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Compared with nitrogen and argon, helium is lighter and can better reduce the beam loss caused by angular scattering during beam transmission. The molecular dissociation cross-section in helium is high and stable at low energies, which makes helium the prevalent stripping gas in low-energy accelerator mass spectrometry (AMS). To study the stripping behavior of 14C ions in helium at low energies, the charge state distributions of carbon ion beams with −1, +1, +2, +3, and +4 charge states were measured at energies of 70–220 keV with a compact 14C-AMS at Guangxi Normal University (GXNU). The experimental data were used to analyze the stripping characteristics of C-He in the energy range of 70–220 keV, and new charge state yields and exchange cross-sections in C-He were obtained at energies of 70–220 keV.
A single-stage accelerator mass spectrometer (GXNU-AMS) developed for radiocarbon and tritium measurements was installed and commissioned at Guangxi Normal University in 2017. After several years of operational and methodological upgrades, its performance has been continuously improved and applied in multidisciplinary fields. Currently, the measurement sensitivity for radiocarbon and tritium is 14C/12C ∼ (3.14 ± 0.05) ×10–15 and 3H/1H ∼ (1.23 ± 0.17)×10–16, respectively, and the measurement accuracy is ∼0.6%, which can meet the measurement requirements in the nuclear, earth, environmental and life science fields. This study presents the performance characteristics of GXNU-AMS and several interesting application studies.
In mainland China, the clinical, epidemiological and genetic features of non-O1/non-O139 Vibrio cholerae (NOVC) bacteraemia have been scarcely investigated. Herein, we describe a patient with NOVC bacteraemia diagnosed in our hospital and present a retrospective analysis of literature reports of 32 other cases in China, detailing the clinical epidemiology, antibiotic resistance and molecular characteristics of isolates. Most patients were male (84.8%; median age, 53 years) and had predisposing factors, such as cirrhosis, malignant tumours, blood diseases and diabetes. In addition to fever, gastroenteritis was the most frequent presenting symptom. The mortality rate during hospitalisation was 12.1%. NOVC bacteraemia cases were more common in June–August, with the majority in coastal provinces and the Yangtze River basin. Only 42.4% of cases were attributed to consumption of marine (aquatic) products. Tetracycline, third-generation cephalosporins, and fluoroquinolones were the most effective antimicrobial agents, and the highest frequencies of resistance were recorded for ampicillin/sulbactam (37.5%), amoxicillin/clavulanic acid (33.3%), ampicillin (29.2%) and sulfamethoxazole (20%). Multi-drug resistant isolates were not detected. Limited data indicate that ctxAB and tcpA genes were absent in all NOVC isolates but other putative virulence genes (hlyA, toxR, hap and rtxA) were common. Ten multilocus sequence types were identified with marked genetic heterogeneity between different isolates. As clinical manifestations of NOVC bacteraemia may vary widely, and isolates exhibit genetic diversity, clinicians and public health experts should be alerted to the possibility of infection with this pathogen because of the high prevalence of liver disease in China.
Correlative light and electron microscopy (CLEM) offers a means of guiding the search for the unique or rare events by fluorescence microscopy (FM) and allows electron microscopy (EM) to zoom in on them for subsequent EM examination in three-dimensions (3D) and with nanometer-scale resolution. FM visualizes the localization of specific antigens by using fluorescent tags or proteins in a large field-of-view to study their cellular function, whereas EM provides the high level of resolution for complex structures. And cryo CLEM combines the advantages of maintaining structural preservation in a near-native state throughout the entire imaging process and by avoiding potentially harmful pre-treatments, such as chemical fixation, dehydration and staining with heavy metals. Besides for frozen-hydrated biological samples, CLEM combines the advantages of a close-to-life preservation of biological materials by keeping them embedded in vitreous ice throughout the entire imaging process and the frozen-hydrated condition is very suitable to maintain fluorescent signals. In recent years, many new instruments and software which intended to optimize the workflow and to obtain better experimental results of CLEM have been presented or even commoditized. While, the specimen damage during transfer from FM to EM and the resolution of CLEM were still need to be improved.
Here we set up a High-vacuum Optical Platform to develop CLEM imaging technology (HOPE), which was designed to realize high-vacuum optical ( fluorescent) imaging for cryo-sample on EM cryo-holder (e.g. Gatan 626). A non-integrated high-vacuum cryo-optical stage, which adapted to the EM cryo holder, was fixed on epi-fluorescence microscope (or super-resolution microscope) to obtain fluorescent images. And then the EM cryo holder would be transferred to EM for collection of EM data. This protocol was aimed to minimize the specimen damage during transfer from FM to EM and it was versatile to expend to different types of light microscopy or electron microscopy. Our HOPE had already passed correlative imaging test, and the results showed that it was convenient and effective.
The impact of climate change on the variability of local discharge was investigated in a glacierized high mountain catchment located in the source area of the Ürümqi river, northwest China. We used past climate records to drive a hydrological model to simulate the discharge from 2000 to 2008. The model was then used to project future discharge variations for the period 2041–60, based on a regionally downscaled climate-change scenario combined with three stages of glacier coverage (i.e. compared to the glacier coverage in 2008): unchanged glacier size (100% glacierized), recession of half the glacier area (50% glacierized) and complete disappearance of glaciers (0% glacierized). In each scenario, snowmelt will begin half a month earlier and the discharge will increase in May. For the 100% glacierized scenario, the discharge will increase by 66 ± 35% in a smaller (3.34 km2) and more glaciated (50%) catchment and 33 ± 20% in a larger (28.90 km2) and proportionally less glaciated (18%) catchment. If the glacier area reduces by half, the discharge will decrease by 8 ± 5% and 9 ± 6%, respectively. Once the glacier disappears, the discharge will decrease by 58 ± 20% and 40 ± 13%, respectively. Together, the results indicate that a warming climate and the resulting glacier shrinkage will cause significant changes in the volume and timing of runoff.
Background: Patients with the postural instability and gait difficulty (PIGD) subtype of Parkinson disease (PD) are at a higher risk of dysfunction and are less responsive to dopamine replacement therapy. The PIGD subtype was found to largely associate with white matter lesions, but details of the diffusion changes within these lesions have not been fully investigated. Voxel-based analysis for diffusion tensor imaging data is one of the preferred measures to compare diffusion changes in each voxel in any part of the brain. Methods: PD patients with the PIGD (n=12) and non-PIGD subtypes (n=12) were recruited to compare diffusion differences in fractional anisotropy, axial diffusivity, and radial diffusivity with voxel-based analysis. Results: Significantly reduced fractional anisotropy in bilateral superior longitudinal fasciculus, bilateral anterior corona radiata, and the left genu of the corpus callosum were shown in the PIGD subtype compared with the non-PIGD subtype. Increased radial diffusivity in the left superior longitudinal fasciculus was found in the PIGD subtype with no statistical differences in axial diffusivity found. Conclusions: Our study confirms previous findings that white matter abnormalities were greater in the PIGD subtype than in the non-PIGD subtype. Additionally, our findings suggested: (1) compared with the non-PIGD subtype, loss of white matter integrity was greater in the PIGD subtype; (2) bilateral superior longitudinal fasciculus may play a critical role in microstructural white matter abnormalities in the PIGD subtype; and (3) reduced white matter integrity in the PIGD subtype could be mainly attributed to demyelination rather than axonal loss.
Glacial lake outburst flood hazards in the Himalayan region have received considerable attention in recent years. Accurate volume estimation for glacial lakes is important for calculating outburst flood peak discharge and simulating flood evolution. Longbasaba lake, a potentially dangerous moraine-dammed lake, is located on the north side of the Himalaya. Its depth was surveyed using the SyQwest Hydrobox™ high-resolution echo sounder, and 6916 measurements were collected in September 2009. The maximum and average depths of the lake were 102 ± 2 and 48 ± 2 m, respectively. The morphology of the lake basin was modeled by constructing a triangulated irregular network, and the lake was found to have a storage capacity of 0.064 ± 0.002 km3. Multi-source remote-sensing images from Landsat MSS, Landsat TM/ETM+ and Terra ASTER and a topographic map were digitized to delineate the outlines of the lake between 1977 and 2009. The results indicate that the length and area of the lake have increased during the past 32 years, with a drastic expansion occurring since 2000. Based on volume and area data of Longbasaba lake in different periods, we deduced an empirical equation of the lake volume-area relationship that can be used to calculate the storage capacity of similar moraine-dammed lakes in the Himalayan region.
Since the L12 structured Al3Ti alloy exists only in a narrow compositional range, further alloying of the single phase Ll2 alloy to improve its property seems hardly successful. Developing two-phase or multiphase Al3Ti alloys may be an effective approach for strengthening and toughening. In this article, a new type of Al3Ti-based alloy which has a Ll2 matrix with precipitates of a second phase is reported. The quaternary alloys based on Al67Mn8Ti25, and modified with Nb additions, consist of an Ll2 matrix and DO22 second phase particles in the annealed state, but the second phase can be dissolved by solution treatment and precipitated during high temperature aging. Remarkable strenghtening and promising compressive ductility were exhibited by the experimental alloy. The influence of composition on the microstructure and properties of the alloys are reported also.
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