应用137Cs示踪技术估算土壤侵蚀的若干问题探讨

[目的]探讨用~(137)Cs示踪技术估算土壤侵蚀量方法(以下简称"~(137)Cs示踪方法")所存在的几个关键问题,促进该方法的标准化和系统化。[方法]对大量已发表的相关文献进行分析,根据作者的研究经验,归纳出~(137)Cs示踪方法在实践应用中所存在的核心问题。[结果]~(137)Cs示踪方法中关于~(137)Cs在空间是均匀分布的假设存在不合理性,不能直接用于定量估算单钻点取样的土壤侵蚀量。~(137)Cs活度的空间变化存在随机性的成分。敏感度和不确定性分析结果证明~(137)Cs活度的空间随机变化量是~(137)Cs示踪方法不确性的最大来源。[结论]可以用多钻点样本平均值来减少~(137)Cs随机变化量所引起的侵蚀估算误差。以统计学为基础的试验设计和采取独立样本的办法可以消除该误差。虽然~(137)Cs模型已被广泛应用,但由于缺乏长期观测资料诸多模型还处在理论研究阶段,没有得到严格的验证和评判。因为不同模型估算的侵蚀量差别甚大,模型验证和筛选对该方法的成功运用至关重要。     

Eel acetylcholinesterase inhibition studies with heteroarylphosphinates

The inhibition of eel acetylcholinesterase by the 4-nitrophenyl esters of 2-furyl(methyl)-, methyl(2-thienyl)-, di-2-furyl-, and di-2-thienylphosphinic acid (I, II, III, and IV, respectively) was investigated at pH 6.90 in 0.067 M phosphate buffer (25.0°C) using stopped-flow instrumentation and automated data processing. Our evaluation of the dissociation constant, K_d, the unimolecular bonding rate constant, k₂, and the bimolecular reaction constant, k_i, are the first reported values for these constants for alkyl/heteroaryl and diheteroaryl esters of phosphinic acids. The largest k_i value (19,330 M^?1 sec^?1) was observed for the reaction of I with the enzyme. The order for the remaining three is II > IV > III. There is no direct relationship between the hydrolysis rates of the esters and their anticholinesterase activities on eel acetylcholinesterase. Likewise, there is no direct relationship between their anticholinesterase activities and the LD₅₀ values in rats.     

A Comprehensive Genotype and Environment Assessment of Wheat Grain Ash Content in Oregon and Washington: Analysis of Variation

A comprehensive analysis of the variation in wheat grain ash content has not been previously conducted. This study assessed the relative contribution of genotype and environment to variation in ash content, with a particular aim of ascertaining the potential for manipulating the trait using contemporary adapted germplasm. A total of 2,240 samples were drawn from four years of multilocation field plots grown in the wheat production areas of Oregon and Washington states. Genotypes included commercial cultivars and advanced breeding lines of soft and hard winter, and soft and hard spring wheats with red and white kernel color, several soft white club wheats, and one soft white spring waxy wheat cultivar. In addition to ash, protein content, test weight, and Single Kernel Characterization System kernel hardness, weight and size were also measured. In total, 20 separate fully balanced ANOVA results were conducted. Whole model R² values were highly significant, 0.62–0.91. Nineteen of the 20 ANOVA results indicated significant genotype effects, but the effects were not large. In contrast, environment effects were always highly significant with F values often one to two orders of magnitude larger than the genotype F values. The grand mean for all samples was 1.368% ash. For individual data sets, genotype means across environments varied ≈0.1–0.3% ash. The genotypes judged noteworthy because they had the highest least squares mean ash content were OR9900553 and ClearFirst soft white winter, NuHills hard red winter, Waxy‐Pen and Cataldo soft white spring, and WA8010 and Lochsa hard spring wheats. Genotypes with lowest least squares mean ash were Edwin (club) soft white winter, OR2040073H hard red winter, WA7952 soft white spring, and WA8038 hard spring wheats. In conclusion, wheat grain ash is more greatly influenced by crop year and location than by genotype. However, sufficient genotype variation is present to plausibly manipulate this grain trait through traditional plant breeding.     

Precursors to damascenone: synthesis and hydrolysis of isomeric 3,9-dihydroxymegastigma-4,6,7-trienes

A series of four isomeric 3,9-dihydroxymegastigma-4,6,7-trienes, 8, has been prepared. The (3S,6R,9S) isomer of 8 proved to be identical to an isomer of this compound tentatively identified as an intermediate in the formation of damascenone from an allene triol. Each of the four isomers, when hydrolyzed independently of each other at pH 3.0 and 25 degrees C, produced product mixtures in which the major product was damascenone (1). Contrary to expectation, 3-hydroxydamascone (5) was not observed in any of the hydrolyses. Consequently, the mechanism of formation of damascenone proposed earlier requires modification. In each hydrolysis, the product mixtures showed the presence of a second isomer of 8, produced by epimerization during hydrolysis. Chiral analysis on a Cyclosil B column revealed that this epimerization was occurring at C(3) in each of the hydrolyses.     

Broccoli processing wastes as a source of peroxidase

A peroxidase isozyme (BP) was purified to homogeneity from broccoli stems ( Brassica oleraceae var. maraton) discarded from industrial processing wastes. BP specific activity was 1216 ABTS [2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid)] units/mg, representing 466-fold that of crude extract. BP is a monomeric glycoprotein containing 16% carbohydrates, with a molecular mass of 49 kDa and an isoelectric point close to 4.2. From kinetic data it showed a two-substrate ping-pong mechanism, and the catalytic efficiency measured as the rate-limiting step of free BP regeneration was 3.4 x 10(6) M(-1) s(-1). The ABTS K m value was 0.2 mM, which was about 20 times lower than that reported for acidic commercial horseradish peroxidase (HRP). Assessment of BP secondary structure showed 30% helical character, similar to HRP and cytochrome c peroxidase. BP lost only 25% activity after 10 min of heating at 55 degrees C and pH 6; it was stable in the pH range from 4 to 9 and showed an optimum pH of 4.6 using ABTS as substrate. BP was active on substrates normally involved in lignin biosynthesis, such as caffeic and ferulic acids, and also displayed good catechol oxidation activity in the presence of hydrogen peroxide. Reverse micellar extraction was successfully used as potential large-scale prepurification of broccoli peroxidase, achieving a purification factor of 7, with 60% activity yield. Stems from the broccoli processing industry have a high potential as an alternative for peroxidase purification.     

Combined transscleral diode laser cyclophotocoagulation and Ahmed gonioimplantation in dogs with primary glaucoma: 51 cases (1996-2004)

OBJECTIVE: To evaluate the combined diode laser cycloablation procedure and adjunctive Ahmed gonioimplant use in dogs with primary glaucoma. DESIGN: Retrospective study. ANIMALS: 48 dogs, 51 eyes with primary glaucoma. PROCEDURE: Medical records from two large private clinical ophthalmology services were reviewed. Signalment, duration of glaucoma, gonioscopic evaluation, laser power and duration settings, immediate postoperative and final intraocular pressure and visual results, short and long-term visual outcome, and surgical complications were recorded. RESULTS: The age range of affected dogs was 3.0-14.0 years, with a mean age of 7.5 +/- 2.6 years. Eleven pure breeds were represented, with the most common being the American Cocker Spaniel. The sex distribution was 22 neutered males, 1 intact male, 23 spayed females, and 2 intact female dogs. The right eye was affected in 33 cases, and the left eye in 18 cases. The average total joules, which was administered with the diode laser, was 109.6 +/- 23.6 J. Immediate surgical complications included fibrin formation in the anterior chamber (15), corneal ulcers (4), hyphema (7), and focal retinal detachment (1). Long-term complications included cataract formation (8 total, 2 of which were significant, vision-threatening), elevated intraocular pressure (IOP) (6), unstable gonioimplant (1), and glaucoma recurrence (14). Additional surgeries performed on the eyes over the course of study included: intrascleral prosthesis (4), enucleation (1), resection of fibrotic scar tissue (5), and repeat laser cycloablation (8). The dogs were examined for a mean follow-up time of 17.6 months (range: 2-83 months postoperatively). Twenty-nine cases were followed greater than one year. Vision was maintained in 42/51 eyes (82%) in the immediate short-term of this study. In all cases included in the study, good control of IOP was achieved in 39/51 (76%) of eyes, and IOP was poor or uncontrolled in 12/51 (24%) of eyes. Twenty out of 41 eyes (49%) maintained fair to excellent vision six months after surgery. Twelve months postoperative observations demonstrated that 12/29 (41%) of the eyes were still visual. CONCLUSIONS: In primary glaucoma, the combined procedure of laser diode cyclophotocoagulation and Ahmed valve implant was associated with return or maintenance of vision in 42/51 eyes (82%) in the immediate short-term of this study, and a long-term IOP control in 39/51 (76%) of the cases, with 12/29 eyes (41%) visual after 12 months.     

Leaf-litter decomposition of 15 tree species in a lowland tropical rain forest in Sarawak: dynamics of carbon,nutrients, and organic constituents

The effects of tree species on the dynamics of nutrient transformations during leaf-litter decomposition are not well understood in tropical rain forests. To examine differences in the dynamics of C, nutrients, and organic constituents during decomposition among tree species, the leaf-litter decomposition of 15 trees was assessed using a litter-bag method in a lowland tropical rain forest in Sarawak. The dynamics of C was parallel to that of weight loss. The dynamics of nutrients were grouped into three patterns. The dynamics of K was characterized by a high leaching loss in the initial stages, and that of Ca and Mg generally showed a gradual decrease over the course of decomposition. The dynamics of N and P showed highly different patterns with the weight loss, and was characterized by relatively higher remaining mass at the end of the experiment. The variations or exceptions of nutrient dynamics among tree species were considered to be related to the initial concentration of each nutrient. For the dynamics of organic constituents, water-soluble carbohydrates disappeared quickly at the initial stages, and acid-soluble carbohydrates were the second fastest decomposing fraction; the decomposition of acid-insoluble residue (AIS) was the slowest. The release of limiting nutrients (N and P) generally followed the disappearance of AIS, but was independent of the disappearance of AIS when the initial concentrations of these nutrients were very low.     

Animal models for human metapneumovirus (HMPV) infections

Since its detection in 2001 the human Metapneumovirus (HMPV), a member of the Paramyxoviridae family, was observed to be a serious pathogen in human respiratory infections during childhood. Meanwhile, several animal models have been established to study the virus-host interactions and pathogenic effects. Mainly, small laboratory animals like mice and cotton rats have been used, although the usage of these two species for HMPV research is controversially discussed and contradictious results were obtained by different groups. Further trials with ferrets, hamsters and non human primates were performed revealing different success in their individual usage. In this review we present the different animal models, summarize their advantages and disadvantages, and discuss the controversial results from different studies.