分类： 环境科学技术及资源科学技术 >> 环境科学技术基础学科 提交时间： 2022-06-13 合作期刊: 《干旱区科学》
摘要： Abstract: Deserts are sensitive to environmental changes caused by human interference and are prone to degradation. Revegetation can promote the reversal of desertification and the subsequent formation of fixed sand. However, the effects of grazing, which can cause the ground-surface conditions of fixed sand to further deteriorate and result in re-desertification, on the greenhouse gas (GHG) fluxes from soils remain unknown. Herein, we investigated GHG fluxes in the Hobq Desert, Inner Mongolia Autonomous Region of China, at the mobile (desertified), fixed (vegetated), and grazed (re-desertified) sites from January 2018 to December 2019. We analyzed the response mechanism of GHG fluxes to micrometeorological factors and the variation in global warming potential (GWP). CO2 was emitted at an average rate of 4.2, 3.7, and 1.1 mmol/(m2h) and N2O was emitted at an average rate of 0.19, 0.15, and 0.09 mol/(m2h) at the grazed, fixed, and mobile sites, respectively. Mean CH4 consumption was as follows: fixed site (2.9 mol/(m2h))>grazed site (2.7 mol/(m2h))>mobile site (1.1 mol/(m2h)). GHG fluxes varied seasonally, and soil temperature (10 cm) and soil water content (30 cm) were the key micrometeorological factors affecting the fluxes. The changes in the plant and soil characteristics caused by grazing resulted in increased soil CO2 and N2O emissions and decreased CH4 absorption. Grazing also significantly increased the GWP of the soil (P
分类： 地球科学 >> 地理学 提交时间： 2023-10-17 合作期刊: 《干旱区科学》
摘要： Groundwater overexploitation is a serious problem in the Turpan Basin, Xinjiang Uygur Autonomous Region of China, causing groundwater level declines and ecological and environmental problems such as the desiccation of karez wells and the shrinkage of lakes. Based on historical groundwater data and field survey data from 1959 to 2021, we comprehensively studied the evolution of groundwater recharge and discharge terms in the Turpan Basin using the groundwater equilibrium method, mathematical statistics, and GIS spatial analysis. The reasons for groundwater overexploitation were also discussed. The results indicated that groundwater recharge increased from 14.58108 m3 in 1959 to 15.69108 m3 in 1980, then continued to decrease to 6.77108 m3 in 2021. Groundwater discharge increased from 14.49108 m3 in 1959 to 16.02108 m3 in 1989, while continued to decrease to 9.97108 m3 in 2021. Since 1980, groundwater recharge-discharge balance has been broken, the decrease rate of groundwater recharge exceeded that of groundwater discharge and groundwater recharge was always lower than groundwater discharge, showing in a negative equilibrium, which caused the continuous decrease in groundwater level in the Turpan Basin. From 1980 to 2002, groundwater overexploitation increased rapidly, peaking from 2003 to 2011 with an average overexploitation rate of 4.79108 m3/a; then, it slowed slightly from 2012 to 2021, and the cumulative groundwater overexploitation was 99.21108 m3 during 19802021. This research can provide a scientific foundation for the restoration and sustainable use of groundwater in the overexploited areas of the Turpan Basin.
分类： 生物学 >> 生物物理学 提交时间： 2016-05-15
Zhang, Shaodan
Zhang, Chun
Zhang, Shaodan
Wang, Bo
Zhu, SenHua
Xie, Yuan
Qing, Guoping
Wang, Ningli
Thomas, Ravi
Thomas, Ravi
摘要： PURPOSE. To assess the cortical structure and cerebral blood flow changes in the brain of patients with primary open-angle glaucoma (POAG). METHODS. High-resolution anatomical magnetic resonance imaging (MRI) and arterial spin labeling (ASL)-MRI were performed in 23 POAG patients and 29 controls. Patients were further divided into early-moderate and advanced groups based on mean deviation (MD) cutoff of 12 dB. A baseline scan was obtained and repeated during visual stimulation to the central preserved visual field in the more affected eye of POAG patients and a randomly selected eye of controls. Gray matter volume (GMV) and cerebral blood flow (CBF) throughout the whole brain were compared between patients and controls. RESULTS. Compared to controls, a region with significant reduction of GMV was detected in the anterior calcarine fissure of advanced POAG patients (P < 0.001, voxels = 503, 1698 mm3). Patients with early-moderate POAG had resting CBF similar to that of controls. However, a region with marked CBF decrease was detected in the anterior calcarine fissure of advanced POAG patients (P < 0.001, voxels = 1687, 13,496 mm(3)). The region with CBF reduction in advanced POAG showed good colocalization with the region with GMV decrease in this group. Following visual stimulation, patients with advanced POAG showed significantly lower increase in CBF in the occipital lobes (P < 0.001, voxels = 112, 896 mm(3)) as compared to controls (P < 0.001, voxels = 1880, 15,040 mm(3)) and early-moderate POAG (P < 0.001, voxels = 2233, 17,864 mm(3)). CONCLUSIONS. Primary open-angle glaucoma patients demonstrate a disease severity-dependent retinotopic pattern of cortical atrophy and CBF abnormalities in the visual cortex. Cerebral blood flow may be a potential biomarker for the brain involvement in glaucoma.
分类： 生物学 >> 生物物理学 提交时间： 2016-05-12
Zhang, Zihao
Zuo, Zhentao
Wang, Bo
Wei, Ning
Xue, Rong
Zhang, Zihao
Wei, Ning
Deng, Xiaofeng
Zhao, Jizong
Weng, Dehe
An, Jing
Xue, Rong
摘要： Purpose: Time-of-flight (TOF) MR angiography has an advantage of contrast and resolution in ultra-high field (7 T) MRI systems. However, increased specific absorption rate (SAR) prohibits the application of spatial saturation band, leading to venous contamination in maximum intensity projection (MIP) images. Methods: A segmented k-space filling scheme with sparse venous saturation pulses was developed for 7 T TOF-MRA. The effectiveness of the segmented TOF sequence was verified by Bloch equation simulation and experiments on 3 T. The protocol on 7 T was optimized and applied for healthy volunteers and patients with vascular diseases. Results: Segmented TOF achieved equivalent contrast and venous suppression effect as conventional methods, while SAR values had a remarkable reduction and obeyed the limit of a 7 T MRI system. The decreased number of saturation pulses allowed shorter acquisition time than existing solutions. The comparison of segmented TOF and conventional TOF revealed flow direction in vascular diseases. Conclusion: Segmented TOF is proved to be a time-efficient way to achieve high-resolution angiograms without venous contamination at ultra-high field. The sequence holds strong promise for non-contrast clinical diagnosis on cerebrovascular diseases. (C) 2015 Elsevier Inc. All rights reserved.
分类： 生物学 >> 生物物理学 提交时间： 2016-05-05
Deng, Xiaofeng
Xu, Long
Zhang, Yan
Wang, Shuo
Zhao, Yuanli
Cao, Yong
Zhang, Dong
Wang, Rong
Ye, Xun
Wu, Jun
Zhao, Jizong
Deng, Xiaofeng
Xu, Long
Zhang, Yan
Wang, Shuo
Zhao, Yuanli
Cao, Yong
Zhang, Dong
Wang, Rong
Ye, Xun
摘要： The authors attempted to demonstrate the difference in language cortex reorganization between cerebral malformations (AVMs), cavernous malformations (CMs), and gliomas by blood oxygen level-dependent (BOLD) functional magnetic resonance imaging. Clinical and imaging data of 27 AVM patients (AVM-L group), 29 CM patients (CM-L group), and 20 glioma patients (Glioma-L group) were retrospectively reviewed, with lesions overlying the left inferior frontal gyrus (Broca area). As a control, patients with lesions involving the right inferior frontal gyrus were also enrolled, including 14 AVM patients (AVM-R group), 20 CM patients (CM-R group), and 14 glioma patients (Glioma-R group). All patients were right-handed. Lateralization indices (LI) of BOLD signal activations were calculated separately for Broca and Wernicke areas. In AVM-L group, right-sided lateralization of BOLD signals was observed in 10 patients (37.0 %), including 6 in the Broca area alone, 1 in the Wernicke area alone, and 3 in both areas. Three patients (10.3 %) of CM-L group showed right-sided lateralization in both Broca and Wernicke areas, and 1 patient (5.0 %) of Glioma-L group had right-sided lateralization in the Wernicke area alone. A significant difference of right-sided lateralization was observed between the AVM-L group and CM-L group (P = 0.018) and also between the AVM-L group and Glioma-L group (P = 0.027). No patient in AVM-R, CM-R, or Glioma-R groups showed right-sided lateralization. Language cortex reorganization may occur in AVM, CM, and glioma patients when the traditional language cortex was involved by lesions, but the potential of reorganization for CM and glioma patients seems to be insufficient compared with AVM patients.
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