1,075 research outputs found
A Search for 6.7 GHz Methanol Masers in M33
We report the negative results from a search for 6.7 GHz methanol masers in
the nearby spiral galaxy M33. We observed 14 GMCs in the central 4 kpc of the
Galaxy, and found 3 sigma upper limits to the flux density of ~9 mJy in
spectral channels having a velocity width of 0.069 km/s. By velocity shifting
and combining the spectra from the positions observed, we obtain an effective
3sigma upper limit on the average emission of ~1mJy in a 0.25 km/s channel.
These limits lie significantly below what we would expect based on our
estimates of the methanol maser luminosity function in the Milky Way. The most
likely explanation for the absence of detectable methanol masers appears to be
the metallicity of M33, which is modestly less than that of the Milky Way
Low energy properties of M-state tunneling systems in metals: New candidates for non-Fermi-liquid systems
We construct a generalized multiplicative renormalization group
transformation to study the low energy dynamics of a heavy particle tunneling
among different positions and interacting with independent conduction
electron channels. Using a -expansion we show that this M-level scales
towards a fixed point equivalent to the channel
Coqblin-Schrieffer model. Solving numerically the scaling equations we find
that a realistic M-level system scales close to this fixed point (FP) and its
Kondo temperature is in the experimentally observable range .Comment: 11 Latex pages, to appear in Phys. Rev. Lett, Figures available from
the author by reques
On The Multichannel Kondo Model"
A detailed and comprehensive study of the one-impurity multichannel Kondo
model is presented. In the limit of a large number of conduction electron
channels , the low energy fixed point is accessible to a
renormalization group improved perturbative expansion in . This
straightforward approach enables us to examine the scaling, thermodynamics and
dynamical response functions in great detail and make clear the following
features: i) the criticality of the fixed point; ii) the universal non-integer
degeneracy; iii) that the compensating spin cloud has the spatial extent of the
order of one lattice spacing.Comment: 28 pages, REVTEX 2.0. Submitted to J. Phys.: Cond. Mat. Reference
.bbl file is appended at the end. 5 figures in postscript files can be
obtained at [email protected]. The filename is gan.figures.tar.z and
it's compressed. You can uncompress it by using commands: "uncompress
gan.figures.tar.z" and "tar xvf gan.figures.tar". UBC Preprin
Scanning micro-Hall probe mapping of magnetic flux distributions and current densities in YBa2Cu3O7 thin films
Mapping of the magnetic flux density B(sub z) (perpendicular to the film plane) for a YBa2Cu3O7 thin-film sample was carried out using a scanning micro-Hall probe. The sheet magnetization and sheet current densities were calculated from the B(sub z) distributions. From the known sheet magnetization, the tangential (B(sub x,y)) and normal components of the flux density B were calculated in the vicinity of the film. It was found that the sheet current density was mostly determined by 2B(sub x,y)/d, where d is the film thickness. The evolution of flux penetration as a function of applied field will be shown
Two-channel Kondo model as a generalized one-dimensional inverse square long-range Haldane-Shastry spin model
Majorana fermion representations of the algebra associated with spin, charge,
and flavor currents have been used to transform the two-channel Kondo
Hamiltonian. Using a path integral formulation, we derive a reduced effective
action with long-range impurity spin-spin interactions at different imaginary
times. In the semiclassical limit, it is equivalent to a one-dimensional
Heisenberg spin chain with two-spin, three-spin, etc. long-range interactions,
as a generalization of the inverse-square long-range Haldane-Shastry spin
model. In this representation the elementary excitations are "semions", and the
non-Fermi-liquid low-energy properties of the two-channel Kondo model are
recovered.Comment: 4 pages, no figure, to be published in J. Phys.: Condens. Matter,
200
Simple description of the anisotropic two-channel Kondo problem
We adapt strong-coupling methods first used in the one-channel Kondo model to
develop a simple description of the spin- two-channel Kondo model
with channel anisotropy. Our method exploits spin-charge decoupling to develop
a compactified Hamiltonian that describes the spin excitations. The structure
of the fixed-point Hamiltonian and quasiparticle impurity S-matrix are
incompatible with a Fermi liquid description.Comment: 4 pages, latex (uses revtex and epsf macros) with 3 figures - all in
a self unpacking uuencoded file. Revisions include changes to Fig. 1(a) and
detailed discussion of the spin excitation
Finite-Size Bosonization of 2-Channel Kondo Model: a Bridge between Numerical Renormalization Group and Conformal Field Theory
We generalize Emery and Kivelson's (EK) bosonization-refermionization
treatment of the 2-channel Kondo model to finite system size and on the EK-line
analytically construct its exact eigenstates and finite-size spectrum. The
latter crosses over to conformal field theory's (CFT) universal
non-Fermi-liquid spectrum (and yields the most-relevant operators' dimensions),
and further to a Fermi-liquid spectrum in a finite magnetic field. Our approach
elucidates the relation between bosonization, scaling techniques, the numerical
renormalization group (NRG) and CFT. All CFT's Green's functions are recovered
with remarkable ease from the model's scattering states.Comment: 4 pages, 1 figure, Revte
Scaling analysis of a model Hamiltonian for Ce impurity in a cubic metal
We introduce various exchange interactions in a model Hamiltonian for
Ce ions in cubic symmetry with three configurations (,,).
With the impurity pseudo spin , our Hamiltonian includes: (i)
One-channel Anderson model; (ii) Two-channel Anderson
model; (iii) An unforseen one-channel Anderson model with a
non-trivial fixed point; (iv) Mixing exchange interaction between the
and the conduction electron partial wave states; (v)
Multiple conduction electron partial wave states. Using the third-order scaling
(perturbative renormalization group) analysis, we study stability of various
fixed points relevant to various exchange interactions for Ce ions in
cubic symmetry.Comment: 68 pages. 4 figures are available upon request from
[email protected] (revised
Trypanocidal and leishmanicidal activity of six limonoids
Six limonoids [kotschyienone A and B (1, 2), 7-deacetylgedunin (3), 7-deacetyl-7-oxogedunin (4), andirobin (5) and methyl angolensate (6)] were investigated for their trypanocidal and leishmanicidal activities using bloodstream forms of Trypanosoma brucei and promastigotes of Leishmania major. Whereas all compounds showed anti-trypanosomal activity, only compounds 1–4 displayed anti-leishmanial activity. The 50% growth inhibition (GI 50) values for the trypanocidal and leishmanicidal activity of the compounds ranged between 2.5 and 14.9 μM. Kotschyienone A (1) was found to be the most active compound with a minimal inhibition concentration (MIC) value of 10 μM and GI 50 values between 2.5 and 2.9 μM. Only compounds 1 and 3 showed moderate cytotoxicity against HL-60 cells with MIC and GI 50 values of 100 μM and 31.5–46.2 μM, respectively. Compound 1 was also found to show activity against intracellular amastigotes of L. major with a GI 50 value of 1.5 μM. The results suggest that limonoids have potential as drug candidates for the development of new treatments against trypanosomiasis and leishmaniasis
Two-Channel Kondo Physics from Tunnelling Impurities with Triangular Symmetry
Tunnelling impurities in metals have been known for some time to have the
potential for exhibiting Kondo-like physics. However previous models based on
an impurity hopping between two equivalent positions have run into trouble due
to the existence of relevant operators that drive the system away from the
non-Fermi-liquid Kondo fixed point. In the case of an impurity hopping among
positions with higher symmetry, such as triangular symmetry, it is shown here
that the non-Fermi-liquid behavior at low temperatures can be generic. Using
various bosonization techniques, the fixed point is shown to be {\em stable}.
However, unlike the conventional two-channel Kondo (2CK) model, it has {\em
four} leading irrelevant operators, implying that while the form of the
singular temperature dependence of physical quantities is similar to the 2CK
model, there will not be simple universal amplitude ratios. The phase diagram
of this system is analyzed and a critical manifold is found to separate the
non-Fermi-liquid from a conventional Fermi liquid fixed point. Generalization
to higher symmetries, such as cubic, and the possibility of physical
realizations with dynamic Jahn-Teller impurities is discussed.Comment: 20 pages, 4 figures, RevTex format, submitted to Phys. Rev.
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