大体积混凝土施工后裂缝处理分析

混凝土因其取材广泛、价格低廉,抗压强度高、可浇注成各种形状,并且耐火性好、不易风化、养护费用低,成为当今世界建筑结构中使用最广泛的建筑材料。但混凝土最主要的缺点是:抗拉能力差,容易开裂。引起裂缝的原因比较复杂,本文旨在通过对裂缝产生的原因进行分析探讨,提出措施和建议,来避免大体积混凝土裂缝的发生。

常见建筑砖砌体裂缝原因及其防治

1 前言 建筑砖砌体裂缝不仅种类繁多,形态各异,而且较普遍, 轻微者影响建筑物美观,造成渗漏水,严重者降低建筑结构 的承载力、刚度、稳定和整体性、耐久性,甚至还会导致整 体倒塌的重大质量事故.因此,正确分析原因、切实加以防 治十分必要,十分迫切.现就笔者多年的工程质量监督实践 谈几点本地区常见建筑砖砌体裂缝查处的体会.

中国珠蕨属孢子形态的研究

利用扫描电子显微镜对我国产珠蕨属 5种植物的孢子进行了观察 .结果表明 ,该属孢子形态较为一致 ,三裂缝 ,辐射对称 ,极面观为钝三角形 ,具明显的角 ,赤道面观为半圆形或超半圆形 .由外壁和周壁共同形成纹饰轮廓 ,周壁紧附于外壁上 ,呈疣状或具颗粒状的疣块状 .作者从孢子形态的角度 。

Elastic properties of transversely isotropic rocks containing aligned cracks and application to anisotropy measurement

Currently,most rock physics models,used for evaluating the elastic properties of cracked or fractured media,take into account the crack properties,but not the background anisotropy.This creats the errors of in the anisotropy estimates by using fi eld logging data.In this work,based on the scattered wavefi eld theory,a sphere-equivalency method of elastic wave scattering was developed to accurately calculate the elastic properties of a vertical transversely isotropic solid containing aligned cracks.By setting the scattered wavefi eld due to a crack equal to that due to an equivalent sphere,an eff ective elastic stiff ness tensor was derived for the cracked medium.The stability and accuracy of the approach were determined for varying background anisotropy values.The results show that the anisotropy of the eff ective media is aff ected by cracks and background anisotropy for transversely isotropic background permeated by horizontally aligned cracks,especially for the elastic wave propagating along the horizontal direction.Meanwhile,the crack orientation has a signifi cant infl uence on the elastic wave velocity anisotropy.The theory was subsequently applied to model laboratory ultrasonic experimental data for artifi cially cracked samples and to model borehole acoustic anisotropy measurements.After considering the background anisotropy,the model shows an improvement in the agreement between theoretical predictions and measurement data,demonstrating that the present theory can adequately explain the anisotropic characteristics of cracked media.

Modeling transmittance through submicron silver slit arrays

Mid-infrared transmittance of submicron silver slit arrays was numerically studied with the finite difference time domain method. The slit width varies from 50 nm to 300 nm and a square feature may attach at either or both slit sides. Although the side length of features is one or two orders of magnitude shorter than the wavelength, the attached nanoscale features can modify the transmittance significantly. The transmittance was also further investigated in detail by looking into the electromagnetic fields and Poynting vectors of selected slit geometries. The investigation results show that such change can be attributed to the cavity resonance effect inside the slit arrays. The work is of great importance to the wavelength-selective devices design in optical devices and thermal application fields.

LNG船殷钢列板缝焊机（MO2）国产化的思考

殷钢列板缝焊机（MO2）为LNG船围护系统建造的核心设备之一，目前该设备仅国外几家公司能够生产。该设备性能的可靠性、稳定性，直接决定着LNG船建造速度。而进口设备也因多种原因，在国内使用存在着各种问题。殷钢列板缝焊机的性能严重制约了LNG船建造的进度和生产成本。本文着重介绍该设备国产化的必要性，国产化研究方向和解决方案。

Modeling infrared radiative properties of nanoscale metallic complex slit arrays

The radiative properties(absorptance, reflectance, and transmittance) of deep slits with five nanoscale slit profile variations at the transverse magnetic wave incidence were numerically investigated by employing the finite difference time domain method. For slits with attached features, their radiative properties can be much different due to the modified cavity geometry and dangled structures, even at wavelengths between 3 and 15 μm. The shifts of cavity resonance excitation result in higher transmittance through narrower slits at specific wavelengths and resonance modes are confirmed with the electromagnetic fields. Opposite roles possibly played by features in increasing or decreasing absorptance are determined by the feature position and demonstrated by Poynting vectors. Correlations among all properties of a representative slit array and the slit density are also comprehensively studied. When multiple slit types coexist in an array(complex slits), a wide-band transmittance or absorptance enhancement is feasible by merging spectral peaks contributed from each type of slits distinctively. Discrepancy among infrared properties of four selected slit combinations is explained while effects of slit density are also discussed.

Roadbed behavior subjected to tilting-train loading at rail joint and continuous welded rail

The tilting-train is very attractive to the railroad users in the world due to the advantage of high speed in curved track using pre-existing infrastructure of railway.Tilting-train has a unique allowable speed and mechanism especially in curved track.In this work,when tilting-train is operated with the allowable speed,the behavior of roadbed is evaluated by examining its settlement and bearing capacity.Additionally,the stability of roadbed is estimated as the roadbed is in the condition of soft soil influenced by the weather effects and cyclic train loading.Numerical results show that the roadbed settlement satisfies the allowable settlement when the elastic moduli of upper roadbed and in-situ soil are greater than 3800 and 4600 kN/m2 for rail joint and 2300 and 3300 kN/m2 for continuous welded rail(CWR).

Variability of Carbonate Pedofeatures in a Loess-Paleosol Sequence and their Use for Paleoreconstructions

Carbonate pedofeatures were studied in details in a loess-paleosol pedocomplex near Kursk, in the central part of the European Plain. The soils studied included a modern Chernozem and five Pleistocene paleosols. Carbonate morphologies and distributions were described in the field. Various morphologies were sampled for further studies including micromorphology in thin sections and submicroscopic studies under a scanning electron microscope. The complex approach of investigation at macro-, micro-, and submicroscopic levels found that most of carbonate pedofeatures are secondary and multiphase. Many of them are related to cryogenic features. The general trend was of decreasing carbonate content in the older paleosols except for increased content in the 1St and 3rd paleosols. Most of carbonate morphologies are similar in the modern soil and paleosols, but pseudomycelium was found only in the modern Chernozem, while soft masses and impregnations are associated with the paleosols. Detailed study on carbonate attributes revealed their specific features in the modern soil and in paleosols. Veins have dissolution features under the modern environment and seem to reprecipitate in form of pseudomycelium. Coatings in paleosols at a depth of the Ist paleosol include specific fine tubes. Powdery soft masses and impregnations in the paleosols are strongly related to cryogenic fissures and paleopermafrost level. Under SEM they consist of tiny crystals, much smaller than in regular soft masses. Several types of hard concretions were identified：rounded, irregular and platy. Small concretions in the modern Chernozem have similar morphology and similar 14C-age as the rounded concretions of the upper paleosols. They are expected to represent the same generation of concretions. Platy concretions fill the bottom part of the large fissures. The 14C-age of hard concretions varies from 3310±80 yrs. B.P in the Ist paleosol up to 20 400 yrs. B.P. in the 3^rd. As a result we found the reflection of several wet-dry and cold-warm stages in carbonate morphologies and distributions. High variability of carbonates at macro-, micro- and submicroscopic levels indicates several generations and multiphase formation of carbonate pedofeatures in the loess-paleosol pedocomplex. Carbonate pedofeatures in the examined pedocomplex are more informative for the study of late Pleistocene and Holocene climatic cycles rather than characterization of a single paleosol.

Yimu San improves obstetric ability of pregnant mice by increasing serum oxytocin levels and connexin 43 expression in uterine smooth muscle

Prolonged farrowing remains one of the critical challenges in intensive pig farming. This study aims to explore the effects and mechanism of Yimu San （YMS）, a Chinese veterinary medicine micro mist, on delivery ability with mouse models. Thirty-two pregnant mice were randomly divided into a control group and Iow-YMS, med-YMS, and high-YMS groups. The labor process time and stillbirth rate were recorded, the levels of serum oxytocin and prostaglandin E2 （PGE2） were measured with enzyme-linked immunosorbent assay （ELISA）. Contractility measure- ments of the isolated uterus and the expression of connexin 43 （Cx43） in uterine smooth muscle were evaluated. The results showed that compared with the control group, the birth process time and stillbirth rate in the med-YMS and high-YMS groups were remarkably lower. The in vitro uterine contractions, levels of oxytocin, PGE2, and Cx43 in the med-YMS and high-YMS groups were significantly higher than those in the control group. The differences of the above measurements between the Iow-YMS group and the control group were not obvious. It can be speculated that YMS could significantly promote labor in pregnant mice by enhancing the levels of oxytocin, Cx43, and PGE2.