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A self-consistent analysis is reported of traditional diffraction-based particle size determination techniques applied to synthetic diffraction profiles generated with the Patterson approach. The results show that dimensions obtained from traditional techniques utilizing peak fitting or Fourier analysis for single-crystal nanoparticles have best-case error bounds of around 5%. For arbitrarily shaped particles, lower error magnitudes are possible only if the zeroes of the thickness fringes are used. The errors for sizes obtained by integral-breadth- and Fourier-decomposition-based techniques depend on the shape of the diffracting domains. In the case of integral-breadth analysis, crystal shapes which scatter more intensity into the central peak of the rocking curve have lower size errors. For Fourier-decomposition analysis, crystals which have non-uniform distributions of chord lengths exhibit nonlinearities in the initial ranges of the normalized Fourier cosine coefficient versus column length (|A L | versus L) plots, even when the entire rocking curve is used in the decomposition. It is recommended that, in routine analysis, all domain size determination techniques should be applied to all reflections in a diffraction pattern. If there is significant divergence among these results, the `average particle size(s)' obtained might not be reliable.

We analysed a carbapenem-resistant

We analysed a carbapenem-resistant Klebsiella pneumoniae (CRKP) outbreak in the coronavirus disease (COVID) ICU. We retrospectively collected data from ICU records. We identified 25 cases between 12 November 2020 and 19 December 2020, and compared them to 42 controls present in the ICU during the same period. The presence of a femoral haemodialysis catheter was strongly associated with invasive CRKP infections (cases, 9 [36%]; controls, 0 [0%]; odds ratio [OR] 95% confidence intervals [CIs], 21 (5; 89)). We found a significant association between old age and CRKP infection with adverse outcomes. Sequence analysis revealed three distinct carbapenemase genes: blaNDM-1, blaOXA-48 and blaKPC-2. We launched rectal swab sampling upon admission to the ICU, cohorted colonized patients and cases and conducted an intensive training programme for newly employed staff. This study revealed that the emergence and dissemination of CRKP in COVID ICUs were associated with increased adverse outcomes. The presence of a femoral haemodialysis catheter was a significant risk factor for CRKP infections.

This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 639846). AlSb is a less studied member of the III-V semiconductor family, and herein, we report the colloidal synthesis of AlSb quantum dots (QDs) for the first time. Different sizes of colloidal AlSb QDs (5 to 9 nm) were produced by the controlled reaction of AlCl3 and Sb[N(Si(Me)(3))(2)](3) in the presence of superhydride. These colloidal AlSb quantum dots showed excitonic transitions in the UV-A region and a tunable band edge emission (quantum yield of up to 18%) in the blue spectral range. Among all III-V quantum dots, these quantum dots show the brightest core emission in the blue spectral region. European Research Council (ERC) 639846

The results of a systematic rigorous study on the accuracy of lattice parameters computed from X-ray diffraction patterns of ideally perfect nanocrystalline powder and thin-film samples are presented. It is shown that, if the dimensions of such samples are below 20 nm, the lattice parameters obtained from diffraction analysis will deviate from their true values. The relative deviation depends on the relevant size parameter through an inverse power law and, for particular reflections, depends on the angular peak positions. This size-dependent error, Δa/a, is larger than the precision of typical X-ray diffraction measurements for ∼20 nm-thick diffracting domains, and it can be several orders of magnitude larger for particles smaller than 5 nm.

A rigorous study of sampling and intensity statistics applicable for a powder diffraction experiment as a function of crystallite size is presented. This analysis yields approximate equations for the expected value, variance and standard deviations for both the number of diffracting grains and the corresponding diffracted intensity for a given Bragg peak. The classical formalism published in 1948 by Alexander, Klug & Kummer [J. Appl. Phys.(1948),19, 742–753] appears as a special case, limited to large crystallite sizes, in the present analysis. It is observed that both the Lorentz probability expression and the statistics equations used in the classical formalism are inapplicable for nanocrystalline powder samples.

In a previous article [Öztürk, Yan, Hill & Noyan (2014). J. Appl. Cryst. 47, 1016–1025] it was shown that the sampling statistics of diffracting particle populations within a polycrystalline ensemble depended on the size of the constituent crystallites: broad X-ray peak breadths enabled some nano-sized particles to contribute more than one diffraction spot to Debye–Scherrer rings. Here it is shown that the equations proposed by Alexander, Klug & Kummer [J. Appl. Phys. (1948), 19, 742–753] (AKK) to link diffracting particle and diffracted intensity statistics are not applicable if the constituent crystallites of the powder are below 10 nm. In this size range, (i) the one-to-one correspondence between diffracting particles and Laue spots assumed in the AKK analysis is not satisfied, and (ii) the crystallographic correlation between Laue spots originating from the same grain invalidates the assumption that all diffracting plane normals are randomly oriented and uncorrelated. Such correlation produces unexpected results in the selection of diffracting grains. For example, three or more Laue spots from a given grain for a particular reflection can only be observed at certain wavelengths. In addition, correcting the diffracted intensity values by the traditional Lorentz term, 1/cos θ, to compensate for the variation of particles sampled within a reflection band does not maintain fidelity to the number of poles contributing to the diffracted signal. A new term, cos θB/cos θ, corrects this problem.

In this study, the sampling statistics of X-ray diffraction data obtained from polycrystalline nanopowders are studied through analytical formulations and numerical modelling. It is shown that the very large acceptance angles of crystalline nanoparticles can cause issues in computing the number of diffracting grains scattering into a given Bragg reflection. These results intimate that formulations previously tested and verified for polycrystalline aggregates with grains larger than 500 nm should be revalidated for particles with coherent scattering lengths below 10 nm.

In this study,we present a numerical framework for modeling three-dimensional (3D) diffraction data in Bragg coherent diffraction imaging (BraggCDI) experiments and evaluating the quality of obtained 3D complex-valued real-space images recovered by reconstruction algorithms under controlled conditions. The approach is used to systematically explore the performance and the detection limit of this phase-retrieval-based microscopy tool. The numerical investigation suggests that the superb performance of Bragg CDI is achieved with an oversampling ratio above 30 and a detection dynamic range above 6 orders. The observed performance degradation subject to the data binning processes is also studied. This numerical tool can be used to optimize experimental parameters and has the potential to significantly improve the throughput of Bragg CDI method.

We report our experiences with conducting ptychography simultaneously with the X-ray fluorescence measurement using the on-the-fly mode for efficient multi-modality imaging. We demonstrate that the periodic artifact inherent to the raster scan pattern can be mitigated using a sufficiently fine scan step size to provide an overlap ratio of >70%. This allows us to obtain transmitted phase contrast images with enhanced spatial resolution from ptychography while maintaining the fluorescence imaging with continuous-motion scans on pixelated grids. This capability will greatly improve the competence and throughput of scanning probe X-ray microscopy.

Some of the most challenging vibration control problems involve the selection and placement of frequency‐dependent damping devices, such as multilayered viscoelastic materials. In complex structures involving the simultaneous use of several passive damping devices, it is difficult to determine the effectiveness of each device directly from measurements. This question motivates the present analysis, which seeks to quantify the power being dissipated by the structure at selected locations for a given force distribution. The analysis begins with an expression for power flow to the structure from a specified force distribution. This expression involves the real part of the admittance matrix looking into the structure at a set of measurement points. By expanding this matrix as a sum over damping elements that mechanically connect measurement points, one can spatially map the power flow into the structure. While thermodynamics requires that this power flow to the structure be equal to the power dissipated by the structure, it does not require equality of the spatial distributions. In order to understand the spatial distribution of power dissipation, time windowing of the impulse responses is introduced. Examples are developed to explore the effects of the time window. [Work supported by ONR under Grant No. N000140810531.]

A method is proposed for constructing spatial maps of modal damping for viscously damped structures. These maps are intended to be useful in assessing the effectiveness of spatially distributed damping, particularly in complex structures that are damped by a variety of mechanisms. The method uses frequency response measurements and modal analysis to determine the natural frequencies and mode shapes of the damped structure. The damping matrix is estimated directly from the frequency response measurements and is expressed as a sum over connectivity matrices weighted by dashpot constants. This sum is substituted into the well‐known approximation for the modal loss factor that results by neglecting off‐diagonal elements of the modally transformed damping matrix. The resulting expression quantifies the contribution of local dashpot properties to the modal loss factor, and may be visually presented as a spatial map of damping. A significant advantage of this approach is its independence from a detailed model of...

Effective design and placement of damping treatments for complex structures benefit greatly from a knowledge of where the vibrational energy is being dissipated. Previously, the authors presented a method for spatially mapping contributions to the modal loss factor of a viscously damped structure [McDaniel et al., J. Acoust. Soc. Am. 125, 2603 (2009)]. The method is based on an inverse approach that uses experimental data to construct a damping matrix as a summation over elemental dashpots that connect measurement points to each other and to ground. This is followed by an assumption that ignores coupling in the modally transformed damping matrix, resulting in an expression for the modal loss factor as a weighted sum of elemental dashpots. In the present work, the method is applied to a vibrating plate with spatially distributed damping. An experiment is numerically simulated in which vibrational responses are measured at a small number of points. From these measurements, contributions to the modal loss fa...