1,657 research outputs found
Preferential adsorption of high density lipoprotein (HDL) in blood plasma/polymer interaction
A few studies on the adsorption of plasma proteins to polymeric surfaces show that major plasma proteins: albumin (Alb), fibrinogen (Fb) and immunoglobulin (IgG) are adsorbed in much smaller quantities from plasma than from protein solutions (1,2). Present results show that this difference in adsorption is due to the preferential adsorption of high density lipoprotein from plasma onto the material surfaces studied (PVC and PS)
Generalization of Gutzwiller Approximation
We derive expressions required in generalizing the Gutzwiller approximation
to models comprising arbitrarily degenerate localized orbitals.Comment: 6 pages, 1 figure, to appear in J.Phys.Soc.Jpn. vol.6
Spin-independent origin of the strongly enhanced effective mass in a dilute 2D electron system
We have accurately measured the effective mass in a dilute two-dimensional
electron system in silicon by analyzing temperature dependence of the
Shubnikov-de Haas oscillations in the low-temperature limit. A sharp increase
of the effective mass with decreasing electron density has been observed. Using
tilted magnetic fields, we have found that the enhanced effective mass is
independent of the degree of spin polarization, which points to a
spin-independent origin of the mass enhancement and is in contradiction with
existing theories
Very large magnetoresistance in lateral ferromagnetic (Ga,Mn)As wires with nanoconstrictions
We have fabricated (Ga,Mn)As nanostructures in which domain walls can be
pinned by sub-10 nm constrictions. Controlled by shape anisotropy, we can
switch the regions on either side of the constriction to either parallel or
antiparallel magnetization. All samples exhibit a positive magnetoresistance,
consistent with domain-wall trapping. For metallic samples we find a
magnetoresistance up to 8%, which can be understood from spin accumulation. In
samples where, due to depletion at the constriction, a tunnel barrier is
formed, we observe a magnetoresistance of up to 2000 %.Comment: 4 pages, 3 figures, submited to Phys. Rev. Let
Phase diagrams of correlated electrons: systematic corrections to the mean field theory
Perturbative corrections to the mean field theory for particle-hole
instabilities of interacting electron systems are computed within a scheme
which is equivalent to the recently developed variational approach to the
Kohn-Luttinger superconductivity. This enables an unbiased comparison of
particle-particle and particle-hole instabilities within the same approximation
scheme. A spin-rotation invariant formulation for the particle-hole
instabilities in the triplet channel is developed. The method is applied to the
phase diagram of the t-t' Hubbard model on the square lattice. At the Van Hove
density, antiferromagnetic and d-wave Pomeranchuk phases are found to be stable
close to half filling. However, the latter phase is confined to an extremely
narrow interval of densities and away from the singular filling, d-wave
superconducting instability dominates
Excitons in T-shaped quantum wires
We calculate energies, oscillator strengths for radiative recombination, and
two-particle wave functions for the ground state exciton and around 100 excited
states in a T-shaped quantum wire. We include the single-particle potential and
the Coulomb interaction between the electron and hole on an equal footing, and
perform exact diagonalisation of the two-particle problem within a finite basis
set. We calculate spectra for all of the experimentally studied cases of
T-shaped wires including symmetric and asymmetric GaAs/AlGaAs and
InGaAs/AlGaAs structures. We study in detail the
shape of the wave functions to gain insight into the nature of the various
states for selected symmetric and asymmetric wires in which laser emission has
been experimentally observed. We also calculate the binding energy of the
ground state exciton and the confinement energy of the 1D quantum-wire-exciton
state with respect to the 2D quantum-well exciton for a wide range of
structures, varying the well width and the Al molar fraction . We find that
the largest binding energy of any wire constructed to date is 16.5 meV. We also
notice that in asymmetric structures, the confinement energy is enhanced with
respect to the symmetric forms with comparable parameters but the binding
energy of the exciton is then lower than in the symmetric structures. For
GaAs/AlGaAs wires we obtain an upper limit for the binding energy
of around 25 meV in a 10 {\AA} wide GaAs/AlAs structure which suggests that
other materials must be explored in order to achieve room temperature
applications. There are some indications that
InGaAs/AlGaAs might be a good candidate.Comment: 20 pages, 10 figures, uses RevTeX and psfig, submitted to Physical
Review
Circuit theory for crossed Andreev reflection and nonlocal conductance
Nonlocal currents, in devices where two normal metal terminals are contacted
to a superconductor, are determined using the circuit theory of mesoscopic
superconductivity. We calculate the conductance associated with crossed Andreev
reflection and electron transfer between the two normal metal terminals, in
addition to the conductance from direct Andreev reflection and quasiparticle
tunneling. Dephasing and proximity effect are taken into account.Comment: Included in special issue Spin Physics of Superconducting
heterostructures of Applied Physics A: Materials Science & Processin
Hidden Quantum Critical Point in a Ferromagnetic Superconductor
We consider a coexistence phase of both Ferromagnetism and superconductivity
and solve the self-consistent mean-field equations at zero temperature. The
superconducting gap is shown to vanish at the Stoner point whereas the
magnetization doesn't. This indicates that the para-Ferro quantum critical
point becomes a hidden critical point. The effective mass in such a phase gets
enhanced whereas the spin wave stiffness is reduced as compared to the pure FM
phase. The spin wave stiffness remains finite even at the para-Ferro quantum
critical point.Comment: 4 pages, Phys. Rev. B (Rapid) accepte
A WZW model based on a non-semi-simple group
We present a conformal field theory which desribes a homogeneous four
dimensional Lorentz-signature space-time. The model is an ungauged WZW model
based on a central extension of the Poincar\'e algebra. The central charge of
this theory is exactly four, just like four dimensional Minkowski space. The
model can be interpreted as a four dimensional monochromatic plane wave. As
there are three commuting isometries, other interesting geometries are expected
to emerge via duality.Comment: 8 pages, phyzzx, IASSNS-HEP-93/61 Texable versio
- …