检疫性有害生物--葡萄花翅小卷蛾

在国内首次提出了葡萄花翅小卷蛾Lobesia botrana(Denis&Schiffermüller)的鉴定依据,并提供该种害虫详细的形态特征、生物学特性以及危害特点等信息,以期使读者较全面地了解葡萄花翅小卷蛾的经济重要性,为进一步研究、检疫和防治该种害虫提供参考。     

怎样防治咬食果树叶片的害虫

一、危害特点 果树叶片和其他植物叶片一样，是进行光合作用、呼吸作用和蒸腾作用的重要器官，也是制造养分、新陈代谢和调节树体内温度水分的功能组织。但是，每年从发叶到落叶期间，特别是5月上旬至9月中旬，是咬食叶片害虫的盛发期。这些害虫主要包括：卷叶类（苹果叶蛾、大卷叶蛾、小卷叶蛾）；巢蛾、     

斯氏线虫感染双钩异翅长蠹的致死中量与致死中时间

测定斯氏线虫对进境原木上的检疫性害虫一双钩异翅长蠹的致死中量和致死中时间,旨在为大规模应用此线虫对双钩异翅长蠹检疫处理提供依据.将TDM模型引入试验结果的分析中,得出了双钩异翅长蠹幼虫和蛹的TDM模型以及LD50与LT50.72h后双钩异翅长蠢老龄幼虫的TDM模型为Pil=1-exp[-3.0514+2.02721g(di)];LD50为1.3244(条线虫/头);LT50为1.2385天.试验结果表明随着时间的延长,LD50都逐渐减少,是因为增加了斯氏线虫与双钩异翅长蠹接触的机会;随着线虫剂量的增加,LT50逐渐减少,幼虫死亡50%所需的时间就少.     

警惕木质包装携带双钩异翅长蠹入境

双钩异翅长蠹是热带和亚热带地区常见的重要林木害虫,寄主广、钻蛀能力强、食性杂、繁殖力极强,是我国禁止进境的检疫性有害生物。在国际贸易中广泛使用的木质包装,易成为双钩异翅长蠹等有害生物的跨境传播载体。本文通过进境木质包装检出双钩异翅长蠹实例以案说法,引导企业规范使用木质包装,避免外来有害生物通过木质包装传入我国。基本情况2021年8月,某企业向某海关申报进口一批来自M国的柚木木皮。海关关员在实施现场查验时,发现承托货物的木质包装未申报,且没有国际植物保护公约(以下简称"IPPC")专用标识,木质包装外表存在大量钻蛀性害虫留下的虫孔、虫粉等为害迹象。     

杨树常见病害的防治技术

阐述了杨树食叶害虫扬扇舟蛾、杨小舟蛾、杨黄卷叶螟、杨白潜蛾、黄刺蛾的发生特点和发生规律,并提出相应的防治方法.     

利用废烟草制农药

在农村，很多农户将不够等级、烟草公司不收购的废烟草当成柴火烧掉，这很可惜。因为废烟草里含有丰富的杀虫物质如烟碱、毒藜碱、原烟碱。烟草的叶、茎、叶筋、碎屑等，都可用作杀虫剂。在果树、茶树、蔬菜等农作物上施用可防治蚜虫、蓟马、椿象、菜青虫、潜叶蛾等害虫。     

小议杨树存在的主要虫害及其防治措施

随着杨树种植面积的逐年增加,由于树种单一、生物多样性降低,导致杨树病虫害的发生非常普遍,特别是杨舟蛾类、杨黄卷叶螟、杨白潜蛾等食叶害虫。根据杨树食叶害虫发生的特点,可采取多种切实可行的防治措施,均收到了良好的效果,保障了杨树的健康生长,促进了杨树产业的持续、稳定发展,生态效益和社会效益更加明显。为此,本文主要针对杨树主要害虫,如天牛、杨小舟蛾和草履蚧的危害特点,提出防治方法。     

Linux下逻辑卷管理的原理与实现

逻辑卷管理的做法是将几个物理的分区（或磁盘）通过软件组合成为一块看起来是独立的大磁盘（卷组）,然后将卷组再分成可使用分区逻辑卷,最终就能够挂载使用了。本文即阐述了逻辑卷管理的原理以及在Linux下逻辑卷管理的实现方法。     

船板市场走势分析

中厚板交易活跃价格有所反弹 进入二季度以来,国内热轧板卷、冷轧板卷、螺纹钢、线材等钢材价格普遍反弹．交易亦趋于活跃,贸易商心态稳定,从而带动中厚板市场价格回升,特别是普板、低合金板交易相对活跃,部分规格的普板、低合金板比较走俏。据统计,5月份国内主要城市16～20毫米Q235B普中板平均价格较4月份上涨250～300元,吨。本轮价格上涨主要基于市场心态的作用,由于中厚板市场持续疲软、低迷,价格下跌不止,到4月份已经基本到了底部。如普碳板的价格一度跌至3000—3100元／吨,价格甚至比螺纹钢价格还要低．且持续了相当长的时间,贸易商思涨心切。     

遗传算法在在线考试系统中的应用——以邮政系统知识竞赛为例

本文提出了遗传算法自动组卷策略,并将遗传算法自动组卷应用于在线知识竞赛系统中,最大程度地满足了用户的需求,具有科学性、合理性和较好的实用性.     

Federal Reserve and private forecasts of growth in investment

This study examines the Federal Reserve and private forecasts of growth in both business and residential investment for 1983-2004 and reaches four main conclusions: First, in support of the asymmetric information hypothesis, the shorter (longer) horizon Federal Reserve forecasts of growth in business (residential) investment contain useful predictive information beyond that included in private forecasts. Second, the Federal Reserve forecasts are all biased. The same is true for the private forecasts of growth in residential (but not entirely for the forecasts of growth in business) investment. Third, the private forecasts overall do better than those of the Federal Reserve in outperforming the univariate forecasts. Fourth, the Federal Reserve and private forecasts of growth in business (residential) investment, while directionally accurate, imply symmetric (asymmetric) loss. We conclude this study by discussing the usefulness of these forecasts.     

Forecast errors before and during the Great Moderation

This paper investigates the change in private sector and Federal Reserve forecasts before and during the Great Moderation. We view the Great Moderation as a natural experiment. Using forecasts produced by the Survey of Professional Forecasters and the Federal Reserve (Greenbook forecasts) we investigate three questions: (1) How large was the decline in forecast errors? (2) Did forecast accuracy improve relative to the decline in volatility of growth and inflation? (3) Did forecasters respond to the Great Moderation? We find that the absolute median error as well as the cross-sectional volatility of forecast errors decreased significantly. Forecasters appeared to have narrowed the dispersion of their forecasts in response to the Great Moderation. Forecast accuracy did not improve relative to the reduction in the volatility of the economy.     

When do cooperation and commitment matter in a monetary union?

This paper offers a framework to study strategic interactions between private players, national fiscal authorities and a common central bank in monetary unions. We establish general conditions, in terms of restrictions on spillover effects of actions by private and public players, under which games that differ in the degree of cooperation and commitment can admit the same equilibrium outcome. We use these conditions to characterize benchmark results on the irrelevance of cooperation and commitment established in recent literature. Moreover, we show for a general setting, in which the benchmark results do not apply, that gains from fiscal cooperation depend on the number of countries and increase as this number gets larger.     

Monetary policy and welfare in a small open economy

This paper analyzes optimal monetary policy in a small open economy featuring monopolistic competition and nominal rigidities. It shows that the utility-based loss function for this economy can be written as a quadratic expression of domestic inflation, output gap and real exchange rate. The presence of an internal monopolistic distortion and a terms of trade externality drives optimal policy away from domestic inflation targeting and affects the optimal level of exchange rate volatility. When domestic and foreign goods are close substitutes for each other, the optimal policy rule implies lower real exchange rate volatility than a domestic inflation targeting regime. The reverse is true when the elasticity of substitution between goods is low.     

Inflation targeting rules and welfare in an asymmetric currency area

This paper studies the effect on monetary policy of differing degrees of competition and differing degrees of nominal rigidity between the members of a monetary union. In particular, we assess the welfare loss brought about by the use of a simple interest rate rule that does not take into account such structural differences. Our results show that, ceteris paribus, to maximize welfare the central bank should react more strongly to inflation pressure generated by the more competitive economies. Our work extends the results of Benigno [Benigno, P., 2004. Optimal monetary policy in a currency area. Journal of International Economics 63, 293-320] by showing that, if the degree of competition differs between countries, the optimal rule could involve placing a greater weight on the more “flexible” countries. Our study suggests that the size of the welfare losses generated by failure to take account of these asymmetries depends crucially on the actual combination of the various asymmetries. As a consequence, we show that, if the optimal weights are chosen under incomplete information regarding the extent and type of asymmetries, the resulting level of welfare could be lower than that produced by the symmetric rule.     

The changing sensitivity of realized portfolio betas to U.S. output growth: An analysis based on real-time data

Our results shed light on the sensitivity of the betas of portfolios formed on market capitalization (“size”) and book-to-market value (“value”) to output growth in the United States. We estimate a state-space model to analyze the sensitivity of portfolio betas to output growth. We measure output growth using real-time and revised data. Output growth has a significant effect on portfolio betas when size and value are high. Such portfolio betas exhibit countercyclical dynamics. They are more sensitive, in absolute terms, to output growth when the latter is measured using real-time data. Their sensitivity to output growth has grown over time. Portfolio betas with respect to output growth have become smaller over time, in contrast, when size is large but value is low.     

It happened again: A Minskian analysis of the subprime loan crisis

The advanced countries are now going through the worst crisis since the Depression, but today's dominant current theories and econometric models proved unable to predict the crisis. The paper investigates whether the financial instability hypothesis of Hyman P. Minsky offers a better explanation. Minsky argued that in a period of economic growth and tranquility economic agents are more prone to take risk, and banks are more willing to finance borrowers. Meanwhile, in the course of the boom over-indebtedness and financial innovations make the financial system more fragile, and more exposed to adverse effects. We show that both these effects made themselves felt in the subprime loan crisis. Specifically, the main determinants of the crisis have been the increasing appetite for risk and financial innovations. So, we conclude that, although this crisis differs in some of its features from previous crashes and from Minsky's account, the mechanisms underscored by Minsky were and are nevertheless at work.     

Asymmetric shocks among U.S. states

The paper applies a factor model to the study of risk sharing among U.S. states. The factor model makes it possible to disentangle movements in output and consumption due to national, regional, or state-specific business cycles from those due to measurement error. The results of the paper suggest that some findings of the previous literature which indicate a substantial amount of inter-state risk sharing may be due to the presence of measurement error in output. When measurement error is properly taken into account, the evidence points towards a lack of inter-state smoothing.