6,856 research outputs found
A viscoplastic constitutive theory for metal matrix composites at high temperature
A viscoplastic constitutive theory is presented for representing the high temperature deformation behavior of metal matrix composites. The point of view taken is a continuum one where the composite is considered a material in its own right, with its own properties that can be determined for the composite as a whole. It is assumed that a single preferential (fiber) direction is identifiable at each material point (continuum element) admitting the idealization of local transverse isotropy. A key ingredient is the specification of an experimental program for the complete determination of the material functions and parameters for characterizing a particular metal matrix composite. The parameters relating to the strength of anisotropy can be determined through tension/torsion tests on longitudinally and circumferentially reinforced thin walled tubes. Fundamental aspects of the theory are explored through a geometric interpretation of some basic features analogous to those of the classical theory of plasticity
Dynamic RKKY interaction between magnetic moments in graphene nanoribbons
Graphene has been identified as a promising material with numerous
applications, particularly in spintronics. In this paper we investigate the
peculiar features of spin excitations of magnetic units deposited on graphene
nanoribbons and how they can couple through a dynamical interaction mediated by
spin currents. We examine in detail the spin lifetimes and identify a pattern
caused by vanishing density of states sites in pristine ribbons with armchair
borders. Impurities located on these sites become practically invisible to the
interaction, but can be made accessible by a gate voltage or doping. We also
demonstrate that the coupling between impurities can be turned on or off using
this characteristic, which may be used to control the transfer of information
in transistor-like devices.Comment: 10 pages, 10 figure
Yukawa Scalar Self-Mass on a Conformally Flat Background
We compute the one loop self-mass-squared of a massless, minimally coupled
scalar which is Yukawa-coupled to a massless Dirac fermion in a general
conformally flat background. Dimensional regularization is employed and a fully
renormalized result is obtained. For the special case of a locally de Sitter
background our result is manifestly de Sitter invariant. By solving the
effective field equations we show that the scalar mode functions acquire no
significant one loop corrections. In particular, the phenomenon of
super-adiabatic amplification is not affected. One consequence is that the
scalar-catalyzed production of fermions during inflation should not be reduced
by changes in the scalar sector before it has time to go to completion.Comment: 23 pages, LaTeX 2epsilon, 3 figures (uses axodraw
Mpemba Effect, Shechtman's Quasicrystals and Students' Exploring Activities
In the 1960s, Tanzanian student Erasto Mpemba and his teacher published an
article with the title "Cool" in the journal Physics Education (Mpemba, E. B. -
Osborne, D. G.: Cool?. In: Physics Education, vol.4, 1969, pp. 172-175.). In
this article they claimed that hot water freezes faster than cold water. The
article raised not only a wave of discussions, and other articles about this
topic, but also a whole series of new experiments, which should verify this
apparent thermodynamic absurdity and find an adequate explanation. Here we give
a review with references to explanations and we bring some proposals for
experimental student work in this area. We introduce Mpemba Effect not only as
a paradoxical physics phenomenon, but we shall present a strong educational
message that the Mpemba story brings to the teachers and their students. This
message also creates a bridge between this phenomenon and the discovery for
which the 2011 Nobel Prize in Chemistry was awarded. It leads to critical
adoption of traditional knowledge and encourages resilience in investigative
exploration of new things
Application of remote sensing to state and regional problems
The methods and procedures used, accomplishments, current status, and future plans are discussed for each of the following applications of LANDSAT in Mississippi: (1) land use planning in Lowndes County; (2) strip mine inventory and reclamation; (3) white-tailed deer habitat evaluation; (4) remote sensing data analysis support systems; (5) discrimination of unique forest habitats in potential lignite areas; (6) changes in gravel operations; and (7) determining freshwater wetlands for inventory and monitoring. The documentation of all existing software and the integration of the image analysis and data base software into a single package are now considered very high priority items
An Integro-Differential Equation of the Fractional Form: Cauchy Problem and Solution
Producción CientíficaWe solve the Cauchy problem defined by the fractional partial differential
equation [∂tt − κD]u = 0, with D the pseudo-differential Riesz operator of first
order, and certain initial conditions. The
solution of the Cauchy problem resulting from the substitution of the Gaussian pulse
u(x, 0) by the Dirac delta distribution ϕ(x) = μδ(x) is obtained as corollary.MINECO grant MTM2014-57129-C2-1-P
Advances in Plant Virus Evolution: Translating Evolutionary Insights into Better Disease Management
Recent studies in plant virus evolution are revealing that genetic
structure and behavior of virus and viroid populations can explain
important pathogenic properties of these agents, such as host resistance
breakdown, disease severity, and host shifting, among others.
Genetic variation is essential for the survival of organisms. The
exploration of how these subcellular parasites generate and maintain
a certain frequency of mutations at the intra- and inter-host
levels is revealing novel molecular virus–plant interactions. They
emphasize the role of host environment in the dynamic genetic
composition of virus populations. Functional genomics has identified
host factors that are transcriptionally altered after virus infections.
The analyses of these data by means of systems biology
approaches are uncovering critical plant genes specifically targeted
by viruses during host adaptation. Also, a next-generation resequencing
approach of a whole virus genome is opening new
avenues to study virus recombination and the relationships between
intra-host virus composition and pathogenesis. Altogether, the
analyzed data indicate that systematic disruption of some specific
parameters of evolving virus populations could lead to more efficient
ways of disease prevention, eradication, or tolerable virus–plant
coexistence.SD was supported by the NJ Agricultural Experiment Station. SFE was supported by grants from the Spanish Ministerio de Ciencia e Innovación (BFU2009-06993) and Generalitat Valenciana (PROMETEO2010/019). Work on CTV was supported by funding from USDA grants 2003-34399-13764 and 2005-34399-16070 to ZX. Work on BNYVV was funded by The Minnesota-North Dakota Research and Education Board, and The Beet Sugar Development Foundation. RAL thanks Ramon L. Jordan (USDA-ARS, MPPL), Rayapati A. Naidu(Washington State University), and Scott Adkins (USDA ARS USHRL) for their logistic support in the realization of the originating symposium.Peer reviewe
Advection and Taylor-Aris dispersion in rivulet flow
Motivated by the need for a better understanding of the transport of solutes in microfluidic flows with free surfaces, the advection and dispersion of a passive solute in steady unidirectional flow of a thin uniform rivulet on an inclined planar substrate driven by gravity and/or a uniform longitudinal surface shear stress are analysed. Firstly, we describe the short-time advection of both an initially semi-infinite and an initially finite slug of solute of uniform concentration. Secondly, we describe the long-time Taylor-Aris dispersion of an initially finite slug of solute. In particular, we obtain the general expression for the effective diffusivity for Taylor-Aris dispersion in such a rivulet, and discuss in detail its different interpretations in the special case of a rivulet on a vertical substrate
Rivulet flow of generalized Newtonian fluids
Steady unidirectional gravity-driven flow of a uniform thin rivulet (i.e. a rivulet with small transverse aspect ratio) of a generalised Newtonian fluid down a vertical planar substrate is considered. The parametric solution for any generalised Newtonian fluid whose viscosity can be expressed as a function of the shear rate, and the explicit solution for any generalised Newtonian fluid whose viscosity can be expressed as a function of the extra stress are obtained. These general solutions are used to describe rivulet flow of Carreau and Ellis fluids, highlighting the similarities and differences between the behaviour of these two fluids. In addition, the general behaviour of rivulets of nearly Newtonian fluids and of rivulets with small or large prescribed flux, as well as the behaviour of rivulets of strongly shear-thinning Carreau and Ellis fluids, are also described. It is found that whereas the monotonic dependence of the viscosity of a Carreau fluid on its three non-dimensional parameters and of an Ellis fluid on two of its three non-dimensional parameters leads to the expected dependence of the behaviour of the rivulet on these parameters (namely that increasing the viscosity of the fluid leads to a larger rivulet), the non-monotonic dependence of the viscosity of an Ellis fluid on the non dimensional parameter that measures the degree of shear thinning leads to a more complicated dependence of the behaviour of the rivulet on this parameter. In particular, it is also found that when the maximum extra stress in the rivulet is sufficiently large a rivulet of an Ellis fluid in the strongly shear-thinning limit in which this parameter becomes large comprises two regions with different viscosities. In the general case of non-zero viscosity in the limit of large extra stress the two regions have different constant viscosities, whereas in the special case of zero viscosity in the limit of large extra stress one region has constant viscosity and the other has a non-constant power-law viscosity, leading to a plug-like velocity profile with large magnitude in the narrow central region of the rivulet
Granular Elasticity without the Coulomb Condition
An self-contained elastic theory is derived which accounts both for
mechanical yield and shear-induced volume dilatancy. Its two essential
ingredients are thermodynamic instability and the dependence of the elastic
moduli on compression.Comment: 4pages, 2 figure
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