Evidence for a new class of defects in highly n-doped Si: donor-pair-vacancy-interstitial complexes.

Electron channeling experiments performed on individually scanned, single columns of atoms show that in highly n-type Si grown at low temperatures the primary electrically deactivating defect cannot belong to either the widely accepted class of donor-vacancy clusters or a recently proposed class of donor pairs. First-principles calculations suggest a new class of defects consisting of two dopant donor atoms near a displaced Si atom, which forms a vacancy-interstitial pair. These complexes are consistent with the present experimental results, the measured open volume of the defects, the observed electrical activity as a function of dopant concentration, and the enhanced diffusion of impurities in the presence of deactivated dopants.

Atomic-scale imaging of individual dopant atoms and clusters in highly n-type bulk Si.

As silicon-based transistors in integrated circuits grow smaller, the concentration of charge carriers generated by the introduction of impurity dopant atoms must steadily increase. Current technology, however, is rapidly approaching the limit at which introducing additional dopant atoms ceases to generate additional charge carriers because the dopants form electrically inactive clusters. Using annular dark-field scanning transmission electron microscopy, we report the direct, atomic-resolution observation of individual antimony (Sb) dopant atoms in crystalline Si, and identify the Sb clusters responsible for the saturation of charge carriers. The size, structure, and distribution of these clusters are determined with a Sb-atom detection efficiency of almost 100%. Although single heavy atoms on surfaces or supporting films have been visualized previously, our technique permits the imaging of individual dopants and clusters as they exist within actual devices.

Randomized controlled trial of tissue plasminogen activator in proximal deep venous thrombosis.

PURPOSE: To compare the efficacy and safety of recombinant human tissue-type plasminogen activator (rt-PA, supplied as Activase) with heparin alone or rt-PA plus heparin in the treatment of venographically documented proximal deep venous thrombosis (DVT) of the leg. PATIENTS AND METHODS: Sixty-four patients underwent 65 randomizations to rt-PA alone (n = 36), rt-PA plus heparin (n = 17), or heparin alone (n = 12) in a prospective, multicenter, randomized, open-label trial, with efficacy assessed by a radiology panel unaware of treatment assignment. Patients randomly assigned to rt-PA received 0.05 mg/kg/hour for 24 hours via a peripheral vein, with a maximum dose of 150 mg. All patients then received heparin and warfarin for the remainder of the hospitalization. Follow-up venography was performed 24 to 36 hours after initiation of therapy. RESULTS: Complete or more than 50% lysis occurred in 10 (28%) patients treated with rt-PA, five (29%) patients with rt-PA plus heparin, and no patient treated with heparin. No lysis occurred in 16 (44%) patients treated with rt-PA plus heparin, and 10 (83%) patients who received heparin alone (p = 0.04). There was one major complication, a nonfatal intracranial hemorrhage in a patient who received rt-PA alone. At 7 to 10 days after initiation of treatment, the level of serum glutamic oxaloacetic transaminase nearly doubled among all patients, including those assigned to receive heparin alone. CONCLUSION: (1) rt-PA and rt-PA plus heparin cause more clot lysis than heparin alone; (2) the addition of heparin to rt-PA does not improve the lysis rate; (3) DVT treated with heparin is commonly associated with a rise in the transaminase level; (4) heparin does not increase the risk of bleeding from rt-PA therapy; and (5) alternative dosing regimens and modes of administration of rt-PA should be investigated to improve further its efficacy and safety in the treatment of acute DVT.

Replacement of the carotid artery using nonreversed saphenous vein.

Carotid artery replacement has been performed with a nonreversed saphenous vein in one patient who had carotid artery resection in association with resection of a squamous carcinoma at the carotid bifurcation. An excellent result was obtained. The technical aspects of this procedure are described herein.

Interposition spiral saphenous vein graft bypass in bilateral simultaneous radical neck dissection.

We advocate the use of the spiral saphenous vein bypass of the IJV when bilateral radical neck dissections are performed with the sacrifice of both IJV. The technique we have described herein is uniformly successful in this setting and associated with only 30 minutes to one hour of increased operative time. This bypass will decrease the postoperative facial edema and associated complications and allow the patient to go on to radiation and chemotherapy in an expeditious and safe manner.

A comparison of isobutyl 2-cyanoacrylate glue, fibrin adhesive, and oxidized regenerated cellulose for control of needle hole bleeding from polytetrafluoroethylene vascular prostheses.

Prolonged anastomotic and needle hole bleeding from synthetic vascular prostheses is a common surgical problem in heparinized patients and in the patient with a coagulopathy. The relative effectiveness of various hemostatic agents has not previously been determined by controlled comparisons. In this study 6 mm polytetrafluoroethylene (PTFE) vascular prostheses were used to perform carotid-carotid and femorofemoral bypasses in eight heparinized dogs. The relative effectiveness of isobutyl 2-cyanoacrylate, fibrin adhesive, and oxidized regenerated cellulose was determined by application of these hemostatic agents to three sources of bleeding: arterial-PTFE anastomoses, PTFE-PTFE anastomoses, and 18-gauge needle holes in PTFE vascular prostheses. The mean time to hemostasis (MTH) was determined for each hemostatic agent. Although application of isobutyl 2-cyanoacrylate resulted in the shortest MTH in each experimental group, the reported inflammatory response that it induces and its possible carcinogenicity limits its availability for clinical use. Application of fibrin adhesive prepared from single-donor hepatitis-screened plasma resulted in a significantly shorter MTH in each experimental group when compared with oxidized regenerated cellulose. We recommend clinical use of fibrin adhesive to control needle hole and anastomotic bleeding from PTFE vascular prostheses.

Nutritional effects of postgastrectomy reconstructions.

To compare the nutritional effects of two modes of reconstruction after total gastrectomy, a Hunt-Lawrence pouch was constructed in five mongrel dogs, whereas five other dogs had a simple Roux-Y esophagojejunostomy performed. Total body weight, daily food intake, serum albumin values, and intestinal absorption of carbohydrates, fats, and amino acids were evaluated in both groups over a period of 3 months. All values decreased postoperatively when compared with the preoperative values; however, there was no significant difference between the two groups. This study suggests that there is no nutritional benefit from a Hunt-Lawrence pouch over a simple Roux-Y esophagojejunostomy after total gastrectomy.

A prospective evaluation of 5-fluorouracil plus cisplatin in advanced squamous-cell cancer of the head and neck.

Recent studies have shown improved efficacy of chemotherapy in patients with advanced squamous-cell cancer of the head and neck. Our purpose was to evaluate prospectively the activity of cisplatin plus 5-fluorouracil (5FU) in 37 patients with advanced stage IV squamous-cell cancer of the head and neck. There were two groups. Group 1 consisted of 19 previously untreated patients with either T4 or N3 disease. They received 100 mg/m2 cisplatin (days 1 and 28) and 120-hour infusion of 1,000 mg/m2/24 hours 5FU (days 1 to 5 and 28 to 32). They subsequently were offered preoperative radiotherapy (RT) and surgery. Group 2 consisted of 18 previously treated patients. They received 5FU and cisplatin in the same dosage every 28 days for either recurrent or metastatic disease. It was found that in group 1 there was an 84% response rate (five complete responses (CR) and 11 partial responses (PR) ). Three of those with PR achieved a CR after RT. Seven patients have had RT plus surgery and are disease free at 8 to 27 month follow-up. Six patients (one CR, five PR) refused surgery and progressed within 4 months. In group 2 there was an 11% response rate after two cycles (two PR), three patients had a minimal response (MR, less than 50% response) and received a mean of four cycles of treatment. Three patients with stable disease received a mean of four cycles of chemotherapy until progression. Two of 11 patients who had received previous chemotherapy plus RT showed an MR; nine of these patients had shown a response to their previous chemotherapy. Only one of 14 patients who had RT plus chemotherapy had a PR, and three had MR. Of five patients who had previous surgery, only one had a PR. All five had received chemotherapy as well. It was concluded that 5FU plus cisplatin is an effective combination in previously untreated patients. In previously treated patients with recurrent disease, there is a substantially lower response rate.

Control of needle hole bleeding with ethyl-cyanoacrylate glue (Krazy Glue).

Needle hole bleeding from polytetrafluoroethylene (PTFE) grafts causes blood loss and prolongs vascular procedures. Past studies have shown the cyanoacrylate glues to polymerize rapidly and cause minimal tissue toxicity. This study was undertaken to evaluate the efficacy of ethyl-2-cyanoacrylate glue (Krazy Glue, KG) in obtaining prompt hemostasis in vascular anastomoses in a heparinized canine model. KG effected complete hemostasis in a significantly shorter time than oxidized cellulose and digital pressure in 18-gauge needle holes in PTFE grafts, graft to graft end-to-end anastomoses, and end of graft to side of artery anastomoses. The only limitation of KG was the development of a glue-adventitia plaque on the arterial side of some of the PTFE-artery anastomoses, causing the need for regluing. KG is an ideal agent for sealing defects in PTFE grafts.