1,477 research outputs found
Micromagnetic simulations of the magnetization precession induced by a spin polarized current in a point contact geometry
This paper is devoted to numerical simulations of the magnetization dynamics
driven by a spin-polarized current in extended ferromagnetic multilayers when a
point-contact setup is used. We present (i) detailed analysis of methodological
problems arising by such simulations and (ii) physical results obtained on a
system similar to that studied in Rippard et al., Phys. Rev. Lett., v. 92,
027201 (2004). We demonstrate that the usage of a standard Slonczewski
formalism for the phenomenological treatment of a spin-induced torque leads to
a qualitative disagreement between simulation results and experimental
observations and discuss possible reasons for this discrepancy.Comment: Invited paper on MMM2005 (San Jose); accepted for publication in J.
Applied Physic
Magnetization precession due to a spin polarized current in a thin nanoelement: numerical simulation study
In this paper a detailed numerical study (in frames of the Slonczewski
formalism) of magnetization oscillations driven by a spin-polarized current
through a thin elliptical nanoelement is presented. We show that a
sophisticated micromagnetic model, where a polycrystalline structure of a
nanoelement is taken into account, can explain qualitatively all most important
features of the magnetization oscillation spectra recently observed
experimentally (S.I. Kiselev et al., Nature, vol. 425, p. 380 (2003), namely:
existence of several equidistant spectral bands, sharp onset and abrupt
disappearance of magnetization oscillations with increasing current, absence of
the out-of-plane regime predicted by a macrospin model and the relation between
frequencies of so called small-angle and quasichaotic oscillations. However, a
quantitative agreement with experimental results (especially concerning the
frequency of quasichaotic oscillations) could not be achieved in the region of
reasonable parameter values, indicating that further model refinement is
necessary for a complete understanding of the spin-driven magnetization
precession even in this relatively simple experimental situation.Comment: Submitted to Phys. Rev. B; In this revised version figure positions
on the page have been changed to ensure correct placements of the figure
caption
Magnetodipolar interlayer interaction effect on the magnetization dynamics of a trilayer square element with the Landau domain structure
We present a detailed numerical simulation study of the effects caused by the magnetodipolar interaction between ferromagnetic ͑FM͒ layers of a trilayer magnetic nanoelement on its magnetization dynamics. As an example, we use a Co/ Cu/ Ni 80 Fe 20 element with a square lateral shape where the magnetization of FM layers forms a closed Landau-like domain pattern. First, we show that when the thickness of the nonmagnetic ͑NM͒ spacer is in the technology relevant region h ϳ 10 nm, magnetodipolar interaction between 90°Neel domain walls in FM layers qualitatively changes the equilibrium magnetization state of these layers. In the main part of the paper, we compare the magnetization dynamics induced by a sub-nsec field pulse in a single-layer Ni 80 Fe 20 ͑Py͒ element and in the Co/ Cu/ Py trilayer element. Here, we show that ͑i͒ due to the spontaneous symmetry breaking of the Landau state in the FM/NM/FM trilayer, its domains and domain walls oscillate with different frequencies and have different spatial oscillation patterns; ͑ii͒ magnetization oscillations of the trilayer domains are strongly suppressed due to different oscillation frequencies of domains in Co and Py; ͑iii͒ magnetization dynamics qualitatively depends on the relative rotation sense of magnetization states in Co and Py layers and on the magnetocrystalline anisotropy kind of Co crystallites. Finally, we discuss the relation of our findings with experimental observations of magnetization dynamics in magnetic trilayers, performed using the element-specific time-resolved x-ray microscopy
High plasma leptin levels confer increased risk of atherosclerosis in women with systemic lupus erythematosus, and are associated with inflammatory oxidised lipids.
BackgroundPatients with systemic lupus erythematosus (SLE) are at increased risk of atherosclerosis, even after accounting for traditional risk factors. High levels of leptin and low levels of adiponectin are associated with both atherosclerosis and immunomodulatory functions in the general population.ObjectiveTo examine the association between these adipokines and subclinical atherosclerosis in SLE, and also with other known inflammatory biomarkers of atherosclerosis.MethodsCarotid ultrasonography was performed in 250 women with SLE and 122 controls. Plasma leptin and adiponectin levels were measured. Lipoprotein a (Lp(a)), oxidised phospholipids on apoB100 (OxPL/apoB100), paraoxonase, apoA-1 and inflammatory high-density lipoprotein (HDL) function were also assessed.ResultsLeptin levels were significantly higher in patients with SLE than in controls (23.7±28.0 vs 13.3±12.9 ng/ml, p<0.001). Leptin was also higher in the 43 patients with SLE with plaque than without plaque (36.4±32.3 vs 20.9±26.4 ng/ml, p=0.002). After multivariate analysis, the only significant factors associated with plaque in SLE were leptin levels in the highest quartile (≥29.5 ng/ml) (OR=2.8, p=0.03), proinflammatory HDL (piHDL) (OR=12.8, p<0.001), age (OR=1.1, p<0.001), tobacco use (OR=7.7, p=0.03) and hypertension (OR=3.0, p=0.01). Adiponectin levels were not significantly associated with plaque in our cohort. A significant correlation between leptin and piHDL function (p<0.001), Lp(a) (p=0.01) and OxPL/apoB100 (p=0.02) was also present.ConclusionsHigh leptin levels greatly increase the risk of subclinical atherosclerosis in SLE, and are also associated with an increase in inflammatory biomarkers of atherosclerosis such as piHDL, Lp(a) and OxPL/apoB100. High leptin levels may help to identify patients with SLE at risk of atherosclerosis
Информационная технология оценки показателей качества жизни пациентов
Оценка качества жизни пациентов на основе многомерного анализа данных (результатов психологического тестирования). Выбор R в качестве основного инструментария.Assessment of the quality of life of patients on the basis of multidimensional data analysis (the results of psychological testing). The choice of R as the main tool
Spin-torque driven magnetization dynamics in a nanocontact setup for low external fields: numerical simulation study
We present numerical simulation studies of the steady-state magnetization
dynamics driven by a spin-polarized current in a point contact geometry for the
case of a relatively large contact diameter (D = 80 nm) and small external
field (H = 30 Oe). We show, that under these conditions the magnetization
dynamics is qualitatively different from the dynamics observed for small
contacts in large external fields. In particular, the 'bullet' mode with a
homogeneous mode core, which was the dominating localized mode for small
contacts, is not found here. Instead, all localized oscillation modes observed
in simulations correspond to different motion kinds of vortex-antivortex (V-AV)
pairs. These kinds include rotational and translational motion of pairs with
the V-AV distance d ~ D and creation/annihilation of much smaller (satellite)
V-AV pairs. We also show that for the geometry studied here the Oersted field
has a qualitative effect on the magnetization dynamics of a 'free' layer. This
effect offers a possibility to control magnetization dynamics by a suitable
electric contact setup, optimized to produce a desired Oersted field. Finally,
we demonstrate that when the magnetization dynamics of the 'fixed' layer
(induced only by the stray field interaction with the 'free' layer) is taken
into account, the threshold current for the oscillation onset is drastically
reduced and new types of localized modes appear. In conclusion, we show that
our simulations reproduce semiquantitatively several important features of the
magnetization dynamics in a point contact system for low external fields
reported experimentally.Comment: 26 pages, 12 figures, submitted to Phys. Rev.
Stochastic dynamic simulations of fast remagnetization processes: recent advances and applications
Numerical simulations of fast remagnetization processes using the stochastic
dynamics are widely used to study various magnetic systems. In this paper we
first address several crucial methodological problems of such simulations: (i)
the influence of the finite-element discretization on the simulated dynamics,
(ii) choice between Ito and Stratonovich stochastic calculi by the solution of
micromagnetic stochastic equations of motion and (iii) non-trivial correlation
properties of the random (thermal) field. Next we discuss several examples to
demonstrate the great potential of the Langevin dynamics for studying fast
remagnetization processes in technically relevant applications: we present
numerical analysis of equilibrium magnon spectra in patterned structures, study
thermal noise effects on the magnetization dynamics of nanoelements in pulsed
fields and show some results for a remagnetization dynamics induced by a
spin-polarized current.Comment: Invited paper submittedto JEMS'04 (Dresden, Germany
Upward high-energy field-aligned electron beams above the polar edge of auroral oval: observations from the SKA-3 instruments onboard the Auroral Probe (Interball-2)
Spatial Resolution Attainable with Cathode Strip Chambers at the Trigger Level
A simple network of comparators applied to the strip signals of a cathode strip chamber allows quick hit localization to within a halfstrip width, or +/- a quarter-strip. A six-plane chamber with 6.4 mm wide strips was tested in a high-energy muon beam. The chamber was placed behind a 30 cm thick iron block. We show that patterns of hits localized to within a halfstrip allowed us to identify 300 GeV/c muon tracks with 99% probability and 0.7 mm spatial resolution in the presence of muon bremsstrahlung radiation. This technique of finding muon tracks will be used in the cathode strip chambers of the CMS Endcap Muon System
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