房屋结构设计中设计优化的运用分析

本文通过分析房屋结构的设计方法,对结构优化在设计房屋结构时的意义及具体应用进行了阐述,希望为建筑行业提供参考。     

基于蓝牙无线数据采集技术的砝码自动检定系统研制

从砝码检定工作的现状分析出发,运用蓝牙无线技术和计算机软件技术,实现了对多台衡量仪器的自动数据采集和处理。研制完成的砝码自动检定系统已得到成功应用。     

Isomeric Routes to Schiff‐Base Single‐layered Covalent Organic Frameworks

With graphene‐like topology and designable functional moieties, single‐layered covalent organic frameworks (sCOFs) have attracted enormous interest for both fundamental research and application prospects. As the growth of sCOFs involves the assembly and reaction of precursors in a spatial defined manner, it is of great importance to understand the kinetics of sCOFs formation. Although several large families of sCOFs and bulk COF materials based on different coupling reactions have been reported, the synthesis of isomeric sCOFs by exchanging the coupling reaction moieties on precursors has been barely explored. Herein, a series of isomeric sCOFs based on Schiff‐base reaction is designed to understand the effect of monomer structure on the growth kinetics of sCOFs. The distinctly different local packing motifs in the mixed assemblies for the two isomeric routes closely resemble to those in the assemblies of monomers, which affect the structural evolution process for highly ordered imine‐linked sCOFs. In addition, surface diffusion of monomers and the molecule‐substrate interaction, which is tunable by reaction temperature, also play an important role in structural evolutions. This study highlights the important roles of monomer structure and reaction temperature in the design and synthesis of covalent bond connected functional nanoporous networks.     

三点四针法小切口重睑术的临床应用

目的:探讨"三点四针法"小切口重睑成形术的临床应用效果。方法:采用"三点四针"小切口法,即将经典"三点式"重睑术中段切口延长至5mm,内、外段切口设计长度3mm,内外段切口各1针,中段切口缝合2针,使重睑线"黄金点"上形成2个点的牢固粘连。结果:116例受术者,115例重睑流畅自然。1例患者术后3个月内左侧重睑皱褶变浅,经原切口修复,效果满意。结论:"三点四针"重睑成形术,创伤小,恢复快,效果确切,操作简易,值得推广。     

Crystal growth of bullet-shaped magnetite in magnetotactic bacteria of the Nitrospirae phylum

Magnetotactic bacteria (MTB) are known to produce single-domain magnetite or greigite crystals within intracellular membrane organelles and to navigate along the Earth''s magnetic field lines. MTB have been suggested as being one of the most ancient biomineralizing metabolisms on the Earth and they represent a fundamental model of intracellular biomineralization. Moreover, the determination of their specific crystallographic signature (e.g. structure and morphology) is essential for palaeoenvironmental and ancient-life studies. Yet, the mechanisms of MTB biomineralization remain poorly understood, although this process has been extensively studied in several cultured MTB strains in the Proteobacteria phylum. Here, we show a comprehensive transmission electron microscopy (TEM) study of magnetic and structural properties down to atomic scales on bullet-shaped magnetites produced by the uncultured strain MYR-1 belonging to the Nitrospirae phylum, a deeply branching phylogenetic MTB group. We observed a multiple-step crystal growth of MYR-1 magnetite: initial isotropic growth forming cubo-octahedral particles (less than approx. 40 nm), subsequent anisotropic growth and a systematic final elongation along [001] direction. During the crystal growth, one major {111} face is well developed and preserved at the larger basal end of the crystal. The basal {111} face appears to be terminated by a tetrahedral–octahedral-mixed iron surface, suggesting dimensional advantages for binding protein(s), which may template the crystallization of magnetite. This study offers new insights for understanding magnetite biomineralization within the Nitrospirae phylum.     

Tomographic study of the seismic velocity at the Soultz-sous-Forêts EGS/HDR site

The 2000 and 2003 hydraulic stimulations carried out at the Soultz-sous-Forêts Hot Dry Rock (HDR) site, Alsace, France, generated a continuous, albeit of small magnitude, seismic activity. For each experiment, the Ecole et Observatoire des Sciences de la Terre (EOST) installed a seismic network of 18 stations (in 2000) and 23 stations (in 2003). More than 3500 seismic events were detected and located in both cases.Changes in the physical properties of the reservoir due to fluid circulation have been estimated by means of a 4D tomography in which the 3D seismic velocity structure is calculated for different time windows. The entire data set has been apportioned to different temporal subsets with a fixed number of events. We used the tomographic algorithm of [Thurber, C.H., 1983. Earthquake locations and 3D crustal structure in the Coyote Lake area, central California. J. Geophys. Res. 88, 8226–8236] for the 2000 data and a new, more accurate method that is based on a double-difference tomography [Zhang, H., Thurber, C.H., 2003. Double-difference tomography: the method and its application to the Hayward fault, California. Bull. Seismol. Soc. Am. 93 (5), 1875–1889] for the 2003 set. The latter approach gives a good resolution within the reservoir volume, and one that is slightly less so in its vicinity. This tomographic study points out the changes in reservoir velocity structure occurring during the stimulation.We discuss the variation of the seismic velocity with time during each of the hydraulic stimulations and compare the velocity changes observed in 2000 and 2003. This analysis has allowed us to define the region of influence of hydraulic activity and determine the effects of water circulation on geothermal reservoir properties.     

Volatilization of organotin species from municipal waste deposits: novel species identification and modeling of atmospheric stability

Organotin compounds are used as pesticides and fungicides as well as additives in plastics. This study identifies the de novo generation of novel volatile organotins in municipal waste deposits and their release via landfill gas. Besides tetramethyltin (Me(4)Sn), a strong neurotoxin, and 5 previously reported organotins, 13 novel ethylated, propylated, and butylated tetraalkyltin compounds were identified. A concentration of 2-4 μg of Sn m(-3) landfill gas was estimated for two landfill sites in Scotland. The atmospheric stability of Me(4)Sn and methylated tin hydrides was determined empirically in a static atmosphere in the dark and under UV light to simulate night- and daytime conditions. Theoretical calculations were carried out to help predict the experimentally obtained stabilities and to estimate the relative stabilities of other alkylated species. Assuming first-order kinetics, the atmospheric half-life for Me(3)SnH was found to be 33 ± 16 and 1311 ± 111 h during day- and nighttime conditions, respectively. Polyalkylation and larger alkyl substitutes tend to reduce the atmospheric stability. These results show that substantial concentrations of neurotoxic organotin compounds can be released from landfill sites and are sufficiently stable in the atmosphere to travel over large distances in night- and daytime conditions to populated areas.     

Synthesis and characterization of low temperature Sn nanoparticles for the fabrication of highly conductive ink

To fabricate a low cost, highly conductive ink for inkjet printing, we synthesized a gram scale of uniformly sized Sn nanoparticles by using a modified polyol process and observed a significant size-dependent melting temperature depression from 234.1?°C for bulk Sn to 177.3?°C for 11.3 nm Sn nanoparticles. A 20 wt% of Sn nanoparticles was dispersed in the 50% ethylene glycol: 50% isopropyl alcohol mixed solvent for the appropriate viscosity (11.6 cP) and surface tension (32 dyn cm(-1)). To improve the electrical property, we applied the surface treatments of hydrogen reduction and plasma ashing. The two treatments had the effect of diminishing the sheet resistance from 1 kΩ/sq to 50 Ω/sq. In addition, conductive patterns (1 cm × 1 cm) were successfully drawn on the Si wafer using an inkjet printing instrument with conductive Sn ink. The maximum resistivity for an hour of sintering at 250?°C was 64.27 μΩ cm, which is six times higher than the bulk Sn resistivity (10.1 μΩ cm).     

Modeling transport and combustion of firebrands from burning trees

Burning embers, commonly called firebrands, are lofted by a fire's buoyant plume and transported downwind to ignite new fires (spot fires) ahead of the main fire. In the present work, transport and combustion of firebrands from burning trees are numerically investigated. A three-dimensional physics-based model is used to precompute the steady-state gas flow and thermal fields induced by a crown fire into which firebrands will be injected. Another preliminary study of the thermal degradation and combustion of woody fuel particles is conducted to determine the burning characteristics of firebrands. Then the trajectories and burning rates of disk-shaped firebrands lofted by the crown fire plume and transported downwind are calculated for various values of the wind speed, Uwind, and of the fire intensity, I. Firebrands of different sizes and densities are first launched from a specified location at the top of the canopy. Firebrands that fall on the ground are in a flaming or a glowing state depending on the product (: initial firebrand density, τ: firebrand thickness). Results show that for firebrands that remain longer in the thermal plume, the distance covered upon landing is independent of the initial particle diameter and correlates well with . The normalized brand mass fraction at landing also correlates with the flight time normalized by the product for flaming firebrands or by the product (D₀: initial firebrand diameter) for glowing firebrands. For firebrands released from random locations within the canopy, the above correlations remain unchanged, thereby demonstrating the generality of the developed approach.