High damping in Fe-Ga-La alloys: Phenomenological model for magneto-mechanical hysteresis damping and experiment

Ferromagnetic high damping (FHA) alloys with a wide temperature range from-150 ℃ to 300 ℃ have unique application value in extreme environments.In the present work,the damping behaviors of Fe21Ga-xLa (x =0.12 wt.％,0.24 wt.％,0.47 wt.％,1.18 wt.％,and 2.33 wt.％La) alloys have been studied in detail,and a new phenomenoiogical model has been proposed.With the increase of La content,the Laves phase (LaGa2) in the matrix increases gradually,and the resistance opposing the domain movement increases as well.Combined with the results of synchrotron radiation X-ray diffraction,neutron diffraction,and magnetic domain observation,the resistance mainly comes from three parts: the average stress related to the lattice distortion of the matrix,the average stress related to the increasing area energy of domain walls (DWs),and the average stress related to the increasing demagnetization energy induced by the Laves phase.Different from the traditional method of reducing internal stress through annealing to improve the damping capacity,the proper internal stress barriers are necessary to Barkhausen jumps to dissipate energy.Therefore,proper doping to balance resistance and mobility of DWs is a reliable way to improve damping capacity.Meanwhile,for Fe-Al and Fe-Cr based Alloys,the new model also has a good fitting effect.This study provides a theoretical and experimental reference for improving the functional properties of ferromagnetic alloys.     

Comparison of four global FAPAR datasets over Northern Eurasia for the year 2000

The Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) has been identified as one of several key satellite-derived biophysical datasets. With multiple global FAPAR datasets now available and a lack of in-situ measurements and comparison studies in the far north, this study attempts to provide the reader with an indication of the performance of four global FAPAR datasets (MODIS, CYCLOPES, JRC and GLOBCARBON) over Northern Eurasia in the year 2000 via comparison. Within the year 2000 growing season, both the MODIS and CYCLOPES datasets recorded on average similar but substantially higher values than the JRC and GLOBCARBON datasets. Among three of the four datasets, a high level of agreement in deciduous broadleaf forests and croplands was observed. Largest disagreement occurred among needleleaf forests and grassland/shrubland. Potential reasons for discrepancies among the datasets include different retrieval methods, use of LAI and land cover, snow effects and others. Findings from this study and other published results suggest that overall, JRC best captures FAPAR over northern Eurasia in the year 2000. However, when considering individual landcover types, any one or more of the four products may be suitable. There exists a real need for more in-situ measurements in this region — the lack of such measurements makes evaluation extremely difficult. It appears that areas north of 60° urgently require further investigation.     

Conformational variability of helix sense reversals in poly(methyl isocyanate)

The conformations and energies of several helix sense reversal geometries in poly(methyl isocyanate) (PMIC) have been determined using the PCFF forcefield. In an extension of previous studies, a larger conformational variability for a helix sense reversal has been investigated. In addition to the reversal geometry previously detailed by several authors that results in a relatively small angle deviation from the rod-like polyisocyanate structure, we report the discovery of reversals of similar energy with much larger angle deviations from linearity. The effect of electrostatic interactions as controlled by the value of the dielectric constant, ε, on the conformation and energy of a reversal is also shown to be important. At ε=1.0 (vacuum) the conformations of the reversals with large and small angle ‘kinks’ have similar energies. However, at ε=2.0 (non-polar organic solvent) and ε=3.5 (bulk state) the reversals corresponding to the large angle kinks have lower energies.     

Thermodynamic model of creep at constant stress and constant strain rate

A thermodynamic model has been developed that describes the entire creep process, including primary, secondary, and tertiary creep, and failure for both constant stress (CS) tests ($\text{σ =}\text{const.}$) and constant strain rate (CSR) tests ($\text{? =}\text{const.}$), in the form of a unified constitutive equation and unified failure criteria. Deformation and failure are considered as a single thermoactivated process in which the dominant role belongs to the change of entropy. Failure occurs when the entropy change is zero. At that moment, the strain rates in CS tests reach the minima and stress in CSR tests reaches the maximum (peak) values. Families of creep (? vs t) and stress-strain (σ vs ?) curves, obtained from uniaxial compression CS and CSR tests of frozen soil, respectively (both presented in dimensionless coordinates), are plotted as straight lines and are superposed, confirming the unity of the deformation and failure process and the validity of the model. A method is developed for determining the parameters of the model, so that creep deformation and the stress-strain relationship of ductile materials such as soils can be predicted based upon information obtained from either type of test.     

Features of pulse substrate bias voltage generation with electron tubes

Features of pulse substrate bias voltage generation with electron tubes in different operation modes are considered. The overstressed mode with low anode voltage and return of electrons to the grid has practical significance at bias voltages in the kilovolt range under the conditions of large substrate current fluctuations. This mode ensures small bias voltage fluctuations and effective use of the primary DC voltage. When the substrate current spontaneously rises above the critical value, the tubes automatically decrease the bias voltage and suppress current spikes and arcing. Such approach may be used in PVD processes, for ion surface treatment and ion plasma immersion implantation.     

One Criterion of Existence of a Himiltonian Cycle

In the paper, the necessary and sufficient conditions of existence of a Hamiltonian cycle in a graph are investigated. It is proven that a graph is Hamiltonian if andonly if the number of elemetns in any independent set of its vertices does not exceed the number of vertices in the minimum separating set for the paths connecting these independent vertices.     

An effective numerical method for solving viscous-inviscid interaction problems

This paper presents a new numerical method to solve the equations of the asymptotic theory of separated flows. A number of measures was taken to ensure fast convergence of the iteration procedure, which is employed to treat the nonlinear terms in the governing equations. Firstly, we selected carefully the set of variables for which the nonlinear finite difference equations were formulated. Secondly, a Newton-Raphson strategy was applied to these equations. Thirdly, the calculations were facilitated by utilizing linear approximation of the boundary-layer equations when calculating the corresponding Jacobi matrix.The performance of the method is illustrated, using as an example, the problem of laminar two-dimensional boundary-layer separation in the flow of an incompressible fluid near a corner point of a rigid body contour. The solution of this problem is non-unique in a certain parameter range where two solution branches are possible.     

Removal of phosphate from aqueous solutions by electro-coagulation

The aim of this paper was to investigate the feasibility of the removal of phosphate from aqueous solution by electro-coagulation (EC). The current density (CD) between 2.5 and 10 mA cm(-2) and duration in the limits of 5-20 min were tried for different concentrations. In order to determine optimal operating conditions, the EC process used for the phosphate removal was examined in dependence with the CD, initial concentrations and time. The results of the experimental batch processing showed high effectiveness of the EC method in removing phosphate from aqueous solutions.     

Differences in X-ray absorption due to cadmium treatment in Saponaria officinalis leaves

A method for detecting cadmium uptake in leaves of Saponaria officinalis doped with a solution of cadmium acetate is described. The technique based on the exposure of dried leaves to X-rays of a wavelength close to that of the metal K-edge could be useful for phytoremediation studies as it could reveal the bioaccumulation in plants due to the treatment either in vivo or in vitro with heavy metals. X-ray microradiography measurements are in agreement with those from peroxidase enzyme assay utilized to follow the oxidative damage induced by heavy metals. At present, as we will see in this report, microradiography has still poorer sensitivity in comparison with enzyme assay, but it has the advantage of being faster, not destructive, and usable even at very high doping levels, where the enzyme assay technique results are fully saturated. Further analysis of the optical density values could lead to a quantitative measurement of the heavy metal in the sample. Thus, the technology developed in this article could be useful for tracing the intake in phytoremediation studies.