Design of long span modular bridges for traffic detours

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2009.Includes bibliographical references (leaf 53).The oncoming large amount of bridge replacements in the next 10 to 20 years called for a detailed examination of available replacement schemes which can have variable impact on user costs. Detouring traffic with a modular bridge proved to be the most desirable scheme in terms of user costs such as traffic delays, detour distances, ultimate highway geometrics, construction crew safety, and safety of drivers. Criteria that encompassed modular bridge design were defined and two companies in North America - Acrow and Mabey - were found to provide bridges within those parameters. A brief analysis of Acrow bridges showed that maximum span lengths range in the order of 100m; this is fairly short compared to spans of many bridges that will be have to soon be replaced. The current bridge system with which modularity is achieved is a set of truss panels which are supported by abutments or piers. In order to span crossing over 100m, piers would have to be placed in the channel or on the head-slopes which is a costly and undesirable construction process. Therefore, a modular bridge which could achieve longer spans was proposed for a 2 lane and a 3 lane wide bridges using as many existing Acrow components as possible. The scheme encompasses a harp cable-stay bridge with cables spaced and sized such that they are fully interchangeable between the various bridge widths and can be built up to any span. These cables are the only additional component as the towers, the girders, and the decks are all made out of existing Acrow components.(cont.) The pylon is balanced with an anchoring cable and ideas for modular foundations for the anchor are presented. A span of approximately 183m is possible for a 3 lane bridge limited by the maximum axial tower capacity and 250m for the 2 lane bridge based on lateral vibrations. The design fully reflects modularity and should promote the use of modular bridges for longer span crossings.by Svetlana Potapova.M.Eng

Properties of cement with addition of volcanic tuffs and zeolite

The article consists of the research results of influence of zeolite and volcanic tuff on the processes of hydration of blended cements and their properties. The studied tuffs are characterized by lower pozzolanic activity in comparison with microsilica and metakaoline, however, their addition to cement provides the production of sulfate-resistance, cold-resistance blended cement with higher strength in comparison with Portland cement without additives

Properties of cement with addition of volcanic tuffs and zeolite

The article consists of the research results of influence of zeolite and volcanic tuff on the processes of hydration of blended cements and their properties. The studied tuffs are characterized by lower pozzolanic activity in comparison with microsilica and metakaoline, however, their addition to cement provides the production of sulfate-resistance, cold-resistance blended cement with higher strength in comparison with Portland cement without additives

Meiotic Knockdown and Complementation Reveals Essential Role of RAD51 in Mouse Spermatogenesis

Meiotic homologous recombination (HR) is important for proper chromosomal segregation during gametogenesis and facilitates evolutionary adaptation via genomic reshuffling. In most eukaryotes, HR is mediated by two recombinases, the ubiquitous RAD51 and the meiosis-specific DMC1. The role of RAD51 in mammalian meiosis is unclear and study of its function is limited due to embryonic lethality of RAD51 knockouts. Here, we developed an in vivo meiotic knockdown and protein complementation system to study RAD51 during mouse spermatogenesis. We show that RAD51 is crucial during meiotic prophase and its loss leads to depletion of late prophase I spermatocytes through a p53-dependent apoptotic pathway. This phenotype is distinct from that observed in the DMC1 knockdown. Our meiotic knockdown and complementation system establishes an experimental platform for mechanistic studies of meiotic proteins with unknown functions or essential genes for which a testis-specific knockout is not possible

Transplacental Therapeutic Drug Monitoring in Pregnant Women with Fetal Tachyarrhythmia Using HPLC-MS/MS

Fetal arrhythmia develops in 0.1–5% of pregnancies and may cause fetal heart failure and fetal hydrops, thus increasing fetal, neonatal, and infant mortality. The timely initiation of transplacental antiarrhythmic therapy (ART) promotes the conversion of fetal tachycardia to sinus rhythm and the regression of the concomitant non-immune fetal hydrops. The optimal treatment regimen search for the fetus with tachyarrhythmia is still of high value. Polymorphisms of these genes determines the individual features of the drug pharmacokinetics. The aim of this study was to study the pharmacokinetics of transplacental anti-arrhythmic drugs in the fetal therapy of arrhythmias using HPLC-MS/MS, as well as to assess the effect of the multidrug-resistance gene ABCB1 3435C > T polymorphism on the efficacy and maternal/fetal complications of digoxin treatment. The predisposition to a decrease in the bioavailability of the digoxin in patients with a homozygous variant of the CC polymorphism showed a probable association with the development of ART side effects. A pronounced decrease in heart rate in women with the 3435TT allele of the ABCB1 gene was found. The homozygous TT variant in the fetus showed a probable association with an earlier response to ART and rhythm disruptions on the digoxin dosage reduction. high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) methods for digoxin and sotalol therapeutic drug monitoring in blood plasma, amniotic fluid, and urine were developed. The digoxin and sotalol concentrations were determined in the plasma blood, urine, and amniotic fluid of 30 pregnant women at four time points (from the beginning of the transplacental antiarrhythmic therapy to delivery) and the plasma cord blood of 30 newborns. A high degree of correlation between the level of digoxin and sotalol in maternal and cord blood was found. The ratio of digoxin and sotalol in cord blood to maternal blood was 0.35 (0.27 and 0.46) and 1.0 (0.97 and 1.07), accordingly. The digoxin concentration in the blood of the fetus at the moment of the first rhythm recovery episode, 0.58 (0.46, 0.8) ng/mL, was below the therapeutic interval. This confirms the almost complete transplacental transfer of sotalol and the significant limitation in the case of digoxin. Previously, ABCB1/P-glycoprotein had been shown to limit fetal exposure to drugs. Further studies (including multicenter ones) to clarify the genetic features of the transplacental pharmacokinetics of antiarrhythmic drugs are needed

Transplacental Therapeutic Drug Monitoring in Pregnant Women with Fetal Tachyarrhythmia Using HPLC-MS/MS

Fetal arrhythmia develops in 0.1–5% of pregnancies and may cause fetal heart failure and fetal hydrops, thus increasing fetal, neonatal, and infant mortality. The timely initiation of transplacental antiarrhythmic therapy (ART) promotes the conversion of fetal tachycardia to sinus rhythm and the regression of the concomitant non-immune fetal hydrops. The optimal treatment regimen search for the fetus with tachyarrhythmia is still of high value. Polymorphisms of these genes determines the individual features of the drug pharmacokinetics. The aim of this study was to study the pharmacokinetics of transplacental anti-arrhythmic drugs in the fetal therapy of arrhythmias using HPLC-MS/MS, as well as to assess the effect of the multidrug-resistance gene ABCB1 3435C > T polymorphism on the efficacy and maternal/fetal complications of digoxin treatment. The predisposition to a decrease in the bioavailability of the digoxin in patients with a homozygous variant of the CC polymorphism showed a probable association with the development of ART side effects. A pronounced decrease in heart rate in women with the 3435TT allele of the ABCB1 gene was found. The homozygous TT variant in the fetus showed a probable association with an earlier response to ART and rhythm disruptions on the digoxin dosage reduction. high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) methods for digoxin and sotalol therapeutic drug monitoring in blood plasma, amniotic fluid, and urine were developed. The digoxin and sotalol concentrations were determined in the plasma blood, urine, and amniotic fluid of 30 pregnant women at four time points (from the beginning of the transplacental antiarrhythmic therapy to delivery) and the plasma cord blood of 30 newborns. A high degree of correlation between the level of digoxin and sotalol in maternal and cord blood was found. The ratio of digoxin and sotalol in cord blood to maternal blood was 0.35 (0.27 and 0.46) and 1.0 (0.97 and 1.07), accordingly. The digoxin concentration in the blood of the fetus at the moment of the first rhythm recovery episode, 0.58 (0.46, 0.8) ng/mL, was below the therapeutic interval. This confirms the almost complete transplacental transfer of sotalol and the significant limitation in the case of digoxin. Previously, ABCB1/P-glycoprotein had been shown to limit fetal exposure to drugs. Further studies (including multicenter ones) to clarify the genetic features of the transplacental pharmacokinetics of antiarrhythmic drugs are needed