3,037 research outputs found
Current-driven vortex domain wall dynamics by micromagnetic simulations
Current-driven vortex wall dynamics is studied by means of a two-dimensional
analytical model and micromagnetic simulation. By constructing a trial function
for the vortex wall in the magnetic wire, we analytically solve for domain wall
velocity and deformation in the presence of the current-induced spin torque. A
critical current for the domain wall transformation from the vortex wall to the
transverse wall is calculated. A comparison between the field- and
current-driven wall dynamics is carried out. Micromagnetic simulations are
performed to verify our analytical results.Comment: 7 pages, 4 figure
Current-driven resonant excitation of magnetic vortex
A magnetic vortex core in a ferromagnetic circular nanodot has a resonance
frequency originating from the confinement of the vortex core. By the
micromagnetic simulation including the spin-transfer torque, we show that the
vortex core can be resonantly excited by an AC (spin-polarized) current through
the dot and that the resonance frequency can be tuned by the dot shape. The
resistance measurement under the AC current successfully detects the resonance
at the frequency consistent with the simulation.Comment: 16 pages, 4 figure
Real-space observation of current-driven domain wall motion in submicron magnetic wires
Spintronic devices, whose operation is based on the motion of a magnetic
domain wall (DW), have been proposed recently. If a DW could be driven directly
by flowing an electric current instead of a magnetic field, the performance and
functions of such device would be drastically improved. Here we report
real-space observation of the current-driven DW motion by using a well-defined
single DW in a micro-fabricated magnetic wire with submicron width. Magnetic
force microscopy (MFM) visualizes that a single DW introduced in the wire is
displaced back and forth by positive and negative pulsed-current, respectively.
We can control the DW position in the wire by tuning the intensity, the
duration and the polarity of the pulsed-current. It is, thus, demonstrated that
spintronic device operation by the current-driven DW motion is possible.Comment: Accepted and published in PR
Electrical rectification effect in single domain magnetic microstrips: a micromagnetics-based analysis
Upon passing an a.c. electrical current along magnetic micro- or nanostrips,
the measurement of a d.c. voltage that depends sensitively on current frequency
and applied field has been recently reported by A. Yamaguchi and coworkers. It
was attributed to the excitation of spin waves by the spin transfer torque,
leading to a time-varying anisotropic magnetoresistance and, by mixing of a.c.
current and resistance, to a d.c. voltage. We have performed a quantitative
analysis by micromagnetics, including the spin transfer torque terms considered
usually, of this situation. The signals found from the spin transfer torque
effect are several orders of magnitude below the experimental values, even if a
static inhomogeneity of magnetization (the so-called ripple) is taken into
account. On the other hand, the presence of a small non-zero average Oersted
field is shown to be consistent with the full set of experimental results, both
qualitatively and quantitatively. We examine, quantitatively, several sources
for this average field and point to the contacts to the sample as a likely
origin.Comment: to be published in Journal of Applied Physic
Significance of myocardial tenascin-C expression in left ventricular remodelling and long-term outcome in patients with dilated cardiomyopathy
Aim Dilated cardiomyopathy (DCM) has a variety of causes, and no useful approach to predict left ventricular (LV) remodelling and long-term outcome has yet been established. Myocardial tenascin-C (TNC) is known to appear under pathological conditions, possibly to regulate cardiac remodelling. The aim of this study was to clarify the significance of myocardial TNC expression in LV remodelling and the long-term outcome in DCM. Methods and results One hundred and twenty-three consecutive DCM patients who underwent endomyocardial biopsy for initial diagnosis were studied. Expression of TNC in biopsy sections was analysed immunohistochemically to quantify the ratio of the TNC-positive area to the whole myocardial tissue area (TNC area). Clinical parameters associated with TNC area were investigated. The patients were divided into two groups based on receiver operating characteristic analysis of TNC area to predict death: high TNC group with TNC area ≥2.3% (22 patients) and low TNC group with TNC area <2.3% (101 patients). High TNC was associated with diabetes mellitus. Comparing echocardiographic findings between before and 9 months after endomyocardial biopsy, the low TNC group was associated with decreased LV end-diastolic diameter and increased LV ejection fraction, whereas the high TNC group was not. Survival analysis revealed a worse outcome in the high TNC group than in the low TNC group (P < 0.001). Multivariable Cox regression analysis revealed that TNC area was independently associated with poor outcome (HR = 1.347, P = 0.032). Conclusions Increased myocardial TNC expression was associated with worse LV remodeling and long-term outcome in DCM
Empirically Driven Use Case Metamodel Evolution
Metamodel evolution is rarely driven by empirical evidences of metamodel
drawbacks. In this paper, the evolution of the use case metamodel used
by the publicly available requirements management tool REM is presented. This
evolution has been driven by the analysis of empirical data obtained during the
assessment of several metrics–based verification heuristics for use cases developed
by some of the authors and previously presented in other international fora.
The empirical analysis has made evident that some common defects found in
use cases developed by software engineering students were caused not only by
their lack of experience but also by the expressive limitations imposed by the underlying
use case metamodel used in REM. Once these limitations were clearly
identified, a number of evolutionary changes were proposed to the REM use case
metamodel in order to increase use case quality, i.e. to avoid those situations in
which the metamodel were the cause of defects in use case specifications.Ministerio de Ciencia y TecnologĂa TIC 2003-02737-C02-0
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