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Dynamics of coherence-induced state ordering under Markovian channels
Long-Mei Yang, Bin Chen, Shao-Ming Fei, Zhi-Xi Wang
Frontiers of Physics. 2018, 13 (5 ): 130310-.
https://doi.org/10.1007/s11467-018-0780-4
We study the dynamics of coherence-induced state ordering under incoherent channels, particularly four specific Markovian channels: amplitude damping channel, phase damping channel, depolarizing channel and bit flit channel for single-qubit states. We show that the amplitude damping channel, phase damping channel, and depolarizing channel do not change the coherence-induced state ordering by l 1 norm of coherence, relative entropy of coherence, geometric measure of coherence, and Tsallis relative α -entropies, while the bit flit channel does change for some special cases.
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General hyperentanglement concentration for polarizationspatial- time-bin multi-photon systems with linear optics
Hong Wang, Bao-Cang Ren, Ai Hua Wang, Ahmed Alsaedi, Tasawar Hayat, Fu-Guo Deng
Frontiers of Physics. 2018, 13 (5 ): 130315-.
https://doi.org/10.1007/s11467-018-0801-3
Hyperentanglement has attracted considerable attention recently because of its high-capacity for longdistance quantum communication. In this study, we present a hyperentanglement concentration protocol (hyper-ECP) for nonlocal three-photon systems in the polarization, spatial-mode, and timebin partially hyperentangled Greenberger–Horne–Zeilinger (GHZ) states using the Schmidt projection method. In our hyper-ECP, the three distant parties must perform the parity-check measurements on the polarization, spatial-mode, and time-bin degrees of freedom, respectively, using linear optical elements and Pockels cells, and only two identical nonlocal photon systems are required. This hyper-ECP can be directly extended to the N -photon hyperentangled GHZ states, and the success probability of this general hyper-ECP for a nonlocal N -photon system is the optimal one, regardless of the photon number N .
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Towards quantum entanglement of micromirrors via a two-level atom and radiation pressure
Zhi-Rong Zhong, Xin Wang, Wei Qin
Frontiers of Physics. 2018, 13 (5 ): 130319-.
https://doi.org/10.1007/s11467-018-0824-9
We propose a method to entangle two vibrating microsize mirrors (i.e., mechanical oscillators) in a cavity optomechanical system. In this scheme, we discuss both the resonant and large-detuning conditions, and show that the entanglement of two mechanical oscillators can be achieved with the assistance of a two-level atom and cavity-radiation pressure. In the resonant case, the operation time is relatively short, which is desirable to minimize the effects of decoherence. While in the large-detuning case, the cavity is only virtually excited during the interaction. Therefore, the decay of the cavity is effectively suppressed, which makes the efficient decoherence time of the cavity to be greatly prolonged. Thus, we observe that this virtual-photon process of microscopic objects may induce the entanglement of macroscopic objects. Moreover, in both cases, the generation of entanglement is deterministic and no measurements on the atom and the cavity are required. These are experimentally important. Finally, the decoherence effect and the experimental feasibility of the proposal are briefly discussed.
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Heralded amplification of single-photon entanglement with polarization feature
Yu-Yu Jin, Sheng-Xian Qin, Hao Zu, Lan Zhou, Wei Zhong, Yu-Bo Sheng
Frontiers of Physics. 2018, 13 (5 ): 130321-.
https://doi.org/10.1007/s11467-018-0823-x
Heralded noiseless amplification is beneficial in overcoming transmission photon loss in a noisy quantum channel. We propose a single-photon-assisted heralded noiseless amplification protocol of the singlephoton entanglement (SPE), where the single-photon qubit has an arbitrary unknown polarization feature. We focus on both the complete and partial photon loss during the transmission process. After the amplification, the parties can recover the pure less-entangled SPE into a maximally entangled SPE and increase its fidelity. Moreover, the polarization feature of the single-photon qubit will be well preserved and not be leaked. Our protocol can be realized under our current experimental condition. Based on the features above, our protocol may be useful in the quantum secure communication schemes that encode information in the polarization degree of freedom of photons.
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Evolution of a two-mode squeezed vacuum for amplitude decay via continuous-variable entangled state approach
Xiang-Guo Meng, Ji-Suo Wang, Bao-Long Liang, Cheng-Xuan Han
Frontiers of Physics. 2018, 13 (5 ): 130322-.
https://doi.org/10.1007/s11467-018-0856-1
Extending the recent work completed by Fan et al . [Front. Phys . 9(1), 74 (2014)] to a two-mode case, we investigate how a two-mode squeezed vacuum evolves when it undergoes a two-mode amplitude dissipative channel, with the same decay rate κ , using the continuous-variable entangled state approach. Our analytical results show that the initial pure-squeezed vacuum state evolves into a definite mixed state with entanglement and squeezing, decaying over time as a result of amplitude decay. We also investigate the time evolutions of the photon number distribution, the Wigner function, and the optical tomogram in this channel. Our results indicate that the evolved photon number distribution is related to Jacobi polynomials, the Wigner function has a standard Gaussian distribution (corresponding to the vacuum) at long periods, losing its nonclassicality due to amplitude decay, and a larger squeezing leads to a longer decay time.
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Cluster synchronization in complex network of coupled chaotic circuits: An experimental study
Ben Cao, Ya-Feng Wang, Liang Wang, Yi-Zhen Yu, Xin-Gang Wang
Frontiers of Physics. 2018, 13 (5 ): 130505-.
https://doi.org/10.1007/s11467-018-0775-1
By a small-size complex network of coupled chaotic Hindmarsh-Rose circuits, we study experimentally the stability of network synchronization to the removal of shortcut links. It is shown that the removal of a single shortcut link may destroy either completely or partially the network synchronization. Interestingly, when the network is partially desynchronized, it is found that the oscillators can be organized into different groups, with oscillators within each group being highly synchronized but are not for oscillators from different groups, showing the intriguing phenomenon of cluster synchronization. The experimental results are analyzed by the method of eigenvalue analysis, which implies that the formation of cluster synchronization is crucially dependent on the network symmetries. Our study demonstrates the observability of cluster synchronization in realistic systems, and indicates the feasibility of controlling network synchronization by adjusting network topology.
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Engineering multipartite steady entanglement of distant atoms via dissipation
Zhao Jin, S.-L. Su, Ai-Dong Zhu, Hong-Fu Wang, Shou Zhang
Frontiers of Physics. 2018, 13 (5 ): 134209-.
https://doi.org/10.1007/s11467-018-0826-7
We propose a scheme for generating an entangled state for three atoms trapped in separate optical cavities that are coupled to each other through two optical fibers based on coherent driving and dissipation, which are induced by the classical fields and the decay of non-local bosonic modes, respectively. In our scheme, the interaction time need not be controlled strictly in the overall dynamics process, and the cavity field decay can be changed into a vital resource. The numerical simulation shows that the fidelity of the target state is insensitive to atomic spontaneous emission, and our scheme is good enough to generate the W state of distant atoms with a high fidelity and purity. In addition, the present scheme can also be generalized to prepare the N -partite W state of distant atoms.
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Discrete Boltzmann model for implosion- and explosion-related compressible flow with spherical symmetry
Ai-Guo Xu, Guang-Cai Zhang, Yu-Dong Zhang, Pei Wang, Yang-Jun Ying
Frontiers of Physics. 2018, 13 (5 ): 135102-.
https://doi.org/10.1007/s11467-018-0777-z
To kinetically model implosion- and explosion-related phenomena, we present a theoretical framework for constructing a discrete Boltzmann model (DBM) with spherical symmetry in spherical coordinates. To achieve this goal, a key technique is to use local Cartesian coordinates to describe the particle velocity in the kinetic model. Therefore, geometric effects, such as divergence and convergence, are described as a “force term”. To better access the nonequilibrium behavior, even though the corresponding hydrodynamic model is one-dimensional, the DBM uses a discrete velocity model (DVM) with three dimensions. A new scheme is introduced so that the DBM can use the same DVM regardless of whether or not there are extra degrees of freedom. As an example, a DVM with 26 velocities is formulated to construct the DBM at the Navier–Stokes level. Via the DBM, one can study simultaneously the hydrodynamic and thermodynamic nonequilibrium behaviors in implosion and explosion processes that are not very close to the spherical center. The extension of the current model to a multiple-relaxation-time version is straightforward.
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High-pressure polymorphs of LiPN2 : A first-principles study
Jian Lv, Xin Yang, Dan Xu, Yu-Xin Huang, Hong-Bo Wang, Hui Wang
Frontiers of Physics. 2018, 13 (5 ): 136104-.
https://doi.org/10.1007/s11467-018-0774-2
In this work, high-pressure phase behavior of LiPN2 within 0–300 GPa was studied by using an unbiased structure searching method in combination with first-principles calculations. Three pressureinduced phase transitions were predicted, as tI16→hR4→cF64→oP8 at 44, 136, and 259 GPa, respectively. The six-fold coordination environments were found for all high-pressure polymorphs, which are substantially different from the four-fold coordination environments observed in the tI16 structure. The hR4 and cF64 structures consist of close-packed PN6 and LiN6 octahedra connected by edge-sharing, whereas the oP8 structure is built up from edge- and face-sharing PN6 and LiN6 octahedra with N lying in the center of the trigonal prisms. The electronic structure analysis reveals that LiPN2 is a semiconductor within the pressure range studied and P-N and Li-N bonds are covalent and ionic, respectively. The results obtained are expected to provide insight and guidance for future experiments on LiPN2 and other alkali metal nitridophosphates.
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A novel hybrid sp-sp2 metallic carbon allotrope
Qun Wei, Quan Zhang, Mei-Guang Zhang, Hai-Yan Yan, Li-Xin Guo, Bing Wei
Frontiers of Physics. 2018, 13 (5 ): 136105-.
https://doi.org/10.1007/s11467-018-0787-x
In this paper, we propose a novel hybrid sp -sp 2 monoclinic carbon allotrope m C12 . This allotrope is a promising light metallic material, the mechanical and electronic properties of which are studied based on first-principles calculations. The structure of this new m C12 is mechanically and dynamically stable at ambient pressure and has a low equilibrium density due to its large cell volume. Furthermore, calculations of the elastic constants and moduli reveal that mC12 has a rigid mechanical property. Finally, it exhibits metallic characteristics, owing to the mixture of sp -sp 2 hybrid carbon atoms.
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Controlled growth of complex polar oxide films with atomically precise molecular beam epitaxy
Fang Yang, Yan Liang, Li-Xia Liu, Qing Zhu, Wei-Hua Wang, Xue-Tao Zhu, Jian-Dong Guo
Frontiers of Physics. 2018, 13 (5 ): 136802-.
https://doi.org/10.1007/s11467-018-0769-z
At heterointerfaces between complex oxides with polar discontinuity, the instability-induced electric field may drive electron redistribution, causing a dramatic change in the interfacial charge density. This results in the emergence of a rich diversity of exotic physical phenomena in these quasi-two-dimensional systems, which can be further tuned by an external field. To develop novel multifunctional electronic devices, it is essential to control the growth of polar oxide films and heterointerfaces with atomic precision. In this article, we review recent progress in control techniques for oxide film growth by molecular beam epitaxy (MBE). We emphasize the importance of tuning the microscopic surface structures of polar films for developing precise growth control techniques. Taking the polar SrTiO3 (110) and (111) surfaces as examples, we show that, by keeping the surface reconstructed throughout MBE growth, high-quality layer-by-layer homoepitaxy can be realized. Because the stability of different reconstructions is determined by the surface cation concentration, the growth rate from the Sr/Ti evaporation source can be monitored in real time. A precise, automated control method is established by which insulating homoepitaxial SrTiO3 (110) and (111) films can be obtained on doped metallic substrates. The films show atomically well-defined surfaces and high dielectric performance, which allows the surface carrier concentration to be tuned in the range of ~1013 /cm2 . By applying the knowledge of microstructures from fundamental surface physics to film growth techniques, new opportunities are provided for material science and related research.
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Ferroelectric polarization reversal tuned by magnetic field in a ferroelectric BiFeO3 /Nb-doped SrTiO3 heterojunction
Pei Li, Zhao-Meng Gao, Xiu-Shi Huang, Long-Fei Wang, Wei-Feng Zhang, Hai-Zhong Guo
Frontiers of Physics. 2018, 13 (5 ): 136803-.
https://doi.org/10.1007/s11467-018-0819-6
Interfacial resistive switching of a ferroelectric semiconductor heterojunction is highly advantageous for the newly developed ferroelectric memristors. Moreover, the interfacial state in the ferroelectric semiconductor heterojunction can be gradually modified by polarization reversal, which may give rise to continuously tunable resistive switching behavior. In this work, the interfacial state of a ferroelectric BiFeO3 /Nb-doped SrTiO3 junction was modulated by ferroelectric polarization reversal. The dynamics of surface screening charges on the BiFeO3 layer was also investigated by surface potential measurements, and the decay of the surface potential could be speeded up by the magnetic field. Moreover, ferroelectric polarization reversal of the BiFeO3 layer was tuned by the magnetic field. This finding could provide a method to enhance the ferroelectric and electrical properties of ferroelectric BiFeO3 films by tuning the magnetic field.
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First-principles study of electronic structure and magnetic properties of SrTi1−x Mx O3 (M= Cr, Mn, Fe, Co, or Ni)
Xin-Long Dong, Kun-Hua Zhang, Ming-Xiang Xu
Frontiers of Physics. 2018, 13 (5 ): 137106-.
https://doi.org/10.1007/s11467-018-0807-x
We used first-principles calculations to conduct a comparative study of the structure and the electronic and magnetic properties of SrTiO3 doped with a transition metal (TM), namely, Cr, Mn, Fe, Co, or Ni. The calculated formation energies indicate that compared with Sr, Ti can be substituted more easily by the TM ions. The band structures show that SrTi0.875 Cr0.125 O3 and SrTi0.875 Co0.125 O3 are half metals, SrTi0.875 Fe0.125 O3 is a metal, and SrTi0.875 Mn0.125 O3 is a semiconductor. The 3d TM-doped SrTiO3 exhibits various magnetic properties, ranging from ferromagnetism (Cr-, Fe-, and Co-doped SrTiO3 ) to antiferromagnetism (Mn-doped SrTiO3 ) and nonmagnetism (Ni-doped SrTiO3 ). The total magnetic moments are 4.0μ B , 6.23μ B , and 2.0μ B for SrTi0.75 Cr0.25 O3 , SrTi0.75 Fe0.25 O3 , and SrTi0.75 Co0.25 O3 , respectively. Room-temperature ferromagnetism can be expected in Cr-, Fe-, and Co-doped SrTiO3 , which agrees with the experimental observations. The electronic structure calculations show that the spin polarizations of the 3d states of the TM atoms are responsible for the ferromagnetism in these compounds. The magnetism of TM-doped SrTiO3 is explained by the hybridization between the TM-3d states and the O-2p states.
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Pressure-induced superconducting ternary hydride H3 SXe: A theoretical investigation
Da Li (李达), Yan Liu (刘妍), Fu-Bo Tian (田夫波), Shu-Li Wei (魏书丽), Zhao Liu (刘召), De-Fang Duan (段德芳), Bing-Bing Liu (刘冰冰), Tian Cui (崔田)
Frontiers of Physics. 2018, 13 (5 ): 137107-.
https://doi.org/10.1007/s11467-018-0818-7
In general, heavy elements contribute only to acoustic phonon modes, which are less important for the superconductivity of hydrides. However, it was revealed that the heavier elements could enhance the phonon-mediated superconductivity in ternary hydrides. In the H3 S–Xe system, a novel H3 SXe compound was discovered by first-principle calculations. The structural phase transitions of H3SXe under high pressures were studied. The R -3m phase of H3 SXe was predicted to appear at pressures above 80 GPa, which transitions to C 2/m , P -3m 1, and Pm -3m phases at pressures of 90, 160, and 220 GPa, respectively. It has been anticipated that the Pm -3m -H3 SXe phase with a similar structural feature as that of Im -3m -H3 S is a potential high-temperature superconductor with a T c of 89 K at 240 GPa. The T c value of H3 SXe is lower than that of H3 S at high pressure. The “H3 S” host lattice of Pm - 3m -H3 SXe is a crucial factor influencing the T c value. The Xe atoms could accelerate the hydrogen-bond symmetrization. With the increase of the atomic number, the T c value linearly increases in the H3 S–noble-gas-element system. This indicates that the superconductivity can be modulated by changing the relative atomic mass of the noble-gas element.
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A critical path approach for elucidating the temperature dependence of granular hopping conduction
Tsz Chun Wu, Juhn-Jong Lin, Ping Sheng
Frontiers of Physics. 2018, 13 (5 ): 137205-.
https://doi.org/10.1007/s11467-018-0814-y
We revisit the classical problem of granular hopping conduction’s σ ∝exp[–(T 0 /T )] temperature dependence, where σ denotes conductivity, T is temperature, and T 0 is a sample-dependent constant. By using the hopping conduction formulation in conjunction with the incorporation of the random potential that has been shown to exist in insulator-conductor composites, it is demonstrated that the widely observed temperature dependence of granular hopping conduction emerges very naturally through the immediate-neighbor critical-path argument. Here, immediate-neighbor pairs are defined to be those where a line connecting two grains does not cross or by-pass other grains, and the critical-path argument denotes the derivation of sample conductance based on the geometric percolation condition that is marked by the critical conduction path in a random granular composite. Simulations based on the exact electrical network evaluation of finite-sample conductance show that the configurationaveraged results agree well with those obtained using the immediate-neighbor critical-path method. Furthermore, the results obtained using both these methods show good agreement with experimental data on hopping conduction in a sputtered metal-insulator composite Agx (SnO2 )1– x , where x denotes the metal volume fraction. The present approach offers a relatively straightforward and simple explanation for the temperature behavior that has been widely observed over diverse material systems, but which has remained a puzzle in spite of the various efforts made to explain this phenomenon.
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Quantum anomalous Hall effect and giant Rashba spin-orbit splitting in graphene system co-doped with boron and 5d transition-metal atoms
Xinzhou Deng, Hualing Yang, Shifei Qi, Xiaohong Xu, Zhenhua Qiao
Frontiers of Physics. 2018, 13 (5 ): 137308-.
https://doi.org/10.1007/s11467-018-0806-y
Quantum anomalous Hall effect (QAHE) is a fundamental quantum transport phenomenon in condensed matter physics. Until now, the QAHE has only been experimentally realized for Cr/V-doped (Bi, Sb)2 Te3 but at an extremely low observational temperature, thereby limiting its potential application in dissipationless quantum electronics. By employing first-principles calculations, we study the electronic structures of graphene co-doped with 5d transition metal and boron atoms based on a compensated n –p co-doping scheme. Our findings are as follows: i) The electrostatic attraction between the n - and p -type dopants effectively enhances the adsorption of metal adatoms and suppresses their undesirable clustering. ii) Hf-B and Os-B co-doped graphene systems can establish long-range ferromagnetic order and open larger nontrivial band gaps because of the stronger spin-orbit coupling with the non-vanishing Berry curvatures to host the high-temperature QAHE. iii) The calculated Rashba splitting energies in Re–B and Pt–B co-doped graphene systems can reach up to 158 and 85 meV, respectively, which are several orders of magnitude higher than the reported intrinsic spin-orbit coupling strength.
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Alkali-metal-induced topological nodal line semimetalin layered XN2 (X= Cr, Mo, W)
Ali Ebrahimian, Mehrdad Mehrdad Dadsetaniz
Frontiers of Physics. 2018, 13 (5 ): 137309-.
https://doi.org/10.1007/s11467-018-0815-x
Based on first principles calculations and the K·p effective model, we propose that alkali metal deposition on the surface of hexagonal XN2 (X= Cr, Mo, W) nanosheets induces topologically nontrivial phases in these systems. When spin orbit coupling (SOC) is disregarded, the electron-like conduction band from N-p z orbitals can be considered to cross the hole-like valence band from X-d 2 z orbitals, thereby giving rise to a topological nodal line state in lithium-functionalized XN2 sheets (Li2 MoN2 and Li2 WN2 ). Such band crossing is protected by the existence of mirror reflection and time reversal symmetry. More interestingly, the bands cross exactly at the Fermi level, and the linear dispersion regions of such band crossings extend to as high as 0.9 eV above the crossing. For Li2 CrN2 , the results reveal the emergence of a Dirac cone at the Fermi level. Our calculations show that lattice compression decreases the thickness of a Li2 CrN2 nanosheet, leading to phase transition to a nodal line semimetal. The evolution of the band gap of Li2 XN2 at the Γ point indicates that the nontrivial topological character of Li2 XN2 nanolayers is stable over a large strain range. When SOC is included, the band crossing point is gapped out giving rise to quantum spin Hall states in Li2 CrN2 nanosheets, while for Li2 MoN2 , the SOC-induced gap at the crossing points is negligible.
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Enhancing the magnetoelectric coupling of Co4 Nb2 O9 [100] by substituting Mg for Co
Zhen Li, Yi-Ming Cao, Yin Wang, Ya Yang, Mao-Lin Xiang, You-Shuang Yu, Bao-Juan Kang, Jin-Cang Zhang, Shi-Xun Cao
Frontiers of Physics. 2018, 13 (5 ): 137503-.
https://doi.org/10.1007/s11467-018-0827-6
We report experimental studies on enhancing the magnetoelectric (ME) coupling of Co4 Nb2 O9 by substituting the non-magnetic metal Mg for Co. A series of single crystal Co4−x Mgx Nb2 O9 (x = 0, 1, 2, 3) with a single-phase corundum-type structure are synthesized using the optical floating zone method, and the good quality and crystallographic orientations of the synthesized samples are confirmed by the Laue spots and sharp XRD peaks. Although the Néel temperatures (T N ) of the Mg substituted crystals decrease slightly from 27 K for pure Co4 Nb2 O9 to 19 K and 11 K for Co3 MgNb2 O9 and Co2 Mg2 Nb2 O9 , respectively, the ME coupling is doubly enhanced by Mg substitution when x = 1. The ME coefficient α ME of Co3 MgNb2 O9 required for the magnetic field (electric field) control of electric polarization (magnetization) is measured to be 12.8 ps/m (13.7 ps/m). These results indicate that the Mg substituted Co4−x Mgx Nb2 O9 (x = 1) could serve as a potential candidate material for applications in future logic spintronics and logic devices.
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Reconceptualizing kinesin’s working cycle as separate chemical and mechanical processes
Hui-Juan Xu, Tong Tong, Rui-Zheng Hou, Hong-Rong Li
Frontiers of Physics. 2018, 13 (5 ): 138206-.
https://doi.org/10.1007/s11467-018-0776-0
The biomolecular motor kinesin uses chemical energy released from a fuel reaction to generate directional movement and produce mechanical work. The underlying physical mechanism is not fully understood yet. To analyze the energetics of the motor, we reconceptualize its chemomechanical cycle in terms of separate fuel reaction and work production processes and introduce a thermodynamic constraint to optimize the cycle. The model predicts that the load dependences of the motor’s velocity, stepping ratio, and dwell time are determined by the mechanical parameters of the motor–track system rather than the fuel reaction rate. This behavior is verified using reported experimental data from wild-type and elongated kinesins. The fuel reaction and work production processes indicate that kinesin is driven by switching between two chemical states, probably following a general pattern for molecular motors. The comparison with experimental data indicates that the fuel reaction processes are close to adiabatic, which is important for efficient operation of the motor. The model also suggests that a soft, short neck linker is important for the motor to maintain its load transport velocity.
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