Time constant and transport delay determination of the gas analyzer

AbstractAlthough methodology to estimate transport delay and time constant of the mass spectrometer (MS) has been discussed for some time, there appears to be a question whether an exponential first order function is an appropriate fit to the analyzer response. We investigated the response of our MS (Perkin-Elmer 1100) to step changes in O2 and CO2 from ambient air to 13% and 5%, respectively, and developed regression technique to estimate transport delay and time constant. Output from the MS coupled to the data acquisition system was sampled at 100 Hz with a PDP 11/10 computer system. Since the general form for a single time constant system with an initial and final values of I and F, with time delay, td, and time constant, τ, is y = F + (I - F) exp ( - (t - td)/τ), data were regressed over time to the straight line transformation - In((y - F)/ (I − F)) = t/τ − td/τ, where t is time and y the experimental data. This is a straight line with slope 1/τ and vertical axis intercept of -td/τ. We find an excellent correlation between gas concentration data and the regression fit (r = 0.99) from 10 to 95% of the response interval, resulting in τ of 0.03 s and transport delay of 0.3 s for the Perkin-Elmer 1100 mass spectrometer. We validated transport delay and time constant corrections on breath-by-breath gas exchange computations during physical exercise, and conclude that the experimental data fit well to the generalized first order exponential equation

Structure of interacting aggregates of silica nanoparticles in a polymer matrix: Small-angle scattering and Reverse Monte-Carlo simulations

Reinforcement of elastomers by colloidal nanoparticles is an important application where microstructure needs to be understood - and if possible controlled - if one wishes to tune macroscopic mechanical properties. Here the three-dimensional structure of big aggregates of nanometric silica particles embedded in a soft polymeric matrix is determined by Small Angle Neutron Scattering. Experimentally, the crowded environment leading to strong reinforcement induces a strong interaction between aggregates, which generates a prominent interaction peak in the scattering. We propose to analyze the total signal by means of a decomposition in a classical colloidal structure factor describing aggregate interaction and an aggregate form factor determined by a Reverse Monte Carlo technique. The result gives new insights in the shape of aggregates and their complex interaction in elastomers. For comparison, fractal models for aggregate scattering are also discussed

Morphology and photoluminescence study of titania nanoparticles

Titania nanoparticles are prepared by sol–gel chemistry with a poly(ethylene oxide) methyl ether methacrylate-block-poly(dimethylsiloxane)-block-poly(ethylene oxide) methyl ether methacrylate triblock copolymer acting as the templating agent. The sol–gel components—hydrochloric acid, titanium tetraisopropoxide, and triblock copolymer—are varied to investigate their effect on the resulting titania morphology. An increased titania precursor or polymer content yields smaller primary titania structures. Microbeam grazing incidence small-angle X-ray scattering measurements, which are analyzed with a unified fit model, reveal information about the titania structure sizes. These small structures could not be observed via the used microscopy techniques. The interplay among the sol–gel components via our triblock copolymer results in different sized titania nanoparticles with higher packing densities. Smaller sized titania particles, (∼13–20 nm in diameter) in the range of exciton diffusion length, are formed by 2% by weight polymer and show good crystallinity with less surface defects and high oxygen vacancies

Phosphorothioate antisense oligonucleotides induce the formation of nuclear bodies

Antisense oligonucleotides are powerful tools for the in vivo regulation of gene expression. We have characterized the intracellular distribution of fluorescently tagged phosphorothioate oligodeoxynucleotides (PS-ONs) at high resolution under conditions in which PS-ONs have the potential to display antisense activity. Under these conditions PS-ONs predominantly localized to the cell nucleus where they accumulated in 20-30 bright spherical foci designated phosphorothioate bodies (PS bodies), which were set against a diffuse nucleoplasmic population excluding nucleoli. PS bodies are nuclear structures that formed in cells after PS-ON delivery by transfection agents or microinjection but were observed irrespectively of antisense activity or sequence. Ultrastructurally, PS bodies corresponded to electron-dense structures of 150-300 nm diameter and resembled nuclear bodies that were found with lower frequency in cells lacking PS-ONs. The environment of a living cell was required for the de novo formation of PS bodies, which occurred within minutes after the introduction of PS-ONs. PS bodies were stable entities that underwent noticeable reorganization only during mitosis. Upon exit from mitosis, PS bodies were assembled de novo from diffuse PS-ON pools in the daughter nuclei. In situ fractionation demonstrated an association of PS-ONs with the nuclear matrix. Taken together, our data provide evidence for the formation of a nuclear body in cells after introduction of phosphorothioate oligodeoxynucleotides

Synthetic Pathways to Mesostructured Superconductors: Quantum Materials from Block Copolymer Self-Assembly

The ability to precisely control the properties of materials using atomic structure developed over the last 50 years directly led to the high-performance semiconductor based devices that have revolutionized modern life. Complex ordered mesoscale structures such as those prepared by block copolymer self-assembly may prove to be a powerful tool for tuning the electronic properties of materials, but few have explored this area, largely due to a lack of connections between the disparate fields of atomic quantum materials and soft matter self-assembly. In particular, the impact of three- dimensional mesoscale order on superconductors has not been explored at all, despite the possibility for emergent properties including increased critical fields, angle- dependent magnetic behavior, and symmetry-forbidden nonlinear magnetic and electronic properties. In this thesis, three routes to mesostructured superconductors using block copolymer self-assembly are developed to bridge this gap and form a stable platform for future mesostructure-superconductivity correlation studies. In the first route, poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblock terpolymers are used to structure-direct niobium (V) oxides, which are subsequently converted to niobium nitrides via an optimized annealing procedure in ammonia gas. The resulting materials are superconductors with Tc of 7.8K. We demonstrate that the length scale and morphology of these materials can be tuned by varying the block copolymer dimensions and show first evidence of magnetic flux pinning on the mesoscale pores of the material. In the second route, intermediate oxynitrides are converted into carbonitrides, using a variety of times, temperatures, and gas compositions to more fully explore the compositional flexibility of the niobium-(oxygen)-nitrogen-carbon pseudo-ternary system. The best resulting carbonitrides have increased Tc of up to 16.0 K, nearing values expected for the bulk material, as well as improved mesostructure retention despite treatment at temperatures of up to 1000 ̊C. To demonstrate the versatility of this approach, materials with four distinct morphologies (alternating gyroid network, perforated lamellae, double gyroid matrix, and inverse hexagonal cylinders) are prepared using a single parent ISO terpolymer. In the final route, mesoporous Si(ON) ceramic single mesocrystals are infiltrated with molten indium at pressures up to 40,000 psi. The resulting materials exhibit an inversion of the magnetic response from a type-I behavior characteristic of bulk In to a type-II behavior, coupled with an order-of-magnitude increase in the upper critical field. These results serve as a first demonstration of the plethora of fascinating emergent properties expected for superconducting mesostructures, and provide a robust, versatile, stable foundation for extensive mesostructure-superconductivity correlation studies

Discovering Synthesis Routes to Hexagonally Ordered Mesoporous Niobium Nitrides Using Poloxamer/Pluronics Block Copolymers

Discovering Synthesis Routes to Hexagonally Ordered Mesoporous Niobium Nitrides Using Poloxamer/Pluronics Block Copolymer