排序方式: 共有42条查询结果,搜索用时 15 毫秒
1.
Today science policy makers in many countries worry about a brain drain, i.e., about permanently losing their best scientists
to other countries. However, such a brain drain has proven to be difficult to measure. This article reports a test of bibliometric
methods that could possibly be used to study the brain drain on the micro-level. An investigation of elite mobility must solve
the three methodological problems of delineating a specialty, identifying a specialty's elite and identifying international
mobility and migration. The first two problems were preliminarily solved by combining participant lists from elite conferences
(Gordon conferences) and citation data. Mobility was measured by using the address information of publication databases. The
delineation of specialties has been identified as the crucial problem in studying elite mobility on the micro- level. Policy
concerns of a brain drain were confirmed by measuring the mobility of the biomedical Angiotensin specialty.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
Sonja Kübelbeck Jules Mikhael Sebastian Schoof Annette Andrieu‐Brunsen Grit Baier 《应用聚合物科学杂志》2017,134(27)
Herein, we report the formation of α‐amylase containing polyelectrolyte complexes (PECs). The method for the encapsulation of α‐amylase is based on interactions between two oppositely charged polyelectrolytes, poly(acrylic acid) (PAA) and polyethylenimine (PEI). We could show that electrostatic interactions ensure the incorporation of the enzyme into the formed polyelectrolyte complexes. The encapsulation has no negative effect on enzyme activity and protects against denaturation of the enzyme initiated by low pH values. The resulting PECs are 150–250 nm in size with narrow size distribution, appear in a spherical shape and are colloidally stable. The complexation of both polyelectrolytes and the immobilization of α‐amylase are investigated using fractionating techniques mainly the analytical ultracentrifugation and asymmetrical‐flow field‐flow fractionation. The formation of PECs represents a simple method for the encapsulation of α‐amylase without the use of organic solvents and requires no additional purifications steps. This one‐step approach, yielding high encapsulation efficiencies, shows the potential as a drug delivery system for sensitive hydrophilic actives in future. α‐amylase is immobilized in polyelectrolyte complexes made of polyethylenimine and poly(acrylic acid). Optimized encapsulation conditions and the resulting polyelectrolyte complexes are investigated via determination of IEP, α‐amylase activity assays, nanoDSC measurements, zeta potential values, dynamic light scattering, microscopy, and fractionating techniques. The encapsulated enzyme is protected against denaturation initiated by low pH values. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45036. 相似文献
3.
4.
In this paper, we present an optimisation model for the energy-efficient planning of future wireless networks. By applying robust optimisation, we extend this model to a robust formulation which considers demand uncertainties. The computability of the resulting model is moderate. Hence, we apply three different cutting plane approaches for an improvement. Furthermore, an extensive case study is performed to examine the price of robustness, to compare the robust solution to conventional planning, and to explore the performance of the cutting planes. 相似文献
5.
This article discusses the methodological problems of integrating scientometric methods into a qualitative study. Integrative
attempts of this kind are poorly supported by the methodologies of both the sociology of science and scientometrics. Therefore
it was necessary to develop a project-specific methodological approach that linked scientometric methods to theoretical considerations.
The methodological approach is presented and used to discuss general methodological problems concerning the relation between
(qualitative) theory and scientometric methods. This discussion enables some conclusions to be drawn as to the relations that
exist between scientometrics and the sociology of science.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
Hildebrandt Andrea; Sommer Werner; Herzmann Grit; Wilhelm Oliver 《Canadian Metallurgical Quarterly》2010,25(4):794
Perceiving and memorizing faces swiftly and correctly are important social competencies. The organization of these interpersonal abilities and how they change across the life span are still poorly understood. We investigated changes in the mean and covariance structure of face cognition abilities across the adult life span. A sample of 448 participants, with age ranging from 18 to 88 years, completed a battery of 15 face cognition tasks. After establishing a measurement model of face cognition that distinguishes between face perception, face memory, and the speed of face cognition, we used multiple group models and age-weighted measurement models to explore age-related changes. The modeling showed that the loadings and intercepts of all measures are age invariant. The factor means showed substantial decrements with increasing age. Age-related decrements in performance were strongest for the speed of face cognition but were also salient for face perception and face memory. The onset of age decrements is apparent in the 60s for face perception, in the late 40s for face memory, and in the early 30s for speed of face cognition. Implications of these findings on a theoretical and methodological level are discussed, and potential consequences for applied settings are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
This paper discusses our efforts in implementing a divide and conquer algorithm (adaptive quadrature) on the HEP computer system. The one PEM HEP system performs in a MIMD fashion by pipelining execution of instructions from different processes. Unlike most divide and conquer approaches, our strategy ensures that the program will never deadlock due to memory expansion or spawning too many processes. Within this constraint we develop and analyse two different implementations: one using a static number of processes and the other a dynamic number of processes. Our results examine the relative performance of these two schemes. In addition we briefly discuss some of our impressions concerning some ‘myths of parallel programming’. 相似文献
8.
Grit Walther Jenny Steinborn Thomas Stefan Spengler Tobias Luger Christoph Herrmann 《The International Journal of Advanced Manufacturing Technology》2010,47(5-8):461-474
Reducing the quantity of waste for disposal and saving natural resources were main drivers for the introduction of the European Directive on waste electrical and electronic equipment (WEEE-directive). This policy focused on an extension of the producer responsibility (EPR) to the end-of-life-phase of their products. Because of the EPR concept, the national transposition of the WEEE-directive, especially the German transposition in the law ElektroG, caused changes in the organisation and material flows that are sometimes not in line with the aim of the directive, which is to enforce the waste management premise “avoidance prior recycling prior disposal”. Thus, the objective of this contribution is to analyse and compare the situation before and after implementation of the ElektroG in Germany, and deduce improvement potentials. Therefore, a co-operation of a municipality and a nearby disassembly company in Germany is analysed and evaluated, taking into account material flows and costs before/after implementation of the ElektroG, as well as degrees of freedom. Based on this analysis, recommendations are deduced for political decision makers and actors of the WEEE treatment system. 相似文献
9.