Mössbauer spectroscopy applied to the study of Nd-Fe-B permanent magnets corrosion

Powdered Nd-Fe-B-type permanent magnets were heated at 200 C for times up to 32 days. The evolution of the Nd₂Fe₁₄B magnetic phase, followed by⁵⁷Fe Mössbauer spectroscopy, evidenced the positive influence of both the hydrogen decrepitation process and Co, Nb and V additives on the corrosion resistance.     

The method of invariants applied to the analysis of 57Fe Mössbauer spectra

The performance of proposed antihydrogen spectroscopy or gravity experiments will crucially depend on the temperature of the initial antihydrogen sample. Measurements by ATRAP and ATHENA have shown that antihydrogen produced with the nested-trap technique is much hotter than the temperature of the surrounding trap. Therefore, novel schemes for antihydrogen recombination as well as for the pre-cooling of antiprotons are being considered. We are investigating a possible antiproton cooling technique based on the laser cooling of negative osmium ions. If demonstrated to be successful, it will allow the sympathetic cooling of antiprotons—or any negatively charged particles—to microkelvin temperatures. As a first milestone toward the laser cooling of negative ions, we have performed collinear laser spectroscopy on negative osmium and determined the transition frequency and the cross-section of the relevant bound–bound electric-dipole transition.     

Mössbauer spectroscopy in the time domain applied to the study of single‐crystalline guanidinium nitroprusside

Guanidinium nitroprusside GNP, (CN₃H₆)₂[Fe(CN)₅NO] has been investigated in single‐crystalline form by nuclear resonant forward scattering (NFS) using synchrotron radiation (Mössbauer spectroscopy in the time domain). This method provides a direct measure of effective absorber thickness and therefore also of the Lamb–Mössbauer factor f _LM. GNP has the advantage that all [Fe(CN₅)NO]^2- anions are practically aligned within the crystal. For the two different crystal orientations, with the crystallographic a- and c-direction parallel to the synchrotron beam, respectively, we have obtained f _LM ^(a)= 0.122(10) and f _LM ^(c)= 0.206(10), i.e., GNP exhibits significant anisotropic vibrational behavior. The quantum beat pattern of the NFS spectra obtained for the two different crystal orientations is discussed on the basis of radiation characteristics of the polarized synchrotron beam and the multipole transitions of oriented ⁵⁷Fe nuclei.     

On the application of selective-excitation double Mössbauer spectroscopy to problems in materials science

Results showing the influence of optical thickness of a scatterer in selective-excitation double M?ssbauer spectroscopy are presented on the example of α-Fe and FeBO₃. Significant transformation of the spectral γ-radiation structure predicted theoretically is demonstrated for single-layered FeBO₃.     

Nonlinear renormalization-group analysis applied to the hydrodynamic light scattering spectrum of4He belowT λ

We calculate the observable critical temperature dependence of the transport coefficients entering the hydrodynamic form of the dynamic structure factor of⁴He belowT . Application of our recently introduced nonlinear renormalization-group analysis yields quantitative agreement with previous light scattering experiments in the hydrodynamic region. This resolves a long-standing problem in the critical dynamics below the superfluid transition of⁴He.Supported in part by the Fonds zur Förderung der wissenschaftlichen Forschung     

Accuracy analysis of explicit Runge–Kutta methods applied to the incompressible Navier–Stokes equations

This paper investigates the temporal accuracy of the velocity and pressure when explicit Runge–Kutta methods are applied to the incompressible Navier–Stokes equations. It is shown that, at least up to and including fourth order, the velocity attains the classical order of accuracy without further constraints. However, in case of a time-dependent gradient operator, which can appear in case of time-varying meshes, additional order conditions need to be satisfied to ensure the correct order of accuracy. Furthermore, the pressure is only first-order accurate unless additional order conditions are satisfied. Two new methods that lead to a second-order accurate pressure are proposed, which are applicable to a certain class of three- and four-stage methods. A special case appears when the boundary conditions for the continuity equation are independent of time, since in that case the pressure can be computed to the same accuracy as the velocity field, without additional cost. Relevant computations of decaying vortices and of an actuator disk in a time-dependent inflow support the analysis and the proposed methods.     

Mössbauer spectroscopy in the investigation of new mineral–related materials

New materials based on the composition of the mineral schafarzikite, FeSb $_{2}\textit {O}_{4}$ , have been synthesised. $^{57}$ Fe- and $^{121}$ Sb- Mössbauer spectroscopy shows that iron is present as Fe $^{2+}$ and that antimony is present as Sb $^{3+}$ . The presence of Pb $^{2+}$ on the antimony sites in materials of composition FeSb $_{1.5}$ Pb $_{0.5}\textit {O}_{4}$ induces partial oxidation of Fe $^{2+}_{}$ to Fe $^{3+}$ . The quasi-one-dimensional magnetic structure of schafarzikite is retained in FeSb $_{1.5}$ Pb $_{0.5}\textit {O}_{4}$ and gives rise to weakly coupled non-magnetic Fe $^{2+}$ ions coexisting with Fe $^{3+}$ ions in a magnetically ordered state. A similar model can be applied to account for the spectra recorded from the compound Co $_{0.5}$ Fe $_{0.5}$ Sb $_{1.5}$ Pb $_{0.5}\textit {O}_{4}$ .     

Application of M?ssbauer spectroscopy to determine the redox potential of the upper mantle

The chemical composition of mineral associations in the rock of mantle xenoliths was investigated, the content of Fe²⁺ and Fe³⁺ being determined by the M?ssbauer spectroscopy technique. The crystallization conditions (temperature, pressure, and oxygen fugacity) of mantle xenoliths and the composition of the coexisting mantle fluids were assessed. The dependence of the iron oxidation state in spinels on the fugacity of oxygen in a particular system was determined.     

Simulation of the Propagation Property of Metal Wires Terahertz Waveguides

The propagation property of metal wires terahertz waveguides is studied and simulated under the framework of the Sommerfeld model. The group velocity dispersion, attenuation amplitude, transverse magnetic mode and propagating energy have been obtained by numerically solving the complex eigenvalue equation for the propagation constant. It is found that the group velocity dispersion and attenuation amplitude decrease with the increasing radii of metal wires. The energy power within the dielectric layer increase with the increase of radiation frequency.     

Theoretical analysis of cavity saturation spectroscopy of weak molecular absorbance

A theoretical analysis of sub-Doppler molecular saturation spectroscopy by use of a confocal Fabry Perot (CFP) cavity is presented. The effects of gas pressure, cavity length and mirror reflectivity on the saturation dip amplitude are analysed. Such a treatment can provide the optimum conditions and a guidance for the experiment of saturating the weak molecular absorption lines.     

Application of Mössbauer spectroscopy for the complex structural analysis of iron oxide-based nanomaterials

The results of complex structural investigation by XRD, TEM, and Mössbauer spectroscopy of nanomaterials based on iron oxides Fe₃O₄ and γ-Fe₂O₃ are presented. The investigated nanomaterials include nanopowders produced chemically and nanostructural powders produced mechanochemically. The magnetic properties of the nanomaterials, measured at ambient temperature, are discussed.     

X-ray optics at the Russian academy of Sciences’ institute of high-purity materials

We examine the current state, prospects for development, and the application of X-ray optics at the IMT-IHPM: X-ray diffraction optics based on X-ray multilayer mirrors and crystals, X-ray acousto-optics based on X-ray diffraction by acoustically modulated crystals, and the application of X-ray methods of diagnostics for the investigation of piezoelectric crystals.     

Direct Measurement of the Correlation Function of Optical–Terahertz Biphotons

JETP Letters - The second-order correlation function which characterizes the quantum correlation between the optical and terahertz photons generated under spontaneous parametric down-conversion has...     

Continuous 100 Hz planar laser-induced fluorescence applied to the study of combustion processes

In this paper, a 100?Hz planar laser-induced fluorescence system based on the off-shelf commercial laser and self-made intensified camera is presented, which is low cost and maintainable to be applied in practical combustion research. By using this device, 100?Hz continuously planar laser-induces fluorescence laser combustion diagnostics was conducted. To evaluate this device, both laboratorial combustors and a scramjet combustor were studied. In these experiments, the structure of flame and expansion and the oscillation process of combustion can be resolved.     

Electrodynamical Characteristics of α-Lactose Monohydrate in the Terahertz Range

Optics and Spectroscopy - Using methods of infrared, terahertz, and submillimeter spectroscopy, experimental transmission and reflection spectra of α-lactose monohydrate have been obtained at...     

Applying the reference-wavelength method to improve the precision of glucose measurement by near infrared spectroscopy

The reference-wavelength method is proposed to diminish the influence of noises on glucose measurement by differentially processing two signals at the reference and measuring wavelengths.At the reference wavelength,the radiation intensity is insensitive to the changes of glucose concentration.Therefore,it can be used as the internal reference to estimate the noise and then to extract the effective glucose signal at the other wavelengths.The validation experiments are constructed in the non-scattering samples with the reference wavelength of glucose at 1525 nm.The results show that the reference-wavelength-based glucose-specific signal extracting method can largely improve the glucose prediction precision from 17.56 to 8.87mg/dL in the two-component experiment and from 26.82 to 9.94 mg/dL in the three-component experiment.     

Laser spectroscopy of YBr: rotational analysis of the B1Π—X1Σ system

The (ν,0) bands, for ν = 0–5, of the B¹Π-X¹Σ transition of YBr between 806.2–891.2 nm have been studied using the technique of laser vaporization/reaction with supersonic cooling and laser-induced fluorescence spectroscopy. Spectra of both the Y⁷⁹Br and Y⁸¹ Br isotopic molecules were observed and analysed. A least-squares fit of all the measured line positions yielded vibrational and rotational constants for the B¹Π state. The equilibrium bond length of the B¹Π state is determined to be 2.622 5(2) Å.     

Results of high temperature processing of high-carbon materials from the lower Cambrian period of the Earth’s history

The paper reports on the observation of spontaneous fission of nuclides, concentrated in fly ash during the combustion of high-carbon (graphite) material, chemogenic siliceous-carbonaceous rocks and carbonaceous shale in the mixture with brown coal. In the samples obtained, the spontaneous fission was measured by track method. The zones of precipitation of spontaneous fission of nuclides and their lighter homologues on thermochromatographic column were determined. A nuclide with a half-life of 62 days was detected in the alkaline trap. The chemical treatment procedure included co-precipitation with iron hydroxide, dissolution in NH₄OH + H₂O₂ solution and distillation by heating up to 100°C followed by AgI co-precipitation. Based on the chemical behavior it can be concluded that the detected radionuclide belongs to the halides. The content of the parent nuclide in high-carbon (graphite) material and chemogenic siliceous-carbonaceous rock corresponds to 10^–14 g/g.