Perovskite quantum dots (QDs) are of interest for solution‐processed lasers; however, their short Auger lifetime has limited lasing operation principally to the femtosecond temporal regime the ...photoexcitation levels to achieve optical gain threshold are up to two orders of magnitude higher in the nanosecond regime than in the femtosecond. Here the authors report QD superlattices in which the gain medium facilitates excitonic delocalization to decrease Auger recombination and in which the macroscopic dimensions of the structures provide the optical feedback required for lasing. The authors develope a self‐assembly strategy that relies on sodiumd—an assembly director that passivates the surface of the QDs and induces self‐assembly to form ordered three‐dimensional cubic structures. A density functional theory model that accounts for the attraction forces between QDs allows to explain self‐assembly and superlattice formation. Compared to conventional organic‐ligand‐passivated QDs, sodium enables higher attractive forces, ultimately leading to the formation of micron‐length scale structures and the optical faceting required for feedback. Simultaneously, the decreased inter‐dot distance enabled by the new ligand enhances exciton delocalization among QDs, as demonstrated by the dynamically red‐shifted photoluminescence. These structures function as the lasing cavity and the gain medium, enabling nanosecond‐sustained lasing with a threshold of 25 µJ cm–2.
The manipulation of the surface properties of quantum dots can be used to control their self‐assembly into macroscopic structures that provide the required optical feedback for lasing. Here the use of a ligand that passivates the quantum dot surface and simultaneously induce self‐assembly into superlattice structures that sustain low‐threshold lasing is reported.
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The rock physics model of coalbed methane (CBM) reservoir is significant for the study of CBM content. However, because of the adsorption and dissociation of the CBM reservoir, it is difficult to ...establish models. In addition, the studies on rock physics modeling of the CBM reservoir are scarce. This paper proposes the basic modeling process. First, the coal rock minerals and methane in adsorbed state are used to calculate elastic parameters of coal rock matrix. Then, the differential equivalent medium model is used to get elastic parameters of the dry rock skeleton. The free methane is mixed with water, and finally the Gassmann equation is applied to obtain elastic parameters of the CBM reservoir model. The study on the CBM reservoir rock physics model's response characteristics has found that there is a sensitive negative correlation between CBM content and P-wave velocity and density. The higher CBM content goes with larger absolute values of intercept, gradient, and seismic amplitude, because their seismic attributes are more sensitive to higher CBM content, whereas the response characteristics are opposite with the lower CBM content. The relationship among the CBM content and absolute values of intercept, gradient, and seismic amplitude in the real data of Qinshui Basin is largely consistent with the response characteristics of the established rock physics model, indicating that the CBM reservoir rock physics model proposed in this paper has a certain feasibility, and the response characteristics of its intercept, gradient, and seismic amplitude are more sensitive to predicting CMB reservoirs.
Highlights • Small auto- and cryopreserved allograft skin grafting expands the utilization ratio of available donor sites, and offers a high graft survival rate. • Persistence of dermis in the ...allograft as the dermal substitute may reduce scar formation. • This technique provides an option for more rapid repair of large-area deep burn wounds.
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Optimal transportation plays a fundamental role in many fields in engineering and medicine, including surface parameterization in graphics, registration in computer vision, and generative models in ...deep learning. For quadratic distance cost, optimal transportation map is the gradient of the Brenier potential, which can be obtained by solving the Monge-Ampère equation. Furthermore, it is induced to a geometric convex optimization problem. The Monge-Ampère equation is highly non-linear, and during the solving process, the intermediate solutions have to be strictly convex. Specifically, the accuracy of the discrete solution heavily depends on the sampling pattern of the target measure. In this work, we propose a self-adaptive sampling algorithm which greatly reduces the sampling bias and improves the accuracy and robustness of the discrete solutions. Experimental results demonstrate the efficiency and efficacy of our method.
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The spatial aliasing of seismic data is usually serious because of the sub-sampling rate of the acquisition system. It induces amplitude artifacts or blurs the migration result when the spatial ...aliasing is not removed before migration. The compressed sensing (CS) method has been proven to be an effective tool to restore a sub-sampled signal which is compressible in another domain. Since the wave-fronts of seismic data are sparse and linear in a local spatiotemporal window, they can be significantly compressed by linear Radon transform or Fourier transform. Therefore, seismic data interpolation can be considered as a CS problem. The approximate solution of a CS problem using L0-norm can be achieved by matching pursuit (MP) algorithm. MP becomes intractable due to the high computing cost induced by the increasing dimension of the problem. In order to tackle this issue, a variant of MP-weighted matching pursuit (WMP)-is presented in this paper. Since there is little spatial aliasing in the data of low frequency and the events are supposed to be linear, the linear Radon spectrogram of the interpolated data of low frequency can be used to predict the energy distribution of data of high frequency in a frequency-wavenumber (FK) domain. The predicted energy distribution is then utilized to form the weighted factor of WMP. With this factor, WMP possesses the ability to distinguish the linear events from the spatial aliasing in the FK domain. WMP is also proven to be an efficient algorithm. Since projection onto convex sets (POCS) is another common sparsity-based method, we use Fourier POCS and WMP to realize high-dimension interpolation in numerical examples. The numerical examples show that the interpolation result of WMP significantly improves the quality of seismic data, and the quality of the migration result is also improved by the interpolation.
This paper studies the minimal monomial basis of the n-variable Birkhoff interpolation problem. First, the authors give a fast B-Lex algorithm which has an explicit geometric interpretation to ...compute the minimal monomial interpolation basis under lexieographie order and the algorithm is in fact a generalization of lex game algorithm. In practice, people usually desire the lowest degree interpolation polynomial, so the interpolation problems need to be solved under, for example, graded monomial order instead of lexicographie order. However, there barely exist fast algorithms for the non- lexicographic order problem. Hence, the authors in addition provide a criterion to determine whether an n-variable Birkhoff interpolation problem has unique minimal monomial basis, which means it owns the same minimal monomial basis w.r.t, arbitrary monomial order. Thus, for problems in this case, the authors can easily get the minimal monomial basis with little computation cost w.r.t, arbitrary monomial order by using our fast B-Lex algorithm.
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37.
Surface Registration via Foliation Xiaopeng Zheng; Chengfeng Wen; Na Lei ...
2017 IEEE International Conference on Computer Vision (ICCV),
2017-Oct.
Conference Proceeding
This work introduces a novel surface registration method based on foliation. A foliation decomposes the surface into a family of closed loops, such that the decomposition has local tensor product ...structure. By projecting each loop to a point, the surface is collapsed into a graph. Two homeomorphic surfaces with consistent foliations can be registered by first matching their foliation graphs, then matching the corresponding leaves. This foliation based method is capable of handling surfaces with complicated topologies and large non-isometric deformations, rigorous with solid theoretic foundation, easy to implement, robust to compute. The result mapping is diffeomorphic. Our experimental results show the efficiency and efficacy of the proposed method.
Conspectus Over the past decade, the impressive development of metal halide perovskites (MHPs) has made them leading candidates for applications in photovoltaics (PVs), X-ray scintillators, and ...light-emitting diodes (LEDs). Constructing MHP nanocrystals (NCs) with promising optoelectronic properties using a low-cost approach is critical to realizing their commercial potential. Self-assembly and regrowth techniques provide a simple and powerful “bottom-up” platform for controlling the structure, shape, and dimensionality of MHP NCs. The soft ionic nature of MHP NCs, in conjunction with their low formation energy, rapid anion exchange, and ease of ion migration, enables the rearrangement of their overall appearance via self-assembly or regrowth. Because of their low formation energy and highly dynamic surface ligands, MHP NCs have a higher propensity to regrow than conventional hard-lattice NCs. Moreover, their self-assembly and regrowth can be achieved simultaneously. The self-assembly of NCs into close-packed, long-range-ordered mesostructures provides a platform for modulating their electronic properties (e.g., conductivity and carrier mobility). Moreover, assembled MHP NCs exhibit collective properties (e.g., superfluorescence, renormalized emission, longer phase coherence times, and long exciton diffusion lengths) that can translate into dramatic improvements in device performance. Further regrowth into fused MHP nanostructures with the removal of ligand barriers between NCs could facilitate charge carrier transport, eliminate surface point defects, and enhance stability against moisture, light, and electron-beam irradiation. However, the synthesis strategies, diversity and complexity of structures, and optoelectronic applications that emanate from the self-assembly and regrowth of MHPs have not yet received much attention. Consequently, a comprehensive understanding of the design principles of self-assembled and fused MHP nanostructures will fuel further advances in their optoelectronic applications. In this Account, we review the latest developments in the self-assembly and regrowth of MHP NCs. We begin with a survey of the mechanisms, driving forces, and techniques for controlling MHP NC self-assembly. We then explore the phase transition of fused MHP nanostructures at the atomic level, delving into the mechanisms of facet-directed connections and the kinetics of their shape-modulation behavior, which have been elucidated with the aid of high-resolution transmission electron microscopy (HRTEM) and first-principles density functional theory calculations of surface energies. We further outline the applications of assembled and fused nanostructures. Finally, we conclude with a perspective on current challenges and future directions in the field of MHP NCs.
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Inorganic cesium lead halide perovskites (CsPbI3) are promising materials for efficient wide-bandgap perovskite solar cells, but they suffer from a phase transition from black α phase to yellow δ ...phase at room temperature. Here, we report a facile method to stabilize the α-phase CsPbI3 films via a single-step film deposition process. A small amount (∼1.5 wt %) of sulfobetaine zwitterion mixed in CsPbI3 precursor solution could facilitate the formation of black-phase CsPbI3 films that show significantly improved phase stability in air. The black-phase stabilization can be explained by the formation of small CsPbI3 grains with average size of ∼30 nm, which increased the grain surface area to stabilizes the α phase. The zwitterions were found to impede the crystallization of CsPbI3 perovskite films via electrostatic interaction with the ions and colloids in the CsPbI3 precursor solution. Solar cells using these zwitterion-stabilized perovskite films showed stabilized power conversion efficiency of 11.4% under 1-sun illumination.
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•Three sulfobetaine zwitterions were used to stabilize the α phase of CsPbI3 films•The zwitterions could impede CsPbI3 crystallization to form small-grained films•The increased grain surface energy stabilized the α phase of CsPbI3 films•Solar cells with these CsPbI3 films showed PCE of 11.4% under 1-sun illumination
Due to the superior photovoltaic performance and enormous potential for commercialization, perovskite materials have attracted much attention in the past years. Particularly, CsPbI3 is a cutting-edge material for efficient wide-bandgap solar cells that can potentially boost the efficiency of silicon solar cells with tandem structure. However, CsPbI3 material suffers from a notorious phase transition from black α phase to yellow δ phase at room temperature, which dramatically reduces the absorbed sun light to reduce photovoltaic performance. Here, sulfobetaine zwitterions were mixed in CsPbI3 precursor solution to stabilize the α phase of CsPbI3 films. Solar cells with these α-CsPbI3 films exhibited excellent performance and stability. The α-phase CsPbI3 films may also be used to fabricate efficient light-emitting diodes or photodetectors. The method of phase manipulation may be used in stabilizing the black phase of other perovskite photovoltaic materials, such as FAPbI3 and CsSnI3.
Stabilizing the α phase of CsPbI3 has become one of the most critical prerequisites for its photovoltaic application. We found that mixing a small amount of sulfobetaine zwitterions in CsPbI3 precursor solution could stabilize the α phase of CsPbI3 films at room temperature. The interaction of zwitterion with CsPbI3 impeded the fast crystallization of CsPbI3, which reduced CsPbI3 grain size to stabilize the α phase. Solar cells with these α-phase CsPbI3 films showed stabilized efficiency of 11.4% under 1-sun illumination.
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This work discovers the equivalence relation between quadrilateral meshes and meromorphic quartic differentials. Each quad-mesh induces a conformal structure of the surface, and a meromorphic quartic ...differential, where the configuration of singular vertices corresponds to the configurations of the poles and zeros (divisor) of the meromorphic differential. Due to Riemann surface theory, the configuration of singularities of a quad-mesh satisfies the Abel–Jacobi condition. Inversely, if a divisor satisfies the Abel–Jacobi condition, then there exists a meromorphic quartic differential whose divisor equals the given one. Furthermore, if the meromorphic quartic differential is with finite trajectories, then it also induces a quad-mesh, the poles and zeros of the meromorphic differential correspond to the singular vertices of the quad-mesh.
Besides the theoretic proofs, the computational algorithm for verification of Abel–Jacobi condition is also explained in detail. Furthermore, constructive algorithm of meromorphic quartic differential on genus zero surfaces is proposed, which is based on the global algebraic representation of meromorphic differentials.
Our experimental results demonstrate the efficiency and efficacy of the algorithm. This opens up a novel direction for quad-mesh generation using algebraic geometric approach.
•Equivalence between a quad-mesh and a meromorphic quartic differential.•Abel–Jacobi condition for singularities of a quad-mesh.•Verification of Abel–Jacobi condition.•Construction of meromorphic differential.
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