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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.
R. Maciel Filho C. B. Batistella P. Sbaite A. Winter C. J. G. Vasconcelos M. R. Wolf Maciel A. Gomes L. Medina R. Kunert 《Petroleum Science and Technology》2006,24(3):275-283
The term atmospheric residue describes the material at the bottom of the atmospheric distillation tower having a lower boiling point limit of about 340°C; the term vacuum residue (heavy petroleum fractions) refers to the bottom of the vacuum distillation, which has an atmospheric equivalent boiling point (AEBP) above 540°C. In this work, the objective is to evaluate the behavior of different kinds of Brazilian atmospheric and vacuum residues using molecular distillation. The Falling Film Molecular Distillator was used. For the results obtained through this process, a significant range of temperature can be explored avoiding the thermal decomposition of the material. So these results are very important to the refinery decisions and improvements. The Experimental Factorial Design results showed that the temperature has more influence on the process than the feed flow rate, when a higher percentage of distillate is required. 相似文献
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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
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Gerd Kunert 《Computing》2002,69(3):265-272
This paper considers a singularly perturbed reaction diffusion problem. It is investigated whether adaptive approaches are
successful to design robust solution procedures. A key ingredient is the a posteriori error estimator. Since robust and mathematically analysed error estimation is possible in the energy norm, the focus is on this choice of norm and its implications. The numerical performance for several model problems confirms
that the proposed adaptive algorithm (in conjunction with an energy norm error estimator) produces optimal results. Hence
the energy norm is suitable for the purpose considered here. The investigations also provide valuable justification for forthcoming
research.
Received October 25, 2001; revised July 12, 2002 Published online: October 24, 2002 相似文献
8.
An efficient sequential optimization approach for complex computer models was presented by Jones et al. (1998). After fitting a stochastic process model based on an initial space filling design, this model is sequentially refined by the expected improvement criterion. This criterion balances the need to search in areas in the design space where the prediction is optimal with the need to search where the model uncertainty is high. This approach can easily be extended to physical processes. Since in practice the overall quality of products of production processes is assessed by more than one response, a multivariate version of the expected improvement criterion is proposed based on desirability functions. This criterion is then used to optimize a metal spinning process. 相似文献
9.
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
10.
Investigations of tantalum coatings on steel by vacuum plasma spraying In this work the possibilities of the production of tantalum coatings by vacuum plasma spraying were investigated. Suitable parameters of the vacuum plasma spraying process were determined, and the quality of vacuum plasma sprayed tantalum coatings was evaluated with regard to chemical composition, adhesion strength, density and corrosion behaviour. To obtain high-quality coatings it was necessary to apply sufficient plasma power as well as an optimal injection of spraying powder into the plasma torch. A complete melting of the tantalum powder particles could not he achieved. The coatings obtained showed a good adhesion strength but a low formability (ductility). The corrosion resistance against HCL and HNO3 was evaluated by curves of the current density versus potential. With the aid of the passive current density it was determined that the corrosion resistance of the sprayed coatings was not as excellent as of compact tantalum. The increased surface roughness was not significant with respect to the corrosion behaviour. The reduced corrosion resistance could be caused probably by a high oxygen content of the tantalum powder, especially by oxides around individual powder particles. In contrast to tantalum, vacuum plasma sprayed titanium coatings showed the same corrosion resistance as compact titanium under the same testing conditions. 相似文献