220 research outputs found
Thermomechanically processed magnesium-silver alloys as antibacterial and biodegradable implant materials
In this study, āsmartā Mg-Ag alloys as antibacterial and biodegradable implant materials were prepared and systematically evaluated. The microstructure of the as cast Mg-Ag alloys with varied silver content was regulated with respect to the grain size and precipitates via different thermomechanical processing. The processing includes casting, homogenization, hot extrusion, equal channel angular pressing (ECAP), friction stir processing (FSP) and rolling with subsequent annealing. The influence of microstructure on tensile properties and degradation behavior was revealed. The cytocompatibility, mineralization, antibacterial properties and degradation mechanism of Mg-Ag alloys were evaluated
Shoshonitic enclaves in the high Sr/Y Nyemo pluton, southern Tibet: Implications for Oligocene magma mixing and the onset of extension of the southern Lhasa terrane
Post-collisional potassic and high Sr/Y magmatism in the Lhasa terrane provides critical constraints on the timing and mechanism of subduction of Indian lithosphere and its role in the uplift of the Tibetan Plateau. Here, we report whole-rock geochemistry, mineral geochemistry, zircon U Pb ages, and in situ zircon Hf isotope ratios for the Nyemo pluton, a representative example of such magmatism. The Nyemo pluton is composed of high Sr/Y host rocks and coeval shoshonitic mafic microgranular enclaves (MMEs). Whole-rock compositions of the host rocks and MMEs form linear trends in Harker diagrams, consistent with modification of both end-members by magma mixing. Although the main high Sr/Y phase of the pluton formed by partial melting of the lower crust of the thickened Lhasa terrane, the MMEs display abnormally enriched light rare earth elements, low whole-rock Īµ_(Nd)(t) and low zircon Īµ_(Hf)(t) that suggest derivation from low degree melting of hydrous and enriched mantle. Based on the occurrence of shoshonitic magma and high La/Yb and high Sr/Y with adakitic affinity host rocks around 30 Ma, the Nyemo pluton is best explained as a record of onset of extension that resulted from convective removal of the mantle lithosphere beneath Tibet in the Oligocene
Study on pharmacokinetics of Amygdalin after oral administration of semen persicae extraction in rat plasma by HPLC
Semen Persicae was a traditional Chinese medicine for the treatment of diseases such as inflammation and hyperlipemia. Amygdalin was one of the main active ingredients of this traditional Chinese medicine. In this paper, pharmacokinetic study was conducted to obtain pharmacokinetic parameters of amygadalin after oral administration of Semen Persicae extraction in rat plasma. HPLC-UV was used to determine the concentration of amygdalin in rat plasma at different time points after administration. The main pharmacokinetic parameters of amygdalin in rat were obtained based on the analysis of the plasma sample. The pharmacokinetics of amygdalin was fitted with a one-compartment model and it eliminated relative slowly in rats.Colegio de FarmacƩuticos de la Provincia de Buenos Aire
Characterization of CDOM in saline and freshwater lakes across China using spectroscopic analysis
Colored dissolved organic matter (CDOM) is a major component of DOM in waters, and plays a vital role in carbon cycling in inland waters. In this study, the light absorption and three-dimensional excitation-emission matrix spectra (EEMs) of CDOM of 936 water samples collected in 2014ā2017 from 234 lakes in five regions across China were examined to determine relationships between lake water sources (fresh versus saline) and their fluorescence/absorption characteristics. Results indicated significant differences regarding DOC concentration and aCDOM(254) between freshwater (6.68āÆmgāÆC Lā1, 19.55āÆm-1) and saline lakes (27.4āÆmgāÆC Lā1, 41.17āÆm-1). While humic-like (F5) and fulvic-like (F3) compounds contributed to CDOM fluorescence in all lake waters significantly, their contribution to total fluorescence intensity (FT) differed between saline and freshwater lakes. Significant negative relationships were also observed between lake altitude with either F5 (R2āÆ=āÆ0.63, NāÆ=āÆ306) or FT (R2āÆ=āÆ0.64, NāÆ=āÆ306), suggesting that the abundance of humic-like materials in CDOM tends to decrease with increased in lakes altitude. In high-altitude lakes, strong solar irradiance and UV exposure may have induced photo-oxidation reactions resulting in decreased abundance of humic-like substances and the formation of low molecular weight compounds. These findings have important implications regarding our understanding of C dynamics in lacustrine systems and the contribution of these ecosystems to the global C cycle
Influence of the Microstructure and Silver Content on Degradation, Cytocompatibility, and Antibacterial Properties of Magnesium-Silver Alloys In Vitro
Implantation is a frequent procedure in orthopedic surgery, particularly in the aging population. However, it possesses the risk of infection and biofilm formation at the surgical site. This can cause unnecessary suffering to patients and burden on the healthcare system. Pure Mg, as a promising metal for biodegradable orthopedic implants, exhibits some antibacterial effects due to the alkaline pH produced during degradation. However, this antibacterial effect may not be sufficient in a dynamic environment, for example, the human body. The aim of this study was to increase the antibacterial properties under harsh and dynamic conditions by alloying silver metal with pure Mg as much as possible. Meanwhile, the Mg-Ag alloys should not show obvious cytotoxicity to human primary osteoblasts. Therefore, we studied the influence of the microstructure and the silver content on the degradation behavior, cytocompatibility, and antibacterial properties of Mg-Ag alloys in vitro. The results indicated that a higher silver content can increase the degradation rate of Mg-Ag alloys. However, the degradation rate could be reduced by eliminating the precipitates in the Mg-Ag alloys via T4 treatment. By controlling the microstructure and increasing the silver content, Mg-Ag alloys obtained good antibacterial properties in harsh and dynamic conditions but had almost equivalent cytocompatibility to human primary osteoblasts as pure Mg
Geochemistry, detrital zircon geochronology and Hf isotope of the clastic rocks in southern Tibet: implications for the Jurassic-Cretaceous tectonic evolution of the Lhasa terrane
In order to reconstruct tectonic evolution history of the southern margin of Asia (i.e., Lhasa terrane) before the India-Asia collision, here we present a comprehensive study on the clastic rocks in the southern Lhasa terrane with new perspectives from sedimentary geochemistry, detrital zircon geochronology and Hf isotope. Clasts from the Jurassic-Early Cretaceous sedimentary sequences (i.e., Yeba and Chumulong Formations) display high compositional maturity and experienced moderate to high degree of chemical weathering, whereas those from the late Early-Late Cretaceous sequences (Ngamring and Shexing Formations) are characterized by low compositional maturity with insignificant chemical weathering. Our results lead to a coherent scenario for the evolution history of the Lhasa terrane. During the Early-Middle Jurassic (ā¼192-168Ma), the Lhasa terrane was speculated to be an isolated geological block. The Yeba Formation is best understood as being deposited in a back-arc basin induced by northward subduction of the Neo-Tethys ocean with sediments coming from the interiors of the Lhasa terrane. The Middle Jurassic-Early Cretaceous Lhasa-Qiangtang collision resulted in the formation of a composite foreland basin with southward-flowing rivers carrying clastic materials from the uplifted northern Lhasa and/or Qiangtang terranes. During the late Early-Late Cretaceous (ā¼104-72Ma), the Gangdese magmatic arc was uplifted rapidly above the sea level, forming turbidites (Ngamring Formation) in the Xigaze forearc basin and fluvial red beds (Shexing Formation) on the retro-arc side. At the end of Late Cretaceous, the Lhasa terrane was likely to have been uplifted to high elevation forming an Andean-type margin resembling the modern South America before the India-Asia collision
Rosiglitazone Restores Endothelial Dysfunction in a Rat Model of Metabolic Syndrome through PPARĪ³- and PPARĪ“-Dependent Phosphorylation of Akt and eNOS
Vascular endothelial dysfunction has been demonstrated in metabolic syndrome (MS). Chronic administration of rosiglitazone ameliorates endothelial dysfunction through PPARĪ³-mediated metabolic improvements. Recently, studies suggested that single dose of rosiglitazone also has direct vascular effects, but the mechanisms remain uncertain. Here we established a diet-induced rat model of MS. The impaired vasorelaxation in MS rats was improved by incubating arteries with rosiglitazone for one hour. Importantly, this effect was blocked by either inhibition of PPARĪ³ or PPARĪ“. In cultured endothelial cells, acute treatment with rosiglitazone increased the phosphorylation of Akt and eNOS and the production of NO. These effects were also abolished by inhibition of PPARĪ³, PPARĪ“, or PI3K. In conclusion, rosiglitazone improved endothelial function through both PPARĪ³- and PPARĪ“-mediated phosphorylation of Akt and eNOS, which might help to reconsider the complex effects and clinical applications of rosiglitazone
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Petrogenesis of Himalayan leucogranites: Perspective from a Combined Elemental and FeāSrāNd isotope study
The petrogenesis of Himalayan leucogranites remains crucial for understanding the thermal and tectonic evolution of the Himalayan orogen. To understand whether they are largely pristine melts of crustal anatexis or have experienced a high degree of fractional crystallization (FC), we present Fe isotopic data of 30 representative Himalayan leucogranites and 9 local metasedimentary rocks. Excepting three garnet leucogranites with low Ī“56Fe (ā0.04ā°ā0.06ā°) that are likely affected by garnet accumulation, tourmaline, and two-mica leucogranites have largely homogeneous Ī“56Fe from 0.13ā° to 0.24ā° irrespective of their highly variable SiO2, MgO, and FeOt contents. Combined with observed mineral assemblages and available fractionation factors, this does not support a high degree of FC (with or without assimilation) in their petrogenesis. The elevated Ī“56Fe relative to the supposed source rocks, represented by metasedimentary rocks and/or metabasite with a Ī“56Fe value of 0.10ā°, by ā¼0.07ā°, may reflect Fe isotope fractionation during crustal anatexis. This study indicates most leucogranites can provide robust constraints on the conditions of crustal anatexis and thus the thermal and tectonic evolution of the Himalayan orogen
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