Two-dimensional Linear Array Research Articles

A two-dimensional linear array fiber amplifier based on the MOPA configuration

A two-dimensional linear array fiber amplifier based on the master oscillator power amplifier (MOPA) configuration is constructed and employed as the laser source of a high resolution 3D imaging LIDAR system. Each branch of the linear array system comprises a dual-stage Yb3+-doped large-mode-area double-clad fiber amplifier. The amplified pulse is of 2.3 ns temporal duration and 30 kHz repetition rate with an average power of 8.5 W when the pump power is 20 W. The optical–optical conversion efficiency is 41.8%. Furthermore, the SRS effect can be suppressed effectively. The M2 values of the output beam are 1.35 and 1.33 in the x- and y-axis directions, respectively.

2-(3-tert-Butyldimethylsiloxy-4-methoxyphenyl)-6-methoxy-3-(3,4,5-trimethoxybenzoyl)indole.

In the crystal structure of the title compound, C(32)H(39)NO(7)Si, all geometric parameters fall within experimental error of expected values. The analysis of molecular-packing plots reveals an infinite two-dimensional linear array running parallel to the b axis, formed by one N[bond]H...O intermolecular hydrogen-bonding interaction. Several potential C[bond]H...O interactions are also present.

Electrical properties of organized assemblies of polypyrrole fabricated chemically on a copper stearate template in Langmuir-Blodgett films

The electrical properties of Langmuir-Blodgett films of polypyrrole fabricated on a copper stearate template have been studied. The films exhibit domains of a highly organized two-dimensional linear array of polypyrrole granules sandwiched between insulating fatty acid layers together with some disorganized domains. The measured in-plane conductivity does not show any appreciable anisotropy and is as high as 1.2 S cm-1 with a thermal activation energy of 0.15 eV. The transverse conductivity of the film in a metal-insulator-metal structure is shown to be Poole-Frenkel emission-limited and has a value of the order of 10-8 S cm-1 in the low-field region. The film then shows a high degree of conductivity anisotropy.

Backscatter coefficient estimation using array transducers

This paper describes an extension of our broadband method for estimating backscatter coefficients from random media to include data from array transducers. Four different transducer designs have now been considered: oneand two-dimensional linear arrays, annular arrays, and single-element focused pistons commonly used in mechanical sector scanners. The analysis shows that if the backscatter echo spectrum is properly normalized, the shape of the piezoelectric elements affects only the magnitude and not the frequency dependence of the backscatter coefficient estimates. Experimental data were acquired using laboratory and clinical imaging instrumentation to verify the analysis. We compared backscatter coefficients measured as a function of frequency from well-defined scattering media that were obtained using a 1-D linear array and focused piston transducers. Instrument-independent results were found that matched theoretical predictions within the measurement error between 2 and 12 MHz. We conclude from this study that accurate backscatter coefficient estimates may be easily obtained using current clinical imaging instrumentation.

Electrical conduction of polypyrrole in Langmuir-Blodgett films fabricated chemically on ferric stearate substrates

The electrical properties of Langmuir-Blodgett (LB) films of polypyrrole fabricated on a ferric stearate template have been studied. The LB films exhibit a highly organized two-dimensional linear array of polymer granules sandwiched between insulating fatty acid layers. Measured in-plane conductivity is as high as 1.25 S cm −1 whereas conductivity along the film normal is 10 −8 S cm −1, revealing a very high degree of anisotropy. A temperature dependence study suggests charge transport by one-dimensional variable range hopping.

Fetal cardiac arrhythmias and their effect on volume blood flow in descending aorta of human fetus.

Using a two-dimensional linear array real-time and pulsed Doppler ultrasound system, volume blood flow measurements were made in 86 normal pregnancies, seven cases of fetal bradycardia, and seven cases of fetal tachycardia at the lower thoracic level of the fetal descending aorta. During fetal cardiac arrhythmias, volume blood flow was maintained within the normal range until the heart rates reached around 50 bpm and 230 bpm, after which the volume blood flow diminished. The changes observed suggest that the Frank-Starling mechanism is functional in the fetal myocardium and demonstrate the stability of the fetal circulation.

Cardiac Doppler flow velocities in human fetuses.

Cardiac Doppler flow velocity studies were performed in normal human fetuses between 18 and 40 weeks of gestation. Two-dimensional linear array and sector scanning techniques were used for the initial evaluation of the fetuses, which included a standard ultrasound examination to determine normal anatomy and estimated gestational age and weight. Fetal cardiac ultrasound examination was then performed, with four-chamber, short-axis/great vessel, long-axis/left ventricular outflow tract, and aortic arch views obtained. Pulsed echo Doppler instrumentation was used to obtain flow velocity measurements through the tricuspid, pulmonary outflow, mitral, and aortic outflow regions. Calculation of transvalve volume flow for mitral and tricuspid valves was performed by combining the valve anulus sizes and calculated mean temporal velocities for the valves. Maximal flow velocities were greater through the tricuspid (mean maximal velocity 51 +/- 1.2 [SE] cm/sec) than through the mitral (47 +/- 1.1 cm/sec; p less than .05) valve regions, with a wide range of scatter for results between fetuses but less than 6% average variation in the individual fetuses during gestation. For 18 fetuses, right heart dimensions and volume flows (mean 307 + 30 ml/kg/min) were greater than left heart dimensions and volume flows (232 +/- 25 ml/kg/min). Doppler echocardiography may prove to be useful as an adjunct to imaging echocardiography for evaluation of fetal cardiac anatomy and function.

Clinical evaluation of a hand-held ultrasound device in pediatric cardiology

Recently a hand-held two-dimensional linear array ultrasound diagnostic system was introduced. To assess the clinical usefulness of this non-invasive system in pediatric echocardiography, an evaluation study was carried out. For this purpose 58 children up to the age of 18 yr were examined. Several of them were known to have a congenital cardiac malformation. The assessment has been based on the image quality of six cardiac structures which include the aortic root, left atrium, right ventricle, interventricular septum, left ventricle and mitral valve. The results indicated differences between children younger than 1 yr and those who are older. Therefore the patients were divided into two groups. In the younger children, only three cardiac structures, the aortic root, left atrium and mitral valve, were recognized with a score above 80%, whereas the remaining structures received a score of 60% or lower. In the older age group the results were much better, as all six cardiac structures were visualized with a score of 80% or more.

Ultrastructural pathology of coxsackie A4 virus infection of mouse striated muscle

Electron microscopic examination of Coxsackie A4 virus-infected hind limb muscles of suckling mice showed generalized myositis with almost total loss of normal muscle cell architecture. Degenerative changes included dilatation of sarcoplasmic reticulum with concurrent disruption of myofibrils, presenting the appearance of dense amorphous masses in some areas; large accumulations of membrane-bound vesicles; swelling, distortion, and mineralization of mitochondria; increase in lipid deposits; pyknosis of the nuclei; edema and inflammatory infiltration. Virus particles were present in a number of different configurations in muscle fibers: individual particles or small accumulations within vacuoles, two-dimensional linear arrays between membranes, and three-dimensional crystalline arrays, usually in close apposition to sarcoplasmic reticulum or sarcolemma.