Robust estimators of the 2-parameter gamma distribution

The available estimators for parameters of the gamma distribution are moment estimators, maximum-likelihood estimators, and approximations to the maximum-likelihood estimators. These estimators are not suitable for small samples; however, they are still being used at the present time. The proposed robust estimators for scale and shape parameters are more suitable for small samples. They have RMS (root-mean-square) errors that are considerably smaller than those of the other estimators. In addition, they are easier to calculate, and are therefore appropriate in many applications     

Rebound pulmonary hypertension after inhalation of nitric oxide

BACKGROUND: We describe the hemodynamic response to initiation and withdrawal of inhaled nitric oxide (NO) in infants with pulmonary hypertension after surgical repair of total anomalous pulmonary venous connection. METHODS: Between January 1, 1992, and January 1, 1995, 20 patients underwent repair of total anomalous pulmonary venous connection. Nine patients had postoperative pulmonary hypertension and received a 15-minute trial of inhaled NO at 80 parts per million. Five of these patients received prolonged treatment with NO at 20 parts per million or less. RESULTS: Mean pulmonary artery pressure decreased from 35.6 +/- 2.4 to 23.7 +/- 2.0 mm Hg (mean +/- standard error of the mean) (p = 0.008), and pulmonary vascular resistance decreased from 11.5 +/- 2.0 to 6.4 +/- 1.0 U.m2 (p = 0.03). After prolonged treatment with NO, pulmonary artery pressure increased transiently in all patients when NO was discontinued. CONCLUSIONS: After operative repair of total anomalous pulmonary venous connection, inhaled NO selectively vasodilated all patients with pulmonary hypertension. Withdrawal of NO after prolonged inhalation was associated with transient rebound pulmonary hypertension that dissipated within 60 minutes. Appreciation of rebound pulmonary hypertension may have important implications for patients with pulmonary hypertensive disorders when interruption of NO inhalation is necessary or when withdrawal of NO is planned.     

Robust Estimators of the 3-Parameter Weibull Distribution

Robust estimators of the location, scale, and shape parameters of the Weibull distribution are proposed. The estimators are easy to calculate and have few of the disadvantages associated with the maximum likelihood estimators. Their rms-errors are considerably smaller than those of the estimators available in the literature.     

Mortality in potential arterial switch candidates with transposition of the great arteries

OBJECTIVE: Prostatic abscesses are uncommon in clinical practice because early antibiotic therapy has reduced complications of prostatitis. Prostatic abscess mainly affects diabetic and immunosuppressed patients. The organisms most frequently involved are Escherichia coli and Staphylococcus, whereas gonococcus is rarely encountered. The results in eight men with prostatic abscess, five of whom were treated with sonographically guided percutaneous drainage, are reported. The diagnosis, clinically suspected in only three patients, was confirmed by transrectal sonography. All patients experienced complete abscess resolution. CONCLUSION: Transrectal sonography is the most reliable imaging method to diagnose prostatic abscess. Percutaneous transperineal or transrectal drainage is the first choice for therapy because of the lower risk of complication compared with surgery.     

New class of primary-feed antennas for use with offset parabolic-reflector antennas

In many practical applications the performance of an offset parabolic-reflector antenna is limited by the offset reflectors' depolarising and beam-squinting properties. The letter describes a new class of primary-feed antennas which overcome these limitations. The new primary-feed types offer a significant improvement in the crosspolar and beam-squinting properties of the offset reflector antenna, without adding significantly to the complexity or mass of the primary-feed system.     

Analysis of rotationally symmetric dielectric-loaded waveguides and horns

A cylindrical mode-matching approach has been used to analyse dielectric-loaded waveguides and horns. The method is capable of analysing structures with many annular regions of different dielectrics. The technique has been validated by comparing with experimental results.     

Beam squint in circularly polarised offset-reflector antennas

The beam-squint phenomenon, which is observed when offset portions of parabolic reflector surfaces are illuminated by circularly polarised primary feeds, can be a critical factor in the design of antennas employing frequency-reuse techniques. The letter describes the derivation of a very simple formula which can be employed to predict the magnitude of the beam-squint effect to an accuracy of better than 0.01 of the antenna halfpower beamwidth. Verification of the formula has been obtained using both computed and experimental data.     

Best linear unbiased estimator of the Rayleigh scale parameterbased on fairly large censored samples

This paper tabulates: coefficients and relative s-efficiency of the best linear unbiased estimator (BLUE) of the scale parameter of the Rayleigh distribution for type II censored samples of size N=20(5)40, r=0(1)4 (number of observations censored from the left) and s=0(1)4 (number of observations censored from the right); and ranks, coefficients, variances, and relative s-efficiencies of the BLUE of a based on a selected few order statistics (k) for sample size N=20(1)40 and k=2(1)4. These estimators have the minimum variance among the BLUE of a based on the same number of order statistics. As compared to maximum likelihood estimators (MLE) and approximate MLE, the s-efficiency of BLUE of ρ is very high. When estimating the parameter using only a few observations, the k-optimum BLUE of ρ is the only choice, as the MLE of ρ is not available. Therefore, these tables for coefficients of BLUE of ρ based on censored samples and few observations for moderately large samples, have many applications