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Biomedical subjects

A C Cheng

Publications and source records attributed to A C Cheng.

68 records · Page 4Linked to original sources
PubMed1993

Mechanical properties of metal connectors soldered by gas torch versus an infrared technique.

PURPOSE: The ultimate tensile strength and percentage elongation of solder joints of three alloy systems were tested. MATERIALS AND METHODS: Solder joints were formed using either an infrared soldering machine or gas-oxygen torch. Intact solder materials were used as controls. RESULTS: There were no significant differences in percentage elongation among different treatment methods of the solders or among various solder materials. All intact solder materials possessed significantly higher ultimate tensile strength than the joints made with either method. For high-noble and noble alloy solders, there were no significant differences in ultimate tensile strength of joints made with either method. For base metal alloy solder, the ultimate tensile strength of joints made with the infrared technique was significantly higher than that made with the gas-oxygen torch technique. CONCLUSIONS: The infrared technique can be used as an alternative to the gas-torch technique for soldering high-noble and noble alloys. It is superior to the gas-torch technique for soldering a cobalt-chromium alloy.

Analysis of Variance↗
PubMed1989

Retroperitoneal seminoma and intratubular germ cell neoplasia.

A 30-year-old man with a 6-month history of flank pain was found to have a large retroperitoneal seminoma. A subsequent ultrasound examination revealed an inhomogeneous echo pattern in the normal-sized right testicle, which on orchiectomy showed extensive intratubular germ cell neoplasia. Level sectioning of the entire testicle revealed no extratubular extension of the tumor cells. The retroperitoneal and testicular lesions could represent double primaries. However, the possibility exists that an apparently intratubular germ cell neoplasm may not actually be an in situ lesion and that the retroperitoneal tumor in our case represents a metastasis from the intratubular germ cell neoplasia of the testicle.

Adult↗
PubMed1984

Synthesis and physicochemical and neurotoxicity studies of 1-(4-substituted-2,5-dihydroxyphenyl)-2-aminoethane analogues of 6-hydroxydopamine.

In an attempt to evaluate the possible relationship between the neurotoxicity of 6-hydroxydopamine and the redox properties and electrophilic reactivity of the 6-hydroxydopamine-p-hydroquinone/p-quinone system, we have synthesized a series of 6-hydroxydopamine analogues in which the C4-hydroxy group is replaced with various electron-donating and electron-withdrawing substituents. With the aid of cyclic voltammetry, the formal oxidation potentials (E degrees ') for the p-hydroquinone/p-quinone redox couples and the rates of cyclization of the p-quinones to the corresponding p-iminoquinones were determined. As expected, electron-rich p-hydroquinones were easily oxidized to the p-quinones, which underwent cyclization slowly, whereas the oxidation of electron-poor p-hydroquinones required higher voltages and yielded p-quinones, which cyclized readily at pH 7.4. The neurotoxic potential of these compounds showed that in vivo destruction of noradrenergic terminals, as measured by inhibition of norepinephrine uptake by rat heart slices, occurred only with those analogues bearing electron-donating substituents. Potent neurotoxic properties were associated only with the 4-amino and 4-hydroxy derivatives, both of which form p-quinones, which do not cyclize readily at pH 7.4. These results support the thesis that the p-quinone derived from 6-hydroxydopamine may be an important species in the mediation of the neurodestruction caused by 6-hydrodopamine.

Animals↗
PubMed1975

The treatment of headaches employing acupuncture.

Thirty-three patients have been treated by acupuncture since July 8, 1974, using body loci, ear points and electrical stimulation. Of the 33 cases, 18 were female and 15 were male, ranging in age from 25 to 77 years. Sixteen patients suffered from migraines, 12 from tension headaches, 2 from cluster headaches, 1 from vascular headaches, and for 2 patients the etiology was uncertain. The duration of the headaches ranged from 3 months to 40 years. The patients received from 3 to 16 treatments. Of the 33 cases, 5 patients had only 3 treatments and 10 patients had 5 or less treatments. Eighteen patients had good results, i.e., no headache at all. Twelve patients had fair results, that is they sometimes had headaches, but they could be controlled with a few repetitions of treatment or by analgesics at a lesser dosage than they were taking at the beginning of treatments. Three patients had no response at all or poor results; however, these discontinued treatment before the author could evaluate whether they were actual absolute no-response cases. Of the 33 patients, 2 patients had a good response after only 2 treatments; 4 had a good response after 10 treatments. However, most of the patients had a good response after 6-8 treatments. A course of treatment usually requires 10 to 14 visits befor definite evaluation of the results can be made. It was observed that patients with fair or particularly poor results usually discontinued treatment too early and/or had concomitant conditions as well. Even though a longer period of time for follow-up is necessary before drawing any conclusions, results have already shown that acupuncture, perhaps, can be a valuable form of treatment for headaches.

Acupuncture Therapy↗
PubMedDate not supplied

Superior orbital fissure syndrome in a latent type 2 diabetic patient.

Although isolated cranial nerve palsies are common in diabetic patients, multiple, simultaneous cranial neuropathies are rare. We describe the second case of a complete superior orbital fissure syndrome including the optic nerve in a middle-aged Papuan man with newly diagnosed diabetes mellitus. The differential diagnosis included septic cavernous sinus thrombosis and Tolosa Hunt syndrome, and management was initially directed at excluding these serious, treatable conditions.

Adult↗
PubMedDate not supplied

Fine needle aspiration cytology diagnosis of papillary tumor of the pancreas.

A case of papillary tumor of the pancreas in a young woman is reported in which the nature of the tumor was recognized preoperatively by fine needle aspiration (FNA) biopsy. The larger cell clumps in the aspirate had a branching papillary appearance in which multiple layers of tumor cells surrounded central vascular stalks. This perivascular clustering of tumor cells, resembling bunches of grapes, was reflected in the subsequent histologic material. Of interest was the presence of metachromatic globules in Wright-Giemsa-stained aspiration smears, corresponding to perivascular myxoid material seen in the histologic sections, which has been described so far, among pancreatic tumors, only among papillary-type tumors.

Adolescent↗