The mechanism by which the Earth and other planets maintain their magnetic fields against ohmic decay is among the longest standing problems in planetary science. Although it is widely acknowledged ...that these fields are maintained by dynamo action, the mechanism by which the dynamo operates is in large part not understood. Numerical simulations of the dynamo process in the Earth's core have produced magnetic fields that resemble the Earth's field, but it is unclear whether these models accurately represent the extremely low values of viscosity believed to be appropriate to the core. Here we describe the results of a numerical investigation of the dynamo process that adopts an alternative approach to this problem in which, through the judicious choice of boundary conditions, the effects of viscosity are rendered unimportant. We thereby obtain a solution that at leading order operates in an Earth-like dynamical regime. The morphology and evolution of the magnetic field and the fluid flow at the core-mantle boundary are similar to those of the Earth, and the field within the core is qualitatively similar to that proposed on theoretical grounds.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Objective To determine the adherence by laboratories across the United States to the standard semen analysis guidelines and parameter reference ranges 10 years after being set by the World Health ...Organization (WHO) in 1999 and to compare compliance between regional laboratories vs. specialty assisted reproductive technology (ART) laboratories. Design Observational study. Setting Regional clinical and reproductive endocrinology andrology laboratories. Intervention(s) Blank or deidentified semen analysis reports were collected from laboratories through direct contact or from reports received as part of clinical care for male infertility. Main Outcome Measure(s) Adherence to semen analysis reference range reporting as recommended by the 1999 WHO guidelines. Result(s) Semen analyses reports were collected from 111 laboratories from 31 different states. Of 111 laboratories, 26 (23%) reported all reference range parameters in accordance with the guidelines. Of 65 ART laboratories, 21 (32%) complied with all reference range parameters as outlined by the guidelines, vs. 5 of 46 non-ART laboratories (11%). Seventy percent of laboratories that did not report 1999 WHO parameters did so because of differences in reference values for normal morphology. Conclusion(s) Adherence to WHO 1999 semen analysis reference range guidelines has not been achieved by ART and non-ART laboratories 10 years after being introduced. Non-ART laboratories report reference ranges less accurately than ART laboratories.
Mechanical stimulation and hormones act via interconnected signaling pathways to influence the function of bone cells. Estrogen receptor (ER) and β-catenin play important role in bone formation and ...have implicated in mechanotransduction in bone cells. To investigate the interaction between mechanotransduction and estrogenic signaling in mesenchymal stem cells (MSCs), this study examined the effect of mechanical strain and estrogen on activation of β-catenin in MSCs, and the role of ER in response to mechanical strain and estrogen in MSCs.
MSCs were exposed to mechanical strain (2%, 1 Hz) and estrogen (100 nM). The ER inhibitor, ICI182,780 was used to assess the role of ER in activation of β-catenin stimulated by mechanical strain and estrogen. Changes of activated β-catenin in the nuclei were determined by immunoflourescent test. The expression of β-catenin was detected by western blotting.
Mechanical strain and estrogen augment, respectively, activation of β-catenin and accumulation of activated β-catenin in the nuclei of MSCs. Combined treatment with estrogen and mechanical strain had higher levels of activated β-catenin than the cells exposed to mechanical strain or estrogen. After MSCs were pre-treated by ICI182,780, the level of activated β-catenin expression induced by mechanical strain or estrogen was depressed. Meanwhile, ICI182,780 blocked effect of combined stimulation on activation of β-catenin in MSCs.
Our study demonstrates that mechanical strain and estrogen both promote the levels of activated β-catenin in MSCs. Estrogen receptor implicates in activation of β-catenin stimulation by mechanical strain and estrogen in MSCs.
We fabricated AlGaN solar-blind avalanche photodiodes (APDs) that were based on separate absorption and multiplication (SAM) structures. It was determined experimentally that the dark current in ...these APDs is rapidly enhanced when the applied voltage exceeds 52 V. Theoretical analyses demonstrated that the breakdown voltage at 52 V is mainly related to the local trap-assisted tunneling effect. Because the dark current is mainly dependent on the trap states as a result of modification of the lifetimes of the electrons in the trap states, the tunneling processes can be modulated effectively by tuning the trap energy level, the trap density, and the tunnel mass.
Bone's adaptability to loading depends upon the process of bone remodeling. This adaptive mechanism is restricted in postmenopausal osteoporosis. Differentiation of mesenchymal stem cells (MSCs) is ...crucial to bone remodeling and regeneration. It is well accepted that mechanical loading influences the fate of MSC differentiation. The aim of this study was to explore the possible restricted mechanism in osteoporotic condition, through investigating response of MSCs from both sham-operated and ovariectomized rats. MSCs were exposed to estrogen and mechanical strain (2%, 1Hz, 6h/day) for 3 days. Osteogenic differentiation and β-catenin protein in MSCs were examined. Exposure to estrogen and mechanical strain alone enhanced expression of Runx2 (Cbfα1), type I collagen (ColI) and activated β-catenin protein in MSCs from both sham-operated and OVX rats. MSCs from both sham-operated and OVX rats stimulated with both mechanical strain and estrogen had higher expression of osteogenic genes and activated β-catenin protein than these cells exposed to estrogen and mechanical strain alone. Osteoporotic MSCs had lower expression of osteogenic genes and protein in the absence and presence of stimulation than did MSCs from sham-operated rats. Cumulatively, our results indicate that mechanical strain and estrogen in vitro enhance osteogenic potential and activation of β-catenin in MSCs from both sham-operated and OVX rats. Estrogen augments strain-induced osteogenic potential and activity of β-catenin in MSCs.
Land use and land cover change as the core of coupled human-environment systems has become a potential field of land change science （LCS） in the study of global environmental change. Based on ...remotely sensed data of land use change with a spatial resolution of 1 km × 1 km on national scale among every 5 years, this paper designed a new dynamic regionalization according to the comprehensive characteristics of land use change including regional differentiation, physical, economic, and macro-policy factors as well. Spatial pattern of land use change and its driving forces were investigated in China in the early 21 st century. To sum up, land use change pattern of this period was characterized by rapid changes in the whole country. Over the agricultural zones, e.g., Huang-Huai-Hai Plain, the southeast coastal areas and Sichuan Basin, a great proportion of fine arable land were engrossed owing to considerable expansion of the built-up and residential areas, resulting in decrease of paddy land area in southern China. The development of oasis agriculture in Northwest China and the reclamation in Northeast China led to a slight increase in arable land area in northern China. Due to the ＂Grain for Green＂ policy, forest area was significantly increased in the middle and western developing regions, where the vegetation coverage was substantially enlarged, likewise. This paper argued the main driving forces as the implementation of the strategy on land use and regional development, such as policies of ＂Western Development＂, ＂Revitalization of Northeast＂, coupled with rapidly economic development during this period.
Accurate and timely maps of urban underlying land properties at the national scale are of significance in improving habitat environment and achieving sustainable development goals. Urban impervious ...surface (UIS) and urban green space (UGS) are two core components for characterizing urban underlying environments. However, the UIS and UGS are often mosaicked in the urban landscape with complex structures and composites. The “hard classification” or binary single type cannot be used effectively to delineate spatially explicit urban land surface property. Although six mainstream datasets on global or national urban land use and land cover products with a 30 m spatial resolution have been developed, they only provide the binary pattern or dynamic of a single urban land type, which cannot effectively delineate the quantitative components or structure of intra-urban land cover. Here we propose a new mapping strategy to acquire the multitemporal and fractional information of the essential urban land cover types at a national scale through synergizing the advantage of both big data processing and human interpretation with the aid of geoknowledge. Firstly, the vector polygons of urban boundaries in 2000, 2005, 2010, 2015 and 2018 were extracted from China's Land Use/cover Dataset (CLUD) derived from Landsat images. Secondly, the national settlement and vegetation percentages were retrieved using a sub-pixel decomposition method through a random forest algorithm using the Google Earth Engine (GEE) platform. Finally, the products of China's UIS and UGS fractions (CLUD-Urban) at a 30 m resolution were developed in 2000, 2005, 2010, 2015 and 2018. We also compared our products with six existing mainstream datasets in terms of quality and accuracy. The assessment results showed that the CLUD-Urban product has higher accuracies in urban-boundary and urban-expansion detection than other products and in addition that the accurate UIS and UGS fractions were developed in each period. The overall accuracy of urban boundaries in 2000–2018 are over 92.65 %; and the correlation coefficient (R) and root mean square errors (RMSEs) of UIS and UGS fractions are 0.91 and 0.10 (UIS) and 0.89 and 0.11 (UGS), respectively. Our result indicates that 71 % of pixels of urban land were mosaicked by the UIS and UGS within cities in 2018; a single UIS classification may highly increase the mapping uncertainty. The high spatial heterogeneity of urban underlying covers was exhibited with average fractions of 68.21 % for UIS and 22.30 % for UGS in 2018 at a national scale. The UIS and UGS increased unprecedentedly with annual rates of 1605.56 and 627.78 km2 yr−1 in 2000–2018, driven by fast urbanization. The CLUD-Urban mapping can fill the knowledge gap in understanding impacts of the UIS and UGS patterns on ecosystem services and habitat environments and is valuable for detecting the hotspots of waterlogging and improving urban greening for planning and management practices. The datasets can be downloaded from https://doi.org/10.5281/zenodo.4034161 (Kuang et al., 2020a).
In offshore engineering, the pipe is the critical component for oil and gas transportation. Its integrity directly influences the transport of oil and gas. Steel strip reinforced thermoplastic pipe ...(SSRTP), as a new type of unbonded flexible pipe, has come into application in the marine resource transportation field because of its good mechanical performance. The severe and complex subsea conditions make SSRTP subjected to principal loading cases. To monitor the working condition of SSRTP, in this article, the possibility of Fiber bragg grating (FBG) monitoring has been discussed to achieve real-time measurement of hoop strain on the sheath under internal pressure. The experimental results are in good agreement with the finite element analysis (FEA) results, which indicates that hoop stain on the sheath can serve as a monitoring parameter and preliminarily realize the health monitoring of SSRTP with the help of FBG technology. Parametric analysis is further conducted to better understand the mechanical performance of SSRTP based on the proposed monitoring parameter. The results indicate that SSRTP takes better advantage of material properties, compared with the steel pipe with the same dimension; the hoop strain on the sheath is slightly decreased by the friction between layers, but is significantly affected by the geometry of SSRTP due to the change of the radial stiffness.
The separate type heat pipe heat exchanger is considered to be a potential selection for developing passive cooling spent fuel pool - for the passive pressurized water reactor. This paper simulates ...the boiling flow behavior in the evaporator of separate type heat pipe, consisting of a bundle of tubes of inner diameter 65mm. It displays two-phase characteristic in the evaporation section of the heat pipe working in low heat flux. In this study, the two-phase flow model in the evaporation section of the separate type heat pipe is presented. The volume of fluid (VOF) model is used to consider the interaction between the ammonia gas and liquid. The flow patterns and flow behaviors are studied and the agitated bubbly flow, churn bubbly flow are obtained, the slug bubble is likely to break into churn slug or churn froth flow. In addition, study on the heat transfer coefficients indicates that the nucleate boiling is the dominant mechanism in large pipes at low mass and heat flux, with the heat transfer coefficient being less sensitive to the total mass flux.
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