Raetrad model extensions for radon entry into multi-level buildings with basements or crawl spaces

The RAETRAD model was generalized to characterize radon generation and movement from soils and building materials into multi-level buildings with basements or crawl spaces. With the generalization, the model retains its original simplicity and ease of use. The model calculates radon entry rates that are consistent with measurements published for basement test structures at Colorado State University, confirming approximately equal contributions from diffusion and pressure-driven air flow at indoor-outdoor air pressure differences of deltaP(i-o) = -3.5 Pa. About one-fourth of the diffusive radon entry comes from concrete slabs and three-fourths comes from the surrounding soils. Calculated radon entry rates with and without a barrier over floor-wall shrinkage cracks generally agree with Colorado State University measurements when a sustained pressure of deltaP(i-o) = -2 Pa is used to represent calm wind (<1 m s(-1)) conditions. Calculated radon distributions in a 2-level house also are consistent with published measurements and equations.     

The effect of environment on high-temperature hold time fatigue behavior of annealed 2.25 pct Cr 1 pct Mo steel

Total strain control fatigue tests with a 120-second hold period at either peak compressive or tensile strain were conducted on annealed 2.25 pct Cr 1 pct Mo steel. Tests were performed at the total strain range of 1.0 pct at 500 °C or 600 °C in air, 1.3 Pa (10⁻² torr) or 1.3 × 10⁻³ Pa (10⁻⁵ torr) vacuum. The nature of the hold and the environment affect fatigue life and surface crack patterns. A compressive hold is more deleterious than a tensile hold in high-temperature air, while the reverse is true in environments in which oxidation is limited. Observations of cracks at the surface and in cross section indicate that an oxidation-fatigue interaction accounts for the damaging effect of a compressive hold in air tests. In vacuum tests, creep damage has the opportunity to accumulate and causes the tension hold to exhibit the shortest fatigue lifetime.     

板坯连铸倒角结晶器的开发与应用

 为减少连铸板坯角部横裂纹,在分析连铸坯角部横裂纹形成机制的基础上,提出了通过倒角结晶器减少角部横裂纹,以改变连铸板坯角部的二维传热,提高矫直时连铸坯的角部温度。数值模拟计算的结果表明,相对于直角连铸坯,倒角连铸坯在矫直区连铸坯角部温度明显提高,消除了角部Z向应力和应变集中。工业生产数据表明,采用倒角结晶器后,矫直区连铸坯角部温度从810~855℃提高到901~932℃,有效避开了钢的高温脆性区,连铸坯角部横裂纹发生率从10.6%稳定控制到1.6%以下,显著减少了连铸坯角部横裂纹。目前倒角结晶器稳定应用于首秦,所生产钢种涵盖了普碳钢、低合金钢、低碳钢和中碳含铌钢等。     

Microstructure and Properties Analysis of Laser Welding and Laser Weld Bonding Mg to Al Joints

Laser welding and laser weld bonding (LWB) Mg to Al joints were obtained in different welding parameters. The penetrations and microstructures of these kinds of joints changed with the increasing of pulse laser power density. Both laser welding and LWB Mg to Al joints with the best properties were obtained in conductive welding mode. In laser welding Mg to Al joint, several intermetallics formed at the bottom of the fusion zone, where some cracks were generated. In laser weld bonding Mg to Al joint, the decomposition of the adhesive caused a baffle effect on the diffusion between the Mg and the Al. The intermetallics formed in the middle of the fusion zone, and the thickness of Mg₁₇Al₁₂ layer was approximately 10 to 20 μm and the Mg₂Al₃ layer was less than 5 μm, which influenced the property of the joint less.     

Assessment of Indoor Air Quality in Interior Alaskan Homes

Interior Alaska has indoor air quality issues similar to those of other far northern communities associated with long cold winters and reduced ventilation rates. Moreover, geological features in the hills around Fairbanks, Alaska increase the likelihood of elevated radon levels. To better quantify these features, our team has gathered data at 68 homes. We used CO2 concentrations as a surrogate for indoor air quality as well as to help determine ventilation rates to be used in subsequent modeling work. We found the CO2 data correlated well using basic mass conservation considerations for yearly averages. The summer CO values ranged from 1 to 9 ppm and the winter values from 0 to 23 ppm. For homes with woodstoves, we found the indoor PM10 concentrations rose after the stoves were fired up. Here PM10 refers to particles smaller than 10 μm. Over 40% of the tested homes in the hills around Fairbanks had radon levels>4?pCi/L compared to a nationwide average of 7%. Active subslab depressurization systems tested were very effective in reducing indoor radon concentrations (average reduction of over 90% for eight homes).     

Failure Resistance of the Historic Stone Bridge Structure of Charles Bridge. I: Susceptibility to Nonstress Effects

The monitoring of deformations of the stone structure of Charles Bridge in Prague proved the gravity and relevance of nonstress effects (temperature, moisture content) on cyclic deformations and permanent strain accompanied by a gradual disintegration of its stone masonry, growing tilt of the breast walls, and development of cracks in the masonry of the stone bridge structure. Each deformation cycle is accompanied by a gradual growth in permanent deformations. The “unmanifested” primary deformation due to, e.g., a temperature change causes a mechanical state of tension, and it is mainly the tensile stresses thus arising that contribute to the development of tensile cracks in the stone masonry.     

Reinforcing Building Facades with Geotextile Fabrics

An investigation is made of potential reinforcement to limit debris hazard of masonry facade walls of conventional buildings subjected to blast effects using geotextile fabrics anchored to the floor slabs and beams. Fourteen simulation tests using geotextile and geogrid fabrics were conducted to provide an initial evaluation of the performance of this protective system. The ultimate capacity, load-deflection, including the proposed connections of these retrofit systems were determined and recorded in these tests. The tests were conducted by increasing a uniform load (water pressure) in a 1.83?m diameter chamber. The tensile strength of the materials used in the experiments varied from 65 to 328?N/m. It was concluded from the experiments that the proposed system is a viable and a functional means for preventing propagation of wall debris. The primary parameters affecting its functionality were the tensile strength of the fabric and its anchorage into the conventional structure.     

6005A铝合金CMT与MIG焊接头组织及性能研究

针对2mm厚6005A铝合金采用冷金属过渡(CMT)和熔化极惰性气体保护(MIG)焊接技术进行焊接,研究了两种焊接接头的力学性能、拉伸断口形貌,接头不同位置的微观组织。研究表明,CMT焊接头的抗拉强度好于MIG焊接头,达到母材的70%,焊缝组织更为细小;两种焊接接头断裂位置均为热影响区,CMT焊接接头为韧性断裂,MIG焊接接头为韧性断裂与准解理断裂的混合断裂。     

Functional magnetic stimulation of the respiratory muscles in dogs

This study assessed the ability of functional magnetic stimulation (FMS) to activate the respiratory muscles in dogs. With the animal supine, FMS of the phrenic nerves using a high-speed magnetic stimulator was performed by placing a round magnetic coil (MC) at the carotid triangle. Following hyperventilation-induced apnea, changes in volume (deltaV) and airway pressure (deltaP) against an occluded airway were determined. FMS of the phrenic nerves produced substantial inspired function (deltaV = 373 +/- 20.5 mL and deltaP = -20 +/- 2.0 cm H2O). After bilateral phrenectomies, maximal inspired deltaV (219 +/- 12.2 mL) and deltaP (-10 +/- 1.0 cm H2O) were produced when the MC was placed near the C6-C7 spinous processes, while maximal expired deltaV (-199 +/- 22.5 mL) and deltaP (11 +/- 2.3 cm H2O) were produced following stimulation near the T9-T10 spinous processes. We conclude: (1) FMS of either the phrenic or upper intercostal nerves results in inspired volume production; (2) FMS of the lower intercostal nerves generates expired volume production; and (3) FMS of the respiratory muscles may be a useful noninvasive tool for artificial ventilation and assisted cough in patients with spinal cord injuries or other neurological disorders.     

Development and Performance Evaluation of Interlocking-Block Masonry

Accelerated mortarless masonry constructions have been developed or are being used in different countries with limited research studies. This paper discusses first the salient features of interlocking-block masonry and then the development of simple interlocking-concrete-block masonry systems, keeping in view the requirements of shape simplicity and ease of manufacture. Testing of wallettes under axial compression, eccentric compression (e∕t ratios of 0, t/6, and t/3), and flexural loading parallel and perpendicular to bed joints were carried out on dry-stacked specimens. Interlocking-block masonry results in relatively high efficiency factors in axial compression and eccentric-to-axial capacity ratio when compared with mortar bedded masonry. Unlike conventional masonry, the flexural capacity of interlocking-block masonry normal to the bed joint is higher than that parallel to the bed joint. A better interlocking mechanism of channel-shaped interlocking blocks, as compared to I-shaped blocks, leads to a relatively higher flexural capacity of the former.     

Investigation of panel crack formation in steel ingots: Part II. Off-corner panel cracks

Model predictions of the thermal and stress evolution in steel ingots, combined with a metallurgical study, have confirmed the mechanism of formation of off-corner panel cracks. The cracks are generated initially in the subsurface of the ingot during the early stages of reheating in the soaking pit. The volume change associated with γ-α transformation plays a major role in the generation of the tensile stresses as in the case of the mid-face panel cracks. Early in the reheating, a subsurface twophase zone of α and γ contracts within a surrounding field of austenite and is placed in tension. Crack formation is enhanced by the precipitation of AlN which embrittles the steel. The subsurface cracks subsequently may penetrate to the surface of the ingot immediately upon its withdrawal from the soaking pit owing to the generation of surface tensile stresses caused by rapid cooling of the ingot surface. Measures to minimize formation of off-corner panel cracks, therefore, include reducing air cooling time (prior to charging ingots to the soaking pit) to prevent γ-α transformation, reheating the ingots slowly in an initially cold soaking pit to reduce the tensile stresses, increasing the air cooling time substantially to force the cracks farther from the surface, and minimizing soaking times and temperatures.     

Investigation of panel crack formation in steel ingots: Part II. Off-corner panel cracks

Model predictions of the thermal and stress evolution in steel ingots, combined with a metallurgical study, have confirmed the mechanism of formation of off-corner panel cracks. The cracks are generated initially in the subsurface of the ingot during the early stages of reheating in the soaking pit. The volume change associated with γ-α transformation plays a major role in the generation of the tensile stresses as in the case of the mid-face panel cracks. Early in the reheating, a subsurface twophase zone of α and γ contracts within a surrounding field of austenite and is placed in tension. Crack formation is enhanced by the precipitation of AlN which embrittles the steel. The subsurface cracks subsequently may penetrate to the surface of the ingot immediately upon its withdrawal from the soaking pit owing to the generation of surface tensile stresses caused by rapid cooling of the ingot surface. Measures to minimize formation of off-corner panel cracks, therefore, include reducing air cooling time (prior to charging ingots to the soaking pit) to prevent γ-α transformation, reheating the ingots slowly in an initially cold soaking pit to reduce the tensile stresses, increasing the air cooling time substantially to force the cracks farther from the surface, and minimizing soaking times and temperatures.     

IF钢非稳态连铸坯洁净度定量分析

通过氧氮分析、定量金相分析及大型夹杂物分析等试验方法,对某钢厂IF钢生产稳态及非稳态浇注的连铸坯进行了对比研究。结果表明,稳态坯w(T[O])和w(N)的平均含量分别为11×10-6和18×10-6,显微夹杂物含量平均为4.0个/mm2,大型夹杂物含量为2.10 mg/kg,洁净度较高。非稳态浇注对连铸坯洁净度有较大程度的危害。中间包开浇头坯受到较为严重的空气二次氧化,洁净度最差;钢包交换和更换浸入式水口时受到的空气二次氧化较小,但是钢渣反应和卷渣行为较为严重;尾坯洁净度受到空气二次氧化和卷渣的共同影响。连铸坯显微夹杂物含量分布,沿铸坯宽度方向一般1/4处最多,1/2处最少;沿铸坯厚度方向内外弧附近明显高于连铸坯中心部位。     

Effect of process parameters on microstructure and mechanical properties of non- annealed cold heading steel SWRCH35KM

In order to realize the on- line softening treatment of non- annealed cold heading steel SWRCH35KM, the influence of controlled rolling and controlled cooling process on the microstructure and mechanical properties of medium carbon cold heading steel was investigated. The results show that the microstructures of spherular pearlite dispersed in 60%-63% ferrite matrix are obtained after step slow cooling process. With the decrease of finish rolling temperature from 850?? to 750??, ferrite grain size refines from 15-16. 9??m to about 10??m, and spheroidization of pearlite tends to significantly. Tensile strength of test steel with step slow cooling process is about 490-510MPa, elongation is 36. 5%-40. 5%, and hardness is 73HRB-78HRB. Compared with the air cooling process, the tensile strength of test steel decreases by about 30-40MPa, elongation increases by 1%-3% and hardness decreases by about 2HRB-3HRB.     

Use of Simulink for Dynamic Air Quality Modeling in Interior Alaska

Interior Alaska has indoor air quality (IAQ) issues similar to those of other far northern communities associated with long cold winters and reduced ventilation rates. We also have some interesting issues associated with elevated radon in homes built in the hills around Fairbanks, as well as elevated particulate levels created by smoke from forest fires that occur in the vast uninhabited portions of the state. To better understand the influences of critical variables such as indoor source strengths and ventilation rates on IAQ associated with forest fires and radon, we have developed a Simulink-based mass conservation model. Using data gathered at two homes in Fairbanks during 2003, we have used this model to predict indoor radon and PM2.5 levels (particles less than 2.5?μm in diameter). We find that we are able to predict both the rise of radon following the shutdown of a radon mitigation system and the variation of indoor PM2.5 by using ventilation rates consistent with what we have measured, PM2.5 source strengths associated with individuals in residences, and penetration and deposition rates compatible with what others have found. We have used situation-specific algorithms for subsurface radon source strength as well as particulate generation associated with cooking.     

Respiratory mechanics after prosthetic reconstruction of the chest wall in normal rats

OBJECTIVE: Prosthetic reconstruction of the chest wall may yield several respiratory changes. Nevertheless, to our knowledge, no comprehensive analysis of respiratory mechanics under this condition has been hitherto performed. METHODS: Respiratory mechanics were evaluated in two groups of rats. In one group (n=8), a polytetrafluoroethylene (PTFE) patch was used; in another group (n=8), a polypropylene mesh (Marlex) associated with methylmethacrylate (PPMM) was employed. All animals were sedated, anesthetized, paralyzed, and mechanically ventilated before and after the prosthetic reconstruction of the chest wall. After airway occlusion at end inspiration, respiratory system, pulmonary, and chest wall resistive pressures (deltaP1rs, deltaP1L, and deltaP1cw, respectively) and viscoelastic/inhomogeneous pressures (deltaP2rs, deltaP2L, and deltaP2cw, respectively) were determined. Respiratory system, lung, and chest wall static (Est(rs), EstL, and Est(cw), respectively), and dynamic elastances (Edyn(rs), EdynL, and Edyn(cw), respectively), and the corresponding delta elastances (deltaE, calculated as Edyn-Est) were also obtained. RESULTS: In both groups, significant increases in deltaP2rs, deltaP2cw, deltaErs, deltaEcw, Est(rs), EstL, and Est(cw) were observed after chest wall reconstruction. However, deltaP2rs, deltaP2cw, deltaErs, deltaEcw, Est(rs), and EstL were significantly higher in the PPMM group than in the PTFE group. CONCLUSIONS: Prosthetic reconstruction of the chest wall yields not only elastic changes, but also there is also an important increase of pressure dissipated against viscoelastic/inhomogeneous segments of the chest wall. Furthermore, taking into account respiratory mechanics, the PTFE patch might be preferred to the PPMM patch.     

Vertical distribution of outdoor radon and thoron in Japan using a new discriminative dosimeter

Passive measurements of outdoor radon and thoron concentrations were conducted from June 1992 to June 1993 at a monitoring station over a soil area (10 m x 6 m) in Chiba city, Japan. The measurement period was divided into 4 parts to investigate seasonal variations of radon and thoron concentrations. Ten passive radon-thoron discriminative dosimeters (R-T dosimeters) were placed in duplicate at 5 different altitudes to show the vertical distributions of outdoor radon and thoron concentrations. Outdoor radon concentrations showed no significant difference within 1.0 m above the ground, and the annual average of outdoor radon concentration was 3.85 +/- 0.19 (SE) Bq m-3. Annual averages of outdoor thoron concentrations at 0.04, 0.15, 0.25, 0.70, and 1.0 m above the ground were 40.5 +/- 4.4, 22.5 +/- 3.7, 13.9 +/- 3.1, 9.5 +/- 2.9 (SE) Bq m-3, and < 9.0 Bq m-3; the lower detection limit of the dosimeter, respectively, and their vertical profiles, n(z) (Bq m-3), were expressed well by the formula n(z) = alpha z beta. Vertical profiles of the atmospheric turbulent diffusion coefficient were also estimated from the observed thoron profiles, as expressed by the power function K(z) = AzB, of which B values were estimated to vary from 1.034 to 1.609 if averaged thoron exhalation rates during the measurement periods were within 0.3 to 2.8 (Bq m-2 s-1).     

Formation of longitudinal,midface cracks in continuously-cast slabs

Based on a series of related investigations, a mechanism for the formation of longitudinal, midface cracks in strand-cast slabs has been elucidated. Metallographic studies, X-ray analyses, and high-temperature tensile testing of as-cast slab samples, together with computer predictions of heat flow, have been combined to show that the cracks open first close to the solidification front where the ductility is extremely low. Tensile strains in the solid shell, resulting from rapid surface cooling or inadequate end-plate taper, concentrate in local regions of high temperature near the meniscus or at the level of nozzlestream impingement on the broad face. While the interior of the shell is opening, the surface which is cooler and more ductile, flows plastically to form a local surface depression. The subsurface cracks may subsequently break through to the surface in the mold or upper sprays if the tensile strains are sufficiently high. The influence of the impinging metal stream, mold-powder practice, metal-level control, steel composition, end-plate taper, submold support and spray practice on the formation of longitudinal, midface cracks is explained in terms of this mechanism.     

交换钢包过程对IF钢连铸板坯表层洁净度的影响

采用ASPEX扫描电镜中的自动特征分析功能研究了交换钢包过程（取样浇次第4、5炉）对IF钢连铸板坯表层的洁净度的影响,且对比研究了交换钢包过程浇铸铸坯（交接坯）与正常浇铸铸坯（正常坯）的表层洁净度.结果表明:正常坯与交接坯中尺寸大于20μm的表层夹杂物可分为三类:（1）簇群状Al₂O₃（包括气泡+簇群状Al₂O₃）;（2）簇群状TiO_x-Al₂O₃夹杂物;（3）保护渣夹杂物.正常坯表层的大型夹杂物主要为簇群状Al₂O₃,没有检测到保护渣夹杂物.换包开浇后铸坯总氧质量分数从14×10-6增至17×10-6,交接坯表层检测到较多的第2夹杂物,说明钢包开浇后钢水被轻微氧化.此外,钢包开浇后剧烈的液面波动也导致了保护渣的卷入.在当前工艺下,换包对IF钢铸坯表层洁净度的影响长度约为11m.      

奥氏体组织对低碳中锰钢冷弯性能的影响

摘要：采用冷弯直径0～60mm，弯曲角度180°，研究了20mm厚度低碳中锰钢的冷弯性能，冷弯后外表均无可见裂纹，判定合格。利用光学显微镜、扫描电镜、透射电镜、电子背散射衍射（EBSD）、X射线衍射仪等手段分析了显微组织，尤其是奥氏体组织在冷弯过程中对冷弯性能的影响。结果表明，冷弯前显微组织由板条马氏体和奥氏体组成，其中原始奥氏体晶界明显；冷弯直径为0mm变形后，样品弧顶部分奥氏体的体积分数由12.3%降至1.1%，维氏硬度由295HV1增至364HV1，晶粒尺寸由4.07μm增至4.30μm。主要原因是在冷弯过程在中奥氏体组织发生塑性变形，奥氏体晶界变形消失，沿冷弯方向呈拉伸带状组织形貌，冷弯形变时奥氏体发生TRIP效应显著。