11,371 research outputs found
Current dependence of grain boundary magnetoresistance in La_0.67Ca_0.33MnO_3 films
We prepared epitaxial ferromagnetic manganite films on bicrystal substrates
by pulsed laser ablation. Their low- and high-field magnetoresistance (MR) was
measured as a function of magnetic field, temperature and current. At low
temperatures hysteretic changes in resistivity up to 70% due to switching of
magnetic domains at the coercitive field are observed. The strongly non-ohmic
behavior of the current-voltage leads to a complete suppression of the MR
effect at high bias currents with the identical current dependence at low and
high magnetic fields. We discuss the data in view of tunneling and mesoscale
magnetic transport models and propose an explicit dependence of the spin
polarization on the applied current in the grain boundary region.Comment: 5 pages, to appear in J. Appl. Phy
Recent advances in minimally invasive colorectal cancer surgery
Laparoscopy has improved surgical treatment of various diseases due to its limited surgical trauma and has developed as an interesting therapeutic alternative for the resection of colorectal cancer. Despite numerous clinical advantages (faster recovery, less pain, fewer wound and systemic complications, faster return to work) the laparoscopic approach to colorectal cancer therapy has also resulted in unusual complications, i.e. ureteral and bladder injury which are rarely observed with open laparotomy. Moreover, pneumothorax, cardiac arrhythmia, impaired venous return, venous thrombosis as well as peripheral nerve injury have been associated with the increased intraabdominal pressure as well as patient's positioning during surgery. Furthermore, undetected small bowel injury caused by the grasping or cauterizing instruments may occur with laparoscopic surgery. In contrast to procedures performed for nonmalignant conditions, the benefits of laparoscopic resection of colorectal cancer must be weighed against the potential for poorer long-term outcomes of cancer patients that still has not been completely ruled out. In laparoscopic colorectal cancer surgery, several important cancer control issues still are being evaluated, i.e. the extent of lymph node dissection, tumor implantation at port sites, adequacy of intraperitoneal staging as well as the distance between tumor site and resection margins. For the time being it can be assumed that there is no significant difference in lymph node harvest between laparoscopic and open colorectal cancer surgery if oncological principles of resection are followed. As far as the issue of port site recurrence is concerned, it appears to be less prevalent than first thought (range 0-2.5%), and the incidence apparently corresponds with wound recurrence rates observed after open procedures. Short-term (3-5 years) survival rates have been published by a number of investigators, and survival rates after laparoscopic surgery appears to compare well with data collected after conventional surgery for colorectal cancer. However, long-term results of prospective randomized trials are not available. The data published so far indicate that the oncological results of laparoscopic surgery compare well with the results of the conventional open approach. Nonetheless, the limited information available from prospective studies leads us to propose that minimally invasive surgery for colorectal cancer surgery should only be performed within prospective trials
A semiclassical analysis of the Efimov energy spectrum in the unitary limit
We demonstrate that the (s-wave) geometric spectrum of the Efimov energy
levels in the unitary limit is generated by the radial motion of a primitive
periodic orbit (and its harmonics) of the corresponding classical system. The
action of the primitive orbit depends logarithmically on the energy. It is
shown to be consistent with an inverse-squared radial potential with a lower
cut-off radius. The lowest-order WKB quantization, including the Langer
correction, is shown to reproduce the geometric scaling of the energy spectrum.
The (WKB) mean-squared radii of the Efimov states scale geometrically like the
inverse of their energies. The WKB wavefunctions, regularized near the
classical turning point by Langer's generalized connection formula, are
practically indistinguishable from the exact wave functions even for the lowest
() state, apart from a tiny shift of its zeros that remains constant for
large .Comment: LaTeX (revtex 4), 18pp., 4 Figs., already published in Phys. Rev. A
but here a note with a new referece is added on p. 1
Killing spinors in supergravity with 4-fluxes
We study the spinorial Killing equation of supergravity involving a torsion
3-form \T as well as a flux 4-form \F. In dimension seven, we construct
explicit families of compact solutions out of 3-Sasakian geometries, nearly
parallel \G_2-geometries and on the homogeneous Aloff-Wallach space. The
constraint \F \cdot \Psi = 0 defines a non empty subfamily of solutions. We
investigate the constraint \T \cdot \Psi = 0, too, and show that it singles
out a very special choice of numerical parameters in the Killing equation,
which can also be justified geometrically
Generalized vortex-model for the inverse cascade of two-dimensional turbulence
We generalize Kirchhoff's point vortex model of two-dimensional fluid motion
to a rotor model which exhibits an inverse cascade by the formation of rotor
clusters. A rotor is composed of two vortices with like-signed circulations
glued together by an overdamped spring. The model is motivated by a treatment
of the vorticity equation representing the vorticity field as a superposition
of vortices with elliptic Gaussian shapes of variable widths, augmented by a
suitable forcing mechanism. The rotor model opens up the way to discuss the
energy transport in the inverse cascade on the basis of dynamical systems
theory.Comment: 14 pages, 21 figure
On the existence of Killing vector fields
In covariant metric theories of coupled gravity-matter systems the necessary
and sufficient conditions ensuring the existence of a Killing vector field are
investigated. It is shown that the symmetries of initial data sets are
preserved by the evolution of hyperbolic systems.Comment: 9 pages, no figure, to appear in Class. Quant. Gra
Miniature mobile sensor platforms for condition monitoring of structures
In this paper, a wireless, multisensor inspection system for nondestructive evaluation (NDE) of materials is described. The sensor configuration enables two inspection modes-magnetic (flux leakage and eddy current) and noncontact ultrasound. Each is designed to function in a complementary manner, maximizing the potential for detection of both surface and internal defects. Particular emphasis is placed on the generic architecture of a novel, intelligent sensor platform, and its positioning on the structure under test. The sensor units are capable of wireless communication with a remote host computer, which controls manipulation and data interpretation. Results are presented in the form of automatic scans with different NDE sensors in a series of experiments on thin plate structures. To highlight the advantage of utilizing multiple inspection modalities, data fusion approaches are employed to combine data collected by complementary sensor systems. Fusion of data is shown to demonstrate the potential for improved inspection reliability
Self-gravitating Klein-Gordon fields in asymptotically Anti-de-Sitter spacetimes
We initiate the study of the spherically symmetric Einstein-Klein-Gordon
system in the presence of a negative cosmological constant, a model appearing
frequently in the context of high-energy physics. Due to the lack of global
hyperbolicity of the solutions, the natural formulation of dynamics is that of
an initial boundary value problem, with boundary conditions imposed at null
infinity. We prove a local well-posedness statement for this system, with the
time of existence of the solutions depending only on an invariant H^2-type norm
measuring the size of the Klein-Gordon field on the initial data. The proof
requires the introduction of a renormalized system of equations and relies
crucially on r-weighted estimates for the wave equation on asymptotically AdS
spacetimes. The results provide the basis for our companion paper establishing
the global asymptotic stability of Schwarzschild-Anti-de-Sitter within this
system.Comment: 50 pages, v2: minor changes, to appear in Annales Henri Poincar\'
Canonical-type connection on almost contact manifolds with B-metric
The canonical-type connection on the almost contact manifolds with B-metric
is constructed. It is proved that its torsion is invariant with respect to a
subgroup of the general conformal transformations of the almost contact
B-metric structure. The basic classes of the considered manifolds are
characterized in terms of the torsion of the canonical-type connection.Comment: 11 pages, The final publication is available at
http://www.springerlink.co
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