1,210 research outputs found
Classification of Extensions of Classifiable C*-algebras
We classify extensions of certain classifiable C*-algebras using the six term
exact sequence in K-theory together with the positive cone of the K_0-groups of
the distinguished ideal and quotient. We then apply our results to a class of
C*-algebras arising from substitutional shift spaces.Comment: 22 pages, Reordered some sections, an application involving graph
algebras is adde
Philosophical Foundations for Citizen Science
Citizen science is increasingly being recognized as an important approach for gathering data, addressing community needs, and creating fruitful engagement between citizens and professional scientists. Nevertheless, the implementation of citizen science projects can be hampered by a variety of barriers. Some of these are practical (e.g., lack of funding or lack of training for both professional scientists and volunteers), but others are theoretical barriers having to do with concerns about whether citizen science lives up to standards of good scientific practice. These concerns about the overall quality of citizen science are ethically significant, because it is ethically problematic to waste resources on low-quality research, and it is also problematic to denigrate or dismiss research that is of high quality. Scholarship from the philosophy of science is well-placed to address these theoretical barriers, insofar as it is fundamentally concerned about the nature of good scientific inquiry. This paper examines three important concerns: (1) the worry that citizen science is not appropriately hypothesis-driven; (2) the worry that citizen science does not generate sufficiently high-quality data or use sufficiently rigorous methods; and (3) the worry that citizen science is tainted by advocacy and is therefore not sufficiently disinterested. We show that even though some of these concerns may be relevant to specific instances of citizen science, none of these three concerns provides a compelling reason to challenge the overall quality of citizen science in principle
Stability analysis of dynamical regimes in nonlinear systems with discrete symmetries
We present a theorem that allows to simplify linear stability analysis of
periodic and quasiperiodic nonlinear regimes in N-particle mechanical systems
(both conservative and dissipative) with different kinds of discrete symmetry.
This theorem suggests a decomposition of the linearized system arising in the
standard stability analysis into a number of subsystems whose dimensions can be
considerably less than that of the full system. As an example of such
simplification, we discuss the stability of bushes of modes (invariant
manifolds) for the Fermi-Pasta-Ulam chains and prove another theorem about the
maximal dimension of the above mentioned subsystems
Classifying -algebras with both finite and infinite subquotients
We give a classification result for a certain class of -algebras
over a finite topological space in which there exists an
open set of such that separates the finite and infinite
subquotients of . We will apply our results to -algebras
arising from graphs.Comment: Version III: No changes to the text. We only report that Lemma 4.5 is
not correct as stated. See arXiv:1505.05951 for the corrected version of
Lemma 4.5. As noted in arXiv:1505.05951, the main results of this paper are
true verbatim. Version II: Improved some results in Section 3 and loosened
the assumptions in Definition 4.
Strain Tuning Three-state Potts Nematicity in a Correlated Antiferromagnet
Electronic nematicity, a state in which rotational symmetry is spontaneously
broken, has become a familiar characteristic of many strongly correlated
materials. One widely studied example is the discovered Ising-nematicity and
its interplay with superconductivity in tetragonal iron pnictides. Since
nematic directors in crystalline solids are restricted by the underlying
crystal symmetry, recently identified quantum material systems with three-fold
rotational (C3) symmetry offer a new platform to investigate nematic order with
three-state Potts character. Here, we report reversible strain tuning of the
three-state Potts nematicity in a zigzag antiferromagnetic insulator, FePSe3.
Probing the nematicity via optical linear dichroism, we demonstrate either
2{\pi}/3 or {\pi}/2 rotation of nematic director by uniaxial strain. The nature
of the nematic phase transition can also be controlled such that it undergoes a
smooth crossover transition, a Potts nematic transition, or a Ising nematic
flop transition. The ability to tune the nematic order with in-situ strain
further enables the extraction of nematic susceptibility, which exhibits a
divergent behavior near the magnetic ordering temperature. Our work points to
an active control approach to manipulate and explore nematicity in three-state
Potts correlated materials.Comment: 20 pages, 4 figures, 6 additional figures. Initial submission on May
30t
Pseudogap behavior in charge density wave kagome material ScVSn revealed by magnetotransport measurements
Over the last few years, significant attention has been devoted to studying
the kagome materials AVSb (A = K, Rb, Cs) due to their unconventional
superconductivity and charge density wave (CDW) ordering. Recently
ScVSn was found to host a CDW below 90K, and, like
AVSb, it contains a kagome lattice comprised only of V ions. Here we
present a comprehensive magnetotransport study on ScVSn. We discovered
several anomalous transport phenomena above the CDW ordering temperature,
including insulating behavior in interlayer resistivity, a strongly
temperature-dependent Hall coefficient, and violation of Kohler's rule. All
these anomalies can be consistently explained by a progressive decrease in
carrier densities with decreasing temperature, suggesting the formation of a
pseudogap. Our findings suggest that high-temperature CDW fluctuations play a
significant role in determining the normal state electronic properties of
ScVSn
Preservation of the metabolic rate of oxygen in preterm infants during indomethacin therapy for closure of the ductus arteriosus
Background:The aim of this study was to assess and quantify the effects of indomethacin on cerebral blood flow (CBF), oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen (CMRO 2) in preterm infants undergoing treatment for a patent ductus arteriosus (PDA).Methods:CBF and CMRO 2 were measured before and after the first dose of a 3-d course of indomethacin to close hemodynamically significant PDA in preterm neonates. Indocyanine-green (ICG) concentration curves were acquired before and after indomethacin injection to quantify CBF and CMRO 2.Results:Eight preterm neonates (gestational age, 27.6 ± 0.5 wk; birth weight, 992 ± 109 g; 6 males:2 females) were treated at a median age of 4.5 d (range, 4-21 d). Indomethacin resulted in an average CBF decrease of 18% (pre- and post-CBF = 12.9 ± 1.3 and 10.6 ± 0.8 ml/100 g/min, respectively) and an OEF increase of 11% (pre- and post-OEF = 0.38 ± 0.02 and 0.42 ± 0.02, respectively) but no significant change in CMRO 2 (pre- and post-CMRO 2 = 0.83 ± 0.07 and 0.76 ± 0.07 ml O 2 /100 g/min, respectively). Corresponding mean blood pressure (BP), arterial oxygen saturation (S a O 2), heart rate, and end-tidal carbon dioxide tension levels remained unchanged.Conclusion:Indomethacin resulted in significant reduction in CBF but did not alter CMRO 2 because of a compensatory increase in OEF. Copyright © 2013 International Pediatric Research Foundation, Inc
Homology and K--Theory Methods for Classes of Branes Wrapping Nontrivial Cycles
We apply some methods of homology and K-theory to special classes of branes
wrapping homologically nontrivial cycles. We treat the classification of
four-geometries in terms of compact stabilizers (by analogy with Thurston's
classification of three-geometries) and derive the K-amenability of Lie groups
associated with locally symmetric spaces listed in this case. More complicated
examples of T-duality and topology change from fluxes are also considered. We
analyse D-branes and fluxes in type II string theory on with torsion flux and demonstrate in details
the conjectured T-duality to with no flux. In the
simple case of , T-dualizing the circles reduces to
duality between with
flux and with no flux.Comment: 27 pages, tex file, no figure
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