Mechanisms of virus assembly probed by Raman spectroscopy: the icosahedral bacteriophage P22

A microdialysis flow cell has been developed for time-resolved Raman spectroscopy of biological macromolecules and their assemblies. The flow cell permits collection of Raman spectra concurrent with the efflux of small solute molecules into a solution of macromolecules and facilitates real-time spectroscopic detection of structural transitions induced by the effluent. Additionally, the flow cell is well suited to the investigation of hydrogen-isotope exchange phenomena that can be exploited as dynamic probes of viral protein folding and solvent accessibility along the assembly pathway. Here, we describe the application of the Raman dynamic probe to the maturation of the icosahedral capsid of bacteriophage P22, a double-stranded DNA virus. The P22 virion is constructed from a capsid precursor (procapsid) consisting of 420 coat subunits (gp5) in an outer shell and a few hundred scaffolding subunits (gp8) within. Capsid maturation involves expulsion of scaffolding subunits coupled with shell expansion at the time of DNA packaging. Raman static and dynamic probes reveal that the scaffolding subunit is highly alpha-helical and highly thermolabile, and lacks a typical hydrophobic core. When bound within the procapsid, the alpha-helical fold of gp8 is thermostabilized; however, this stabilization confers no apparent protection against peptide NH-->ND exchange. A molten globule model is proposed for the native scaffolding subunit that functions in procapsid assembly. Accompanying capsid expansion, a small conformational change (alpha-helix-->beta-strand) is also observed in the coat subunit. Domain movement mediated by hinge bending is proposed as the mechanism of capsid expansion. On the basis of these results, a molecular model is proposed for assembly of the P22 procapsid.     

Semi-Markov models with an application to power-plant reliabilityanalysis

Systems with, (1) a finite number of states, and (2) random holding times in each state, are often modeled using semi-Markov processes. For general holding-time distributions, closed formulas for transition probabilities and average availability are usually not available. Recursion procedures are derived to approximate these quantities for arbitrarily distributed holding-times; these recursion procedures are then used to fit the semi-Markov model with Weibull distributed holding-times to actual power-plant operating data. The results are compared to the more familiar Markov models; the semi-Markov model using Weibull holding-times fits the data remarkably well. In particular comparing the transition probabilities shows that the probability of the system being in the state of refitting converges more quickly to its limiting value as compared to convergence in the Markov model. This could be because the distribution of the holding-times in this state is rather unlike the exponential distribution. The more flexible semi-Markov model with Weibull holding-times describes more accurately the operating characteristics of power-plants, and produces a better fit to the actual operating data     

Effect of Microstructure on the Accelerated Creep of 20CrMoV12‐1 and P 91 Steels

In the initial part the change of microstructure for steel X20 CrMoV 121 is discussed in terms of the distribution of carbide precipitates and its effects on accelerated creep resistance and hardness are presented. In the following, experimental results of microstructure and accelerated creep resistance are presented for the steels X20CrMoV 121 and P91 annealed for up to 8760 hours at 650°C and 750°C before the testing. A similar evolution of the distribution of carbide particles of a size above 102 nm is found for both steels, while the accelerated creep resistance is diminished much stronger for the steel X20CrMoV 121. This difference is due to a greater stability of NbC than that of VC precipitates, both related to the evolution of the chemical composition of complex chromium, molybdenum and iron carbide particles.     

Annealing of laser patterned PMMA coated with gold and gallium

Poly(methyl methacrylate) (PMMA) surface was patterned by laser scanning and Ga and Au layers of different thicknesses were sputtered onto modified polymer surface. The metal/PMMA structures were annealed at 160 °C for 1 h and the changes in the surface morphology were examined by AFM and STM techniques. It was found that sufficiently thick and continuous metal coverage protect the underlying pattern structure.     

Multicriteria optimization as enabler for Sustainable Ceramic Matrix Composites

Over the past 40 years, development of Ceramic Matrix Composites (CMCs) has focused mainly on the improvement of material performance and optimization of cost-efficient production routes. Recently, more fields of application have opened up for CMCs, in which environmental impacts are relevant. These impacts have barely been investigated so far but receive growing interest due to increasing awareness of the environmental consequences. Our innovative approach frames material properties in relation to environmental impacts (e.g., global warming potential in CO₂ emission) by varying process parameters to balance optimum performance against environmental considerations. First, the process of wet filament winding has been investigated up to the Carbon Fiber Reinforced Plastic (CFRP) state by changing both the curing and tempering temperatures. During the production of CFRP plates, mass and energy flows were tracked in each step. Three point-bending and interlaminar shear tests have been performed on the resulting samples to identify basic mechanical properties. The environmental impacts are determined by a cradle-to-gate Life Cycle Assessment (LCA), using the software SimaPro. The resulting tradeoffs between mechanical properties and environmental impacts show nonlinear behavior, thus revealing optimum points above which improved mechanical properties are associated with significantly higher CO₂ emissions.     

Exploitation of enhanced fluorescence via cross-coupling principles toward the design of an optical integrated thin-film sensor for nanotechnology and biomedical applications

A novel fluorescence thin-film integrated sensor has been proposed that retains the beneficial selectivity characteristics typical of optical and electronic sensors, while improving the signal-to-noise ratio in a miniature geometry. The sensor can be tuned to measure a wide variety of biological species by varying its thin-film corrugation period. The optical properties of the sensor are determined, in large part, by optical cross coupling through a corrugated metal film and enhanced fluorescence. The surface plasmon to surface plasmon cross coupling was theoretically modeled and experimentally tested. Finally, prospective applications of this sensor in the key areas of nanotechnology and bioengineering are discussed.     

Porphyrin migration and aggregation in a poly(methylmethacrylate) matrix

The aging of thin polymer films is interesting for the development of nonlinear optical media. In this study, the optical properties of porphyrin‐doped poly(methylmethacrylate) (PMMA) films are investigated before and after annealing. Both absorption and luminescence spectroscopies were used to characterize the changes that occurred during the thermal treatment. The surface and bulk characteristics of the doped films were also measured using atomic force microscopy, X‐ray‐induced photoelectron spectra, and DSC. We found that the aging of the thin polymer films led the porphyrin molecules to diffuse in the direction of the polymer surface. This led to the random formation of porphyrin aggregates on the surface, followed by absorption band shift and little luminescence quenching. These results suggest that porphyrin‐doped PMMA films could be used as long‐term stable active optical materials. POLYM. COMPOS., 35:665–670, 2014. © 2013 Society of Plastics Engineers     

Sorption of C. I. Disperse Red 60 in polystyrene and PMMA films and polyester and Nylon 6 textiles in the presence of supercritical carbon dioxide

C. I. Disperse Red 60 (DR60) was absorbed into polymer films and textile fibers in the presence of supercritical carbon dioxide at pressures between 5 and 33MPa and at temperatures between 308.2 and 423.2 K. Polystyrene (PS) and poly(methyl methacrylate) (PMMA) films and polyester (polyethylene terephthalate: PET) and Nylon 6 textiles were used as absorbents. The amount of equilibrium sorption of dye increased both with pressure and temperature. The sorption behavior was successfully analyzed with the quasi dual-mode sorption model.     

Mutations that extend the specificity of the endonuclease activity of lambda terminase

Fetal DNA has been detected in maternal plasma during pregnancy. We investigated the clearance of circulating fetal DNA after delivery, using quantitative PCR analysis of the sex-determining region Y gene as a marker for male fetuses. We analyzed plasma samples from 12 women 1-42 d after delivery of male babies and found that circulating fetal DNA was undetectable by day 1 after delivery. To obtain a higher time-resolution picture of fetal DNA clearance, we performed serial sampling of eight women, which indicated that most women (seven) had undetectable levels of circulating fetal DNA by 2 h postpartum. The mean half-life for circulating fetal DNA was 16.3 min (range 4-30 min). Plasma nucleases were found to account for only part of the clearance of plasma fetal DNA. The rapid turnover of circulating DNA suggests that plasma DNA analysis may be less susceptible to false-positive results, which result from carryover from previous pregnancies, than is the detection of fetal cells in maternal blood; also, rapid turnover may be useful for the monitoring of feto-maternal events with rapid dynamics. These results also may have implications for the study of other types of nonhost DNA in plasma, such as circulating tumor-derived and graft-derived DNA in oncology and transplant patients, respectively.