中国食用豆出口贸易现状及其增长的影响因素

为促进中国食用豆出口贸易的发展提供政策参考,从出口的规模、结构和市场分布方面归纳分析2002—2013年中国食用豆出口贸易现状,并利用恒定市场份额模型分析中国食用豆出口增长的影响因素。结果表明:2002—2013年中国食用豆出口额保持快速增长,出口品种主要以芸豆、绿豆和赤豆为主,出口市场主要是亚洲和美洲地区,但整体的市场份额并未明显提高,食用豆的国际竞争力有所下降。市场需求是影响中国食用豆出口增长的重要因素,但其影响逐渐减弱;产品竞争力逐渐成为食用豆出口增长的关键因素,出口结构向有利于出口的方向转变,对食用豆出口增长的促进作用日趋显著。     

马蹄形无压隧洞恒定渐变流水面线计算的新解析法

对马蹄形无压隧洞的恒定非均匀流沿程水面线进行了深入研究,基于恒定渐变流基本微分方程,通过采用数值分析理论,得到流程S与始、末段水深h1、h2的解析函数,通过该函数可直接计算沿程水面线。该方法比《水工隧洞设计规范》中推荐的分段求和试算法更简单、便捷,特别对水深较敏感段,规范推荐试算法误差较大,并且逐段试算推求水深将导致末端断面水深误差逐步累积,导致误差大,精度下降。最后通过工程实例计算比较得出：新解析法计算成果与规范推荐法（程序）计算成果基本一致,甚至优于规范推荐的分段试算法,完全满足工程实践要求。     

羟丙基-β-环糊精包合甲氧苄啶的研究

为了研究甲氧苄啶(Trimethoprim,TMP)与羟丙基-β-环糊精(HP-β-CD)在水溶液中的包合作用、包合过程中的热力学参数变化及包合比,试验分别采用相溶解度法、等摩尔系列法、摩尔比率法测定了TMP与HP-β-CD的包合表观常数、包合过程的熵变、焓变、自由能变化及包合比。结果表明,在不同温度下,TMP与HP-β-CD在水溶液中均可形成1∶1摩尔比的包合物,相溶解度图呈A_L型;TMP与HP-β-CD的包合过程可自发进行(△G＜0),且为放热反应(△H＜0),同时也是熵值增大的过程(△S＞0);说明TMP与HP-β-CD在水溶液中均可自发形成1∶1摩尔比的包合物,从而增加其溶解度。选择适宜的包合温度将有利于包合过程的进行。     

Soil phosphorus and water effects on growth,nutrient and carbohydrate concentrations, δ<Superscript>13</Superscript>C,and nodulation of mimosa (<Emphasis Type="Italic">Albizia julibrissin</Emphasis> Durz.) on a highly weathered soil

Growth and physiological performance of multipurpose tree species can be severely constrained by low phosphorus (P) availability in highly weathered soils. Limitations to plant growth are accentuated by seasonal dry periods. The overall objective of this study was to examine P fertilization and irrigation effects on survival, growth, biomass partitioning, foliar nutrients, intrinsic water-use efficiency (WUE) indexed by δ¹³C, Rhizobium nodulation, and carbohydrate content as an indicator of resprouting potential, of mimosa (Albizia julibrissin Durz.), a N₂-fixing tree species being tested for browse in agroforestry practices in south-central USA. In a field experiment carried out during two growing seasons near Booneville, Arkansas, USA, mimosa had a strong growth response to irrigation. The trial was arranged in a split plot design with three replications with irrigation as main plot treatment and P as sub-plot treatment. Mean total plant aboveground biomass at the end of the second growing season was 9.8 and 44.1 g plant⁻¹ for the rainfed treatment without and with 300 mm of irrigation water, respectively. Placed P fertilization increased mean total aboveground biomass from 19 g plant⁻¹ for the 0-P treatment to 69 g plant⁻¹ for the treatment with 90 kg P ha⁻¹ year⁻¹. Similarly, irrigation consistently increased stem basal diameter, total height, survival, root, stem, foliar and total aboveground biomass, and number of nodules per plant. Phosphorus fertilization increased basal diameter, and root and stem biomass in both irrigation treatments, survival and nodulation in the rainfed treatment, and foliar and total aboveground biomass in the rainfed +300 mm irrigation treatment. There was a decrease of foliar δ¹³C suggesting that WUE decreased with P fertilization. In a pot experiment, seedlings were subjected to a factorial combination of two irrigation treatments and six P levels in a randomized complete block design. Irrigation increased basal diameter, root, stem, foliar and total biomass, leaf area and nodulation, whereas P fertilization (i.e., levels from 0 to 3.68 g P kg⁻¹ soil) had similar effect in all the above variables except foliar biomass. Foliar P concentration to obtain 90% of the maximum total plant biomass (critical level) was estimated at 0.157%. Total nonstructural and water soluble carbohydrate, and starch concentrations increased non-linearly with irrigation and P addition suggesting impaired re-growth potential after defoliation of seedlings with reduced water supply and at low soil P availability. Results of this study indicated strong limitations for growth and regrowth potential of mimosa on a highly weathered soil with very low P availability and seasonal water content shortages. Placed (i.e., near the plant base) application of P appeared to be a good strategy to fertilize perennial woody plants.     

Calculation of Constant Pressure Values for Relief Valves in the Fire Suppression Systems of High-Rise Buildings

The calculation of constant pressure values for relief valves in the fire suppression systems of high-rise buildings usually is based on the working pressure of pipe systems by experience.However,this method only is applied in the condition that the relief valves are installed on the effluent pipes of pumps.In order to confirm the proper constant pressure values of relief valves in fire suppression systems,a formula is deduced using hydraulics theory.The applications of the formula in fire suppression systems are also discussed.The constant pressure values for relief valves are directly related to three factors,namely,the flux and pressure of the fire pump,the located height of the relief valves,and the head loss of flux from the pump exit to the inlets of the relief valves.It is necessary to analyze the working condition of fire suppression systems and to be certain of the permissive pressure range for overpressure.     

祖国大陆对台湾农产品出口增长的影响因素分析

从分析影响因素出发,确定影响祖国大陆对台湾地区农产品出口额增长的主导因素,为促进两岸农产品贸易的发展提供决策依据,为加强双方在农产品贸易领域的合作提供政策建议。文章利用联合国粮农组织数据库、中国海关统计数据,运用恒定市场份额（CMS模型）分析方法,针对祖国大陆对台湾地区农产品出口增长的问题进行分析。结果表明：加入WTO后,祖国大陆对台湾地区农产品出口增长主要是受进口需求因素和出口竞争力因素的影响,而结构因素的影响则微不足道。通过分析,得出以下结论：增长的市场容量是祖国大陆对台湾地区农产品出口增长的一个重要因素,竞争力的下降导致出口增长不断减弱,祖国大陆对台湾地区市场未进行有效的开拓,两岸农产品贸易还有很大的增长潜力。     

中国胶合板贸易波动实证分析

运用恒定市场份额模型,从市场规模、市场分布、竞争力3方面探讨了1992-2006年中国胶合板出口大幅增长的成因.实证研究发现:竞争力的提高是中国胶合板出口增长的决定性因素;市场规模效应对出口的促进作用不明显,但有一定增长;市场分布效应一直阻碍着出口的扩大,这种负向效应有减小的趋势.     

小麦多品种混播对条锈病的控制及稳产作用研究

通过对6个不同抗性水平的小麦品种进行不同组合的混播,系统调查了各品种净作和多品种混播田小麦条锈病的病情发展动态。     

Changes in δC composition of soil carbonates driven by organic matter decomposition in a Mediterranean climate: A field incubation experiment

The current view on the relationship between the δ¹³C of pedogenic carbonates and soil organic matter is based on static studies, in which soil profiles are analysed at a given moment of their development. A dynamic approach to this question should also be possible by studying under field conditions how the δ¹³C of carbonates changes as organic matter decomposes. No such study has been undertaken owing to the slowness of the changes in the δ¹³C of carbonates, since it has been calculated that a detectable change will occur only after millenia. Nevertheless, this may not be true where soil CO₂ efflux is intense, as expected in soil zones with high microbial activity. In this paper we test the latter assumption by incubating mixtures of plant material and carbonate-rich red earth in the field at depths of 5, 20 and 40 cm. Four types of plant material were tested: Medicago sativa, Eucalyptus globulus, Quercus ilex and Pinus halepensis. Because the isotopic composition of these plant materials is known, we can determine the isotopic composition of the respired C and study how it relates to the (expected) changes in the δ¹³C. After two years of field incubation, the changes in δ¹³C of carbonates were high enough to be reliably detected and quantified, thus showing that the isotopic composition of soil carbonates can change quite rapidly in biologically active soil horizons. The observed changes are possible only if we assume that the increase in δ¹³C in the overall path respired C → pedogenic carbonate is much higher than the usually applied standard factors (about 15‰). These enrichments can be explained by assuming, as does the currently accepted paradigm, that the precipitation of new carbonates occurs in an open system in which the penetration of free-air CO₂ plays a major role. On the other hand, these enrichments can also be explained by an alternative interpretation, which assumes that the dissolution–precipitation carbonate cycles occur in systems that can be at least temporarily closed. Thus, we suggest that both possibilities (carbonate dissolution and precipitation in either an open or closed system) can coexist in a given soil, even though one or the other will dominate in any given time period.     

Isotopologue ratios of N2O emitted from microcosms with NH4 fertilized arable soils under conditions favoring nitrification

Soils represent the major source of the atmospheric greenhouse gas nitrous oxide (N₂O) and there is a need to better constrain the total global flux and the relative contribution of the microbial source processes. The aim of our study was to determine variability and control of the isotopic fingerprint of N₂O fluxes following NH₄⁺-fertilization and dominated by nitrification. We conducted a microcosm study with three arable soils fertilized with 0–140 mg NH₄⁺–N kg⁻¹. Fractions of N₂O derived from nitrification and denitrification were determined in parallel experiments using the ¹⁵N tracer and acetylene inhibition techniques or by comparison with unfertilized treatments. Soils were incubated for 3–10 days at low moisture (30–55% water-filled pore space) in order to establish conditions favoring nitrification. Dual isotope and isotopomer ratios of emitted N₂O were determined by mass spectrometric analysis of δ¹⁸O, average δ¹⁵N (δ¹⁵N^bulk) and ¹⁵N site preference (SP = difference in δ¹⁵N between the central and peripheral N positions of the asymmetric N₂O molecule). N₂O originated mainly from nitrification (>80%) in all treatments and the proportion of NH₄⁺ nitrified that was lost as N₂O ranged between 0.07 and 0.45%. δ¹⁸O and SP of N₂O fluxes ranged from 15 to 28.4‰ and from 13.9 to 29.8‰, respectively. These ranges overlapped with isotopic signatures of N₂O from denitrification reported previously. There was a negative correlation between SP and δ¹⁸O which is opposite to reported trends in N₂O from denitrification. Variation of average ¹⁵N signatures of N₂O (δ¹⁵N^bulk) did not supply process information, apparently because a strong shift in precursor signatures masked process-specific effects on δ¹⁵N^bulk. Maximum SP of total N₂O fluxes and of nitrification fluxes was close to reported SP of N₂O from NH₄⁺ or NH₂OH conversion by autotrophic nitrifiers, suggesting that SP close to 30‰ is typical for autotrophic nitrification in soils following NH₄⁺-fertilization. The results suggest that the δ¹⁸O/SP fingerprint of N₂O might be used as a new indicator of the dominant source process of N₂O fluxes in soils.