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At least 595 records · Page 33Linked to original sources

PubMed2003

Enhancement of transpiration by ethylene is responsible for absence of internodal elongation in floating rice at low humidity.

Internodal elongation in floating rice (Oryza sativa) is known to be enhanced by treatment with ethylene or gibberellic acid (GA3) at high relative humidity (RH). However, ethylene-induced internodal elongation is inhibited at low RH, while GA3-induced internodal elongation is hardly affected by humidity. We examined the effects of ethylene and GA3 on the rate of transpiration in stem segments incubated at 30% or 100% RH. Ethylene promoted the transpiration of stem segments at 30% RH, but not at 100% RH, while GA3 had little effect on transpiration at either 30% or 100% RH. We propose that the absence of ethylene-induced internodal elongation at low RH is due, at least in part, to ethylene-induced transpiration.

Abscisic Acid↗

PubMed2004

Manipulation of the onset of ectomycorrhiza formation by indole-3-acetic acid, activated charcoal or relative humidity in the association between oak microcuttings and Piloderma croceum: influence on plant development and photosynthesis.

A Petri dish system in which development of oak (Quercus robur L.) microcuttings is stimulated by the late stage ectomycorrhizal (EM) fungus Piloderma croceum J. Erikss. & Hjortst. in a long pre-symbiotic stage was optimised to allow synchronous, rhythmic plant growth. Addition of indole-3-acetic acid or activated charcoal to the medium caused an early and more intensive EM formation coupled with suppression of most developmental effects of P. croceum. Leaf area, chlorophyll fluorescence, and content were compared in inoculated and uninoculated plants grown at two relative humidity levels (45 and 95%) and under consideration of three possible answers to inoculation, that is, no or EM formation after the 1st or the 2nd shoot flush. The culture conditions for uninoculated plants were suboptimal, leading toward photochemical stress reflected by a non photochemical quenching (qE) increase and a reduced Chl content at the end of the assay. Prior to EM formation, inoculation itself enhanced the optimal (Fv/Fm) and effective (phiPSII) quantum yield in leaves of the 1st shoot flush under reduced relative humidity. It also fully protected the plants against stress during the complete assays. The results indicate that inoculated plants only form EM once they have acquired a sufficient development level and C-providing capacity. However, the fungus actively improves the development and photosynthesis of plants up to the pre-mycorrhizal stage, helping them to reach this capacity.

Charcoal↗

PubMed1976

Respirator cartridge efficiency studies: VII. Effect of relative humidity and temperature.

Cartridge service life is not appreciably affected at relative humidities below 50%. However, performance is severely compromised when the humidity exceeds 65%. Experimental values are compared from those calculated from the adsorption isotherm, Mecklenburg and modified Wheeler equations. Calculations indicate that temperature does not play a significant role in service life predictions.

Adsorption↗

PubMed1987

Improving turkey poult quality by correcting incubator humidity to match eggshell conductance.

One of the most important factors determining hatchability of avian eggs is their proper water budget during incubation. We show here that water budget changes of turkey eggs effect not only hatchability but also poult quality. In addition to an increase in hatchability of 3.3%, poult quality was increased by 7.3%. This was achieved by sorting eggs into low (less than 18.5), medium (18.5 to 22.0) and high (greater than 22.0) eggshell mass-specific water vapour, conductance categories and incubating them in matching incubation humidities of 21.8, 26.6 and 31.4 Torr, corresponding to relative humidities of 45, 55 and 65% at 37.5 degrees C, respectively. A total diffusive water loss of 11.5% (range 10 to 14%) of the initial egg mass in 25 d of incubation yielded maximal hatchability and poult quality.

Animals↗

PubMed1998

Response of turkeys to relative humidity at high ambient temperature.

1. The effects of relative humidity on growth rate and thermoregulation at high ambient temperature were evaluated in turkeys. Male turkeys were exposed to ambient temperature (Ta) of 35 degrees C and relative humidity (RH) of 40% to 75% and 50% to 85%, at ages of 13 to 19 weeks (trial 1) and 10 to 15 weeks (trial 2), respectively. 2. Body weight and food intake in both trials increased as RH increased up to 70% to 75%. When RH increased further to 80% to 85% (Trial 2) both body weight and food intake declined significantly. 3. Blood CO2 partial pressure (pCO2) did not change significantly at different RHs (trial 1). However, in trial 2 it dropped significantly at 80% to 85% RH. This response coincided with an increase in blood pH. 4. The effect of RH on body temperature (Tb) was not significant in either trial. 5. Triiodothyronine (T3) concentrations increased with the increase in RH up to 70% to 75% RH (trials 1 and 2). A significant decrease was observed when RH was further increased to 80% to 85% RH (Trial 2). Positive linear correlations between T3 and food intake or weight gain were observed in both trials. 6. The results indicate that turkeys can thermoregulate efficiently in the face of extreme changes in RH and that only at high RH (above 75%) did the performance of turkeys deteriorate.

Aging↗

PubMed2005

The effects of stationary periods and external temperature and humidity on thermal stress conditions within sheep transport vehicles.

AIM: To identify the contributions of stationary periods and external climatic environments to thermal stress conditions for sheep on livestock transport vehicles during journeys in summer. METHODS: Two livestock transport vehicles carrying sheep, operating under commercial conditions in New Zealand, were monitored during February and March 2002. Temperature and humidity were logged in five pens inside each vehicle, as well as externally. From these data, the temperature-humidity index (THI) was calculated. Global positioning equipment was used to log the location of the vehicle and whether it was moving or stationary. Regression analysis was used to identify factors that made a significant contribution to the THI within the vehicle. Regression models included the effects of vehicle, journey, initial ambient temperature or THI, pen position and duration of each stationary period. RESULTS: The THI in the livestock pens generally increased when vehicles were stationary. The highest THI value (95) was recorded in a vehicle on an enclosed deck of a Cook Strait ferry. Ambient conditions, the initial THI of a pen, and duration of the stationary period were all significant contributors to increases in the THI. Some increases in the THI occurred in stationary vehicles despite ambient conditions being mild, suggesting that lack of airflow was a critical factor. During stationary periods, 34% of THI readings exceeded 75, and, on average, the THI increased by 0.16 for every minute of a stationary period. CONCLUSIONS: Increases in the THI that could be detrimental to the welfare of sheep could occur on stationary sheep transport vehicles at most daytime ambient temperatures during summer. For a given stocking density and vehicle design, the THI of a pen increased in proportion to the duration of the stationary period. Mild ambient conditions (<25 degrees C) provided some protection against excessive THI increases if the duration of the stop was limited, but drivers are best advised to park their vehicles where there is airflow, and to minimise the duration of stops where possible. Livestock transport vehicles during summer should not be placed on enclosed ferry decks where airflow is absent or minimal.

Animal Husbandry↗

PubMedDate not supplied

Humidity measurements in passive heat and moisture exchangers applications: a critical issue.

A reliable, quantitative assessment of humidification performances of passive heat and moisture exchangers in mechanically-ventilated patients is still to be achieved, although relevant efforts have been made to date. One of the major problems to tackle consists in the difficulty of humidity measurements, both in vivo (during either anaesthesia or intensive care unit treatments) and in vitro set-ups. In this paper a review of the basic operation principles of humidity sensors as well as an analysis of their usage within in vivo and in vitro tests are presented. Particular attention is devoted to the limitations arising from the specific measurement set-up, as they may affect the results notably.

Hot Temperature↗

PubMed2000

Interaction of temperature, humidity, driver preferences, and refrigerant type on air conditioning compressor usage.

Recent studies have shown large increases in vehicle emissions when the air conditioner (AC) compressor is engaged. Factors that affect the compressor-on percentage can have a significant impact on vehicle emissions and can also lead to prediction errors in current emissions models if not accounted for properly. During 1996 and 1997, the University of California, Riverside, College of Engineering-Center for Environmental Research and Technology (CE-CERT) conducted a vehicle activity study for the California Air Resources Board (CARB) in the Sacramento, CA, region. The vehicles were randomly selected from all registered vehicles in the region. As part of this study, ten vehicles were instrumented to collect AC compressor on/off data on a second-by-second basis in the summer of 1997. Temperature and humidity data were obtained and averaged on an hourly basis. The ten drivers were asked to complete a short survey about AC operational preferences. This paper examines the effects of temperature, humidity, refrigerant type, and driver preferences on air conditioning compressor activity. Overall, AC was in use in 69.1% of the trips monitored. The compressor was on an average of 64% of the time during the trips. The personal preference settings had a significant effect on the AC compressor-on percentage but did not interact with temperature. The refrigerant types, however, exhibited a differential response across temperature, which may necessitate separate modeling of the R12 refrigerant-equipped vehicles from the R134A-equipped vehicles. It should be noted that some older vehicles do get retrofitted with new compressors that use R134A; however, none of the vehicles in this study had been retrofitted.

Air Conditioning↗

PubMed1982

Human exposure to sulfur dioxide and ozone in a high temperature-humidity environment.

In order to examine the role of high temperature and humidity in the possible synergistic action of ozone and sulfur dioxide on human pulmonary function previously reported by some investigators and repudiated by others, we randomly exposed eight healthy young male nonsmokers to filtered air, 0.4 ppm SO2, 0.4 ppm O3, and 0.4 ppm SO2 plus 0.4 ppm O3 at 35 degrees C--85% rh for 2 hours. Subjects exercised for 15 minutes of each half hour at a workload sufficient to elicit a minute ventilation of 30 liters (BTPS). Pulmonary function tests were performed prior to, during, and following exposure. Observed alterations in pulmonary functions in the SO2 + O3 exposure reflected the changes occurring during the O3 exposure, clearly indicating that no synergistic effects related to the additional presence of SO2 were evident in this study. We considered factors suggested as causes for a potential synergism in comparing the conflicting studies on O3 and SO2, and suggest that factors other than temperature-humidity and/or sulfate aerosol production must be sought.

Adult↗

PubMed2004

Estimating service lives of organic vapor cartridges II: a single vapor at all humidities.

A widely used equation model for estimating service lives of organic vapor air-purifying respirator cartridges has been updated with more recent research results. It has been expanded to account for effects of high relative humidities. Adsorption capacity competition between water vapor and organic vapor is largely explained by mutual exclusion of adsorption volume of the activated carbon. The Dubinin/Radushkevich equation is used to describe the adsorption isotherms of both water and organic vapors. Effects of relative humidity and adsorbed water on adsorption rates are described by an empirical correlation with breakthrough times. The dynamic natures of adsorption and competition are incorporated using an expanding zone model with displaced water rollup. The complete model has been tested and verified with published and unpublished data from many sources.

Adsorption↗

PubMed1999

Stability of freeze-dried tablets at different relative humidities.

The purpose of the study was to evaluate the stability of two different freeze-dried tablet formulations at different relative humidities (RHs). The tablets contained 25 mg hydrochlorothiazide (HCT) as a model drug and were prepared by freeze-drying a suspension and an oil-in-water (o/w) emulsion. Formulation A was a rapidly disintegrating tablet and consisted of 80 mg of maltodextrine DE38; 8 mg of polyethyleneglycol (PEG 6000), 8 mg of xanthan gum, and 25 mg of HCT. Formulation B was a lyophilized dry emulsion tablet that consisted of 160 mg of Miglyol 812, 80 mg of maltodextrin DE38, 16 mg of methylcellulose (Methocel) A15LV, and 25 mg of HCT. Tablets were packaged in different packing materials: polyvinylchloride (PVC)/aluminum blister packs, PVC-polyvinylidenechloride (PVDC)/aluminum blister packs, closed containers with a dessicant tablet, and open containers. The tablets were stored at three relative humidities (45%, 60%, and 85% RH) and were characterized on mechanical strength, residual moisture, porosity, content uniformity, and scanning electron microscopy (SEM) during a period of 6 months. After 1 month at 60% and 85% RH, a strong increase in moisture content (from 2.7% to 6.8%) was seen for the tablets packed in the open and closed containers and for the PVC/aluminum blistered tablets. This increase was higher for formulation A compared to formulation B since B contained 160 mg of triglycerides and was more hydrophobic. This increase in water content was correlated with a decrease in mechanical strength. The tablets also showed a change in microstructure and porosity. At a moisture content of 7.2%, formulation A showed a structural "collapse" since water acts as a plasticizer for the amorphous glass, lowering the glass transition temperature Tg. This phenomenon even occurred in PVC/aluminum blister packs at 85% RH. The structural collapse was associated with a complete loss of microstructure as detected by porosimetric analysis and SEM. For the PVC-PVDC/aluminum blistered tablets, the increase in moisture content and decrease in mechanical strength at 85% RH occurred much slower, and the water uptake and strength loss were less intensive. No significant breakdown of HCT could be observed in both formulations with all of the packing materials. Packaging of freeze-dried tablets with PVC/aluminum blister packs, PVC/PVDC/aluminum blister packs, or closed containers did not offer protection against moisture uptake, mechanical strength loss, and structural collapse.

Aluminum↗

PubMed1994

The effects of humidity on volume recombination in ionization chambers.

Saturation curves were measured with a parallel-plate ionization chamber for air with humidities of 0%-81%. From the curves, values of m--which is equal to (alpha/eK+ K-)1/2 where alpha is the recombination coefficient, e the charge of an ion, and K+ and K- are mobilities of positive and negative ions, respectively-were obtained. It was confirmed that humidity was the decisive cause of the increase in the value of m with the lifetime of ions in the ionization chamber. It was found that the value of m increases sharply in a range of small values of the product of the ion lifetime and the partial pressure of water vapour and increases more slowly at high values of this parameter.

Artifacts↗

PubMed2005

Effect of ambient humidity on light transmittance through skin phantoms during cryogen spray cooling.

Cryogen spray cooling (CSC) is a technique employed to reduce the risk of epidermal damage during dermatologic laser surgery. However, while CSC protects the epidermis from non-specific thermal damage, it might reduce the effective fluence reaching the target chromophore due to scattering of light by the spray droplets and subsequent water condensation/freezing on the skin surface. The objective of this work was to study the effect of ambient humidity (omega) on light transmittance during CSC. An integrating sphere was employed to measure the dynamics of light transmittance through a deformable agar phantom during CSC. The study included two representative CSC spurt patterns studied using four omega: 57, 40, 20 and 12%. Results show that during CSC, as omega increased, light transmittance decreased. For the highest humidity level (57%) studied, light transmittance reached a minimum of 55% approximately 30 ms after spurt termination. In a controlled environment with omega = 12%, light transmittance reached a minimum of 87% approximately 30 ms after spurt termination. The reduced light transmittance immediately after spurt termination was most likely because of scattering of light caused by condensation of water vapour due to aggressive cooling of ambient air in the wake of the cryogen spurt.

Aerosol Propellants↗

PubMed2003

Determination of epsomite-hexahydrite equilibria by the humidity-buffer technique at 0.1 MPa with implications for phase equilibria in the system MgSO4-H2O.

Epsomite (MgSO(4).7H(2)O) and hexahydrite (MgSO(4).6H(2)O) are common minerals found in marine evaporite deposits, in saline lakes as precipitates, in weathering zones of coal and metallic deposits, in some soils and their efflorescences, and possibly on the surface of Europa as evaporite deposits. Thermodynamic properties of these two minerals reported in the literature are in poor agreement. In this study, epsomite-hexahydrite equilibria were determined along four humidity-buffer curves at 0.1 MPa and between 25 and 45 degrees C. Results obtained for the reaction epsomite = hexahydrite + H(2)O, as demonstrated by very tight reversals along each humidity buffer, can be represented by ln K(+/- 0.012) = 20.001 - 7182.07/T, where K is the equilibrium constant, and T is temperature in Kelvin. The derived standard Gibbs free energy of reaction is 10.13 +/- 0.07 kJ/mol, which is essentially the same value as that calculated from vapor pressure measurements reported in the literature. However, this value is at least 0.8 kJ/mol lower than those calculated from the data derived mostly from calorimetric measurements.

Buffers↗

PubMed2005

Evaluation of nebulizer performance under various humidity conditions.

Jet nebulizers are a drug delivery tool commonly used for treating respiratory diseases. When a nebulizer generates aerosols, the rate at which droplets evaporate depends on humidity conditions around the nebulizer outlet. Because the relative humidity (RH) of the air affects the evaporation rate, the aerosol distribution and drug delivery dose is also affected by RH. Four nebulizers were chosen for comparison in this study: PARI LC Plus (PARI Respiratory Equipment, Inc., Midlothian, VA), SideStream (Medic-Aid Ltd., UK), VixOne (Westmed, Inc., Tucson, AZ), and Micromist (Hudson Respiratory Care Inc., Temecula, CA). Two different formulations were used: albuterol (liquid solution) and budesonide (suspension). Particle distribution (mass median aerodynamic diameter [MMAD] and geometric standard deviation [GSD]), nebulizer efficiency (total efficiency and respirable fraction [RF] efficiency for particles less than 4.7 microm), and dead volume (the amount of solution remaining after nebulization) were compared at the RH of 5%, 50%, and 80%. Our results showed that the MMAD increased (p value varied from <0.001 to 0.016) with the increase in RH, except for with the VixOne unit with albuterol (p = 0.24). The MMAD from the budesonide always appeared higher than from the albuterol. The RF (and thus, the inhalation dose) was lower with a higher RH. Except for the PARI LC Plus with budesonide, the RF decreased approximately 15-27% when the RH rose from 5% to 50%. For the PARI LC Plus nebulizer, the lower dead volume (0.22 mL) with higher residual drugs (62.3% of total drug) was obtained at an RH of 5% comparing the RH of 50% and 80% because of the unit's unique design.

Aerosols↗

PubMed1981

Ventilator problems caused by humidity in the air supplied from simple compressors.

Relative humidity of air produced by simple compressors used to drive ventilators was measured at different working pressures. At normal working pressures, a relative humidity of 100% was found and condensation occurred, mainly at the high pressure air/oxygen mixer valve. This resulted in blockages and loss of accuracy which could have serious consequences for patients. It was concluded that simple compressors are unsuitable and that medical air must be used.

Air↗

PubMed1991

Logistic models describing effects of temperature and humidity on residual effectiveness of chlorpyrifos and cyfluthrin formulations against German cockroaches (Dictyoptera: Blattellidae).

Multifactored logistic models were developed for chlorpyrifos and cyfluthrin formulations based on mortality data from laboratory studies with the German cockroach, Blattella germanica (L.). Insecticides were applied to stainless steel surfaces and aged at three different temperatures (23, 30, and 37 degrees C) and two levels of relative humidity (40 and 70%). After the insecticides dried, the treated panels were placed opposite plywood panels to simulate a crack and crevice application. At appropriate aging times, treated panels were removed from environmental chambers for bioassay. The combined effects of high temperature, high humidity, and aging of residues caused the greatest decline in cockroach mortality for chlorpyrifos. Increasing temperature and aging of residues resulted in decreased cockroach mortality for cyfluthrin formulations; however, mortality was greater than 87% for all formulations through 84 d. Information from this study can be incorporated into integrated pest management programs for German cockroaches.

Animals↗

PubMed2001

Effects of incubational humidity and hen age on embryo composition in broiler hatching eggs from young breeders.

There is a paucity of information regarding the influence of incubational humidity on the characteristics of broiler embryos from young hens that often produce chicks of marginal quality. Therefore, the effects of broiler breeder age (26, 28, and 30 wk) in young broiler breeders and incubator humidity (43, 53, and 63% RH) on embryonic growth between 16 and 21 d of incubation, hatching chick weight, and embryo and chick body compositions were evaluated. Hatching broiler chick BW at 21 d was lower for 26-wk-old breeders compared to those at 28 and 30 wk, and the lowest RH decreased relative wet embryo weight. Embryonic growth, on wet and DM bases, was increased in eggs from the youngest hens. Embryo moisture content (EM) was lower at 16, 17, and 19 d of incubation in eggs from breeders at 26 wk when compared to those at 28 wk of age. The effects of RH on embryo crude protein and fat composition were not consistent and varied with breeder age and length of incubation. It was demonstrated that broiler breeder age affects embryogenesis and hatching chick BW. Furthermore, EM was influenced by breeder age, and changes in incubational RH between 43 and 63% affected embryogenesis without having associated effects on EM or consistent effects on embryo crude fat and protein content. Nevertheless, a depression in embryogenesis with a reduction in incubational RH to 43% may accentuate poor posthatch performance of chicks from young breeders.

Age Factors↗