8,523 research outputs found
Brou\'e's abelian defect group conjecture holds for the Harada-Norton sporadic simple group
In representation theory of finite groups, there is a well-known and
important conjecture due to M. Brou\'e. He conjectures that, for any prime ,
if a -block of a finite group has an abelian defect group , then
and its Brauer corresponding block of the normaliser of in
are derived equivalent (Rickard equivalent). This conjecture is called
Brou\'e's abelian defect group conjecture. We prove in this paper that
Brou\'e's abelian defect group conjecture is true for a non-principal 3-block
with an elementary abelian defect group of order 9 of the Harada-Norton
simple group . It then turns out that Brou\'e's abelian defect group
conjecture holds for all primes and for all -blocks of the Harada-Norton
simple group .Comment: 36 page
On narrowing coated conductor film: emergence of granularity-induced field hysteresis of transport critical current
Critical current density Jc in polycrystalline or granular superconducting
material is known to be hysteretic with applied field H due to the focusing of
field within the boundary between adjacent grains. This is of concern in the
so-called coated conductors wherein superconducting film is grown on a
granular, but textured surface of a metal substrate. While previous work has
mainly been on Jc determined using induced or magnetization currents, the
present work utilizes transport current via an applied potential in strip
geometry. It is observed that the effect is not as pronounced using transport
current, probably due to a large difference in criterion voltage between the
two types of measurements. However, when the films are narrowed by patterning
into 200-, 100-, or 80-micron, the hysteresis is clearly seen, because of the
forcing of percolation across higher-angle grain boundaries. This effect is
compared for films grown on ion-beam-assisted-deposited (IBAD) YSZ substrate
and those grown on rolling-assisted-biaxially-textures substrates (RABiTS)
which have grains that are about ten times larger. The hysteresis is more
pronounced for the latter, which is more likely to have a weak grain boundary
spanning the width of the microbridge. This is also of concern to applications
in which coated conductors will be striated in order to reduce of AC losses.Comment: text-only: 10 pages, plus 5 figures on 5 page
Superconducting YBa2Cu3O7-δ nanocomposites using preformed ZrO2 nanocrystals : growth mechanisms and vortex pinning properties
Although high temperature superconductors are promising for power applications, the production of low-cost coated conductors with high current densitiesat high magnetic fieldsremains challenging. A superior superconducting YBa2Cu3O7- nanocomposite is fabricated via chemical solution deposition (CSD) using preformed nanocrystals (NCs). Preformed, colloidally stable ZrO2 NCs are added to the trifluoroacetic acid based precursor solution and the NCs' stability is confirmed up to 50 mol% for at least 2.5 months. These NCs tend to disrupt the epitaxial growth of YBa2Cu3O7-, unless a thin seed layer is applied. A 10 mol% ZrO2 NC addition proved to be optimal, yielding a critical current density J(C) of 5 MA cm(-2) at 77 K in self-field. Importantly, this new approach results in a smaller magnetic field decay of J(C)(H//c) for the nanocomposite compared to a pristine film. Furthermore, microstructural analysis of the YBa2Cu3O7- nanocomposite films reveals that different strain generation mechanisms may occur compared to the spontaneous segregation approach. Yet, the generated nanostrain in the YBa2Cu3O7- nanocomposite results in an improvement of the superconducting properties similar to the spontaneous segregation approach. This new approach, using preformed NCs in CSD coatings, can be of great potential for high magnetic field applications
Hybrid model for vascular tree structures
This paper proposes a new representation scheme of the cerebral blood
vessels. This model provides information on the semantics of the
vascular structure: the topological relationships between vessels and
the labeling of vascular accidents such as aneurysms and stenoses.
In addition, the model keeps information of the inner surface geometry
as well as of the vascular map volume properties, i.e. the tissue
density, the blood flow velocity and the vessel wall elasticity.
The model can be constructed automatically in a pre-process from a set
of segmented MRA images. Its memory requirements are optimized on the
basis of the sparseness of the vascular structure. It allows fast
queries and efficient traversals and navigations. The visualizations
of the vessel surface can be performed at different levels of
detail. The direct rendering of the volume is fast because the model
provides a natural way to skip over empty data.
The paper analyzes the memory requirements of the model along with the
costs of the most important operations on it.Postprint (published version
Brou\'e's abelian defect group conjecture holds for the double cover of the Higman-Sims sporadic simple group
In the representation theory of finite groups, there is a well-known and
important conjecture, due to Brou\'e saying that for any prime p, if a p-block
A of a finite group G has an abelian defect group P, then A and its Brauer
corresponding block B of the normaliser N_G(P) of P in G are derived
equivalent. We prove in this paper, that Brou\'e's abelian defect group
conjecture, and even Rickard's splendid equivalence conjecture are true for the
faithful 3-block A with an elementary abelian defect group P of order 9 of the
double cover 2.HS of the Higman-Sims sporadic simple group. It then turns out
that both conjectures hold for all primes p and for all p-blocks of 2.HS.Comment: 20 pages. arXiv admin note: substantial text overlap with
arXiv:1011.442
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