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81.
Vibha Singhal Supritha Nimmala Meghan Slattery Kamryn T. Eddy Karen K. Miller Anne Klibanski Madhusmita Misra 《Nutrients》2022,14(13)
Background: While physiologic estrogen replacement results in increases in areal bone mineral density (aBMD) in hypoestrogenic adolescent girls and young adult women with AN, data are lacking regarding its impact on measures of volumetric BMD (vBMD), bone geometry, and structure. Methods: 23 young women with anorexia nervosa (AN) and 27 normal-weight healthy controls (HC) between 14–25 years old were followed for 12 months. AN participants received transdermal 17β-estradiol (continuously) with 10 days of cyclic oral progesterone (100 mg daily) every month for the study duration (AN-E+). DXA was used to measure aBMD and body composition, high resolution peripheral quantitative CT (HRpQCT) to assess vBMD, bone geometry and structure at the distal radius and tibia, and microfinite element analysis to estimate strength. Results: Groups did not differ for age. Median baseline BMI z-scores were −1.13 (−1.58, −0.38) in AN-E+ vs. 0.08 (−0.40, 0.84) in HC (p < 0.0001). For most HRpQCT parameters and strength estimates, young women with AN receiving physiologic estrogen replacement demonstrated similar changes over 12 months as did normoestrogenic HC. Additionally, radial cortical tissue mineral density, cortical vBMD, and failure load increased (p = 0.01; p = 0.02; p = 0.004 respectively) over 12 months in AN-E+ compared to HC. Conclusions: With physiologic estrogen replacement, bone accrual improved in AN to approximate changes observed in normoestrogenic controls followed without any intervention, with additional benefits observed for cortical tissue mineral density, cortical vBMD, and failure load at the radius in AN vs. controls. Thus, this strategy for estrogen replacement effectively mimics the effects of endogenous estrogen on bone structure and estimated strength. 相似文献
82.
Electronic structure and magnetic properties of FeSe are calculated using the density functional approach. Due to the metallic properties, magnetic moments of the iron atoms in two nonequivalent positions in the unit cell are different from ionic values for Fe and Fe and are equal to and , making the system ferrimagnetic. The total magnetic moment for the unit cell is . Under isotropic compression, the total magnetic moment decreases non-monotonically and correlates with the non-monotonic dependence of the density of states at the Fermi level . For 7% compression, the magnetic order changes from the ferrimagnetic to the ferromagnetic. At 14% compression, the magnetic order disappears and the total magnetic moment becomes zero, leaving the system in a paramagnetic state. This compression corresponds to the pressure of 114 GPa. The magnetic ordering changes faster upon application of an isotropic external pressure due to the sizeable anisotropy of the chemical bondings in FeSe. The ferrimagnetic and paramagnetic states occur under pressures of 5.0 and 8.0 GPa, respectively. The system remains in the metallic state for all values of compression. 相似文献
83.
This study built theoretical and practical models to evaluate the corrosion resistance of concrete for coastal offshore structures in Vietnam. A mathematical model was developed in the form of a system of nonlinear partial differential equations characterizing the diffusion “free calcium hydroxide” in a solid of a concrete structure. The model describes the process of non-stationary mass conductivity observed in the “concrete structure—marine environment” system under non-uniform arbitrary initial conditions, as well as combined boundary conditions of the second and third kind, taking into account the nonlinear nature of the coefficients of mass conductivity k and mass transfer β. It was shown that the solution of the boundary value problem of non-stationary mass conductivity allows us to conclude about the duration of the service life of a concrete structure, which will be determined by the processes occurring at the interface: in concrete—mass conductivity, depending on the structural and mechanical characteristics of hydraulic structures, and in the liquid phase—mass transfer, determined by the conditions of interaction at the interface of the indicated phases. 相似文献
84.
Based on lithium aluminosilicate glass, the composition of glass was optimized by replacing SiO2 with B2O3, and the influence of glass composition on structure and performance was studied. With the increase in B2O3 concentrations from 0 to 6.5 mol%, Al2O3 always existed in the form of four-coordinated [AlO4] in the network structure, and B2O3 mainly entered the network in the form of four-coordinated [BO4]. The content of Si-O-Si linkages (Q4(0Al)) was always dominant. The incorporation of boron oxide improved the overall degree of polymerization and connectivity of the lithium aluminosilicate glass network structure. An increase in the degree of network polymerization led to a decrease in the thermal expansion coefficient of the glass and an increase in Vickers hardness and density. The durability of the glass in hydrofluoric acid and NaOH and KOH solutions was enhanced overall. 相似文献
85.
To deeply understand the adsorption process of oxygen on the surface of a plutonium gallium system and to reveal the chemical reaction mechanism at the initial stage of oxidative corrosion on the surface of plutonium gallium alloy at a theoretical level, the adsorption behavior of oxygen molecules on the surface of a plutonium gallium system was investigated by a first-principles approach based on density flooding theory. The results show that the molecular bond length increases and finally breaks when the surface oxygen molecule is adsorbed on the surface of plutonium gallium system and dissociates into two atomic states. The most likely adsorption position of oxygen molecules on the surface of plutonium gallium system is hole-site vertical adsorption with the adsorption energy size of 10.7 eV. The bonding between oxygen atom and surface is mainly due to the overlapping hybridization of Pu-6s, Pu-7s, Pu-6d, Ga-3d and O-2p orbitals. Oxygen molecules mainly interact with the atoms of the first layer on the surface of the plutonium gallium system. The oxygen atoms after stable adsorption are able to diffuse to the subsurface of the plutonium gallium system after overcoming the energy barrier of 16.7 eV and form a stable structure. The research results reveal the initial reaction process and adsorption law of oxygen on the surface of plutonium gallium system from microscopic level, which is helpful to further explore the surface corrosion prevention technology of plutonium gallium system and improve the reliability and safety of plutonium gallium alloy components. 相似文献
86.
Stitham J Arehart E Gleim SR Li N Douville K Hwa J 《British journal of pharmacology》2007,152(4):513-522
BACKGROUND AND PURPOSE: The human prostacyclin receptor (hIP), a G-protein coupled receptor (GPCR) expressed mainly on platelets and vascular smooth muscle cells, plays important protective roles in the cardiovascular system. We hypothesized that significant insights could be gained into the structure and function of the hIP through mutagenesis of its energetically unfavourably located transmembrane charged residues. EXPERIMENTAL APPROACH: Within its putative transmembrane helices fourteen hydrophilic residues, both unique and conserved across GPCRs, were systematically mutated to assess for effects on receptor structure and function. KEY RESULTS: Mutations of ten of the fourteen charged residues to alanine exhibited defective binding and/or activation. Key potential interactions were identified between 6 core residues; E116(3.49)-R117(3.50) (salt bridge TMIII), D274(7.35)-R279(7.40) (salt bridge TMVII), and D60(2.50)-D288(7.49) (H-bond network TMII-TMVII). Further detailed investigation of E116(3.49) (TMIII) with mutation to a glutamine showed a 2.6-fold increase in agonist-independent basal activity. This increase in activity accounts for a proportion ( approximately 13%) of full agonist induced activation. We further characterized two novel naturally occurring human mutations, R77(2.33)C and R279(7.40)C recently identified in a 1455 human genomic DNA sample screen. The R77(2.33)C variant appeared to exclusively affect expression, while the R279(7.40)C variant, exhibited considerable deficiencies in both agonist binding and activation. CONCLUSIONS AND IMPLICATIONS: Transmembrane charged residues play important roles in maintaining the hIP binding pocket and ensuring normal activation. The critical nature of these charged residues and the presence of naturally occurring mutations have important implications in the rational design of prostacyclin agonists for treating cardiovascular disease. 相似文献
87.
目的建立蒲黄中对照品的研究方法。方法结合大孔吸附树脂、聚酰胺、Sephadex-LH20柱色谱方法对蒲黄中香蒲新苷(typhaneoside,1)、异鼠李素-3-O-新橙皮苷(isorhamnetin-3-O-neohes-peridoside,2)、柚皮素(naringenin,3)和异鼠李素(isorhamnetin,4)进行分离纯化,通过理化性质和光谱数据进行结构鉴定,TLC和HPLC进行纯度检查。结果制备得到的香蒲新苷、异鼠李素-3-O-新橙皮苷、柚皮素和异鼠李素的纯度分别为99.2%、99.7%、98.0%和96.2%。结论制备方法可作为蒲黄鉴别和含量测定用对照品。 相似文献
88.
脑苷脂类化合物是一类广泛存在于菌类、植物类、动物类及海洋生物组织细胞膜中含量很低的内源性生物活性物质。本文就近年来发现的脑苷脂类化合物的化学结构特点与生物进化相关性、脑苷脂类的生物合成与体内转化、生物活性与药理作用、应用前景等方面的研究进行综述和展望,为此类活性成分的深入研究提供参考。 相似文献
89.
90.