Experimental performance of adaptive beamforming in a sonarenvironment with a towed array and moving interfering sources

The performances of adaptive array algorithms are known to suffer from a strong degradation in scenarios with moving interfering sources. In this article, basic adaptive beamforming techniques are compared using shallow sea sonar data recorded in a towed horizontal array environment with moving interfering sources originated from shipping noise. Our experimental results show the relationship between the practical performances of adaptive and conventional beamforming techniques compared in terms of output SINR or a related measure given by the noncompensated postbeamforming interference power. These results demonstrate noticeable performance improvements that can be achieved using several robust algorithms relative to traditional adaptive beamforming schemes     

The type 1 angiotensin-II receptor mediates intracellular calcium mobilization in rat luteal cells

The intracellular cytosolic calcium concentration ([Ca]i) was determined in cultured rat luteal cells using the calcium-chelating dye fura-2 and microspectrofluorimetry. Angiotensin-II (Ang-II) induced a dose-dependent transient increase in [Ca]i (ED50, 9.0 +/- 6.5 nM). After the initial peak in [Ca]i, cytosolic calcium returned to a secondary elevated basal level that was dependent upon the presence of extracellular calcium. Pretreatment of rat luteal cells with Ang-II (100 nM) desensitized a subsequent response to a higher concentration (1 microM), but did not desensitize a prostaglandin F2 alpha (PGF2 alpha)-induced calcium flux. Although the peak increases in [Ca]i induced by Ang-II (1 microM) and PGF2 alpha (10 microM) were not significantly different, the plateau phase stimulated by PGF2 alpha was significantly higher (P < 0.05) than that stimulated by Ang-II (1 microM). Pretreatment of luteal cells with the type 2 Ang-II receptor antagonist PD 123319 (10 microM) did not inhibit calcium mobilization; however, Ang-II (1 microM)-induced calcium mobilization was dose dependently blocked by the type 1 Ang-II receptor antagonist Losartan (DuP 753). The ID50 for Losartan was 5.2 +/- 1.8 nM. Pretreatment of the luteal cells with the endoplasmic reticulum calcium ATPase inhibitor thapsigargin (1 microM) also blocked Ang-II-induced calcium mobilization. These data demonstrate the presence of the type 1 Ang-II receptor in rat luteal cells, through which Ang-II dose dependently mobilizes calcium from an intracellular source, probably the endoplasmic reticulum.     

Natural history of coronary atherosclerosis using quantitative angiography in men, and implications for clinical trials of coronary regression. The Harvard Atherosclerosis Reversibility Project Study Group

Previous studies of the natural history of coronary disease generally relied on estimates of percent stenosis derived from visual assessment of the coronary angiogram. In a study of 26 patients, serial quantitative angiography was performed 3 years apart to determine changes in both absolute measurements of the luminal diameter and relative percent stenosis. Initially, the mean minimal diameter of 74 coronary obstructions was 1.94 +/- 0.09 mm, the mean "normal" reference diameter was 3.06 +/- 0.11 mm, and the mean percent stenosis was 37%. At follow-up, there was a mild reduction of 0.12 +/- 0.04 mm (6%) in the minimal diameter (p < 0.005), and an increase in percent stenosis to 39% (p = 0.03). The average diameter of 85 arterial segments without a focal obstruction either initially or at follow-up showed mild but significant progression (-0.11 +/- 0.04 mm; p = 0.02). Using a minimal change of 0.27 mm in arterial diameter as a categoric variable, progression occurred in 26% of 74 arterial segments, no significant change in 65%, and regression in 9%. The only significant determinant of disease progression was the initial severity of disease. Obstructed arteries with a larger initial minimal diameter and presumably milder disease progressed more rapidly than did those with a smaller diameter (r = -0.42; p = 0.0002). There was no effect of age on the rate of progression (r = 0.02; p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)     

Computer graphics on a hexagonal grid

Aberrations in digital images can be attenuated by computing the image at higher-than-display resolution, convolving it with a two-dimensional filter kernel and decimating the filtered image back to display resolution for presentation. Traditionally, this has been performed using a rectangular sampling grid, which is parallel to the display scan direction. In this paper, the application of a hexagonal sampling grid is proposed. Rectangular and hexagonal processing are discussed, and it is shown that despite the differences in their mathematical bases, their algorithmic implementations are similar. A series of test patterns are presented and evaluated. It is concluded that hexagonal processing results in a greater reduction in aliasing in regions of vertical/near vertical features of images than is achieved by rectangular processing, without any degradation in other regions, and with negligible additional computational effort.     

Medium-term follow-up of the Ionescu-Shiley heterograft valve

Utilizing a questionnaire specifically designed to uncover potential thromboembolic episodes, we personally interviewed 97 patients who underwent valve replacement with the Ionescu-Shiley valve between January, 1977, and June, 1980. In both the aortic and mitral positions, the attrition rate after the first year was low; cumulative survival at 3 to 4 years was 78% (aortic) and 61% (mitral). None of the deaths were attributed to primary valve failure. Patients with aortic prostheses, none of whom were anticoagulated, had a cumulative thromboembolism-free rate of 94% at 3 to 4 years. Patients with mitral prostheses had a thromboembolism-free rate of 71% at 3 to 4 years with 80% of the episodes occurring in patients in atrial fibrillation. Most emboli produced only transient symptoms, and only 1 patient has residual impairment. The Ionescu-Shiley valve performs well in the early years after valve replacement. Anticoagulation should be strongly considered for patients with mitral prostheses who are in atrial fibrillation.     

Comparative investigation into the corrosion of different bronze alloys suitable for outdoor sculptures

Several bronze alloys, suitable for production of outdoor sculptures, were developed in the frame of the European project “Eurocare-Bronzart”. The elemental composition of the alloys was searched to fulfil specific criteria such as: reduction of lead content, good resistance toward corrosion and aesthetic characteristics conformable to artistic purposes. After metallurgical characterization, the resistance toward corrosion was evaluated in artificial environments. Ageing experiments were performed in a salt spray cabinet and in a climatic chamber in the presence of a controlled concentration of SO₂. The Thin Layer Activation (TLA) method was applied to calculate the thickness loss of activated specimens exposed to artificial corrosive atmospheres. After artificial ageing experiments the surface of the materials was investigated by SEM-EDS techniques.The bronze alloys containing different percentage of nickel showed the best properties of resistance toward corrosion.     

Phenomenological approach to the role of C3A in the hardening of portland cement pastes

This paper is a contribution to the growing belief that the C₃A acts as a catalyst on the calcium silicates during hydration. This is based on the finding that the rates of reactions of the silicates are linear functions of the C₃A content of the cement.The effect of C₃A on the ultimate strength is also discussed numerically along with evidence that shows that the rate of hardening, per se, affects the ultimate strength through its effect on the structure of the hardening cement paste.