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951.
de La Figuera J Pohl K de La Fuente OR Schmid AK Bartelt NC Carter CB Hwang RQ 《Physical review letters》2001,86(17):3819-3822
Using scanning tunneling microscopy we have observed thermally induced dislocation glide in monolayer Cu films on Ru(0001) at room temperature. The motion is governed by a Peierls barrier that depends on the detailed structure of the dislocations, in particular upon whether the threading dislocations that terminate them are dissociated or not. Calculations based on the Frenkel-Kontorova model reproduce the threading dislocation structure and provide estimates of the Peierls barrier and dislocation stiffness which are consistent with experiment. 相似文献
952.
Nanostructured copper filaments in electrochemical deposition 总被引:8,自引:0,他引:8
Wang M Zhong S Yin XB Zhu JM Peng RW Wang Y Zhang KQ Ming NB 《Physical review letters》2001,86(17):3827-3830
In this Letter we report a novel self-organized copper electrodeposition in an ultrathin layer of CuSO4 electrolyte. The macroscopic fingering branches of the deposit consist of long copper filaments covered with periodic corrugated nanostructures. The mechanism of the nanostructure formation is explored and the origin of the significant descent of the branching rate in electrodeposition is discussed. We suggest that this growth phenomenon provides deeper insights into the role of diffusion and migration on pattern formation in electrodeposition. 相似文献
953.
Xenopus oocyte maturation is an example of an all-or-none, irreversible cell fate induction process. In response to a submaximal concentration of the steroid hormone progesterone, a given oocyte may either mature or not mature, but it can exist in intermediate states only transiently. Moreover, once an oocyte has matured, it will remain arrested in the mature state even after the progesterone is removed. It has been hypothesized that the all-or-none character of oocyte maturation, and some aspects of the irreversibility of maturation, arise out of the bistability of the signal transduction system that triggers maturation. The bistability, in turn, is hypothesized to arise from the way the signal transducers are organized into a signaling circuit that includes positive feedback (which makes it so that the system cannot rest in intermediate states) and ultrasensitivity (which filters small stimuli out of the feedback loop, allowing the system to have a stable off-state). Here we review two simple graphical methods that are commonly used to analyze bistable systems, discuss the experimental evidence for bistability in oocyte maturation, and suggest that bistability may be a common means of producing all-or-none responses and a type of biochemical memory. (c) 2001 American Institute of Physics. 相似文献
954.
E. F. Jones P. M. Gore J. H. Hamilton A. V. Ramayya A. P. de Lima R. S. Dodder J. Kormicki J. K. Hwang C. J. Beyer X. Q. Zhang S. J. Zhu G. M. Ter-Akopian Yu. Ts. Oganessian A. V. Daniel J. O. Rasmussen I. Y. Lee J. D. Cole M. W. Drigert W.-C. Ma 《Physics of Atomic Nuclei》2001,64(7):1157-1164
The levels in 162Gd were identified in spontaneous fission studies. Its transition energies are remarkably similar to those in 160Gd. From that work, an analysis of yrast bands in even-even proton to neutron-rich Ba to Pb nuclei led to the discovery of a new phenomenon, shifted identical bands (SIB). SIBs are yrast bands in neighboring nuclei (a, b) with moments of inertia which are identical when shifted by a constant amount κ, so J 1a (1+κ)=J 1b , from 2+ to 8+ and higher to 16+. Out of over 700 comparisons, 55 SIBs were found from stable to the most neutron-rich Ce-W nuclei with $\left| {\bar k} \right|$ between 1.5% and 13%, where the spread in κ is less than ±1%, and only four identical bands ( $\bar k \cong 0$ ). As examples, we found for 158Sm-160Gd, $\bar k = \left( { - 3.2_{ - 0.2}^{ + 0.1} } \right)\%$ (where the ± is the total spread in κ from ?3.1 to ?3.4); 156Nd-160Gd, (?10.6 ?0.2 +0.4 )%; 158Sm-160Sm, (3.4 ?0.3 +0.5 )%. The J 1 values were fitted to a variable moment of inertia model with parameters J 0 and C whose values correlate with the SIB J 1 values. The SIBs are not correlated either with deformation or with the N p N n product of the IBA model. 相似文献
955.
Xiong Guohong Wang Zhiyu Qian Guodong Fan Xianping Wang Minquan 《Journal of Sol-Gel Science and Technology》2000,18(1):21-27
Using a newly developed in-situ syntheses technique during sol-gel process, copper phthalocyanine (CuPc) is synthesized in-situ in silica xerogel matrix homogeneously. It has been confirmed by UV-Vis and IR spectroscopies that the copper ions which existed in the form of complex-ions [Cu(H2O)4]2+ and [CuCl4]2– in the stages of sol and wet gel were destroyed in the heat treatment process, meanwhile the copper phthalocyanine molecules were synthesized in-situ gradually during the wet gel to xerogel transition. The dimerization phenomenon of CuPc in the composite is suppressed greatly because the in-situ synthesized CuPc molecules were well isolated in the micro-pores of the xerogel matrix. The doping concentration of Copper phthalocyanine in sol-gel derived matrix can be enhanced also by this in-situ synthesis method. 相似文献
956.
Electrochemical studies of the effect of lanthanide ions on the activity of glutamate dehydrogenase 总被引:6,自引:0,他引:6
Using the electrochemical method based on the "diffusion" layer concept of the convective system, the effect of lanthanide ions La3+ and Eu3+ on the activity of glutamate dehydrogenase (GLDH) has been determined. In suitable concentrations, the lanthanide ions La3+ and Eu3+ can activate the GLDH in the reductive amination of alpha-Ketoglutarate (alpha-KG). The activation mechanism would be that the lanthanide ions could interrupt the binding of NAD+ to GLDH by combining preferentially to NAD+. This mechanism was proposed by the voltammetric studies. 相似文献
957.
Effect of stimulation rate on phoneme recognition by nucleus-22 cochlear implant listeners 总被引:3,自引:0,他引:3
This study investigated the effect of pulsatile stimulation rate on medial vowel and consonant recognition in cochlear implant listeners. Experiment 1 measured phoneme recognition as a function of stimulation rate in six Nucleus-22 cochlear implant listeners using an experimental four-channel continuous interleaved sampler (CIS) speech processing strategy. Results showed that all stimulation rates from 150 to 500 pulses/s/electrode produced equally good performance, while stimulation rates lower than 150 pulses/s/electrode produced significantly poorer performance. Experiment 2 measured phoneme recognition by implant listeners and normal-hearing listeners as a function of the low-pass cutoff frequency for envelope information. Results from both acoustic and electric hearing showed no significant difference in performance for all cutoff frequencies higher than 20 Hz. Both vowel and consonant scores dropped significantly when the cutoff frequency was reduced from 20 Hz to 2 Hz. The results of these two experiments suggest that temporal envelope information can be conveyed by relatively low stimulation rates. The pattern of results for both electrical and acoustic hearing is consistent with a simple model of temporal integration with an equivalent rectangular duration (ERD) of the temporal integrator of about 7 ms. 相似文献
958.
Lei ZH Yahara S Nohara T Tai BS Xiong JZ Ma YL 《Chemical & pharmaceutical bulletin》2000,48(2):290-292
Two new cardiac glycosides called cheiranthosides VI (2) and VII (3) were isolated together with a known one, glucoerysimoside (1) from the seeds of Erysimum cheiranthoides. Based on spectroscopic data, the structures of 2 and 3 were characterized as periplogenin 3-O-beta-D-glucopyranosyl(1-->4)-beta-D-fucopyranoside and periplogenin 3-O-beta-D-glucopyranosyl(1-->4)-beta-D-antiaropyranoside, respectively. 相似文献
959.
Xu W Dutta D Xiong F Anderson B Auberbach L Averett T Bertozzi W Black T Calarco J Cardman L Cates GD Chai ZW Chen JP Choi S Chudakov E Churchwell S Corrado GS Crawford C Dale D Deur A Djawotho P Filippone BW Finn JM Gao H Gilman R Glamazdin AV Glashausser C Glöckle W Golak J Gomez J Gorbenko VG Hansen JO Hersman FW Higinbotham DW Holmes R Howell CR Hughes E Humensky B Incerti S de Jager CW Jensen JS Jiang X Jones CE Jones M Kahl R Kamada H Kievsky A Kominis I Korsch W Kramer K Kumbartzki G 《Physical review letters》2000,85(14):2900-2904
We have measured the transverse asymmetry A(T') in 3He(e,e(')) quasielastic scattering in Hall A at Jefferson Laboratory with high precision for Q2 values from 0.1 to 0.6 (GeV/c)(2). The neutron magnetic form factor G(n)(M) was extracted based on Faddeev calculations for Q2 = 0.1 and 0.2 (GeV/c)(2) with an experimental uncertainty of less than 2%. 相似文献
960.
Coupling of optical parametric processes in an optical superlattice through quadratic nonlinearity was analyzed theoretically. Solving the coupled equations, we found that efficient quasi-phase-matched third-harmonic (TH) generation depends not only on the magnitude of the coupling coefficients but also on their ratio. Theoretically, all the fundamental energy can be transferred to the TH at a particular ratio. In other cases, there exists an optimum condition that corresponds to a maximum TH conversion efficiency. The result is of practical importance for the design of TH devices. 相似文献