12,673 research outputs found
Topological shape optimization of multifunctional tissue engineering scaffolds with level set method
© 2016, Springer-Verlag Berlin Heidelberg. A tissue engineering scaffold provides a proper environment to support physiological loads, and enhance cell migration and delivery for re-modeling of regenerating tissue. Hence, in the design of scaffolds, it is required to control the scaffold architecture with mechanical and mass transport properties simultaneously. In this paper, a level set-based topology optimization method will be developed to systematically generate three dimensional (3D) microstructures for tissue engineering scaffolds, with the prescribed properties for mechanical stiffness, fluid porosity and permeability. To create the internal architecture for scaffolds with desired properties, the numerical homogenization method will be used to evaluate the effective properties of the microstructure for building the periodic composite media, and a parametric level set method will be introduced to find the optimized shape and topology of the microstructure. Several numerical examples are used to demonstrate the effectiveness of the proposed method in achieving scaffolds with desired multifunctional properties, within the numerically estimated cross-property bounds between the effective bulk modulus and permeability under different porosities
Plaquette order and deconfined quantum critical point in the spin-1 bilinear-biquadratic Heisenberg model on the honeycomb lattice
We have precisely determined the ground state phase diagram of the quantum
spin-1 bilinear-biquadratic Heisenberg model on the honeycomb lattice using the
tensor renormalization group method. We find that the ferromagnetic,
ferroquadrupolar, and a large part of the antiferromagnetic phases are stable
against quantum fluctuations. However, around the phase where the ground state
is antiferroquadrupolar ordered in the classical limit, quantum fluctuations
suppress completely all magnetic orders, leading to a plaquette order phase
which breaks the lattice symmetry but preserves the spin SU(2) symmetry. On the
evidence of our numerical results, the quantum phase transition between the
antiferromagnetic phase and the plaquette phase is found to be either a direct
second order or a very weak first order transition.Comment: 6 pages, 9 figures, published versio
Querying cohesive subgraphs by keywords
© 2018 IEEE. Keyword search problem has been widely studied to retrieve related substructures from graphs for a keyword set. However, existing well-studied approaches aim at finding compact trees/subgraphs containing the keywords, and ignore a critical measure, density, to reflect how strongly and stablely the keyword nodes are connected in the substructure. In this paper, we study the problem of finding a cohesive subgraph containing the query keywords based on the k-Truss model, and formulate it as minimal dense truss search problem, i.e., finding minimal subgraph with maximum trussness covering the keywords. We first propose an efficient algorithm to find the dense truss with the maximum trussness containing keywords based on a novel hybrid KT-Index (Keyword-Truss Index). Then, we develop a novel refinement approach to extract the minimal dense truss based on the anti-monotonicity property of k-Truss. Experimental studies on real datasets show the outperformance of our method
Submillimeter continuum observations of Sagittarius B2 at subarcsecond spatial resolution
We report the first high spatial resolution submillimeter continuum
observations of the Sagittarius B2 cloud complex using the Submillimeter Array
(SMA). With the subarcsecond resolution provided by the SMA, the two massive
star-forming clumps Sgr B2(N) and Sgr B2(M) are resolved into multiple compact
sources. In total, twelve submillimeter cores are identified in the Sgr B2(M)
region, while only two components are observed in the Sgr B2(N) clump. The gas
mass and column density are estimated from the dust continuum emission. We find
that most of the cores have gas masses in excess of 100 M and column
densities above 10 cm. The very fragmented appearance of Sgr
B2(M), in contrast to the monolithic structure of Sgr B2 (N), suggests that the
former is more evolved. The density profile of the Sgr B2(N)-SMA1 core is well
fitted by a Plummer density distribution. This would lead one to believe that
in the evolutionary sequence of the Sgr B2 cloud complex, a massive star forms
first in an homogeneous core, and the rest of the cluster forms subsequently in
the then fragmenting structure.Comment: 4 pages, 2 figures, accepted by A&A letter
Two-dimensional structures of ferroelectric domain inversion in LiNbO3 by direct electron beam lithography
We report on the fabrication of domain-reversed structures in LiNbO3 by means
of direct electron beam lithography at room temperature without any static
bias. The LiNbO3 crystals were chemically etched after the exposure of electron
beam and then, the patterns of domain inversion were characterized by atomic
force microscopy (AFM). In our experiment, an interesting phenomenon occurred
when the electron beam wrote a one-dimensional (1-D) grating on the negative
c-face: a two-dimensional (2-D) dotted array was observed on the positive c-
face, which is significant for its potential to produce 2-D and
three-dimensional photonic crystals. Furthermore, we also obtained 2-D
ferroelectric domain inversion in the whole LiNbO3 crystal by writing the 2-D
square pattern on the negative c-face. Such a structure may be utilized to
fabricate 2-D nonlinear photonic crystal. AFM demonstrates that a 2-D
domain-reversed structure has been achieved not only on the negative c-face of
the crystal, but also across the whole thickness of the crystal.Comment: 17 pages, 4 figure
Motion planning and control strategy of a cable-driven body weight support gait training robot
In this paper, a cable-driven body weight support gait training robot (C-BWSGTR) that provides patients with partial body weight support as well as a kind of stable gait training driving force was
designed; this device enabled those patients to walk again. Firstly, the overall
configuration of the C-BWSGTR was determined, and the structural
composition and working principle of the robot were established. Secondly, the
vector algebra method was applied to carry out the kinematic analysis and
establish the mathematical model of the C-BWSGTR. The displacement
of each cable during the patient gait training was also calculated. Thirdly, the
motion planning of the C-BWSGTR was carried out in stages, using the
time–phase distribution relationship based on an S-shaped speed curve.
Meanwhile, the displacement, speed, and acceleration of each
cable during the patient gait training were calculated and
corresponding change curves were generated. Finally, a position servo composite
control strategy for the C-BWSGTR was designed by analyzing the robot's
dynamic characteristics of the forward channel transfer function. The simulation
analysis and prototype experiment in this paper verified that the designed
composite position servo control strategy can meet the requirements of the
system with respect to stability and a fast response
of the system to the loading command.</p
STED microscopy reveals in-situ photoluminescence properties of single nanostructures in densely perovskite thin films.
All-inorganic perovskite nanomaterials have attracted much attention recently due to their prominent optical performance and potential application for optoelectronic devices. The carriers dynamics of all-inorganic perovskites has been the research focus because the understanding of carriers dynamics process is of critical importance for improving the fluorescence conversion efficiency. While photophysical properties of excited carrier are usually measured at the macroscopic scale, it is necessary to probe the in-situ dynamics process at the nanometer scale and gain deep insights into the photophysical mechanisms and their localized dependence on the thin-film nanostructures. Stimulated emission depletion (STED) nanoscopy with super-resolution beyond the diffraction limit can directly provide explicit information at a single particle level or nanometer scale. Through this unique technique, we firstly study the in-situ dynamics process of single CsPbBr3 nanocrystals(NCs) and nanostructures embedded inside high-dense samples. Our findings reveal the different physical mechanisms of PL blinking and antibunching for single CsPbBr3 NCs and nanostructures that correlate with thin-film nanostructural features (e.g. defects, grain boundaries and carrier mobility). The insights gained into such nanostructure-localized physical mechanisms are critically important for further improving the material quality and its corresponding device performance
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