Dual-Phase structure of polymer electrolytes comprised of NBR/SBR latex films swollen with lithium salt solution

Dual-phase polymer electrolytes (DPE) that have high ionic conductivity (> 10^?3 S/cm) and good mechanical strength were prepared by mixing NBR and SBR latices and casting films. The latex films absorbed large quantities of lithium salt solution (e.g., 1M lithium perchlorate in γ-butyrolactone) to obtain DPE films but did not dissolve with swelling. The NBR phase is polar and was impregnated selectively with the polar lithium salt solution, whereas the SBR phase is nonpolar and formed a mechanically-supportive matrix. Transmission electron microscopic (TEM), electron energy loss spectral (EELS), and energy-dispersive x-ray (EDX) analyses showed microscopically the dual-phase structure. Evidence for swelling by lithium salt solution was found only in the NBR phase and not in the SBR phase by EDX microanalysis. Ionic conductivity as a function of NBR content or swelling degree showed clearly that a percolation threshold for ionic conductivity exists. © 1994 John Wiley & Sons, Inc.     

Vibration analysis and measurement of a gradient coil insert in a 4 T MRI

High speed switching of current in gradient coils within high magnetic field strength Magnetic Resonance Imaging (MRI) scanners may result in high acoustic sound pressure levels in and around these machines. Many studies have already been conducted to characterize the sound field in and around MRIs and various methods have been investigated to attenuate the noise generated. To characterize the vibration properties of the gradient coil, a modified Finite Element (FE) model was developed according to the dimensional design of an available gradient coil insert and the concentration of the copper windings in the coil. The finite element analysis results were verified through experimental modal testing of the same gradient coil in a free-free state (no boundary constraints). Comparisons show that the FE model predicts the vibration properties extremely accurately. Based on the verified FE model, boundary conditions (supports) were added to the model to simulate the operating condition when the gradient coil insert is in place in an MRI machine. Vibration analysis results from the FE model were again verified through experimental vibration testing with the gradient coil insert installed in a 4 T MRI and excited using swept sinusoidal time waveforms. Through a comparison of the vibration signals generated it was found that the vibration resonances, both from the FE model and the experimental vibration testing, shift to higher frequencies after the boundary constraints were applied, as was expected. The predicted vibration response was very close to that measured from the gradient coil insert in operation. The FE modeling procedure that has been developed could easily be used to accurately predict the vibration properties of other gradient coil designs. Furthermore, the vibration analysis results from the FE model could be used in acoustic noise analysis to predict the sound pressure level produced by different types of input current pulse sequences.     

Pulsed optically pumped far infrared laser and maser action in OCS

Twenty new optically pumped far-infrared laser transitions have been observed in OCS, including four “maser” transitions of 3.6–8.2 mm wavelength. The operating conditions and assignments of these lines are reported. Rabi splitting of the FIR gain profile caused by the high intensity of the CO₂ TEA laser pump is found to be very important for some lines.     

A two-step Q-switching technique for producing high power in a single longitudinal mode

An electro-optic Q-switch has been opened in two steps to allow slow pulse build-up giving, in conjunction with a resonant reflector, a high degree of mode selection in a way analogous to the use of saturable absorbers. Using this technique, a flash pumped NdCaWO₄ laser has produced reliable operation in a single longitudinal and transverse mode with an output power of 250 kW.     

Mid infrared and far infrared studies of the propyne optically pumped laser

An extensive study of the propyne optically pumped laser is presented. 32 new far infrared and 8 new mid infrared outputs are reported, together with pump frequency offset data. Complete assignments of some far infrared transitions and partial assignments of the mid infrared outputs are given. Very strong interactions occur between the mid and far infrared laser transitions. These interactions are of vital importance in obtaining high output energies.     

Reversible lithium insertion and copper extrusion in layered oxysulfides

All of the copper in the layered oxysulfides Sr2MnO2Cu1.5S2 and Sr2MnO2CU3.5S3 may be extruded as the element and the copper ions replaced quasi-reversibly by lithium ions in reductive topotactic ion exchange reactions; dramatic changes in magnetic properties result.     

Scanning time efficient slinky for non-contrast MRA at low field.

To eliminate slab boundary artifact (SBA) for non-contrast multi-slab three-dimensional time-of-flight magnetic resonance angiogram (3D TOF MRA), we have previously developed a novel technique, termed SLINKY (Sliding Interleaved kY) acquisition in which a thin slab continuously "walks" along the z-axis while data are acquired in an interleaved fashion along the kY-axis. It has been demonstrated in our earlier works that SLINKY can suppress the SBA without any assumption of blood flow behavior, such as velocity or direction. At the same time, SLINKY keeps the same SNR as conventional multiple overlapping thin slab acquisition (MOTSA). Yet, this method is sensitive to any phase error along the ky axis. In our earlier application of SLINKY, we used navigator echoes to measure and correct the phase errors along the kY axis. The cost of using navigator echo collection is an increase in the imaging time. We therefore propose an improved SLINKY technique which does not use navigator echo collection for correcting phase errors, reducing the imaging time while keeping the same suppression of slab boundary artifacts. The present study demonstrates that by using a specifically designed RF pulse, the navigator echo collection can be avoided without incurring any extra ghosting or SNR reduction in the reconstructed images.     

Observation of spider silk by femtosecond pulse laser second harmonic generation microscopy

An asymmetric β-sheet structure of spider silk is said to induce optical second harmonic generation. In this paper, using an in-house nonscanning type femtosecond pulse laser second harmonic generation microscope, we characterized the behavior of the β-sheet of spider silk under an applied external force. The orientation of the β-sheets was more unidirectional when the silk was extended. One of the origins of the high mechanical strength of the dragline is suggested to be the physical arrangement of its β-sheets.