AFM observation of polyethylene single crystals: selective handedness of screw dislocations in a chair type

The three-dimensional morphology of polyethylene single crystals grown from dilute solution has been examined by atomic force microscopy. Single crystals were deposited on a soft ground of aqueous solution of poly(vinyl alcohol) (PVA) to avoid the collapse of thin lamellar crystals with thickness of 10 nm. The observation of single crystals on dried PVA clarifies the morphology of a chair type crystal as well as well-known hollow pyramidal type. It has been confirmed that the screw dislocations in the chair type follow a selection rule of the handedness in a manner to relieve the distortion in the chair type.     

Lateral habits ofn-alkane single crystals

The lateral crystal habits ofn-alkanes (n-C _n H_2n+2) have been observed just below the melting points by optical microscopy forn=18, 19, 20, 22, 24, 34, 44, 50 and 65. The shape of the crystals depends on the crystal phase: circular in the rotator phase, lenticular in phase C, and diamond in the low-temperature phase. The rounding of the lateral shape can be explained in terms of thermal roughening of the lateral faces in the disordered phases at high temperature.     

Integrated-optic device for a fibre laser Doppler velocimeter

We first demonstrate an integrated-optic device for a fibre laser Doppler velocimeter, which consists of a waveguide interferometer and a frequency shifter in z-propagation Ti-diffused LiNbO3. The device is also pigtailed with a single-mode fibre to pick up a Doppler-shifted signal. Using the fabricated device, the velocity of a moving object was successfully heterodyne-detected with a signal/noise ratio of 30dB.     

A novel therapeutic approach for rectal varices: a case report of rectal varices treated with double balloon-occluded embolotherapy

We present a patient with continuous melena, diagnosed as rectal varices bleeding. She had a history of esophageal varices, which was treated by endoscopic ligation therapy. Eight years after the treatment of esophageal varices, the continuous melena began. Colonoscopic examination showed that the melena was caused by rectal varices, which were so severe that they could not be treated by either endoscopic sclerotherapy or surgical devascularization. Taking into considering the overall risk of treating rectal varices, we chose the approach of double balloon-occluded embolotherapy (DBOE) with 5% ethanolamine oleate with iopamodol as a liquid embolic material. DBOE is one of the interventional radiology techniques (Morita et al., Acta Hepatol Jpn 1994;35:109-120), but in this case was a completely new and novel clinical procedure for rectal varices. After the DBOE therapy, the condition of rectal varices was markedly improved. Thus, DBOE might be a new tool for treating inoperable rectal varices.     

Structural change in the Brill transition of Nylon m/n (1) Nylon 10/10 and its model compounds

Structural changes in the Brill transitions of Nylon 10/10 and its model compounds have been investigated by carrying out the temperature-dependent measurements of X-ray diffraction and infrared spectra along with the DSC measurement. The crystal structure at room temperature was found to be the so-called α form with the all-trans zigzag methylene segments. When the samples were heated, the infrared progression bands of the methylene segments, which are sensitive to the length of all-trans segmental parts, were found to change their spectral patterns in the transition temperature region: the progression bands decreased in intensity and disappeared above the transition region. At the same time several new bands were observed to appear, which were found to correspond to the progression bands of (CH₂)₇-(CH₂)₅trans-zigzag segments. These spectral changes indicate that the methylene segments were conformationally disordered by an invasion of some gauche bonds and as a result the effective length of trans-zigzag segments became shorter. This conformational disordering was found to occur more remarkably in the methylene segment of NH-(CH₂)₁₀-NH part than the CO-(CH₂)₈-CO part. At the same time the infrared bands of amide groups, in particular the bands sensitive to the twisting angles about the CH₂-amide bonds were found to show the remarkable change, indicating the local conformational change from planar-zigzag to twisted form in the CH₂-amide moiety. The frequency shift of amide A band (NH stretching mode) indicated a weakening of intermolecular hydrogen bonds, which however, did not disappear up to the melting region. From these data combined with the X-ray diffraction data, the structural disordering in the Brill transition phenomena was deduced concretely.     

Influence of third monomer on the crystal phase transition behavior of ethylene-tetrafluoroethylene copolymer

Crystal phase transition between the low- and high-temperature phases has been investigated for ethylene (E)-tetrafluoroethylene (TFE) alternating copolymer (ETFE) containing the third monomeric species by the temperature dependent measurements of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) and differential scanning calorimetry. Nonafluoro-1-hexene (NFH) and hexafluoropropylene (HFP) were chosen as the third monomers, where they are different in the side-branch length, -(CF₂)₃CF₃ and -CF₃, respectively. In the case of E/TFE/NFH copolymer (ET-C4F9), the crystal phase transition temperature of the original ETFE two-components copolymer was not very much affected by the existence of NFH in the range of NFH content from 0.7 to 3 mol%. Contrarily, the crystal phase transition temperature of E/TFE/HFP copolymer (ET-CF3) was found to decrease drastically with increasing HFP content. The melting temperature and the higher-order structure were also affected sensitively depending on the HFP content. This difference in phase transition behavior between ET-C4F9 and ET-CF3 copolymers is reasonably interpreted as follows: the short side groups (-CF₃) of HFP monomeric unit are included in the crystal lattice of E/TFE chains and the unit cell is expanded gradually with an increment of the HFP content, resulting in the decrease in phase transition point because of easier thermal motion of the chains. On the other hand, the long side groups [-(CF₂)₃CF₃] of NFH monomeric units are excluded out of the crystal lattice and located on the lamellar surfaces or in the amorphous region and do not affect very much the phase transition temperature even when the NFH content is increased. In association with such a change in crystal structure, the long period of stacked lamellar structure was found to decrease remarkably in the case of NFH, whereas it does not change very much for HFP, consistent with the interpretation of the above-mentioned WAXD data.     

Robust digital control of a DC–DC buck converter with low frequency samplings

A robust DC?CDC converter which can covers extensive load change and also input voltage changes with one controller is needed. Then the demand to suppress output voltage change becomes still severer. We propose an approximate 2-degree-of-freedom (2DOF) digital controller which realized start-up response and dynamic load response independently. The controller makes a control bandwidth wider, and at the same time makes variations of the output voltage small at sudden changes of a load and an input voltage. In this paper, a new approximate 2DOF digital control system with additional zeros is proposed. Using the additional zeros, the second-order differential transfer characteristics between equivalent disturbances and a output voltage are realized. Therefore, the new controller makes variations of the output voltage smaller and the sudden changes of the load and the input voltage. This controller is actually implement on a DSP and is connected to the DC?CDC converter. Experimental results demonstrate that this type of digital controller can satisfy given severe specifications with low frequency sampling.     

Residual Stress in Siliceous Glass Between Mullite Crystals

A birefringence of siliceous glass, which is coexisting with mullite crystals, was studied by an optical polarizing microscope. The cause of the birefringence was assumed to be the residual stress induced by a large contraction difference between the mullite and glass on cooling. The stress has been evaluated to be as high as—0.3 GPa, and to correspond to the elastic one which began to develop at the glass transition point.