Determination of Geometrical Properties of Mechanically Delaminated Ultrathin Talc Platelets

The three-dimensional particle size and shape of mechanically delaminated talc thin platelets were determined by combining two different methods. The plate diameter was determined by microscopy with the aid of an image analyser and the thickness from the X-ray crystallite size perpendicular to the basal plane. The net line broadening of the X-ray diffraction peak, necessary for the determination of X-ray crystallite size, was evaluated by electron microscopy. In order to correct X-ray diffractometry for instrumental broadening, the platelet thickness of a representative specimen was obtained directly using a transmission electron microscope coupled with a laborious slice technique with an ultramicrotome.     

Evaluation of dispersion state of the two racemic compounds of troglitazone in pharmaceutical granules using IR-to-THz imaging

Troglitazone exists as four isomers in equal amount and these isomers compose two racemic compounds, RR/SS and RS/SR. The objective of this study was to discriminate between the racemic compounds and between the crystal and amorphous forms of troglitazone in solid dispersions (SDs) using IR-to-THz imaging. SDs of troglitazone with polyvinylpyrrolidone (PVP, carrier) were prepared by the closed melting method. SDs were heated at various temperatures and water content. The mid-to-far infrared measurements for the powder samples were performed by using the synchrotron radiation source at the BL43IR in SPring-8. Crystalline RR/SS (L) and RS/SR (H) showed different spectra, that is, each form had a specific peak, respectively. However, amorphous forms prepared from each crystalline form exhibited the same spectra. Using the chemo-metric analysis, the existing component was decided in each pixel and the distribution of crystalline L, H and amorphous troglitazone in SDs could be illustrated. For the sample heated at 105 °C, 75%RH, scattered plots of H and amorphous against PVP showed the trend for H was negative; on the other hand, amorphous showed positive correlation. This result suggested that H existed separately, whereas amorphous would be dissolved in PVP. Based on these evaluations, it was clear that the physical state and distribution of troglitazone in SDs, including the discrimination between L, H, and amorphous, reflect the preparation conditions. Chemical imaging can observe a difference in the dispersed state of drug and ingredient in a visible image by performing statistical processing.     

Internal rotation in propionic acid: near-infrared-induced isomerization in solid argon

The conformational system of propionic acid (CH3CH2COOH) is studied in solid argon. It is predicted by the ab initio calculations that this molecule has four stable conformers. These four structures are denoted Tt, Tg+/-, Ct, and Cg+/-, and they differ by the arrangement around the C-O and Calpha-C bonds. The ground-state Tt conformer is the only form present at 8 K after deposition of an argon matrix containing propionic acid. For the CH3CH2COOH and CH3CH2COOD isotopologues, narrow-band excitation of the first hydroxyl stretching overtone of the conformational ground state promotes the Calpha-C and C-O internal rotations producing the Tg+/- and Ct conformers, respectively. A subsequent vibrational excitation of the produced Tg+/- form induces its conversion to the Cg+/- conformer by rotation around the C-O bond. In the dark, all of the produced conformers decay to the conformational ground state at different rates. The decay kinetics and its temperature dependence allow the identification of the conformers by IR absorption spectroscopy, which is supported by ab initio calculations of their vibrational spectra. For the CH3CH2COOD isotopologue, the excitation of molecules isolated in different matrix sites results in site-dependent photoisomerization rates for the Calpha-C and C-O internal rotations, which also confirm the identification of the photoproducts.     

Mixing and condensation in a wet granular medium

We have studied the effect of small amounts of added liquid on the dynamic behavior of a granular system consisting of a mixture of glass beads of two different sizes. Segregation of the large beads to the top of the sample is found to depend in a nontrivial way on the liquid content. A transition to viscoplastic behavior occurs at a critical liquid content, which depends upon the bead size. We show that this transition can be interpreted as a condensation due to the hysteretic liquid bridge forces connecting the beads, and we provide the corresponding phase diagram.     

Modeling,design, growth and characterization of red wavelength range microcavity emitters for plastic optic fiber applications

Resonant cavity light emitting diodes (RC-LEDs) and vertical cavity surface emitting lasers (VCSELs) for the red wavelength range are presented in the paper. A wide variety of simulation tools were employed in the device design and optimization and the good agreement between simulations and measurements enabled effective device development. Our red wavelength range RC-LEDs were mainly intended for short-haul communication systems based on polymethyl methacrylate plastic optical fiber and were optimized accordingly. They are achieving, under different structure and working regime variants, high output power (15 mW), high external efficiency (9.5%), record small-signal modulation bandwidth (f _-3dB up to 350 MHz), error-free back-to-back transmission rates beyond 622 Mbits/s, adjustable far-field pattern and good POF coupling efficiency with reasonably wide tolerances and without using auxiliary optics. In view of the possible use of graded-index POFs, free-space transmission and other high bandwidth or high spectral purity applications, VCSELs in the red wavelength range were also realized. They have achieved sub-milliamp room-temperature (RT) continuous-wave (CW) lasing for an 8 m diameter emission window and exhibited an external quantum efficiency of 6.65% for 10 m devices in RT CW operation. The VCSEL structures were far from optimal – not even incorporating all the RC-LED structure refinements – and significant improvement in performance characteristics are predicted for the optimized layer structure.     

Three-dimensional modelling of micromachined-ultrasonic-transducer arrays operating in water

We report on the 3-D modelling of periodic arrays of capacitive micromachined ultrasonic transducers (cMUTs) operating in fluid. Specific developments have been performed to model biperiodic transducer arrays and to take into account radiation into any stratified media at the front-side as well as the back-side of the device. The model is based on a periodic finite-element-analysis/boundary-element-method (FEA/BEM). It is applied to micromachined ultrasonic transducers (MUTs), based on silicon-nitride-circular-membrane arrays on a silicon substrate, and operating in water. The spectrum characteristics of MUTs excited in phase are investigated, showing that very-large-band emission is achievable as previously demonstrated by many authors. However, other contributions are also found, depending on the excitation conditions, that do not radiate in the fluid. These contributions are identified as guided modes that could generate significant cross-talk effects. The origin and the nature of these modes is analyzed to gain insight in the actual operation of MUTs.     

Model-based optimization of ultrasonic transducers

Numerical simulation and automated optimization of Langevin-type ultrasonic transducers are investigated. These kind of transducers are standard components in various applications of high-power ultrasonics such as ultrasonic cleaning and chemical processing. Vibration of the transducer is simulated numerically by standard finite element method and the dimensions and shape parameters of a transducer are optimized with respect to different criteria. The novelty value of this work is the combination of the simulation model and the optimization problem by efficient automatic differentiation techniques. The capabilities of this approach are demonstrated with practical test cases in which various aspects of the operation of a transducer are improved.     

Search for the neutrino magnetic moment in the nonequilibrium reactor-antineutrino energy spectrum

We study the time evolution of a typical reactor-antineutrino energy spectrum during the reactor operating period and the decay of the residual-antineutrino spectrum after the reactor is stopped. We find that relevant variations in the spectra of soft recoil electrons produced via weak and magnetic $\bar \nu _e e$ scattering can play a significant role in current and planned searches for the neutrino magnetic moment at reactors.