Effects Of Ambient Relative Humidity Research Articles

A Universal Scaling Formulation of the Generalized Peck’s Equation for Corrosion Limited Lifetime in Self-Heated ICs

Since the early 1980s, the highly accelerated stress test in conjunction with conventional Temperature-Humidity-Bias testing has been the industry-standard method for interpreting relative humidity (RH) and temperature (T) dependent failure modes in non-hermetically packaged ICs, solar modules, and other electronic components. In recent years, however, testing requirements based on JEDEC standards and the corresponding lifetime extrapolation to end-use conditions using Peck’s equation have been criticized as overly conservative for modern self-heated logic/power ICs. In practice, the self-heated ICs correlate RH, and T in a way that is not explicitly accounted for by Peck’s equation. In this study, we investigate the IC lifetime due to electrochemical failures – Cu-Al bond wire corrosion – by considering the effects of ambient RH, T, duty cycle, and self-heating temperature rise using an integrated self-consistent finite element-based Multiphysics model and propose a generalized Peck’s equation for self-heated ICs. Our study reveals how the asymmetry between On and Off-state heating leads to dramatic suppression of the effective RH experienced by an integrated circuit and, most importantly, identifies that the corrosion of Cu-Al bond wire occurs in spikes during the on-off transition when both RH and T are high. The generalized Peck’s equation also predicts an elegant scaling relationship among the fundamental variables associated with a self-heated IC lifetime. The prediction is validated by experimental lifetime data from self-heated IC published in the literature. The experimental validation of the physics-informed generalized Peck’s equation suggests the possibility of more accurate (and optimistic) lifetime predictions of modern ICs and solar modules.

Effect of relative humidity on the long-term operation of a single mask triple GEM chamber

The characteristic studies of a Single Mask (SM) triple Gas Electron Multiplier (GEM) detector are carried out using Ar/CO2 gas mixture in 70/30 volume ratio in continuous flow mode. A 55Fe X-ray source is used for this work. The gain and energy resolution are studied from the 5.9 keV X-ray energy spectra. After correcting the effects of ambient temperature and pressure variation, the effect of ambient relative humidity on the gain and energy resolution of the chamber is investigated. The details of the experimental setup, measurement methods and results are presented in this article.

Impact of Relative Humidity on the vertical distribution of aerosols over India

Water uptake by aerosol particles significantly changes its light-scattering characteristics, alters the physical and optical properties of aerosols. In this article, we present the effect of ambient relative humidity (RH) on the optical properties of surface and columnar aerosols under different RH conditions during different seasons over India. In particular, relation between surface RH and surface aerosol properties, surface RH and aerosol optical depth (AOD) and profile of RH on the AOD is presented. An increase in the surface aerosol scattering coefficient (σscat) and total aerosol number concentration (N(d)) is observed under high humidity (50–100%) condition than low humidity (0–30%). This is more prominent in the winter and pre-monsoon seasons. An increase in the AOD is observed as surface RH increase in all the seasons except in monsoon season where it showed an inverse relation. The profile measurements (Lidar and radiosonde) also showed a consistent increase in AOD (0-6 km) from low to high RH (0-6 km) conditions. This relationship is significant during winter followed by the post-monsoon, pre-monsoon, and monsoon seasons. An increase in AOD with RH is observed regardless of altitude in all seasons, except during the monsoon at higher altitudes (2-6 km). Our findings clearly demonstrated that during the winter and monsoon (pre- and post-monsoon) seasons, aerosols within (above) the boundary layer are more sensitive to the RH. This relationship has been tested in different surface conditions across India using CALIPSO and IMD radiosonde measurements. These measurements also confirmed an increase in AOD with increasing RH in all the regions except East Coast (EC) region. Irrespective of the region, this feature is more prominent at lower altitudes (0–1.5 km) during winter and higher altitudes (1.5-6 km) during other seasons. At higher altitudes, only a few regions (Central India, Indo-Gangetic Plain, and West Coast) showed an inverse relationship between AOD and RH during the monsoon and post-monsoon seasons. Further, our results illustrated the contribution of hygroscopic particles to the RH increases the AOD in a given season. This finding implies that hygroscopic growth caused by water-soluble particles in the lower troposphere can significantly alter the magnitude of aerosol radiative forcing both at the surface and at the top of the atmosphere.

Evaporation flow characteristics of respiratory droplets: Dynamic property under multifarious ambient conditions

This study numerically investigated the impact of ambient conditions on the evaporation process of full-range cough expelled droplets. The multi-component Eulerian-Lagrangian framework was adopted to simulate droplet evaporation within the inhomogeneous humidity fields. The results found that effect of ambient relative humidity (RH) on droplet evaporation was more pronounced than that of temperature. When the ambient relative humidity was higher than 40%RH, the evaporation of droplets with a diameter smaller than 100 μm would be significantly decelerated. Meanwhile, in normal indoor environments, 175μm could be a marginal diameter, in which droplets with larger initial diameters would probably not be fully evaporated before settling to the ground. Moreover, a novel cost-efficient approach, representing the instantaneous droplet diameter by functions of dt=φ(RH,t,T), was developed to fulfil the time-dependent dynamic size distributions of evaporated droplets under various ambient conditions directly from the data by this study. The implementation of this approach into User Defined Function (UDF) was demonstrated and it would significantly reduce the computational resource on simulating droplet-related scenarios as it does not require costly calculations on the evaporation processes of each droplet repeatedly in every simulation. This development is limited to cough droplets so far and further fulfilment on droplets database regarding other respiratory behaviours would be highly suggested.

EFFECT OF AMBIENT RELATIVE HUMIDITY AND SOAKING TIME ON THE FORMATION OF OCTADECYLTRICHLOROSILANE COATINGS ON BOROSILICATE GLASS SUBSTRATES FOR ALKALI-METAL VAPOR CELLS

The most sensitive spin-exchange relaxation-free (SERF) magnetometer generally requires a working temperature greater than 100∘C. To date, octadecyltrichlorosilane (OTS) coating is one of the best candidates for this temperature range. However, the performance and consistency of the OTS coatings within the alkali-metal vapor cells are still poor. In this paper, the formation of OTS coatings on borosilicate glass (BG) substrates was investigated. The effects of ambient relative humidity (RH) on the formation of OTS coatings were examined by atomic force microscopy (AFM) and contact angle measurement. The results showed that 75[Formula: see text] RH can improve the order of the OTS coatings and reduce the root mean square (RMS) roughness of the OTS coatings. Under three different ambient RHs, the soaking time of OTS molecules should be greater than 60[Formula: see text]min to form complete OTS coating.

Effects of High-speed Wind, Humidity, and Temperature on the Generation of a SARS-CoV-2 Aerosol; a Novel Point of View

The new coronavirus (SARS-CoV-2) is rapidly spreading across communities around the world. Respiratory droplet transmission is a common transmission route for many airborne diseases, including novel coronavirus disease (COVID-19). Wearing the face mask prevents respiratory droplet transmission. Both face mask leakage and non-use of the face mask under high-speed wind conditions can increase the risk of SARS-CoV-2 transmission. The respiratory droplets’ behavior during sneezing or coughing (i.e., the size and the distance between droplets) depends on face mask wearing. The respiratory droplets during coughing and sneezing break apart into extremely small respiratory droplets (i.e., cloud of aerosol) upon interaction with the high-speed wind condition. The volume-of-fluid (VOF) method has been used to study the deformation and breakup of a single respiratory droplet placed in high-speed wind flow in the presence of smaller neighboring respiratory droplets. The effect of the diameter of respiratory droplets and the distance between them on the breakup mechanism has been investigated using open-source field operation and manipulation (OpenFOAM) libraries. The results are presented for the dimensionless distance and the normalized diameter of the secondary respiratory droplet in the ranges of 2 to 6 and 0.4 to 0.8, respectively. According to the results of simulations, the spreading of SARS-CoV-2 increases with a decrease in respiratory droplet breakup time. In addition, the effects of ambient relative humidity and temperature on the cloud of respiratory particles were analyzed.

Effect of relative humidity on corrosion behavior of SAC305 and Sn–37Pb solders under polyvinyl chloride fire smoke atmosphere

The effect of ambient relative humidity from 50 to 98% on the corrosion characteristics of SAC305 and Sn–37Pb solders under the polyvinyl chloride fire smoke atmosphere was researched. The corrosion kinetics results reveal that the mass loss and corrosion rate of both solders show an increasing trend when the relative humidity is lower than 90%. While the mass loss and corrosion rate at 98% relative humidity present a significant decrease compared with those at 90% relative humidity, which may be ascribed to the impeded diffusion of oxygen under saturated humidity environment. The corrosion rate analysis indicates that SAC305 solder is more susceptible to corrosion. Besides, the corrosion microstructures reveal that the corrosion products grow more and more with the increase of relative humidity, but are most serious at 90% relative humidity. Sn21Cl16(OH)14O6 with SnO and SnO2 are detected as the main corrosion products of SAC305 solder by EDS, XRD and XPS analysis. While the corrosion products of Sn–37Pb solder are Sn21Cl16(OH)14O6 and PbCl2.

Effects of mixture parameters variation on the performance of corrugated plate dryer

Both experimental and theoretical works had been done to study the effects of mixture parameters on the performance of corrugated plate (CP) dryer. A water-air experimental branch had been established to simulate water-steam separation in a CP dryer. The effect of ambient relative humidity on the dryer experiment is analyzed. The diameter distribution of water droplets in air-water mixture at (CP) dryer entrance was measured by laser particle size analyzer. The effects of droplet diameter, moisture content and mixture flow velocity on the separation efficiency, pressure drop and the re-entrainment were studied. At the same time, a theoretical model for trajectory tracking of water particle in CP channel was established to illustrate experimental results. The conclusion shows that: 1) this effect of ambient relative humidity cannot be ignored or error could be introduced to experimental results. 2) The separation efficiency increases with the increase of inlet particle size, increases with the increase of inlet moisture content and increases first and then decreases with the increase of inlet velocity. 3) Critical airflow speed of re-entrainment decreases as the inlet moisture content increases. 4) The pressure drop is exponentially increasing with inlet airflow speed.

Simulation of Picking Up Metal Microcomponents Based on Electrochemistry.

The technology of picking up microcomponents plays a decisive role in the assembly of complex systems in micro- and nanoscale. The traditional method of picking up microcomponents with a mechanical manipulation tool can easily cause irreversible damage to the object, and only one object can be manipulated at a time. Furthermore, it is difficult to release the object with this method, and the release location is not accurate. With the aim of solving the above problems, the present study proposes an electrochemistry-based method for picking up metal microcomponents. First, the effect of ambient relative humidity on pickup was analyzed, and the effect of current density and electrolyte concentration on the deposition was examined. Then, a force analysis in the process of manipulation was carried out. Through the analysis of influence factors, the ideal experimental parameters were obtained theoretically. Finally, a simulation was carried out with COMSOL Multiphysics based on the above analysis. Copper microwires with a diameter of 60 μm and lengths of 300, 500, and 700 μm were successfully picked up and released using a pipette with a nozzle diameter of 15 μm. Compared with the traditional method, this method is simple to manipulate. Furthermore, it has a high success rate, causes less damage to the object, and good releasing accuracy.

Influence of Ambient Relative Humidity on Seasonal Trends of the Scattering Enhancement Factor for Aerosols in Chiba, Japan

In this study, we used ground instruments, namely, a visibility meter, an integrating nephelometer, an aethalometer, a lidar, and a weather monitor, to measure the scattering enhancement factor, f(RH), which quantifies the effect of ambient relative humidity (RH) on aerosol light-scattering, and to generate a model of its annual variation in the city of Chiba, Japan. First, the f(RH) values were calculated with chemical analysis data. Second, visibility-meter and aethalometer data were used to model the monthly trends of f(RH) at 550 nm. The f(RH) values were higher during summer than during the other three seasons, which can be attributed to the general pattern of the regional climatology as well as the loading of different particle types into the lower troposphere. Third, the f(RH) values at 532 nm were obtained from lidar and aethalometer measurements. Low and constant f(RH) values were observed during November, whereas higher and increasing f(RH) values were observed during May. Also, dust events during March 2015 showed decreasing f(RH) with increasing RH .

A hybrid concentrated solar thermal collector/thermo-electric generation system

A bi-generation system combining direct absorption flat plate solar collector for medium temperatures air-heating applications integrated with a thermoelectric generator was modeled under optically concentrated solar radiation conditions. In order to improve the performance of the bi-generation system, the proposed system was simulated under the effect of evaporative cooling at the cold side of the thermoelectric modules in order to create a cooling effect that decreases the temperature of the cold junction, thus enhancing the electrical conversion efficiency of the thermoelectric modules. Rung-Kutta 4th order method is used to solve the ordinary differential, equation, while Newton-Raphson iterative technique is used to solve the nonlinear algebraic system of the model governing equations. The results have reflected a significant effect for the evaporative cooling on the system performance particularly at high values of optical concentration ratio. Furthermore, an augmentation of 19.13% in the total electrical power output was predicted at a concentration ratio of 20 suns. Simulation results had also shown that more stable electrical performance of the system when adopting evaporative cooling method compared to forced convection. It was found that there was an optimum value of water mass flow rate, at which the maximum power output was generated. Finally, relative humidity was shown to have a less significant impact on the performance at high temperature operation, since the effect of high water vapor partial pressure at the heat sink (cold junction), when the system is operating at elevated temperature, dominated over the effect of ambient relative humidity according to the evaporation rate governing model.

Measuring OVOCs and VOCs by PTR-MS in an urban roadside microenvironment of Hong Kong: relative humidity and temperature dependence, and field intercomparisons

Abstract. Volatile organic compound (VOC) control is an important issue of air quality management in Hong Kong because ozone formation is generally VOC limited. Several oxygenated volatile organic compound (OVOC) and VOC measurement techniques – namely, (1) offline 2,4-dinitrophenylhydrazine (DNPH) cartridge sampling followed by high-performance liquid chromatography (HPLC) analysis; (2) online gas chromatography (GC) with flame ionization detection (FID); and (3) offline canister sampling followed by GC with mass spectrometer detection (MSD), FID, and electron capture detection (ECD) – were applied during this study. For the first time, the proton transfer reaction–mass spectrometry (PTR-MS) technique was also introduced to measured OVOCs and VOCs in an urban roadside area of Hong Kong. The integrated effect of ambient relative humidity (RH) and temperature (T) on formaldehyde measurements by PTR-MS was explored in this study. A Poly 2-D regression was found to be the best nonlinear surface simulation (r = 0.97) of the experimental reaction rate coefficient ratio, ambient RH, and T for formaldehyde measurement. This correction method was found to be better than correcting formaldehyde concentrations directly via the absolute humidity of inlet sample, based on a 2-year field sampling campaign at Mong Kok (MK) in Hong Kong. For OVOC species, formaldehyde, acetaldehyde, acetone, and MEK showed good agreements between PTR-MS and DNPH-HPLC with slopes of 1.00, 1.10, 0.76, and 0.88, respectively, and correlation coefficients of 0.79, 0.75, 0.60, and 0.93, respectively. Overall, fair agreements were found between PTR-MS and online GC-FID for benzene (slope = 1.23, r = 0.95), toluene (slope = 1.01, r = 0.96) and C2-benzenes (slope = 1.02, r = 0.96) after correcting benzene and C2-benzenes levels which could be affected by fragments formed from ethylbenzene. For the intercomparisons between PTR-MS and offline canister measurements by GC-MSD/FID/ECD, benzene showed good agreement, with a slope of 1.05 (r = 0.62), though PTR-MS had lower values for toluene and C2-benzenes with slopes of 0.78 (r = 0.96) and 0.67 (r = 0.92), respectively. All in all, the PTR-MS instrument is suitable for OVOC and VOC measurements in urban roadside areas.

Changes in Microbial Populations of WPC34 and WPC80 Whey Protein During Long-Term Storage

The effect of ambient relative humidity (70 and 90%, RH) and temperature and a 70 and 90% RH and temperatures (25, 30 and 35C) on microbial spoilage of whey protein concentrate (WPC34) and whey protein concentrate (WPC80) stored for up to 18 months were investigated. WPC34 and 80 were packaged in bags marked as standard (Std) and high performance (HP), and every 3 months changes in the behavior of aerobic mesophilic bacteria, yeast and mold and lipolytic bacteria were monitored. Initial populations of aerobic mesophilic bacteria in WPC80 and WPC34 averaged 2.7 and 1.6 log CFU/g, respectively. Yeast and mold populations of WPC34 in HP bags increased slightly during storage at 30 and 35C in a 70 and 90% RH, respectively, while lipolytic associated bacteria were not determined in the same samples. The pH of samples in all bags declined while water activity (aw) slightly increased during storage especially at higher RH and temperatures. Pratical Applications Information on the effect of adverse long-term storage conditions on whey protein concentrate (WPC) is needed for effective supply of this product to Africa and other semi-arid regions. This study investigated differences between ambient relative humidity storage, temperatures and type of bags on native microbial population, water activity and pH of WPC. It also, provides WPC manufacturers a better insight with regards to storage conditions and type of bags that can maintain longer shelf life. The data from this study could be used for quality control purposes and or development of a better bag suited for storage above ambient conditions.

Movement and control of evaporating droplets released from an open surface tank in the push–pull ventilation system

Push–pull ventilation systems are effective local ventilation methods to control airborne contaminants generated in industrial buildings, among which droplets are typical. In this paper, the numerical simulations of water droplets released from an open surface tank into the push–pull flow field are carried out and the effects of ambient relative humidity and the pull-flow velocity on the ventilation system performance are discussed based on the droplet evaporation and movement. It was found that the movement and evaporation of droplets were closely related to the push–pull flow mechanism and the droplet initial diameter. When the control effect was good due to the presence of air closure in the flow field (pull-flow velocity ranging from 1.5 m/s to 3.0 m/s), droplets were unlikely to move away from the closure and the evaporation of droplets smaller than 40 μm was obvious. Whereas when the control effect was poor (pull-flow velocity equaling 1.0 m/s), large droplets still moved around the tank surface but small droplets were subject to dispersing, and in such a case droplets smaller than 60 μm evaporated obviously. Moreover, the effect of ambient relative humidity (ranging from 0 to 80%) on controlling droplets was rather limited and no more than ±6%. In addition, the system could save airflow rate and energy consumption by reducing the pull-flow velocity which was excessive originally in ventilation design. Finally, the paper put forward a new index to evaluate the control effect from another standpoint based on whether the droplets did harm to the environment.

Gas Permeability Properties of Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

Environmental issues, such as the depletion of fossil resources and waste disposal, have instigated the development of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), a biobased and biodegradable polymer, bacterially produced from palm oil. PHBHHx is a versatile polymer and this study aims to further characterize it for the possible application as food packaging material. In this respect, barrier properties for gases such as O2, water vapor and CO2 are of great importance. PHBHHx films were made using compression molding. Results show that the O2 permeability (PO2) of PHBHHx is 6–25 times lower as compared to common low barrier materials such as polypropylene (PP), polyethylene (PE) and polystyrene (PS), close to the PO2 of poly(ethylene terephthalate) (PET) and poly(lactic acid) (PLA), but more than 900 times higher as compared to ethylene vinyl alcohol (EVOH), which is a high barrier polymer used in multilayer packaging. The water vapor permeability of PHBHHx is similar to materials such as PLA, EVOH, polyamide and PET, but slightly higher than more apolar polymers like PP and PE. The CO2 permeability (PCO2) of PHBHHx is lower as compared to PP, PE and PS (2–20 times), but higher as compared to PET (>7 times) and EVOH and poly(vinyl alcohol) (>650 times). In addition, the effect of ambient relative humidity (RH) and temperature on PO2 of PHBHHx was investigated. The results show that PO2 at 23 °C, 0 % RH is increased with 8, 18 and 33 % at RH of 50, 70 and 90 % respectively. At 10 °C, PO2 decreased with 62 %, whereas at 38 °C PO2 increased with 200 % in comparison to PO2 at 23 °C (0 % RH). Overall, it can be concluded that PHBHHx shows potential for certain applications in food packaging, however efforts should be made to further improve the permeability properties.

Ionic liquid-based actuators working in air: The effect of ambient humidity

The ionic electromechanically active polymer (iEAP) actuators with ionic liquid electrolytes are distinguished by their ability for operation in ambient air, but also respond to the change in ambient relative humidity. Contrarily to the iEAP actuators with water-solvated electrolytes, water content of an ionic liquid electrolyte has been considered either of little importance in iEAP actuators or to cause unfavorable effects such as hydrolysis of some anions such as BF4−.The effect of ambient relative humidity on the electromechanical properties of an iEAP actuator with 1-ethyl-3-methylimidazolium trifluoromethanesulphonate (EMITFS) electrolyte, porous carbon electrodes and Nafion membrane is investigated. The ambient humidity has an extensive impact on the frequency response of the actuator. In addition, electrochemical impedance spectroscopy is employed to specify the equivalent schematics for the iEAP actuator.The physicochemical parameters, especially viscosity and conductivity, of ionic liquids are strongly dependent on their water content and have therefore huge impact on actuation characteristics. The other constituents of the laminate are also hygroscopic, which amplifies and accelerates the water sorption even further.

Comparison of In Vitro Deposition of Pharmaceutical Aerosols in an Idealized Child Throat with In Vivo Deposition in the Upper Respiratory Tract of Children

Deposition of drug emitted from two commercially available inhalers was measured in an in vitro child oral airway model and compared to existing in vivo data to examine the ability of the child model to replicate in vivo deposition. In vitro deposition of drug from a QVAR® pressurized metered dose inhaler (pMDI) and Pulmicort® Turbuhaler® dry powder inhaler (DPI) in an Idealized Child Throat (1) and downstream filter was measured using UV spectroscopy and simulated realistic breathing profiles. Potential effects of ambient relative humidity ranging from 10% to 90% on deposition were also considered. In vitro QVAR pMDI deposition in the idealized mouth-throat at 50% RH (39.2 ± 2.3% of delivered dose) compared well (p>0.05) with in vivo extrathoracic deposition in asthmatic children age 8 to 14 (45.8 ± 12.3%). In vitro Turbuhaler DPI deposition in the idealized mouth-throat at 50% RH (69.0 ± 1.5%) matched in vivo extrathoracic deposition (p>0.05) in 6 to 16 year old children with cystic fibrosis (70.4 ± 21.2%). The effects of ambient humidity were found to be insignificant for Turbuhaler and minor for QVAR. The Idealized Child Throat successfully mimics in vivo deposition data in school age children for the inhalers tested, and may provide a standard platform for optimizing pediatric treatment with inhaled pharmaceutical aerosols.

Effects of ambient conditions on the thermodynamic performance of hybrid nuclear-combined cycle power plant

SUMMARY This paper provides a theoretical study of the effects of ambient conditions on the thermodynamic performance of a hybrid combined-nuclear cycle power plant. The operational parameters investigated are based on the first and second laws of thermodynamics, which include the ambient air temperature and ambient relative humidity (Φ). The results obtained for the gas turbine model are shown to agree very well with operational data from the Al-Zour Emergency power plant in Kuwait. The ambient temperature was studied within the range of 0–55 °C. The analysis shows that the ambient air temperature has strong effects on plant performance and that operating the system at a high temperature will degrade the performance. Power output is reduced when the temperature is above the standard ambient temperature of 15 °C, and this loss rate is about 17% at 55 °C. The effect of ambient relative humidity (Φ) becomes significant only at higher temperatures. The ambient temperature has a large effect on the exergy destruction of the heat recovery steam generator exhaust, but it has little effect on other components of the plant. The analysis also indicates that reducing the temperature from 55 to 15 °C could help decrease the total exergy destruction of the plant by only 2%. Copyright © 2011 John Wiley & Sons, Ltd.

Relative humidity effects on contact angle and water drop penetration time of hydrophobized fine sand

The purpose of this study was to determine the effects of ambient relative humidity (RH) on contact angle and water drop penetration time (WDPT) using a series of sand samples hydrophobized with stearic acid. The contact angle was estimated using the sessile drop method. The contact angle increased first sharply and then slightly with increasing stearic acid content up to about 5.0 g kg−1. The contact angle did not change with increasing stearic acid content above 5.0 g kg−1. The contact angle increased with increasing RH from 33 to 94%. The RH did not affect the contact angle of samples with a stearic acid content above 5.0 g kg−1, where the particles were considered to be completely coated by hydrophobic organic material. The contact angle increased with increasing RH in sands partially coated with hydrophobic material, which might have resulted from an increase in adsorbed water molecules on the remaining high-energy mineral surfaces. The WDPT increased with increasing RH. The higher the RH, the lower the stearic acid content at which extreme repellency (WDPT ≥ 3600 s) appeared. Samples with a contact angle below 75° or with surface free energy above 72 mN m−1 (equivalent to the surface tension of water) were non-repellent (WDPT < 1 s). Samples with a contact angle above 90° or with surface free energy below 50 mN m−1 were extremely repellent. There was no effect of RH on the relationship between WDPT and contact angle (or surface free energy), indicating that the effect of RH was comparable on both measurements.

Allometry of evaporative water loss in marsupials: implications of the effect of ambient relative humidity on the physiology of brushtail possums(Trichosurus vulpecula)

To better understand the effects of ambient relative humidity (RH) on physiological variables and the implications of RH-correcting evaporative water loss (EWL) data for marsupials, we examined the effect of RH on EWL, body temperature (Tb), metabolic rate (MR) and thermal conductance (C) of the brushtail possum (Trichosurus vulpecula), a medium-sized marsupial. Correcting EWL data for 27 species of marsupial for water vapour pressure deficit (DeltaWVP) in the chamber during measurement significantly increased, rather than decreased, the variability of the allometric relationship for EWL. For the brushtail possum, both ambient temperature (Ta) and RH significantly affected EWL. At Ta=25 degrees C, EWL was independent of RH at "63% RH, but decreased linearly at higher RH values. At Ta=30 degrees C, EWL was significantly related to RH from 26% to 92% RH. There was a significant effect of Ta on Tb and dry thermal conductance (Cdry; higher at 30 degrees C), but no effect of RH. For MR and wet thermal conductance (Cwet) there was a significant effect of Ta (MR higher and Cwet lower at 25 degrees C), and RH at Ta=30 degrees C (MR higher and Cwet lower at the lowest RH) but not at 25 degrees C. Our results indicate that brushtail possums do not necessarily show the linear relationship between ambient RH and EWL expected for an endotherm, possibly because of behavioural modification of their immediate microclimate. This may account for the failure of WVP deficit correction to improve the allometric EWL relationship for marsupials. Chamber RH is an important environmental factor to be considered when measuring standard physiological variables such as MR and Cwet.