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181.
随着社会经济的发展及人们环保意识的不断增强,公共交通事业的发展及其投资力度不断加大,公共交通在给人们带来方便的同时也在带动着经济的发展.通过扩展的生产函数模型,采用普通最小二乘方法对2003-2012年间的公共交通数据进行估计分析,并找出有异常值的样本点,然后利用稳健MM估计方法进行估计,结果表明公共交通变量对经济的影响具有正相关作用. 相似文献
182.
The transient recoverable deformation ratio after melt elongation at various elongational rates and maximum elongations was
investigated for pure polystyrene and for a 85 wt.% polystyrene/15 wt.% linear low density polyethylene (PS/LLDPE 85:15) blend
at a temperature of 170 oC. The ratio p of the zero shear rate viscosity of LLDPE to that of PS is p = 0.059 ≈ 1:17. Retraction of the elongated LLDPE droplets back to spheres and end-pinching is observed during recovery.
A simple additive rule is applied in order to extract the contribution of the recovery of the elongated droplets from the
total recovery of the blend. In that way, the recoverable portion of the PS/LLDPE blend induced by the interfacial tension
is determined and compared with the results of a theory based on an effective medium approximation. The effective medium approximation
reproduces well the time scale of the experimental data. In addition, the trends that the recoverable deformation increases
with elongational rate and maximum elongation are captured by the theoretical approach. 相似文献
183.
Regime diagram of the development of long-wave near-wall disturbances in a hypersonic boundary layer
A regime diagram of the development of slow near-wall disturbances induced by an unsteady self-induced pressure perturbation in a hypersonic boundary layer is constructed for a disturbance wavelength greater than the boundary layer thickness. It is shown that the main factors shaping the perturbed flow are the gas enthalpy near the body surface, the intensity of the viscous-inviscid interaction, and the nature (sub- or supersonic) of the main part of the boundary layer. Nonlinear boundary-value problems are formulated for regimes in which the near-wall boundary layer region plays a decisive role. Numerical and analytical solutions are obtained in the linear approximation. It is shown that intensification of the viscous-inviscid interaction or an increase in the role of the supersonic main region of the boundary layer impart generally supersonic properties to the main part of the boundary layer, i.e. the upstream propagation of the disturbances is damped and the disturbance growth downstream becomes more intense. Damping of the viscous-inviscid interaction and an increase in the role of the subsonic main part of the boundary layer have the opposite effect. Surface cooling increases the effect of the main part of the boundary layer on the formation of pressure disturbances and surface heating leads to an increase in the effect of the near-wall boundary layer region. It is also shown that for the regimes considered disturbances propagate in a direction opposite to that of the free stream from the turbulent flow region located downstream of the local disturbance development region.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, 2004, pp. 59–71. Original Russian Text Copyright © 2004 by Bogolepov and Neiland. 相似文献
184.
本文首先对国家自然科学基金在1986-1991年间资助摩擦学基础研究的情况进行了简洁的分析,接着就其资助办法作了介绍,最后着重对如何利用科学基金促进摩擦学的发展问题作了讨论,指出应当把坚持应用摩擦学学科发展战略的研究成果、鼓励和支持创新性研究、积极支持交叉学科研究和注意扶植新的学科生长点、加强摩擦学研究与实际应用相结合和促进优秀青年摩擦学研究人才的迅速成长等作为国家自然科学基金资助摩擦学基础研究的 相似文献
185.
Tomoko KANEKO-ISHINO Fumitoshi ISHINO 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2015,91(10):511-538
Mammals, including human beings, have evolved a unique viviparous reproductive system and a highly developed central nervous system. How did these unique characteristics emerge in mammalian evolution, and what kinds of changes did occur in the mammalian genomes as evolution proceeded? A key conceptual term in approaching these issues is “mammalian-specific genomic functions”, a concept covering both mammalian-specific epigenetics and genetics. Genomic imprinting and LTR retrotransposon-derived genes are reviewed as the representative, mammalian-specific genomic functions that are essential not only for the current mammalian developmental system, but also mammalian evolution itself. First, the essential roles of genomic imprinting in mammalian development, especially related to viviparous reproduction via placental function, as well as the emergence of genomic imprinting in mammalian evolution, are discussed. Second, we introduce the novel concept of “mammalian-specific traits generated by mammalian-specific genes from LTR retrotransposons”, based on the finding that LTR retrotransposons served as a critical driving force in the mammalian evolution via generating mammalian-specific genes. 相似文献
186.
Assessing the Ability of an Online Environment to Facilitate the Critical Features of Teacher Professional Development 下载免费PDF全文
Providing teachers effective professional development (PD) is an ongoing challenge in the field of education. Emergence of technological innovations in the form of computer‐based asynchronous and synchronous communication has provided new opportunities to improve and expand teacher PD opportunities beyond the physical walls of a school. The purpose of this meta‐analysis is to examine the ability of online learning environments to facilitate the critical features of teacher PD identified in Desimone (2009) as content focus, active learning, coherence, duration, and collective participation. Analysis of the 20 empirical studies sought to reveal the purpose of the study, methodologies utilized, and major findings. Multiple studies indicated the ability of an online environment to engage teachers in active learning, collective participation, and content‐focused learning activities. Additionally, the results of this meta‐analysis revealed a lack of empirical studies that have examined the ability of online teacher PD to support the critical features of coherence and duration. Findings of this research have implications for a future research agenda and policy considerations related to online teacher PD initiatives. 相似文献
187.
Next Generation Science Standards (NGSS) science and engineering practices are ways of eliciting the reasoning and applying foundational ideas in science. As research has revealed barriers to states and schools adopting the NGSS, this mixed‐methods study attempts to identify characteristics of professional development (PD) that will support NGSS adoption and to improve teacher readiness. In‐service science teachers from across the nation were targeted for the survey and responses represented 38 states. Research questions included: How motivated and prepared are in‐service 7–12 teachers to use NGSS science and engineering practices? What is the profile of 7–12 in‐service teachers who are motivated and feel prepared to use NGSS science and engineering practices? The study revealed that teachers identified engineering most frequently as a PD need to improve their NGSS readiness. High school teachers rated themselves as more prepared than middle school and all teachers who use Modeling Instruction expressed higher NGSS readiness. These findings and their specificity contribute to current knowledge, and can be utilized by districts in selecting PD to support teachers in preparing to implement the NGSS successfully. 相似文献
188.
The Effects of a Mathematics Infusion Curriculum on Middle School Student Mathematics Achievement 下载免费PDF全文
M. David Burghardt James Lauckhardt Maria Kennedy Deborah Hecht Luisa McHugh 《School science and mathematics》2015,115(5):204-215
Increasing mathematical competencies of American students has been a focus for educators, researchers, and policy makers alike. One purported approach to increase student learning is through connecting mathematics and science curricula. Yet there is a lack of research examining the impact of making these connections. The Mathematics Infusion into Science Project, funded by the National Science Foundation, developed a middle school mathematics‐infused science curriculum. Twenty teachers utilized this curriculum with over 1,200 students. The current research evaluated the effects of this curriculum on students' mathematics learning and compared effects to students who did not receive the curriculum. Students who were taught the infusion curriculum showed a significant increase in mathematical content scores when compared with the control students. 相似文献
189.
Here, we present a fast and simple hydrogen peroxide assay that is based on time-resolved fluorescence. The emission intensity of a complex consisting of terbium ions (Tb3+) and phthalic acid (PA) in HEPES buffer is quenched in the presence of H2O2 and this quenching is concentration-dependent. The novel PATb assay detects hydrogen peroxide at a pH range from 7.5 to 8.5 and with a detection limit of 150 nmol L−1 at pH 8.5. The total assay time is less than 1 min. The linear range of the assay can be adapted by a pH adjustment of the aqueous buffer and covers a concentration range from 310 nmol L−1 to 2.56 mmol L−1 in total which encompasses four orders of magnitude. The assay is compatible with high concentrations of all 47 tested inorganic and organic compounds. The PATb assay was applied to quantify H2O2 in polluted river water samples. In conclusion, this fast and easy-to-use assay detects H2O2 with high sensitivity and precision. 相似文献
190.
Bhagwat PrasadAmit Garg Hardik TakwaniSaranjit Singh 《Trends in analytical chemistry : TRAC》2011,30(2):360-387
Metabolite identification (Met ID) is important during the early stages of drug discovery and development, as the metabolic products may be pharmacologically active or toxic in nature. Liquid chromatography-mass spectrometry (LC-MS) has a towering role in metabolism research.This review discusses current approaches and recent advances in using LC-MS for Met ID. We critically assess and compare various mass spectrometers, highlighting their strengths and limitations. Citing appropriate examples, we cover recent LC and ion sources, isotopic-pattern matching, hydrogen/deuterium-exchange MS, data dependent analyses, MSE, mass defect filter, 2D and 3D approaches for the elucidation of molecular formula, polarity switching, and background-subtraction and noise-reduction algorithms. A flow chart outlines a comprehensive strategy for Met ID, including a focus on reactive metabolites. 相似文献