3,320 research outputs found
Ruderman-Kittel-Kasuya-Yosida interactions on a bipartite lattice
Carrier-mediated exchange coupling, known as Ruderman-Kittel-Kasuya-Yosida
(RKKY) interaction, plays a fundamental role in itinerant ferromagnetism and
has great application potentials in spintronics. A recent theorem based on the
imaginary-time method shows that the oscillatory RKKY interaction becomes
commensurate on bipartite lattice and predicts that the effective exchange
coupling is always ferromagnetic for the same sublattice but antiferromagnetic
for opposite sublattices. We revisit this important problem by real- and
imaginary-time methods and find the theorem misses important contributions from
zero modes. To illustrate the importance of zero modes, we study the spin
susceptibility in graphene nanoribbons numerically. The effective exchange
coupling is largest on the edges but does not follow the predictions from the
theorem
Phase diagrams of the metallic zigzag carbon nanotube
We investigate a metallic zigzag carbon nanotube by means of a Hubbard model
which includes both on-site and nearest neighbour interactions. Assuming weak
interactions, a renormalization group analysis of the equivalent two-leg ladder
followed by bosonization and refermionization results in a Gross-Neveu model
with an enlarged symmetry relative to the original Hamiltonian. For the undoped
case the symmetry of the Gross-Neveu model is SO(8), but for the doped case the
particle-hole symmetry is broken and the symmetry reduces to SO(6). Four ground
state phases are found in the undoped carbon nanotube with repulsive
interactions, a d-wave Mott insulator, an s-wave Mott insulator, a p-density
wave and a charge density wave. The doped case has two ground state phases, a
d-wave superconductor and a phase where a p-density wave and a charge density
wave co-exist. We also explore the global phase diagram with a general
interaction profile and find several additional states, including a chiral
current phase where current flows around the nanotube along the zigzag bonds.Comment: 16 pages, 9 figure
Development of a Laboratory Animal Model for Functional Studies of three Human Pregnancy Proteins: α-Foetoprotein (AFP), β-Glycoprotein (SP-l) and Pregnancy Zone Protein (PZP)
A murine model for the study of the function of three human pregnancy-associated serum proteins has been developed. The human proteins are pregnancy zone protein (PZP) of maternal origin, pregnancy-specific β1-glycoprotein (SPil) of placental origin and ocfoetoprotein (AFP) of foetal origin. The maternal serum levels of murine SP-l (PAMP-2) and murine AFP during pregnancy reflect the growth of the placenta and foetuses respectively, indicating the usefulness of the model in teratogenic studies
Trends in laboratory animal science and welfare
No abstract availabl
A New Galaxy in the Local Group: the Antlia Dwarf Galaxy
We report the discovery of new member of the Local Group in the constellation
of Antlia. Optically the system appears to be a typical dwarf spheroidal galaxy
of type dE3.5 with no apparent young blue stars or unusual features. A
color-magnitude diagram in I, V-I shows the tip of the red giant branch, giving
a distance modulus of 25.3 +/- 0.2 (1.15 Mpc +/- 0.1) and a metallicity of -1.6
+/- 0.3. Although Antlia is in a relatively isolated part of the Local Group it
is only 1.2 degrees away on the sky from the Local Group dwarf NGC3109, and may
be an associated system.Comment: AJ in press, 15 pages, 7 figures, figure 2 in b/w for space saving,
full postscript version available at
http://www.ast.cam.ac.uk/~gkth/antlia-pp.htm
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