LaCo2B2: A Co-based layered superconductor with a ThCr2Si2-type structure

LaCo2B2 with a ThCr2Si2-type structure composed of alternately stacked La and CoB layers exhibits metallic electrical conductivity and Pauli paramagnetic behavior down to 2K. Bulk superconductivity with a Tc of ~4K emerges upon substitution with dopant elements; i.e., isovalent substitution to form (La1-xYx)Co2B2, or aliovalent substitution to form La(Co1-xFex)2B2. Highly covalent bonding between Co 3d and B 2p levels in the CoB layers, which is caused by the B 2p level being shallower than the Fermi level, removes magnetic ordering from Co 3d electrons even in the undoped samples.Comment: 3 figure

Free boson formulation of boundary states in W_3 minimal models and the critical Potts model

We develop a Coulomb gas formalism for boundary conformal field theory having a $W$ symmetry and illustrate its operation using the three state Potts model. We find that there are free-field representations for six $W$ conserving boundary states, which yield the fixed and mixed physical boundary conditions, and two $W$ violating boundary states which yield the free and new boundary conditions. Other $W$ violating boundary states can be constructed but they decouple from the rest of the theory. Thus we have a complete free-field realization of the known boundary states of the three state Potts model. We then use the formalism to calculate boundary correlation functions in various cases. We find that the conformal blocks arising when the two point function of $\phi_{2,3}$ is calculated in the presence of free and new boundary conditions are indeed the last two solutions of the sixth order differential equation generated by the singular vector.Comment: 25 page

Imaging correlates of molecular signatures in oligodendrogliomas.

Molecular subsets of oligodendroglioma behave in biologically distinct ways. Their locations in the brain, rates of growth, and responses to therapy differ with their genotypes. Retrospectively, we inquired whether allelic loss of chromosomal arms 1p and 19q, an early molecular event and favorable prognostic marker in oligodendrogliomas, were reflected in their appearance on magnetic resonance imaging. Loss of 1p and 19q was associated with an indistinct border on T(1) images and mixed intensity signal on T(1) and T(2). Loss of 1p and 19q was also associated with paramagnetic susceptibility effect and with calcification, a common histopathological finding in oligodendrogliomas. These data encourage prospective evaluation of molecular alterations and magnetic resonance imaging characteristics of glial neoplasms

Non-propagating degrees of freedom in supergravity and very extended G_2

Recently a correspondence between non-propagating degrees of freedom in maximal supergravity and the very extended algebra E_11 has been found. We perform a similar analysis for a supergravity theory with eight supercharges and very extended G_2. In particular, in the context of d=5 minimal supergravity, we study whether supersymmetry can be realised on higher-rank tensors with no propagating degrees of freedom. We find that in this case the very extended algebra fails to capture these possibilities.Comment: 12 pages, 1 figure. v2: transformation properties of higher-rank tensors under SU(2) R-symmetry analysed and refs added. v3: improved discussion, published versio

On the sigma-model structure of type IIA supergravity action in doubled field approach

In this letter we describe how to string together the doubled field approach by Cremmer, Julia, Lu and Pope with Pasti-Sorokin-Tonin technique to construct the sigma-model-like action for type IIA supergravity. The relation of the results with that of obtained in the context of searching for Superstring/M-theory hidden symmetry group is discussed.Comment: 9 pp, LATEX; published in JETP Let

Charge and orbital order in Fe_3O_4

Charge and orbital ordering in the low-temperature monoclinic structure of magnetite (Fe_3O_4) is investigated using LSDA+U. While the difference between t_{2g} minority occupancies of Fe^{2+}_B and Fe^{3+}_B cations is large and gives direct evidence for charge ordering, the screening is so effective that the total 3d charge disproportion is rather small. The charge order has a pronounced [001] modulation, which is incompatible with the Anderson criterion. The orbital order agrees with the Kugel-Khomskii theory.Comment: 4 pages, 2 figure