20,881 research outputs found
Multinomial selection index
Comparison of multivariate statistical analysis techniques for multinomial selection indice
Economical Filtration in Deep X-ray Therapy
A problem in deep x-ray therapy is to deliver to a deep seated malignant tumor, a sufficiently large dose of x-rays to affect the malignancy without permanent injury to the skin and intervening tissue. To accomplish this it is necessary to obtain a very penetrating beam of x-rays
Sample preparation for nanoanalytical electron microscopy using the FIB lift-out method and low energy ion milling
Thinning specimens to electron transparency for electron microscopy analysis can be done by conventional (2 - 4 kV) argon ion milling or focused ion beam (FIB) lift-out techniques. Both these methods tend to leave ''mottling'' visible on thin specimen areas, and this is believed to be surface damage caused by ion implantation and amorphisation. A low energy (250 - 500 V) Argon ion polish has been shown to greatly improve specimen quality for crystalline silicon samples. Here we investigate the preparation of technologically important materials for nanoanalysis using conventional and lift-out methods followed by a low energy polish in a GentleMill™ low energy ion mill. We use a low energy, low angle (6 - 8°) ion beam to remove the surface damage from previous processing steps. We assess this method for the preparation of technologically important materials, such as steel, silicon and GaAs. For these materials the ability to create specimens from specific sites, and to be able to image and analyse these specimens with the full resolution and sensitivity of the STEM, allows a significant increase of the power and flexibility of nanoanalytical electron microscopy
Cosmic Neutrino Last Scattering Surface
Neutrinos decoupled from the rest of the cosmic plasma when the Universe was
less than one second old, far earlier than the photons which decoupled at
t=380,000 years. Surprisingly, though, the last scattering surface of the
neutrinos is much closer to us than that of the photons. Here we calculate the
properties of the last scattering surfaces of the three species of neutrinos.Comment: Important reference to earlier work of Bisnovatyi-Kogan and Seidov
added, and mis-spelling of Opher reference correcte
Algebraic and combinatorial aspects of sandpile monoids on directed graphs
The sandpile group of a graph is a well-studied object that combines ideas
from algebraic graph theory, group theory, dynamical systems, and statistical
physics. A graph's sandpile group is part of a larger algebraic structure on
the graph, known as its sandpile monoid. Most of the work on sandpiles so far
has focused on the sandpile group rather than the sandpile monoid of a graph,
and has also assumed the underlying graph to be undirected. A notable exception
is the recent work of Babai and Toumpakari, which builds up the theory of
sandpile monoids on directed graphs from scratch and provides many connections
between the combinatorics of a graph and the algebraic aspects of its sandpile
monoid.
In this paper we primarily consider sandpile monoids on directed graphs, and
we extend the existing theory in four main ways. First, we give a combinatorial
classification of the maximal subgroups of a sandpile monoid on a directed
graph in terms of the sandpile groups of certain easily-identifiable subgraphs.
Second, we point out certain sandpile results for undirected graphs that are
really results for sandpile monoids on directed graphs that contain exactly two
idempotents. Third, we give a new algebraic constraint that sandpile monoids
must satisfy and exhibit two infinite families of monoids that cannot be
realized as sandpile monoids on any graph. Finally, we give an explicit
combinatorial description of the sandpile group identity for every graph in a
family of directed graphs which generalizes the family of (undirected)
distance-regular graphs. This family includes many other graphs of interest,
including iterated wheels, regular trees, and regular tournaments.Comment: v2: Cleaner presentation, new results in final section. Accepted for
publication in J. Combin. Theory Ser. A. 21 pages, 5 figure
Flourinated aryl ether polymers exhibiting dual fluoroolefin functionality and methods of forming same
Disclosed are telechelic fluoropolymers and methods for forming the polymers. The fluoropolymers can be formed via step-growth polymerization of bis(trifluorovinyloxy)biphenyls with bisphenols. The formed telechelic polymers possess fluoroolefin functionality at the trifluorovinyl aromatic ether endgroups. Internal groups can include difluorodioxyvinylene groups and trifluoroethyl groups. Formation methods of the telechelic polymers can be controlled so as to control molecular weight and degree of unsaturation of the polymers. The end groups and the internal groups can be further reacted independently of each other, e.g., under different temperature conditions, to form a variety of polymers and/or crosslinked polymeric networks
Professional Development Needs of Mid-Career Agriculture Teachers
Nationwide, agricultural education faces a shortage of teachers (National Teach Ag Campaign, 2014; Foster, Lawver, & Smith, 2016). To remedy this, both recruitment and retention efforts are necessary. While extensive research in agricultural education has focused on needs of beginning teachers, less research has focused on needs of agriculture teachers at later career stages. As such, the purpose of this phenomenological qualitative study was to explore challenges, activities, and professional development needs of mid-career agriculture teachers, particularly those within the “Experimentation/Activism” and “Reassessment/Self-Doubt” stages identified by Huberman (1989). The study narrowly focused on a census of 35 teachers from across the country who applied for a professional development program designed for mid-career agriculture teachers. Mid-career teachers identified lack of time, course planning, and programmatic expectations as challenges or obstacles. The teachers reported a desire to fulfill professional development needs by networking, reenergizing, and improving stress management. Specifically, teachers reported participating in professional organizations, joining teacher listservs, and networking through the National Association of Agricultural Educators’ Communities of Practice for engagement and support. Findings suggest continued professional development offerings and additional research related to mid-career agriculture teacher well-being are warranted
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