Hysteresis loops of magnetoactive elastomers (MAE) exhibit several peculiar features, including low coercivity in comparison with mechanically hard materials and a striking mismatch between first ...consecutive magnetization loops. The difference between loops diminishes during cycling of the applied magnetic field, thus displaying a training effect. The article presents the results of our research on a hypothesis explaining this phenomenon. Magnetization of a multigrain ferromagnetic particle is modeled at fields not exceeding the anisotropy field of the constituent grain material. It is shown that because of rotation of particles in an elastomer matrix, different branches of their hysteresis loops stem from the magnetization switching of different grain groups. This process is illustrated in detail by use of simple systems with a small number of grains. The results of simulation are supported with magnetic measurements of both MAE samples and epoxied powder. Coercivity of the modeled trained loops is in the order-of-magnitude agreement with the experiment.
•A new model of magnetorheological elastomers magnetization is proposed.•Magnetization loops of the elastomers are simulated.•Elastic barrier impeding particles rotation reduces coercivity of a ...sample.•Linear elasticity shifts the hysteresis loops to the negative field values.
To model magnetization loops of magnetorheological elastomers (MREs) with magnetically hard filler, we consider an assembly of single-domain particles possessing inversion-symmetrical shape and embedded in a soft polymer matrix. To describe the intrinsic behavior of the particle magnetic moments under an applied field, the Stoner-Wohlfarth approach is employed. Unlike the case of solid matrix, the particle in a MRE is able to rotate relative to its elastic environment, so that its equilibrium orientation results from the balance between the magnetic torque (exerted by the applied field at any magnetic moment that does not point along the field) and the elastic torque generated by the matrix. We assume that elastic resistance to the field-induced particle rotation could be presented as comprising of two contributions. The first one is valid for any not perfectly spherical particle and is independent of the particle–matrix adhesion. It reflects the fact that, when trying to rotate, the particle has to “shoulder its way” by deforming the adjoining regions of the matrix. In that case, for angular deviations up to 90° from the initial position, the resistance torque increases. However, as soon as the rotation angle grows up to the value but infinitesimally exceeding 90°, the elastic torque changes its sign and from now on forces the particle to rotate to 180°, where it attains the geometrical position that coincides with the initial one. Evidently, this process is of the barrier type: both orientations of the particle are equal in elastic energy. The second mechanism stems from the “memory” that a given particle has of its initial state and may be caused, for example, by some macromolecules grafted to its surface while curing the matrix of the MRE. This restoring force always tends to drag the particle to its 0° (initial) position. Therefore, the observed magnetization of a MRE sample comes out as a result of joint interplay of the Stoner-Wohlfarth and the two elastic mechanisms. In our simulations, we show that the proposed model in a natural way accounts for the two essential features observed (solely or together) in experiment, namely: (i) weak net coercivity of the MREs, whose filler particles as themselves are highly coercive, and (ii) asymmetric positions of the magnetization loops with respect to H=0 point at the (M-H) plane.
Abstract
As the injector of the new fourth-generation SKIF
synchrotron light source at the BINP SB RAS (Novosibirsk, Russia),
the linear accelerator will provide a 200 MeV electron beam. A
precise ...measurement of the beam is very important for the control of
the linac and even the entire light source. A set of diagnostic
instruments for tuning the linac and measuring the beam parameters
starting from the electron RF gun to the output of accelerator has
been designed. The instrumentation should cover the dynamic
diagnostic range of 0.6 to 200 MeV and a beam duration from the
initial 100 ps to 3 ps at the output of the accelerator. The set
includes eight fluorescent screens to measure beam transverse size,
two Cherenkov probes and RF-cavity sensors to record beam duration,
a dipole magnetic spectrometer to measure energy and energy spread,
a Faraday cup (FC) and fast current transformers (FCTs) to measure
beam charge current, and beam position monitors (BPMs) to check the
beam position. This paper aims to give an overview of the beam
instrumentation and briefly describes the design and parameters of
each diagnostic system. The results of numerical and dynamics
simulations of some of the instruments are briefed. Possible
scenarios of linac tuning are discussed.
—In this paper, the influence of the effects of potential well distortion and longitudinal microwave instability on the longitudinal size of the electron beam in the VEPP-4M collider is considered. ...As a result, the value of the longitudinal broadband impedance was obtained, which can be used to calculate the longitudinal size of the beam in any collider mode.
To evaluate the soybean polyphenol glucosides bioconversion to aglycone forms by different β-glucosidases-producing filamentous fungi to enhance their antioxidant activity. Soybean defatted flour was ...submitted to solid-state fermentation with Aspergillus niger, Aspergillus niveus and Aspergillus awamori. The fungi studied produced approximately the same β-glucosidase activity units amount when p-nitrophenyl-β- d-glucopyranoside was used as substrate for the assay. However, electrophoretic analysis, using 4-methylumbellipheryl-β- d-glucopyranoside as substrate, showed that β-glucosidase produced by A. niveus was more active. Fermented methanolic extracts showed an increase in polyphenol and genistein contents and antioxidant activities. The highest genistein content was found in soybean fermented by A. niveus. Methanolic extracts of the soybean fermented by the different fungi showed a similar capacity of scavenging H₂O₂ generated in vivo by the tumour promoter 12-O-tetradecanoyl phorbol-13-acetate. A. niveus synthesized a β-glucosidase with higher specificity to hydrolyse genistin β-glycosidic bond than those produced by A. awamori and A. niger. The utilization of these β-glucosidases-producing fungi in soybean fermentation processes resulted in the obtaining of methanolic extracts with different antioxidant potentials that could be used either therapeutically or as an antioxidant in nonphysiological oxidative stress conditions, as the one induced in skin by UV radiation.
The efficiency of the injection from the linear accelerator into the damping ring of the injection complex at Budker Institute of Nuclear Physics has been experimentally studied. The estimations of ...the injection efficiency are in good agreement with the measurements. A method for increasing the efficiency of injection from the linear accelerator into the damping ring has been implemented in order to enhance the productivity of the injection complex. To this end, the RF cavity has been replaced and the RF frequency was changed from 700 to 11 MHz. Recent measurements have shown a two-fold increase in the productivity. Besides that, the behavior of the longitudinal profile of a bunch during the first turns in the damping ring and the dependence of the profile on the beam current have been studied.
Tungsten samples irradiated by an electron beam on a BETA generator are studied to model plasma heat loads in a vacuum chamber of a fusion reactor. The residual stresses in the irradiated samples, ...including those fabricated according to ITER specifications, are measured via X-ray diffraction.
This paper describes stations, both existing and under development, for the diagnostics of beam parameters of the 3rd stage of the Novosibirsk free electron laser (FEL). A modification of the method ...for measuring electron energy spread using the spectrum of spontaneous undulator radiation under the operating conditions of the Novosibirsk FEL is presented.
The energy recovery linear accelerator of the Novosibirsk Free Electron Laser facility can be used as a source of short X-ray pulses. Bremsstrahlung is produced by the electron current of the ...accelerator passing through a thin foil with a bunch repetition frequency of several megahertz and a picosecond duration of an individual bunch. This article discusses the possibilities of creating such a source and the results of the first experiments.
We present experimental results for T20 component of the tensor analyzing power for incoherent π− photoproduction on a deuteron. The experiment was performed on an internal tensor-polarized gas ...deuterium target of the VEPP-3 electron storage ring in 2021 using the proton-proton coincidence method. The data are compared with the results of numerical simulation.
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