Free radical formation during machining and fracture of polymers

Electron paramagnetic resonance measurements of free radical formation during cutting and grinding of polymer

Silk-fibronectin protein alloy fibres support cell adhesion and viability as a high strength, matrix fibre analogue

Silk is a natural polymer with broad utility in biomedical applications because it exhibits general biocompatibility and high tensile material properties. While mechanical integrity is important for most biomaterial applications, proper function and integration also requires biomaterial incorporation into complex surrounding tissues for many physiologically relevant processes such as wound healing. In this study, we spin silk fibroin into a protein alloy fibre with whole fibronectin using wet spinning approaches in order to synergize their respective strength and cell interaction capabilities. Results demonstrate that silk fibroin alone is a poor adhesive surface for fibroblasts, endothelial cells, and vascular smooth muscle cells in the absence of serum. However, significantly improved cell attachment is observed to silk-fibronectin alloy fibres without serum present while not compromising the fibres' mechanical integrity. Additionally, cell viability is improved up to six fold on alloy fibres when serum is present while migration and spreading generally increase as well. These findings demonstrate the utility of composite protein alloys as inexpensive and effective means to create durable, biologically active biomaterials.T32 EB006359 - NIBIB NIH HH

IODP Proposal 626: "Cenozoic Equatorial Age Transect – Following the Palaeo-equator"

As the largest ocean, the Pacific is intricately linked to major changes in the global climate system that took place during the Cenozoic. Throughout the Cenozoic the Pacific plate has had a northward component. Thus, the Pacific is unique, in that the thick sediment bulge of biogenic rich deposits from the currently narrowly focused zone of equatorial upwelling is slowly moving away from the equator. Hence, older sections are not deeply buried and can be recovered by drilling. Previous ODP Legs 138 and 199 were designed as transects across the paleo-equator in order to study the changing patterns of sediment deposition across equatorial regions, while this proposal aims to recover an orthogonal “age-transect” along the paleo-equator. Both previous legs were remarkably successful in giving us new insights into the workings of the climate and carbon system, productivity changes across the zone of divergence, time dependent calcium carbonate dissolution, bio- and magnetostratigraphy, the location of the ITCZ, and evolutionary patterns for times of climatic change and upheaval. Together with older DSDP drilling in the eastern equatorial Pacific, both Legs also helped to delineate the position of the paleo-equator and variations in sediment thickness from approximately 150°W to 110°W. As we have gained more information about the past movement of plates, and where in time “critical” climate events are located, we now propose to drill an age-transect (“flow-line”) along the position of the paleo-equator in the Pacific, targeting selected time-slices of interest where calcareous sediments have been preserved best. Leg 199 enhanced our understanding of extreme changes of the calcium carbonate compensation depth across major geological boundaries during the last 55 million years. A very shallow CCD during most of the Paleogene makes it difficult to obtain well preserved sediments, but we believe our siting strategy will allow us to drill the most promising sites and to obtain a unique sedimentary biogenic carbonate archive for time periods just after the Paleocene- Eocene boundary event, the Eocene cooling, the Eocene/Oligocene transition, the “one cold pole” Oligocene, the Oligocene-Miocene transition, and the Miocene, contributing to the objectives of the IODP Extreme Climates Initiative, and providing material that the previous legs were not able to recover

Solutions of the dispersion equation in the region of overlapping of zero-sound and particle-hole modes

In this paper the solutions of the zero-sound dispersion equation in the random phase approximation (RPA) are considered. The calculation of the damped zero-sound modes \omega_s(k) (complex frequency of excitation) in the nuclear matter is presented. The method is based on the analytical structure of the polarization operators \Pi(\omega,k). The solutions of two dispersion equations with \Pi(\omega,k) and with Re(\Pi(\omega,k)) are compared. It is shown that in the first case we obtain one-valued smooth solutions without "thumb-like" forms. Considering the giant resonances in the nuclei as zero-sound excitations we compare the experimental energy and escape width of the giant dipole resonance (GDR) in the nucleus A with \omega_s(k) taken at a definite wave vector k=k_A.Comment: 14 pages, 5 figures; revised versio

Penetration depth of low-coherence enhanced backscattered light in sub-diffusion regime

The mechanisms of photon propagation in random media in the diffusive multiple scattering regime have been previously studied using diffusion approximation. However, similar understanding in the low-order (sub-diffusion) scattering regime is not complete due to difficulties in tracking photons that undergo very few scatterings events. Recent developments in low-coherence enhanced backscattering (LEBS) overcome these difficulties and enable probing photons that travel very short distances and undergo only a few scattering events. In LEBS, enhanced backscattering is observed under illumination with spatial coherence length L_sc less than the scattering mean free path l_s. In order to understand the mechanisms of photon propagation in LEBS in the subdiffusion regime, it is imperative to develop analytical and numerical models that describe the statistical properties of photon trajectories. Here we derive the probability distribution of penetration depth of LEBS photons and report Monte Carlo numerical simulations to support our analytical results. Our results demonstrate that, surprisingly, the transport of photons that undergo low-order scattering events has only weak dependence on the optical properties of the medium (l_s and anisotropy factor g) and strong dependence on the spatial coherence length of illumination, L_sc, relative to those in the diffusion regime. More importantly, these low order scattering photons typically penetrate less than l_s into the medium due to low spatial coherence length of illumination and their penetration depth is proportional to the one-third power of the coherence volume (i.e. [l_s \pi L_sc^2 ]^1/3).Comment: 32 pages(including 7 figures), modified version to appear in Phys. Rev.