The role of intercrystalline links in the environmental stress cracking of high density polyethylene

Results of dynamic mechanical spectroscopy, infrared spectroscopy, and tensile stress-strain data show that the non-ionic surfactant Igepal CO-630, often used as a stress cracking agent, and water are absorbed by high density polyethylene to cause an internal stress relaxation of the intercrystalline tie molecules. The resulting molecular rearrangements produce changes in both the crystalline and amorphous regions. Thus, a molecular mechanism is proposed for the long-term aging process based on the results of accelerated aging in the presence of an environmental stress cracking agent.     

Bladder Volume Sensing by Local Distension Measurement

Restoration of volitional control of the micturition reflex requires the use of bladder volume sensors. A method of measuring bladder volume by monitoring local distension has been developed in the laboratory. Tests conducted in experimental animals yielded 15 percent accuracy with bladder volume at micturition reflex threshold.     

Simulation and characterization of microreactors for aerosol generation

This paper shows the application of T-shaped micromixers for the generation of aerosols with nanoscale droplets by the mixing of a hot vapor–gas mixture with a cold gas. The fast mixing within a T-shaped micromixer leads to a high supersaturation of the vapor and therefore to an instantaneous, homogeneous nucleation and particle growth. Different mixer geometries, mixing ratios, and gas temperatures have been investigated by numerical simulation to yield optimum mixing results over a wide range of operational parameters. Optimized microreactor geometries were designed and fabricated in silicon with Pyrex glass lids. Special attention was paid to thermal insulation and particle deposition at the channel walls. This concerns not only the mixing chip, but also the design of the fluidic mount with only few bends and corners. Initial experimental results for particle deposition and aerosol generation are presented. High temporal temperature gradients up to 10⁶ K/s lead to a rapid condensation and forming of nanosized particles with a mean diameter of 20–50 nm and a narrow size distribution.     

Deactivation behaviour of Photoexcited Aryltropylium Ions. IV. Influence of Ion Pair Formation

Aryltropylium salts exhibit an unusually effective self quenching of fluorescence in dependence on their concentration in dichlòromethane. The quenching process is investigated by static and time resolved fluorescence measurements. The observed biexponential fluorescence decay is interpreted by the emissions of ion pairs and free cations. The rate constant of fluorescence quenching by formation ion pair is two orders of magnitude greater than the diffusion constant.     

Distribution of water in ceramic green bodies during drying

In order to investigate drying mechanisms at different stages, the distribution of water within the ceramic green bodies at different scales has been examined. The experimental measurements, using a simple weighing technique and Magnetic Resonance Imaging (MRI), show that during the first stage of drying involving shrinkage the material is constituted of uniquely solid and water with no gradient in water content within the sample. Then, during the second stage of drying, significant differences of water content as a function of position appear. As a complement, at the grain scale, observations using environmental scanning electron microscopy were made giving useful information on the solid–liquid–gas interfaces in the near surface part of the green body. Finally, the gradients in the water distribution were exploited to make a simple estimate of the diffusion coefficient of water with its dependence on the moisture content.     

Transfer RNA mimicry in a new group of positive-strand RNA plant viruses, the furoviruses: differential aminoacylation between the RNA components of one genome

The effects of the organic calcium channel blocker verapamil and the beta-receptor blocker propranolol on dipole (phi(d)) and surface (phi(s)) potentials of bilayer lipid membranes were studied. The boundary potentials (phi(b)= phi(d) + phi(s)) of black lipid membranes, monitored by conductance measurements in the presence of nonactin and by capacitive current measurements were compared with phi(s) calculated from the electrophoretic mobility of lipid vesicles. It was shown that the increase of boundary potential, induced by the adsorption of the positively charged propranolol, was caused solely by an increase in surface potential. Although phi(s) also increases due to the adsorption of verapamil, phi(b) diminishes. A sharp decrease of the dipole potential was shown to be responsible for this effect. From Langmuir adsorption isotherm the dissociation constant Kd of verapamil was estimated. The uncharged form of verapamil (Kd=(0.061+/-0.01) mM at pH 10.5) has a tenfold higher affinity to a neutral bilayer membrane than the positively charged form. The alteration of membrane dipole potential due to verapamil adsorption may have important implications for both membrane translocation and partitioning of small or hydrophobic ions and charged groups of membrane proteins.     

Temporal and regional changes during focal ischemia in rat brain studied by proton spectroscopic imaging and quantitative diffusion NMR imaging

The early development of focal ischemia after permanent occlusion of the right middle cerebral artery (MCA) was studied in six rats using interleaved measurements by diffusion-weighted NMR imaging (DWI) of water and two variants of proton spectroscopic imaging (SI), multiecho SI (TE: 136, 272, 408 ms) and short TE SI (TE: 20 ms). Measurements on a 4.7-T NMR imaging system were performed between the control phase and approximately 6 h postocclusion. In the center of the ischemic lesion of all rats, the apparent diffusion coefficient (ADC) decreased rapidly to 84.4 +/- 4.2% (mean +/- SD) of the control values approximately 2 min postocclusion. Approximately 6 h postocclusion, the ADC was reduced to 67.1 +/- 5.9%. In contrast, large differences between the animals were observed for the temporal increase of lactate (Lac) in the ipsilateral hemisphere. The maximum Lac signal was reached in four rats after 0.5-1.5 h, and in two rats was not reached even after 6 h postocclusion. Six h postocclusion, SI spectra measured at a TE of 136 ms revealed a decrease in the CH3 signal of N-acetylaspartate (NAA) to 67 +/- 13% of the control values. Differences were observed between the spatial regions of decreased NAA and increased Lac. In the lesions, a T2 relaxation time of Lac of 292 +/- 40 ms, considering a J-coupling constant of 6.9 Hz, was measured. Furthermore, a prolongation of the T2 of the CH3 signal of creatine/phosphocreatine (Cr/PCr) was observed in the lesion, from 163 +/- 22 ms during control to 211 +/- 41 ms approximately 6 h postocclusion. The experiments proved that DWI and proton SI are valuable tools to provide complementary information on processes associated with brain infarcts.     

Detection of homonuclear decoupled in vivo proton NMR spectra using constant time chemical shift encoding: CT-PRESS

We revisited the cytogenetic alterations of the cervical adenocarcinoma cell line HeLa through the use of spectral karyotyping (SKY), comparative genomic hybridization (CGH), and fluorescence in situ hybridization (FISH). SKY analysis unequivocally characterized all abnormal chromosomes. Chromosomal breakpoints were primarily assigned by simultaneous assessment of SKY painted chromosomes and inverted 4,6-diamidino2-phenylindole banding from the same cell. Twenty clonally abnormal chromosomes were found. Comparison with previously reported HeLa G-banding karyotypes revealed a remarkably stable cytogenetic constitution because 18 of 20 markers that were found were present before. The classification of 12 markers was refined in this study. Our assignment of the remaining six markers was consistent with those described in the literature. The CGH map of chromosomal copy number gains and losses strikingly matched the SKY results and was, in a few instances, decisive for assigning breakpoints. The combined use of molecular cytogenetic methods SKY, CGH, and FISH with site-specific probes, in addition to inverted 4,6-diamidino-2-phenylindole or conventional G-banding analysis, provides the means to fully assess the genomic abnormalities in cancer cells. Human papillomaviruses (HPVs) are frequently integrated into the cellular DNA in cervical cancers. We mapped by FISH five HPV18 integration sites: three on normal chromosomes 8 at 8q24 and two on derivative chromosomes, der(5)t(5;22;8)(qll;q11q13;q24) and der(22)t(8; 22)(q24;q13), which have chromosome 8q24 material. An 8q24 copy number increase was detected by CGH. Dual-color FISH with a c-MYC probe mapping to 8q24 revealed colocalization with HPV18 at all integration sites, indicating that dispersion and amplification of the c-MYC gene sequences occurred after and was most likely triggered by the viral insertion at a single integration site. Numerical and structural chromosomal aberrations identified by SKY, genomic imbalances detected by CGH, as well as FISH localization of HPV18 integration at the c-MYC locus in HeLa cells are common and representative for advanced stage cervical cell carcinomas. The HeLa genome has been remarkably stable after years of continuous cultivation; therefore, the genetic alterations detected may have been present in the primary tumor and reflect events that are relevant to the development of cervical cancer.     

BART SFO Extension Aerial Guideways: Using Nonlinear Analysis to Control and Minimize Seismic Damage

Bay Area Rapid Transit (BART) is extending service from the existing southern terminus of BART, at Colma Station, to San Francisco International Airport (SFO), a distance of 14 km (8.7 mi). Included in this project are approximately 1.93 km (1.2 mi) of aerial guideways. Design criteria required preliminary sizing of guideway columns by using the response spectrum analysis method. Final design required using nonlinear time-history analysis to verify that strains in column reinforcement and concrete did not exceed 60% of allowable ultimate strain. Analysis of the BART guideways by both the response spectrum and time-history methods provides an opportunity to compare the two methods of analysis. Analysis results show that comparable results can be obtained from the two methods under some combinations of structure stiffness and strength. However, wide divergence between the two methods also can occur for other combinations of structure strength and stiffness. Nonlinear modeling also determined that the continuously welded rails with direct fixation fasteners used for the track system on the guideways distribute longitudinal seismic forces and can serve as an effective restraining device across bridge expansion joints.