induced asthma.

Adolescent↗
PubMed2002

ABA-activated SnRK2 protein kinase is required for dehydration stress signaling in Arabidopsis.

Protein phosphorylation has pivotal roles in ABA and osmotic stress signaling in higher plants. Two protein phosphatase genes, ABI1 and ABI2, are known to regulate these signaling pathways in Arabidopsis: The identity of ABA-activated protein kinases required for the ABA signaling, however, remains to be elucidated. Here we demonstrate that two protein kinases, p44 and p42, were activated by ABA in Arabidopsis T87 cultured cells, and at least one protein kinase, p44, was activated not only by ABA but also by low humidity in Arabidopsis plants. Analysis of T-DNA knockout mutants and biochemical analysis using a specific antibody revealed that the p44 is encoded by a SnRK2-type protein kinase gene, SRK2E. The srk2e mutation resulted in a wilty phenotype mainly due to loss of stomatal closure in response to a rapid humidity decrease. ABA-inducible gene expression of rd22 and rd29B was suppressed in srk2e. These results show that SRK2E plays an important role in ABA signaling in response to water stress.

Abscisic Acid↗
PubMed2006

Responses of ammonium sulfate particles coated with glutaric acid to cyclic changes in relative humidity: hygroscopicity and Raman characterization.

Atmospheric particles, which may have an organic coating, exhibit cyclical phase changes of deliquescence and crystallization in response to changes in the ambient relative humidity(RH). Here, we measured the hygroscopicity and Raman spectra of solid ammonium sulfate ((NH4)2SO4) particles initially coated with water-soluble glutaric acid in two consecutive cycles of deliquescence and crystallization utilizing an electrodynamic balance. (NH4)2SO4 particles with glutaric acid coating (49 wt % glutaric acid) had different hygroscopicity and morphology in the two cycles. Once the particles deliquesced, the dissolution of the solid (NH4)2SO4 core and the glutaric acid coating formed mixed (NH4)2SO4-glutaric acid solution droplets, which was confirmed by Raman characterization. Coating studies with either deliquescence or crystallization measurements, or one complete cycle of these two measurements may not fully assess the effects of the organic coatings on aerosol hygroscopicity. We also present an analysis on the kinetic and chemical effects of organic coating on aerosol hygroscopicity. Glutaric acid coating does not impede the evaporation and condensation rates of water molecules compared to the rates of (NH4)2S04 particles in the two cycles. The coating likely affects the hygroscopicity of aerosol particles through dissolution and its chemical interactions with (NH4)2S04.

Adsorption↗
PubMed1980

Lactation responses of dairy cattle to concentrate feeding in the humid tropics.

Ten second lactation cows in late lactation were used in a 219 to 229 day trial to determine the influence of level of concentrate feeding on milk yield in the presence of abundant forage. Five cows were fed on a 2:1 (HH) milk-concentrate ratio throughout the trial while the other 5 were on a 4:1 (LL) milk-concentration ratio. Average daily milk production (kg/cow) were 14.6 and 13.1 for the HH and LL groups respectively; differences between means were non-significant (P = 0.05). The mean butterfat content was 3.5% for both treatments. Significant differences in the efficiency of milk prodution favouring low concentrate feeding were observed. It was concluded that where forage is abundant and of fairly good quality (about 9% crude protein) only minimal concentrate feeding is required for dairy cows in late lactation.

Animal Feed↗