Magnetic properties of disordered ferrite and ilmenite-hematite thin films

We have synthesized thin films of disordered zinc ferrite (ZnFe₂O₄) and ilmenite-hematite (FeTiO₃-Fe₂O₃) solid solution, the former and the latter of which are interesting from the viewpoints of magnetooptics and spintronics, respectively, by utilizing sputtering and pulsed laser deposition methods, and have explored their magnetic, magnetooptical, and electrical properties. Although ZnFe₂O₄ possesses a normal spinel structure as its stable phase, some of the Fe³⁺ ions occupy the tetrahedral as well as the octahedral sites in ZnFe₂O₄ of which the sputtered thin film is composed. Consequently, the as-deposited thin film manifests large magnetization even at room temperature although the magnetic phase transition temperature of the stable phase of ZnFe₂O₄ is as low as 10 K. Also, the thin film exhibits a cluster spin glass transition at a temperature as high as 325 K. Furthermore, the ZnFe₂O₄ thin films exhibit large Faraday effects at a wavelength of 400 nm or so. The ilmenite-hematite solid solution is one of the ferrimagnetic semiconductors. Most of the compositions possess Curie temperatures higher than room temperature, and the type of carrier can be tuned only by changing the composition. We have succeeded in synthesizing solid-solution thin films of various compositions grown epitaxially on sapphire substrates with a (0 0 0 1) plane, and have shown that the thin films are ferrimagnetic semiconductors.     

Wavelength tunability of L-band fiber ring lasers using mechanically induced long-period fiber gratings

We report on oscillation wavelength control in erbium-doped fiber ring lasers by adjusting the period of a mechanically induced long-period fiber grating (LPFG) inserted into the fiber ring resonator. Pump light is provided by a 974 nm laser diode (LD), the emission of which is coupled into the fiber ring resonator through a wavelength-division multiplexing coupler. Laser oscillation occurs with a threshold pump LD current of 40 mA, corresponding to a threshold pump power of 5 mW. When a periodic pressure of 0.81 N/mm is applied to form the LPFG, the fiber ring laser exhibits the tunable range of 40.9 nm, i.e., from 1563.1 to 1604 nm, by changing the grating period.     

Quantitative assessment of regional systolic and diastolic functions and temporal heterogeneity of myocardial contraction in patients with myocardial infarction using cine magnetic resonance imaging and Fourier fitting

Purpose

The objective of this study is to determine regional left ventricle (LV) function and temporal heterogeneity of LV wall contraction by analyzing regional time–volume curve (TVC) after Fourier fitting and to assess altered systolic and diastolic functions and temporal indices of myocardial contraction in infarcted segments in comparison with noninfarcted myocardium in patients with myocardial infarction (MI).

Methods

Steady-state cine magnetic resonance (MR) and late gadolinium-enhanced (LGE) MR images were acquired using a 1.5-T MR system in 60 patients with MI. Regional LV function was determined by analyzing regional TVC in 16 segments. The fitted regional TVC was generated by Fourier curve fitting with five harmonics. Regional LV ejection fraction (EF), peak ejection rate (PER), peak filling rate (PFR), time to end-systole and time to peak filling (TPF) were determined from TVC and the first derivative curve.

Results

On LGE MR imaging (MRI), MI was observed in 307 of 960 segments (32.0%). Regional EF and PER averaged in LGE segments were 49.3±14.5% and 2.83±0.65 end-diastolic volume (EDV)/s, significantly lower than those in normal segments (66.7±11.9% and 3.63±0.60 EDV/s, P<.001 and P<.01, respectively). In addition, regional PFR, an index of diastolic function, was significantly reduced in LGE segments (1.94±0.54 vs. 2.86±0.68 EDV/s, P<.01). Time to end-systole and TPF were significantly greater in LGE segments (380.2±57.6 and 169.3±45.4 ms) than in normal segments (300.9±55.1 and 132.3±43.0 ms, P<.01 and P<.01, respectively).

Conclusions

Analysis of regional TVC on cine MRI after Fourier fitting allows quantitative assessment of regional systolic and diastolic LV functions and temporal heterogeneity of LV wall contraction in patients with MI.     

Electrical activities of stacking faults and partial dislocations in 4H-SiC homoepitaxial films

The electrical activities of stacking faults (SFs) and partial dislocations in 4H-SiC homoepitaxial films were investigated by using the electron-beam-induced current (EBIC) technique. The basal plane dislocation was dissociated into Si_(g) 30^° and C_(g) 30^° partials under electron-beam irradiation, with a SF formed in between. The SF shows bright contrast at RT and dark contrast at 50 K in EBIC images. The reasons were discussed according to the quantum-well state of SF. C_(g) 30^° partial is always more electrically active than Si_(g) 30^° partial at each specific accelerating voltage. The EBIC contrasts of those two partials were discussed with the number of recombination centers.     

EPR Study of Single Crystals of PROXYLs

Electron paramagnetic resonance study of the single crystals of two PROXYLs, trans-2,5-bis(4-methylphenyl)-2,5-dimethylpyrrolidine-1-oxy [(±)-1] and trans-2-(4-methylphenyl)-2,5-dimethyl-5-phenylpyrrolidine-1-oxy [(±)-2] was conducted. The obtained spectra were always fitted well by a single Lorentzian. The principal g-values (g _x , g _y , g _z ) of (±)-1 and (±)-2 were determined as (2.00990, 2.00639, 2.00266) and (2.01106, 2.00742, 2.00389), respectively. The profiles of half width at half maximum (HWHM) depending on two polar angles, θ and ϕ, were measured in all directions. The angular profiles of the exchange interaction (|J ₀|) were attempted to be estimated by dividing the experimental HWHM by the calculated total second moment (M ₂ ^tot) with the crystallographic data. For (±)-1, |J ₀| along the c-axis was estimated to be much larger than that along the a- or b-axis. This suggests that (±)-1 is a one-dimensional magnet along the c-axis. Authors' address: Yohei Noda, Electron Spin Chemistry Laboratory, Department of Chemistry, Graduate School of Science, Kyoto University, 606-8502 Kyoto, Japan     

Optimized amplification of femtosecond optical pulses by dispersion management for octave-spanning optical frequency comb generation

We report a method for optimizing the amplification of femtosecond optical pulses by using dispersion management. The amount of dispersion provided to the seed optical pulse of an erbium-doped fiber (EBF) has an optimal region that enhances the output power of an amplifier. The power enhancement is accompanied by spectral broadening, which originates from adiabatic narrowing in the erbium-doped fiber. The amplified optical pulses can be used to generate an octave-spanning optical frequency comb (OFC) by employing a highly nonlinear fiber (HNLF).     

Effects of an air-layer-subdivision technique on the sound transmission through a single plate

Many studies on the sound transmission through a single plate have been carried out theoretically and experimentally. The transmission-loss characteristics, in general, follow mass law. Therefore, increasing mass of a plate is a fundamental measure to improve the insulation performance. This method, however, has limitations and might not be a reasonable alternative in current standards. Furthermore, the transmission loss at the critical frequency of coincidence is deteriorated significantly even if the mass is rather large. In this paper, the effect of the air-layer-subdivision technique is studied in detail from the viewpoint of the sound transmission problem of a single plate. An analytical model of an infinite single plate with a subdivided layer is considered and the improvement of the transmission loss is estimated. The limitations of the technique are clarified with some parametric studies. In order to validate the predictions, an experiment was carried out. The transmission loss of a glass board with the air layer subdivided by acryl partitions was measured in the experiment. They were in good agreement with the theoretical ones near and above the coincidence.     

Mixed-mode oscillations and cluster patterns in an electrochemical relaxation oscillator under galvanostatic control

We studied the dynamics of a prototypical electrochemical model, the electro-oxidation of hydrogen in the presence of poisons, under galvanostatic conditions. The lumped system exhibits relaxation oscillations, which develop mixed-mode oscillations (MMOs) for low preset currents. A fast-slow analysis of the homogeneous dynamics reveals that the MMOs arise from a fast oscillating subsystem and a one-dimensional slow manifold. In the spatially extended system, the galvanostatic constraint imposes a synchronizing global coupling that drives the system into cluster patterns. The properties of the cluster patterns (CPs) result from an intricate interplay of the nature of the local oscillators, the global constraint, and a nonlocal coupling through the electrolyte. In particular, we find that the global constraint suppresses small-amplitude oscillations of MMOs and prevents domains oscillating out of phase from occupying equal regions in phase space. The nonlocal coupling causes each individual clustered region to oscillate on a different limit cycle. Typically multistability of CPs is found. Coexisting patterns possess different oscillation periods and a different total fraction in space that occupies the in-phase or out-of-phase state, respectively.     

Promotion of one-pot Robinson annelation achieved by gradual pressure and temperature manipulation under supercritical conditions

The one-pot Robinson annelation from 2-methyl-cyclohexane-1,3-dione with 3-buten-2-one can be achieved in high yield (95%) and high selectivity (95%) by pressure and temperature manipulation using supercritical carbon dioxide in the presence of MgO catalyst, whose method could be applied for various ketones to synthesize fused polycyclic compounds.     

Interaction of polyoxyethylene cholesteryl ethers with liposomal membranes

In order to deduce the mechanisms of hemolysis induced with the nonionic surfactants, polyoxyethylene cholesteryl ethers, C₂₇H₄₅(OCH₂CH₂) _n OH (n=8, 25, 30, 50) and polyoxyethylene dihydrocholesteryl ethers, C₂₇H₄₇(OCH₂CH₂) _n OH (n=15, 30, 50), the interaction of these surfactants with the liposomal membrane as a simple model membrane was investigated in terms of a leakage of the entrapped marker, and a change of the membrane fluidity. The time-courses of the marker leakage were characterized with two kinetic parameters, the initial induction period and the apparent first-order rate constant. The polyoxyethylene chain length was an important factor in the membrane-lytic activities, and the maximal rate as well as the maximal amount of the marker leakage was observed with n=25–30 in these surfactants series. However, the apparent activation energies derived from the two kinetic parameters increased almost linearly with the hydrophilic chain length. The used surfactants tended to fluidize the liposomal membrane in the concentration ranges of surfactants where the marker leakage is not at all or only slightly induced — but with the higher concentration of the cholesteryl derivatives, the apparent fluidity was significantly reduced. From these observations, the mechanisms of the membrane-lysis are discussed.