北方寒地中华金叶榆扦插育苗快速繁殖技术研究

中华金叶榆是目前我国北方高寒地区景观园林中使用量最大的一种彩叶树。现主要存在苗木繁殖速度慢,育苗成本高,苗木质量不高等问题。本文综述了北方寒地扦插育苗快速繁殖中华金叶榆的简易技术和方法,为高寒地区繁殖和生产中华金叶榆苗木提供技术指导和参考。     

Does a “survival-by-exporting” effect for SMEs exist?

The trade literature has long discussed the existence of some benefits attributed to exporting (learning-by-exporting), among others, the improvement in survival chances. This paper examines whether exporting SMEs enjoy better survival prospects than non-exporting SMEs. We investigate the determinants of survival of exporting and non-exporting SMEs and explore whether the exporting behaviour plays a significant role in explaining their probability of exit. For this purpose, we estimate discrete time proportional hazard models that account for unobserved individual heterogeneity. The dataset is a sample of Spanish manufacturing SMEs drawn from the Encuesta sobre Estrategias Empresariales (ESEE) for 1990–2002. After controlling for firm, industry and economy characteristics, we find evidence supporting the existence of a sizeable “surviving-by-exporting” effect. That is, exporting SMEs face a significantly lower probability of failure than non-exporters.     

Initial Financial Conditions,Unobserved Heterogeneity and the Survival of Nascent Canadian Manufacturing Firms

The firm dynamics literature has stressed productivity, size, and age effects in firm duration. Understanding the implications of financial state has largely been unexplored because of the lack of quality data on private entrant firms. This paper investigates the role of start‐up financial conditions (debt‐to‐asset ratio) on the duration of entrant manufacturing firms using a unique administrative firm‐level database called T2LEAP. The debt‐to‐asset ratio has an economically and statistically significant effect on firm hazard after controlling for usual covariates and unobserved heterogeneity. Further, a non‐monotonic relationship between firm hazard and leverage appears. Firm hazard varies positively with leverage for firms in the top two leverage quintiles, whereas hazard rates fall with leverage in the lower quintiles. Copyright © 2011 John Wiley & Sons, Ltd.     

中国新型城镇化建设应通过产城融合来保障人的生存和发展

解决好人的生存和发展保障问题是以人为核心的新型城镇化的应有之义,传统城镇化出现“城市病”问题的根源在于人的发展对经济发展的让位。就业的实现和水平的提高在保障人的生存和发展中是根本性的、全面性的和可持续性的,推进产业与城市的融合发展可成为实现这一目标的突破点。文章认为,产城融合的新型城镇化建设必须在制度设计中植入和强化人的发展权理念;培育和扶持乡镇集体经济发展,推进农村社区建设和功能完善,创新农民主导的就地转移的新型城镇化模式;探索资源分配共享机制,促进城乡居民发展权的公平性与均衡性;优化城镇空间布局,在产业与城市的协调发展中增强人的发展的可持续性。     

复水奶粉中单增李斯特氏菌的生存评估

[目的]对复水奶粉中单增李斯特氏菌的生长与存活进行评估.[方法]通过人工方法以102cfu/mL的浓度添加单增李斯特氏菌于复水奶粉样品中,在不同温度和pH值条件下贮存,通过菌落计数分析单增李斯特氏菌的生存特性.[结果]在-1.5～37℃之间,单增李斯特氏菌能够生长,在-1.5℃时生长速率最慢,随温度升高生长速率也随之加快,在37℃时生长最快,在45℃时不能生长.在接近中性pH值范围内的复水奶粉中,单增李斯特氏菌在高温条件下(30℃)比在低温条件下(4℃)生长快,但在低温条件下(4℃),单增李斯特氏菌对酸和碱的耐受程度比在高温条件下(30℃)的耐受程度大.[结论]由于复水奶粉的pH值接近中性,比较适合单增李斯特氏菌的生长,如果污染了单增李斯特氏菌,在低温条件下贮存能够控制单增李斯特氏菌的生长.     

Defending Gibrat’s Law as a long-run regularity

According to Gibrat’s Law of Proportionate Effect, the growth rate of a given firm is independent of its size at the beginning of the period examined. While earlier studies tended to confirm the Law, more recent research generally rejects it. This article reconciles these two streams of literature, taking into account the role of market selection and learning in reshaping a given population of firms through time. Consistently with previous studies, we find that Gibrat’s Law has to be rejected ex ante, since smaller firms tend to grow faster than their larger counterparts. However, a significant convergence toward Gibrat-like behavior can be detected ex post. This finding is an indication that market selection “cleans” the original population of firms, so that the resulting industrial “core” does not depart from a Gibrat-like pattern of growth. From a theoretical point of view, this result is consistent with those models based on passive and active learning, and can be seen as a defense of the validity of the Law in the long-run.

Credit Events and the Valuation of Credit Derivatives of Basket Type

Thispaper provides a simple model for valuing a credit derivativewhose payoff depends on the identity (or identities) of the first(or first two) to occur of a given list of credit events, suchas defaults. The joint survival probability of occurrence timesof credit events is formulated in terms of stochastic intensityprocesses under the assumption of conditional independence. Basedon the joint survival probability, we can easily obtain the pricingformulas of such credit derivatives under the risk-neutral valuationframework. When the default intensity processes follow the extendedVasicek model, closed-form solutions of the pricing formulasare given.     

多株高糖面包酵母生理特性比较

高糖面包酵母作为微生物发酵剂和疏松剂,主要用于面包、甜馒头等高糖发酵类食品的生产。目前,我国销售的高糖酵母生理特性差异很大,为了节约生产成本、提高面包产品质量,本实验通过测定4种市售高糖面包酵母的冷冻存活率、蔗糖酶活力、耐糖性以及高糖发酵力,来了解各品牌酵母的功能特性,筛选出各项指标均较为优秀的市售高糖面包酵母。实验表明,安琪高糖酵母在冷冻4周后,存活率相对较高,适合冷冻或者冷藏面团使用,法国燕子的耐糖性与发酵力最为突出,梅山高糖的蔗糖酶活力较高。     

Performance of methods to conduct mediation analysis with time-to-event outcomes

Previous studies have discouraged the use of the Cox proportional hazards (PH) model for traditional mediation analysis as it might provide biased results. Accelerated failure time (AFT) models have been proposed as an alternative for Cox PH models. In addition, the use of the potential outcomes framework has been proposed for mediation models with time-to-event outcomes. The aim of this paper is to investigate the performance of traditional mediation analysis and potential outcomes mediation analysis based on both the Cox PH and the AFT model. This is done by means of a Monte Carlo simulation study and the illustration of the methods using an empirical data set. Both the product-of-coefficients method of the traditional mediation analysis and the potential outcomes framework yield unbiased estimates with respect to their own underlying indirect effect value for simple mediation models with a time-to-event outcome and estimated based on Cox PH or AFT.