17,495 research outputs found
The Electronic and Superconducting Properties of Oxygen-Ordered MgB2 compounds of the form Mg2B3Ox
Possible candidates for the Mg2B3Ox nanostructures observed in bulk of
polycrystalline MgB2 (Ref.1) have been studied using a combination of
Z-contrast imaging, electron energy loss spectroscopy (EELS) and
first-principles calculations. The electronic structures, phonon modes, and
electron phonon coupling parameters are calculated for two oxygen-ordered MgB2
compounds of composition Mg2B3O and Mg2B3O2, and compared with those of MgB2.
We find that the density of states for both Mg2B3Ox structures show very good
agreement with EELS, indicating that they are excellent candidates to explain
the observed coherent oxygen precipitates. Incorporation of oxygen reduces the
transition temperature and gives calculated TC values of 18.3 K and 1.6 K for
Mg2B3O and Mg2B3O2, respectively.Comment: Submitted to PR
Power-law random walks
We present some new results about the distribution of a random walk whose
independent steps follow a Gaussian distribution with exponent
. In the case we show that a stochastic
representation of the point reached after steps of the walk can be
expressed explicitly for all . In the case we show that the random
walk can be interpreted as a projection of an isotropic random walk, i.e. a
random walk with fixed length steps and uniformly distributed directions.Comment: 5 pages, 4 figure
The vitality, adulteration and impurities of Clover, Alfalfa and Timothy seed for sale in Iowa in 1906.
Clover and timothy are the most important hay crops grown in Iowa. The census of 1905 gives the area devoted to the growing of red clover in the state as 237,309 acres; of timothy as 3,642,424 acres. These figures do not Include the area devoted to minor clover crops such as alsike and white clover. It may be said, however, that only a small area in the state is devoted to the growing of the former. The white clover crop covers a much larger area than any other of the leguminous plants. It is, however, seldom sown as a forage crop, but it is largely spontaneous in pastures. Borne seasons it is abundant and in others it Constitutes only a small part of the forage in pastures. In addition to its use for this purpose it is sown in lawns as a nurse crop. Alfalfa is cultivated only to a limited extent in Iowa; the area thus devoted is not ascertainable, but is small. The demand for alfalfa seed is continually increasing, largely because of the success attending its cultivation in suitable soils and locations. This success has induced a large number of farmers to try it in an experimental way
Service Learning as Scholarship in Teacher Education
This article describes how two teacher education service-learning programs illustrate alternative interpretations of scholarship. A tutoring-mentoring program in a teaching oriented masters institution and a motor skill development program in a land grant doctoral-research institution are described relative to how each illustrates forms of scholarship as interpreted by Boyer ( 1990). We discuss how these forms of scholarship the scholarship of discovery, integration, teaching, and application--relate to stated institutional mission and evaluation practices. Service-learning experiences for preservice teachers can have the multiple benefits of promoting an ethic of service and social responsibility, demonstrating excellence in teacher education, and exemplifying scholarly endeavors
Morphological Observations of Mineralizing Pericardium Cardiac Grafts
Pericardial patch grafters were implanted in the hearts of young sheep for periods ranging from two to 120 days. Explants seven to 21 days old revealed the formation of a pseudoneointima (PNI) on the blood contacting surface of the pericardium. The PNI was more heavily mineralized than the pericardium. Mineralization was most intense on the blood contacting surface of the PNI and on the chamber surface of the pericardium. After three weeks of implantation, the PNI was much thinner and was organized into a thin fibrous capsule without any signs of mineralization. In the pericardium, mineral deposits were seen in fibroblasts. Moreover, cell-related mineralization was evident prior to calcification of the surrounding collagen matri
Search for antiproton decay at the Fermilab Antiproton Accumulator
A search for antiproton decay has been made at the Fermilab Antiproton
Accumulator. Limits are placed on thirteen antiproton decay modes. The results
include the first explicit experimental limits on the muonic decay modes of the
antiproton, and the first limits on the decay modes e- gamma gamma, and e-
omega. The most stringent limit is for the decay mode pbar-> e- gamma. At 90%
C.L. we find that tau/B(pbar-> e- gamma) > 7 x 10^5 yr. The most stringent
limit for decay modes with a muon in the final state is for the decay pbar->
mu- gamma. At 90% C.L. we find that tau/B(pbar-> mu- gamma) > 5 x 10^4 yr.Comment: 20 pages, 8 figures. Submitted to Phys. Rev. D. Final results on 13
channels (was 15) are presente
A statistical mechanics description of environmental variability in metabolic networks
Many of the chemical reactions that take place within a living cell are irreversible. Due to evolutionary pressures, the number of allowable reactions within these systems are highly constrained and thus the resulting metabolic networks display considerable asymmetry. In this paper, we explore possible evolutionary factors pertaining to the reduced symmetry observed in these networks, and demonstrate the important role environmental variability plays in shaping their structural organization. Interpreting the returnability index as an equilibrium constant for a reaction network in equilibrium with a hypothetical reference system, enables us to quantify the extent to which a metabolic network is in disequilibrium. Further, by introducing a new directed centrality measure via an extension of the subgraph centrality metric to directed networks, we are able to characterise individual metabolites by their participation within metabolic pathways. To demonstrate these ideas, we study 116 metabolic networks of bacteria. In particular, we find that the equilibrium constant for the metabolic networks decreases significantly in-line with variability in bacterial habitats, supporting the view that environmental variability promotes disequilibrium within these biochemical reaction system
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