High-resolution Two-dimensional Images Research Articles

Continuous measurement of intracardiac and pulmonary blood flow velocities with transesophageal pulsed doppler echocardiography: technique and initial clinical experience

Pulsed Doppler techniques have become well established adjuncts to conventional echocardiography in the noninvasive diagnosis of various cardiac malfunctions. Disadvantages of the transthoracic approach, such as inaccessibility and instability of the probe position, limit the continuous application of pulsed Doppler echocardiography during surgery. This study presents a new technique using the transesophageal approach that combines pulsed Doppler measurements with two-dimensional echocardiographic imaging (TDE). The first intraoperative experience with this new enhancement to two-dimensional transesophageal echocardiography (TEE) showed that this relatively noninvasive technique is a safe method allowing constant monitoring of cardiac and pulmonary blood flow velocities. The simultaneous high-resolution two-dimensional imaging facilitates spatial orientation and placement of the sample volume, as well as continued control of the sampling location. The typical flow velocity patterns in standard TEE views are described. The mitral valve and pulmonary artery offer particularly favorable conditions for continuous high-quality TDE measurements. It is concluded that the new technique may further increase the value of TEE to clinicians in the perioperative period.

On the Effect of Substitutional Elements on the Out-Of-Step Distance in the Long Period Ordered Ag2Mg-Based Alloys

The long-period structure of Ag3Mg is studied by substituting some Mg-atoms with one of the elements Zn, Au, Cu, Al, and Sn. These elements are chosen to be able to vary the electron per atom ratio considerably. The out-of-step distances in each case are measured both, from the diffraction patterns and from the high-resolution two-dimensional lattice images. The concentrations of the samples are determined by means of X-ray microanalysis of the same areas where images and diffraction patterns are obtained.

On the structure of {100} platelet defects in type la diamond

Abstract The elucidation of defect structure using two-dimensional lattice images is a difficult and time-consuming procedure owing to the number of variable experimental parameters in a high resolution experiment. In this paper the most important experimental parameters are determined prior to the attempt at structure determination, using a number of different techniques including image matching of perfect diamond images and matching the width and appearance of the central Fresnel fringe at the platelet. Having determined the experimental parameters, the image matching was then carried out using five different models for the platelet. It is found that the high resolution two-dimensional lattice images are sensitive to platelet structure and are consistent with a previously unknown platelet model, the double nitrogen layer zigzag model.

Bistatic Synthetic-Aperture Radar Imaging of Rotating Objects

The imaging properties of a focused radar aperture synthesized by object rotation are considered. The ring-shaped aperture synthesized by the object rotation can provide high-resolution two-dimensional imaging using only monochromatic irradiation. The case of monochromatic irradiation is extended to the polychromatic case and to equivalent bistatic geometries. These techniques offer practical methods for radar imaging of rotating objects with scattering centers visible over large angular extents.

A high resolution electron microscope study of martensite and martensitic interfaces in titanium-manganese

The high resolution two-dimensional lattice fringe imaging technique of transmission electron microscopy has been used to observe a Ti-5% (by mass) Mn alloy, which transforms martensitically from a high temperature body-centred cubic parent phase to a martensite hexagonal close-packed phase. In conjunction with the experimental work, computer simulations of the images have been made by using a program based on the multi-slice approach to the dynamical theory of electron diffraction. The experimental work has produced for the first time two-dimensional lattice fringe images of a parent-martensite interface as well as showing the existence of steps of atomic dimensions, corresponding to twinning dislocations in the internal martensite twin interfaces. These results also suggest an explanation for the fine striated substructure of the martensite. However, the simulations show that the images of the parentmartensite and martensite-twin interface cannot be interpreted in terms of atomic models of these interfaces. The implications of these observations and results on the study of the fine-scale structure of interfaces are discussed.

Electron-microscope study of the crystal structures of mixed oxides in the systems Rb2O–Ta2O5, Rb2O–Nb2O5and K2O–Ta2O5with composition ratios near 1:3. I. Stacking characteristics ofMO6layers

The crystal structures of phases, previously designated as 11L, 9L and 16L, which were commonly found in the title systems are suggested from their high-resolution two-dimensional electron-microscope images. Two types of blocks are found which are composed of five and six layers of pentavalent-metal oxide octahedra and are closely related to the pyrochlore structure. The 11L structure is of rhombohedral {\tt ABCABC} stacking of the former type of block, and the 9L structure is of hexagonal {\tt B}_{0}{\tt A}_{0}^{\prime}{\tt B}_{0}{\tt A}_{0}^{\prime} stacking of the latter type of block. The 16L structure is found to be an alternate stacking of the two types of blocks. The method of stacking of the blocks is the same for the three structures and is found to be favorable from the point of view of local charge balance.

Tutorial review of synthetic-aperture radar (SAR) with applications to imaging of the ocean surface

A synthetic aperture radar (SAR) can produce high-resolution two-dimensional images of mapped areas. The SAR comprises a pulsed transmitter, an antenna, and a phase-coherent receiver. The SAR is borne by a constant velocity vehicle such as an aircraft or satellite, with the antenna beam axis oriented obliquely to the velocity vector. The image plane is defined by the velocity vector and antenna beam axis. The image orthogonal coordinates are range and cross range (azimuth). The amplitude and phase of the received signals are collected for the duration of an integration time after which the signal is processed. High range resolution is achieved by the use of wide bandwidth transmitted pulses. High azimuth resolution is achieved by focusing, with a signal processing technique, an extremely long antenna that is synthesized from the coherent phase history. The pulse repetition frequency of the SAR is constrained within bounds established by the geometry and signal ambiguity limits. SAR operation requires relative motion between radar and target. Nominal velocity values are assumed for signal processing and measurable deviations are used for error compensation. Residual uncertainties and high-order derivatives of the velocity which are difficult to compensate may cause image smearing, defocusing, and increased image sidelobes. The SAR transforms the ocean surface into numerous small cells, each with dimensions of range and azimuth resolution. An image of a cell can be produced provided the radar cross section of the cell is sufficiently large and the cell phase history is deterministic. Ocean waves evidently move sufficiently uniformly to produce SAR images which correlate well with optical photographs and visual observations. The relationship between SAR images and oceanic physical features is not completely understood, and more analyses and investigations are desired.