Moisture Environmental Conditions Research Articles

Mechanical behavior of epoxy resin with graphite additive subjected to water absorption

Abstract Epoxy resin-based composites find extensive applications across various industries due to their unique mechanical properties. They are commonly used in gas and petrochemical industries for pipes and fittings in transmission lines. The primary objective of this study is to investigate changes in the mechanical properties of epoxy resin-based composites under different environmental moisture conditions. To achieve this, epoxy resin with varying weight percentages of graphite additive (0, 5, 10, 15, and 25 wt%) was used. The water absorption characteristics of the specimens were assessed by immersing samples in potable water (PW), distilled water (DW), a 10 vol% alkaline solution (NaCl), and a 10 vol% acidic solution (HCl), following ASTM standards. Both dry and wet samples were examined for various mechanical strengths. The results indicate that, for all weight percentages of graphite additive, water absorption follows the increasing order: NaCl < PW < DW < HCl, as compared to the blank resin case. In terms of mechanical testing, increasing the weight percentage of graphite additive resulted in a 24 % decrease in Barcol hardness and a 39 % decrease in impact strength, while the hot deflection temperature (HDT) increased for 5 wt% and showed no significant effects for the other cases.

The Effect of Environmental Moisture Conditions on the Calculated Incident Radiant Heat Flux by Plate Thermometers

This study investigates the effect of environmental moisture conditions on the calculated incident radiant heat flux (irradiance) by plate thermometers (PT). Alterations were made to the moisture content of the PT insulation layers to achieve these conditions. Irradiance was calculated using a pre-determined equation based on fully insulated conditions and validated using a Schmidt-Boelter radiometer. The study consisted of two phases; (i) investigating the effect of preheating PT to the accurate irradiance, (ii) investigating the effect of moisture in the PT on the measurement of irradiance. Calculated irradiance agreed with measured for preheated PT, but not with unheated PT. Four representative moisture conditions were identified for phase two, whereby samples were equilibrated at 0, 45, 65, and 98 wood moisture equivalent (%WME). No noticeable difference identified between measured and calculated irradiance was detected within 0–65%WME. PT with 98%WME showed a difference between the irradiance as the moisture inside the PT insulation absorbed energy from the PT to vaporize. Therefore, using preheated PT with any %WME under 65 is recommended to obtain accurate enough irradiance measurements. The result can use to improve determining the fire spread mechanisms and accurate measurements of irradiance in outdoor fires such as informal settlements fires.

New Data on the Middle–Late Holocene Evolution of Vegetation Cover in the Northern Baikal Region

A continuous peat bog section from a barely accessible mid-mountain area in the northwestern Baikal region has been obtained for the first time. The materials were studied by methods such as pollen–spore analysis, analysis of plant cell remains, and radiocarbon dating (calibrated data). The smallest peat accumulation rates in East Siberia during the Holocene are revealed. In accordance with the calculated peat accumulation rates, the time resolution is 100 years in the lower part of the section, it is while up to 800 years in the upper one. Six local palynozones and five botanic zones have been distinguished using factor analysis. The vegetation cover changes and environmental moisture conditions for the last 7670 years are reconstructed. The altitude of the forest line is specified for the first time in a quarter of a century.

Degradation of rhenium carbide obtained by mechanochemical synthesis at oxygen and moisture environmental conditions

Abstract In this paper, rhenium carbide (Re2C) synthesized by mechanosynthesis was characterized by SEM and HRTEM, as well as XRD. The Re2C was stored at oxygen and moisture environmental conditions in order to know the chemical stability for 2, 12, 27 and 54 months. The results of storage after 54 months indicate that Re2C is partially degraded into ReO3, while WC-Co milling material is totally degraded into H2WO4, W18O49, CoO and C. Finally, a schematic diagram of the degradation of Re2C and WC-Co at oxygen and moisture environmental conditions is proposed and partially validated by thermodynamic analysis.

Hydrometeorology organizes intra-annual patterns of tree growth across time, space and species in a montane watershed.

Tree radial growth is often systematically limited by water availability, as is evident in tree ring records. However, the physiological nature of observed tree growth limitation is often uncertain outside of the laboratory. To further explore the physiology of water limitation, we observed intra-annual growth rates of four conifer species using point dendrometers and microcores, and coupled these data to observations of water potential, soil moisture, and vapor pressure deficit over 2yr in the Northern Rocky Mountains, USA. The onset of growth limitation in four species was well explained by a critical balance between soil moisture supply and atmospheric demand representing relatively mesic conditions, despite the timing of this threshold response varying by up to 2months across topographic and elevation gradients, growing locations, and study years. Our findings suggest that critical water deficits impeding tissue growth occurred at relatively high water potential values, often occurring when hydrometeorological conditions were relatively wet during the growing season (e.g. in early spring in some cases). This suggests that species-specific differences in water use strategies may not necessarily affect tree growth, and that tissue growth may be more directly linked to environmental moisture conditions than might otherwise be expected.

Aging-Induced Electrical Resistance Changes in an RDX-Loaded Nitrate Ester Propellant with Polyglycol Adipate (PGA) and Polyethylene Glycol (PEG) Cross-Linked Binders Subject to Various Thermal and Moisture Environmental Conditions

ABSTRACTTwo Cyclotrimethylenetrinitramine (RDX)-loaded nitrate ester propellant formulations with polyglycol adipate and polyethylene glycol binders, respectively, are subjected to accelerated aging at 70°C in various humidity environments ranging from 0 to 100% relative humidity (RH). The electrical resistance of each sample is monitored throughout aging, along with high-performance liquid chromatography (HPLC) and gas chromatography (GC) used to measure the mass fraction of the stabilizers and nitroso/nitro derivatives at the beginning and end of aging. Stabilizer and nitroso/nitro derivative dimethyl sulfoxide (DMSO) solutions are used to evaluate the electrical resistance of these species as a function of mass fraction. The results indicate a weak correlation of the sample electrical resistance with stabilizer and nitroso/nitro mass fraction and a strong correlation with the moisture content of the sample. Moisture is postulated to affect the electrical resistance of the samples predominately by acid induced hydrolytic decomposition of the nitrate esters present and then further the cross-linked polymeric binders, causing an elevation of the mass fraction of acid species and a decrease in the sample pH.

Competition of surface reactions of tritium release from irradiated Li4SiO4 pebbles

Out-of-pile tritium release experiments were performed on Li4SiO4 pebbles produced from lithium hydroxide under various compositions of sweep gas (He, 1.1% H2/He) and environmental moisture conditions. The experimental results indicate that tritium gas can be released directly from “dry” Li4SiO4 under pure He gas. This phenomenon did not happen on “wet” samples, which means that the chemical form of released tritium is sensitive to moisture. Adding H2 to sweep gas may increase the overall desorption rate of tritium gas through H2 isotope exchange reaction, which occurs at a lower temperature than those of directly released tritium gas. Yet, the threshold of the H2 isotope exchange reaction is higher than the desorption reaction of tritiated water. Consequently, the effect of H2 isotope exchange reaction would reduce significantly on water adsorbed Li4SiO4 samples.

Delayed efficacy of Beauveria bassiana foliar spray applications against Colorado potato beetle: Impacts of number and timing of applications on larval and next-generation adult populations

Spray programs comprising multiple or single foliar applications of the fungal pathogen Beauveria bassiana strain GHA (Bb-GHA) made during morning (AM) vs. evening (PM) hours were tested against Colorado potato beetle Leptinotarsa decemlineata (CPB) in small research plots of potatoes over multiple field seasons, and efficacy against larval and first-generation adult populations was evaluated. The pathogen (formulated as BotaniGard WP®) was applied at the rate of 2.5×1013 conidia in a spray volume of 468–480Lperha. Modes of efficacy were investigated by collecting pre-pupal larvae and holding them in soil cages in the field and laboratory. Results revealed that larval control achievable with multiple-spray programs was poor regardless of environmental moisture conditions, but that emerging adult populations were reduced by an average of 80% (range 58–93%) relative to control populations. Programs comprising a single application of Bb targeted against late-instar larvae reduced adult populations by an average of 60% (range 36–75%). Overall mean differences in efficacy of PM vs. AM applications were not significant in terms of larval control and defoliation damage. Emergence of next-generation adults was significantly lower in the PM vs. AM treatments, but differences were small in terms of percent control. Average yields from the Bb-GHA multiple-spray programs were 18% greater than those from the controls; the mean 5% increase resulting from the Bb-GHA single-spray programs was not significant. Observations indicated that moderate to high rates of inoculation and infection were achieved under a broad range of environmental conditions in the crop canopy, but larvae persisted until they entered the soil to pupate. Most deaths due to mycosis occurred among pre-pupal larvae in their pupation cells in the soil. These results, in combination with similar findings of delayed efficacy reported by other researchers, indicate that foliar applications of Bb could be a significant component of an IPM program aimed at suppressing CPB populations on large farms or over large areas.

Effects of moisture on glass fiber-reinforced polymer composites

Glass fiber polymer composites are used in wind turbine blades because of their high-specific strength and stiffness, good fatigue properties, and low cost. The wind industry is moving offshore to satisfy economies of scale with larger turbines. High humidity in this environment degrades mechanical performance of wind turbine blades over their lifetime. Here, environmental moisture conditions were simulated by immersing glass fiber-reinforced polymer specimens in salt water for a period of up to 8 years. The mechanical properties of specimens were analyzed before and after immersion to evaluate the degradation mechanisms. Single-fiber tensile testing was also performed at different moisture conditions. The water-diffusion mechanism was studied to quantify the diffusion coefficients as a function of salt concentration, sample geometry, and fiber direction. Three degradation mechanisms were observed: polymer plasticization, fiber stress corrosion, and interface degradation, where the latter was found to be the most detrimental for wind-industry applications.

A Numerical Study of Urban Aerosol Impacts on Clouds and Precipitation

Abstract The impacts of urban aerosols on clouds and precipitation are investigated using a spectral (bin) microphysics cloud model. For this purpose, extensive numerical experiments with various aerosol concentrations are performed under different environmental moisture conditions. To take into account the urban heat island and urban air pollution, it is considered that there is low-level heating in the urban area and that the aerosol concentration in the urban area is higher than that in the surrounding rural area. Simulation results show that a low-level updraft induced by the urban heat island leads to the formation of a low-level cloud and then a deep convective cloud downwind of the urban area. The onset of precipitation produced by the low-level cloud is delayed at higher aerosol concentrations. This is because when the aerosol concentration is high, a narrow drop size distribution results in a suppressed collision–coalescence process and hence in late raindrop formation. However, after the deep convective cloud develops, a higher aerosol concentration generally leads to the development of a stronger convective cloud. This is mainly due to increased release of latent heat resulting from the enhanced condensation process with increasing aerosol concentration. The low collision efficiency of smaller cloud drops and the resulting stronger updraft at higher aerosol concentrations result in higher liquid water content at higher levels, leading to the enhanced riming process to produce large ice particles. The melting of a larger amount of hail leads to precipitation enhancement downwind of the urban area with increasing urban aerosol concentration in all moisture environments considered.

Effect of moisture variation on oxygen consumption rate of corroding steel in chloride contaminated concrete

This paper is based on experimental investigations carried out on the effect of varying relative humidity on oxygen consumption rate of corroding reinforcement steel in concrete under impressed potential macro-cell cathodic reaction for which the previous research data is limited. The objective of this research is to investigate the qualitative as well as the quantitative relation between the oxygen consumption rate of corroding reinforcement carbon steel in chloride contaminated concrete and ambient relative humidity under continuous as well as cyclic exposure conditions. For this purpose, corrosion cells with locally separated anode and cathode steel reinforcement bars under four different environmental conditions (namely air dry, submerged, 95% relative humidity and alternate wetting–drying) have been tested under strict laboratory control. By analyzing the results of these tests, it was possible to understand the behavior of oxygen consumption rate of corroding steel reinforcement in chloride contaminated concrete under varying moisture environmental conditions.

Mold appearance and modeling on selected corn stover components during moisture sorption

Occurrence of mold was visually monitored for 26 days on samples of major anatomical components of corn stover maintained at several storage temperatures ( T) and water activities ( a w). Glass desiccators with saturated salt solutions placed in temperature controlled chambers provided simulated storage conditions with temperatures ranging from 10 °C to 40 °C and water activities ranging from 0.11 to 0.98. Mold affected leaf, stalk skin, and stalk pith equally at water activity greater than 0.9. As expected, a combination of increased water activity greater than 0.9 and temperatures greater than 30 °C was conducive to mold growth. Based on material moisture content during the initial mold growth, it was postulated that among the corn stover components the stalk pith was the least resistant to mold growth followed by stalk skin and leaf for the studied range of temperature and water activity. Mold growth models fitted well with the observation. A linear mold-free days predictions using a three-parameter regression model ( T, a w, and T × a w) was superior ( R 2 = 0.99) to other models considered. The exponential spoilage model using two parameter T and a w also gave comparable performance ( R 2 = 0.95). Among the independent factors, T × a w product was the most significant ( p = 0.0069) followed by T ( p = 0.0114), and a w ( p = 0.3140) in explaining the experimental data. The developed models can be applied to predict the safe storage period of corn stover components exposed to various temperature and moisture environmental conditions.

Regional expression of the 1988 U.S. Midwest drought in seasonal δ13C of tree rings

This study analyzes δ13C of subdivisions of the 1988 and 1989 growth rings from three conifer species (Pinus resinosa, Pinus strobus, and Picea glauca) across a network of nine sites over four states in the upper U.S. Midwest to infer seasonal and interannual environmental moisture conditions. Both years were characterized by different spatial patterns of drought (expressed through rainfall and Palmer Drought Indices), with the area of 1989 drought being smaller and shifting westward relative to 1988. Rings were subdivided into four equal segments from which holocellulose was separated. The range of δ13C variation within each ring was typically 1–2‰ for both years, and the single site where all three species co‐occurred revealed coherent seasonal δ13C patterns for the pines but no correlation of the spruce δ13C patterns with those of the pines. Various averaged combinations of monthly Palmer Drought Severity Index (PDSI) and precipitation assigned to each subdivision versus both δ13C and discrimination (Δ ≈ δ13Cair − δ13Cplant) yielded significant correlations (generally higher with PDSI) and even stronger correlations when the spruce data were removed. The fraction of average monthly cumulative precipitation (relative to 1900–2001 means) for these 2 years was more strongly related to δ13C than either monthly precipitation or monthly fraction of average precipitation, but was not as strongly related to δ13C as was PDSI. Furthermore, the pattern of increasing δ13C in 1988 observed at several sites is an indicator of the increasing moisture stress of that year, and the difference between the 1988 and 1989 average isotopic compositions of the third and fourth subdivisions matched the regional moisture shift well.

An asymptotic characterisation of the moisture diffusion in polymer matrix composites with cyclic environmental conditions

This paper presents and illustrates a straightforward method to determinate the concentration of the humidity in non steady and transient states in the core of the resin matrix composite panel exposed to cyclic temperature and moisture environmental conditions during a long time. In order to complete the previous studies, an analytical solution in transient state is proposed. Several examples are presented to demonstrate the assessment and performance in this method compared to the classical step-by-step integration.

The overwintering of Fasciola hepatica eggs under semi-arid and temperate Mediterranean climate (Madrid, Spain).

In this experimental work, conducted over two consecutive years (1988 and 1989), we have analyzed the overwintering possibilities of Fasciola hepatica eggs deposited in winter in a semi-arid and temperate Mediterranean area (Madrid, Spain). Eggs did not survive for more than a week in faeces at environmental moisture conditions. In contrast, over a 75% of the eggs maintained in permanently wet faeces survived winter temperatures, showing no high mortality until important thermic increment from June. The success of overwintering was higher in eggs arrested in wet faeces than included in water (55% "versus" 20% of hatching in spring), and it was unrelated to the deposition time (excretion in early or late winter). The hatching period of overwintered eggs started in May, at the same time as those excreted in early spring. Therefore, overwintering of eggs will have an effect on the level but not on the start of the spring contamination with miracidia. The dry winters of this semi-arid area greatly restrict the overwintering eggs contamination to soils next to streams, ponds or irrigation channels.