We synthesized available data for decomposition of pine (Pinus) needle litter in pine forests to determine the litter chemical characteristics and climate factors that explained variation in the limit value, i.e. the level of accumulated mass loss at which the decomposition process either continues at a very low rate or possibly stops. Our data base included 56 separate studies on decomposition of pine needle litter, spanning Scots pine, lodgepole pine, Aleppo pine, stone pine and white pine, mainly incubated at the site of collection. Studies had 5 to 19 samplings, on average 10, and the decomposition was followed to a mass loss ranging from 47 to 83%, on average 67%. The periods from 3.0 to 5.4 years, on average 3.9 years, were of sufficient duration to allow estimates of limit values of decomposition. We used a linear mixed model with regression effects to relate limit values to potential explanatory variables, namely the sites' long-term mean annual temperature (MAT) and mean annual precipitation (MAP) and to substrate-chemistry factors. Regarding the latter, we explored two models; one that included initial concentrations of water solubles, lignin, N, P, K, Ca, Mg, and Mn and one that included only lignin, N, Ca, and Mn to focus on those nutrients known to influence lignin degradation. Using backward elimination significant explanatory variables were determined. For litter decomposed in its site of origin we found the limit value to depend mainly on the initial concentration of Mn, with higher Mn concentrations resulting in higher accumulated mass loss. Thus, litter with higher Mn reached a higher limit value and left a smaller stable fraction. This is likely due to the fact that Mn is an essential component of ligninolytic enzymes important for degrading litter in the later stages of decomposition. Manganese has received little attention in decomposition studies to date. Given its significance in this synthesis, the role of Mn in influencing variation in the late stages of decomposition among ecosystems and among litters of other genera besides Pinus deserves further attention
The variation in nutrient resorption has been studied at different taxonomic levels and geographic ranges. However, the variable traits of nutrient resorption at the individual species level across its distribution are poorly understood. We examined the variability and environmental controls of leaf nutrient resorption of Quercus variabilis, a widely distributed species of important ecological and economic value in China. The mean resorption efficiency was highest for phosphorus (P), followed by potassium (K), nitrogen (N), sulphur (S), magnesium (Mg) and carbon (C). Resorption efficiencies and proficiencies were strongly affected by climate and respective nutrients concentrations in soils and green leaves, but had little association with leaf mass per area. Climate factors, especially growing season length, were dominant drivers of nutrient resorption efficiencies, except for C, which was strongly related to green leaf C status. In contrast, green leaf nutritional status was the primary controlling factor of leaf nutrient proficiencies, except for C. Resorption efficiencies of N, P, K and S increased significantly with latitude, and were negatively related to growing season length and mean annual temperature. In turn, N, P, K and S in senesced leaves decreased with latitude, likely due to their efficient resorption response to variation in climate, but increased for Mg and did not change for C. Our results indicate that the nutrient resorption efficiency and proficiency of Q. variabilis differed strongly among nutrients, as well as growing environments. Our findings provide important insights into understanding the nutrient conservation strategy at the individual species level and its possible influence on nutrient cycling.
ASP (alkali, surfactant, polymer) flooding has obtained good results in the field. However, it has serious "scale" and "emulsion" and "chromatographic separation" problems, and because of the reaction of alkali with the formation, it cannot be used at high temperature conditions. A relatively pure surfactant that attains ultra-low Interfacial Tension (IFT) between crude oil and formation water without adding alkali into the system needs to be developed.A mechanism (or condition) for surfactants to form ultra-low IFT at low concentrations is put forward. According to this mechanism, the chemical structure of 5 series of surfactants is designed, more than 30 specific surfactants were synthesized, all the above surfactants types and most of the specific surfactants attained ultra-low IFT (less than 9X10 -3 mN/m) with the crude oil and formation water systems. In the above surfactants, a series of "Betaine Amphoteric Surfactants" (a relatively pure surfactant with only one or two effective molecular structures) are the most promising. The surfactant was comprehensively evaluated. Besides the make-up water, it does not require additional "alkali", "salts", "co-surfactants", "alcohols" or "solvents" into the system; the IFT between the driving fluid and crude oil of many reservoirs can reach an ultra-low IFT value at concentrations of only 10 ~ 3000ppm; it is tolerant to salinities up to 229,000ppm, divalent ions 21,000ppm, temperatures 98℃. Test on cores shows that the recoveries of flooding by SP (surfactant, polymer) systems using this surfactant are higher than that by ASP systems using alkyl-benzene-sulphonates as the surfactant and NaOH as the alkali, its total recovery can reach above 70% OOIP. Micro-visual oil displacement experiments show that this surfactant can also change the pore surface wettability and further increase the recovery.The above results show that this is a very promising surfactant for chemical flooding, it can be used in very challenging reservoir conditions (very few reservoirs have conditions harsher than those listed above); the mechanism to achieve ultra-low IFT , which is put forward, is useful to the development of new surfactants for EOR and to chemical EOR itself; Surfactants that do not require alkali, co-surfactants, alcohols, salts and solvents in the system to attain ultra-low IFT should promote better understanding of the function of surfactants in chemical flooding.
a b s t r a c tAs the 2003 Paris heatwave showed, elevated temperatures in buildings can cause thousands of deaths. This makes the assessment of overheating risk a critical exercise. Unfortunately current methods of creating example weather time series for the assessment of overheating are based on a single weather variable, and hence on only one driver of discomfort or mortality. In this study, two alternative approaches for the development of current and future weather files are presented: one (pHSY-1) is based on Weighted Cooling Degree Hours (WCDH), the other (pHSY-2) is based on Physiologically Equivalent Temperature (PET). pHSY-1 and pHSY-2 files were produced for fourteen locations. These were then compared with the existing probabilistic future Design Summer Year (pDSY) and the probabilistic future Test Reference Year. It was found that both pHSY-1 and pHSY-2 are more robust than the pDSY. It is suggested that pHSY-1 could be used for assessing the severity and occurrence of overheating, while pHSY-2 could be used for evaluating thermal discomfort or heat stress. The results also highlight an important limitation in using different metrics to compare overheating years. If the weather year is created by a ranking of a single environmental variable, to ensure consistent results assessment of the building should be with a similar single metric (e.g. hours >28C or WCDH), if however the weather year is based upon several environmental variables then a composite metric (e.g. PET or Fanger's PMV) should be used. This has important implications for the suitability of weather files for thermal comfort analysis.
The development and evaluation of a series of betaine amphoteric surfactants which have been synthesized recently is introduced in this paper.This series of products were synthesized by adjusting the structure of the lipophilic group. A product of this series was comprehensively evaluated. The results show that interfacial tension (IFT) between this betaine amphoteric surfactant solutions and Daqing crude oil can reach an ultra-low value (10 -3 mN/m ~ 10 -4 mN/m) with no alkali or weak alkali (Na 2 CO 3 ) and at ultra-low concentrations of surfactants of only 10 ~ 3000 ppm (wt). When the salinity of the make up water is 0 ~ 153,700 mg/L, concentration of divalent ions 0 ~ 1,500mg/L and concentration of polymer 0 ~ 2,000 mg/L, it hardly effects the IFT value, the IFT of the surfactant solutions with crude oil maintains an ultra-low value. Experiments in cores indicate that the displacement efficiency of the compound solution composed of polymers and surfactants (0.1% concentration) is higher than that of alkali/polymer/surfactant (ASP) solution (surfactant concentration 0.3%) used in the oil field now, the total recovery can reach 70 % OOIP or higher. It is shown that the IFT of the fluid gathered at the outlet of the cores, when flooding by 0.35 PV of this type of surfactant (0.2 % concentration), can still be in the range of 10 -3 mN/m ~ 10 -4 mN/m, this means that the entire volume of the core is flooded by ultra-low IFT fluid, which is seldom seen when using other types of surfactants. It is also shown that the surfactant can change the wettability and increase the recovery efficiency in micro-visual oil displacement experiments.The above results show that this is a very promising surfactant for ultra-low IFT chemical flooding. It can be used in a wide range of reservoir conditions (both low and high salinities, divalent ion contents, temperatures, clay contents, different alkali etc.) to significantly increase the oil recovery. Since it only needs a very low concentration of surfactant to obtain an ultra-low IFT, the economics of chemical flooding using this type of surfactant should be better than that using conventional ones.
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