ABSTRACT
High time resolution and accuracy are of critical importance in the studies of timing analysis and time delay localization of gamma-ray bursts (GRBs), soft gamma-ray repeaters (SGRs) and ...pulsars. The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) consisting of two micro-satellites, GECAM-A and GECAM-B, launched on 2020 December 10, is aimed at monitoring and locating X-ray and GRBs all over the sky. To achieve its scientific goals, GECAM is designed to have the highest time resolution (0.1 $\mu {\rm s}$) among all GRB detectors ever flown. Here, we make a comprehensive time calibration campaign including both on-ground and on-orbit tests to derive not only the relative time accuracy of GECAM satellites and detectors, but also the absolute time accuracy of GECAM-B. Using the on-ground calibration with a $\rm ^{22}Na$ radioactive source, we find that the relative time accuracy between GECAM-A and GECAM-B is about 0.15 $\mu {\rm s}$ (1σ). To measure the relative time accuracy between all detectors of a single GECAM satellite, cosmic-ray events detected on orbit are utilized since they could produce many secondary particles simultaneously record by multiple detectors. We find that the relative time accuracy among all detectors onboard GECAM-B is about 0.12 $\mu {\rm s}$ (1σ). Finally, we use the novel Li-CCF method to perform the absolute time calibration with Crab pulsar and SGR J1935+2154, both of which were jointly observed by GECAM-B and Fermi/GBM, and obtain that the time difference between GECAM-B and Fermi/GBM is 3.06 ± 6.04 $\mu {\rm s}$ (1σ).
The corrosion and electrochemical behaviour of carefully prepared ultra-lightweight magnesium-lithium (Mg-Li) alloys were investigated and compared. The alloy compositions studied were selected to ...provide the ability to compare unique microstructures and crystal structures, which arise from specific alloying additions of Li. Mg-4%Li is hexagonal closed-packed (HCP) alloy with Li in solid solution of Mg (α-Mg); Mg-14%Li is a fully solid solution BCC (β-Li) alloy, whilst Mg-7.5%Li is a duplex (α-Mg + β-Li) alloy. Testing in 0.1 M NaCl revealed that the corrosion performance and electrochemical response of the Mg-Li system evolved with the composition and crystallographic structure. For Mg-4%Li alloy, filiform-like corrosion morphology can be observed on the corroded surface, whilst a mixture of filiform-like corrosion to the α-Mg and localised dissolution of β-Li existed on the corroded surface of Mg-7.5%Li alloy. In the case of the BCC structured Mg-14%Li alloy, minor pitting was observed, concomitant with a generally low corrosion rate (particularly low corrosion rate for typical Mg alloys) and an increasing corrosion resistance with exposure time were also revealed. A combination of exposure testing inclusive of hydrogen collection and mass loss, in addition to potentiodynamic polarisation and impedance spectroscopy elucidated and quantified the corrosion performance of three differently structured Mg-Li alloys. It revealed that in spite of being composed of reactive elements of Mg and Li, the formation of β-Li phases with BCC structure could facilitate the formation of a highly protective surface film which results in a predictable and consistently low corrosion rate of the Mg-14%Li alloy.
•Corrosion behaviour was dependent on the crystal structure of Mg-Li alloys.•Mg-4Li, Mg-7.5Li and Mg-14Li (wt.%) alloys were HCP, HCP + BCC and BCC structure, respectively.•Corrosion attack preferentially occurred in α-Mg phase of Mg-7.5Li alloy.•Mg-14Li alloy revealed a high corrosion resistance which increased with immersion time.•A highly protective surface film could form on Mg-14Li alloy with single β-Li phase.
Microstructural evolution, corrosion behavior and mechanical properties of cast Mg-Zn-Y alloys as a function of volume fraction of long period stacking ordered (LPSO) phases were investigated. ...Results revealed that 18R-LPSO phase was formed in Mg-0.9%Zn-1.6%Y (ZW12), Mg-2.1%Zn-5.2%Y (ZW25) and Mg-3.1%Zn-7.6%Y (ZW38) alloys. LPSO phases in these alloys acted as micro-cathode to accelerate corrosion progress due to their nobler nature than that of α-Mg matrix. The galvanic-couple effect between LPSO phases and α-Mg matrix dominated the corrosion rate of the cast Mg-Zn-Y alloys in the long-term corrosion process. As a result, ZW12 alloy displayed the best corrosion resistance due to the least volume fraction of micro-cathodes (i.e. LPSO phases). In addition, compared with ZW25 alloy, the compact and thick LPSO phases in ZW38 alloy hindered the corrosion progress to a small degree since it was not preferentially oriented against corrosion front. The shape of corrosion pits was correlated to the shape of Mg dendrites that was a result of the volume fraction and distribution of LPSO phases. LPSO phases could enhance mechanical strength, but the increment was slight when the volume fraction of LPSO phases reached up to 20.3%.
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•Galvanic corrosion dominates corrosion resistance of Mg-Zn-Y alloys.•Corrosion pits are related to the quantity and distribution of LPSO phases.•Corrosion films on the LPSO phases and Mg matrix are different.•Strength is improved slightly when the concentration of LPSO phases exceeds 20.3%.
Anyons are exotic quasiparticles obeying fractional statistics, whose behavior can be emulated in artificially designed spin systems. Here we present an experimental emulation of creating anyonic ...excitations in a superconducting circuit that consists of four qubits, achieved by dynamically generating the ground and excited states of the toric code model, i.e., four-qubit Greenberger-Horne-Zeilinger states. The anyonic braiding is implemented via single-qubit rotations: a phase shift of π related to braiding, the hallmark of Abelian 1/2 anyons, has been observed through a Ramsey-type interference measurement.
Creating oxide interfaces with precise chemical specificity at the atomic layer level is desired for the engineering of quantum phases and electronic applications, but highly challenging, owing ...partially to the lack of in situ tools to monitor the chemical composition and completeness of the surface layer during growth. Here we report the in situ observation of atomic layer-by-layer inner potential variations by analysing the Kikuchi lines during epitaxial growth of strontium titanate, providing a powerful real-time technique to monitor and control the chemical composition during growth. A model combining the effects of mean inner potential and step edge density (roughness) reveals the underlying mechanism of the complex and previously not well-understood reflection high-energy electron diffraction oscillations observed in the shuttered growth of oxide films. General rules are proposed to guide the synthesis of atomically and chemically sharp oxide interfaces, opening up vast opportunities for the exploration of intriguing quantum phenomena at oxide interfaces.
Summary
Background
A series of cases of symmetrical acral keratoderma have been described recently in China. However, no studies about its demographic information and epidermal barrier function have ...been documented.
Objectives
To describe the clinical manifestation, demographic information and clinicopathological features of 71 cases with symmetrical acral keratoderma.
Patients and methods
Seventy‐one cases with symmetrical acral keratoderma were retrospectively reviewed. Their demographic information, clinical manifestations, histopathology and epidermal barrier function were analysed.
Results
Among these patients, there were 64 males and seven females, ranging in age from 4 to 53 years with an average age at onset of 27 ± 8·9 years. Clinical manifestation was characterized by brown hyperkeratotic patches over the dorsum of the hands, palms and feet, dorsal digits and wrists, elbows, knees and ankles. The lesions became dramatically whitish with mild swelling immediately after soaking in water and resolved spontaneously in winter. In patients, a moderate increase of transepidermal water loss (TEWL) from 16·16 ± 6·15 to 9·9 ± 4·21 g m−2 h−1 (P = 0·0054) and a moderate decrease of skin hydration from 65·9 ± 5·06 to 42·58 ± 10·73 (P < 0·01) in comparison with the control group were observed. Histopathological examination revealed epidermal hyperkeratosis, acanthosis and papillomatous hyperplasia as well as dermal infiltration with a few lymphocytes.
Conclusions
Symmetrical acral keratoderma is characterized by symmetry, acra, keratinization and marked seasonal changes. The epidermal barrier function of the skin was negatively affected.
What's already known about this topic?
A series of cases of symmetrical acral keratoderma have been described recently in China.
However, no studies of demographic information and epidermal permeability barrier function have been documented.
What does this study add?
Symmetrical acral keratoderma is characterized by symmetry, acra, keratinization and marked seasonal changes.
The epidermal barrier function of the skin was negatively affected.
The ability of the ivy sign on contrast-enhanced T1-weighted MR imaging (CEMR) to reflect cerebral perfusion and postoperative revascularization in Moyamoya disease remains largely unknown. We aimed ...to compare the capabilities of CEMR and FLAIR.
CEMR, FLAIR, arterial spin-labeling, and DSA were performed in 44 patients with Moyamoya disease. The ivy sign was scored separately on CEMR and FLAIR using the Alberta Stroke Program Early CT Score. The status of leptomeningeal collaterals was scored on DSA. The postoperative Matsushima grade was evaluated at least 3 months after surgical revascularization.
Scoring of the ivy sign on CEMR showed excellent interrater reliability, and FLAIR vascular hyperintensity showed moderate interrater reliability. Correlation analyses revealed that DSA scores were more consistent with the CEMR-based ivy sign score (
=
0.25,
= .03) than with FLAIR vascular hyperintensity (
= 0.05,
= .65). The CEMR-based ivy sign score was significantly correlated with CBF in late-Suzuki stage Moyamoya disease (
= -2.64,
= .02). The CEMR-based ivy sign score at baseline was significantly correlated with the postoperative Matsushima grade (
=
0.48,
= .03).
In this study, CEMR outperformed FLAIR in capturing the ivy sign in Moyamoya disease. In addition, the CEMR-based ivy sign score provided adequate information on hemodynamic status and postoperative neovascularization. The current study suggested that CEMR could be considered as an alternative to FLAIR in future studies investigating leptomeningeal collaterals in Moyamoya disease.
Mg–10Gd–3Y–0.5Zr alloys with and without 1% Zn additions have been investigated using optical microscopy, scanning electron microscope and X-ray diffraction. The microstructures, ageing hardening ...behaviors and mechanical properties of the two alloys are compared. The extruded-T5 specimens exhibit remarkable age hardening responses during ageing from 200 to 250
°C. The highest peak hardness and strength of the two alloys are obtained when they are aged at 200
°C. Addition of 1% Zn to Mg–10Gd–3Y–0.5Zr alloy results in the greater magnitude ageing effect and better mechanical properties as well as better heat resistance. Furthermore, secondary ageing is carried out at 200
°C following preliminary ageing at 250
°C for both Mg–10Gd–3Y–0.5Zr and Mg–10Gd–3Y–1Zn–0.5Zr alloys. The ultimate tensile strength values after secondary ageing are slightly lower compared with the highest strength of the two alloys, but secondary ageing offers a better combination of high strength and ductility.
Phase‐change memory (PCM) materials, such as chalcogenide alloys, have the ability for fast and reversible transition between their amorphous and crystalline states. Owing to the large ...optical/electrical contrast of the two states, PCM materials have been developed for data storage. It has been generally accepted that thermal effects, caused by laser irradiation or electrical pulses, control the amorphization by melting the sample and subsequent quenching, while crystallization is realized by thermal annealing. An important element that has not been considered extensively, however, is the role of electronic excitation by optical or electrical pulse. Strictly speaking, until electrons and holes recombine, the system under external stimulus is in a non‐equilibrium environment, especially when the excitation intensity is high. This raises an important question: can the excitation alone induce phase transition for PCM data storage without the usual thermal melting? Here, we will review the recent experimental and theoretical indications and evidence in support of the electronic excitation‐induced phase change in PCM materials and discuss potential ramifications of the athermal phase‐change phenomenon for data storage.
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