357 research outputs found
Human genetics and genomics a decade after the release of the draft sequence of the human genome
10.1186/1479-7364-5-6-577Human Genomics56577-62
Exact solutions of Dirac equation on (1+1)-dimensional spacetime coupled to a static scalar field
We use a generalized scheme of supersymmetric quantum mechanics to obtain the
energy spectrum and wave function for Dirac equation in (1+1)-dimensional
spacetime coupled to a static scalar field.Comment: 7 pages, Late
Polynomial SUSY in Quantum Mechanics and Second Derivative Darboux Transformation
We give the classification of second-order polynomial SUSY Quantum Mechanics
in one and two dimensions. The particular attention is paid to the irreducible
supercharges which cannot be built by repetition of ordinary Darboux
transformations. In two dimensions it is found that the binomial superalgebra
leads to the dynamic symmetry generated by a central charge operator.Comment: 10 pages, LaTeX, preprint SPbU-IP-94-0
SUSY Intertwining Relations of Third Order in Derivatives
The general solution of the intertwining relations between a pair of
Schr\"odinger Hamiltonians by the supercharges of third order in derivatives is
obtained. The solution is expressed in terms of one arbitrary function. Some
properties of the spectrum of the Hamiltonian are derived, and wave functions
for three energy levels are constructed. This construction can be interpreted
as addition of three new levels to the spectrum of partner potential: a ground
state and a pair of levels between successive excited states. Possible types of
factorization of the third order supercharges are analysed, the connection with
earlier known results is discussed.Comment: 17
Magnetotransport Mechanisms in Strongly Underdoped YBa_2Cu_3O_x Single Crystals
We report magnetoresistivity measurements on strongly underdoped YBa_2Cu_3O_x
(x=6.25, 6.36) single crystals in applied magnetic fields H || c-axis. We
identify two different contributions to both in-plane and out-of-plane
magnetoresistivities. The first contribution has the same sign as the
temperature coefficient of the resistivity \partial ln(\rho_i)/\partial T
(i={c,ab}). This contribution reflects the incoherent nature of the
out-of-plane transport. The second contribution is positive, quadratic in
field, with an onset temperature that correlates to the antiferromagnetic
ordering.Comment: 4 pages, 3 figure
Electron Dynamics in NdCeCuO: Evidence for the Pseudogap State and Unconventional c-axis Response
Infrared reflectance measurements were made with light polarized along the a-
and c-axis of both superconducting and antiferromagnetic phases of electron
doped NdCeCuO. The results are compared to
characteristic features of the electromagnetic response in hole doped cuprates.
Within the CuO planes the frequency dependent scattering rate,
1/, is depressed below 650 cm; this behavior is a
hallmark of the pseudogap state. While in several hole doped compounds the
energy scales associated with the pseudogap and superconducting states are
quite close, we are able to show that in NdCeCuO
the two scales differ by more than one order of magnitude. Another feature of
the in-plane charge response is a peak in the real part of the conductivity,
, at 50-110 cm which is in sharp contrast with the
Drude-like response where is centered at . This
latter effect is similar to what is found in disordered hole doped cuprates and
is discussed in the context of carrier localization. Examination of the c-axis
conductivity gives evidence for an anomalously broad frequency range from which
the interlayer superfluid is accumulated. Compelling evidence for the pseudogap
state as well as other characteristics of the charge dynamics in
NdCeCuO signal global similarities of the cuprate
phase diagram with respect to electron and hole doping.Comment: Submitted to PR
Two-dimensional SUSY-pseudo-Hermiticity without separation of variables
We study SUSY-intertwining for non-Hermitian Hamiltonians with special
emphasis to the two-dimensional generalized Morse potential, which does not
allow for separation of variables. The complexified methods of SUSY-separation
of variables and two-dimensional shape invariance are used to construct
particular solutions - both for complex conjugated energy pairs and for
non-paired complex energies.Comment: 14 pages, Late
String Cosmology: A Review
We give an overview of the status of string cosmology. We explain the
motivation for the subject, outline the main problems, and assess some of the
proposed solutions. Our focus is on those aspects of cosmology that benefit
from the structure of an ultraviolet-complete theory.Comment: 55 pages. v2: references adde
Effect of a Normal-State Pseudogap on Optical Conductivity in Underdoped Cuprate Superconductors
We calculate the c-axis infrared conductivity in
underdoped cuprate superconductors for spinfluctuation exchange scattering
within the CuO-planes including a phenomenological d-wave pseudogap of
amplitude . For temperatures decreasing below a temperature , a gap for develops in in the
incoherent (diffuse) transmission limit. The resistivity shows 'semiconducting'
behavior, i.e. it increases for low temperatures above the constant behavior
for . We find that the pseudogap structure in the in-plane optical
conductivity is about twice as big as in the interplane conductivity
, in qualitative agreement with experiment. This is a
consequence of the fact that the spinfluctuation exchange interaction is
suppressed at low frequencies as a result of the opening of the pseudogap.
While the c-axis conductivity in the underdoped regime is described best by
incoherent transmission, in the overdoped regime coherent conductance gives a
better description.Comment: to be published in Phys. Rev. B (November 1, 1999
Effective Actions and Phase Fluctuations in d-wave Superconductors
We study effective actions for order parameter fluctuations at low
temperature in layered d-wave superconductors such as the cuprates. The order
parameter lives on the bonds of a square lattice and has two amplitude and two
phase modes associated with it. The low frequency spectral weights for
amplitude and relative phase fluctuations is determined and found to be
subdominant to quasiparticle contributions. The Goldstone phase mode and its
coupling to density fluctuations in charged systems is treated in a
gauge-invariant manner. The Gaussian phase action is used to study both the
-axis Josephson plasmon and the more conventional in-plane plasmon in the
cuprates. We go beyond the Gaussian theory by deriving a coarse-grained quantum
XY model, which incorporates important cutoff effects overlooked in previous
studies. A variational analysis of this effective model shows that in the
cuprates, quantum effects of phase fluctuations are important in reducing the
zero temperature superfluid stiffness, but thermal effects are small for .Comment: Some numerical estimates corrected and figures changed. to appear in
PRB, Sept.1 (2000
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