229 research outputs found
Simple groups, product actions, and generalized quadrangles
The classification of flag-transitive generalized quadrangles is a long-standing open problem at the interface of finite geometry and permutation group theory. Given that all known flag-transitive generalized quadrangles are also point-primitive (up to point–line duality), it is likewise natural to seek a classification of the point-primitive examples. Working toward this aim, we are led to investigate generalized quadrangles that admit a collineation grouppreserving a Cartesian product decomposition of the set of points. It is shown that, under a generic assumption on, the number of factors of such a Cartesian product can be at most four. This result is then used to treat various types of primitive and quasiprimitive point actions. In particular, it is shown thatcannot haveholomorph compoundO’Nan–Scott type. Our arguments also pose purely group-theoretic questions about conjugacy classes in nonabelian finite simple groups and fixities of primitive permutation groups.</jats:p
Structure and magnetic order in Fe2+xV1-xAl
We present a detailed structural investigation via neutron diffraction of
differently heat treated samples Fe2VAl and Fe2+xV1-xAl. Moreover, the magnetic
behaviour of these materials is studied by means of mSR and
Mossbauer-experiments. Our structural investigation indicates that quenched
Fe2VAl, exhibiting the previously reported "Kondo insulating like" behaviour,
is off-stoichiometric (6%) in its Al content. Slowly cooled Fe2VAl is
structurally better ordered and stoichiometric, and the microscopic magnetic
probes establish long range ferromagnetic order below TC = 13K, consistent with
results from bulk experiments. The magnetic state can be modelled as being
generated by diluted magnetic ions in a non-magnetic matrix. Quantitatively,
the required number of magnetic ions is too large as to be explained by a model
of Fe/V site exchange. We discuss the implications of our findings for the
ground state properties of Fe2VAl, in particular with respect to the role of
crystallographic disorder.Comment: accepted for publication in J. Phys.: Condens. Matte
Electronic Structure, Local Moments and Transport in Fe_2VAl
Local spin density approximation calculations are used to elucidate
electronic and magnetic properties of Heusler structure Fe_2VAl. The compound
is found to be a low carrier density semimetal. The Fermi surface has small
hole pockets derived from a triply degenerate Fe derived state at Gamma
compensated by an V derived electron pocket at the X point. The ideal compound
is found to be stable against ferromagnetism. Fe impurities on V sites,
however, behave as local moments. Because of the separation of the hole and
electron pockets the RKKY interaction between such local moments should be
rapidly oscillating on the scale of its decay, leading to the likelihood of
spin-glass behavior for moderate concentrations of Fe on V sites. These
features are discussed in relation to experimental observations of an unusual
insulating state in this compound.Comment: 16 pages, RevTeX, 5 figure
Implications of COVID-19 on Public Policy, Supply Chain Disruptions, and Monitoring Methods
Transmission of the severe acute respiratory syndrome coronavirus 2, referred to as COVID-19, has persisted beyond 2020 and led to a global pandemic with far reaching consequences. Many changes in public policy and health measures were developed and implemented with the intention of slowing the spread of the novel virus. Disruptions from the global pandemic created major supply chain consequences due to stockpiling of essential goods (alcohol-based hand sanitizers and surface disinfectants), impacts on trade routes, and limitations on modes of transportation due to border closures. Rapid increase in the use of hand sanitizers and surface disinfectants significantly affected the production capacity of high-quality ethanol (e.g., USP and FCC grade) resulting in regulatory changes in countries facing shortages. Prompt enactment of government policies allowed for use of alcohol with higher impurities to offset heightened demand and increase commercial availability. Changes in monitoring methods were also observed, where many agencies began to track viral shedding through municipal wastewater. In this chapter, we will discuss the impacts of COVID-19 on public policies and health measures, economics as it relates to supply chain disruptions, and the implementation of novel monitoring methods to survey the spread of COVID-19
The Aggregation Inhibitor Peptide QBP1 as a Therapeutic Molecule for the Polyglutamine Neurodegenerative Diseases
Misfolding and abnormal aggregation of proteins in the brain are implicated in the pathogenesis of various neurodegenerative diseases including Alzheimer's, Parkinson's, and the polyglutamine (polyQ) diseases. In the polyQ diseases, an abnormally expanded polyQ stretch triggers misfolding and aggregation of the disease-causing proteins, eventually resulting in neurodegeneration. In this paper, we introduce our therapeutic strategy against the polyQ diseases using polyQ binding peptide 1 (QBP1), a peptide that we identified by phage display screening. We showed that QBP1 specifically binds to the expanded polyQ stretch and inhibits its misfolding and aggregation, resulting in suppression of neurodegeneration in cell culture and animal models of the polyQ diseases. We further demonstrated the potential of protein transduction domains (PTDs) for in vivo delivery of QBP1. We hope that in the near future, chemical analogues of aggregation inhibitor peptides including QBP1 will be developed against protein misfolding-associated neurodegenerative diseases
Single-sex schistosome infections of definitive hosts: Implications for epidemiology and disease control in a changing world
Integrated modeling and validation for phase change with natural convection
Water-ice systems undergoing melting develop complex spatio-temporal
interface dynamics and a non-trivial temperature field. In this contribution,
we present computational aspects of a recently conducted validation study that
aims at investigating the role of natural convection for cryo-interface
dynamics of water-ice. We will present a fixed grid model known as the enthalpy
porosity method. It is based on introducing a phase field and employs mixture
theory. The resulting PDEs are solved using a finite volume discretization. The
second part is devoted to experiments that have been conducted for model
validation. The evolving water-ice interface is tracked based on optical images
that shows both the water and the ice phase. To segment the phases, we use a
binary Mumford Shah method, which yields a piece-wise constant approximation of
the imaging data. Its jump set is the reconstruction of the measured phase
interface. Our combined simulation and segmentation effort finally enables us
to compare the modeled and measured phase interfaces continuously. We conclude
with a discussion of our findings
Invariant higher-order variational problems II
Motivated by applications in computational anatomy, we consider a
second-order problem in the calculus of variations on object manifolds that are
acted upon by Lie groups of smooth invertible transformations. This problem
leads to solution curves known as Riemannian cubics on object manifolds that
are endowed with normal metrics. The prime examples of such object manifolds
are the symmetric spaces. We characterize the class of cubics on object
manifolds that can be lifted horizontally to cubics on the group of
transformations. Conversely, we show that certain types of non-horizontal
geodesics on the group of transformations project to cubics. Finally, we apply
second-order Lagrange--Poincar\'e reduction to the problem of Riemannian cubics
on the group of transformations. This leads to a reduced form of the equations
that reveals the obstruction for the projection of a cubic on a transformation
group to again be a cubic on its object manifold.Comment: 40 pages, 1 figure. First version -- comments welcome
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