Molecular mechanics parameterization of thionucleoside disulfides for modeling cross-linked duplex DNA

We describe a solution to a molecular mechanics parameterization problem involving disulfide bonds between thionucleosides. Key torsional and bending parameters developed from ab initio calculations were incorporated into the AMBER* force-field in order to accurately represent the disulfide linkage in DNA cross-linked via this bond.     

Homogenization of Ti-Hastelloy-N

To homogenize Ti-Hastelloy-N, the segregated MC-type carbide stringers must be dissolved during solution annealing and enough time allowed for the carbide forming elements to diffuse uniformly throughout the matrix. A solubility product-l/Τplot and simple diffusion equation were used to estimate the parameters for a successful homogenization treatment. Compared to the material which contained stringers, the homogenized material had: 1) greater postirradiation ductility with significantly reduced scatter in values and 2) better resistance to intergranular cracking caused by tellurium vapor at 1033 K. The basic principles used to develop the homogenization treatment are applicable to other Ti or Nb stabilized alloys.     

Mg-xGd-Zr合金均匀化过程研究

实验采用光学金相、扫描电镜和布氏硬度测试等方法,研究了Mg-xGd-Zr(x=1%、2%、3%)合金不同均匀化制度下的组织形貌变化,并对合金中方块相的形成进行了分析。结果表明,随着Gd含量的升高,合金中共晶组织增加晶粒尺寸减小,3种合金合适的热处理工艺,分别为793K×6h、793K×8h和793K×12h。在均匀化过程中随着时间的延长共晶组织发生分解,但方块相依旧存在,且其数量与合金中Gd含量呈正比,同时Gd含量从铸态的41.5%~56.2%升高至均匀化态的72.5%~88.5%。     

Homogenization of primary microsegregation

The homogenization kinetics of a segregated binary alloy have been studied using electron probe microanalysis after annealing for various times at several temperatures. The concentration and number of microsegregation nodes are quantitatively examined in detail and compared with the evolution of the whole solidification substructure revealed by X-ray images and metallography. The comparison leads to the conclusion that nodes are representative of all solidification substructure and can be taken as a characteristic. The combined study also shows that nodes dissolve in two stages, starting preferentially along cell walls and continuing later in a more uniform fashion. However, a single activation energy near that for bulk diffusion is obtained for the whole process, showing that the homogenization is a collective process and volume diffusion limited.     

土工格室的渐近均匀化分析

在线弹性范围内,根据均匀化理论,结合有限元方法预测了土工格室加筋层等效弹性模量.通过将不同的方法计算出的弹件模量与复合地基试验资料对比,证实了采用均匀化理论分析土工格室的弹性模量是可行的.     

Al-Mg-Si-Cu合金均匀化退火工艺研究

针对Al-Mg-Si-Cu合金的均匀化退火工艺进行了研究,通过实验找到了枝晶偏析完全消除、非平衡相熔解、过饱和的过渡元素相沉淀及溶质的浓度完全均匀化且力学性能较佳的均匀化退火工艺。     

Evaluation of Two Homogenization Techniques for Modeling the Elastic Behavior of Granular Materials

This paper discusses the capabilities of two homogenization techniques to accurately represent the elastic behavior of granular materials considered as assemblies of randomly distributed particles. The stress-strain relationship for the assembly is determined by integrating the behavior of the interparticle contacts in all orientations, using two different homogenization methods, namely the kinematic method and the static method. The numerical predictions obtained by these two homogenization techniques are compared to results obtained during experimental studies on different granular materials. Relations between elastic constants of the assembly, interparticle properties, and fabric parameters are discussed, as well as the capabilities of the models to take into account inherent and stress-induced anisotropy for different stress conditions.     

Homogenization for Dispersion and Reduction in Length of Carbon Nanotubes

An important aspect that limits the use of carbon nanotubes (CNTs) is the difficulty in obtaining homogeneously dispersed CNTs of uniform length. Hence, homogenization of multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) was carried out using bullet blender and the dispersion behavior was compared with that of ultrasonication. 1% sodium dodecyl sulphate (SDS), Triton-x-100 and polyethylene glycol 4000 were used as dispersing agents during homogenization. The dispersed CNTs were studied using transmission electron microscopy, ImageJ and Raman spectroscopy. Though dispersion and reduction in length of MWCNTs were observed both with ultrasonication and homogenization, lowest length range with about 75% reduction in polydispersity index was obtained on homogenization. Longer time of ultrasonication resulted in damage to small MWCNTs. Well dispersed and shorter MWCNTs were obtained with Triton-x-100 while reduction in length was minimum with SDS. SWCNTs of less than 1 μm length could be obtained by homogenization with Triton-x-100.     

2024铝合金的均匀化热处理研究

采用光学显微镜(OM)、差热分析(DSC)、扫描电镜(SEM)、能谱分析(EDS)和X射线衍射(XRD)等方法,研究2024铝合金铸态与均匀化态的显微组织演化和成分分布。结果表明:2024铝合金的铸态组织枝晶偏析严重,在晶界存在很多低熔点共晶相,Cu,Mg和Mn元素在晶内及晶界分布不均匀;经过均匀化处理后,合金组织中的非平衡相逐渐溶解,各组元分布趋于均匀;该合金的过烧温度为503.1℃,合理均匀化制度为495℃,24 h,该制度与均匀化动力学方程得到的结论基本一致。     

GH202合金铸锭均匀化扩散工艺的研究

主要针对GH202合金热加工塑性低,在自耗锭低倍检验时出现点状偏析的现象,通过研究均匀化扩散退火制度,达到使铸锭均匀化来减轻甚至消除点状偏析,达到提高合金热加工塑性、改善组织不均匀性的目的.     

Vocal mechanics as the basis for phonosurgery

OBJECTIVE: A number of modifications in laryngoplastic phonosurgery have recently been proposed. This report is intended to clarify the concept on which the surgery should be based, vocal mechanics, for further rational development of the surgery. STUDY DESIGN: The results of various previous surgeries were compared. In an attempt to elucidate what makes the difference in the results, simulation of voice production was conducted with the use of excised larynges. METHODS: Excised larynges were mounted on a tube so as to be blown from below. Experimental variables in the model included the glottal area initially set, stiffness of the vocal folds, and subglottal pressure. The conditions under which the voice became hoarse were examined. RESULTS: The voice became hoarse under the following major conditions: 1) the initial glottal area exceeded a certain value, 2) stiffness was too high, and 3) the glottis was too tightly closed. Clinical representation for each condition was made, particularly for excessively tight glottal closure such as in spasmodic dysphonia. A new type of surgical treatment for spasmodic dysphonia, lateralization thyroplasty, was briefly reported, which restored the voice to normal without recurrence for 1 year at the time of this writing. CONCLUSIONS: A potential new type of laryngoplastic phonosurgery should be conformed to the mechanics of voice production. In treating dysphonia, it is often necessary to switch from etiologic or radical treatment, if infertile, to symptomatic treatment instead, at the level of mechanics.     

Molecular modeling of N-isopropyl lisergamides analogous to LSD using molecular mechanics and quantum mechanical calculations

A male white patient 58 years-old was submitted to colonoscopy for follow-up of surgical resection of an advanced colorectal carcinoma 33 months ago. Small polyps were observed in the colons and histopathological examination proved to be tubular adenomas with moderate dysplasia. At the hepatic flexure of the transverse colon a large flat-elevated laterally spreading tumor measuring 2.5 cm in diameter was observed. After spraying of methilene-blue 0.1% the margins of the lesion were demarcated and following saline injection under the lesion it was completely resected in one single procedure. Histologically, the lesion was diagnosed as intramucosal adenocarcinoma.     

Homogenization of sputum with dithiothreitol for early diagnosis of pulmonary malignancies

Homogenization of sputum with dithiothreitol (DTT) has not been used in cytology for the detection of malignant cells. We examined the efficacy of this method as compared to the conventional "pick and smear" (PS) method. Smears were prepared from sputum samples using the PS technique to act as the control. The remaining sputum was digested with an equal volume of 0.3% DTT in 70% ethanol at room temperature. The cells were washed with 35% ethanol and smears prepared. The DTT-treated specimens gave a much higher concentration of evenly distributed cells. The background was clear and the morphology comparable to that of the control. More positive cases were detected with the DTT than the conventional PS technique. Homogenization of sputum with DTT is a simple and effective method of screening for pulmonary malignancies.     

Homogenization of Masonry Using Numerical Simulations

Homogenization is one of the most important steps in the numerical analysis of masonry structures where the continuum method is used. In the present study, equivalent elastic properties, strength envelope, and different failure patterns of masonry material are homogenized by numerically simulating responses of a representative volume element (RVE) under different stress conditions. The RVE is modeled with distinctive consideration of the material properties of mortar and brick. In the numerical simulation, various displacement boundaries are applied on the RVE surfaces to derive the stress-strain relation under different conditions. The equivalent overall material properties of the RVE are averaged by integrating the stresses and strains over the entire area. Failure of masonry is defined by three different modes, namely, tensile failure of mortar (Mode I), shear failure of mortar or combined shear failure of brick and mortar (Mode II), and compressive failure of brick (Mode III). The homogenized elastic properties and failure model can be used to analyze large-scale masonry structures.     

Elastoplastic Mesoscale Homogenization of Composite Materials

Mesoscale homogenization provides a computationally efficient way of capturing some degree of local variation in the behavior of a composite microstructure. In this work, techniques are explored in which the local two-phase microstructure is homogenized using the moving-window generalized method of cells (GMC) technique. Both elastic and plastic material behavior is investigated using GMC-generated anisotropic stress-strain curves. An optimization procedure is used to define Hill’s yield criterion parameters which best fit the GMC-generated data. Two perfectly plastic models are developed based on the GMC results; these are called the subcell initial yield model and the matrix average yield model. A technique is also developed which incorporates hardening behavior. Different windowing techniques are investigated: an overlapping windowing technique which requires more computational time, and a nonoverlapping technique which requires less computational time. It is found that the matrix average model using small nonoverlapping windows is the best technique in the cases studied, combining accuracy and computational efficiency.     

Nitroimidazoles for imaging hypoxic myocardium

1. Data on deaths from pesticide poisoning occurring in England and Wales in 1990 and 1991 have been collated. Pesticides were responsible for 44 of 3978 deaths from poisoning (excluding carbon monoxide and other gases) over this period. 2. At least 66% of all pesticide fatalities were due to suicide and overall there was a predominance of males (male:female ratio 2.4:1). Eighty per cent of deaths occurred in those more than 44 years old and no child under 10 years old died, although almost 50% of suspected pesticide poisoning incidents involve this age group. 3. Herbicides were responsible for 35 of the 44 deaths; seven were caused by insecticides, one by a molluscicide and one by an unspecified agent. The herbicide, paraquat, was responsible for 33 of 44 deaths (75%) and, although fewer fatalities have occurred from this cause in recent years, paraquat remains the most common cause of fatal pesticide poisoning in England and Wales.     

铜银合金接触线用线坯的合金化均匀性及稳定控制

本文介绍了以大型工频感应电炉作为熔化炉,采用SCR连铸连轧工艺生产铜合金接触线用坯料时,在产业化条件下,利用大型工频感应电炉的原理,结合铜银合金接触性对银含量的要求和连铸连轧工艺对加料速度的要求,摸索出产业化条件下铜银合金接触线用坯料的合金化均匀性及稳定控制的规律。