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排序方式: 共有480条查询结果,搜索用时 15 毫秒
471.
Proteins constitute the building blocks of biological materials such as tendon, bone, skin, spider silk or cells. An important trait of these materials is that they display highly characteristic hierarchical structures, across multiple scales, from nano to macro. Protein materials are intriguing examples of materials that balance multiple tasks, representing some of the most sustainable material solutions that integrate structure and function. Here we review progress in understanding the deformation and fracture mechanisms of hierarchical protein materials by using a materials science approach to develop structure-process-property relations, an effort defined as materiomics. Deformation processes begin with an erratic motion of individual atoms around flaws or defects that quickly evolve into formation of macroscopic fractures as chemical bonds rupture rapidly, eventually compromising the integrity of the structure or the biological system leading to failure. The combination of large-scale atomistic simulation, multi-scale modeling methods, theoretical analyses combined with experimental validation provides a powerful approach in studying deformation and failure phenomena in protein materials. Here we review studies focused on the molecular origin of deformation and fracture processes of three types of protein materials. The review includes studies of collagen - Nature’s super-glue; beta-sheet rich protein structures as found in spider silk - a natural fiber that can reach the strength of a steel cable; as well as intermediate filaments - a class of alpha-helix based structural proteins responsible for the mechanical integrity of eukaryotic cells. The article concludes with a discussion of the significance of universally found structural patterns such as the staggered collagen fibril architecture or the alpha-helical protein motif. 相似文献
472.
This article interprets the new implementation of an asymptotic homogenization method for effective bending stiffness of heterogeneous beam structures with periodic microstructure along its axial direction in an intuitionistic way. With this interpretation, the authors then develop a new method of evaluating effective shear stiffness for their Timoshenko beam model. This method can be easily implemented numerically in commercial software. Different kinds of elements and modeling techniques available in commercial software can be applied to model the unit cell. Several examples are given to demonstrate the effectiveness of this new method. 相似文献
473.
Ramazan Topkaya Sinan Kazan Resul Yilgin Numan Akdoğan Mustafa Özdemir Bekir Aktaş 《Journal of Superconductivity and Novel Magnetism》2014,27(6):1503-1512
Dynamic and static magnetizations of an exchange biased bilayer system which is constructed as a proximity of a CoO layer on an Fe-layer grown on the (100) oriented MgO substrate by ion beam sputtering technique have been investigated by ferromagnetic resonance (FMR) and vibrating sample magnetometry (VSM) techniques. The room-temperature FMR measurements reveal that the Fe layer is epitaxially grown on MgO substrate with four-fold magnetocrystalline anisotropy and the hard magnetization axis of the sample is the [100] crystallographic directions of MgO substrate. We have determined the g-value, effective magnetization, magnetocrystalline anisotropy constants and contributions to FMR linewidth due to the intrinsic Gilbert damping and inhomogeneity of magnetization by using Landau–Lifshitz–Gilbert (LLG) equation. We observed an unusual FMR line shape attributed to impedance switching of resonance cavity and complex component of conductivity of sample system. The low-temperature FMR measurement shows asymmetric hysteretic behavior of resonance field related to magnetic coupling of ferromagnetic and antiferromagnetic layers. From both FMR and VSM measurements between 10–300 K, the magnetocrystalline anisotropy is observed to dominate above blocking temperature, while unidirectional anisotropy is observed to dominate below blocking temperature over internal magnetic anisotropy. FMR spectra have a comparatively small linewidth between 40–100 Oe, which indicates to a high crystallinity of the Fe film. Gilbert constant was calculated as 0.007 from the linewidth fitting of FMR spectra. This small value is a suitable for reducing the critical switching current used in magnetic tunneling junction. Detailed exchange bias studies were carried out for hard and easy axis of the sample in the temperature range of 10–300 K. From both low-temperature FMR and VSM measurements, the blocking temperature of the system was determined as ~60 K. 相似文献
474.
This paper shows the ex situ thermal treatment effects of the ZrO2 thin films obtained by TVA (thermionic vacuum arc) technique on the optical properties (e.g., transmittance, refractive index and band-gap energy) of ZrO2 thin films. The crystal structure, surface and optical properties were investigated for ZrO2 thin films deposited on glass substrates by thermionic vacuum arc (TVA) method. The thermal treatment effect on the optical properties of the thin films was determined. The XRD analysis showed that the deposited ZrO2 thin films have baddeleyite (monoclinic) and zirconium (hexagonal) structures. The thicknesses and refractive index were determined by interferometric measurements. The thin films were thermal treated at different temperatures (350 °C, 450 °C and 550 °C), and the analysis showed that the optical properties of ZrO2 deposited thin films were improved by thermal treatment at 450 °C. 相似文献
475.
Baldik R Aytekin H Celebi N Ataksor B Taşdelen M 《Radiation protection dosimetry》2006,118(1):122-125
In this study, the results of atmospheric radon measurements that were performed for the Amasra underground coal mine in Zonguldak bituminous coal basin (Turkey) are presented. The radon measurements were performed for 40 days between November 2004 and December 2004 using passive nuclear etched track detectors. The radon concentrations vary from a minimum value 49 Bq m(-3) in a site located at +40 m to a maximum value 223 Bq m(-3) in a site located at -100 m. Mean concentration is 117 (Bq m(-3)). This value is well below the action level of 500-1,500 Bq m(-3) recommended by the International Commission on Radiological Protection (ICRP) (1993). The mean effective dose value for workers of this mine of 3.4 microSv per day was obtained. This result shows that protection against radiological hazards would not be necessary for workers of this mine((2)). 相似文献
476.
Radon measurements were carried out in Kozlu, Karadon and Uzülmez underground coal mines of Zonguldak bituminous coal basin in Turkey. Passive-time integrating method, which is the most widely used technique for the measurement of radon concentration in air, was applied by using nuclear etched track detectors (CR-39) in the study area. The radon concentration measurements were performed on a total of 42 points in those three mines. The annual exposure, the annual effective dose and lifetime fatality risk, which are the important parameters for the health of workers, were estimated based on chronic occupational exposure to the radon gas, which is calculated using UNCEAR-2000 and ICRP-65 models. The radon concentrations at several coal production faces are higher than the action level of 1000 Bq m(-3). It is suggested that the ventilation rates should be rearranged to reduce the radon concentration. 相似文献
477.
TlSbSe2 samples used for electrical measurements were cleaved from larger crystals grown by using the Bridgman-Stockbarger method. Electrical properties of TlSbSe2 have been carried out as a function of temperature (203-258 K) at different dc electric fields. The dc studies revealed the non-ohmic type of conduction (log I versus log V plot). The field lowering coefficientβ is evaluated from log I versus E1/2 plot. It is found that the dominant conduction mechanism in these samples is Poole-Frenkel type. The activation energies are also calculated at different voltages. It is seen that the activation energy decreases with increase of applied voltage. 相似文献
478.
Marmarosh Cheri L.; Whipple Rachel; Schettler Melanie; Pinhas Sandra; Wolf Jami; Sayit Sinan 《Canadian Metallurgical Quarterly》2009,13(4):255
The current study examined the relationship between 63 intake clients’ and 28 college student’s attachment styles and their attitudes of group psychotherapy. The authors examined the relationship between attachment anxiety and avoidance and the subscales of the Group Therapy Survey-R (Carter, Mitchell, & Krautheim, 2001). Results revealed a significant relationship between attachment avoidance in adult romantic relationships and increased fears of being vulnerable in group psychotherapy. As hypothesized, avoidance in romantic relationships was related to fears of shame and humiliation in group therapy. Contrary to predictions, clients’ anxiety ratings were negatively related to negative myths of group psychotherapy. The greater the clients rated fears of being rejected and abandoned, the less they rated negative myths about group treatment. Neither attachment anxiety nor avoidance was related to ratings of group therapy efficacy. Implications of the findings for future research and practice are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
479.
为了获得水溶性Fe_3O_4纳米粒子,以聚乙二醇(PEG)磷酸酯为亲水性配体,在甲苯/四氢呋喃/水三元混合溶剂体系下通过快速配体交换法将油酸包覆的油溶性磁性Fe_3O_4纳米粒子转变成聚乙二醇磷酸酯包覆的水溶性Fe_3O_4纳米粒子。考察了四氢呋喃等溶剂在实现快速配体交换中所起到的作用。利用透射电子显微镜(TEM)、动态光散射(DLS)、X射线粉末衍射仪(XRD)、傅立叶红外光谱仪(FTIR)、振动样品磁强计(VSM)对磁性Fe_3O_4纳米粒子进行了分析表征。结果表明:四氢呋喃可以促进PEG磷酸酯与Fe_3O_4纳米粒子表面的有效接触并使得油酸分子从纳米粒子表面快速地脱附下来,此外,还消除了配体交换过程中出现的乳化效应。四氢呋喃的应用实现了快速配体交换法制备水溶性PEG磷酸酯包覆的磁性纳米粒子。 相似文献
480.