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991.
The governing equation of wave motion of viscoelastic SWCNTs (single-walled carbon nanotubes) with surface effect under magnetic field is formulated on the basis of the nonlocal strain gradient theory. Based on the formulated equation of wave motion, the closed-form dispersion relation between the wave frequency (or phase velocity) and the wave number is derived. It is found that the size-dependent effects on the phase velocity may be ignored at low wave numbers, however, is significant at high wave numbers. Phase velocity can increase by decreasing damping or increasing the intensity of magnetic field. The damping ratio considering surface effect is larger than that without considering surface effect. Damping ratio can increase by increasing damping, increasing wave number, or decreasing the intensity of magnetic field. 相似文献
992.
Between many prominent contributions of Markus Büttiker to mesoscopic physics, the scattering theory approach to the electron transport and noise stands out for its elegance, simplicity, universality, and popularity between theorists working in this field. It offers an efficient way to theoretically investigate open electron systems far from equilibrium. However, this method is limited to situations where interactions between electrons can be ignored, or considered perturbatively. Fortunately, this is the case in a broad class of metallic systems, which are commonly described by the Fermi liquid theory. Yet, there exist another broad class of electron systems of reduced dimensionality, the so-called Tomonaga–Luttinger liquids, where interactions are effectively strong and cannot be neglected even at low energies. Nevertheless, strong interactions can be accounted exactly using the bosonization technique, which utilizes the free-bosonic character of collective excitations in these systems. In the present work, we use this fact in order to develop the scattering theory approach to the bosonization of open quasi-one dimensional electron systems far from equilibrium. 相似文献
993.
In this paper, the viscoelastic wave propagation in an embedded viscoelastic single-walled carbon nanotube (SWCNT) is studied based on the nonlocal strain gradient theory. The characteristic equation for the viscoelastic wave in SWCNTs is derived. The emphasis is placed on the influence of the tube diameter on the viscoelastic wave dispersion. A blocking diameter is observed, above which the wave could not propagate in SWCNTs. The results show that the blocking diameter is greatly dependent on the damping coefficient, the nonlocal and the strain gradient length scale parameters, as well as the Winkler modulus of the surrounding elastic medium. These findings may provide a prospective application of SWCNTs in nanodevices and nanocomposites. 相似文献
994.
Living polymers are formed by reversible association of primary units (unimers). Generally the chain statistical weight involves
a factor σ < 1 suppressing short chains in comparison with free unimers. Living polymerization is a sharp thermodynamic transition
for σ ≪ 1 which is typically the case. We show that this sharpness has an important effect on the kinetics of living polymerization
(one-dimensional association). The kinetic model involves i) the unimer activation step (a transition to an assembly-competent
state); ii) the scission/recombination processes providing growth of polymer chains and relaxation of their length distribution.
Analyzing the polymerization with no chains but unimers at t = 0 , with initial concentration of unimers M ≳ M
* (M* is the critical polymerization concentration), we determine the time evolution of the chain length distribution and find
that: 1) for M
* ≪ M ≪ M
*/σ the kinetics is characterized by 5 distinct time stages demarcated by 4 characteristic times t1, t2, t3 and t*; 2) there are transient regimes (t
1 ≲ t ≲ t
3) when the molecular-weight distribution is strongly non-exponential; 3) the chain scissions are negligible at times shorter
than t2. The chain growth is auto-accelerated for t
1 ≲ t ≲ t
2 : the cut-off chain length (= polymerization degree 〈n〉w
N
1 ∝ t
2 in this regime. 4) For t
2 < t < t
3 the length distribution is characterized by essentially 2 non-linear modes; the shorter cut-off length N1 is decreasing with time in this regime, while the length scale N2 of the second mode is increasing. (5) The terminal relaxation time of the polymer length distribution, t*, shows a sharp maximum in the vicinity of M*; the effective exponent
is as high as ∼ σ-1/3 just above M*. 相似文献
995.
J. B. Satinover D. Sornette 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(3):369-384
Human beings like to believe they are in control of their
destiny. This ubiquitous trait seems to increase motivation and persistence,
and is probably evolutionarily adaptive [J.D. Taylor, S.E. Brown, Psych. Bull. 103, 193 (1988); A. Bandura,
Self-efficacy: the exercise of control (WH Freeman, New
York, 1997)]. But how good really is our
ability to control? How successful is our track record in these areas? There
is little understanding of when and under what circumstances we may
over-estimate [E. Langer, J. Pers. Soc. Psych. 7, 185 (1975)] or even lose our ability to control and optimize outcomes,
especially when they are the result of aggregations of individual
optimization processes. Here, we demonstrate analytically using the theory
of Markov Chains and by numerical simulations in two classes of games, the
Time-Horizon Minority Game [M.L. Hart, P. Jefferies, N.F. Johnson, Phys. A 311, 275 (2002)] and the Parrondo Game
[J.M.R. Parrondo, G.P. Harmer, D. Abbott, Phys. Rev. Lett.
85, 5226 (2000); J.M.R. Parrondo, How to cheat a bad mathematician (ISI, Italy, 1996)], that agents
who optimize their strategy based on past information may actually perform
worse than non-optimizing agents. In other words, low-entropy (more
informative) strategies under-perform high-entropy (or random) strategies.
This provides a precise definition of the “illusion of control” in certain
set-ups a priori defined to emphasize the importance of optimization.
An erratum to this article is available at . 相似文献
996.
Zhongzhi Zhang Shuigeng Zhou Tao Zou Lichao Chen Jihong Guan 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(2):259-264
We make a mapping from Sierpinski fractals to a new class
of networks, the incompatibility networks, which are scale-free,
small-world, disassortative, and maximal planar graphs. Some
relevant characteristics of the networks such as degree
distribution, clustering coefficient, average path length, and
degree correlations are computed analytically and found to be
peculiarly rich. The method of network representation can be applied
to some real-life systems making it possible to study the complexity
of real networked systems within the framework of complex network
theory. 相似文献
997.
998.
培养兴趣,引导创新——《信息光学》理论教学改革实践 总被引:2,自引:0,他引:2
重点研究了针对《信息光学》理论性强的课程和学生在学习过程中兴趣下降以及一知半解等问题,着重从提高学生理论学习兴趣,引导学生创新为出发点,通过改进PPT课件,吸引学生注意,采用深入浅出、举一反三、师生互动、启发式教学方法、理论与实际相结合、教学科研相结合等多种方法和手段,帮助学生建立正确的物理概念,促进学生对数学公式所代表的物理意义的理解,达到改善理论教学效果的目的。同时结合创新性实验建设,培养创新型和复合型人才。 相似文献
999.
In this work, we devote to explore excited‐state intramolecular proton transfer (ESIPT) behavior for a novel fluorescent molecule naphthalimide‐based 2‐(2‐hydroxyphenyl)‐benzothiazole (HNIBT) [New J. Chem. 2019, 43, 9152.] in toluene and methanol (MeOH) solvents. Exploring weak interactions, stable HNIBT‐enol, and HNIBT‐MeOH‐enol complex can be found in S0 state via TDDFT/B3LYP/6‐311+G(d,p) level. Given photoexcitation, intramolecular hydrogen bond O1? H2···N3 of HNIBT‐enol and HNIBT‐MeOH‐enol is dramatically enhanced, which offers impetus for facilitates ESIPT reaction. After repeated comparisons, we verify the unavailability of intermolecular hydrogen bonding effects between HNIBT‐enol and MeOH molecules. In view of excitation, HOMO (π) → LUMO (π*) transition and the changes of electronical densities indeed impulse ESIPT tendency. Via constructing potential energy curves (PECs), for both HNIBT‐enol and HNIBT‐MeOH‐enol complex, the ESIPT could only occur along with intramolecular hydrogen bond O1? H2···N3. Through comparison, the potential barrier falls from 4.124 kcal/mol (HNIBT‐enol) to 2.132 kcal/mol (HNIBT‐MeOH‐enol). Therefore, we confirm that the ESIPT of the HNIBT system happens more easily in the MeOH solvent compared with the toluene solvent. 相似文献
1000.
Counting parameters has become customary in the density functional theory community as a way to infer the transferability of popular approximations to the exchange‐correlation functionals. Recent work in data science, however, has demonstrated that the number of parameters of a fitted model is not related to the complexity of the model itself, nor to its eventual overfitting. Using similar arguments, here, we show that it is possible to represent every modern exchange‐correlation functional approximations using just one single parameter. This procedure proves the futility of the number of parameters as a measure of transferability. To counteract this shortcoming, we introduce and analyze the performance of three statistical criteria for the evaluation of the transferability of exchange‐correlation functionals. The three criteria are called Akaike information criterion, Vapnik‐Chervonenkis criterion, and cross‐validation criterion and are used in a preliminary assessment to rank 60 exchange‐correlation functional approximations using the ASCDB database of chemical data. 相似文献