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Search Results: 1 - 10 of 120357 matches for " Hailong Wang "
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Saddles, Twists, and Curls: Shape Transitions in Freestanding Nanoribbons
Hailong Wang,Moneesh Upmanyu
Physics , 2011,
Abstract: Efforts to modulate the electronic properties of atomically thin crystalline nanoribbons requires precise control over their morphology. Here, we perform atomistic simulations on freestanding graphene nanoribbons (GNRs) to first identify the minimal shapes, and then employ a core-edge framework based on classical plate theory to quantify the width dependence in more general systems. The elastic edge-edge interactions force ultra-narrow ribbons to be flat, which then bifurcate to twisted and bent shapes at critical widths that vary inversely with edge stress. Compressive edge stresses results in twisted and saddle shapes that are energetically indistinguishable in the vicinity of the bifurcation. Increasing widths favor the saddle shapes with (longitudinal) ribbon curvatures that vary non-linearly with width and edge stress. Positive edge stresses result in a flat-to-curled transition with similar scalings. At large widths with negligible edge-edge interactions, rippling instabilities set in, i.e. edge ripples and midline dimples for compressive and tensile edge stresses. Our results highlight the utility of the core-edge framework in developing a unified understanding of the interplay between geometry and mechanics that sets the morphology of crystalline nanoribbons.
Rippling Instabilities in Suspended Nanoribbons
Hailong Wang,Moneesh Upmanyu
Physics , 2011, DOI: 10.1103/PhysRevB.86.205411
Abstract: Morphology mediates the interplay between the structure and electronic transport in atomically thin nanoribbons such as graphene as the relaxation of edge stresses occurs preferentially via out-of-plane deflections. In the case of end-supported suspended nanoribbons that we study here, past experiments and computations have identified a range of equilibrium morphologies, in particular for graphene flakes, yet a unified understanding of their relative stability remains elusive. Here, we employ atomic-scale simulations and a composite framework based on isotropic elastic plate theory to chart out the morphological stability space of suspended nanoribbons with respect to intrinsic (ribbon elasticity) and engineered (ribbon geometry) parameters, and the combination of edge and body actuation. The computations highlight a rich morphological shape space that can be naturally classified into two competing shapes, bending-like and twist-like, depending on the distribution of ripples across the interacting edges. The linearized elastic framework yields exact solutions for these rippled shapes. For compressive edge stresses, the body strain emerges as a key variable that controls their relative stability and in extreme cases stabilizes co-existing transverse ripples. Tensile edge stresses lead to dimples within the ribbon core that decay into the edges, a feature of obvious significance for stretchable nanoelectronics. The interplay between geometry and mechanics that we report should serve as a key input for quantifying the transport along these ribbons.
Subjective Well-Being in Nostalgia: Effect and Mechanism  [PDF]
Min Rao, Xiaotian Wang, Hailong Sun, Kun Gai
Psychology (PSYCH) , 2018, DOI: 10.4236/psych.2018.97102
Abstract: Nostalgia is a complex emotional state that the individual produces when he is missing the past. It has a close relationship with subjective well-being. Studies have shown that nostalgia can construct a sense of life and social support that promotes more emotional and emotional satisfaction and enhances subjective well-being. By combing the past literature, this paper analyzes the influence of nostalgia on subjective well-being from the perspectives of emotional happiness and life satisfaction, and further elaborates its mechanism of action. The article concludes with a prospect for future research.
Numerical simulation on seasonal transport variations and mechanisms of suspended sediment discharged from the Yellow River to the Bohai Sea

LI Guosheng,WANG Hailong,LIAO Heping,

地理学报 , 2010,
Abstract: Based on sediment and discharge flux data for the Yellow River, realistic forcing fields and bathymetry of the Bohai Sea, a suspended sediment transport module is driven by a wave-current coupled model to research seasonal variations and mechanisms of suspended load transport to the Bohai Sea. It could be concluded that surface sediment concentration indicates a distinct spatial distribution characteristic that varies seasonally in the Bohai Sea. Sediment concentration is rather high near the Yellow River estuary, seasonal variations of which are controlled by quantity of sediment from the Yellow River, suspended sediment concentration reaches its maximum during summer and fall. Furthermore, sediment concentration decreases rapidly in other seas far from the Yellow River estuary and maintains a very low level in the center of the Bohai Sea, and is dominated by seasonal variations of climatology wind field in the Bohai Sea. Only a small amount of sediments imported from the Yellow River are delivered northwestward to the southern coast of the Bohai Bay. Majority of sediments are transported southeastward to the Laizhou Bay, where sediments are continuously delivered into the center of the Bohai Sea in a northeastward direction, and part of them are transported eastward alongshore through the Bohai Strait. 69% of sediments from the Yellow River are deposited near the river delta, 31% conveyed seaward, within which, 4% exported to the northern Yellow Sea through the Bohai Strait. Wind wave is the most essential contributor to seasonal variations of sediment concentration in the Bohai Sea, and the contribution of tidal currents is also significant in shallow waters when wind speed is low.
A model study on seasonal spatial-temporal variability of the Lagrangian Residual Circulations in the Bohai Sea

LI Guosheng,WANG Hailong,LI Bailiang,

地理学报 , 2005,
Abstract: The spatial distribution and seasonal variation of the tide-induced Lagrangian Residual Circulations (LRC hereafter), wind-driven LRC, and the coupling dynamic characteristics were simulated using ECOM, given the Hellerman and Rosenstein global monthly-mean wind stresses. The results showed that the tide-induced LRC of the harmonic constituent m2 bears an identical pattern in four seasons in the Bohai Sea: the surface one is weak with random directions; however, there exist a southeast current from the Bohai Strait to the Laizhou bay, and a weakly anticlockwise gyre in the south of the Bohai Strait for the bottom layer LRC. The magnitude of bottom layer tide-induced LRC is larger than the surface one, and moreover, it contributes significantly to the whole LRC in the Bohai Sea. Unlike the identical structure of the tide-induced LRC, the wind driven LRC varies seasonally under the prevailing monsoon. It forms a distinct gyre under the summer and winter monsoons in July and January respectively, but it seems weak and non-directional in April and September.
Optimal Investment Decision on Open-end Funds
Wei Cheng,Guifang Ren,Hailong Wang
International Business Research , 2009, DOI: 10.5539/ibr.v1n1p101
Abstract: The study of open-end fund is conducted in this paper in terms of the theory of Random process and the theory of Sequential Decision, which based on the benefit of investors and the cost of transaction (commission occurred in the transaction). In addition the thesis introduces the method of factor of random discounting, by which investors can choose the optimal way of investment, which is calculated in an analogue case.
Botnet Detection Architecture Based on Heterogeneous Multi-sensor Information Fusion
HaiLong Wang,Jie Hou,ZhengHu Gong
Journal of Networks , 2011, DOI: 10.4304/jnw.6.12.1655-1661
Abstract: As technology has been developed rapidly, botnet threats to the global cyber community are also increasing. And the botnet detection has recently become a major research topic in the field of network security. Most of the current detection approaches work only on the evidence from single information source, which can not hold all the traces of botnet and hardly achieve high accuracy. In this paper, a novel botnet detection architecture based on heterogeneous multi-sensor information fusion is proposed. The architecture is designed to carry out information integration in the three fusion levels of data, feature, and decision. As the core component, a feature extraction module is also elaborately designed. And an extended algorithm of the Dempster-Shafer (D-S) theory is proved and adopted in decision fusion. Furthermore, a representative case is provided to illustrate that the detection architecture can effectively fuse the complicated information from various sensors, thus to achieve better detection effect.
Morphology of epitaxial core-shell nanowires
Hailong Wang,Moneesh Upmanyu,Cristian Ciobanu
Physics , 2008, DOI: 10.1021/nl8020973
Abstract: We analyze the morphological stability against azimuthal, axial, and general helical perturbations for epitaxial core-shell nanowires in the growth regimes limited by either surface diffusion or evaporation-condensation surface kinetics. For both regimes, we find that geometric parameters (i.e., core radius and shell thickness) play a central role in determining whether the nanowire remains cylindrical or its shell breaks up into epitaxial islands similar to those observed during Stranski-Krastanow growth in thin epilayers. The combination of small cores and rapid growth of the shell emerge as key ingredients for stable shell growth. Our results provide an explanation for the different core-shell morphologies reported in the Si-Ge system experimentally, and also identify a growth-induced intrinsic mechanism for the formation of helical nanowires.
Shaping van der Waals nanoribbons via torsional constraints: Scrolls, folds and supercoils
Alireza Shahabi,Hailong Wang,Moneesh Upmanyu
Physics , 2014,
Abstract: Interplay between structure and function in atomically thin crystalline nanoribbons is sensitive to their conformations yet the ability to prescribe them is a formidable challenge. Here, we report a novel paradigm for controlled nucleation and growth of scrolled and folded shapes in finite-length nanoribbons. All-atom computations on graphene nanoribbons (GNRs) and experiments on macroscale magnetic thin films reveal that decreasing the end distance of torsionally constrained ribbons below their contour length leads to formation of these shapes. The energy partitioning between twisted and bent shapes is modified in favor of these densely packed soft conformations due to the non-local van Der Waals interactions in these 2D crystals; they subvert the formation of supercoils that are seen in their natural counterparts such as DNA and filamentous proteins. The conformational phase diagram is in excellent agreement with theoretical predictions. The facile route can be readily extended for tailoring the soft conformations of crystalline nanoscale ribbons, and more general self-interacting filaments
Interband Coherence Induced Correction to Adiabatic Pumping in Periodically Driven Systems
Hailong Wang,Longwen Zhou,Jiangbin Gong
Physics , 2015, DOI: 10.1103/PhysRevB.91.085420
Abstract: Periodic driving can create topological phases of matter absent in static systems. In terms of the displacement of the position expectation value of a time-evolving wavepacket in a closed system, a type of adiabatic dynamics in periodically driven systems is studied for general initial states possessing coherence between different Floquet bands. Under one symmetry assumption, the displacement of the wavepacket center over one adiabatic cycle is found to be comprised by two components independent of the time scale of the adiabatic cycle: a weighted integral of the Berry curvature summed over all Floquet bands, plus an interband coherence induced correction. The found correction is beyond a naive application of the quantum adiabatic theorem but survives in the adiabatic limit due to interband coherence. Our theoretical results are hence of general interest towards an improved understanding of the quantum adiabatic theorem. Our theory is checked using a periodically driven superlattice model with nontrivial topological phases. In addition to probing topological phase transitions, the adiabatic dynamics studied in this work is now also anticipated to be useful in manifesting coherence and decoherence effects in the representation of Floquet bands.
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