955 research outputs found
Competing phases in the high field phase diagram of (TMTSF)ClO
A model is presented for the high field phase diagram of (TMTSF)ClO,
taking into account the anion ordering, which splits the Fermi surface in two
bands. For strong enough field, the largest metal-SDW critical temperature
corresponds to the N=0 phase, which originates from two intraband nesting
processes. At lower temperature, the competition between these processes puts
at disadvantage the N=0 phase vs. the N=1 phase, which is due to interband
nesting. A first order transition takes then place from the N=0 to N=1 phase.
We ascribe to this effect the experimentally observed phase diagrams.Comment: 5 pages, 3 figures (to appear in Phys. Rev. Lett.
Fermi Surface of Alpha-Uranium at Ambient Pressure
We have performed de Haas-van Alphen measurements of the Fermi surface of
alpha-uranium single crystals at ambient pressure within the alpha-3 charge
density wave (CDW) state from 0.020 K - 10 K and magnetic fields to 35 T using
torque magnetometry. The angular dependence of the resulting frequencies is
described. Effective masses were measured and the Dingle temperature was
determined to be 0.74 K +/- 0.04 K. The observation of quantum oscillations
within the alpha-3 CDW state gives new insight into the effect of the charge
density waves on the Fermi surface. In addition we observed no signature of
superconductivity in either transport or magnetization down to 0.020 K
indicating the possibility of a pressure-induced quantum critical point that
separates the superconducting dome from the normal CDW phase.Comment: 11 pages, 4 figures, 3 table
The ABCD (Agriculture Biologique, Conseil et Développement), a French professional degree in organic farming, consulting and development
The creation of a professional degree in organic farming, known as an ABCD, is the result of the desire to provide training at the national level that is supported by the agriculture sector and that brings together the know-how of universities and higher education institutions specialised in agronomy and those of a network of teaching establishments specialised in technical education in the field. This degree aims at forming agents and advisors capable of working in a wide range of fields such as production, processing, distribution, control-certification and marketing. It is mainly intended for adults interested in career development and students who would like to further their education. Four training sites are involved and all teaching is done through a virtual digital university using information and communication technologies
Ancestrais, Tartarugas E Moisés – Interface Dialógica Entre Arqueologia E Antropologia Na Etnografia Dos Hupd’äh (rio Negro)
O artigo visa problematizar a noção de ancestralidade, recurso conceitual comum aos temas de patrimônio e à interpretação arqueológica. Para tanto, utilizamos aportes teóricos da antropologia e da arqueologia em diálogo com a experiência etnográfica junto aos Hupd’äh - Maku (Alto Rio Negro). Esse povo parece associar um aspecto de ancestralidade da mitologia bÃblica judaica cristã à s sua própria noção de ancestralidade. Pretende-se demonstrar como os contextos arqueológicos associados etnograficamente podem complexificar as noções de patrimônio (material e imaterial) e de ancestralidade. 81(9)6-2
Phases of two coupled Luttinger liquids
A model of two interacting one--dimensional fermion systems (``Luttinger
liquids'') coupled by single--particle hopping is investigated. Bosonization
allows a number of exact statements to be made. In particular, for forward
scattering only, the model contains two massless boson sectors and an Ising
type critical sector. For general interactions, there is a spin excitation gap
and either s-- or d--type pairing fluctuations dominate. It is shown that the
same behavior is also found for strong interactions. A possible scenario for
the crossover to a Fermi liquid in a many chain system is discussed.Comment: revised version, some changes, 11 pages, no figures, RexTeX3.
Crystal Structure and Magnetism of the Linear-Chain Copper Oxides Sr5Pb3-xBixCuO12
The title quasi-1D copper oxides (0=< x =<0.4) were investigated by neutron
diffraction and magnetic susceptibility studies. Polyhedral CuO4 units in the
compounds were found to comprise linear-chains at inter-chain distance of
approximately 10 A. The parent chain compound (x = 0), however, shows less
anisotropic magnetic behavior above 2 K, although it is of substantially
antiferromagnetic (mu_{eff}= 1.85 mu_{B} and Theta_{W} = -46.4 K) spin-chain
system. A magnetic cusp gradually appears at about 100 K in T vs chi with the
Bi substitution. The cusp (x = 0.4) is fairly characterized by and therefore
suggests the spin gap nature at Delta/k_{B} ~ 80 K. The chain compounds hold
electrically insulating in the composition range.Comment: To be published in PR
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