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941.
A-type K(+) current can act as a trigger for bursting in the absence of a slow variable 总被引:1,自引:0,他引:1
Models of bursting in single cells typically include two subsystems with different timescales. Variations in one or more slow variables switch the system between a silent and a spiking state. We have developed a model for bursting in the pituitary lactotroph that does not include any slow variable. The model incorporates fast, noninactivating calcium and potassium currents (the spike-generating mechanism), as well as the fast, inactivating A-type potassium current (I(A)). I(A) is active only briefly at the beginning of a burst, but this brief impulse of I(A) acts as a burst trigger, injecting the spike trajectory close to an unstable steady state. The spiraling of the trajectory away from the steady state produces a period of low-amplitude spiking typical of lactotrophs. Increasing the conductance of A-type potassium current brings the trajectory closer to the unstable steady state, increasing burst duration. However, this also increases interburst interval, and for larger conductance values, all activity stops. To our knowledge, this is the first example of a physiologically based, single-compartmental model of bursting with no slow subsystem. 相似文献
942.
This article considers automatic performance tuning of time-step-based parallel solution methods for initial value problems (IVPs) of systems of ordinary differential equations (ODEs). We apply auto-tuning to the parallel execution of a class of explicit predictor–corrector (PC) methods of Runge–Kutta (RK) type on shared-memory architectures. The performance of parallel multi-threaded implementation variants of these methods depends on various factors only known at runtime, for example, the coupling structure of the ODE system to be solved, the memory access pattern resulting from this coupling structure, and the number of threads executing the program. 相似文献
943.
Lyudmila A. Novokshonova Natalia Yu. Kovaleva Yurii A. Gavrilov Vadim G. Krasheninnikov Ilia O. Leipunskii Alexey N. Zhigach Michail N. Larichev Michail V. Chebunin 《Polymer Bulletin》1997,39(1):59-65
New method of investigation of active sites non-uniformity was developed. The method is based on mass-spectrometric study
of temperature programmed desorption (TPD) products from the catalyst surface at initial stages of olefin gasphase polymerization.
The conditions of polymerization allowed to obtain the short macrochains on catalyst surface. Two well-resolved intense maxima
in the temperature ranges of 180 – 210 °C and 280 – 320 °C on the TPD curves from SiO2/TiCl4/AlEt2Cl catalyst surface after polymerization were observed in a result of thermal destruction of active Ti−C bonds and the evolution
of hydrocarbon molecules of different length (up to 14 monomer units in chain). One may conclude that in this catalyst there
are at least two types of active sites varying in the activation energy of thermal destruction of Ti−C bonds. The distribution
of active sites over activation energy of Ti−C bond thermal destruction was calculated.
Received: 28 April 1997/Accepted: 12 May 1997 相似文献
944.
Irina Sapurina Natalia E. Kazantseva Natalia G. Ryvkina Jan Proke Petr Sha Jaroslav Stejskal 《应用聚合物科学杂志》2005,95(4):807-814
Polyaniline or polypyrrole composites with fir or oak wood have been prepared by in situ polymerization of the corresponding monomers in an aqueous suspension of wood sawdust. The percolation threshold of compressed coated particles is located below 5 wt % of the conducting component and, above this limit, the conductivity of most composites was higher than 10?3 S cm?1. The conductivity of composites containing ca 30 wt % of conducting polymer was of the order of 10?1 S cm?1, an order of magnitude lower than that of the corresponding homopolymers, polyaniline and polypyrrole. The conductivity stability has been tested at 175°C. The polypyrrole‐based composites generally lasted for a longer time than pyrrole homopolymers, also on account of the improved mechanical integrity of the samples provided by the presence of wood. The reverse order was found with polyaniline composites. The dielectric properties of the composites were determined in the range of 100 MHz–3 GHz, indicating that thick layers of composite material, ~ 100 mm, are needed for the screening of the electromagnetic radiation below ?10 dB level in this frequency range. Nevertheless, considering the potential production cost of composites and their low weight, such composite materials could be of practical interest in the shielding of electromagnetic interference. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 807–814, 2005 相似文献
945.
Jude O. Iroh Yanrong Zhu Kunal Shah Kirill Levine Ramakrishnan Rajagopalan Tamer Uyar M. Donley R. Mantz J. Johnson Natalia N. Voevodin V. N. Balbyshev A. N. Khramov 《Progress in Organic Coatings》2003,47(3-4):365-375
Electrochemical synthesis is a powerful tool for surface modification, substrate cleaning and formulation of thin films and bulk materials. It is especially suited for surface modification of fibers, metals and films. In the past decade electrochemical method has become the preferred technique for in situ passivation, and coating of commodity metals such as aluminum, zinc, copper and steel.
We have successfully synthesized different kinds of conducting polymers, including polypyrrole (PPy)–polyaniline (PANi) composites. The processability and corrosion performance of PPy/PANi, composite coatings are significantly better than those for either PPy or PANi, coatings.
In this paper, we will discuss the use of electrochemical technique in the synthesis and characterization of multi-functional corrosion resistant conducting polymer coatings for aerospace and automotive applications. 相似文献
946.
Isobutylaluminum aryloxides as metallocene activators in Homo‐ and copolymerization of olefins
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Evgeny E. Faingol'd Natalia M. Bravaya Andrei N. Panin Olga N. Babkina Stanislav L. Saratovskikh Victor I. Privalov 《应用聚合物科学杂志》2016,133(14)
The article describes that sterically hindered isobutylaluminum aryloxides with bulky tBu substituents at 2,6‐ positions of aryl fragment, i.e. (2,6‐di‐tBu,4‐R‐C6H2O)AliBu2 (R = H ( 1‐DTBP ), Me ( 1‐BHT ), tBu ( 1‐TTBP )) and (2,6‐di‐tBu,4‐R‐C6H2O)2AliBu (R=H( 2‐DTBP ), Me( 2‐BHT )) can serve as cocatalysts for metallocene complexes. Isobutylaluminum aryloxides have been applied for activation of rac‐Et(2‐MeInd)2ZrMe2 in homopolymerization of ethylene, propylene, copolymerization of ethylene and propylene, and terpolymerization of ethylene, propylene, and 5‐ethylidene‐2‐norbornene at Al/Zr = 300 mol/mol. The type of R substituent at 4‐position has a significant effect on catalyst activity. The catalytic system with 1‐TTBP showed the highest activity in all homo‐ and copolymerization processes. Diisobutylaluminum aryloxides provide much higher activity to the systems in all polymerization processes and stronger ability for propylene incorporation in copolymer than diaryloxides. The activities of the systems with isobutylaluminum aryloxides are similar or exceed that of the system with MAO as activator as have shown for propylene polymerization. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43276. 相似文献
947.
Vaida Auzelyte Mikael Elfman Per Kristiansson Christer Nilsson Jan Pallon Natalia Arteaga Marrero Marie Wegdén 《Microelectronic Engineering》2006,83(10):2015-2020
Proton beam writing was performed on a lithographic resist to determine the main parameters required to achieve the minimum feature size, maximum pattern lateral density and maximum aspect ratio. A 2.5 MeV proton beam focused to sizes between 1.5 and 2.5 μm was used to expose SU-8 negative resist. The number of protons per pixel was varied in the exposure of SU-8 with thicknesses between 5 and 95 μm. Patterns consisting of single pixels, single-pixel lines and multi-pixel areas with different densities were fabricated. The smallest structures achieved were posts 1.5 μm in diameter with 4:1 structure-space ratio in 15 μm thick resist and the highest aspect ratio structures of 20:1 in 40 μm resist were produced. It was found that the minimum feature size depended only on the beam size, and ±10% post size accuracy could be achieved within 40-70% variation of the number of protons. MeV proton beam allows a direct fabrication of complex shapes without a mask in single-step irradiation and, in addition, no proximity correction is needed. We present examples of MeV proton beam written single and multi-pixel microstructures with easily reproducible high aspect ratios and densities. 相似文献
948.
Mature knowledge allows engineering disciplines the achievement of predictable results. Unfortunately, the type of knowledge used in software engineering can be considered to be of a relatively low maturity, and developers are guided by intuition, fashion or market-speak rather than by facts or undisputed statements proper to an engineering discipline. Testing techniques determine different criteria for selecting the test cases that will be used as input to the system under examination, which means that an effective and efficient selection of test cases conditions the success of the tests. The knowledge for selecting testing techniques should come from studies that empirically justify the benefits and application conditions of the different techniques. This paper analyzes the maturity level of the knowledge about testing techniques by examining existing empirical studies about these techniques. We have analyzed their results, and obtained a testing technique knowledge classification based on their factuality and objectivity, according to four parameters. 相似文献
949.
Numan Michael; Numan Marilyn J.; Pliakou Natalia; Stolzenberg Danielle S.; Mullins Olivia J.; Murphy Jennifer M.; Smith Carl D. 《Canadian Metallurgical Quarterly》2005,119(6):1588
The medial preoptic area (MPOA), ventral pallidum (VP), and nucleus accumbens (NA) receive dopaminergic afferents and are involved in maternal behavior. Experiments investigated whether dopamine (DA) receptor antagonism in NA disrupts maternal behavior, determined the type of DA receptor involved, and investigated the involvement of drug spread to VP or MPOA. Injection of SCH 23390 (D1 DA receptor antagonist) into NA of postpartum rats disrupted retrieving at dosage levels that were ineffective when injected into MPOA or VP. Motor impairment was not the cause of the deficit. Injection of eticlopride (D2 DA receptor antagonist) into NA or VP was without effect. Results emphasize the importance of DA action on D1 receptors in NA for retrieval behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
950.
Mark V. Kartsovnik Michael Kunz Ludwig Schaidhammer Florian Kollmannsberger Werner Biberacher Natalia D. Kushch Akira Miyazaki Hideki Fujiwara 《Journal of Superconductivity and Novel Magnetism》2016,29(12):3075-3080
The mutual influence of the conduction electron system provided by organic donor layers and magnetic system localized in insulating layers of the molecular charge transfer salt κ-(BETS)2FeBr4 has been studied. It is demonstrated that besides the high-field re-entrant superconducting state, the interaction between the two systems plays important role for the low-field superconductivity. The coupling of normal-state charge carriers to the magnetic system is reflected in magnetic quantum oscillations and can be evaluated based on the angle-dependent beating behavior of the oscillations. On the other hand, the conduction electrons have their impact on the magnetic system, which is revealed through the pressure-induced changes of the magnetic phase diagram of the material. 相似文献