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Significant intervals of energy transforms in bubbles freely oscillating in liquids

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Journal of Hydrodynamics 2017年第2期29卷 217-225页

作者： karel Vokurka Physics Department Technical University of LiberecLiberecCzech Republic

A wall motion of a bubble freely oscillating in a liquid is studied from the point of view of energy conversions at different instants. It is shown that the time of the bubble oscillation can be divided into two distinct intervals. In the first long interval （here called PK and KP intervals） the prevailing energy conversion is between the potential energy of the bubble and the kinetic energy of the liquid. In the second short interval （here called KI and IK intervals） the kinetic energy of the liquid is transformed into the internal energy of the gas/vapor in the bubble interior and into some other forms of energy. By observing the bubble wall motion in the PK and KP intervals, it is shown that only the value of the maximum bubble radius in the corresponding oscillation can be determined. However, only the knowledge of the maximum bubble radii is insufficient for formulation of a correct theoretical model. Unfortunately this fact is often not noticed in the literature.

关键词： Energy transforms free bubble oscillations energy conversions in bubbles

Quasi-periodic variations of low energy cosmic rays

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Science China(Technological Sciences) 2016年第4期59卷 547-557页

作者： KUDELA karel SABBAH Ismail IEP SAS Kosice Slovakia Department of Natural Sciences College of Health Sciencesthe Public Authority for Applied Education and TrainingKuwait

Cosmic rays(CR)play an important role in space weather-related *** temporal variability,both of a quasi-periodic character as well as an irregular one,has been studied from ground-based direct measurements,as well as from cosmogenic nuclides,over a long *** attempt to describe the current knowledge of selected quasi-periodicities in CR flux in the energy range above the atmospheric threshold,from direct *** power spectrum density(PSD)of the CR time series as measured by neutron monitors(NMs)and by muon detectors has a rather complicated *** with the shape(slope)of the PSD,knowledge of the contribution of quasi-periodic variations(q-per)to the CR signal is of importance for the modulation,as well as for checking the links of CR to space weather,and/or to space climate *** rotation of the Earth and solar rotation cause two types of mechanisms behind the certain q-per observed in secondary CR on the Earth’s *** activity and solar magnetic field cyclicities contribute to the q-per signals in CR if studied over a longer *** complexity of the spatial structure of the interplanetary magnetic field(IMF)and its evolution within the heliosphere,in addition to the changes in the geomagnetic field,cause variability in contributions of the q-per in *** spectra are useful tools for checking the fine structure of q-per and their temporal *** a long time NMs and muon telescopes provide information about q-per in CR.

关键词： cosmic rays periodicities neutron monitors muon detectors

On Relations of Vector Optimization Results with C^(1,1) Data

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Acta Mathematica Sinica,English Series 2010年第11期26卷 2031-2040页

作者： Duan BEDNA■íK karel PASTOR Department of Mathematics University of Hradec Králové Department of Mathematical Analysis and Applications of Mathematics Faculty of SciencePalack■ University

In this article we prove that some of the sufficient and necessary optimality conditions obtained by Ginchev, Guerraggio, Luc [Appl. Math., 51, 5-36 （2006）] generalize （strictly） those presented by Guerraggio, Luc [J. Optim. Theory Appl., 109, 615-629 （2001）]. While the former paper shows examples for which the conditions given there are effective but the ones from the latter paper fail, it does not prove that generally the conditions it proposes are stronger. In the present note we complete this comparison with the lacking proof.

关键词： C1'1 function generalized second-order directional derivative Dini derivative weakly efficient minimizer isolated minimizer of second-order

A Two-Level Method for Nonsymmetric Eigenvalue Problems

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Acta Mathematicae Applicatae Sinica 2005年第1期21卷 1-12页

作者： karel Kolman Mathematical Institute Academy of Sciences of the Czech Republic ■itná 25 11567 Praha 1 Czech Republic

A two-level discretization method for eigenvalue problems is *** to the standard Galerkin finite element discretization technique performed on a fine gridthis method discretizes the eigenvalue problem on a coarse grid and obtains an improved eigenvector(eigenvalue) approximation by solving only a linear problem on the fine grid (or two linear problemsfor the case of eigenvalue approximation of nonsymmetric problems). The improved solution has theasymptotic accuracy of the Galerkin discretization solution. The link between the method and theiterated Galerkin method is established. Error estimates for the general nonsymmetric case arederived.

关键词： eigenvalue problems finite elements postprocessing two-level method two-grid method iterated Galerkin method

Error Estimates for the Time Discretization of a Semilinear Integrodifferential Parabolic Problem with Unknown Memory Kernel

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Numerical Mathematics(Theory,Methods and Applications) 2017年第1期10卷 116-144页

作者： Marijke Grimmonprez karel Van Bockstal Marian Slodicka Department of Mathematical Analysis Ghent UniversityGalglaan 29000 GhentBelgium

This paper is devoted to the study of an inverse problem containing a semilinear integrodifferential parabolic equation with an unknown memory *** equation is accompanied by a Robin boundary *** missing kernel can be recovered from an additional global measurement in integral *** this contribution,an error analysis is performed for a time-discrete numerical scheme based on Backward Euler’s *** theoretical results are supported by some numerical experiments.

关键词： Parabolic inverse problem convolution kernel error estimates

Flame Synthesis of Zr/ZSM-5 Catalysts with Tunable Acidity for the Oxidative Dehydrogenation of Propane to Propene

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Journal of Thermal Science 2024年第1期33卷 268-283页

作者： DANIEL Samuel FONZEU MONGUEN Cedric karel WU Lingnan TIAN Zhenyu Institute of Engineering Thermophysics Chinese Academy of SciencesBeijing 100190China University of Chinese Academy of Sciences Beijing 100049China

Tuning the surface acidity of ZSM-5 catalyst is essential to achieve desired propene selectivity and *** several ratios of Zr were utilized to modify ZSM-5 via flame spray pyrolysis technique coupled with a pulse spray evaporation *** interaction between Zr and ZSM-5 in the flame influenced the physicochemical and acidity properties of the Zr/*** increasing Zr ratio in ZSM-5 shows coated layers of irregular nano-sized Zr with an increase in crystallite sizes due to the synergetic effect between Zr and *** surface chemical analysis revealed increased lattice oxygen on the Zr modified ZSM-5(1:4) sample compared to other *** acidity analysis revealed the Lewis and Br?nsted acid distribution in the weak and medium acid sites on the catalyst ***,the increase in Zr loading decreased the concentration of Br?nsted acid sites and tuned the catalyst surface to more Lewis acidity,promoting propene selectivity and hindering the over-oxidation of *** modified ZSM-5 catalysts were examined in a fixed bed reactor within 300℃-700℃ at a gas hourly space velocity(GHSV) of 6000 mL·g(catalysts)^(-1)·h^(-1) for the oxidative dehydrogenation of propane(ODHP) to *** the catalysts,Zr/ZSM-5(1:4) exhibited the best propene yield, with 57.19% propane conversion and 75.54% selectivity to propene and the highest *** work provides a promising strategy for tuning the surface acidity of ZSM-5 with Zr for ODHP applications.

关键词： flame synthesis Zr modified ZSM-5 catalyst ODHP surface acidity lattice oxygen

Endoscopic full-thickness resection: current status

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World Journal of Gastroenterology 2015年第31期21卷 9273-9285页

作者： Arthur Schmidt Benjamin Meier karel Caca Department of Gastroenterology and Oncology

Conventional endoscopic resection techniques such as endoscopic mucosal resection or endoscopic submucosal dissection are powerful tools for treatment of gastrointestinal neoplasms. However,those techniques are restricted to superficial layers of the gastrointestinal wall. Endoscopic full-thickness resection(EFTR) is an evolving technique,which is just about to enter clinical routine. It is not only a powerful tool for diagnostic tissue acquisition but also has the potential to spare surgical therapy in selected patients. This review will give an overview about current EFTR techniques and devices.

关键词： Endoscopic full-thickness resection Over-the-scope

Ultrafast photoinduced dynamics in quantum dot-based systems for light harvesting

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Nano Research 2015年第7期8卷 2125-2142页

作者： Kaibo Zheng Khadga Karki karel Zidek Tonu Pullerits Department of Chemical Physics Lund University Box 124 22 100 Lund Sweden

Colloidal semiconductor nanocrystals, referred to as quantum dots, offer simple low-temperature solution-based methods for constructing optoelectronic devices such as light emitting diodes and solar cells. We review recent progress in the understanding of photoinduced processes in key components of a certain type of quantum dot solar cells where the dots sensitize a suitable metal oxide, such as ZnO or TiO2, for electron injection, and NiO for hole injection. The electron and hole injection dynamics are discussed in detail as a function of the quantum dot size and core-shell structure, the linker molecule type, and the morphology of the accepting metal oxide. Hole trapping is identified as a major factor limiting the performance of quantum dot-based devices. We review possible strategies for improvement that use core-shell structures and directed excitation energy transfer between quantum dots. Finally, the generation and injection of multiple excitons are revisited. We show that the assumption of a linear relationship between the intensity of transient absorption signal and the number of excitons does not generally hold, and this observation can partially explain highly disparate results for the effidency of generating multiple exdtons. A consistent calculation procedure for studies of multiple exciton generation is provided. Finally we offer a brief personal outlook on the topic.

关键词： colloidal quantum dots electron transfer, energy transfer,core shell quantum dots, quantum dot solar cell

How to make the end of a gene,the simple way

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BIOCELL 2022年第6期46卷 1453-1457页

作者： karel H.M.VAN WELY Centro Nacional de Biotecnología/CSIC Madrid28049Spain

Transcription termination of nearly all protein-coding genes in mammals requires 3’end processing by a multiprotein complex that will cleave and polyadenylate the messenger RNA *** a variety of enzyme complexes intervene,3’end processing was thought to be fundamentally complex and subject to a multitude of regulatory *** possibility to select just one out of several polyadenylation sites,in particular,has caused much questioning and *** appear to be separate mechanisms however can be combined into a defined set of rules,allowing for a relatively simple interpretation of 3’end ***,readiness of the terminal exon splice site determines when a transcript reaches the maturity to select a nearby polyadenylation *** pausing then acts in concert,extending the timeframe during which the transcription complex is close to polyadenylation *** RNA polymerase pausing is governed by the same type of sequences in bacteria and metazoans,mammalian transcription termination resembles its prokaryote counterpart more than generally thought.

关键词： RNA transcription RNA polymerase II pausing Splicing Termination Polyadenylation