432 research outputs found
Projective dimension is a lattice invariant
We show that, for a free abelian group and prime power , every
direct sum decomposition of the group lifts to a direct sum
decomposition of . This is the key result we use to show that, if is a
commutative von Neumann regular ring, and a set of idempotents in
, then the projective dimension of the ideal as an
-module is the same as the projective dimension of the ideal ,
where is the boolean algebra generated by . This answers a thirty year old open question of R. Wiegand. The proof
is based on gaussian elimination on an matrix, with
adaptations enabling one to pass from the integers modulo to the
integers.Comment: LaTex. 16 page
The color of polarization in cuprate superconductors
A technique for the identification of individual anisotropic grains in a heterogeneous and opaque material involves the observation of grain color in reflected light through crossed polarizers (color of polarization). Such colors are generally characteristic of particular phases. When grains of many members of the class of hole carrier cuprate superconductors are so viewed, using a xenon light source (600 K color temperature), a characteristic color of polarization is observed. This color was studied in many of these cuprate superconductors and a strong correlation was found between color and the existence of superconductivity. One of the members of the electron carrier cuprate superconductors (Nd(1.85)Ce(.15)CuO(4-x) was examined and found that it possesses the same color of polarization as all the electron hole carrier cuprate superconductors so far examined. The commonality of the characteristic color in the cuprate superconductors indicated that the presence of this color is independent of the nature of charge carriers. The correlation of this color with existence of superconductivity suggests that the origin of the color relates to the origin of superconductivity in the cuprate superconductors. Photometric techniques are also discussed
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
Design and operation of a cryogenic charge-integrating preamplifier for the MuSun experiment
The central detector in the MuSun experiment is a pad-plane time projection
ionization chamber that operates without gas amplification in deuterium at 31
K; it is used to measure the rate of the muon capture process . A new charge-sensitive preamplifier, operated at
140 K, has been developed for this detector. It achieved a resolution of 4.5
keV(D) or 120 RMS with zero detector capacitance at 1.1 s
integration time in laboratory tests. In the experimental environment, the
electronic resolution is 10 keV(D) or 250 RMS at a 0.5 s
integration time. The excellent energy resolution of this amplifier has enabled
discrimination between signals from muon-catalyzed fusion and muon capture on
chemical impurities, which will precisely determine systematic corrections due
to these processes. It is also expected to improve the muon tracking and
determination of the stopping location.Comment: 18 pages + title page, 13 figures, to be submitted to JINST; minor
corrections, added one reference, updated author lis
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
Climate change litigation: a review of research on courts and litigants in climate government
Studies of climate change litigation have proliferated over the past two decades, as lawsuits across the world increasingly bring policy debates about climate change mitigation and adaptation, as well as climate change‐related loss and damage to the attention of courts. We systematically identify 130 articles on climate change litigation published in English in the law and social sciences between 2000 and 2018 to identify research trajectories. In addition to a budding interdisciplinarity in scholarly interest in climate change litigation we also document a growing understanding of the full spectrum of actors involved and implicated in climate lawsuits and the range of motivations and/or strategic imperatives underpinning their engagement with the law. Situating this within the broader academic literature on the topic we then highlight a number of cutting edge trends and opportunities for future research. Four emerging themes are explored in detail: the relationship between litigation and governance; how time and scale feature in climate litigation; the role of science; and what has been coined the “human rights turn” in climate change litigation. We highlight the limits of existing work and the need for future research—not limited to legal scholarship—to evaluate the impact of both regulatory and anti‐regulatory climate‐related lawsuits, and to explore a wider set of jurisdictions, actors and themes. Addressing these issues and questions will help to develop a deeper understanding of the conditions under which litigation will strengthen or undermine climate governance. This article is categorized under: Policy and Governance > Multilevel and Transnational Climate Change Governanc
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
Observation of a Transition from BCS to HTSC-like Superconductivity in Ba_{1-x}K_xBiO_3 Single Crystals
A study of temperature dependences of the upper critical field B_{c2}(T) and
surface impedance Z(T)=R(T)+iX(T) in Ba_{1-x}K_xBiO_3 single crystals that have
transition temperatures in the range 6 x>0.4) reveals
a transition from BCS to unusual type of superconductivity. B_{c2}(T) curves
corresponding to the crystals that have T_c>20 K have positive curvature (like
in some HTSC), and those of the crystals with T_c<15 K fall on the usual
Werthamer-Helfand-Hohenberg curve. R(T) and X(T) dependences of the crystals
with T_c~30 K and T_c~11 K are respectively linear (like in HTSC) and
exponential (BCS) in the temperature range T << T_c. The experimental results
are discussed in connection with the extended saddle point model by Abrikosov.Comment: 5 pages, 5 figure
Upper critical field for electrons in two-dimensional lattice
We address a problem of the upper critical field in a lattice described by a
two-dimensional tight-binding model with the on-site pairing. We develop a
finite-system-approach which enables investigation of magnetic and
superconducting properties of electrons on clusters, consisting of a few
thousand sites. We discuss how the quasiparticle density of states changes with
the applied external magnetic field and present the temperature dependence of
the upper critical field. We also briefly discuss possible extension of the
model to account for the properties of high-temperature superconductors.Comment: 4 pages, 3 postscript figures, revte
Ergodic versus nonergodic behavior in oxygen deficient high-T_c superconductors
The oxygen defects induced phase transition from nonergodic to ergodic state
in superconductors with intragrain granularity is considered within the
superconductive glass model. The model predictions are found to be in a
qualitative agreement with some experimental observations in deoxygenated
high-T_c single crystals
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