549 research outputs found
Domain Wall Resistance in Perpendicular (Ga,Mn)As: dependence on pinning
We have investigated the domain wall resistance for two types of domain walls
in a (Ga,Mn)As Hall bar with perpendicular magnetization. A sizeable positive
intrinsic DWR is inferred for domain walls that are pinned at an etching step,
which is quite consistent with earlier observations. However, much lower
intrinsic domain wall resistance is obtained when domain walls are formed by
pinning lines in unetched material. This indicates that the spin transport
across a domain wall is strongly influenced by the nature of the pinning.Comment: 9 pages, 3 figure
Angular dependence of domain wall resistivity in SrRuO films
is a 4d itinerant ferromagnet (T 150 K) with
stripe domain structure. Using high-quality thin films of SrRuO we study
the resistivity induced by its very narrow ( nm) Bloch domain walls,
(DWR), at temperatures between 2 K and T as a function of the
angle, , between the electric current and the ferromagnetic domains
walls. We find that which provides the first experimental
indication that the angular dependence of spin accumulation contribution to DWR
is . We expect magnetic multilayers to exhibit a similar
behavior.Comment: 5 pages, 5 figure
Primary Extra-gastrointestinal Stromal Tumor of Retroperitoneum
Background Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. More rarely neoplasms with histology and immunohistochemistry similar to GISTs may occur outside the gastrointestinal tract (omentum, mesentery and retroperitoneum) and are so-called Extra-gastrointestinal Stromal Tumors (EGISTs). EGISTs arising in the retroperitoneum are extremely rare: to date, only 58 cases have been reported in the literature. Case Report We herein report a case of a primary EGIST of the retroperitoneum surgically treated. The pre-operative radiological evaluation showed a retroperitoneal mass, placed in left paravertebral region. Results Morphological and immunohistochemical features led to a diagnosis of extra-gastrointestinal stromal tumor (intermediate-low risk form). Conclusions As a result of the rarity of reports of primary EGISTs of retroperitoneum we need to analyze the data of reported cases in order to gain a better understanding about the pathogenesis, prognosis and optimal treatment of this disease
Harmonically confined, semiflexible polymer in a channel: response to a stretching force and spatial distribution of the endpoints
We consider an inextensible, semiflexible polymer or worm-like chain which is
confined in the transverse direction by a parabolic potential and subject to a
longitudinal force at the ends, so that the polymer is stretched out and
backfolding is negligible. Simple analytic expressions for the partition
function, valid in this regime, are obtained for chains of arbitrary length
with a variety of boundary conditions at the ends. The spatial distribution of
the end points or radial distribution function is also analyzed.Comment: 14 pages including figure
Effect of a Domain Wall on the Conductance Quantization in a Ferromagnetic Nanowire
The effect of the domain wall (DW) on the conductance in a ballistic
ferromagnetic nanowire (FMNW) is revisited by exploiting a specific
perturbation theory which is effective for a thin DW; the thinness is often the
case in currently interested conductance measurements on FMNWs. Including the
Hund coupling between carrier spins and local spins in a DW, the conductance of
a FMNW in the presence of a very thin DW is calculated within the
Landauer-B\"{u}ttiker formalism. It is revealed that the conductance plateaus
are modified significantly, and the switching of the quantization unit from
to ``about '' is produced in a FMNW by the introduction of a
thin DW. This accounts well for recent observations in a FMNW.Comment: 5 pages, 2 figures, Corrected typos and added reference
Effective action and density functional theory
The effective action for the charge density and the photon field is proposed
as a generalization of the density functional. A simple definition is given for
the density functional, as the functional Legendre transform of the generator
functional of connected Green functions for the density and the photon field,
offering systematic approximation schemes. The leading order of the
perturbation expansion reproduces the Hartree-Fock equation. A renormalization
group motivated method is introduced to turn on the Coulomb interaction
gradually and to find corrections to the Hartree-Fock and the Kohn-Sham
schemes.Comment: New references and a numerical algorithm added, to appear in Phys.
Rev. B. 30 pages, no figure
Reflection of electrons from a domain wall in magnetic nanojunctions
Electronic transport through thin and laterally constrained domain walls in
ferromagnetic nanojunctions is analyzed theoretically. The description is
formulated in the basis of scattering states. The resistance of the domain wall
is calculated in the regime of strong electron reflection from the wall. It is
shown that the corresponding magnetoresistance can be large, which is in a
qualitative agreement with recent experimental observations. We also calculate
the spin current flowing through the wall and the spin polarization of electron
gas due to reflections from the domain wall.Comment: 7 pages, 4 figure
Relating the Lorentzian and exponential: Fermi's approximation,the Fourier transform and causality
The Fourier transform is often used to connect the Lorentzian energy
distribution for resonance scattering to the exponential time dependence for
decaying states. However, to apply the Fourier transform, one has to bend the
rules of standard quantum mechanics; the Lorentzian energy distribution must be
extended to the full real axis instead of being bounded from
below (``Fermi's approximation''). Then the Fourier transform
of the extended Lorentzian becomes the exponential, but only for times , a time asymmetry which is in conflict with the unitary group time evolution
of standard quantum mechanics. Extending the Fourier transform from
distributions to generalized vectors, we are led to Gamow kets, which possess a
Lorentzian energy distribution with and have exponential
time evolution for only. This leads to probability predictions
that do not violate causality.Comment: 23 pages, no figures, accepted by Phys. Rev.
Trialogue on the number of fundamental constants
This paper consists of three separate articles on the number of fundamental
dimensionful constants in physics. We started our debate in summer 1992 on the
terrace of the famous CERN cafeteria. In the summer of 2001 we returned to the
subject to find that our views still diverged and decided to explain our
current positions. LBO develops the traditional approach with three constants,
GV argues in favor of at most two (within superstring theory), while MJD
advocates zero.Comment: Version appearing in JHEP; 31 pages late
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