393 research outputs found
A hierarchy of parametrizing varieties for representations
The primary purpose is to introduce and explore projective varieties,
, parametrizing the full collection of those
modules over a finite dimensional algebra which have dimension vector
. These varieties extend the smaller varieties previously studied by the
author; namely, the projective varieties encoding those modules with dimension
vector which, in addition, have a preassigned top or radical layering.
Each of the is again partitioned by the action
of a linear algebraic group, and covered by certain
representation-theoretically defined affine subvarieties which are stable under
the unipotent radical of the acting group. A special case of the pertinent
theorem served as a cornerstone in the work on generic representations by
Babson, Thomas, and the author. Moreover, applications are given to the study
of degenerations
The 2015 Paris Agreement on Climate Change: Significance and Implications for the Future
On December 12, 2015, nearly 200 countries created a major new agreement on climate change, accompanied by national commitments to act. The Paris Agreement has rightly been celebrated as a breakthrough, but was unquestionably constrained by the need for compromise, and its details will continue to be developed at the international, national, and local levels. On January 9, 2016, a panel of expert commentators and delegation members from a variety of national jurisdictions convened at the annual American Association of Law Schools meeting to analyze the Paris Agreement; they considered how the agreement evolved from prior efforts, the structure of its commitments, and its implications for the future. This Dialogue presents a transcript of the discussion, which has been edited for style, clarity, and space considerations
Almost clean rings and arithmetical rings
It is shown that a commutative B\'ezout ring with compact minimal prime
spectrum is an elementary divisor ring if and only if so is for each
minimal prime ideal . This result is obtained by using the quotient space
of the prime spectrum of the ring modulo the equivalence
generated by the inclusion. When every prime ideal contains only one minimal
prime, for instance if is arithmetical, is Hausdorff and
there is a bijection between this quotient space and the minimal prime spectrum
, which is a homeomorphism if and only if is
compact. If is a closed point of , there is a pure ideal
such that . If is almost clean, i.e. each element is the
sum of a regular element with an idempotent, it is shown that is totally disconnected and, , is
almost clean; the converse holds if every principal ideal is finitely
presented. Some questions posed by Facchini and Faith at the second
International Fez Conference on Commutative Ring Theory in 1995, are also
investigated. If is a commutative ring for which the ring of
quotients of is an IF-ring for each proper ideal , it is proved that
is a strongly discrete valuation ring for each maximal ideal and
is semicoherent for each proper ideal
Parameter-free expression for superconducting Tc in cuprates
A parameter-free expression for the superconducting critical temperature of
layered cuprates is derived which allows us to express Tc in terms of
experimentally measured parameters. It yields Tc values observed in about 30
lanthanum, yttrium and mercury-based samples for different levels of doping.
This remarkable agreement with the experiment as well as the unusual critical
behaviour and the normal-state gap indicate that many cuprates are close to the
Bose-Einstein condensation regime.Comment: 5 pages, 2 figures. Will be published in Physical Review
Poor screening and nonadiabatic superconductivity in correlated systems
In this paper we investigate the role of the electronic correlation on the
hole doping dependence of electron-phonon and superconducting properties of
cuprates. We introduce a simple analytical expression for the one-particle
Green's function in the presence of electronic correlation and we evaluate the
reduction of the screening properties as the electronic correlation increases
by approaching half-filling. The poor screening properties play an important
role within the context of the nonadiabatic theory of superconductivity. We
show that a consistent inclusion of the reduced screening properties in the
nonadiabatic theory can account in a natural way for the - phase
diagram of cuprates. Experimental evidences are also discussed.Comment: 12 Pages, 6 Figures, Accepted on Physical Review
Evaluating the potential for the environmentally sustainable control of foot and mouth disease in Sub-Saharan Africa
Strategies to control transboundary diseases have in the past generated unintended negative consequences for both the environment and local human populations. Integrating perspectives from across disciplines, including livestock, veterinary and conservation sectors, is necessary for identifying disease control strategies that optimise environmental goods and services at the wildlife-livestock interface. Prompted by the recent development of a global strategy for the control and elimination of foot-and-mouth disease (FMD), this paper seeks insight into the consequences of, and rational options for potential FMD control measures in relation to environmental, conservation and human poverty considerations in Africa. We suggest a more environmentally nuanced process of FMD control that safe-guards the integrity of wild populations and the ecosystem dynamics on which human livelihoods depend while simultaneously improving socio-economic conditions of rural people. In particular, we outline five major issues that need to be considered: 1) improved understanding of the different FMD viral strains and how they circulate between domestic and wildlife populations; 2) an appreciation for the economic value of wildlife for many African countries whose presence might preclude the country from ever achieving an FMD-free status; 3) exploring ways in which livestock production can be improved without compromising wildlife such as implementing commodity-based trading schemes; 4) introducing a participatory approach involving local farmers and the national veterinary services in the control of FMD; and 5) finally the possibility that transfrontier conservation might offer new hope of integrating decision-making at the wildlife-livestock interface
Measurements of Spin Polarization of Epitaxial SrRuO3 Thin Films
We have measured the transport spin-polarization of epitaxial thin films of
the conductive ferromagnetic oxide, SrRuO3, using Point Contact Andreev
Reflection Spectroscopy (PCAR). In spite of the fact that spin-up and spin-down
electronic densities of states at the Fermi level for SrRuO3 calculated from
band structure theory are practically the same, the experimental transport spin
polarization for these films was found to be about 50%. This result is a direct
consequence of the Fermi velocity disparity between the majority and minority
bands and is in good agreement with our theoretical estimates.Comment: 12 pages pdf onl
Disorder and Quantum Fluctuations in Superconducting Films in Strong Magnetic Fields
We find that the upper critical field in a two-dimensional disordered
superconductor can increase essentially at low temperatures. This happens due
to the formation of local superconducting islands weakly coupled via the
Josephson effect. The distribution of the superconducting islands is derived.
It is shown that the value of the critical field is determined by the interplay
of the proximity effect and quantum phase fluctuations. We find that the shift
of the upper critical field is connected with the pinning properties of a
superconductor.Comment: 4 page
Transport spin polarization of Ni_xFe_{1-x}: electronic kinematics and band structure
We present measurements of the transport spin polarization of Ni_xFe_{1-x}
(0<x<1) using the recently-developed Point Contact Andreev Reflection
technique, and compare them with our first principles calculations of the spin
polarization for this system. Surpisingly, the measured spin polarization is
almost composition-independent. The results clearly demonstrate that the sign
of the transport spin polarization does not coincide with that of the
difference of the densities of states at the Fermi level. Calculations indicate
that the independence of the spin polarization of the composition is due to
compensation of density of states and Fermi velocity in the s- and d- bands
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