High-performance optical modulator with a wide center electrode and thin x-cut LiNbO/sub 3/ substrate

We propose an excellent large-bandwidth back-slot lithium niobate (LN) modulator with a wide center electrode of typically 50 /spl mu/m or wider and relatively thin electrodes. From the calculation, a modulator with a 3-dBe bandwidth of 34 GHz and a half-wave voltage of 2.0 V for a 50-/spl Omega/ characteristic impedance system was realized theoretically. This means when their half-wave voltages are identical, by applying a wider electrode, the modulator bandwidth becomes 2.6 times larger than that of a conventional one. We also confirmed experimentally that the wide center electrode structure is effective for back-slot LN modulators.     

Multiple crystalline morphologies of N-Alkyl chitosan solution cast films

Summary In addition to spherulites, two novel crystalline morphologies, i. e. need-like crystal and sheet-like crystals were found in formic acid solution cast films of N-methyl chitosan and N-ethyl chitosan during casting at 25°C and relative humidity 65%. Their size was larger in 1∼2 order of magnitude than chitin needle-like single crystals and chitosan lamellar single crystals reported previously due to the high molecular weight. The formation mechanism of these crystalline morphologies was discussed. Correspondence to Yanming Dong Email: ymdong@xmu.edu.cn, Fax +86-592-2188054     

High-performance permanent magnetic circuit designed for small-angle X-ray scattering using synchrotron radiation source

A new type of permanent magnetic circuit with several prominent characteristics was developed and applied to the studies of oriented macromolecular assemblies by small-angle X-ray scattering using synchrotron radiation source.     

Overall comparison of subpicosecond electron beam diagnostics by the polychromator, the interferometer and the femtosecond streak camera

Measurements of longitudinal bunch length of subpicosecond and picosecond electron beams have been performed by three methods with three radiation sources at the 35 MeV S-band twin liner accelerators at Nuclear Engineering Research Laboratory, University of Tokyo. The methods we adopt are the femtosecond streak camera with a nondispersive reflective optics, the coherent transition radiation (CTR) Michelson interferometer and the 10 ch polychromator that detects the spectrum of CTR and coherent diffraction radiation (CDR). The measurements by the two CTR methods were independently done with the streak camera and their results were consistent with one another. As a result, the reliability of the polychromator for the diagnostics of less than picosecond electron bunch and the usefulness of the diagnostics for the single shot measurement were verified. Furthermore, perfect nondestructive diagnostics for subpicosecond bunches was performed utilizing CDR interferometry. Then the good agreement between CDR interferometry and the streak camera was obtained.     

Oxidation of ferrous sulfate in weakly acidic solution by gas bubbling

The oxidation of Fe²⁺ ion in aqueous solution in a pH region between 4.7 and 5.5 was studied. By supplying dilute NaOH solution from an automatic titrator, pH of the solution was maintained constant during the oxidation. The reaction is comprised of the sequential steps of the dissolution of gaseous oxygen and the oxidation of Fe²⁺ ion by dissolved oxygen. The latter reaction proceeds along two paths: homogeneous reaction in the solution (rate constant:k) and heterogeneous reaction on the surface of ferric hydroxide precipitate (rate constant:ks). The measured time variation of the concentrations of Fe²⁺ ion and dissolved oxygen was explained by simultaneous rate equations. Linear relationships were found between logk and pH and between logks and pH having slopes of 2 and unity, respectively. An activation energy of 103 kJ/mol was obtained fork. The overall rate of oxidation of Fe²⁺ ion was chemically controlled at pH lower than 5.0 and temperature lower than 298 K. On the other hand, it was controlled by both chemical reactions and the dissolution of oxygen at higher pH and temperature.     

Study of surface relaxation mechanism of liquid3He in porous glass by using SQUID NMR

Nuclear spin relaxation of liquid³He in porous glass has been studied. In addition to measurements of the longitudinal spin relaxation timeT ₁ by a usual pulsed SQUID NMR, measurements of the transverse spin relaxation timeT ₂ have been performed by using a newly developed SQUID NMR method to observe a spin echo signal. Temperature and frequency dependences ofT ₁ andT ₂ have been measured. A simple model is proposed which explains the main features of the experimental results.     

Preparation of aldehydocelluloses from completely allylated methylcellulose,allylated ethylcellulose,and tri-O-allylcellulose by ozonization

In order to prepare aldehydocelluloses which are more stable than periodate-oxidized cellulose, completely allylated methylcellulose, allylated ethylcellulose, and tri-O-allylcellulose were subjected to ozonization followed by reduction with dimethylsulfide. The aldehydocelluloses thus prepared without any degradation showed the presence of many free aldehyde groups by IR and ¹³C-NMR spectrometries, as well as the presence of hydroxyl groups which were produced by deallylation. The degree of substitution (DS) by aldehyde group was 0.6 for the products from both completely allylated methylcellulose and tri-O-allylcellulose, and 0.02 for that from allylated ethylcellulose.     

High-Temperature Strength of Sinter-Forged Silicon Nitride with Lutetia Additive

A sinter-forging technique was successfully applied to fabricate a silicon nitride with a lutetia (Lu₂O₃) additive. The sinter-forged specimen had a strongly anisotropic microstructure where rodlike silicon nitride grains preferentially aligned perpendicular to the forging direction. The specimen exhibited superior strength of ∼700 MPa at 1500°C. This strength was highest when compared with previous silicon nitrides at temperatures >1400°C. Such superior high-temperature strength was attributed to grain alignment as well as to the refractory grain-boundary glassy phase and the existence of glass-free grain boundaries.