Editorial

Gemeenskappe se prioriteite in gesondheidsdiensThere are other human retroviruses too - a note on myelopathy associated with HTLV-IIs there a need for surgical oncologists' in South Africa

Ground state representations of loop algebras

Let g be a simple Lie algebra, Lg be the loop algebra of g. Fixing a point in S^1 and identifying the real line with the punctured circle, we consider the subalgebra Sg of Lg of rapidly decreasing elements on R. We classify the translation-invariant 2-cocycles on Sg. We show that the ground state representation of Sg is unique for each cocycle. These ground states correspond precisely to the vacuum representations of Lg.Comment: 22 pages, no figur

Twisted duality of the CAR-Algebra

We give a complete proof of the twisted duality property M(q)'= Z M(q^\perp) Z* of the (self-dual) CAR-Algebra in any Fock representation. The proof is based on the natural Halmos decomposition of the (reference) Hilbert space when two suitable closed subspaces have been distinguished. We use modular theory and techniques developed by Kato concerning pairs of projections in some essential steps of the proof. As a byproduct of the proof we obtain an explicit and simple formula for the graph of the modular operator. This formula can be also applied to fermionic free nets, hence giving a formula of the modular operator for any double cone.Comment: 32 pages, Latex2e, to appear in Journal of Mathematical Physic

Lattice dynamics and structural stability of ordered Fe3Ni, Fe3Pd and Fe3Pt alloys

We investigate the binding surface along the Bain path and phonon dispersion relations for the cubic phase of the ferromagnetic binary alloys Fe3X (X = Ni, Pd, Pt) for L12 and DO22 ordered phases from first principles by means of density functional theory. The phonon dispersion relations exhibit a softening of the transverse acoustic mode at the M-point in the L12-phase in accordance with experiments for ordered Fe3Pt. This instability can be associated with a rotational movement of the Fe-atoms around the Ni-group element in the neighboring layers and is accompanied by an extensive reconstruction of the Fermi surface. In addition, we find an incomplete softening in [111] direction which is strongest for Fe3 Ni. We conclude that besides the valence electron density also the specific Fe-content and the masses of the alloying partners should be considered as parameters for the design of Fe-based functional magnetic materials.Comment: Revised version, accepted for publication in Physical Review

Singularities of equidistants and global centre symmetry sets of Lagrangian submanifolds

We define the Global Centre Symmetry set (GCS) of a smooth closed m-dimensional submanifold M of R^n, $n \leq 2m$, which is an affinely invariant generalization of the centre of a k-sphere in R^{k+1}. The GCS includes both the centre symmetry set defined by Janeczko and the Wigner caustic defined by Berry. We develop a new method for studying generic singularities of the GCS which is suited to the case when M is lagrangian in R^{2m} with canonical symplectic form. The definition of the GCS, which slightly generalizes one by Giblin and Zakalyukin, is based on the notion of affine equidistants, so, we first study singularities of affine equidistants of Lagrangian submanifolds, classifying all the stable ones. Then, we classify the affine-Lagrangian stable singularities of the GCS of Lagrangian submanifolds and show that, already for smooth closed convex curves in R^2, many singularities of the GCS which are affine stable are not affine-Lagrangian stable.Comment: 26 pages, 2 figure

An Obstruction to Quantization of the Sphere

In the standard example of strict deformation quantization of the symplectic sphere $S^2$, the set of allowed values of the quantization parameter $\hbar$ is not connected; indeed, it is almost discrete. Li recently constructed a class of examples (including $S^2$) in which $\hbar$ can take any value in an interval, but these examples are badly behaved. Here, I identify a natural additional axiom for strict deformation quantization and prove that it implies that the parameter set for quantizing $S^2$ is never connected.Comment: 23 page. v2: changed sign conventio

From conformal embeddings to quantum symmetries: an exceptional SU(4) example

We briefly discuss several algebraic tools that are used to describe the quantum symmetries of Boundary Conformal Field Theories on a torus. The starting point is a fusion category, together with an action on another category described by a quantum graph. For known examples, the corresponding modular invariant partition function, which is sometimes associated with a conformal embedding, provides enough information to recover the whole structure. We illustrate these notions with the example of the conformal embedding of SU(4) at level 4 into Spin(15) at level 1, leading to the exceptional quantum graph E4(SU(4)).Comment: 22 pages, 3 color figures. Version 2: We changed the color of figures (ps files) in such a way that they are still understood when converted to gray levels. Version 3: Several references have been adde

Molecular characterisation of echinococcus granulosus species/strains in human infections from Turkana, Kenya

Background: Cystic echinococcosis (CE) or hydatid disease is a neglected, economically important zoonotic disease endemic in pastoralist communities, in particular the Turkana community of Kenya. It is caused by the larval stage of the highly diverse species complex of Echinococcus granulosus sensu lato (s.l). The situation on the genetic diversity in humans in Kenya is not well established.Objective: To characterise Echinococcus granulosus (s.l) species/strains isolated from humans undergoing surgery in Turkana, Kenya.Design: A Cross sectional study.Setting: The Kakuma Mission Hospital and Centre for Microbiology Research, Kenya Medical Research InstituteSubjects: Eighty (80) parasite samples from 26 subjects were analysed by Polymerase chain reaction – Restriction fragment length polymorphism (PCR-RFLP) targeting the nad 1 gene for molecular characterizationResults: Two different genotypes of E. granulosus were identified from the samples analysed: E. granulosus sensu stricto (G1-G3) 85% of the samples analysed and E. canadensis G6/7 (15%). Most of the hydatid cysts (35%) were isolated from the liver. Other sites where cysts were isolated from include: kidney, abdomen, omentum, retroperitonium and the submandibular. Majority of cysts presented as CE1 (50%) and CE3B (42%) images according to WHO ultrasound classification. Both males and females were infected with E. granulosus s.s but only the females showed infection with E. canadensis G6/7. Chi-square test revealed significant difference between age of individuals and cysts classification by ultrasound. In addition, there was an association between cyst presentation (single or multiple) and genotype whereby all the E. canadensis G6/7 cases presented as single cysts in the infected persons.Conclusion: This study corroborates previous reports that E. canadensis G6/7 strain is present in Turkana, a place where initially only E. granulosus s.s (G1-G3) was known to be present and that E. granulosis (G1-G3) remains the most widespread genotype infecting humans in the Turkana community

Metal insulator transition in TlSr2CoO5 from orbital degeneracy and spin disproportionation

To describe the metal insulator transition in the new oxide TlSr2CoO5 we investigate its electronic structure by LDA and model Hartree-Fock calculations. Within LDA we find a homogeneous metallic and ferromagnetic ground state, but when including the Coulomb interaction more explicitly within the Hartree-Fock approximation, we find an insulating state of lower energy with both spin and orbital order. We also interpret our results in terms of a simple model.Comment: 8 pages, 9 figure

Magnetoelastic effects in Jahn-Teller distorted CrF2_2 and CuF2_2 studied by neutron powder diffraction

We have studied the temperature dependence of crystal and magnetic structures of the Jahn-Teller distorted transition metal difluorides CrF$_2$ and CuF$_2$ by neutron powder diffraction in the temperature range 2-280 K. The lattice parameters and the unit cell volume show magnetoelastic effects below the N\'eel temperature. The lattice strain due to the magnetostriction effect couples with the square of the order parameter of the antiferromagnetic phase transition. We also investigated the temperature dependence of the Jahn-Teller distortion which does not show any significant effect at the antiferromagnetic phase transition but increases linearly with increasing temperature for CrF$_2$ and remains almost independent of temperature in CuF$_2$. The magnitude of magnetovolume effect seems to increase with the low temperature saturated magnetic moment of the transition metal ions but the correlation is not at all perfect