中国木材进口趋势详解

木材行业是中国重要的基础产业,随着国民经济和人民水平生活水平的不断提高,对木材需求量快速上升,然而中国对天然林资源的使用,实行的是禁伐和限伐,因此国内木材供应量远远满足不了国内需求.作为目前世界上最主要的木业加工、生产及出口国,中国是全球最大的木材进口国之一.笔者通过详解近几年中国木材进口数据,原木及锯材的进口情况,从...     

Multi‐core scalable and efficient pathfinding with Parallel Ripple Search

Game developers are often faced with very demanding requirements on huge numbers of agents moving naturally through increasingly large and detailed virtual worlds. With the advent of multi‐core architectures, new approaches to accelerate expensive pathfinding operations are worth being investigated. Traditional single‐processor pathfinding strategies, such as A^* and its derivatives, have been long praised for their flexibility. We implemented several parallel versions of such algorithms to analyze their intrinsic behavior, concluding that they have a large overhead, yield far from optimal paths, do not scale up to many cores or are cache unfriendly. In this article, we propose Parallel Ripple Search, a novel parallel pathfinding algorithm that largely solves these limitations. It utilizes a high‐level graph to assign local search areas to CPU cores at “equidistant” intervals. These cores then use A^* flooding behavior to expand towards each other, yielding good “guesstimate points” at border touch on. The process does not rely on expensive parallel programming synchronization locks but instead relies on the opportunistic use of node collisions among cooperating cores, exploiting the multi‐core's shared memory architecture. As a result, all cores effectively run at full speed until enough way‐points are found. We show that this approach is a fast, practical and scalable solution and that it flexibly handles dynamic obstacles in a natural way. Copyright © 2012 John Wiley & Sons, Ltd.     

Development of species sensitivity distributions for wildlife using interspecies toxicity correlation models

Species sensitivity distributions (SSD) are probability distributions of chemical toxicity of multiple species and have had limited application in wildlife risk assessment because of relatively small data sets of wildlife toxicity values. Interspecies correlation estimation (ICE) models predict the acute toxicity to untested taxa from known toxicity of a single surrogate species. ICE models were used to predict toxicity values to wildlife species and generate SSDs for 23 chemicals using four avian surrogates. The hazard levels associated with the fifth percentile of the distribution (HD5) were compared for ICE SSDs and independent SSDs created with measured data. SSDs were composed of either avian only or avian and mammalian taxa. ICE HD5s were within 5-fold of 90% of measured HD5s and were generally higher than measured HD5s. The first percentile of the distribution (HD1) and the fifth percentile of the lower confidence limit (HDL) of ICE SSDs produced values that were not significantly different from measured HD5s. Using a bird surrogate to predicttoxicity to birds and the Norway rat to predict toxicity to mammals improved some estimates of ICE HD5s compared with those generated using only bird surrogates. These results indicate that ICE models can be used to generate SSDs comparable to those derived from measured wildlife toxicity data and provide robust estimates of the HD5.     

汽车照明系统的设计及超精密自由曲面加工技术

随着汽车产业的高速发展和市场的激烈竞争,现代汽车照明系统对发光效率、安全性能、以及美观的要求也越来越高。汽车照明中的自由曲面反射镜及LED照明系统的设计和加工是至关重要的。有别于传统光学系统的设计,汽车照明系统的非成像光学的设计是个多学科、复杂的过程。设计结果的好坏直接影响到照明系统的发光效率、能耗、以及汽车的安全性能。随着光学系统设计和超精密加工技术的进步,越来越多的光学元件采用了非球面以及自由曲面,汽车照明系统的效率以及性能得以极大的提高。本文阐述了汽车照明的非成像光学系统的设计和超精密加工技术。     

Genotype and environment effects on nitrate accumulation in a diversity set of lettuce accessions at commercial maturity: the influence of nitrate uptake and assimilation, osmotic interactions and shoot weight and development

BACKGROUND: The causes of the natural variation in nitrate accumulation and associated traits are studied using a diverse population of 48 mature lettuce accessions grown hydroponically in winter and summer seasons. Information on the effects of genotype, environment and their interactions will inform future selection strategies for the production of low‐nitrate varieties more suited to meeting EU requirements for harvested produce. RESULTS: The effects of genotype (G), environment (E) and G × E interactions were all significant, with nitrate concentrations lower but covering a wider range in summer. Concentrations of nitrate‐N were positively correlated with those of water and total‐N and negatively with assimilated‐C in the shoot in both seasons, with all relationships partitioned according to morphotype and/or seasonal type. Corresponding relationships between nitrate‐N and assimilated‐N or with shoot fresh or dry weight were generally weak or inconsistent. Nitrate concentrations at an early growth stage were strongly related to those at maturity in winter, but not in summer when light levels were less variable. CONCLUSION: The effects of genotype and environment on nitrate accumulation in lettuce are strongly influenced by morphotype, with most G × E interactions between accessions within the same morphotype predominantly of the non‐crossover type. All low‐nitrate‐accumulating genotypes have increased concentrations of organic solutes (concentration regulation) and reduced water (volume regulation) to help stabilise osmotic potential within the shoots. Variability in nitrate accumulation arises more from differences in uptake than in efficiency of its chemical reduction. Genotypic differences in nitrate accumulation can be masked by changes in head morphology during maturation, provided that they are not confounded by substantial changes in intercepted light. Recent selection strategies do not appear to have produced lower‐nitrate‐accumulating cultivars. Copyright © 2011 Society of Chemical Industry     

Moderators of the relation between substance use level and problems: Test of a self-regulation model in middle adolescence.

The authors tested predictions, derived from a self-regulation model, about variables moderating the relationship between level of substance use (tobacco, alcohol, and marijuana) and problems associated with use. Data were from two independent studies of adolescents, with mean ages of 15.4 and 15.5 years (Ns=1,699 and 1,225). Factor analysis indicated correlated dimensions of control problems and conduct problems. Protective moderation was found for variables indexing good self-control; risk-enhancing moderation was found for variables indexing poor self-control. These effects were generally independent of deviance-prone attitudes and externalizing symptomatology. Multiple-group structural modeling indicated moderation occurred for paths from life stress and coping motives and for paths from level to control and conduct problems. Moderation effects were also found for parental variables, peer variables, and academic competence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Successful treatment of transient acquired factor X deficiency by plasmapheresis with concomitant intravenous immunoglobulin and steroid therapy

Many nontropical rodent species display seasonal changes in reproductive physiology and metabolism, as well as in immune function. Field studies of seasonal changes in immune function typically report decreased immune function in the short days of winter compared to summer; presumably, reduced immunity in winter reflects increased glucocorticoid secretion in response to environmental stressors. In contrast, laboratory studies of photoperiodic changes in immunity invariably demonstrate increased immune function in short compared to long days. Although the precise mechanisms regulating short-day enhancement of immune function are not known, it is hypothesized that increased immunity is due to the increased duration of melatonin secretion in short compared to long days. However, melatonin can act both directly (i.e, via melatonin receptors located on lymphatic tissue) and indirectly (i.e., via alterations in gonadal steroids) to affect immune function. The present study examined the effects of exogenous melatonin administration on both cell-mediated and humoral immune function in adult male deer mice (Peromyscus maniculatus), as well as the role of gonadal steroid hormones in mediating these effects. Mice either were castrated to remove circulating androgens or received sham operations and were implanted with empty capsules or capsules containing melatonin. Individual mice implanted with melatonin underwent reproductive regression and displayed enhanced splenocyte proliferation to the T-cell mitogen concanavalin A; antigen-specific serum immunoglobulin M production was unaffected by melatonin treatment. Castration had no effect on either cell-mediated or humoral immune function. Taken together, these results suggest that exogenous melatonin enhances cell-mediated, but not humoral, immune function in adult male deer mice and that this effect is independent of gonadal steroid hormones. These results are consistent with a direct effect of melatonin on immunity.