7,815 research outputs found
On some numerical difficulties in integrating the equations for one-dimensional nonequilibrium nozzle flow
Numerical difficulties in integrating equations for one dimensional nonequilibrium nozzle flow of ga
Organ preservation solutions: linking pharmacology to survival for the donor organ pathway
PURPOSE OF REVIEW: To provide an understanding of the scientific principles, which underpinned the development of organ preservation solutions, and to bring into context new strategies and challenges for solution development against the background of changing preservation technologies and expanded criteria donor access. RECENT FINDINGS: Improvements in organ preservation solutions continue to be made with new pharmacological approaches. New solutions have been developed for dynamic perfusion preservation and are now in clinical application. Principles defining organ preservation solution pharmacology are being applied for cold chain logistics in tissue engineering and regenerative medicine. SUMMARY: Organ preservation solutions support the donor organ pathway. The solution compositions allow additives and pharmacological agents to be delivered direct to the target organ to mitigate preservation injury. Changing preservation strategies provide further challenges and opportunities to improve organ preservation solutions
Interaction of gases with lunar materials
The surface chemistry of Apollo 17 lunar fines samples 74220 (the orange soil) and 74241 (the gray control soil) has been studied by measuring the adsorption of nitrogen, argon, and oxygen (all at 77 K) and also water vapor (at 20 or 22 C). In agreement with results for samples from other missions, both samples had low initial specific surface areas, consisted of nonporous particles, and were attacked by water vapor at high relative pressure to give an increased specific surface area and create a pore system which gave rise to a capillary condensation hysteresis loop in the adsorption isotherms. In contrast to previous samples, both of the Apollo 17 soils were partially hydrophobic in their initial interaction with water vapor (both samples were completely hydrophilic after the reaction with water). The results are consistent with formation at high temperatures without subsequent exposure to significant amounts of water
Interaction of gases with lunar materials
Quantitative efforts to assess the surface properties of lunar fines, particularly water induced porosity are discussed. Data show that: (1) changes induced in lunar fines are not visible in high energy electron micrographs, (2) scanning micrographs show no change in particle size distribution as a result of reaction with water, (3) water induced changes are internal to the particles themselves, (4) normal laboratory atmosphere blocks alteration reaction with water, and (5) surface properties of mature lunar soils appear to be almost independent of chemical composition and mineralogy, but there are some variations in their reactivity toward water
Institutional Design and Regulatory Performance: Rethinking State Certificate of Need Programs
The success of state efforts to control rising health care costs depends on the incentives contained in the legislative design of regulatory policies and in the administrative capacity and autonomy of state agencies. States have regulated the construction and expansion of health care facilities and services for more that two decades through “certificate of need” (CON) programs designed to limit the diffusion of expensive new medical technologies and to avoid the duplication of health care facilities. Although the cost-control record of state certificate of need programs has been widely criticized, Rhode Island’s experience with a reformed CON process from 1985 to 1995 suggests that properly designed capital expenditure controls can impose order on the rapid diffusion of new medical technologies. Staunch political opposition from health providers, however, raises serious questions about the ability of state officials to implement such reforms. In the end, Rhode Island’s experience with capital expenditure regulation in the 1980s and 1990s underscores the importance of institutional design and policy making capacity on regulatory performance
Presupernova collapse models with improved weak-interaction rates
Improved values for stellar weak interaction rates have been recently
calculated based upon a large shell model diagonalization. Using these new
rates (for both beta decay and electron capture), we have examined the
presupernova evolution of massive stars in the range 15-40 Msun. Comparing our
new models with a standard set of presupernova models by Woosley and Weaver, we
find significantly larger values for the electron-to-baryon ratio Ye at the
onset of collapse and iron core masses reduced by approximately 0.1 Msun. The
inclusion of beta-decay accounts for roughly half of the revisions, while the
other half is a consequence of the improved nuclear physics. These changes will
have important consequences for nucleosynthesis and the supernova explosion
mechanism.Comment: 4 pages, 2 figure
Twist and writhe dynamics of stiff filaments
This letter considers the dynamics of a stiff filament, in particular the
coupling of twist and bend via writhe. The time dependence of the writhe of a
filament is for a linear filament and for a curved filament. Simulations are used to study the relative
importance of crankshaft motion and tube like motion in twist dynamics.
Fuller's theorem, and its relation with the Berry phase, is reconsidered for
open filamentsComment: 7 Pages with 2 figure
Comment on "Elasticity Model of a Supercoiled DNA Molecule"
We perform simulations to numerically study the writhe distribution of a
stiff polymer. We compare with analytic results of Bouchiat and Mezard (PRL 80
1556- (1998); cond-mat/9706050).Comment: 1 page, 1 figure revtex
Writhing Photons and Berry Phases in Diffusive Wave Scattering
We study theoretically the polarization state of light in multiple scattering
media in the limit of weak gradients in refractive index. Linearly polarized
photons are randomly rotated due to the Berry phase associated with the
scattering path. For circularly polarized light independent speckle patterns
are found for the two helical states. The statistics of the geometric phase is
related to the writhe distribution of semiflexible polymers such as DNA.Comment: 4 pages, 1 figur
Elasticity model of a supercoiled DNA molecule
Within a simple elastic theory, we study the elongation versus force
characteristics of a supercoiled DNA molecule at thermal equilibrium in the
regime of small supercoiling. The partition function is mapped to the path
integral representation for a quantum charged particle in the field of a
magnetic monopole with unquantized charge.
We show that the theory is singular in the continuum limit and must be
regularised at an intermediate length scale. We find good agreement with
existing experimental data, and point out how to measure the twist rigidity
accurately.Comment: Latex, 4 pages. The figure contains new experimental data, giving a
new determination of the twist rigidit
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