Direct Observation of Structural Defects in Laser-Deposited Superconducting Y-Ba-Cu-O Thin Films

The defect structure of in situ pulsed, laser-deposited, thin films of the high-transition temperature superconductor Y-Ba-Cu-O has been observed directly by atomic resolution electron microscopy. In a thin film with the nominal composition YBa(2)Cu(3)O(7) (123), stacking defects corresponding to the cationic stoichiometry of the 248, 247, and 224 compounds have been observed. Other defects observed include edge dislocations and antiphase boundaries. These defects, which are related to the nonequilibrium processing conditions, are likely to be responsible for the higher critical currents observed in these films as compared to single crystals.

GaAs Clusters in the Quantum Size Regime: Growth on High Surface Area Silica by Molecular Beam Epitaxy

Molecular beam epitaxy has been used to grow microcrystalline clusters of gallium arsenide (GaAs) in the size range from 2.5 to 60 nanometers on high-purity, amorphous silica supports. High-resolution transmission electron microscopy reveals that clusters as small as 3.5 nanometers have good crystalline order with a lattice constant equal to that of bulk GaAs. Study of the microcrystallite surfaces by x-ray photoelectron spectroscopy shows that they are covered with a shell (1.0 to 1.5 nanometers thick) of native oxides of gallium and arsenic (Ga(2)O(3) and As(2)O(3)), whose presence could explain the low luminescence efficiency of the clusters. Optical absorption spectra of the supported GaAs are consistent with the blue-shifted band edge expected for semiconductor microcrystallites in the quantum size regime.

Intraoperative antegrade colon irrigation--in the management of obstructing left-sided colon cancer

The management of obstructing left-sided colon cancer remains controversial. The advent of intraoperative antegrade colonic irrigation (I.A.C.I.) has allowed primary anastomosis to be performed in the obstructed bowel. From July 1985 to Feb. 1989, there were eleven patients with obstructing left-sided colon cancer admitted to Changhwa Christian Hospital. Eight of these patients, five men and three women, age ranged from 31 to 80 years old, accepted the I.A.C.I. procedure and followed by the one-staged operations. The I.A.C.I. procedure was advocated by Dudley et al in 1980. Postoperatively, there was no case which suffered from clinical leakage or sepsis, except two cases with mild wound infection. Consequently, there was no operative mortality.

Stercoraceous perforation of the colon

Non-traumatic colon perforations are usually caused by malignancy, diverticulum and colitis. They rarely result from stool impaction. A 74-year-old woman with stercoracous perforation of the colon is reported. She had a long history of constipation and hypertension treated irregularly with cathartics, enemas, diuretics and beta-blockers. Resection of the perforated colon with a proximal diverting colostomy and Hartman's procedure was performed. The patient tolerated the operation and subsequent reanastomosis 6 weeks later. In the case of elderly patients with constipation, early management of the constipation is mandatory, although this condition of stercoraceous perforation is rare.

Laser Raman studies on cobrotoxin

Laser Raman spectra of cobrotoxin under various conditions have been obtained. Comparison of the spectra of native cobrotoxin in lyophilized form and in aqueous solution indicates that the secondary structures of cobrotoxin are not significantly affected by the removal of the aqueous solvent. On going from the native to the partially reduced and the completely reduced, carboxy-methylated forms, characteristic peaks of the C-S-S-C and tyrosine ring in the region of 500--900 cm-1 showed definite changes in structure. The partially reduced form gave two peaks at 502 and 524 cm-1, suggesting difference in the conformation of the remaining disulfide bonds. As indicated by the present work, the conformation of the main chain of cobrotoxin in the native unperturbed state, in the partially reduced and in the completely reduced forms are the coexistence of beta-pleated sheet with random-coil structure, predominantly random coil, and predominantly random coil with the existence of an alpha-helix type structure, respectively. The effect of pH on the conformation of cobrotoxin in solution appeared to give rise to the change of the local structure of two aromatic residues common to all snake neurotoxins.

Conformational prediction for snake venom toxins and laser Raman scattering of a cardiotoxin from Taiwan cobra (Naja naja atra) venom

Secondary structure regions in snake venom toxins were predicted using the prediction method of Chou and Fasman (Chou, P. Y., and Fasman, G. D. (1974), biochemistry 13,222) and an averaging scheme assuming structural homology in each type of toxins. The results indicate that, in general, snake toxins contain only some beta-sheet regions and beta bends. The content of secondary structures thus predicted does vary to some extent. The predicted results correlate well with conclusions from physicochemical studies. Interestingly, beta-bend regions predicted for the two types of neurotoxins, short-neurotoxin-type and long-neurotoxin-type, are primarily located in the middle of disulfide loops in spite of large differences in primary sequences. Comparisons between predicted results and the crystal structure of erabutoxin b determined at 2.75 A resolution suggest that the two types of neurotoxin are both sequencely and conformationally related while cardiotoxins could have an entirely different molecular topology. The Raman spectrum of a Taiwan cobra cardiotoxin indicates that the content of beta-pleated-sheet structure could be greater than that in neurotoxins.