The prospective applications of metallic glasses are limited by their lack of ductility, attributed to shear banding inducing catastrophic failure. A concise depiction of the local atomic arrangement ...(local atomic packing and chemical short‐range order), induced by shear banding, is quintessential to understand the deformation mechanism, however still not clear. An explicit view of the complex interplay of local atomic structure and chemical environment is presented by mapping the atomic arrangements in shear bands (SBs) and in their vicinity in a deformed Vitreloy 105 metallic glass, using the scanning electron diffraction pair distribution function and atom probe tomography. The results experimentally prove that plastic deformation causes a reduction of geometrically favored polyhedral motifs. Localized motifs variations and antisymmetric (bond and chemical) segregation extend for several hundred nanometers from the SB, forming the shear band affected zones. Moreover, the variations within the SB are found both perpendicular and parallel to the SB plane, also observable in the oxidation activity. The knowledge of the structural–chemical changes provides a deeper understanding of the plastic deformation of metallic glasses especially for their functional applications and future improvements.
Direct mapping of local atomic bonding and packing in deformed metallic glass is reported, with identification of the structural/chemical variation in and across the shear bands, forming the shear‐affected zones. The results confirm theoretical predictions for local softening in the deformed areas and provide necessary information to further engineer the catastrophic deformation failure of metallic glasses.
TOPAS and its academic variant TOPAS‐Academic are nonlinear least‐squares optimization programs written in the C++ programming language. This paper describes their functionality and architecture. The ...latter is of benefit to developers seeking to reduce development time. TOPAS allows linear and nonlinear constraints through the use of computer algebra, with parameter dependencies, required for parameter derivatives, automatically determined. In addition, the objective function can include restraints and penalties, which again are defined using computer algebra. Of importance is a conjugate gradient solution routine with bounding constraints which guide refinements to convergence. Much of the functionality of TOPAS is achieved through the use of generic functionality; for example, flexible peak‐shape generation allows neutron time‐of‐flight (TOF) peak shapes to be described using generic functions. The kernel of TOPAS can be run from the command line for batch mode operation or from a closely integrated graphical user interface. The functionality of TOPAS includes peak fitting, Pawley and Le Bail refinement, Rietveld refinement, single‐crystal refinement, pair distribution function refinement, magnetic structures, constant wavelength neutron refinement, TOF refinement, stacking‐fault analysis, Laue refinement, indexing, charge flipping, and structure solution through simulated annealing.
TOPAS is nonlinear least‐squares optimization computer program written primarily for the analysis of crystallographic problems.
Irena, a tool suite for analysis of both X‐ray and neutron small‐angle scattering (SAS) data within the commercial Igor Pro application, brings together a comprehensive suite of tools useful for ...investigations in materials science, physics, chemistry, polymer science and other fields. In addition to Guinier and Porod fits, the suite combines a variety of advanced SAS data evaluation tools for the modeling of size distribution in the dilute limit using maximum entropy and other methods, dilute limit small‐angle scattering from multiple non‐interacting populations of scatterers, the pair‐distance distribution function, a unified fit, the Debye–Bueche model, the reflectivity (X‐ray and neutron) using Parratt's formalism, and small‐angle diffraction. There are also a number of support tools, such as a data import/export tool supporting a broad sampling of common data formats, a data modification tool, a presentation‐quality graphics tool optimized for small‐angle scattering data, and a neutron and X‐ray scattering contrast calculator. These tools are brought together into one suite with consistent interfaces and functionality. The suite allows robust automated note recording and saving of parameters during export.
PDFgetX3 is a new software application for converting X‐ray powder diffraction data to an atomic pair distribution function (PDF). PDFgetX3 has been designed for ease of use, speed and automated ...operation. The software can readily process hundreds of X‐ray patterns within a few seconds and is thus useful for high‐throughput PDF studies that measure numerous data sets as a function of time, temperature or other environmental parameters. In comparison to the preceding programs, PDFgetX3 requires fewer inputs and less user experience and it can be readily adopted by novice users. The live‐plotting interactive feature allows the user to assess the effects of calculation parameters and select their optimum values. PDFgetX3 uses an ad hoc data correction method, where the slowly changing structure‐independent signal is filtered out to obtain coherent X‐ray intensities that contain structure information. The output from PDFgetX3 has been verified by processing experimental PDFs from inorganic, organic and nanosized samples and comparing them with their counterparts from a previous established software. In spite of the different algorithm, the obtained PDFs were nearly identical and yielded highly similar results when used in structure refinement. PDFgetX3 is written in the Python language and features a well documented reusable code base. The software can be used either as a standalone application or as a library of PDF processing functions that can be called from other Python scripts. The software is free for open academic research but requires paid license for commercial use.
Thanks to their portability and the non‐equilibrium character of the discharges, microplasmas are finding application in many scientific disciplines. Although microplasma research has traditionally ...been application driven, microplasmas represent a new realm in plasma physics that still is not fully understood. This paper reviews existing microplasma sources and discusses charged particle kinetics in various microdischarges. The non‐equilibrium character highlighted in this manuscript raises concerns about the accuracy of fluid models and should trigger further kinetic studies of high‐pressure microdischarges. Finally, an outlook is presented on the biomedical application of microplasmas.
Unlike the real line, the real space Rd, for d ≥ 2, is not canonically ordered. As a consequence, such fundamental univariate concepts as quantile and distribution functions and their empirical ...counterparts, involving ranks and signs, do not canonically extend to the multivariate context. Palliating that lack of a canonical ordering has been an open problem for more than half a century, generating an abundant literature and motivating, among others, the development of statistical depth and copula-based methods. We show that, unlike the many definitions proposed in the literature, the measure transportation-based ranks and signs introduced in Chernozhukov, Galichon, Hallin and Henry (Ann. Statist.45 (2017) 223–256) enjoy all the properties that make univariate ranks a successful tool for semiparametric inference. Related with those ranks, we propose a new center-outward definition of multivariate distribution and quantile functions, along with their empirical counterparts, for which we establish a Glivenko–Cantelli result. Our approach is based on McCann (Duke Math. J.80 (1995) 309–323) and our results do not require any moment assumptions. The resulting ranks and signs are shown to be strictly distribution-free and essentially maximal ancillary in the sense of Basu (Sankhyā21 (1959) 247–256) which, in semiparametric models involving noise with unspecified density, can be interpreted as a finite-sample form of semiparametric efficiency. Although constituting a sufficient summary of the sample, empirical center-outward distribution functions are defined at observed values only. A continuous extension to the entire d-dimensional space, yielding smooth empirical quantile contours and sign curves while preserving the essential monotonicity and Glivenko–Cantelli features of the concept, is provided. A numerical study of the resulting empirical quantile contours is conducted.
Abstract
Energetic particles produced by neutral beams are observed to excite energetic-particle-driven geodesic acoustic modes in tokamaks. We study the effects of anisotropy of distribution ...function of the energetic particles on the excitation of such instabilities with ORB5, a gyrokinetic particle-in-cell code. Numerical results are shown for linear electrostatic simulations with ORB5. The growth rate is found to be sensitively dependent on the phase-space shape of the distribution function. The behavior of the instability is qualitatively compared to the theoretical analysis of dispersion relations. Realistic neutral beam energetic particle anisotropic distributions are obtained from the heating solver RABBIT and are introduced into ORB5 as input distribution function. Results show a dependence of the growth rate on the injection angle. A qualitative comparison between the numerical results and experimental measurements is presented. An explanation for the differences is advanced.
For the first time the cumulative distribution function and histogram of the crossover frequency of a contemporary operational amplifier ADA4898-2 is experimentally studied. Using a USB lock–in ...amplifier, which allows automatic frequency sweep of the current response of a non-inverting amplifier with significant static amplification, we measure the crossover frequency of 200 samples of ADA4898-2 operational amplifiers. This new method gives a significant advantage in accuracy and speed of study of every operational amplifier. The theory we use is based on the universal relation between time dependent output and input voltages. This common relation for all operational amplifiers is applicable for frequencies much smaller than the crossover frequency and the frequencies of non-dominant poles. In other words, this approximation is adequate, when an operational amplifier is included in a circuit with significant amplification.
•Experimental measurements of operational amplifier crossover frequency.•Automatic frequency sweep allows advantage in measurement accuracy and speed.•Method based on universal relation between time dependent output and input voltages.•Cumulative distribution function obtained from the measurements.•Histogram of the crossover frequency obtained from the measurements.
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•The micropore and mesopore models of bituminous coal were established.•Simulation of unary CH4, CO2 and N2 adsorbed into micro- and meso-pores of coal by Monte Carlo simulation.•Pore ...size had a great influence on gas adsorption and diffusion.•In micro- and meso-pores, the effective distance and radius of action between coal molecules and gas molecules were different.
The characteristics of gas loading, diffusion and adsorption in pore models of coal molecules within variety pore sizes were different. The Grand canonical Monte Carlo and Molecular Dynamic were conducted in this paper to investigate the loading, adsorption and diffusion characteristics of CH4, CO2, and N2 in micropores and mesopores. Three micropore models (0.5, 1 and 2 nm) and two mesopore models (5 and 8 nm) were established to study the microscopic mechanism of three gases loading, adsorption and diffusion. The results shown that the loading amounts in pore models increased with increasing pore size. However, the tight adsorption amounts and adsorption heats decreased with increasing pore size. The tight adsorption amounts, loading amounts and adsorption heats all followed CO2 > CH4 > N2. There were exponential changes between isometric heats and loading amounts. The diffusion characteristic of three gases in the pores was CH4 > N2 > CO2, and the larger pores were more conducive to gas diffusion. Radial Distribution Function was implemented to study the action radius between gases and C atoms of coal molecules. There was the smallest effective distance and the largest effective radius between CO2 and C atoms. The action distance between N2 and C atoms was the largest, and the action scope between them was the smallest.
Nanozymes are nanomaterials with biocatalytic properties under physiological conditions and are one class of artificial enzymes to overcome the high cost and low stability of natural enzymes. ...However, surface ligands on nanomaterials will decrease the catalytic activity of the nanozymes by blocking the active sites. To address this limitation, ligand‐free PtAg nanoclusters (NCs) are synthesized and applied as nanozymes for various enzyme‐mimicking reactions. By taking advantage of the mutual interaction of zeolitic imidazolate frameworks (ZIF‐8) and Pt precursors, a good dispersion of PtAg bimetal NCs with a diameter of 1.78 ± 0.1 nm is achieved with ZIF‐8 as a template. The incorporation of PtAgNCs in the voids of ZIF‐8 is confirmed with structural analysis using the atomic pair‐distribution function and powder X‐ray diffraction. Importantly, the PtAgNCs present good catalytic activity for various enzyme‐mimicking reactions, including peroxidase‐/catalase‐ and oxidase‐like reactions. Further, this work compares the catalytic activity between PtAg NCs and PtAg nanoparticles with different compositions and finds that these two nanozymes present a converse dependency of Ag‐loading on their activity. This study contributes to the field of nanozymes and presents a potential option to prepare ligand‐free bimetal biocatalysts with sizes in the nanocluster regime.
Ligand‐free PtAg nanoclusters grow in the voids of ZIFs as shown by combing the atomic pair‐distribution function (PDF) and powder X‐ray diffraction (PXRD) and transmission electron microscope (TEM). Moreover, their enzyme mimics performance is evaluated by three different enzymatic reactions and compared with bigger PtAg nanoparticles and monometallic nanoclusters and the mechanism is further discussed.
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