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At least 217 records · Page 12Linked to original sources
PubMed2005

Effect of relative humidity on preharvest survival of bacterial and viral pathogens on the surface of cantaloupe, lettuce, and bell peppers.

The purpose of this study was to compare the effects of humidity on the preharvest survival of microbial pathogens on cantaloupe, lettuce, and bell peppers. An additional goal was to evaluate Clostridium perfringens as an indicator of fecal contamination on produce. The microorganisms used in this study included Escherichia coli, E. coli O157:H7, Shigella sonnei, Salmonella enterica subsp. enterica, Clostridium perfringens, hepatitis A virus (HAV), feline calicivirus (FCV), and coliphage PRD1. The study took place in a controlled environment chamber that allowed for the control of temperature (18 to 26 degrees C) and relative humidity. Survival rates under high (mean, 85.7 to 90.3%) and low (mean, 45.1 to 48.4%) relative humidity were compared. The surfaces of the edible portion of each plant were inoculated with the study microorganisms. Samples were collected throughout 2 weeks. More microorganisms survived significantly longer (P < 0.05) on cantaloupe than on lettuce and bell peppers. The type of produce on which each organism experienced the highest inactivation rate tended to change with relative humidity. The survival of microorganisms on produce surfaces was not uniformly affected by relative humidity. Of the studied microorganisms, HAV, PRD1, and C. perfringens were found to have the lowest inactivation rates, whereas FCV and E. coli ATCC 25922 tended to become inactivated most rapidly. C. perfringens generally survived longer than all other bacteria and FCV in all experiments. This trend suggests that C. perfringens may be an acceptable indicator of bacterial contamination and survival in various environments and on different types of crops.

Agriculture↗
PubMed1997

[Simulation of a decoupling generalized predictive control algorithm for temperature-humidity system].

A decoupling generalized predictive control algorithm was presented in this paper. This algorithm was proposed to control the temperature-humidity system of a practical air-conditioning environmental chamber. By introducing absolute humidity as an intermediate variable, temperature and humidity of the system can be decoupled. Then the two decoupled systems are controlled by generalized predictive control (GPC) algorithm at different sample rates. Many simulation experiments demonstrated the effectiveness of the algorithm. Besides, decoupling of temperature and humidity will be extremely helpful to the application of GPC on the real system. This is also the effective method to control the temperature and humidity system.

Air Conditioning↗
PubMed2001

[Influence of temperature and relative humidity on epizootiological features of Zoophthora anhuiensis in Myzus persicae colonies].

The colony of green peach aphid, Myzus persicae(Sulzer), which was initiated with 3 pathogen-free apterae and another 3 ones inoculated with the conidia of the entomophthoraceous fungus, Zoophthora anhuiensis(Li) Humber, was maintained on detached cabbage leaves at the regimes of 10-25 degrees C and 90-100% of relative humidity(RH), and allowed for free reproduction and fungal infection. Based on 26 day observations, it was showed that the development of Z. anhuiensis in the colony was rapid at 15 or 10 degrees C, regardless of the humidity range concerned. The cumulative mortality of the aphids attributed to Z. anhuiensis infection was 72.9-98.2% at 10 degrees C on day 26, and 78.7-94.4% at 15 degrees C on day 24, indicating the occurrence of epizootic in the colony. At 20 degrees C, a high-level epizootic occurred only at 100% RH, with a cumulative mortality of 71.6% on day 24, contrasting to a much lower mortality (5.1-12.8%) at the other three humidity regimes. However, the maximal mortality at 25 degrees C on day 20 was only 27.2% even at 100% RH. Obviously, Z. anhuiensis caused aphid epizootic more easily at lower temperature, and to less degree was affected by the humidity. The disease prevalence (represented by the cumulative mortality) was correlated well to temperature, its interaction with relative humidity, and the days from initiation (r2 = 0.82, alpha < 0.01).

Animals↗
PubMed2002

[Simulation models of thermal-humidity parameters of the space suit].

The paper describes a mathematical model of and methods of calculating thermal-humidity fields in a spacewalking suit. The authors made an integral calculation of thermal and mass transfer in the spacesuit. A system of equations is solved analytically and numerically with the use of a combined method. As a result of model calculations, determined were integral spacesuit characteristics including total amount of rejected heat, heat rejected by the WC suit, humidity rejected by ventilation, and humidity accumulated in different spacesuit layers. Comparison of calculation and experimental data for spacesuit Orlan showed that maximal differences in temperature, humidity, thermal and humidity flows, and other system parameters did not exceed 13%.

Humans↗
PubMed2004

[Effect of cooling therapy on the heart rate and mean arterial pressure of rats with the second-degree scald burn in hot and humid environment].

OBJECTIVE: To observe the changes of heart rate (HR) and mean arterial pressure MAP after immediate cooling therapy (ICT) in rats with superficial second-degree scald burn in hot and humid environment, and assess the effect of the cooling dressing materials. METHODS: Twenty-four Wistar rats were randomized equally into 4 groups including normal temperature control (NTC) group, normal temperature cooling therapy (NCT) group, hot and humid control (HHC) group and hot and humid cooling therapy (HCT) group. Different interventions were applied as indicated in the rats with superficial second-degree scald burn, with the dry bulb temperature Tdb at 26.33+/-1.29 degrees celsius; and relative humidity (rh) of 71.05%+/-4.57% for two normal temperature groups, and Tdb at 35.33+/-0.35 degrees Celsius; and rh of 70.81%+/-1.38% for the two hot and humid groups. The exposure time was 120 min in NCT and HCT groups, and the HR and MAP were measured every 20 min. RESULTS: MAP is not influenced by environmental temperature and the cooling therapy (P>0.05), whereas HR was higher in HHC than in NTC group and also in HCT than in NCT group (P=0.003), lower in HCT and NCT groups than in HHC and NTC groups (P=0.002), respectively. HR did not undergo any significant changes during the observation in the 4 groups (P>0.05). HR was higher in HHC and HCT than in NTC and NCT groups at 65, 85, 105 and 125 min after the burns, but compared with the two control groups, cooling therapy decreased HR at 5, 25, 45 and 85 min. CONCLUSION: Cooling therapy does not affect MAP but efficiently decreases HR, which may prevent further heat injury.

Animals↗
PubMed2005

[Fabrication of relative humidity optical fiber sensor based on nafion-crystal violet sensing film].

With two kinds of sensing methods for relative humidity based on fluorescence and visible absorption respectively, crystal violet was opted as the molecule probe for humidity. The optical chemical sensing film for humidity was prepared when crystal violet was embedded in the Nafion gel. The relative humidity sensor was fabricated after the sensing film had been coupled with other components, such as optical fiber and detector, which possessed short response time ( < 2 min), high sensitivity (< or = 5% RH), wide dynamic range (30%-100%) and good reversibility (RSD < or = 2.6%) for relative humidity at 640 nm wavelength.

Air↗
PubMedDate not supplied

[Spore germination and mycelial growth of streptomycetes at different humidity levels].

This study is the first to show the ability of streptomycetes to develop at a very low humidity level. All of the streptomycetes studied produced growth at low humidity (aw 0.86 and 0.67). This capacity was most markedly pronounced in Streptomyces odorifer, whose spores were capable of germinating, and mycelial germs increased in length, at the air humidity aw 0.50. The formation of lateral branches (mycelium branching) at this humidity was noted only in single S. odorifer germs and only after 72 h of incubation. Study of streptomycete growth on an agarized medium with different osmotic pressures, created by various glycerol concentrations in the medium, showed that, at aw 0.67, the spores of all the streptomycetes studied germinate, producing mycelial germs but not microcolonies. The ecological significance of mycelial prokaryotes in soil microbial communities that develop and function under conditions of extremely low humidity is discussed.

Culture Media↗
PubMed1987

[Comparative humidity measurements in semiclosed and semiopen systems with the additional use of artificial noses].

The administration of dry anesthetic gases for ventilation lasting more than 1 h leads to morphological changes of the tracheobronchial epithelium that may cause postoperative pulmonary complications. Therefore, additional humidification is suggested for ventilation during anesthesia, particularly when using semiopen breathing systems. Recommendations concerning the use of semiclosed systems are controversial: previous studies have shown sufficient humidification on the one hand, and insufficient water content in the inspired air on the other hand. In this study, comparative humidity measurements in a semiopen and a semiclosed system were carried out during anesthesia and mechanical ventilation. We particularly wanted to find out whether placement of the fresh gas inlet into the circle before or behind the soda lime canister influences the humidity of the inspired gas. In addition, we tested three types of "heat and moisture exchanges"--Engström "Edith", Siemens "Servo Humidifier", and Portex "Humid Vent". A total of 58 patients between 23 and 78 years of age were studied. They were divided into three groups. Group I: In 10 patients comparative humidity measurements were carried out using both a semiopen and a semiclosed system. Group II: The time course of water saturation during a 3-h period was determined in 10 patients ventilated with a semiopen and 8 patients ventilated with a semiclosed circle system. Group III: In 20 patients we tested the effect of "heat and moisture exchangers". All patients were intubated and ventilated with the Spiromat 656 and the Circle System 8 (Drger) that made ventilation in both a semiclosed and a semiopen system possible. The humidity measurements were carried out using a psychometric method.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

[The tenacity of bacteria in the airborne state. IV: Experimental studies on the viability of airborne E. coli 0:78 under the influence of different temperature and humidity].

In a static aerosol chamber the tenacity of airborne E. coli 0:78 was determined at a permanent temperature of 22 degrees C and different relative humidities (10, 15-20, 30, 75 and 85%) and also at a permanent humidity of 30-40% and different temperatures (22, 28, 30, 34 and 40 degrees C). The greatest viability of the bacteria with a half-life-time of 390 min was found at 22 degrees C and 85% humidity. At 10% humidity the half-life-time was only 55 min. At a humidity of 30-40% the tenacity decreased from 37 to 14 min half-life-time, when the temperature increased from 22 to 40 degrees C. In preliminary examinations it could be shown that the method of cultivation and age of the bacterial suspension had an influence on the tenacity in the airborne state.

Air Microbiology↗
PubMedDate not supplied

Characteristics of the circadian rhythm in diffusive resistance of Abutilon theophrasti leaves in humid and dry environments.

Diffusive resistance of the upper and lower leaf surfaces of Abutilon theophrasti Medic, was measured with an automatic diffusive resistance meter. Plants were maintained in growth chambers under 4 different environments: 1. high humidity, well-watered, 2. high humidity, dry, 3. low humidity, well-watered, 4. low humidity, dry. Diffusive resistance measurements were obtained every 4 h for up to 3 days when the plants were subjected to either daily regimes consisting of 15 h of light followed by 9 h of darkness or to continuous illumination. Leaf movements were also monitored. Diffusive resistance was rhythmic (circadian) under all the environmental conditions examined. The pattern of diffusive resistance was the same regardless of whether the humidity and/or soil moisture were high or low. The rhythms of diffusive resistance of the upper and lower leaf surfaces differed, however, in amplitude and in the phase at which the minimum value was reached. Diffusive resistance of the leaf was highest (peak of the rhythm) when the leaf blade was in a nearly horizontal position.

Circadian Rhythm↗
PubMedDate not supplied

Effect of humidity on infection of turkeys with Alcaligenes faecalis.

Turkeys maintained at 75% to 80% relative humidity were more adversely affected by Alcaligenes faecalis infection than turkeys maintained at 20 to 35% relative humidity. Alcaligenes faecalis was reisolated earlier and more often from turkeys maintained at the higher humidity. Clinically, the turkeys maintained at high humidity exhibited both sinusitis and conjunctivitis earlier than the turkeys at low humidity. In both groups, antibody titers as determined by a microagglutination test developed by 2 weeks postinoculation and started to decline after the third week, lymphocytosis was demonstrated at 1 week postinoculation, and a lymphopenia developed at 5 weeks postinoculation.

Agglutination Tests↗
PubMed1993

[Effect of different relative humidity in the incubator on skin temperature of newborn infants with low birth weight].

BACKGROUND: In a group of 8 LWB infants we tried to investigate the influence of different levels of rel. humidity inside the incubator on rectal and skin temperature and on the pattern of temperature distribution over the body surface. METHOD: In low (45 rel.%) and high (83 rel.%) incubator humidity we measured rectal temperature and, using infrared telethermography, skin temperatures at 12 different sites of the body. RESULTS: After increasing ambient humidity mean skin temperature rose significantly (p < 0.01) from 35.87 to 36.10 degrees C. The pattern of temperature distribution also changed with increasing humidity, showing pronounced warming of the periphery. Rectal temperature did not change significantly. CONCLUSION: With rising ambient humidity skin temperature increase in LBW infants, and the distribution of surface temperature becomes more even.

Body Temperature Regulation↗
PubMed1995

Temperature and humidity: significant factors in resin/enamel bonding.

This study examined the effects of temperature and humidity variations on the bond strength of sand blasted Ni-Cr-Mo alloy (Talladium) cylinders cemented to etched bovine enamel using composite resin (Panavia Ex). Bonding was carried out in a humidity chamber under varying combinations of temperature (24 degrees C and 37 degrees C), and relative humidity (32% and 85%). After storage in water at 37 degrees C for 24 hours all specimens were shear tested to failure. The results showed that bond failure was consistently cohesive with resin shear strength at 37 degrees C being significantly reduced by high humidity. At 24 degrees C, resin shear strength was not significantly affected by humidity variations.

Analysis of Variance↗
PubMed1997

Rigid gas-permeable contact lenses in high and low humidity.

BACKGROUND: Contact lenses may alter tear film evaporation. Evaporation varies with respect to air temperature and relative humidity. Hence, tear evaporation may be a significant factor for many occupations, such as military pilots, in the arid environments in which they operate. METHODS: The study tested rigid gas-permeable (RGP) contact lens wearer comfort and corneal staining in lower and higher relative humidity environments. RESULTS: A trend was found that in a lower humidity environment, RGP contact lens comfort may decrease for some subjects. Corneal surface integrity was not compromised by the variation in relative humidity level, as determined by fluorescein dye analysis. CONCLUSION: Within the range of humidity tested, for normal successful RGP patients, drier environments do not substantially reduce lens comfort.

Adult↗
PubMedDate not supplied

[New potentials for monitoring the temperature and the relative and absolute humidity of the air-oxygen mixture during the prolonged artificial ventilation of newborn infants].

A new HTM-902 monitor (UCCP, Germany/Serviceinstrument, Russia) was used for continuous measurements of the temperature and relative and absolute humidity of inspired gas during prolonged mechanical ventilation in 86 neonates with respiratory failure caused by the respiratory distress syndrome (n = 42), meconium aspiration syndrome (n = 28), and congenital pneumonia (n = 16). All measurements were performed with a special probe connected to the inspiratory contour through a standard adapter close to the patient's T-piece. The monitor helped maintain the optimal values of the inspired gas conditioning during assisted ventilation of the neonates. The optimal relationships between gas temperature and humidity can be attained only with humidifiers with a servocontrol of temperature and heated wire inside the inspiratory circle tube. For maintaining adequate humidity of inspired gas after any changes in the ventilator flow rate or in the temperature inside the incubator, the heating power of the humidifier had to be corrected. However, even with servocontrolled humidifiers and humidity regulation, an increase of temperature inside the incubator over 35 degrees C made impossible the maintenance of the inspired gas humidity at the level of 96-100% with its temperature at the level of the patient's T-piece no higher than 37 degrees C.

Air↗
PubMed1998

What is optimum humidity?

The relevant aspects of the normal physiology of the airway mucosa and the customary ways of describing humidity are briefly reviewed. The need for surrogate markers of optimum humidity is identified, and two such markers are proposed. The relationship between the humidity of the inspired gas and mucosal function is examined using a model that is then validated. Optimum humidity is achieved when the inspired gas is at body core temperature and 100% relative humidity.

Body Water↗
PubMed2005

A scanning electron and atomic force microscopy study of the surface morphology and composition of CsI films as affected by evaporation rate and humid-air exposure.

Evaporation rate and subsequent exposure to humid air affect the surface morphology and composition of cesium iodide (CsI) films and, in turn, their photoemissive efficiency when used as photocathodes. The surface morphology and elemental composition of 300-nm-thick CsI films grown at two different rates (1 nm/s and 0.04 nm/s), both freshly evaporated and after 24-h exposure to humid air were investigated by means of atomic force microscopy and scanning electron microscopy/electron diffraction spectroscopy. The CsI film freshly evaporated at a slow rate exhibited a granular surface presenting circular holes or craters where the CsI material was moved from the center to the boundaries. After 24-h exposure to humid air, this film coalesced in large grain showing a marked increase of surface roughness. Conversely, the CsI film grown at a fast rate mostly retained its original surface uniformity and homogeneity with no presence of holes and craters after 24-h exposure to humid air. Further, surface roughness and average peak height decreased, but the surface coalesced in large grains spaced by small fractures where the CsI coverage was almost lost. In conclusion, the films grown at a fast evaporation rate were affected by 24-h exposure to humid air less than those grown at a slow rate, and are thus expected to possess a greater long-term stability.

Journal Article↗
PubMed2005

Photochemical sources of organic acids. 2. Formation of C5-C9 carboxylic acids from alkene ozonolysis under dry and humid conditions.

The dependence of organic acid generation by alkene ozonolysis on relative humidity, thermalized Criegee intermediate scavengers, and alkene structure is investigated. Carboxylic acids generated from the ozonolysis of 1-hexene, 1-octene, 1-decene, trans-3-octene, and 1-methylcyclohexene were analyzed as trimethylsilyl (TMS) derivatives. Experiments were performed under dry (relative humidity (RH) < 1%) and humid (RH = 65%) conditions with cyclohexane or n-butyl ether as an OH scavenger. Pentanoic acid is produced from 1-hexene and trans-3-octene with yields 8.5 +/- 2.6 and 5.0 +/- 1.5% under dry conditions and 5.1 +/- 1.5 and 2.8 +/- 0.8% under humid conditions, respectively. Heptanoic acid yields from 1-octene are 8.3 +/- 2.5 and 4.4 +/- 1.3% under dry and humid conditions, respectively. Ozonolysis of 1-methylcyclohexene produced six C5-C7 multifunctional carboxylic acids, with a total yield of 7%. Several other acids and aldehydes were also monitored and quantified. An additional set of experiments with added stabilized Criegee intermediate (SCI) scavengers was performed for 1-octene ozonolysis under dry conditions. The results indicate that SCIs and their reaction with water are minor contributors to acid formation in the atmosphere and suggest that many of the acids are formed directly.

Journal Article↗