50 research outputs found
Control of interlayer exchange coupling in Fe/Cr/Fe trilayers by ion beam irradiation
The manipulation of the antiferromagnetic interlayer coupling in the
epitaxial Fe/Cr/Fe(001) trilayer system by moderate 5 keV He ion beam
irradiation has been investigated experimentally. It is shown that even for
irradiation with very low fluences (10^14 ions/cm^2) a drastic change in
strength of the coupling appears. For thin Cr-spacers (below 0.6 - 0.7 nm) the
coupling strength decreases with fluence, becoming ferromagnetic for fluences
above (2x10^14 ions/cm^2). The effect is connected with the creation of
magnetic bridges in the layered system due to atomic exchange events caused by
the bombardment. For thicker Cr spacers (0.8 - 1.2 nm) an enhancement of the
antiferromagnetic coupling strength is found. A possible explanation of the
enhancement effect is given.Comment: Submitted to PR
Effect of Cr spacer on structural and magnetic properties of Fe/Gd multilayers
In this work we analyse the role of a thin Cr spacer between Fe and Gd layers
on structure and magnetic properties of a [Fe(35A)/Cr(tCr)/Gd(50A)/Cr(tCr)]x12
superlattice. Samples without the Cr spacer (tCr=0) and with a thin tCr=4A are
investigated using X-ray diffraction, polarized neutron and resonance X-ray
magnetic reflectometry, SQUID magnetometery, magneto-optical Kerr effect and
ferromagnetic resonance techniques. Magnetic properties are studied
experimentally in a wide temperature range 4-300K and analysed theoretically
using numerical simulation on the basis of the mean-field model. We show that a
reasonable agreement with the experimental data can be obtained considering
temperature dependence of the effective field parameter in gadolinium layers.
The analysis of the experimental data shows that besides a strong reduction of
the antiferromagnetic coupling between Fe and Gd, the introduction of Cr
spacers into Fe/Gd superlattice leads to modification of both structural and
magnetic characteristics of the ferromagnetic layers
Catalog of dessins d'enfants with \le 4 edges
In this work all the dessins d'enfant with no more than 4 edges are listed
and their Belyi pairs are computed. In order to enumerate all dessins the
technique of matrix model computations was used. The total number of dessins is
134; among them 77 are spherical, 53 of genus 1 and 4 of genus 2. The orders of
automorphism groups of all the dessins are also found.
Dessins are listed by the number of edges. Dessins with the same number of
edges are ordered lexicographically by their lists of 0-valencies. The
corresponding matrix model for any list of 0-valencies is given and computed.
Complex matrix models for dessins with 1 -- 3 edges are used. For the dessins
with 4 edges we use Hermitian matrix model, correlators for which are computed
in [1].Comment: 64 pages, 134 figure
Magnetization and ferromagnetic resonance in a Fe/Gd multilayer: Experiment and modelling
Static and dynamic magnetic properties of a [Fe(35 Å<rf)/Gd(50 Å)]12 superlattice are investigated experimentally in the temperature range 5-295 K using SQUID magnetometery and the ferromagnetic resonance (FMR) technique at frequencies 7-38 GHz. The obtained magnetization curves and FMR spectra are analysed theoretically using numerical simulation on the basis of the effective field model. At every given temperature, both static and resonance experimental data can be approximated well within the proposed model. However, a considerable temperature dependence of the effective field parameter in gadolinium layers has to be taken into account to achieve reasonable agreement with the experimental data in the entire temperature range studied. To describe the peculiarities of experimental FMR spectra, a non-local diffusion-type absorption term in Landau-Lifshitz equations is considered in addition to the Gilbert damping term. Possible reasons for the observed effects are discussed. © 2017 IOP Publishing Ltd
Characterization of a c-Rel inhibitor that mediates anticancer properties in hematologic malignancies by blocking NF-κB-controlled oxidative stress responses
NF-\u3baB plays a variety of roles in oncogenesis and immunity that may be beneficial for therapeutic targeting, but strategies to selectively inhibit NF-\u3baB to exert antitumor activity have been elusive. Here, we describe IT-901, a bioactive naphthalenethiobarbiturate derivative that potently inhibits the NF-\u3baB subunit c-Rel. IT-901 suppressed graft-versus-host disease while preserving graft-versus-lymphoma activity during allogeneic transplantation. Further preclinical assessment of IT-901 for the treatment of human B-cell lymphoma revealed antitumor properties in vitro and in vivo without restriction to NF-\u3baB-dependent lymphoma. This nondiscriminatory, antilymphoma effect was attributed to modulation of the redox homeostasis in lymphoma cells resulting in oxidative stress. Moreover, NF-\u3baB inhibition by IT-901 resulted in reduced stimulation of the oxidative stress response gene heme oxygenase-1, and we demonstrated that NF-\u3baB inhibition exacerbated oxidative stress induction to inhibit growth of lymphoma cells. Notably, IT-901 did not elicit increased levels of reactive oxygen species in normal leukocytes, illustrating its cancer selective properties. Taken together, our results provide mechanistic insight and preclinical proof of concept for IT-901 as a novel therapeutic agent to treat human lymphoid tumors and ameliorate graft-versus-host disease
Ant-aphid relations in Costa Rica, Central America (Hymenoptera: Formicidae; Hemiptera: Aphididae)
We present the first catalogue of ant-aphid associations (Hymenoptera: Formicidae / Hemiptera: Aphididae) of Costa Rica. 29 species of ants and 18 species of aphids establish 48 relationships. Those interactions seem not to be rare in Costa Rica
Iron borate films: Synthesis and characterization
We report the first successful synthesis of iron borate films. FeBO 3 films on GaBO 3 single crystal sub strates have been prepared by a liquid phase epitaxy route. In order to determine optimal crystallization regimes, a series of experiments has been carried out. Electron microscope studies have allowed mon itoring different phases of the film formation. The compositions of the film and of the substrate have been determined by energy dispersive spectroscopy. X ray diffraction analysis has allowed an accurate determination of a mismatch between the lattice parameters of the film and of the substrate. Electron magnetic resonance studies of the FeBO 3 film confirm the existence of magnetic ordering. The values of the effective Dzyaloshinskii field as well as the Néel temperature are in good accordance with those previously determined for FeBO 3 single crystal