Relative Humidity Gradient Research Articles

Water balance profiles, humidity preference and survival of two sympatric cockroach egg parasitoids Evania appendigaster and Aprostocetus hagenowii (Hymenoptera: Evaniidae; Eulophidae)

The impact of desiccation on habitat selection, foraging and survival has been characterized for many insects. However, limited information is available for parasitic wasps. In this study, water balance, relative humidity (RH) preference, and effect of humidity on survival of solitary Evania appendigaster (L.) (Hymenoptera: Evaniidae) and gregarious Aprostocetus hagenowii (Ratzeburg) (Hymenoptera: Eulophidae) were examined. These species are both oothecal parasitoids of the American cockroach Periplaneta americana (L.) (Dictyoptera: Blattidae). E. appendigaster had significantly higher cuticular permeability (CP) and a lower surface area to volume ratio but a similar percentage of total body water content compared to A. hagenowii. No differences in these attributes were found between sexes of each parasitoid species. The percentage of total body water loss rates among E. appendigaster males and females and A. hagenowii females were similar but significantly lower than that of A. hagenowii males. All parasitoids except E. appendigaster males exhibited reduced survival times as the RH of their enclosure decreased from 87% to 38%, but this phenomenon did not occur when parasitoids were given a sugar solution. In environmental chambers with a 44–87% RH gradient, both sexes of E. appendigaster resided significantly more often in the 87% RH chamber than in the 44% RH chamber. For A. hagenowii, females preferred both the driest and the wettest chambers and males preferred the driest ones. These results demonstrate the water balance profile and its relationship to life history traits and differential responses to RH in these competing parasitoid wasps, suggesting the role of physiological and behavioral adaptations in shaping their ecological niche.

The Scrovegni Chapel: The results of over 20 years of indoor climate monitoring

This paper presents the results of 20 years of monitoring indoor microclimate conditions inside the Scrovegni Chapel in Padova (Italy). Since the late 1970s, the chapel has been the subject of a series of monitoring to assess the degree of conservation of the frescos and of the building structures. The early studies allowed to operate in the best for what concerns the choice of the proper instrumentation and their positioning. It was thus possible to operate before the beginning of any restoration work measuring values of surface temperature, vertical and horizontal gradients of air temperature and relative humidity. The approach has highlighted the importance of heat transfer as well as exchanges of mass between the indoor air and wall surfaces. A subsequent monitoring period allows to measure the air temperature, humidity and surface temperatures after the restoration works. During the same period, it was commissioned to assess the requirements for the air treatment plant. Monitoring is continuous in time and a reasoned comparison of the different indoor microclimatic conditions, which over the years have been met, is here proposed. These indications suggest possible improvements of the monitoring system and of the management of indoor microclimate.

Community assembly in a tropical cloud forest related to specific leaf area and maximum species height

AbstractQuestionWe tested whether co‐existing tree species in tropical dwarf forests were deterministically assembled along gradients of air temperature, relative humidity and light availability, according to two important functional traits, specific leaf area (SLA) and maximum species height (Hmax).LocationTropical montane cloud forest, Bawangling Nature Reserve, Hainan Island, south China.MethodsNull model analyses were used in conjunction with trait and species composition data collected to test our hypotheses at four plot sizes (25 m2, 100 m2, 400 m2 and 900 m2), addressing whether the consistent importance of variation in SLA and Hmax extends to these unique forests, as well as theoretical predictions concerning how patterns change with plot size.ResultsLow SLA species were significantly over‐represented within forest communities for the two largest plot sizes, and taller‐growing tree species were over‐represented across all four plot sizes. Plot‐level analyses indicated that low SLA species were associated with lower temperatures.ConclusionsOur results show that tropical dwarf forests are deterministically assembled with respect to these two traits, and are consistent with other studies indicating that SLA responds to abiotic filters. Co‐existing tree species were not significantly divergent for these two traits, indicating that variation in these two traits among trees does not contribute to niche differences (i.e. limiting similarity) and therefore co‐existence within forest plots. Finally, our study demonstrates that patterns of community assembly change with plot size; however, trait convergence did not increase with plot size as previously predicted.

Cell level modeling of the hygrothermal characteristics of open cathode polymer electrolyte membrane fuel cells

Open cathode designs that utilize ambient air for both cooling and oxygen supply are a useful feature for low- to medium-power polymer electrolyte membrane fuel cell (PEMFC) stacks. Elimination of balance-of-plant subsystems greatly reduces the complexity, parasitic power, and cost of the overall system, and therefore increases the appeal of open cathodes. The present research addresses the key challenges of open-cathode PEMFCs related to thermal management and membrane hydration, two highly coupled phenomena. Accurate knowledge of the temperature and relative humidity (RH) distributions in the cell is essential in order to optimize heat removal by suitable strategies. In the present work, a three-dimensional numerical model is developed that can predict the hygrothermal characteristics in a complete open-cathode cell. The model is validated using experimental data obtained with Ballard Power Systems' FCgen®-1020ACS stack under a range of operating conditions. The model is then used to analyze the key flow conditions and properties that control the hygrothermal behavior of open-cathode stacks. Based on the obtained results, flow conditions can affect temperature and RH distributions significantly; in-plane plate thermal conductivity can provide a uniform temperature distribution while adversely reducing the RH; and edge cooling can increase temperature and RH gradients in the cell. Recommendations for hygrothermal design and operation of open cathode stacks are provided.

The relative humidity dependence of the permeability of cement paste measured using GARField NMR profiling

The relative humidity (RH) dependence of the water permeability of cement is calculated from the water concentration profile of a paste exposed to an RH gradient and the desorption isotherm. The profile is measured using GARField, standing for Gradient at Right Angles to Field, NMR. The isotherm is derived from other earlier NMR measurements. The Darcy equation gives the intrinsic permeability as 4.6×10−21m2. The apparent intrinsic permeability to water flow shows a broad “U” shape dependence on RH, with a minimum of 7×10−22m2 at RH 55%. The “U” shape is attributed to the fact that the transport mechanism involves a coupling of liquid and vapour modes. The data is further analysed in terms of a model of coupled liquid and vapour diffusion and Darcy flow due to Baroghel-Bouny et al. (Cem. Concr. Res. 2011 41 828) from which the relative liquid water and vapour permeabilities are calculated. They are strongly RH dependent. The former increases with increasing RH; the latter decreases.

Isolation of transport mechanisms in PEFCs using high resolution neutron imaging

Liquid water saturation profiles were determined using high resolution neutron radiography for commercially available fuel cell materials and hardware. Temperature, pressure, and relative humidity (concentration) gradients were imposed on the cell to determine individual influences on water content for each gradient. The asymmetric anode/cathode channel/land architecture used in this work results in significant water accumulation in the anode diffusion media with saturation values of up to ∼50%. Anode water content was found to change substantially with imposed pressure or concentration gradient, whereas the cathode saturation profile remained relatively consistent, indicating the channel/land ratio and thickness have a determinant role in diffusion media retention. The data generated in this work has been made publicly available through www.pemfcdata.org, and should be useful for computational modelers seeking validation data.

A Planetary Boundary Layer Height Climatology Derived from ECMWF Reanalysis Data

Abstract A planetary boundary layer (PBL) height climatology from ECMWF reanalysis data is generated and analyzed. Different methods are first compared to derive PBL heights from atmospheric temperature, pressure, and relative humidity (RH), which mostly make use of profile gradients, for example, in RH, refractivity, and virtual or potential temperature. Three methods based on the vertical gradient of RH, virtual temperature, and potential temperature were selected for the climatology generation. The RH-based method appears to capture the inversion that caps the convective boundary layer very well as a result of its temperature and humidity dependence, while the temperature-based methods appear to capture the PBL better at high latitudes. A validation of the reanalysis fields with collocated radiosonde data shows generally good agreement in terms of mean PBL height and standard deviation for the RH-based method. The generated ECMWF-based PBL height climatology shows many of the expected climatological features, such as a fairly low PBL height near the west coast of continents where stratus clouds are found and PBL growth as the air is advected over warmer waters toward the tropics along the trade winds. Large seasonal and diurnal variations are primarily found over land. The PBL height can exceed 3 km, mostly over desert areas during the day, although large values can also be found in areas such as the ITCZ. The robustness of the statistics was analyzed by using information on the percentage of outliers. Here in particular, the sea-based PBL was found to be very stable.

Atmospheric composition and micro-climate in the Alhambra monument, Granada (Spain), in the context of preventive conservation

The world famous Alhambra monument in Granada, Southern Spain, listed as UNESCO world cultural heritage since 1984, represents probably the most beautiful example of Islamic art and architecture from the Middle Ages in Europe. It is visited by ca. 2 million people annually. Granada is situated in a natural basin, surrounded by mountains with altitudes up to 3500 m. Due to this topography and the prevailing low wind speeds, pollution-derived and especially traffic-derived particulate matter often accumulates in the urban air. In order to evaluate the potential conservation risks from the surrounding air, the atmospheric composition in the Alhambra monument was evaluated. Indoor temperature and relative humidity fluctuations were evaluated for their potential degenerative effects. Furthermore, the atmospheric composition in the Alhambra was analyzed in terms of inorganic gases (NO2, SO2, O3, and NH3) and black carbon. It was found that the open architecture protected the indoor environments from developing a potentially harmful microclimate, such as the build-up of humidity resulting from the huge number of daily tourists. On the downside, the strong ventilation made the indoor air hardly different from outdoor air, as characterized by strong diurnal temperature and relative humidity gradients and high traffic-derived pollutant levels.

Mass transfer of water vapor, carbon dioxide and oxygen on modified cellulose fiber-based materials

Abstract Mass transfer properties of fibre network and coated paper are essential for understanding the barrier properties of the products and further advance in their application. In this study, different unmodified and coated papers, e.g., (Poly lactic acid (PLA), zein grafted paper) were prepared and characterized with regard to mass transfer properties. Water vapor, carbon dioxide (CO2) and oxygen (O2) transmission rates through the cellulose paper films were measured and the results discussed. The effects of sample film thickness and samples were found to be strongly dependent on the temperature and the relative humidity difference (mass transfer driving force). On the other hand water vapor permeabilities relative humidity. Water vapor diffusivities of the samples were also measured from the uptake rate measurements using Fickian diffusion slab model for a wide range of relative modified samples were found to be generally low compared to unmodified (reference) paper sample. Among the investigated samples, PLA/polyhedral oligomeric silsesquioxane POSS-bentonite modified paper sample showed higher mass transfer resistance to water vapour and the gases investigated in this study (CO2and O2). It showed lower water transmission rate (104 g/m2.day) compared to PLA-coated paper (130 g/m2.day), zein coated paper (179 g/m2.day) and control sample (359 g/m2.day) at the relative humidity gradient RH=74% and temperature of 25 oC. The oxygen transmission rate for PLA/(POSS-Bentonite) coated paper was found to be lower than for the other modified papers. Zein grafted paper showed better barrier property for water vapor than oxygen. Water vapor permeation through paper films shows an Arrhenius type of dependency with temperature, indicating activated process. The activation energies reveal diffusion dominated process for all paper samples investigated in this study, according to the solution-diffusion mechanism used to describe the permeation processes.

Desorption Experimental Analysis and Modeling of Drying Shrinkage and Relative Humidity in Non-Saturated Concrete

Abstract. The paper investigates the gradient of relative humidity over time at different depth from dried surface and the relationship between relative humidity and concrete shrinkage. It shows that a drop in relative humidity over time is remarkable, and that drying shrinkage is linearly related to humidity. By measuring the weight of the sample and calculation of the capillary pressure, the relationship between the saturation and the capillary pressure is presented. Based on the experiment and Kelvin’s law, a model of shrinkage for non-saturated concrete taking the surface energy into account is presented. A comparison of computed and observed drying shrinkage is made, finding that the two values are in agreement very well.

Isolation of Transport Mechanisms in PEFCs with High Resolution Neutron Imaging

Cell water balance and anode to cathode water transport were investigated using high resolution neutron radiography in the through-plane direction. Induced pressure and relative humidity gradients were imposed across the membrane electrode assembly to determine how these gradients alter saturation profiles in the diffusion media. The asymmetric anode/cathode channel pitch used in this study resulted in large anode water saturation changes with applied gradients while cathode saturation remained more constant. A new low-cost core-shell diffusion media is introduced as a potential replacement of current diffusion media. This new material was found to reduce overall cell water content, but suffers poor overall performance due to excessive ohmic losses, and more work is needed to develop this concept.

Effect of morphology on water sorption in cellular solid foods. Part II: Sorption in cereal crackers

Experimental dynamical moisture profiles of crackers with a fine and coarse morphology are successfully predicted using a pore scale network model. Experimental profiles are obtained using a single point imaging (SPI) NMR technique that enables 3D mapping of the moisture content of relatively immobile water at low water activity.The relative vapor conductivity trough the structure is 33% and 64% for the fine and coarse structured crackers, respectively. It can be argued that this is due to their difference in cell connectivity and not directly related to their difference in average cell diameter (0.33 and 0.75mm, respectively). It was found that the retarded local sorption dynamics of the solid matrix has a noticeable influence on the moisture profiles that arise in the first hours. This is crucial for the moisture sorption dynamics of sub centimeter size samples, for which there is a distinct non-equilibrium between the vapor and the sorbed water phase. The local sorption at low water activity is a factor 3 faster for the fine structure cracker compared to the coarse one. This is due to their differences in average lamellae thickness (54 and 93μm, respectively).However, for the description of the overall moisture sorption dynamics of the few cm thick samples, on a time scale of days, it valid to assume local equilibrium and to use an effective diffusivity model. The relative vapor conductivity together with the porosity and the derivative of the sorption isotherm determines the effective moisture diffusivity for these open structures, which is a factor 3 lower for the fine structured cracker compared to the coarse one. The single sided moisture sorption in the 2.5 thick cracker samples is not even completed after 5days, mainly because at higher water content (near 20%) there is very little gradient in relative humidity to drive the vapor transport. This is reflected in the predicted effective moisture diffusivities which for the coarse cracker decrease from 16×10−9m/s2 (at 1% MC, 16% aw) to 7.6×10−10m/s2 (at 20% MC, 86% aw).

Effect of environmental humidity and coating on aroma transfer through treated papers

Coupled transfers of aroma compounds and water vapour were investigated by varying the relative humidity gradient of storage (50% or 90%) of two paper packaging at 25°C. These papers differed in their coating surface: both were identically impregnated then supercalendered, and only one was twice coated on both sides with a synthetic barrier substance. Permeability and solubility coefficients were determined. The coating treatment was more effective to decrease the permeabilities of water vapour and ethyl ester than the effect of RH. On the contrary, the RH modified the water content of the treated papers and affected more strongly their permeability and solubility to cis-3-hexenol and benzaldehyde. The cis-3-hexenol transfer through the non-coated paper and the benzaldehyde transfer through the coated paper decreased due to a probable competition with sorbed water although it increases for the cis-3-hexenol of a plasticisation phenomenon.

Internal relative humidity distribution in concrete considering self-desiccation at early ages

The internal relative humidity (RH) and humidity gradients in concrete at early ages have significant influence upon the properties of concrete, where exists, great discrepancy among the test results under different methods. By comparing and analyzing the common measuring methods of the RH in concrete, a newly developed measuring method will be introduced in this study, which could measure the internal RH in cement-based materials accurately, conveniently and digitally. The changing laws of the internal RH in concrete at early ages were discussed. And the numerical simulation of the internal RH was carried out, using the calculated parameters appropriately. The results indicate that the measuring results under the newly developed system was more accurate than that by the predrilled-hole method, while the external environment does not have any effect on the measured results obtained by using the new measurement system. There exist obvious humidity gradients in concrete. In concrete with low water/cement ratio, self-desiccation considerably influence on internal RH distribution. The finite element analysis results from moisture diffusion theory were in good agreement with experimental results. Key words: Concrete, low water-cement ratio, admixtures, early ages, internal relative humidity, a new measurement system, self-desiccation, finite element analysis.

Ferric sulfates on Mars: A combined mission data analysis of salty soils at Gusev crater and laboratory experimental investigations

[1] A temporal visible near-infrared (VIS-NIR) spectral variation was observed from Tyrone yellowish salty soils based on seven periodic Pancam 13 filter observations made by the Spirit rover. The major change was the reduction of spectral slope from 434 nm to 753 nm. Based on the results from a set of systematic laboratory experiments on the stability field and phase transition pathway of typical ferric sulfates, we suggest that the strong dehydration processes of ferricopiapite, either through amorphization or chemical alteration, could be the reasons for the spectral changes of Tyrone yellowish salty soils, excavated from a deep trench. The change of soil property suggests that they were originally not in equilibrium with the surface atmospheric conditions, that there is a relative humidity (RH) gradient existing in the upper few tens of centimeters depth below the surface. A layer of salt-rich regolith beneath the surface will change the underground temperature profile, especially to keep a low-temperature zone with a small temperature oscillation (than diurnal cycle at surface) in a salt-enriched regolith layer. This temperature profile will provide a relatively high RH and small RH variation and thus will facilitate the preservation of hydrous sulfates with high degree of hydration during the moderate obliquity period on Mars. Additionally, the sulfates with high degrees of hydration are excellent RH buffers in a local environment. The subsurface hydrous sulfates can be the sources for high level of water-equivalent hydrogen found at two large equatorial regions on Mars by Neutron Spectrometer on Mars Odyssey Orbiter.

Measurement of the Internal Relative Humidity Distribution in Concrete

The internal relative humidity (RH) and humidity gradients in concrete at early ages have a significant influence upon the properties of concrete, where exists a great discrepancy among the test results under different methods. By comparing and analyzing the traditional measuring methods of the RH in concrete, a new measuring method will be developed in this study, which could measure the internal RH in cement-based materials accurately, conveniently and digitally. The changing laws of the internal RH in concrete at early ages were discussed. The results indicate that the measuring results under the new developed system was more accurate than that by the predrilled hole method, while the external environment does not have any effect on the measured results obtained by using the new measurement system. What’s more, the results achieved by the new developed system approached the real RH in concrete very quickly; the RH near the surface of the specimen decreased quickly, while the RH in the center of the specimen decreased slowly, the moisture contents unevenly distributed through the various height of the specimen. Hence, there exists an obvious humidity gradient in concrete.

Estimating climatological planetary boundary layer heights from radiosonde observations: Comparison of methods and uncertainty analysis

Planetary boundary layer (PBL) processes control energy, water, and pollutant exchanges between the surface and free atmosphere. However, there is no observation‐based global PBL climatology for evaluation of climate, weather, and air quality models or for characterizing PBL variability on large space and time scales. As groundwork for such a climatology, we compute PBL height by seven methods, using temperature, potential temperature, virtual potential temperature, relative humidity, specific humidity, and refractivity profiles from a 10 year, 505‐station radiosonde data set. Six methods are directly compared; they generally yield PBL height estimates that differ by several hundred meters. Relative humidity and potential temperature gradient methods consistently give higher PBL heights, whereas the parcel (or mixing height) method yields significantly lower heights that show larger and more consistent diurnal and seasonal variations (with lower nighttime and wintertime PBLs). Seasonal and diurnal patterns are sometimes associated with local climatological phenomena, such as nighttime radiation inversions, the trade inversion, and tropical convection and associated cloudiness. Surface‐based temperature inversions are a distinct type of PBL that is more common at night and in the morning than during midday and afternoon, in polar regions than in the tropics, and in winter than other seasons. PBL height estimates are sensitive to the vertical resolution of radiosonde data; standard sounding data yield higher PBL heights than high‐resolution data. Several sources of both parametric and structural uncertainty in climatological PBL height values are estimated statistically; each can introduce uncertainties of a few 100 m.

Turbulence characteristics over tropical station Gadanki (13.5°N, 79.2°E) estimated using high‐resolution GPS radiosonde data

Seasonal variation of the turbulence parameters, refractivity structure constant Cn2, eddy dissipation rate ɛ, and eddy diffusivity K, is presented using 3 years (April 2006 to March 2009) of high vertical resolution GPS radiosonde measurements over the tropical station Gadanki (13.5°N, 79.2°E). First, a correlation analysis was done in order to study the relative contributions of temperature (T) and relative humidity (RH) to the refractive index gradient (M). A strong positive (negative) correlation between M and RH (T) gradients is noticed up to 10 km. Above 10 km, a strong positive correlation between M and T gradients is seen, except at altitudes near the tropopause. In the present study we flag the turbulent layers using the Thorpe sorting method and estimate the structure constant Cn2 for the turbulent layers. The probability of occurrence of Cn2 is derived from the cumulative distribution at each height and is found to decrease from 10−7 to 10−17 m−2/3 with height. The probability of the occurrence of Cn2 conditioned to the occurrence of turbulence as a function of height is derived, and it is found that only the mean and the 90th percentile profile reach an altitude of ∼27 km. The demarcation between the boundary layer and the free atmosphere as well as between the troposphere and the stratosphere are quite clear from the turbulence profile, which allows us to identify the boundary layer and tropopause heights from turbulence profiles. Thus, the present analysis introduces an alternative approach to identify the height of the boundary layer as well as the tropopause and also to characterize the probability of turbulence and thickness of turbulent eddies in the atmosphere with a finer scale size (down to 5 m) for the first time from a tropical latitude.

Vapor Permeability Measurements: Impact of Cup Sealing, Edge Correction, Flow Direction, and Mean Relative Humidity

Abstract Water vapor permeability is a basic hygrothermal characteristic of a porous material. At first sight, the cup test used for measuring the property looks simple. Conditions to be fulfilled, however, are that the vapor flow crosses the sample only, is one-dimensional, and that flow direction has no impact on the result. Flow through the sample only demands a perfectly vapor-tight edge-high seal between sample and cup. That condition was tested using different sealing solutions. The results learned that more precautions than expected were needed. If the flow is not one-dimensional, for example, because such perfect seal is only realizable for a sample larger than the cup mouth, an edge correction must be applied to the value measured. As far as direction is concerned, measurements on a couple of hygroscopic materials gave different vapor permeability results for inward and outward flows. Long-lasting sorption after a fast initial hygroscopic moisture uptake appeared to be the reason for that. Dry, wet, and very wet cup testing shows that vapor permeability of hygroscopic materials increases with relative humidity. Some attribute that effect to surface flow from higher to lower relative humidity in the adsorbed water layers once beyond 50 % relative humidity. If that hypothesis was correct, apparent vapor permeability of hygroscopic layers, in situations where partial water vapor pressure and relative humidity gradients oppose, should be much lower than that measured with a wet cup. During the cold season opposing gradients are present in assemblies with a hygroscopic layer at the outside, covered by a vapor retarding finish. Yet, hot box testing on that kind of assemblies did not reveal vapor permeabilities lower than the wet cup value, although interstitial condensation between the hygroscopic and vapor retarding layer was a fact.

Films from oat spelt arabinoxylan plasticized with glycerol and sorbitol

AbstractThe development of packaging films based on renewable materials is an important and active area of research today. This is the first extensive study focusing on film‐forming properties of an agrobiomass byproduct, namely, oat spelt arabinoxylan. A plasticizer was needed for cohesive film formation, and glycerol and sorbitol were compared. The tensile properties of the films varied with the type and amount of the polyol. With a 10% (w/w) plasticizer content, the films containing glycerol had higher tensile strength than the films containing sorbitol, but with a 40% plasticizer content, the result was the opposite. Sorbitol‐plasticized films retained their tensile properties better than films with glycerol during 5 months of storage. The films were semicrystalline with similar crystallinity indices of 0.20–0.26. The largest crystallites (9.5 nm) were observed in the film with 40% glycerol. The softening of films with 40% (w/w) glycerol started at a significantly lower relative humidity (RH) than that of the corresponding sorbitol‐containing films. The films with sorbitol also had lower water vapor permeability (WVP) than the films with glycerol. The films plasticized with 10% (w/w) sorbitol had a WVP value of 1.1 g mm/(m2·d·kPa) at the RH gradient of 0/54%. The oxygen permeability of films containing 10% (w/w) glycerol or sorbitol was similar: 3 cm3·μm/(m2·d·kPa) at 50–75% RH. A higher plasticizer content resulted in more permeable films. Permeation of sunflower oil through the films was not detected. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009