Real-time depth sectioning: Isolating the effect of stress on structure development in pressure-driven flow

Transient structure development at a specific distance from the channel wall in a pressure-driven flow is obtained from a set of real-time measurements that integrate contributions throughout the thickness of a rectangular channel. This “depth sectioning method” retains the advantages of pressure-driven flow while revealing flow-induced structures as a function of stress. The method is illustrated by applying it to isothermal shear-induced crystallization of an isotactic polypropylene using both synchrotron x-ray scattering and optical retardance. Real-time, depth-resolved information about the development of oriented precursors reveals features that cannot be extracted from ex-situ observation of the final morphology and that are obscured in the depth-averaged in-situ measurements. For example, at 137 °C and at the highest shear stress examined (65 kPa), oriented thread-like nuclei formed rapidly, saturated within the first 7 s of flow, developed significant crystalline overgrowth during flow and did not relax after cessation of shear. At lower stresses, threads formed later and increased at a slower rate. The depth sectioning method can be applied to the flow-induced structure development in diverse complex fluids, including block copolymers, colloidal systems, and liquid-crystalline polymers

The art of being human : a project for general philosophy of science

Throughout the medieval and modern periods, in various sacred and secular guises, the unification of all forms of knowledge under the rubric of ‘science’ has been taken as the prerogative of humanity as a species. However, as our sense of species privilege has been called increasingly into question, so too has the very salience of ‘humanity’ and ‘science’ as general categories, let alone ones that might bear some essential relationship to each other. After showing how the ascendant Stanford School in the philosophy of science has contributed to this joint demystification of ‘humanity’ and ‘science’, I proceed on a more positive note to a conceptual framework for making sense of science as the art of being human. My understanding of ‘science’ is indebted to the red thread that runs from Christian theology through the Scientific Revolution and Enlightenment to the Humboldtian revival of the university as the site for the synthesis of knowledge as the culmination of self-development. Especially salient to this idea is science‘s epistemic capacity to manage modality (i.e. to determine the conditions under which possibilities can be actualised) and its political capacity to organize humanity into projects of universal concern. However, the challenge facing such an ideal in the twentyfirst century is that the predicate ‘human’ may be projected in three quite distinct ways, governed by what I call ‘ecological’, ‘biomedical’ and ‘cybernetic’ interests. Which one of these future humanities would claim today’s humans as proper ancestors and could these futures co-habit the same world thus become two important questions that general philosophy of science will need to address in the coming years

On Characterizing the Data Access Complexity of Programs

Technology trends will cause data movement to account for the majority of energy expenditure and execution time on emerging computers. Therefore, computational complexity will no longer be a sufficient metric for comparing algorithms, and a fundamental characterization of data access complexity will be increasingly important. The problem of developing lower bounds for data access complexity has been modeled using the formalism of Hong & Kung's red/blue pebble game for computational directed acyclic graphs (CDAGs). However, previously developed approaches to lower bounds analysis for the red/blue pebble game are very limited in effectiveness when applied to CDAGs of real programs, with computations comprised of multiple sub-computations with differing DAG structure. We address this problem by developing an approach for effectively composing lower bounds based on graph decomposition. We also develop a static analysis algorithm to derive the asymptotic data-access lower bounds of programs, as a function of the problem size and cache size

Neutrino-Neutrino Scattering and Matter-Enhanced Neutrino Flavor Transformation in Supernovae

We examine matter-enhanced neutrino flavor transformation ($\nu_{\tau(\mu)}\rightleftharpoons\nu_e$) in the region above the neutrino sphere in Type II supernovae. Our treatment explicitly includes contributions to the neutrino-propagation Hamiltonian from neutrino-neutrino forward scattering. A proper inclusion of these contributions shows that they have a completely negligible effect on the range of $\nu_e$-$\nu_{\tau(\mu)}$ vacuum mass-squared difference, $\delta m^2$, and vacuum mixing angle, $\theta$, or equivalently $\sin^22\theta$, required for enhanced supernova shock re-heating. When neutrino background effects are included, we find that $r$-process nucleosynthesis from neutrino-heated supernova ejecta remains a sensitive probe of the mixing between a light $\nu_e$ and a $\nu_{\tau(\mu)}$ with a cosmologically significant mass. Neutrino-neutrino scattering contributions are found to have a generally small effect on the $(\delta m^2,\ \sin^22\theta)$ parameter region probed by $r$-process nucleosynthesis. We point out that the nonlinear effects of the neutrino background extend the range of sensitivity of $r$-process nucleosynthesis to smaller values of $\delta m^2$.Comment: 38 pages, tex, DOE/ER/40561-150-INT94-00-6

The retting of hemp II. Controlled retting of hemp

Retting of hemp is a biological process that results in the separation of the fiber bundles of the outer cortical sheath from the woody core and from each other by decomposition of the surrounding less resistant thin-walled cell~. Since the decomposition process is a continuing one, it must be terminated before damage to the fiber has commenced and yet it must be allowed to continue sufficiently long so that the fibers come away readily from the woody stalk and upon hackling separate from each other. The quality of the fiber is largely dependent upon the success of retting and the proper decision as to its end-point. Fiber from field-retted hemp cannot be expected to approach the uniformity and quality of that retted by controlled methods. Field retting in Iowa is dependent upon dew and rain to supply moisture for the activity of the microorganisms, which are predominantly fungi (8). Dew alone is usually quite insufficient to permit the hemp to ret completely. Hemp rets unevenly in the field because dew is deposited on the exposed surface of the stalks, causing retting to proceed more rapidly in this region than on the under side. This is partly overcome by turning the hemp during the process of retting, but in spite of this practice, retting is by no means uniform. When frequent rains accompanied by warm weather occur early in the fall, there is some danger of damage to the fiber through over-retting (7). Thus, field-retted hemp usually is a mixture of unretted, partly retted, well retted and overretted material

The retting of hemp III. Biochemical changes accompanying retting of hemp

Information as to the nature of the chemical changes that occur during the biological retting of hemp is scanty. Flax retting has been far more extensively studied, mostly by European workers; but it has frequently been implied that the principles involved and the problems met with are similar in flax and hemp retting. This subject is well reviewed by Thaysen and Bunker (9). It has been repeatedly stated that the essential biochemical change is the decomposition of the pectic substances present in the middle lamella of the parenchymatous tissue cells as a result of which the bundles become readily separable from the wood and the epidermis. It cannot be said, however, that there is clear analytical evidence for this statement. Moreover, there must be concurrent utilization of other tissue constituents, and progressively an attack on the fiber bundles, manifest in practice by the ultimate weakening and deterioration that occurs in over-retting. The processes that occur in retting constitute in fact the first stages in the decomposition of the hemp straw. Desirable changes that result in the liberation of the fibers pass imperceptibly into undesirable changes that result in impairment of quality. There is no certain way of determining when retting is complete. Reliance ordinarily is placed upon the judgment of the observer, which is based on the appearance of the straw and on simple mechanical tests. Whether the completion of retting under controlled conditions in tanks can properly be judged by standards similar to those applied to field-retted material is doubtful. Although the ultimate result is similar in that the fibers can be separated from the straw, it is not necessarily to be expected that the biochemical changes brought about by populations so different in character as those active in field retting, and those in deep tanks, are identical. In order to obtain information on the nature of the changes that occur to the constituents of the straw, samples of field retted and controlled retted hemp have been analyzed in some detail

MSW-like Enhancements without Matter

We study the effects of a scalar field, coupled only to neutrinos, on oscillations among weak interaction current eigenstates. The effect of a real scalar field appears as effective masses for the neutrino mass eigenstates, the same for \nbar as for \n. Under some conditions, this can lead to a vanishing of $\delta m^2$, giving rise to MSW-like effects. We discuss some examples and show that it is possible to resolve the apparent discrepancy in spectra required by r-process nucleosynthesis in the mantles of supernovae and by Solar neutrino solutions.Comment: 9 pages, latex, 1 figur