Non-Orthogonal Random Access in MIMO Cognitive Radio Networks: Beamforming, Power Allocation, and Opportunistic Transmission.

We study secondary random access in multi-input multi-output cognitive radio networks, where a slotted ALOHA-type protocol and successive interference cancellation are used. We first introduce three types of transmit beamforming performed by secondary users, where multiple antennas are used to suppress the interference at the primary base station and/or to increase the received signal power at the secondary base station. Then, we show a simple decentralized power allocation along with the equivalent single-antenna conversion. To exploit the multiuser diversity gain, an opportunistic transmission protocol is proposed, where the secondary users generating less interference are opportunistically selected, resulting in a further reduction of the interference temperature. The proposed methods are validated via computer simulations. Numerical results show that increasing the number of transmit antennas can greatly reduce the interference temperature, while increasing the number of receive antennas leads to a reduction of the total transmit power. Optimal parameter values of the opportunistic transmission protocol are examined according to three types of beamforming and different antenna configurations, in terms of maximizing the cognitive transmission capacity. All the beamforming, decentralized power allocation, and opportunistic transmission protocol are performed by the secondary users in a decentralized manner, thus resulting in an easy implementation in practice.

Preventive strategies of renal insufficiency in patients with diabetes undergoing intervention or arteriography (the PREVENT Trial).

Few studies have compared the ability of sodium bicarbonate plus N-acetylcysteine (NAC) and sodium chloride plus NAC to prevent contrast-induced nephropathy (CIN) in diabetic patients with impaired renal function undergoing coronary or endovascular angiography or intervention. Diabetic patients (n = 382) with renal disease (serum creatinine ≥1.1 mg/dl and estimated glomerular filtration rate <60 ml/min/1.73 m(2)) were randomly assigned to receive prophylactic sodium chloride (saline group, n = 189) or sodium bicarbonate (bicarbonate group, n = 193) before elective coronary or endovascular angiography or intervention. All patients received oral NAC 1,200 mg 2 times/day for 2 days. The primary end point was CIN, defined as an increase in serum creatinine >25% or an absolute increase in serum creatinine ≥0.5 mg/dl within 48 hours after contrast exposure. There were no significant between-group differences in baseline characteristics. The primary end point was met in 10 patients (5.3%) in the saline group and 17 (9.0%) in the bicarbonate group (p = 0.17), with 2 (1.1%) and 4 (2.1%), respectively, requiring hemodialysis (p = 0.69). Rates of death, myocardial infarction, and stroke did not differ significantly at 1 month and 6 months after contrast exposure. In conclusion, hydration with sodium bicarbonate is not superior to hydration with sodium chloride in preventing CIN in patients with diabetic nephropathy undergoing coronary or endovascular angiography or intervention.

Transient complete atrioventricular block associated with curcumin intake.

Curcumin is a polyphenol responsible for the yellow color of turmeric, a curry spice. A large body of evidence showed that curcumin possessed a variety of beneficial activities. We report a case of transient complete atrioventricular block in a 38-year-old man, after intake of curcumin containing pills for on 1 month. Since all other possible causes of conduction disturbance were excluded and causal relation was achieved by re-intake of the same amount of turmeric containing pills, side-effect of the curcumin containing pills was identified as the most likely diagnosis. After cessation of the pills, no further conduction disturbances and associated symptoms were noticed for the ensuing 6 months since discharge.

Coronary artery thrombosis associated with Paclitaxel in advanced ovarian cancer.

A 63-year-old woman was diagnosed with ovarian cancer and peritoneal carcinomatosis. The day after paclitaxel was administered, an acute myocardial infarction occurred. Emergency coronary angiography revealed a filling defect in the left main coronary artery and total occlusion in the distal left anterior descending coronary artery, with no luminal irregularity or narrowing. Intravascular ultrasonography showed no significant plaque in the left main coronary artery. A thrombophilia work-up was negative, and the patient was treated with tirofiban, clopidogrel, and aspirin. The follow-up coronary angiogram showed that the occlusion of the distal obtuse marginal branch and distal left anterior descending artery had cleared. Paclitaxel has been associated with acute myocardial infarction. However, the pathogenesis of myocardial infarction associated with paclitaxel is not known. This case raises the possibility that paclitaxel can induce coronary artery thrombosis, resulting in myocardial infarction.

[Clinical factors that predicts successful eradication of Helicobacter pylori].

BACKGROUND/AIMS: Antibiotic resistance and compliance are regarded to be important which affect the eradication of Helicobacter pylori (H. pylori). However, it is not easy to apply the antibiotic resistance test in clinical field. We investigated other clinical factors predicting the successful eradication of H. pylori. METHODS: From January 2004 to March 2005, 195 patients with documented H. pylori infection received proton pump inhibitor (PPI)-based triple therapy for one week and were assessed for the underlying chronic illnesses, smoking, alcohol habit, therapeutic indication and compliance. RESULTS: The intention-to-treat (ITT) eradication rates were 69.2%, while per protocol (PP) analysis with 169 patients showed an initial eradication rate of 79.9%. The eradication rates of H. pylori according to the underlying disease were 73.9% (17/23) in diabetes, 66.7% (18/27) in hypertension, 66.7% (2/3) in renal disease, 100% (9/9) in liver disease, 63.7% (7/11) in cardiovascular disease and 64.3% (9/14) in chronic NSAIDs user. There was no statistical difference in the eradication rates according to the therapeutic indication, underlying disease, sex, age, smoking, alcohol, and PPI. However, the eradication rate was statistically lower in patients with multiple underlying diseases. Eradication rate was significantly higher in patients with good compliance than in those with poor compliance in taking medications (p<0.05). CONCLUSIONS: Underlying chronic disease does not affect the H. pylori eradication rate significantly. In clinical practice, apart from antibiotic resistance test, drug compliance is the most important factor affecting the H. pylori eradication rate.