General Electric

About: General Electric is a company organization based out in Boston, Massachusetts, United States. It is known for research contribution in the topics: Turbine & Signal. The organization has 76365 authors who have published 110557 publications receiving 1885108 citations. The organization is also known as: General Electric Company & GE.

Tracking system to monitor the position and orientation of a device using multiplexed magnetic resonance detection

Abstract: A tracking system employs magnetic resonance signals to monitor the position and orientation of at least one device such as a catheter within a subject. The device has a plurality of receiver coils which are sensitive to magnetic resonance signals generated in the subject. These signals are detected in the presence of magnetic field gradients and thus have frequencies which are substantially proportional to the location of the coil along the direction of the applied gradient. Signals are detected responsive to sequentially applied mutually orthogonal magnetic gradients to determine the device's position and orientation in several dimensions. The position and orientation of the device as determined by the tracking system is superimposed upon independently acquired medical diagnostic images. One or more devices can be simultaneously tracked.

Optimum Simple Step-Stress Plans for Accelerated Life Testing

Abstract: This paper presents optimum plans for simple (two stresses) step-stress tests where all units are run to failure. Such plans minimize the asymptotic variance of the maximum likelihood estimator (MLE) of the mean life at a design stress. The life-test model consists of: 1) an exponential life distribution with 2) a mean that is a log-linear function of stress, and 3) a cumulative exposure model for the effect of changing stress. Two types of simple step-stress tests are considered: 1) a time-step test and 2) a failure-step test. A time-step test runs a specified time at the first stress, whereas, a failure-step test runs until a specified proportion of units fail at the first stress. New results include: 1) the optimum time at the first stress for time-step test and 2) the optimum proportion failing at the low stress for a failure-step test, and 3) the asymptotic variance of these optimum tests. Both the optimum time-step and failure-step tests have the same asymptotic variance as the corresponding optimum constant-stress test. Thus step-stress tests yield the same amount of information as constant-stress tests.

Electron Spin Resonance in Semiconductors

Abstract: Publisher Summary This chapter describes the application of electron spin resonance techniques to a particular group of crystalline semiconductors, including Si and related group IV elements and compounds, InSb and related 111-V compounds, and ZnS and related 11-VI compounds. The semiconductors discussed in the chapter have a number of characteristics that make them particularly interesting subjects for resonance study. One characteristic is that the semiconductors are intrinsically diamagnetic and show no cooperative magnetic phenomena, such as ferromagnetism and antiferromagnetism. Crystals that are examined in the chapter are typically dilute in magnetically active impurities and have narrow resonance lines. Another characteristic is the tetrahedral symmetry about each lattice site. However, semiconductors are an ideal group of materials for investigating the effects of covalency. There are several features of the resonance technique that make it a particularly useful tool for the study of semiconductors. Electrical, optical, and other properties of semiconductors are extremely sensitive to small concentrations of impurities. Spin resonance is one of the most sensitive and powerful tools for investigating the detailed nature of impurity sites. Moreover, it is often possible to study one impurity in the presence of much larger concentrations of other impurities.

A Method for the Neutralization of Electron Space Charge by Positive Ionization at Very Low Gas Pressures

Abstract: Neutralization of space charge around a hot filament by imprisoned positive ions in gas at very low pressures.---(I) Design of tube. If a very small filament, diameter 0.01 cm, is run axially through a cylindrical anode with closed ends, positive ions formed between the electrodes can only rarely escape and will describe orbits around the filament until they lose sufficient energy by collision with gas molecules to enable them to fall into the cathode. The imprisoned ions, during their lives, neutralize a certain amount of the space charge between the electrodes. The effect should increase with the absolute temperature and with the ratio of the cross-section of the anode cylinder to that of the filament. A theoretical calculation indicates that in He at ${10}^{\ensuremath{-}5}$ mm, an ion which misses the filament on its first passage across the tube may circulate around the filament 300 times before discharging to the cathode. (2) Results in $\mathrm{He}$, $H$, $\mathrm{Ne}$, and $\mathrm{Hg}$ at pressures ranging from ${10}^{\ensuremath{-}2}$ to ${10}^{\ensuremath{-}7}$ mm are shown in curves. Comparison of the currents when the cylinder ends were connected (1) to the anode and (2) to the cathode gave the effect of the positive ions, and also their number, and therefore the increase in current per ion, $\ensuremath{\alpha}$. At pressures so low that the 3/2 power space-charge law holds in an ordinary tube, imprisoned ions may still produce large deviations from this law, in favorable cases the current with the ions being 5 or 10 times the current as ordinarily limited by space charge. The relatively much greater effect in Hg vapor than in He is shown to agree well with the theory. If $\ensuremath{\alpha}$ depended only on mean free path, however, it should vary as $\frac{1}{p}$, but the results gave ${(\frac{1}{p})}^{\frac{2}{3}}$. This difference shows the influence of other factors. However, theoretical mean free paths are of the same order of magnitude as those calculated from $\ensuremath{\alpha}$. Moreover, in Hg vapor at 4.2 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}7}$ mm, the time required to reach equilibrium after the positive ions began to accumulate was found by oscillograms to be about the same as the calculated life of an ion, 1.4 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ sec. The simple theory, then, seems to be pretty well verified.