课程文献中心 更多>>

关键词： polarization microscopy   single-shot imaging   birefringent structure  

摘要： Polarization light microscopes are powerful tools for probing molecular order and orientation in birefringent materials. While a number of polarization microscopy techniques are available to access steady-state properties of birefringent samples, quantitative measurements of the molecular orientation dynamics on the millisecond time scale have remained a challenge. We propose polarized shearing interference microscopy (PSIM), a single-shot quantitative polarization imaging method, for extracting the retardance and orientation angle of the laser beam transmitting through optically anisotropic specimens with complex structures. The measurement accuracy and imaging performance of PSIM are validated by imaging a birefringent resolution target and a bovine tendon specimen. We demonstrate that PSIM can quantify the dynamics of a flowing lyotropic chromonic liquid crystal in a microfluidic channel at an imaging speed of 506 frames per second (only limited by the camera frame rate), with a field-of-view of up to 350 x 350 mu m(2) and a diffraction-limit spatial resolution of similar to 2 mu m. We envision that PSIM will find a broad range of applications in quantitative material characterization under dynamical conditions.

关键词： Lithium compounds  

摘要： In this work, the detailed reaction mechanism of the astrochemically relevant exoergic and barrierless H + LiH+ -> H-2 + Li+ reaction is investigated by both time-dependent wave packet and quasi-classical trajectory (QCT) methods on the ab initio electronic ground state potential energy surface reported by Martinazzo et al. [Martinazzo et al., J. Chem. Phys., 2003, 119, 11241]. The interference terms due to the coherence between the partial waves are quantified. When plotted along the scattering angle they reveal interference of constructive or destructive nature. Significant interference was found in the differential cross-section (DCS) which is a symbolic of the non-statistical nature of the reaction. This is further complemented by calculating the lifetime of the collision complex by the QCT method. It is found that the reaction follows a direct stripping mechanism at higher collision energies and yields forward scattered products from collisions involving high total angular momentum. At low collision energies, the reaction follows a mixed direct/indirect mechanism but with a dominant indirect contribution. The product state-resolved DCSs reveal that two opposite mechanisms co-exist, both at low and high collision energies. The microscopic scattering mechanism of the reaction is found to be unaffected by the ro-vibrational excitation of the reagent diatom.

关键词： Peptides and proteins   Kinetic modeling   Oligomers   Aggregation   Nucleation  

摘要： We combined kinetic, thermodynamic, and structural information from single-molecule (protein folding) and two-molecule (association) explicit-solvent simulations for determination of kinetic parameters in protein aggregation nucleation with insulin as the model protein. A structural bioinformatics approach was developed to account for heterogeneity of aggregation-prone species, with the transition complex theory found applicable in modeling association kinetics involving non-native species. Specifically, the kinetic pathway for formation of aggregation- (N) prone oligomeric species was found to contain a structurally specific dominant binding mode, making the kinetic process similar to native protein association. The kinetic parameters thus obtained were used in a population balance model, and accurate predictions for aggregation nucleation time varying over 2 orders of magnitude with changes in either insulin concentration or an aggregation-inhibitor ligand concentration were obtained, while an empirical parameter set was not found to be transferable for prediction of ligand effects. Further, this physically determined kinetic parameter set provided several mechanistic insights, such as identification of the rate-limiting step in aggregation nucleation and a quantitative explanation for the switch from Arrhenius to non-Arrhenius aggregation kinetics around the melting temperature of insulin.

关键词： p-Laplacian parabolic equations   nonlocal boundary conditions   blow-up  

摘要： The purpose of this paper is to deal with the blow-up problems of the following p-Laplacian parabolic equations with nonlocal boundary conditions: (h(u)) t =. center dot |. u|p-2. u + k1(t)f (u) in x (0, t *), |.u|p-2. u.. = k2(t) g(u) dx on. x (0, t*), u(x, 0) = u0(x) = 0 in , where p> 2, . Rn (n = 2) is a bounded convex region, and the boundary. is smooth. With the help of differential inequality techniques and Sobolev inequalities, we prove that the blow-up does occur on some certain conditions of the data. In addition, we obtain upper bounds and lower bounds of the blow-up time in . Rn (n >= 2).

关键词： Rate constants  

摘要： The reaction probabilities, integral cross sections, energy efficiency and rate constants are investigated for the F + C2H6 reaction using the quantum reaction dynamics, wave packet method. The ground-state integral cross section calculated using a six-degree-of-freedom approach is in very good agreement with the quasi-classical trajectory results. We find that the H-CH2CH3 stretching motion has the largest enhancement to reactivity, followed by the H-CH2-CH3 bending motion. However, the stretching motion between CH2 and CH3 slightly hinders the reactivity. The energy-form efficacy based on an equal amount of total energy shows that translational energy is more effective in enhancing the reactivity than vibrational energy of the H-CH2CH3 stretching motion at a relatively lower translational energy, while the reverse is true at a relatively high translational energy. An energy-shifting method is employed to calculate the full-dimensional rate constants. The quantum rate constants agree well with one of the two main experimental measurements, and the activation energy has an excellent agreement with the one calculated using canonical variational transition-state theory.

关键词： thermodynamics   carrier injection   perovskite   quantum dot   spectral stability   deep-blue LEDs  

摘要： Precisely tuning emission spectra through the component control of mixed halides has been proved to be an efficient method for procuring deep-blue perovskite LEDs (PeLEDs). However, the inferior color instability and lifetime attenuation, originated from vacancy- and trap-mediated mechanisms under an external field, remain an uninterruptedly formidable challenge for the commercial development of PeLEDs. Here, an ultrafast thermodynamics-induced injection enhancement strategy was employed to promote efficient carrier recombination within perovskite quantum dots (QDs), accompanied by less inefficient charge accumulation and trap generation, enabling deep-blue PeLEDs with improved thermal and spectral stability. The resultant PeLEDs feature an external quantum efficiency (EQE) of 3.66%, a max luminance of 2100 cd/m(2) at the electroluminescence (EL) of 460 nm, and a halftime of 288 s. This work provides a general platform for promoting the EL performances and a deep insight into unraveling the degradation mechanism of blue PeLEDs.

关键词： Liquids  

摘要： The structural relaxation slows down drastically upon approaching the glass transition, accompanied by the significant growth of dynamic heterogeneity. The fundamental question of elusiveness and interest is whether there exists an underlying quantitative relationship between structural relaxation and dynamic heterogeneity. Here, we reveal that (b) over tilde which is related to the reduced mean square displacements to overcome the energy barriers of activated jumps, instead of the kinetic fragility m, is the genuine key parameter connecting dynamic heterogeneity with structural relaxation for varying types of glass formers. Furthermore, based on the dependence of dynamic heterogeneity on the Debye-Waller factor we obtained a direct quantitative relation between dynamic heterogeneity and structural relaxation is built for different glass-forming liquids. More importantly, a scaling collapse of structural relaxation and dynamic heterogeneity is achieved by the important parameter (b) over tilde. These results are of fundamental and critical importance for developing a unified theory of glassy dynamics.

关键词： Algorithms   Quantum mechanics   Mathematical methods   Circuits   Hamiltonians  

摘要： Simulating molecular dynamics (MD) within a comprehensive quantum framework has been a long-standing challenge in computational chemistry. An exponential scaling of computational cost renders solving the time dependent Schrodinger equation (TDSE) of a molecular Hamiltonian, including both electronic and nuclear degrees of freedom (DOFs), as well as their couplings, infeasible for more than a few DOFs. In the Born-Oppenheimer (BO), or adiabatic, picture, electronic and nuclear parts of the wave function are decoupled and treated separately. Within this framework, the nuclear wave function evolves along potential energy surfaces (PESs) computed as solutions to the electronic Schrodinger equation parametrized in the nuclear DOFs. This approximation, together with increasingly elaborate numerical approaches to solve the nuclear time dependent Schrodinger equation (TDSE), enabled the treatment of up to a few dozens of degrees of freedom (DOFs). However, for particular applications, such as photochemistry, the BO approximation breaks down. In this regime of non-adiabatic dynamics, solving the full molecular problem including electron-nuclear couplings becomes essential, further increasing the complexity of the numerical solution. Although valuable methods such as multiconfigurational time-dependent Hartree (MCTDH) have been proposed for the solution of the coupled electron-nuclear dynamics, they remain hampered by an exponential scaling in the number of nuclear DOFs and by the difficulty of finding universal variational forms. In this Account, we present a perspective on novel quantum computational algorithms, aiming to alleviate the exponential scaling inherent to the simulation of many-body quantum dynamics. In particular, we focus on the derivation and application of quantum algorithms for adiabatic and non-adiabatic quantum dynamics, which include efficient approaches for the calculation of the BO potential energy surfaces (PESs). Thereafter, we study the time-evoluti

关键词： Alexandrov-Bakelman-Pucci estimate   Anisotropic Laplacian   Positive drift   Singular perturbation   Two-dimensional Brownian motion  

摘要： We show an Alexandrov-Bakelman-Pucci (ABP) estimate for a PDE with anisotropic Laplacian in two dimensions in unbounded domains, where the drift vector varies in a segment of the positive quadrant. The unbounded domains are assumed to be bounded below in the x-direction, as well as in the y-direction. The constant in the upper estimate of the ABP-estimate, which depends in the usual theorems for bounded domains on the diameter of this domain, depends in our case on the small parameter e, appearing in the anisotropic Laplacian. The result is motivated by certain problems of singular perturbation in stochastic control theory, and our methods are probabilistic. (c) 2021 The Author. Published by Elsevier Inc. This is an open access article under the CC BY license (http://***/licenses/by/4.0/). MSC: primary 35B45, 35J15;secondary 60J25