1,571 research outputs found
Nonexistence of Certain Skew-symmetric Amorphous Association Schemes
An association scheme is amorphous if it has as many fusion schemes as
possible. Symmetric amorphous schemes were classified by A. V. Ivanov [A. V.
Ivanov, Amorphous cellular rings II, in Investigations in algebraic theory of
combinatorial objects, pages 39--49. VNIISI, Moscow, Institute for System
Studies, 1985] and commutative amorphous schemes were classified by T. Ito, A.
Munemasa and M. Yamada [T. Ito, A. Munemasa and M. Yamada, Amorphous
association schemes over the Galois rings of characteristic 4, European J.
Combin., 12(1991), 513--526]. A scheme is called skew-symmetric if the diagonal
relation is the only symmetric relation. We prove the nonexistence of
skew-symmetric amorphous schemes with at least 4 classes. We also prove that
non-symmetric amorphous schemes are commutative.Comment: 10 page
Laplacian spectral characterization of roses
A rose graph is a graph consisting of cycles that all meet in one vertex. We
show that except for two specific examples, these rose graphs are determined by
the Laplacian spectrum, thus proving a conjecture posed by Lui and Huang [F.J.
Liu and Q.X. Huang, Laplacian spectral characterization of 3-rose graphs,
Linear Algebra Appl. 439 (2013), 2914--2920]. We also show that if two rose
graphs have a so-called universal Laplacian matrix with the same spectrum, then
they must be isomorphic. In memory of Horst Sachs (1927-2016), we show the
specific case of the latter result for the adjacency matrix by using Sachs'
theorem and a new result on the number of matchings in the disjoint union of
paths
Random matrix theory and symmetric spaces
In this review we discuss the relationship between random matrix theories and
symmetric spaces. We show that the integration manifolds of random matrix
theories, the eigenvalue distribution, and the Dyson and boundary indices
characterizing the ensembles are in strict correspondence with symmetric spaces
and the intrinsic characteristics of their restricted root lattices. Several
important results can be obtained from this identification. In particular the
Cartan classification of triplets of symmetric spaces with positive, zero and
negative curvature gives rise to a new classification of random matrix
ensembles. The review is organized into two main parts. In Part I the theory of
symmetric spaces is reviewed with particular emphasis on the ideas relevant for
appreciating the correspondence with random matrix theories. In Part II we
discuss various applications of symmetric spaces to random matrix theories and
in particular the new classification of disordered systems derived from the
classification of symmetric spaces. We also review how the mapping from
integrable Calogero--Sutherland models to symmetric spaces can be used in the
theory of random matrices, with particular consequences for quantum transport
problems. We conclude indicating some interesting new directions of research
based on these identifications.Comment: 161 pages, LaTeX, no figures. Revised version with major additions in
the second part of the review. Version accepted for publication on Physics
Report
Comments on gluon scattering amplitudes via AdS/CFT
In this article we consider n gluon color ordered, planar amplitudes in N=4
super Yang Mills at strong 't Hooft coupling. These amplitudes are approximated
by classical surfaces in AdS_5 space. We compute the value of the amplitude for
a particular kinematic configuration for a large number of gluons and find that
the result disagrees with a recent guess for the exact value of the amplitude.
Our results are still compatible with a possible relation between amplitudes
and Wilson loops.
In addition, we also give a prescription for computing processes involving
local operators and asymptotic states with a fixed number of gluons. As a
byproduct, we also obtain a string theory prescription for computing the dual
of the ordinary Wilson loop, Tr P exp[ i\oint A ], with no couplings to the
scalars. We also evaluate the quark-antiquark potential at two loops.Comment: 27 pages, 9 figures,v3:minor correction
Coherent transmission through a one dimensional lattice
Based on the Keldysh nonequilibrium Green function (NGF) technique, a general
formula for the current and transmission coefficient through a one dimensional
lattice is derived without the consideration of electron-electron interactions.
We obtain an analytical condition for perfect resonant transmission when the
levels of sites are aligned, which depends on the parity of the number of
sites. Localization-delocalization transition in a generic one dimensional
disordered lattice is also analyzed, depending on the correlation among the
hopping parameters and the strength of the coupling to reservoirs. The
dependence of the number and lineshape of resonant transmission and linear
conductance peaks on the structure parameters of the lattice is also given in
several site cases.Comment: 22 pages, 3 figures, Revtex, minor revision mad
Retrorectal endometrioid cyst: a case report
<p>Abstract</p> <p>Introduction</p> <p>Developmental cysts are the most common retrorectal cystic lesions in adults, whereas reports of endometrioid cysts in this anatomic location are extremely rare.</p> <p>Case presentation</p> <p>A 21-year-old nulliparous Greek woman presented with chronic noncyclic pelvic pain, and a retrorectal cyst was diagnosed. The lesion was resected through a laparotomy and, on histologic examination, was found to be an endometrioid cyst. The treatment was completed with a six-month course of a gonadotropin-releasing hormone analogue. One year after surgery, the woman remained free of symptoms, and pelvic imaging showed no recurrence of the lesion. Reviewing the literature, we found only three previous reports of an endometrioid cyst in this anatomic location.</p> <p>Conclusion</p> <p>In women of reproductive age, endometriosis must be included in the differential diagnosis of retrorectal cysts.</p
The Human Fungal Pathogen Cryptococcus neoformans Escapes Macrophages by a Phagosome Emptying Mechanism That Is Inhibited by Arp2/3 Complex-Mediated Actin Polymerisation
The lysis of infected cells by disease-causing microorganisms is an efficient but risky strategy for disseminated infection, as it exposes the pathogen to the full repertoire of the host's immune system. Cryptococcus neoformans is a widespread fungal pathogen that causes a fatal meningitis in HIV and other immunocompromised patients. Following intracellular growth, cryptococci are able to escape their host cells by a non-lytic expulsive mechanism that may contribute to the invasion of the central nervous system. Non-lytic escape is also exhibited by some bacterial pathogens and is likely to facilitate long-term avoidance of the host immune system during latency. Here we show that phagosomes containing intracellular cryptococci undergo repeated cycles of actin polymerisation. These actin ‘flashes’ occur in both murine and human macrophages and are dependent on classical WASP-Arp2/3 complex mediated actin filament nucleation. Three dimensional confocal imaging time lapse revealed that such flashes are highly dynamic actin cages that form around the phagosome. Using fluorescent dextran as a phagosome membrane integrity probe, we find that the non-lytic expulsion of Cryptococcus occurs through fusion of the phagosome and plasma membranes and that, prior to expulsion, 95% of phagosomes become permeabilised, an event that is immediately followed by an actin flash. By using pharmacological agents to modulate both actin dynamics and upstream signalling events, we show that flash occurrence is inversely related to cryptococcal expulsion, suggesting that flashes may act to temporarily inhibit expulsion from infected phagocytes. In conclusion, our data reveal the existence of a novel actin-dependent process on phagosomes containing cryptococci that acts as a potential block to expulsion of Cryptococcus and may have significant implications for the dissemination of, and CNS invasion by, this organism.\ud
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A detailed description of the phenotypic spectrum of North Sea Progressive Myoclonus Epilepsy in a large cohort of seventeen patients
MycoBank gearing up for new horizons.
MycoBank, a registration system for fungi established in 2004 to capture all taxonomic novelties, acts as a coordination hub between repositories such as Index Fungorum and Fungal Names. Since January 2013, registration of fungal names is a mandatory requirement for valid publication under the International Code of Nomenclature for algae, fungi and plants (ICN). This review explains the database innovations that have been implemented over the past few years, and discusses new features such as advanced queries, registration of typification events (MBT numbers for lecto, epi- and neotypes), the multi-lingual database interface, the nomenclature discussion forum, annotation system, and web services with links to third parties. MycoBank has also introduced novel identification services, linking DNA sequence data to numerous related databases to enable intelligent search queries. Although MycoBank fills an important void for taxon registration, challenges for the future remain to improve links between taxonomic names and DNA data, and to also introduce a formal system for naming fungi known from DNA sequence data only. To further improve the quality of MycoBank data, remote access will now allow registered mycologists to act as MycoBank curators, using Citrix software
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