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Critical Impact (critical + impact)

Distribution by Scientific Domains

Business, Economics, Finance and Accounting	40%

Selected Abstracts

Astrocyte metabolism is disturbed in the early development of experimental hydrocephalus

JOURNAL OF NEUROCHEMISTRY, Issue 1 2003
Daniel Kondziella
Abstract The proper diagnosis of the arrested or the progressive form of hydrocephalus has a critical impact on treatment, but remains difficult. The assessment of early changes in cerebral metabolism might help in the development of adequate non-invasive diagnostic tools. This study examined the alterations in label incorporation in neurotransmitter amino acids and other compounds in kaolin-induced progressive hydrocephalus in rats by means of magnetic resonance spectroscopy (MRS) combined with the administration of [1- 13C]glucose and [1,2- 13C]acetate. Some 2, 4 and 6 weeks after kaolin injection into the cisterna magna, cerebrum, brainstem and cerebellum were dissected. Interestingly, labelling of most amino acids derived from [1- 13C]glucose showed no alterations, whereas labelling from [1,2- 13C]acetate was affected. Two weeks after induction of hydrocephalus the taurine concentration was decreased, whereas the concentration of [1,2- 13C]lactate was increased in the cerebrum and that of [1,2- 13C]GABA in the brainstem. Furthermore, labelling from [1,2- 13C]acetate was significantly decreased in [4,5- 13C]glutamate, [1,2- 13C]glutamate and [1,2- 13C]GABA in cerebrum from 4 weeks after hydrocephalus induction. The concentration of N -acetylaspartate, a neuronal marker, was unchanged. However, labelling of the acetyl group from [1- 13C]glucose was decreased in cerebellum and brainstem at 6 weeks after the induction of hydrocephalus. As glucose is metabolized predominately by neurones, whereas acetate is exclusively taken up by astrocytes, these results indicate that mostly astrocytic, and only later neuronal, metabolism is disturbed in the kaolin model of hydrocephalus. If verified in patients using in vivo MRS, impaired astrocyte metabolism might serve as an early indication for operative treatment. [source]

Flow modeling and simulation for vacuum assisted resin transfer molding process with the equivalent permeability method

POLYMER COMPOSITES, Issue 2 2004
Renliang Chen
Vacuum assisted resin transfer molding (VARTM) offers numerous advantages over traditional resin transfer molding, such as lower tooling costs, shorter mold filling time and better scalability for large structures. In the VARTM process, complete filling of the mold with adequate wet-out of the fibrous preform has a critical impact on the process efficiency and product quality. Simulation is a powerful tool for understanding the resin flow in the VARTM process. However, conventional three-dimensional Control Volume/Finite Element Method (CV/FEM) based simulation models often require extensive computations, and their application to process modeling of large part fabrication is limited. This paper introduces a new approach to model the flow in the VARTM process based on the concept of equivalent permeability to significantly reduce computation time for VARTM flow simulation of large parts. The equivalent permeability model of high permeable medium (HPM) proposed in the study can significantly increase convergence efficiency of simulation by properly adjusting the aspect ratio of HPM elements. The equivalent permeability model of flow channel can simplify the computational model of the CV/FEM simulation for VARTM processes. This new modeling technique was validated by the results from conventional 3D computational methods and experiments. The model was further validated with a case study of an automobile hood component fabrication. The flow simulation results of the equivalent permeability models were in agreement with those from experiments. The results indicate that the computational time required by this new approach was greatly reduced compared to that by the conventional 3D CV/FEM simulation model, while maintaining the accuracy, of filling time and flow pattern. This approach makes the flow simulation of large VARTM parts with 3D CV/FEM method computationally feasible and may help broaden the application base of the process simulation. Polym. Compos. 25:146,164, 2004. © 2004 Society of Plastics Engineers. [source]

Pricing American options on foreign currency with stochastic volatility, jumps, and stochastic interest rates

THE JOURNAL OF FUTURES MARKETS, Issue 9 2007
Jia-Hau Guo
By applying the Heath,Jarrow,Morton (HJM) framework, an analytical approximation for pricing American options on foreign currency under stochastic volatility and double jump is derived. This approximation is also applied to other existing models for the purpose of comparison. There is evidence that such types of jumps can have a critical impact on earlyexercise premiums that will be significant for deep out-of-the-money options with short maturities. Moreover, the importance of the term structure of interest rates to early-exercise premiums is demonstrated as is the sensitivity of these premiums to correlation-related parameters. © 2007 Wiley Periodicals, Inc. Jrl Fut Mark 27:867,891, 2007 [source]

Making the Business School More ,Critical': Reflexive Critique Based on Phronesis as a Foundation for Impact

BRITISH JOURNAL OF MANAGEMENT, Issue 2010
Elena P. Antonacopoulou
This paper explores how the business school can become more critical by advancing the notion of reflexive critique. Drawing on diverse literatures propounding a critical perspective, this paper integrates the various interpretations of ,what it is to be critical' and proposes phronesis as a foundation for responding to and extending the relevance and rigour debate by articulating what it means for business schools to have a critical impact on management practice. A phronetic analysis of management education provides an innovative lens for understanding the power of critique in engaging academics and business practitioners in the co-creation of knowledge. This is illustrated by distilling the main insights from the experience of introducing an innovative course entitled ,Critical Thinking' offered to MBA students over a five-year period. The paper discusses the importance of critique in the business curriculum and explains the rationale for introducing the course and its objectives, as well as the learning and teaching techniques employed. The analysis considers how reflexive critique can be a platform for integrating a critical analysis of management informed by management research and academic thinking in relation to business practitioners' practical experiences of managing. The paper concludes with a review of the main lessons learned and the implications for future initiatives intended to foster engagement of theory and practice and the collaboration of academics and business practitioners. [source]

Single-Step Electron Transfer on the Nanometer Scale: Ultra-Fast Charge Shift in Strongly Coupled Zinc Porphyrin,Gold Porphyrin Dyads

CHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2008
Jérôme Fortage Dr.
Abstract The synthesis, electrochemical properties, and photoinduced electron transfer processes of a series of three novel zinc(II),gold(III) bisporphyrin dyads (ZnPSAuP+) are described. The systems studied consist of two trisaryl porphyrins connected directly in the meso position via an alkyne unit to tert -(phenylenethynylene) or penta(phenylenethynylene) spacers. In these dyads, the estimated center to center interporphyrin separation distance varies from 32 to 45,Å. The absorption, emission, and electrochemical data indicate that there are strong electronic interactions between the linked elements, thanks to the direct attachment of the spacer on the porphyrin ring through the alkyne unit. At room temperature in toluene, light excitation of the zinc porphyrin results in almost quantitative formation of the charge shifted state .+ZnPSAuP., whose lifetime is in the order of hundreds of picoseconds. In this solvent, the charge-separated state decays to the ground state through the intermediate population of the zinc porphyrin triplet excited state. Excitation of the gold porphyrin leads instead to rapid energy transfer to the triplet ZnP. In dichloromethane the charge shift reactions are even faster, with time constants down to 2,ps, and may be induced also by excitation of the gold porphyrin. In this latter solvent, the longest charge-shifted lifetime (,=2.3,ns) was obtained with the penta-(phenylenethynylene) spacer. The charge shift reactions are discussed in terms of bridge-mediated super-exchange mechanisms as electron or hole transfer. These new bis-porphyrin arrays, with strong electronic coupling, represent interesting molecular systems in which extremely fast and efficient long-range photoinduced charge shift occurs over a long distance. The rate constants are two to three orders of magnitude larger than for corresponding ZnPAuP+ dyads linked via meso -phenyl groups to oligo-phenyleneethynylene spacers. This study demonstrates the critical impact of the attachment position of the spacer on the porphyrin on the electron transfer rate, and this strategy can represent a useful approach to develop molecular photonic devices for long-range charge separations. [source]