Energy Window Research Articles

Conformational adaptation and large amplitude motions of 1-phenyl-2,2,2-trifluoroethanol with two water molecules: a rotational spectroscopic and ab initio investigation.

The 1 : 2 adduct of 1-phenyl-2,2,2-trifluoroethanol (PhTFE), a chiral fluoroalcohol, with two water molecules (PhTFE⋯2H2O) was investigated via chirped pulse Fourier-transform microwave (CP-FTMW) spectroscopy and theoretical calculations. A systematic search of the PhTFE⋯2H2O conformational landscape identified 38 stable minima at the B3LYP-D3BJ/def2-TZVPPD level of theory, 27 of which are within an energy window of 10 kJ mol-1 after applying zero-point energy corrections. Rotational spectra of a single PhTFE⋯2H2O conformer along with eight deuterated and three oxygen-18 isotopologues were assigned. Interestingly, the observed PhTFE⋯2H2O conformer contains PhTFE II, the second most stable monomer conformer, and the most stable PhTFE I dihydrate is ca. 4 kJ mol-1 higher in energy. In contrast, PhTFE I⋯H2O was identified experimentally and theoretically as the most stable 1 : 1 conformer. Furthermore, the observed dihydrate structure experiences large amplitude motions connecting three theoretical minima which differ only in which water oxygen lone pairs are involved in the hydrogen-bonds, i.e., the free OH pointing directions. Additionally, the ortho and para-H2O tunnelling splittings were detected and attributed to the interchange water hydrogen atoms which interact with the aromatic part of PhTFE but not for the water interacting with PhTFE hydroxy group. Extensive theoretical modelling was carried out to gain insight into the associated large amplitude motions including tunnelling, supported by the experimental isotopic and tunnelling splitting data.

Vanadium-decorated 2D polyaramid material for high-capacity hydrogen storage: Insights from DFT simulations

Herein, systematic computational investigations comprising density functional theory and ab initio molecular dynamics simulations (AIMD) have been conducted to assess the viability of vanadium decoration over the newly synthesized 2D polyaramid material (2DPA-I) as a potentially reversible hydrogen storage substrate for light fuel cell vehicles. The binding energies of V at different positions over 2DPA-I were compared, and the optimum site for V decoration was in the plane of 2DPA-I. The H2 binding ability of V-decorated 2DPA-I was improved over that of pristine 2DPA-I by 185.71 %. A single V atom decorated over 2DPA-I can effectively bind 7 H2 molecules, with a gravimetric H2 storage capacity of ~7.3 wt% and desorption temperature ~330 K at a favourable binding energy window (~−0.4 eV) to facilitate reversible H2 binding. V-decorated 2DPA-I remained stable at elevated temperatures as verified by AIMD simulations, and a substantial energy barrier of ~3 eV exists for the movement of the V atom across the 2DPA-I surface. The interaction of V with 2DPA-I and H2 with V-decorated 2DPA-I proceeds with a charge flow from the V atom towards H2 and 2DPA-I, respectively. The binding energy and charge transfer analysis of the interaction of H2 with V-decorated 2DPA-I indicates possible Kubas interactions. We predict that V-decorated 2DPA-I has immense potential for on-board H2 storage applications in light fuel cell vehicles.

Accelerating GW Calculations of Point Defects with the Defect-Patched Screening Approximation.

The GW approximation has been widely accepted as an ab initio tool for calculating defect levels with the many-electron effect included. However, the GW simulation cost increases dramatically with the system size, and unfortunately, large supercells are often required to model low-density defects that are experimentally relevant. In this work, we propose to accelerate GW calculations of point defects by reducing the simulation cost of many-electron screening, which is the primary computational bottleneck. The random-phase approximation of many-electron screening is divided into two parts: one is the intrinsic screening, calculated using a unit cell of pristine structures, and the other is the defect-induced screening, calculated using the supercell within a small energy window. Depending on specific defects, one may only need to consider the intrinsic screening or include the defect contribution. This approach avoids the summation of many conduction states of supercells and significantly reduces the simulation cost. We have applied it to calculate various point defects, including neutral and charged defects in two-dimensional and bulk systems with small or large bandgaps. The results are consistent with those from the direct GW simulations. This defect-patched screening approach not only clarifies the roles of defects in many-electron screening but also paves the way to fast screen defect structures/materials for novel applications, including single-photon sources, quantum qubits, and quantum sensors.

Surface analysis insight note: Illustrating the effect of adventitious contamination on Pt photoemission peak intensities

Adventitious carbon contaminations are not only omnipresent and used for charge referencing of XPS spectra but also can alter the apparent presence of the element peaks that span over the large spectral window of binding energies. This Insight note describes the effect of an adventitious contamination layer on Pt and presents, in brief, the approach whereby the component spectra are derived for ion beam cleaned Pt samples that can then utilize linear mathematics to peak fit said spectra thus quantifying the amount of each component including that assigned to the contamination itself of Pt metal.

3D quantum Hall effect in a topological nodal-ring semimetal

A quantized Hall conductance (not conductivity) in three dimensions has been searched for more than 30 years. Here we explore it in 3D topological nodal-ring semimetals, by employing a minimal model describing the essential physics. In particular, the bulk topology can be captured by a momentum-dependent winding number, which confines the drumhead surface states in a specific momentum region. This confinement leads to a surface quantum Hall conductance in a specific energy window in this 3D system. The winding number for the drumhead surface states and Chern number for their quantum Hall effect form a two-fold topological hierarchy. We demonstrate the one-to-one correspondence between the momentum-dependent winding number and wavefunction of the drumhead surface states. More importantly, we stress that breaking chiral symmetry is necessary for the quantum Hall effect of the drumhead surface states. The analytic theory can be verified numerically by the Kubo formula for the Hall conductance. We propose an experimental setup to distinguish the surface and bulk quantum Hall effects. The theory will be useful for ongoing explorations on nodal-ring semimetals.

Influence of window recess on solar loads, heat loss and external condensation

The current architectural preference for the recess of windows is in line with the forefront of the building facade. The recess of a window has consequences for: solar loads, heat loss, and risk of outside condensation. This paper presents an analysis of these issues in relation to variations in recess depth and differences in orientation of the window. The solar load in buildings is highly influenced by the depth of the window recess, depending on the orientation. Solar gains both contribute to heating the building during the heating season, but also to overheating in other periods. The latter being especially important for other buildings than residential buildings. This is analysed for different window orientations and size (height and width) as wells as the recess depth. Recess depth also influences the overall heat loss though the facade and window and is analysed through detailed calculations. Last, but not least, condensation on the external face of modern low energy windows causes a serious issue regarding visual comfort in the mornings during periods with clear weather and low outdoor temperatures. Analyses of the recess depth influence on the outside condensation risk is presented. The issues regarding the recess depth for facade windows is analysed using dynamic simulations of different window and recess depths in different orientations in combination with 2D static calculations of the overall heat loss coefficient for the total window and facade construction in typical highly insulated facade constructions.

Improved cement sheath thickness measurement and its application in cement sheath variation monitoring

Monitoring cement sheath thickness by the logging tool that utilizes Am–Be neutron generator as radiation source is crucial for the secure exploitation of oil and gas fields. Generally, a positive source distance probe is adopted to evaluate the cement sheath thickness by recording single energy window count, but the measurement result is greatly impacted by the working state of instrument. To get accurate changes about the thickness of cement sheath, this paper proposes a dual energy window combination method by photoelectric window and Compton backscatter window based on the scattering and attenuation theory of gamma ray in the medium. Subsequently, the relationship between the counting ratio of low window to high energy window and the thickness of cement sheath is established. By adjusting MCNP model settings, it can be concluded that the borehole fluid, the density of cement sheath, and the thickness of casing effects on the counting ratio of energy window A to energy window C for measuring cement sheath thickness can be disregarded. Besides, high-density formation and corrected borehole diameter are beneficial for evaluating the cement sheath thickness. According to these results, the simulation example shows that the thickness calculation error of the method at the overall cement sheath variations is less than 9%. The research result can provide reference for underground cement sheath monitoring and evaluation method.

Hardware, methodology and applications of 2+D backscatter Mössbauer spectroscopy with simultaneous x-ray and γ-ray detection

A unique method is presented for the acquisition and analysis of 57Fe backscatter Mössbauer spectra with simultaneous detection of the resonant 14.4 keV γ-rays and the characteristic 6.4 keV x-rays, using a custom-built multi-parameter analyser constructed on the basis of commercial analogue to digital converters and high-speed digital latches. The system allows for the simultaneous registration of Doppler-modulation velocities and photon energies, with up to 4096 and 8192 digital channels respectively. This arrangement is in contrast to most related systems, which detect at a single narrow energy window per detector. Samples of arbitrary atomic structure, morphology and surface topography can be studied without altering the setup or the analysis procedure, provided that the samples are at least micrometre sized. The hardware and software that are used to acquire data with minimal dead time are described and the custom and self-contained methods for post-measurement energy discrimination, background correction and velocity-axis folding are discussed. The data are fit using a general Hamiltonian model for the nuclear energy levels of 57Fe and a quantum mechanical description of the angular momentum coupling is utilised, with consideration of the crystalline and chemical disorder of the sample under examination. Three examples of distinct magnetic systems, with thicknesses ranging from m to 6 mm, that were studied using this method are presented, these are: an amorphous CoFeB-based ribbon with ultra-soft coercivity for high-frequency applications, magnetically hard Nd-Fe-B thick films on Si substrates, examined in both as-deposited and annealed states, and a sample from the nickel-rich iron meteorite NWA 6259 that contains the atomically ordered, elevated coercivity, phase of FeNi, tetrataenite. The wide applicability and usefulness of this method is thus demonstrated on three distinct sample morphologies that required little to no surface preparation prior to examination.

Identifying topological corner states in two-dimensional metal-organic frameworks

Due to the diversity of molecular building blocks, the two-dimensional (2D) metal-organic frameworks (MOFs) are ideal platforms to realize exotic lattice models in condensed matter theory. In this work, we demonstrate the universal existence of topological corner states in 2D MOFs with a star lattice configuration, and confirm the intriguing higher-order nontrivial topology in the energy window between two Kagome-bands, or between Dirac-band and four-band. Furthermore, combining first-principles calculations and scanning tunneling microscopy measurements, the unique topological corner state is directly identified in monolayer Ni3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) grown on the Au(111) substrate. Our results not only illustrate the first organic topological state in the experiments, but also offer an exciting opportunity to study higher-order topology in 2D MOFs with the large insulating band gap.

99mTc/123I Dual-Radionuclide Correction for Self-Scatter, Down-Scatter, and Tailing Effect for a CZT SPECT with Varying Tracer Distributions.

SPECT systems distinguish radionuclides by using multiple energy windows. For CZT detectors, the energy spectrum has a low energy tail leading to additional crosstalk between the radionuclides. Previous work developed models to correct the scatter and crosstalk for CZT-based dedicated cardiac systems with similar 99mTc/123I tracer distributions. These models estimate the primary and scatter components by solving a set of equations employing the MLEM approach. A penalty term is applied to ensure convergence. The present work estimates the penalty term for any 99mTc/123I activity level. An iterative approach incorporating Monte Carlo into the iterative image reconstruction loops was developed to estimate the penalty terms. We used SIMIND and XCAT phantoms in this study. Distribution of tracers in the myocardial tissue and blood pool were varied to simulate a dynamic acquisition. Evaluations of the estimated and the real penalty terms were performed using simulations and large animal data. The myocardium to blood pool ratio was calculated using ROIs in the myocardial tissue and the blood pool for quantitative analysis. All corrected images yielded a good agreement with the gold standard images. In conclusion, we developed a CZT crosstalk correction method for quantitative imaging of 99mTc/123I activity levels by dynamically estimating the penalty terms.

Quantitative 177Lu SPECT/CT imaging for personalized dosimetry using a ring-shaped CZT-based camera

BackgroundDosimetry after radiopharmaceutical therapy with 177Lu (177Lu-RPT) relies on quantitative SPECT/CT imaging, for which suitable reconstruction protocols are required. In this study, we characterized for the first time the quantitative performance of a ring-shaped CZT-based camera using two different reconstruction algorithms: an ordered subset expectation maximization (OSEM) and a block sequential regularized expectation maximization (BSREM) combined with noise reduction regularization. This study lays the foundations for the definition of a reconstruction protocol enabling accurate dosimetry for patients treated with 177Lu-RPT.MethodsA series of 177Lu-filled phantoms were acquired on a StarGuide™ (GE HealthCare), with energy and scatter windows centred at 208 (± 6%) keV and 185 (± 5%) keV, respectively. Images were reconstructed with the manufacturer implementations of OSEM (GE-OSEM) and BSREM (Q.Clear) algorithms, and various combinations of iterations and subsets. Additionally, the manufacturer-recommended Q.Clear-based reconstruction protocol was evaluated. Quantification accuracy, measured as the difference between the SPECT-based and the radionuclide calibrator-based activity, and noise were evaluated in a large cylinder. Recovery coefficients (RCs) and spatial resolution were assessed in a NEMA IEC phantom with sphere inserts. The reconstruction protocols considered suitable for clinical applications were tested on a cohort of patients treated with [177Lu]Lu-PSMA-I&T.ResultsThe accuracy of the activity from the cylinder, although affected by septal penetration, was < 10% for all reconstructions. Both algorithms featured improved spatial resolution and higher RCs with increasing updates at the cost of noise build-up, but Q.Clear outperformed GE-OSEM in reducing noise accumulation. When the reconstruction parameters were carefully selected, similar values for noise (~0.15), spatial resolution (~1 cm) and RCs were found, irrespective of the reconstruction algorithm. Analogue results were found in patients.ConclusionsAccurate activity quantification is possible when imaging 177Lu with StarGuide™. However, the impact of septal penetration requires further investigations. GE-OSEM is a valid alternative to the recommended Q.Clear reconstruction algorithm, featuring comparable performances assessed on phantoms and patients.

Detection of a C4 Criegee Intermediate: Fourier-Transform Microwave Spectroscopy of Methacrolein Oxide.

Pure rotational transitions of methacrolein oxide (MACRO) were observed by Fourier-transform microwave spectroscopy. Among the four low-lying conformers existing within an energy window of 3 kcal/mol, only the lowest-energy conformer, the anti-trans conformer, was detected in a discharged jet of a 1,3-diiode-2-methylprop-1-ene and O2 mixture diluted in Ar. Nineteen pure rotational transitions, in the frequency range from 10 to 25 GHz, most of them showing A/E splitting due to the methyl-top internal rotation, were observed and analyzed by the XIAM program, yielding the internal rotation barrier of 559 cm-1, which very well agrees with a theoretically calculated value, 558 cm-1, at the CCSD(T)/cc-pVTZ level of theory.

Development and performance of SIAT bPET: a high-resolution and high-sensitivity MR-compatible brain PET scanner using dual-ended readout detectors.

Positron emission tomography/magnetic resonance imaging (PET/MRI) is a powerful tool for brain imaging, but the spatial resolution of the PET scanners currently used for brain imaging can be further improved to enhance the quantitative accuracy of brain PET imaging. The purpose of this study is to develop an MR-compatible brain PET scanner that can simultaneously achieve a uniform high spatial resolution and high sensitivity by using dual-ended readout depth encoding detectors. The MR-compatible brain PET scanner, named SIAT bPET, consists of 224 dual-ended readout detectors. Each detector contains a 26 × 26 lutetium yttrium oxyorthosilicate (LYSO) crystal array of 1.4 × 1.4 × 20 mm3 crystal size read out by two 10 × 10 silicon photomultiplier (SiPM) arrays from both ends. The scanner has a detector ring diameter of 376.8mm and an axial field of view (FOV) of 329mm. The performance of the scanner including spatial resolution, sensitivity, count rate, scatter fraction, and image quality was measured. Imaging studies of phantoms and the brain of a volunteer were performed. The mutual interferences of the PET insert and the uMR790 3T MRI scanner were measured, and simultaneous PET/MRI imaging of the brain of a volunteer was performed. A spatial resolution of better than 1.5mm with an average of 1.2mm within the whole FOV was obtained. A sensitivity of 11.0% was achieved at the center FOV for an energy window of 350-750keV. Except for the dedicated RF coil, which caused a ~ 30% reduction of the sensitivity of the PET scanner, the MRI sequences running had a negligible effect on the performance of the PET scanner. The reduction of the SNR and homogeneity of the MRI images was less than 2% as the PET scanner was inserted to the MRI scanner and powered-on. High quality PET and MRI images of a human brain were obtained from simultaneous PET/MRI scans. The SIAT bPET scanner achieved a spatial resolution and sensitivity better than all MR-compatible brain PET scanners developed up to date. It can be used either as a standalone brain PET scanner or a PET insert placed inside a commercial whole-body MRI scanner to perform simultaneous PET/MRI imaging.

Deciphering the non-covalent interactions in the furan⋯hexane complex using rotational spectroscopy and theoretical analyses.

The rotational spectrum of a binary complex formed between furan and n-hexane was investigated using a chirped pulse Fourier transform microwave spectrometer in the range of 2-6GHz. While furan has only one conformer, n-hexane exists in multiple conformations. The conformational landscape of the binary complex was systematically explored by using a semiempirical conformational search tool, namely CREST. The CREST conformational candidates were subjected to further geometry optimization and harmonic frequency calculations at the B3LYP-D3BJ/def2-TZVP level of theory, resulting in 34 minima within an energy window of 5 kJ mol-1. The three most stable furan⋯hexane minima all contain the most stable n-hexane conformer subunit and are separated by relatively low conformational conversion barriers. Additional calculations were carried out to support the conclusive identification of the global minimum structure responsible for the set of assigned rotational transitions. These include calculations at the B3LYP-D3BJ level with the aug-cc-pVTZ and 6-311++G(d,p) basis sets and the MP2/def2-TZVP level, as well as the single point energy calculations at the CCSD(T)-F12/cc-pVDZ level. Further non-covalent interaction and principal interacting orbital analyses show that the synergy of the πfuran → σ*hexane and σhexane → π*furan interactions plays an important role in stabilizing the observed furan-hexane conformer.

A study on energy window-based scatter correction methods in 99mTc and 123I imaging

Tc-99m and I-123 are radionuclides commonly used for diagnostic examination in nuclear medicine. Detection of the scattered photons by the Compton interactions in the photopeak energy window is a factor affecting the image quality. DEW and TEW scatter correction methods are used to improve the image quality degrade by Compton scattered photons. In the study, planar and SPECT images of sphere, rod and cardiac phantom containing different activities were acquired with a gamma camera system. DEW/TEW corrected and uncorrected images for Tc-99m/I-123 were evaluated qualitatively and quantitatively. Both for planar and SPECT images, the DEW and TEW scatter correction methods were found to improve the image quality at varying rates.

Statistical analysis and Monte-Carlo simulation of printed supercapacitors for energy storage systems

This study presents a comprehensive statistical analysis of experimental parameters for 12 printed supercapacitors (SCs) using previously proposed equivalent circuit models (ECMs). Statistical distributions and descriptive statistics, including mean, P-value, and standard deviation (std), are reported indicating a normal distribution for various SC parameters. A statistical method is introduced to determine the maximum potential std in capacitance of multiple SCs within an energy storage module, ensuring voltage limits are not exceeded. A linear relationship is discovered between the applied voltage on the module comprising three SCs in series and the maximum potential std of capacitance, ensuring safe operation. Additionally, a statistical method predicts the energy window range of the SC module after operating an IC chip, enabling better decision-making and system management. Monte-Carlo (MC) simulations predict the long-term charge and discharge performance of individual SCs and the series-connected modules. Results indicate that as long as the parameters’ std remains below a defined threshold, charging behavior remains consistent. The MC simulations provide insight into voltage window ranges after 31 days of self-discharge, aiding in performance prediction and risk assessment. The statistical study approach empowers researchers in the field of printed SC energy storage, supporting performance evaluation, design validation, and evidence-based decision-making.

X-ray absorption fine structure (XAFS)-based radionuclide research at the KIT Light Source

Abstract. In the past two decades, X-ray absorption spectroscopy (XAS) and related synchrotron-based radionuclide speciation techniques have become indispensable, supporting open issues in fundamental radiochemistry and nuclear waste disposal alike. Physicochemical structure information – encoded in the element-specific X-ray absorption fine structure (XAFS) – is obtained by the precise determination of the linear mass absorption coefficient μ(E) of a specimen in an X-ray energy window ΔE encompassing an electronic bonding level of a selected atom type. The characteristic modulations of μ(E) in the vicinity of an “absorption edge” (i.e., the steeply rising absorption probability of photons tuned to the binding energy of inner shell “core” electrons) are attributed to electronic transitions into unoccupied states due to the photoelectric effect. While absorption features close to the edge (arising from excitations into molecular orbitals or empty band structure levels close to the Fermi level) are generally denoted as an X-ray absorption near-edge structure (XANES), the scattering states at higher excitation energies are causing the well-known extended X-ray absorption fine structure (EXAFS). EXAFS oscillations of the post-edge μ(E) are caused by the periodicity of the constructive and destructive interference of outbound and backscattered inbound photoelectron waves (superimposing at the absorbing atom site) when continuously increasing the excitation energy. Quantitative analysis of EXAFS data based on electron scattering theory is a well-established short-range structural probe, providing precise values of interatomic distances (between the absorber atom and its neighbors) and additional information on the type, number, and ordering of neighbor atoms within a local cluster. Recent significant advancements in the quantum theoretical description of core-excited final states have been successful in overcoming persisting ambiguities in XANES data interpretation. Meanwhile, although there are more than 50 synchrotron radiation centers operational in the world, facilities with specialized beamline infrastructure and safety protocols to allow experiments on radioactive samples with activities beyond the exemption limits are still scarce. At the KIT Light Source (at the Karlsruhe Institute of Technology, Karlsruhe, Germany), the Institute for Nuclear Waste Disposal (Institut für Nukleare Entsorgung, INE) operates two beamline end-stations dedicated to the investigation of radionuclide materials by XAFS spectroscopy and related techniques, i.e., the INE-Beamline (operational since 2005) and the ACT station of the CAT-ACT (CATalysis and ACTinide) wiggler beamline (operational since 2016). Samples with total activities amounting to 1.0×106 times the isotope specific exemption limits and 200 mg of fissile isotopes 235U and 239Pu are feasible at both beamlines. Highly versatile detection systems and sample holders – generally avoiding extensive shielding or sample handling in a glove box – have been conceived since the initial commissioning of the beamlines and have enabled unique XAFS measurements such as the first ever investigation of aqueous technetium species at the Tc L3 edge. Investigations of highly radioactive specimens (e.g., spent nuclear fuel or nuclear waste glass fragments) are feasible, regardless of the actual contact dose rate if the radiation field is limited to a few microsieverts per hour at the edge of the experimental table.

The 13C(α,n)16O cross section measurement at low energies at LUNA

One of the main neutron sources for the astrophysical s-process is the 13C(α,n)16O. This reaction takes place in thermally pulsing asymptotic giant branch (TP-AGB) stars in a stellar environmental with temperature of about 90 MK. To model the nucleosynthesis process connected with the reaction, it is important the cross section reaction evaluation inside the so called Gamow peak, in the energy window 150-240 keV. In this work the results of the first 13C(α,n)16O direct measurement performed by the LUNA collaboration in the underground laboratory of LNGS are presented.The measurement covers the energy range 230-300 keV, being the first direct measurement to reach the s-process Gamow window. Lower uncertainties with respect to previous measurements in literature are provided and this allows to reduce overall uncertainties on reaction rates calculation. Selected stellar models have been computed to estimate the impact of our revised reaction rate. Using the lower reaction rate at -2σ, for stars of nearly solar composition, we find sizeable variations for some isotopes, whose production is influenced by the activation of close-by branching points that are sensitive to the neutron density, in particular 60Fe, 205Pb and and 152Gd.

Monte Carlo simulation of SPECT characterization for 223 Ra post-injection scintigraphy.

223 Ra is a promising α-emitting radionuclide for prostate cancer metastasis palliative treatment. Post-injection scintigraphy is of major importance to verify the concentration of the radiopharmaceutical in the targeted sites. Given the low activity administered to patients, the choice of acquisition parameters, including the collimator type, the energy window's width and the photopeak energy to be used, is primordial for the image quality. The purpose of our work was to select the SPECT configuration suitable for 223 Ra post-injection scintigraphy. We conducted simulation studies with a Symbia T6 Siemens SPECT-CT, available in our department. 223 Ra photons energy spectra were assessed for low energy high resolution (LEHR), medium energy (ME) and high energy (HE) collimators. Then, depending on the energy window, we calculated the scatter fraction, the sensitivity and the spatial resolution. Scatter fraction was low for all collimators; however, the contribution of photons that scattered more than twice under the low energy photopeaks was important in the case of LEHR. Sensitivity's best values were obtained in the case of the LEHR collimator; nevertheless, the spatial resolution was very low for this collimator. The latter was best for ME and HE collimators. A combination between a good sensitivity, a high spatial resolution and a low scatter fraction has been determined in the case of the ME collimator, followed by HE collimator as an alternative. To increase the image acquisition statistics with ME collimator, we recommend to use simultaneous energy windows: 20% centered at 82 keV, 20% centered at 154 keV and 20% centered at 270 keV.

Modulating grain boundary-mediated plasticity of high-entropy alloys via chemo-mechanical coupling

Intrinsic chemical disorder and the subsequent interfacial roughening have posed formidable challenges in elucidating the grain boundary (GB)-mediated plasticity in high-entropy alloys (HEAs). Here using a self-propelling atomistic algorithm to probe the complex energy landscape of the CoCrFeMnNi HEAs, in conjunction with location-specific perturbations across GBs exposed to different environments, we investigate atomic-reconfiguration ensembles near GBs and their sensitivities to various chemo-mechanical conditions. Two distinct modes, collective and random, are discovered, and their partitions are dictated by multiple factors, including the activation energy window, external mechanical loading, and local compositions. Remarkably, Fe disproportionately promotes the collective events and facilitates the slip activities near GBs, while Cr atoms suppress the emission of partial dislocations from GBs. These findings imply promising solutions – via synergistic combination of microalloying, heat treatment, and mechanical loading – to selectively trigger desired plasticity modes at needed deformation stage, and hence to achieve an enhanced tunability of HEAs’ mechanical behaviors.