Modulation Reconstruction Research Articles

Stable tetravalent Ni species generated by reconstruction of FeB-wrapped NiMoO pre-catalysts enable efficient water oxidation at large current densities

High valence transition metals offer highly active electrocatalytic sites for oxygen evolution reaction (OER) but suffer from high formation energy and are thermodynamically unstable in the resting state. Herein, we report the generation of NiFeOOH with highly oxidized and stable tetravalent Ni species through reconstruction and electronic structure modulation. The resulted NiFeOOH electrocatalyst catalyzes OER with ultralow overpotentials of 166 and 213 mV at 10 and 100 mA cm-2, respectively, and high stability (> 100 h) at an ultrahigh current density of 1000 mA cm-2. The formation of stable tetravalent Ni species in NiFeOOH nanosheets/rods structure results in higher Ni-O covalency and enhanced the reactivity of lattice oxygen, thus transferring the reaction path and reducing the reaction energy barrier for OER. This work paves the way for the rational design of electrocatalysts with high-valence metal species and activated lattice oxygen for stable water oxidation at large current densities.

Publisher’s Note: “Strain induced second-order Jahn–Teller reconstruction and magnetic moment modulation at monovacancy in graphene” [J. Appl. Phys. 130, 034303 (2021)

Publisher’s Note: “Strain induced second-order Jahn–Teller reconstruction and magnetic moment modulation at monovacancy in graphene” [J. Appl. Phys. 130, 034303 (2021)

Strain induced second-order Jahn–Teller reconstruction and magnetic moment modulation at monovacancy in graphene

Using density functional theory simulations, we examine the electronic structure of an isolated monovacancy defect in graphene under symmetry-breaking deformation. Results show that the defect experiences a second-order Jahn–Teller reconstruction at a critical strain of 1.7%. It stabilizes the orientation of the JT bond relative to the loading direction and breaks the threefold degeneracy of the defect structure. We call it Jahn–Teller re-reconstruction (JTRR), and it is mechanically reversible. The reversibility and stabilization of the orientation depend on the direction cosine between the JT bond and the loading direction. Also, a change in the loading direction by 90° can change the orientation of the JT bond by 120°. An atomic-scale analysis suggests that the maximum bond force arising from “the derivative of the kinetic energy of electrons” defines the critical strain. JTRR alters the electron occupation in the individual electronic orbitals at the defect site. The electronic charge redistribution and the density of states at the defective sites reveal that the pz orbitals dominate the reconstruction process. Furthermore, JTRR changes the magnitude of the magnetic moment at the defective site from 1.36 μB to 1.22 μB. This unravels a new way of controlling the magnetic behavior of monovacancy by applying symmetry-breaking mechanical strain. Results also show that passivation of the dangling bond can subside or eliminate the reconstruction process depending on the number of valence electrons available in the passivating atom.

Simplified size adjusted dose reference levels for adult CT examinations: A regional study

PurposeTo investigate retrospective classification of adult patients into small, average, and large based on effective diameter (EDia) from localizer image of computed tomography (CT) scans and to develop regional diagnostic reference levels (DRLs) and achievable doses (AD). MethodThe patients falling within the mean ± standard deviation (SD) of EDia were classified as average; those below this range as small and above as large. The CTDIvol,dose-length-product (DLP) and size-specific dose estimates (SSDE) of all adult patients undergoing CT examinations in 8 CT facilities for 11 months (Dec. 2019 - Oct. 2020) were evaluated. The 75th and 50th percentile values were compared with national and international values. ResultsOf the total of 69,434 CT examinations, nearly 80% fell within average size. The 75th percentile values of CTDIvol and DLP for small patients for abdomen-pelvic exams were nearly half of average sized patients. Similarly, the 75th percentile values for large patients were nearly double. Similar findings were not found for chest exams. Analysis of image quality and dose factors such as noise, mean axial length, slice thickness, mean number of sequences, use of iterative reconstruction and tube current modulation (TCM) resulted in identification of opportunities for improvement and optimization of different CT facilities. ConclusionsDRLs for adult patients were found to vary widely with patient size and thus establishing DRLs only for standard sized patient is not adequate. Simplified and intuitive methods for size classification was shown to provide meaningful information for optimization for patients outside the standard size adult.

Alkylammonium Halides for Facet Reconstruction and Shape Modulation in Lead Halide Perovskite Nanocrystals.

ConspectusThe interactions of halides and ammonium ions with lead halide perovskite nanocrystals have been extensively studied for improving their phase stability, controlling size, and enhancing their photoluminescence quantum yields. However, all these nanocrystals, which showed intense and color tunable emissions, mostly retained the six faceted cube or platelet shapes. Shape tuning needs the creation of new facets, and instead of composition variations by foreign ions interactions/substitutions, these require facet stabilizations with suitable ligands. Among most of the reported cases of lead halide perovskites, alkyl ammonium ions are used as a capping agent, which substituted in the surface Cs(I) sites of these nanocrystals. Hence, new surface ligands having a specific binding ability with different facets other than those in cube/platelet shapes are required for bringing stability to new facets and, hence, for tuning their shapes.In this Account, interactions of alkyl ammonium ions on the surface of perovskite nanocrystals and their impact on surface reconstructions are reviewed. Emphasizing the most widely studied CsPbBr3 nanocrystals, the usefulness and impact of alkyl ammonium ions on the phase stability, high-temperature annealing, enhancement of the brightness and doping in these nanocrystals are first discussed. Then, nanocrystals formed under limited primary alkyl ammonium ions and also with specific tertiary ammonium ions having new facets are elaborated. Further, the treatment of excess alkyl ammonium halides to these newly formed multifaceted polyhedron nanocrystals under different conditions, which led to armed and step-armed structures, are discussed. The change in optical properties during these shape transformations is also presented. Finally, the shape-change mechanism with alkyl ammonium halide-induced dissolutions of {200} and {112} facets and formation of {110} and {002} facets are discussed. Further, in summary, future prospects of new ligand designing for stabilizing new facets of perovskite nanocrystals and obtaining new shapes and properties are proposed.

Layer-dependent interface reconstruction and strain modulation in twisted WSe2.

Twistronics has emerged as one of the most attractive playgrounds for manipulating the interfacial structures and electronic properties of two-dimensional materials. However, the layer-dependent lattice reconstruction and resulted strain distribution in marginally twisted transition metal dichalcogenides still remain elusive. Here we report a systematic study by both electron diffraction quantification and atomic-resolution imaging on the interface reconstruction of twisted WSe2, which shows a strong dependence on the constituent layer numbers and twist angles. The competition between the interlayer interaction, which varies with local atomic configurations, and the intralayer elastic deformation, related to the layer thickness, leads to rich superlattice motifs and strain modulation patterns, i.e. triangular for odd and kagome-like textures for even layer numbers, against the rigid stacking moiré model. The strain effects of small twist angles are further demonstrated by electrical transport measurements, manifesting intriguing conducting states at low temperatures beyond the flat band features of large twist angles. Our work not only provides a comprehensive understanding of layer-dependent twist structures, but also may shed light on the future design of twistronic devices.

Low-dose chest CT and the impact on nodule visibility

IntroductionThe need to continually optimise CT protocols is essential to ensure the lowest possible radiation dose for the clinical task and individual patient. The aim of this study was to explore the effect of reducing effective mAs on nodule detection and radiation dose across six scanners. MethodsAn anthropomorphic chest phantom was scanned using a low-dose chest CT protocol, with the effective mAs lowered to the lowest permissible level. All other acquisition parameters remained consistent. Images were evaluated by five radiologists to determine their sensitivity in detecting six simulated nodules within the phantom. Image noise was calculated together with DLP. ResultsThe lowest possible mAs achievable ranged from 7 to 19 mAs. The two highest mAs setting (17 mAs + 19 mAs) had kV modulation enabled (100 kV instead of 120 kV) which consequently resulted in a higher nodule detection rate. Overall nodule detection averaged at 91% (range 80–97%). Out of a possible 180 nodules, 16 were missed, with 12 of those 16 being the same nodule. Noise was double for the Somatom Sensation scanner when compared to the others; however, this scanner did not have iterative reconstruction and it was installed over 10 years ago. There was a strong correlation between image noise and scanner age. ConclusionThis study highlighted that nodules can be detected at very low effective mAs (<20 mAs) but only when other acquisition parameters are optimised i.e. iterative reconstruction and kV modulation. Nodule detection rates were affected by nodule location and image noise. Implications for practiceThis study consolidates previous findings on how to successfully optimise low-dose chest CT. It also highlights the difficulty with standardisation owing to factors such as scanner age and different vendor attributes.

Simultaneous treatment for patellar instability and genu valgum in skeletally immature patients: a preliminary study.

Genu valgum is a risk factor for patellar instability. The study purpose was to report on preliminary results of medial patellofemoral ligament (MPFL) reconstruction and simultaneous growth modulation, in patients with patellar instability and genu valgum. A total of seven patients (eight knees) with MPFL reconstruction and medial transphyseal screw insertion for genu valgum correction were assessed using full-length radiographs. Genu valgum corrected from 13.1° to 3.7° at mean 11.7 months, without compromising patellar stability. One patient each had 6° overcorrection and 5° rebound valgus. Guided growth using transphyseal screw during MPFL reconstruction could achieve deformity correction without interference with MPFL graft placement.

Surface reconstruction and charge modulation in BaFe2As2 superconducting film

Whether or not epitaxially grown superconducting films have the same bulk-like superconducting properties is an important concern. We report the structure and the electronic properties of epitaxially grown Ba(Fe1−xCox)2As2 films using scanning tunneling microscopy and scanning tunneling spectroscopy (STS). This film showed a different surface structure, R45° reconstruction, from those of as-cleaved surfaces from bulk crystals. The electronic structure of the grown film is different from that in bulk, and it is notable that the film exhibits the same superconducting transport properties. We found that the superconducting gap at the surface is screened at the Ba layer surface in STS measurements, and the charge density wave was observed at the surface in sample in the superconducting state.

Iterative reconstruction and automatic tube voltage selection reduce clinical CT radiation doses and image noise

IntroductionComputed Tomography (CT) use has increased in recent years with trends indicating increasing population doses as a result. Optimization of clinical radiation doses through technological developments has demonstrated potential to reduce patient dose from CT. This study aimed to quantify these dose reductions across a large clinical cohort. MethodsPatient cohort was divided into three groups, assigned by CT optimisation technique. Group one underwent scanning with automated tube current modulation only. Group two underwent scanning with automated tube current modulation and iterative reconstruction and group three underwent scanning with automated tube current modulation, iterative reconstruction and automatic tube voltage modulation. Patient dose length product doses were retrospectively collected for the three groups. Clinical radiation doses between the groups were compared for four common CT examinations (Brain, pulmonary angiography, abdomen and thorax abdomen pelvis scans). ResultsOf 4011 patients, group one comprised of 1643 patients (40.96%), group two 1077 patients (26.85%) and group three 1291 patients (32.19%). No differences were found when comparing AP diameter between groups (p ≥ 0.05). Statistically significant dose reductions of 16–31% were achieved using iterative reconstruction alone (p = 0.001) and 24–42% with both iterative reconstruction and automatic tube voltage selection (p = 0.001). Objective noise improved when iterative reconstruction was used (p < 0.05). ConclusionThe application of optimization software confers significant dose savings during routine clinical CT examinations. Figures are based on a large clinical cohort, with equipment, staff and procedural protocols remaining consistent throughout. Dose reductions are likely to reflect the clinical dose reducing potential of the optimization software investigated.

Strategies for CT tissue segmentation for Monte Carlo calculations in nuclear medicine dosimetry.

CT images are used for patient specific Monte Carlo treatment planning in radionuclide therapy. The authors investigated the impact of tissue classification, CT image segmentation, and CT errors on Monte Carlo calculated absorbed dose estimates in nuclear medicine. CT errors as a function of patient size, CT reconstruction, and tube current modulation methods were assessed in a phantom experiment on a clinical CT system. The impact of tissue segmentation methods and CT number variations on EGSnrc Monte Carlo calculated absorbed dose distributions was assessed for 99mTc and 131I in the ICRP/ICRU male phantom and in a patient PET/CT-scanned with 124I prior to radioiodine therapy. CT number variations <20 HU were obtained for whole-body CT examinations at effective CT doses ∼2 mSv. Monte Carlo calculated absorbed doses depended on both the number of media types and accurate calibration of the CT number-to-density conversion ramp. Tissue segmentation by a 13-tissue CT conversion ramp, calibrated by a stoichiometric method, resulted in low (<4%) dose errors in selected organs for both isotopes. A calibrated CT scanner specific conversion ramp is required for accurate patient specific dosimetry in nuclear medicine. Accurate dosimetry was obtained with a 13-tissue ramp that included five different bone types.

Combining Automatic Tube Current Modulation with Adaptive Statistical Iterative Reconstruction for Low-Dose Chest CT Screening

ObjectiveTo reduce radiation dose while maintaining image quality in low-dose chest computed tomography (CT) by combining adaptive statistical iterative reconstruction (ASIR) and automatic tube current modulation (ATCM).MethodsPatients undergoing cancer screening (n = 200) were subjected to 64-slice multidetector chest CT scanning with ASIR and ATCM. Patients were divided into groups 1, 2, 3, and 4 (n = 50 each), with a noise index (NI) of 15, 20, 30, and 40, respectively. Each image set was reconstructed with 4 ASIR levels (0% ASIR, 30% ASIR, 50% ASIR, and 80% ASIR) in each group. Two radiologists assessed subjective image noise, image artifacts, and visibility of the anatomical structures. Objective image noise and signal-to-noise ratio (SNR) were measured, and effective dose (ED) was recorded.ResultsIncreased NI was associated with increased subjective and objective image noise results (P<0.001), and SNR decreased with increasing NI (P<0.001). These values improved with increased ASIR levels (P<0.001). Images from all 4 groups were clinically diagnosable. Images with NI = 30 and 50% ASIR had average subjective image noise scores and nearly average anatomical structure visibility scores, with a mean objective image noise of 23.42 HU. The EDs for groups 1, 2, 3 and 4 were 2.79±1.17, 1.69±0.59, 0.74±0.29, and 0.37±0.22 mSv, respectively. Compared to group 1 (NI = 15), the ED reductions were 39.43%, 73.48%, and 86.74% for groups 2, 3, and 4, respectively.ConclusionsUsing NI = 30 with 50% ASIR in the chest CT protocol, we obtained average or above-average image quality but a reduced ED.

Reduction of effective dose and organ dose to the eye lens in head MDCT using iterative image reconstruction and automatic tube current modulation

To compare the effective and eye lens radiation dose in helical MDCT brain examinations using automatic tube current modulation in conjunction with either standard filtered back projection (FBP) technique or iterative reconstruction in image space (IRIS). Of 400 adult brain MDCT examinations, 200 were performed using FBP and 200 using IRIS with the following parameters: tube voltage 120 kV, rotation period 1 second, pitch factor 0.55, automatic tube current modulation in both transverse and longitudinal planes with reference mAs 300 (FBP) and 200 (IRIS). Doses were calculated from CT dose index and dose length product values utilising ImPACT software; the organ dose to the lens was derived from the actual tube current-time product value applied to the lens. Image quality was assessed by two independent readers blinded to the type of image reconstruction technique. The average effective scan dose was 1.47±0.26 mSv (FBP) and 0.98±0.15 mSv (IRIS), respectively (33.3% decrease). The average organ dose to the eye lens decreased from 40.0±3.3 mGy (FBP) to 26.6±2.0 mGy (IRIS, 33.5% decrease). No significant change in diagnostic image quality was noted between IRIS and FBP scans (P=0.17). Iterative reconstruction of cerebral MDCT examinations enables reduction of both effective and organ eye lens dose by one third without signficant loss of image quality.

Radiation Dose Reduction via Sinogram Affirmed Iterative Reconstruction and Automatic Tube Voltage Modulation (CARE kV) in Abdominal CT

ObjectiveTo evaluate the feasibility of sinogram-affirmed iterative reconstruction (SAFIRE) and automated kV modulation (CARE kV) in reducing radiation dose without increasing image noise for abdominal CT examination.Materials and MethodsThis retrospective study included 77 patients who received CT imaging with an application of CARE kV with or without SAFIRE and who had comparable previous CT images obtained without CARE kV or SAFIRE, using the standard dose (i.e., reference mAs of 240) on an identical CT scanner and reconstructed with filtered back projection (FBP) within 1 year. Patients were divided into two groups: group A (33 patients, CT scanned with CARE kV); and group B (44 patients, scanned after reducing the reference mAs from 240 to 170 and applying both CARE kV and SAFIRE). CT number, image noise for four organs and radiation dose were compared among the two groups.ResultsImage noise increased after CARE kV application (p < 0.001) and significantly decreased as SAFIRE strength increased (p < 0.001). Image noise with reduced-mAs scan (170 mAs) in group B became similar to that of standard-dose FBP images after applying CARE kV and SAFIRE strengths of 3 or 4 when measured in the aorta, liver or muscle (p ≥ 0.108). Effective doses decreased by 19.4% and 41.3% for groups A and B, respectively (all, p < 0.001) after application of CARE kV with or without SAFIRE.ConclusionCombining CARE kV, reduction of mAs from 240 to 170 mAs and noise reduction by applying SAFIRE strength 3 or 4 reduced the radiation dose by 41.3% without increasing image noise compared with the standard-dose FBP images.

Neue Entwicklungen in der MSCT

Progress in MSCT is focused on new applications and software development. A hot topic is multispectral imaging which allows for tissue differentiation using at least two energy-levels. Besides differentiation of calcification and jodine in CT-angiography and oncologic imaging, there is also increasing interest in other application fields. Ultrafast imaging nearly eliminates breathing and pulsation artifacts allowing examination of non-compliant patients without sedation or anesthesia. Perfusion can now be extended to large body regions using large detectors or applying shuffle-techniques. New software developments include iterative reconstruction and organ specific dose modulation allowing for dose reduction and for protection of radiosensitive organs.

Embedded Co nanostructures on Au(0 0 1) substrate studied by scanning tunneling microscopy

Surface structures and morphology of Co deposited on Au(0 0 1) surface have been studied by scanning tunneling microscopy (STM) up to nominal Co thickness d n of 2.4 monolayers (ML). The room-temperature (RT) growth shows pseudomorphic bcc Co growth with island structures. The structure and morphology of the samples change markedly after post-annealing at 230 °C. STM images have revealed two kinds of regular nanostructure aligned to the 〈1 0 0〉 direction. They are composed of Au(0 0 1) surface with a characteristic reconstruction modulation and the buried Co nano islands with a surfactant Au layer. It is clarified from the height profiles in STM that the core (rim) of the buried Co islands consists of 5 (4) ML Co with 1 (2) ML for Au surfactant for 2.4 ML Co deposition.

Ocular Surface Reconstruction Using Autologous Rabbit Oral Mucosal Epithelial Sheets Fabricated Ex Vivo on a Temperature-Responsive Culture Surface

Autologous stem cell transplantation for total limbal stem cell deficiency is immunologically preferable, to avoid allograft rejection. This study was undertaken to investigate the possibility of a novel tissue engineering approach for ocular surface reconstruction, using autologous oral mucosal epithelial stem cells expanded ex vivo on temperature-responsive cell culture surfaces. Rabbit oral mucosal epithelial cells cultured on temperature-responsive culture surfaces with mitomycin-C-treated 3T3 feeder cells for 2 weeks produced confluent epithelial cell sheets. Putative progenitor cell populations were estimated by colony-forming assays. Autologous transplantation of these cell sheets to surgically manipulated eyes was performed, and ocular surface reconstruction and cell phenotypic modulation were examined. All cultured oral epithelial cells were nonenzymatically harvested as transplantable intact cell sheets by reducing culture temperature to 20 degrees C. Oral epithelial cells were stratified in three to five cell layers more similar to corneal epithelium than to oral mucosal epithelium. Colony-forming assays and immunofluorescence for p63, beta1-integrin, and connexin 43 indicated retention of viable stem and/or progenitor cell populations in cell sheets. Autologous transplantation to rabbit corneal surfaces successfully reconstructed the corneal surface, with restoration of transparency. Four weeks after transplantation, epithelial stratification was similar to that in the corneal epithelium, although the keratin expression profile retained characteristics of the oral mucosal epithelium. Cell sheet harvest technology enables fabrication of viable, transplantable, tissue-engineered epithelial cell sheets that retain putative progenitor cells from autologous oral mucosal epithelial cells. Promising clinical capabilities for autologous tissue-engineered epithelial cell sheets for ocular surface reconstruction are indicated.