Mechanical properties of a degradable phosphate glass fibre reinforced polymer composite for internal fracture fixation

NOTICE: this is the author’s version of a work that was accepted for publication in Materials Science and Engineering. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Materials Science and Engineering, [VOL 30, ISSUE 7, (2010)] DOI: 10.1016/j.msec.2010.04.017

Aggregation kinetics of stiff polyelectrolytes in the presence of multivalent salt

Using molecular dynamics simulations, the kinetics of bundle formation for stiff polyelectrolytes such as actin is studied in the solution of multivalent salt. The dominant kinetic mode of aggregation is found to be the case of one end of one rod meeting others at right angle due to electrostatic interactions. The kinetic pathway to bundle formation involves a hierarchical structure of small clusters forming initially and then feeding into larger clusters, which is reminiscent of the flocculation dynamics of colloids. For the first few cluster sizes, the Smoluchowski formula for the time evolution of the cluster size gives a reasonable account for the results of our simulation without a single fitting parameter. The description using Smoluchowski formula provides evidence for the aggregation time scale to be controlled by diffusion, with no appreciable energy barrier to overcome.Comment: 6 pages, 5 figures, Phys. Rev. E (Accepted

Dynamics of Labor Demand: Evidence from Plant-level Observations and Aggregate Implications

This paper studies the dynamics of labor demand at the plant and aggregate levels. The correlation of hours and employment growth is negative at the plant level and positive in aggregate time series. Further, hours and employment growth are about equally volatile at the plant level while hours growth is much less volatile than employment growth in the aggregate data. Given these differences, we specify and estimate the parameters of a plant-level dynamic optimization problem using simulated method of moments to match plant-level observations. Our findings indicate that non-convex adjustment costs are critical for explaining plant-level moments on hours and employment. Aggregation generates time series implications which are broadly consistent with observation. Further, we find that a model with quadratic adjustment costs alone can also broadly match the aggregate facts.

Preparation of US Engineering Students for International Practice

There are many driving forces for the preparation of engineering students for international practice. Engineers must design and develop products for multinational markets. Materials and components must be sought worldwide to be competitive. Engineers may practice directly in foreign countries for part of a career. Multinational company engineers must work with international teams. Several basic elements are needed to prepare engineers for international practice: foreign language proficiency, cultural background development, international business knowledge, and international technical knowledge. Further detailed descriptions of what is needed are provided by the Institute for International Education and the US Foreign Service Officer Program. Some engineering schools currently employ one or more of the following mechanisms to prepare their students for international practice: • Traditional study abroad programs • Study abroad plus language • Electronic trans-national teams • Group term abroad • Double degree approach • Engineering cultures study • Engineers without borders • Technical internships abroad Currently only a very small percentage of US engineering students participate in any of these mechanisms for international experience. Only 4139 engineering students studied abroad in 1999-2000, for example. Electronic experiences, which can be scaled up more easily than study or work abroad, may provide one way to increase this low percentage. One major situation that needs improvement is the expansion of international experiences for engineering faculty members

Letter from Israel C. Russel to John Muir, 1893 Nov 14.

[letterhead][in margin: Aug 26 = 150wide 2 to 3 ft deep]Ann Arbor, November 14 1893My dear Muir:In conversation with you while in route for Alaska, in 1890, you told about a lake somewhere in southeastern Alaska. of the same nature as Ma[illegible]n lake. Switzerland. [As?] the lake referred to has never been [illegible] so far as I am aware, I venture to ask if you will kindly send me a few facts concerning it. Will you tell me what glacier holds it in [check?] its l location, size etc. I wish to use the information in a t[illegible] book I am preparing and will give full credit. Hoping that you can oblige me. I remain sincerely yourIsrael C. RussellAnn Arbor. Mich.0174

Local structure of percolating gels at very low volume fractions

The formation of colloidal gels is strongly dependent on the volume fraction of the system and the strength of the interactions between the colloids. Here we explore very dilute solutions by the means of numerical simulations, and show that, in the absence of hydrodynamic interactions and for sufficiently strong interactions, percolating colloidal gels can be realised at very low values of the volume fraction. Characterising the structure of the network of the arrested material we find that, when reducing the volume fraction, the gels are dominated by low-energy local structures, analogous to the isolated clusters of the interaction potential. Changing the strength of the interaction allows us to tune the compactness of the gel as characterised by the fractal dimension, with low interaction strength favouring more chain-like structures

A Long-Lived Accretion Disk Around a Lithium-Depleted Binary T Tauri Star

We present a high dispersion optical spectrum of St 34 and identify the system as a spectroscopic binary with components of similar luminosity and temperature (both M3+/-0.5). Based on kinematics, signatures of accretion, and location on an H-R diagram, we conclude that St 34 is a classical T Tauri star belonging to the Taurus-Auriga T Association. Surprisingly, however, neither component of the binary shows LiI 6708 A, absorption, the most universally accepted criterion for establishing stellar youth. In this uniquely known instance, the accretion disk appears to have survived longer than the lithium depletion timescale. We speculate that the long-lived accretion disk is a consequence of the sub-AU separation companion tidally inhibiting, though not preventing, circumstellar accretion. Comparisons with pre-main sequence evolutionary models imply, for each component of St 34, a mass of 0.37+/-0.08 Msun and an isochronal age of 8+/-3 Myr, which is much younger than the predicted lithium depletion timescale of ~ 25 Myr. Although a distance 38% closer than that of Taurus-Auriga or a hotter temperature scale could reconcile this discrepancy at 21-25 Myr, similar discrepancies in other systems and the implications of an extremely old accreting Taurus-Auriga member suggest instead a possible problem with evolutionary models. Regardless, the older age implied by St 34's depleted lithium abundance is the first compelling evidence for a substantial age spread in this region. Additionally, since St 34's coeval co-members with early M spectral types would likewise fail the lithium test for youth, current membership lists may be incomplete.Comment: 4 pages, including 2 figures. Accepted for publication in ApJ Let