Gradual tilting of crystallographic orientation and configuration of dislocations in GaN selectively grown by vapour phase epitaxy methods

Cross-sectional transmission electron microscope (TEM) observation was performed for selectively grown gallium nitride (GaN) in order to examine the dependence of GaN microstructure on the growth conditions. The GaN films were grown by hydride vapour phase epitaxy (HVPE) or metalorganic vapour phase epitaxy (MOVPE) on GaN covered with a patterned mask. Thin foil specimens for TEM observation were prepared with focused ion beam (FIB) machining apparatus. It was demonstrated that the c-axis of GaN grown over the terrace of the mask tilts towards the centre of the terrace when the GaN is grown in a carrier gas of N2. The wider terrace results in a larger tilting angle if other growth conditions are identical. The tilting is attributed to 'horizontal dislocations' (HDs) generated during the overgrowth of GaN on the mask terrace. The HDs in HVPE-GaN have a semi-loop shape and are tangled with one another, while those in MOVPE-GaN are straight and lined up to form low-angle grain boundaries.

Outcome of patients with Graves' disease after long-term medical treatment guided by triiodothyronine (T3) suppression test.

The value of the T3 suppressed 20-min uptake test for the prediction of post-treatment outcome was studied in 193 unselected patients with Graves' disease treated with thionamide drugs and T3. One hundred and twenty-nine of 193 patients were studied previously and followed thereafter (Group A). Sixty-four were newly treated patients: thirty-three (Group B) were treated at the same hospital as Group A; thirty-one (Group C) were treated at another hospital. In total 126 patients out of 193 satisfied our criteria for suppression (total suppression rate, 65%). The suppression rate for new patients (55% in Group B, 52% in Group C) was similar to that for Group A in 1977 (49%) after comparable duration of treatment. The suppression rate for Group A increased with prolongation of the treatment period (49% in 1977 and 71% in 1981). As to the time course of suppression, it was observed that about two-thirds of the suppressed patients satisfied the criteria for suppression within 3 years of starting treatment. The number of suppressed patients per year decreased thereafter as the treatment periods increased. However, the yearly suppression rate did not decrease with time. The time course of suppression in each patient could not be predicted from the results of initial thyroid function tests. The overall remission rate among the 120 suppressed patients followed for 1-13 (mean, 4) years was 96%, which was almost equal to the value obtained in Group A in 1977 (95%) with the average follow-up period of 2 years. Among the 46 patients in Group A followed for 5-13 (mean, 7) years, no increase in relapse was observed with prolonged follow-up periods. Examination on the relationship between the duration of treatment and the post-treatment outcome revealed that, as a whole, the duration of treatment for the patients with relapse were rather short as compared with those for the patients in remission. These results confirm the usefulness of our T3 suppression test for predicting sustained remission of Graves' disease after treatment, and clearly indicate that long-term medical therapy could increase the number of remissions in patients with Graves' disease.

Stimulation of nonspecific resistance to infection induced by 6-O-acyl muramyl dipeptide analogs in mice.

The experimental system utilized in investigating the correlation between the chemical structures of muramyl peptides and their protective activities in the sepsis type of systemic infections caused by Escherichia coli was applied in evaluating the enhancement of resistance to infection induced by 32 synthetic glycopeptide analogs, including 6-O-acyl derivatives and 1-alpha-O-benzyl derivatives of muramyl dipeptide (N-acetyl muramyl-L-alanyl-D-isoglutamine). In assessing the 6-O-acyl derivatives of muramyl dipeptide, we found that the degree of protective activity was attributable to the kinds of fatty acids introduced. Acylation of the 6-hydroxy group on the muramic acid moiety in muramyl dipeptide with natural mycolic acid or a synthetic fatty acid possessing either an alpha-branched or an alpha-branched, beta-hydroxylated group resulted in a decrease in or a disappearance of the protective activity of muramyl dipeptide. Acylation with a normal fatty acid or an iso fatty acid resulted in a retention or enhancement of muramyl dipeptide activity. The activity of acylated derivatives containing linear fatty acids was stimulated by increasing the chain length up to 18 carbon atoms. The highest degree of protective activity occurred with the derivatives acylated with straight-chain fatty acids, particularly with the derivatives acylated with palmitic acid and arachidic acid. Benzylation of the 1-hydroxy group of muramyl dipeptide resulted in a decrease in or a loss of protective activity.