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Fast Processes (fast + process)
Selected AbstractsPolymerization of acrylamide photoinitiated by tris(2,2,-bipyridine)ruthenium(II),amine in aqueous solution: Effect of the amine structureJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2001Claudia R. Rivarola Abstract The photopolymerization of acrylamide (AA) initiated by the metallic complex tris(2,2,-bipyridine)ruthenium(II) [Ru(bpy)3+2] in the presence of aliphatic and aromatic amines as co-initiators was investigated in aqueous solution. Aromatic amines, which are good quenchers of the emission of the metal-to-ligand-charge-transfer excited state of the complex, are more effective co-initiators than those that do not quench the luminescence of Ru(bpy)3+2, such as aliphatic amines and aniline. Laser-flash photolysis experiments show the presence of the reduced form of the complex, Ru(bpy)3+1, for all the amines investigated. For aliphatic amines, the yield of Ru(bpy)3+1 increases with temperature, and on the basis of these experiments, a metal-centered excited state is proposed as the reactive intermediate in the reaction with these amines. The decay of the transient Ru(bpy)3+1 is faster in the presence of AA. This may be understood by an electron-transfer process from Ru(bpy)3+1 to AA, regenerating Ru(bpy)3+2 and producing the radical anion of AA. It is proposed that this radical anion protonates in a fast process to give the neutral AA radical, initiating in this way the polymerization chain. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4265,4273, 2001 [source] Energy relaxation processes of photo-generated carriers in Mg doped (0001)GaN and (1-101)GaNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008J. Saida Abstract Energy relaxation processes of photo-generated excess carriers in Mg doped GaN epitaxial layers were investigated at room temperature, with photoluminescence intensity correlation method using femto-second pulse laser as the excitation source. The decay curve was well fitted by exponential decay with two time constants. The slow process of the order of 100 ps was attributed to the energy relaxation of electrons in the conduction band, while the fast process of the order of several pico-seconds was attributed to the capture process in the impurity band near the valence band. Little difference has been found out between the results for (0001)GaN and those for (1-101)GaN. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Frenkel defect pair creation channels in KBr, NaBr and NaCl between 10 K and 100 K: a MD studyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005K. S. SongArticle first published online: 19 JAN 200 Abstract Recent molecular dynamics (MD) study of exciton relaxation showed that starting from a free Frenkel-type exciton in undistorted lattice, the maximum relaxation is reached within about 1,2 ps at temperatures of 10K,100K in NaBr, KBr and NaCl. We present here several results, which include: the quenching of the triplet exciton luminescence; the fast conversion to Frenkel pairs near the quenching temperature. We propose a tentative model, which identifies various channels of defect creation, namely the low temperature dynamic production, the very fast process near the quenching temperature, and the slow thermally activated creation of Frenkel defect pair. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Creation of excitations and defects in insulating materials by high-current-density electron beams of nanosecond pulse durationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005D. I. Vaisburd Abstract The paper is concerned with fast and ultra-fast processes in insulating materials under the irradiation by a high-current-density electron beam of a nanosecond pulse duration. The inflation process induced by the interaction of a high-intensity electron beam with a dielectric is examined. The "instantaneous" distribution of non-ionizing electrons and holes is one of the most important stages of the process. Ionization-passive electrons and holes make the main contribution to many fast processes with a characteristic time in the range 10,14 ÷ 10,12 s: high-energy conductivity, intraband luminescence, etc. A technique was developed for calculation of the "instantaneous" distribution of non-ionizing electrons and holes in a dielectric prior to electron-phonon relaxation. The following experimental effects are considered: intraband luminescence, coexistence of intraband electron luminescence and band-to-band hole luminescence in CsI, high energy conductivity; generation of mechanical fields and their interaction with cracks and dislocations. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High-speed serial-kinematic SPM scanner: design and drive considerations,ASIAN JOURNAL OF CONTROL, Issue 2 2009Kam K. Leang Abstract This paper describes the design of a flexure-guided, two-axis nanopositioner (scanner) driven by piezoelectric stack actuators. The scanner is specifically designed for high-speed scanning probe microscopy (SPM) applications, such as atomic force microscopy (AFM). A high-speed AFM scanner is an essential component for acquiring high-resolution, three-dimensional, time-lapse images of fast processes such as the rapid movement of cells and the diffusion of DNA molecules. A two-axis SPM scanner is proposed, where the slow and fast scanning axes are serially connected and flexure guided to minimize runout. The scanner's achievable scan range is approximately 10µm × 10µm. Finite element analysis is utilized to optimize the mechanical resonance frequencies of the scanner. Experimental results show a first major resonance in the slow and fast axis at 1.5 and 29,kHz, respectively. This paper also discusses the various tradeoffs between speed, range, electrical requirements, and scan trajectory design for high-speed nanopositioning. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] CONTROL ISSUES IN HIGH-SPEED AFM FOR BIOLOGICAL APPLICATIONS: COLLAGEN IMAGING EXAMPLEASIAN JOURNAL OF CONTROL, Issue 2 2004Q. Zou ABSTRACT This article considers the precision positioning problem associated with high-speed operation of the Atomic Force Microscope (AFM), and presents an inversion-based control approach to achieve precision positioning. Although AFMs have high (nanoscale) spatial resolution, a problem with current AFM systems is that they have low temporal resolution, i.e., AFM imaging is slow. In particular, current AFM imaging cannot be used to provide three-dimensional, time-lapse images of fast processes when imaging relatively-large, soft samples. For instance, current AFM imaging of living cells takes 1,2 minutes (per image frame) , such imaging speeds are too slow to study rapid biological processes that occur in seconds, e.g., to investigate the rapid movement of cells or the fast dehydration and denaturation of collagen. This inability, to rapidly image fast biological processes, motivates our current research to increase the operating speed of the AFM. We apply an inversion-based feedback/feedforward control approach to overcome positioning problems that limit the operating speed of current AFM systems. The efficacy of the method, to achieve high-speed AFM operation, is experimentally evaluated by applying it to image collagen samples. [source] Cyclometallated Iridium Complexes as Sensitizers for Dye-Sensitized Solar CellsCHEMISTRY - AN ASIAN JOURNAL, Issue 3 2010Etienne Baranoff Dr. A sensitive matter: New sensitizers based on cyclometallated iridium (III) complexes have been studied. Despite poor absorption properties, efficiencies up to 2.5,% were observed. It was seen that poor light-harvesting properties of the dyes are the main reasons for those efficiencies, which may be improved with better light-absorbing ligands. Electron-dynamic investigations show that very fast processes are taking place. [source] Photochemical Z,E Isomerization of a Hemithioindigo/Hemistilbene ,-Amino AcidCHEMPHYSCHEM, Issue 11 2007Thorben Cordes Abstract The molecule HTI, which combines hemithioindigo and hemistilbene molecular parts, allows reversible switching between two isomeric states. Photochromic behaviour of the HTI molecule is observed by irradiation with UV/Vis light. The photochemical reaction, a Z/E isomerization around the central double bond connecting the two molecular parts, is investigated by transient absorption and emission spectroscopy. For a special HTI molecule, namely, an ,-amino acid, the Z,E isomerization process occurs on a timescale of 30 ps. In the course of the reaction fast processes on the 1,10 ps timescale are observed which point to motions of the molecule on the potential-energy surface of the excited state. The combination of transient absorption experiments in the visible spectral range with time-resolved fluorescence and infrared measurements reveal a photochemical pathway with three intermediate states. Together with a theoretical modelling procedure the experiments point to a sequential reaction scheme and give indications of the nature of the involved intermediates. [source] | ||||||||||