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"Liu, H"
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Transport of Nitric Oxide in the Winter Mesosphere and Lower Thermosphere
Nitric oxide (NO) plays key roles both in thermospheric energetics and upper‐lower atmosphere coupling. However, mesospheric NO in the polar night region has often been underestimated in whole atmosphere models, and the exact causes are not well understood. Recent high‐resolution (HR) WACCM‐X simulations show significant increase in NO in the polar night, and our analysis reveals distinct differences in the vertical transport between the HR and coarse resolution (CR) simulations: The residual mean vertical wind in the mesosphere and lower thermosphere (MLT) region displays mesoscale flow channels that are strong and alternate between upward and downward directions in the former, with large net downward transport over the polar region. In the latter it is much weaker and even upward over large latitude ranges. Moreover, the resolved waves in the HR simulations induce downward eddy transport of NO in the MLT much stronger than the parameterized diffusion in CR simulations. Plain Language Summary The Earth's thermosphere is heated by the solar extreme ultraviolet irradiance and by energetic particle precipitation during solar and geomagnetic storms, and NO is one of the most important cooling agent in the thermosphere. The NO level increases rapidly during storm time, making it a natural thermostat for the thermosphere. Moreover, NO is long‐lived in polar night region, where it can descend along with the general circulation into the middle atmosphere (MA) and effectively destroy ozone. It is therefore an important species for the energy balance of the upper atmosphere and the chemistry and dynamics of the MA. However, until recently NO in the winter middle and upper atmosphere is often underestimated in global models that simulate the whole atmosphere system. Newly developed HR whole atmosphere simulations, on the other hand, start to show considerable improvement. Our analysis presented in this study reveals rigorous downward transport in the winter MLT from the HR model that is not seen in coarse‐resolution simulations. The strong downward transport is mainly driven by gravity waves resolved by the HR model. Key Points Nitric oxide level in the winter mesosphere is higher in high‐resolution (HR) WACCM‐X simulations, in better agreement with observations Downward transport driven by resolved gravity waves in the mesosphere and lower thermosphere plays a critical role Residual mean vertical wind from the HR simulations displays mesoscale flow channels
Journal Article
Case files : general surgery
\"This book presents over 50 clinical cases illustrating essential concepts in general surgery. Perfect for the clerkship and the USMLE Step 2, each case includes an extended discussion, definitions of key terms, clinical pearls, and USMLE-style review questions. This interactive learning system helps you to learn instead of memorize.\"--Jacket.
Book
Vegetation‐Driven Spatial Heterogeneity of Land Surface Temperature Changes on the Chinese Loess Plateau
A comprehensive understanding of the processes and mechanisms driving Holocene temperature changes is crucial for resolving the ongoing Holocene temperature controversy. Here, we reconstructed land surface temperature (LST) variations over the past 27,000 years in two loess‐paleosol profiles from the Chinese Loess Plateau based on soil bacterial lipid signatures. By combining our data with other published records derived from the same proxy, we identify notable spatial inconsistencies in LST trends across geographically proximate areas with distinct vegetation cover, despite the expectation that air temperature trends should be consistent. By integrating modern meteorological data, we propose that rainfall‐induced changes in surface vegetation dynamics are a key factor contributing to this divergence. This contributes to our understanding of past climate dynamics in East Asia and underscores the importance of considering vegetation effects when interpreting paleoclimate data and resolving controversies over Holocene temperature trends. Plain Language Summary Land‐atmosphere interactions are crucial for understanding how regional temperatures change. Here, we looked at land surface temperature (LST) changes by analyzing soil bacterial markers. We found that LST trends varied notably across regions that were close to each other but had different types of vegetation. In the southern and eastern Chinese Loess Plateau (CLP), where vegetation is more abundant, LST changes generally matched patterns of magnetic properties of the soil, organic carbon content, and regional air temperatures. However, in the northern and western CLP, where vegetation is sparse, LSTs showed noticeable differences from air temperatures, with higher LSTs during the Last Glacial Maximum and lower LSTs during the middle Holocene. These spatial differences suggest that regional vegetation variations played a key role in the temperature changes we observed. Our findings are further supported by modern meteorological records, which demonstrate that the influence of vegetation on the temperature disparity between LSTs and air temperatures intensifies as rainfall and vegetation cover decrease, especially when rainfall is less than 600 mm. This study highlights the important role of vegetation in historical LST changes and helps us better understand Holocene temperature trends and land‐atmosphere interactions in East Asia. Key Points Notable differences exist in Holocene land surface temperature (LST) variations on the Chinese Loess Plateau Rainfall‐induced changes in surface vegetation dynamics modulated LST changes Surface vegetation changes contribute to the Holocene temperature controversies
Journal Article
Blood-derived amyloid-β protein induces Alzheimer’s disease pathologies
The amyloid-β protein (Aβ) protein plays a pivotal role in the pathogenesis of Alzheimer’s disease (AD). It is believed that Aβ deposited in the brain originates from the brain tissue itself. However, Aβ is generated in both brain and peripheral tissues. Whether circulating Aβ contributes to brain AD-type pathologies remains largely unknown. In this study, using a model of parabiosis between APPswe/PS1dE9 transgenic AD mice and their wild-type littermates, we observed that the human Aβ originated from transgenic AD model mice entered the circulation and accumulated in the brains of wild-type mice, and formed cerebral amyloid angiopathy and Aβ plaques after a 12-month period of parabiosis. AD-type pathologies related to the Aβ accumulation including tau hyperphosphorylation, neurodegeneration, neuroinflammation and microhemorrhage were found in the brains of the parabiotic wild-type mice. More importantly, hippocampal CA1 long-term potentiation was markedly impaired in parabiotic wild-type mice. To the best of our knowledge, our study is the first to reveal that blood-derived Aβ can enter the brain, form the Aβ-related pathologies and induce functional deficits of neurons. Our study provides novel insight into AD pathogenesis and provides evidence that supports the development of therapies for AD by targeting Aβ metabolism in both the brain and the periphery.
Journal Article
Impacts of Gravity Waves on the Thermospheric Circulation and Composition
The high‐resolution Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension (WACCM‐X) is used to study the impacts of gravity waves (GWs) on the thermospheric circulation and composition. The resolved GWs are found to propagate anisotropically with stronger eastward components at most altitudes. The dissipation of these waves in the thermosphere produces a net eastward forcing that reaches peak values between 200 and 250 km at mid‐high latitudes in both hemispheres. Consequently, the mean circulation is weakened in the winter hemisphere and enhanced in the summer, which in turn impacts the thermospheric composition. Most notably, the column integrated O/N2 in both hemispheres is reduced and agrees better with observations. The mean thermospheric GW forcing in the meridional direction has comparable amplitude and acts to modify the gradient‐wind relationship. Plain Language Summary Small‐scale waves originate from the lower atmosphere have been shown to propagate into the thermosphere. To study their effects a high‐resolution whole atmosphere model has been employed. Using this high‐resolution model, which can partially resolve the small‐scale waves, we can directly quantify the force exerted by these waves on the general circulation in the thermosphere. We found that such force is strong, and affects the thermospheric circulation in both winter and summer hemisphere. This consequently changes the distribution of important thermospheric species. One measure of the thermospheric composition is the ratio of atomic oxygen and molecular nitrogen, which is an indicator of the relative abundance of atomic and molecular species. This ratio has been grossly over‐estimated in previous modeling studies. It is reduced as a result of the circulation change, and is much better agreement with observations. Key Points Gravity waves (GWs) resolved by high‐resolution WACCM‐X displays anisotropic propagation GW forcing alters thermospheric circulation The circulation change leads to a much improved thermospheric O/N2
Journal Article
A water retention curve and unsaturated hydraulic conductivity model for deformable soils: consideration of the change in pore-size distribution
This paper presents a hysteretic water retention curve (WRC) and unsaturated hydraulic conductivity model for deformable soils based on the change in pore-size distribution (PSD). The PSD plays a decisive role in the water retention behaviour of soils. Although its evolution during deformation is rather complicated, experimental data showed that the overall shapes and distribution characteristics of the PSD function are not significantly altered. Based on these findings, the PSD function at a deformed state is obtained by horizontal shifting and vertical scaling of the corresponding PSD function at a reference state. On this basis, a hysteretic WRC model is formulated to account for the influences of deformation and hysteresis on the variation of saturation, using seven model parameters with clear physical meanings. The proposed model is then incorporated in the Mualem model to predict the unsaturated hydraulic conductivity for deformable soils, using only one additional parameter. A large number of published laboratory tests are used to validate the proposed model, showing that it can reasonably capture important features of retention and permeability properties for deformable soils in most cases under consideration.
Journal Article
Economic impact and cost-effectiveness of fracture liaison services: a systematic review of the literature
Fracture liaison services (FLS), implemented in different ways and countries, are reported to be a cost-effective or even a cost-saving secondary fracture prevention strategy. This presumed favorable cost-benefit relationship is encouraging and lends support to expanded implementation of FLS per International Osteoporosis Foundation Best Practice Standards. This study summarizes the economic impact and cost-effectiveness of FLS implemented to reduce subsequent fractures in individuals with osteoporosis. This systematic review identified studies reporting economic outcomes for FLS in osteoporotic patients aged 50 and older through a comprehensive search of MEDLINE, EMBASE, Cochrane Central, and PubMed of studies published January, 2000 to December, 2016. Grey literature (e.g., Google scholar, conference abstracts/posters) were also hand searched through February 2017. Two independent reviewers screened titles and abstracts and conducted full-text review on qualified articles. All disagreements were resolved by discussion between reviewers to reach consensus or by a third reviewer. In total, 23 qualified studies that evaluated the economic aspects of FLS were included: 16 cost-effectiveness studies, 2 cost-benefit analyses, and 5 studies of cost savings. Patient populations varied (prior fragility fracture, non-vertebral fracture, hip fracture, wrist fracture), and FLS strategies ranged from mail-based interventions to comprehensive nurse/physician-coordinated programs. Cost-effectiveness studies were conducted in Canada, Australia, USA, UK, Japan, Taiwan, and Sweden. FLS was cost-effective in comparisons with usual care or no treatment, regardless of the program intensity or the country in which the FLS was implemented (cost/QALY from $3023–$28,800 US dollars (USD) in Japan to $14,513–$112,877 USD in USA. Several studies documented cost savings. FLS, implemented in different ways and countries, are reported to be cost-effective or even cost-saving. This presumed favorable cost-benefit relationship is encouraging and lends support to expanded implementation of FLS per International Osteoporosis Foundation Best Practice Standards.
Journal Article
Unexpected connections between the stratosphere and ionosphere
The coupling of the ionosphere to processes from below remains an elusive and difficult problem, as rapidly changing external drivers from above mask variations related to lower atmospheric sources. Here we use superposition of unique circumstances, current deep solar minimum and a record‐breaking stratospheric warming event, to gain new insights into causes of ionospheric perturbations. We show large (50–150%) persistent variations in the low‐latitude ionosphere (200–1000 km) that occur several days after a sudden warming event in the high‐latitude winter stratosphere (∼30 km). We rule out solar irradiance and geomagnetic activity as explanations of the observed variation. Using a general circulation model, we interpret these observations in terms of large changes in atmospheric tides from their nonlinear interaction with planetary waves that are strengthened during sudden warmings. We anticipate that further understanding of the coupling processes with planetary waves, accentuated during the stratospheric sudden warming events, has the potential of enabling the forecast of low‐latitude ionospheric weather up to several days in advance.
Journal Article
Ionospheric variability due to planetary waves and tides for solar minimum conditions
Large ionospheric variability is found at low to middle latitudes when a quasi‐stationary planetary wave is specified in the winter stratosphere in the National Center for Atmospheric Research thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model for solar minimum conditions. The variability includes change of electric field/ion drift, F2 peak density and height, and the total electron content. The electric field/ion drift change is the largest near dawn in the numerical experiments. Analysis of model results suggests that, although the quasi‐stationary planetary wave does not propagate deep into the ionosphere or to low latitudes due to the presence of critical layers and strong molecular dissipation, the planetary wave and tidal interaction leads to large changes in tides, which can strongly impact the ionosphere at low and middle latitudes through the E region wind dynamo. Large zonal gradients of zonal and meridional winds from the tidal components and the zonal gradient of electric conductivities at dawn can produce large convergence/divergence of Hall and Pedersen currents, which in turn produces a polarization electric field. The ionospheric changes are dependent on both the longitude and local time, and are determined by the amplitudes and phases of the superposing wave components. The model results are consistent with observed ionospheric changes at low and middle latitudes during stratospheric sudden warming events, when quasi‐stationary planetary waves become large.
Journal Article