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131.
A. Fiasconaro W. Ebeling E. Gudowska-Nowak 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(3):403-414
We give an overview over recent studies on the model of Active Brownian Motion (ABM) coupled to reservoirs providing free
energy which may be converted into kinetic energy of motion. First, we present an introduction to a general concept of active
Brownian particles which are capable to take up energy from the source and transform part of it in order to perform various
activities. In the second part of our presentation we consider applications of ABM to ratchet systems with different forms
of differentiable potentials. Both analytical and numerical evaluations are discussed for three cases of sinusoidal, staircaselike
and Mateos ratchet potentials, also with the additional loads modelled by tilted potential structure. In addition, stochastic
character of the kinetics is investigated by considering perturbation by Gaussian white noise which is shown to be responsible
for driving the directionality of the asymptotic flux in the ratchet. This stochastically driven directionality effect is visualized as a strong nonmonotonic dependence of the statistics of the right versus left trajectories of motion
leading to a net current of particles. Possible applications of the ratchet systems to molecular motors are also briefly discussed. 相似文献
132.
Microscopic phonon theory of semiconductor nanocrystals (NCs) is reviewed in this paper. Phonon modes of Si and Ge NCs with
various sizes of up to 7 nm are investigated by valence force field theory. Phonon modes in spherical SiGe alloy NCs approximately
3.6 nm (containing 1147 atoms) in size have been investigated as a function of the Si concentration. Phonon density-of-states,
quantum confinement effects, as well as Raman intensities are discussed.
相似文献
133.
A.K. Kushwaha 《理论物理通讯》2008,50(6):1422-1426
A rigid-ion model is used to calculate the force constants and effective
dynamical charges of sulphide and selenide spinels. The Raman and infrared
phonon modes of normal cubic sulphide spinels MCr2Se4
(M = Mn, Co, Fe, Hg, Zn, and Cd) and selenide spinels MCr2Se4
(M = Hg, Zn, and Cd) are calculated at the first Brillouin zone-centre using above model. The
significant outcome of the present work is (i) the interatomic interaction
between Cr-S (Se) dominates over the
Cr-S(Se) and S-S(Se-Se) type of
interatomic interactions, (ii) the effective dynamical charges of the
bivalent metal ions are nearly zero, and (iii) the selenide spinels are less
ionic than the sulphide spinels and the ionicity decreases as
MnCr2S4 >
FeCr2S4 >
CoCr2S4 > and
CdCr2C4 >
ZnCr2C4 >
HgCr2C4
(C = S and Se). The zone-center phonon frequencies, calculated using these parameters, are
found to be in very good agreement with the observed results. 相似文献
134.
可控地构造具有一定功能的表面人工低维结构,并且总结、理解体系微观结构对其宏观性质影响的一般规律,不仅对探索低维基本物理以及其中的新奇量子现象至关重要,更是微电子工业保持持续发展的关键前提.这方面的研究包括发展新的生长技术实现对体系形成过程的精确控制,对获得的材料做高分辨率的表征;从理论上则要理解体系的生长过程,阐明热力学、动力学的作用机理,从而指导制备技术的发展.深入研究表面人工低维结构的性质更可能导致新物理现象与原理的发现,产生全新的器件概念,进一步反馈给体系功能的设计,推动基础研究与应用探索的发展.文章简要介绍了表面物理国家重点实验室近年来在表面人工低维结构的功能设计与构造方面的研究成果 相似文献
135.
Pierre-Henri Chavanis 《Physica A》2008,387(28):6917-6942
We introduce a stochastic model of 2D Brownian vortices associated with the canonical ensemble. The point vortices evolve through their usual mutual advection but they experience in addition a random velocity and a systematic drift generated by the system as a whole. The statistical equilibrium state of this stochastic model is the Gibbs canonical distribution. We consider a single species system and a system made of two types of vortices with positive and negative circulations. At positive temperatures, like-sign vortices repel each other (“plasma” case) and at negative temperatures, like-sign vortices attract each other (“gravity” case). We derive the stochastic equation satisfied by the exact vorticity field and the Fokker-Planck equation satisfied by the N-body distribution function. We present the BBGKY-like hierarchy of equations satisfied by the reduced distribution functions and close the hierarchy by considering an expansion of the solutions in powers of 1/N, where N is the number of vortices, in a proper thermodynamic limit. For spatially inhomogeneous systems, we derive the kinetic equations satisfied by the smooth vorticity field in a mean field approximation valid for N→+∞. For spatially homogeneous systems, we study the two-body correlation function, in a Debye-Hückel approximation valid at the order O(1/N). The results of this paper can also apply to other systems of random walkers with long-range interactions such as self-gravitating Brownian particles and bacterial populations experiencing chemotaxis. Furthermore, for positive temperatures, our study provides a kinetic derivation, from microscopic stochastic processes, of the Debye-Hückel model of electrolytes. 相似文献
136.
This paper proposes a generalized dynamics model and a leader-follower control architecture for skid-steered tracked vehicles towing polar sleds. The model couples existing formulations in the literature for the powertrain components with the vehicle-terrain interaction to capture the salient features of terrain trafficability and predict the vehicles response. This coupling is essential for making realistic predictions of the vehicles traversing capabilities due to the power-load relationship at the engine output. The objective of the model is to capture adequate fidelity of the powertrain and off-road vehicle dynamics while minimizing the computational cost for model based design of leader-follower control algorithms. The leader-follower control architecture presented proposes maintaining a flexible formation by using a look-ahead technique along with a way point following strategy. Results simulate one leader-follower tractor pair where the leader is forced to take an abrupt turn and experiences large oscillations of its drawbar arm indicating potential payload instability. However, the follower tractor maintains the flexible formation but keeps its payload stable. This highlights the robustness of the proposed approach where the follower vehicle can reject errors in human leader driving. 相似文献
137.
P. Navratil P. Peterka P. Vojtisek I. Kasik J. Aubrecht P. Honzatko V. Kubecek 《Opto-Electronics Review》2018,26(1):29-34
Self-swept erbium fiber laser emitting around 1.56?μm is reported in detail. Both sweep directions were registered: pointing toward longer and shorter wavelengths, redshift and blueshift sweeping, respectively. We describe method of determining the direction of the wavelength drift using the monochromator based optical spectrum analyzer. Possible root for this sweeping regime, i.e., the gain modulation along active fiber, is discussed with the help of a simple model calculating the overall cavity gain that can predict the direction of the laser wavelength sweeping. 相似文献
138.
Dr. Sourav Maiti Dr. Jayanta Dana Prof. Dr. Hirendra N. Ghosh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(3):692-702
The photovoltaic performance of quantum-dot solar cells strongly depends on the charge-carrier relaxation and recombination processes, which need to be modulated in a favorable way to obtain maximum efficiency. Recently, significant efforts have been devoted to investigate the carrier dynamics of nanocrystal sensitizers, both in solution and deposited on TiO2 photoanodes, with the aim to correlate the excitonics with solar-energy conversion efficiency. This Minireview summarizes some proof of the concepts that efficiency can be directly correlated to the exciton dynamics of quantum-dot solar cells. The presented findings are based on CdSeS alloy, CdSe/CdS core/shell, Au/CdSe nanohybrids, and Mn-doped CdZnSSe nanocrystals, where the favourable excitonic processes are optimized to enhance the efficiency. Future prospects and limitations are addressed as well. 相似文献
139.
Y. T. Angel Wong Vinicius Martins Dr. Bryan E. G. Lucier Prof. Dr. Yining Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(8):1848-1853
Metal–organic frameworks (MOFs) have shown great potential in gas separation and storage, and the design of MOFs for these purposes is an on-going field of research. Solid-state nuclear magnetic resonance (SSNMR) spectroscopy is a valuable technique for characterizing these functional materials. It can provide a wide range of structural and motional insights that are complementary to and/or difficult to access with alternative methods. In this Concept article, the recent advances made in SSNMR investigations of small gas molecules (i.e., carbon dioxide, carbon monoxide, hydrogen gas and light hydrocarbons) adsorbed in MOFs are discussed. These studies demonstrate the breadth of information that can be obtained by SSNMR spectroscopy, such as the number and location of guest adsorption sites, host–guest binding strengths and guest mobility. The knowledge acquired from these experiments yields a powerful tool for progress in MOF development. 相似文献
140.
Shobhit S. Chaturvedi Rajeev Ramanan Sodiq O. Waheed Jon Ainsley Martin Evison Jennifer M. Ames Christopher J. Schofield Tatyana G. Karabencheva-Christova Christo Z. Christov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(21):5422-5426
The human KDM7 subfamily histone H3 Nϵ-methyl lysine demethylases PHF8 (KDM7B) and KIAA1718 (KDM7A) have different substrate selectivities and are linked to genetic diseases and cancer. We describe experimentally based computational studies revealing that flexibility of the region linking the PHD finger and JmjC domains in PHF8 and KIAA1718 regulates interdomain interactions, the nature of correlated motions, and ultimately H3 binding and demethylation site selectivity. F279S an X-linked mental retardation mutation in PHF8 is involved in correlated motions with the iron ligands and second sphere residues. The calculations reveal key roles of a flexible protein environment in productive formation of enzyme-substrate complexes and suggest targeting the flexible KDM7 linker region is of interest from a medicinal chemistry perspective. 相似文献