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 & Rotor (electric). The organization has 76365 authors who have published 110557 publications receiving 1885108 citations. The organization is also known as: General Electric Company & GE.

A review of coercivity mechanisms (invited)

Abstract: Mechanisms of magnetization reversal and factors determining coercivity are reviewed for various permanent‐magnet materials.

Dynamics of Laminar Premixed Flames Forced by Harmonic Velocity Disturbances

Abstract: This paper describes the dynamics of constant-burning-velocity premixed flames responding to harmonic velocity disturbances. Results are derived from analytical and computational solutions of the nonlinear G equation and compared with available experimental data. It is shown that the flame dynamics are controlled by the superposition of two waves propagating along the flame sheet: those originating at the flame-anchoring point and from flow nonuniformities along the flame. They may either constructively or destructively superpose, and so the overall linear flame response depends upon two Strouhal numbers, St 2 and Stc, related to the amount of time taken for a flow (St c ) and flame-front (St 2 ) disturbance to propagate the flame length, normalized by the acoustic period. The nonlinear flame response is controlled by flame propagation normal to itself, which smoothens out the wrinkles induced by the forcing at an amplitude-dependent rate. The flame's nonlinear response is shown to exhibit two qualitatively different behaviors. For parameter values at which these disturbances constructively interfere, the nonlinear flame response saturates. When the flame disturbances destructively interfere, the nonlinear transfer function may actually exceed its linear value before saturating. This result explains experimentally observed variations of the nonlinear flame response with frequency.

Methods and apparatus for reducing gas turbine engine emissions

Abstract: A low emission turbine includes a reverse flow can-type combustor that generally includes a primary and secondary fuel delivery system that can be independently controlled to produce low CO, UHC, and NOx emissions at design set point and at conditions other than design set point. The reverse flow can-type combustor generally includes an annularly arranged array of swirler and mixer assemblies within the combustor, wherein each swirler and mixer in the array includes a primary and secondary fuel delivery system that can be independently controlled. Also disclosed herein is a can-type combustor that includes fluid passageways that perpendicularly impinge the backside of a heat shield. Processes for operating the can-type combustors are also disclosed.

A concentration-independent method to measure exchange rates in PARACEST agents.

Abstract: The efficiency of chemical exchange dependent saturation transfer (CEST) agents is largely determined by their water or proton exchange kinetics, yet methods to measure such exchange rates are variable and many are not applicable to in vivo measurements. In this work, the water exchange kinetics of two prototype paramagnetic agents (PARACEST) are compared by using data from classic NMR line-width measurements, by fitting CEST spectra to the Bloch equations modified for chemical exchange, and by a method where CEST intensity is measured as a function of applied amplitude of radiofrequency field. A relationship is derived that provides the water exchange rate from the X-intercept of a plot of steady-state CEST intensity divided by reduction in signal caused by CEST irradiation versus 1/omega(1)(2), referred to here as an omega plot. Furthermore, it is shown that this relationship is independent of agent concentration. Exchange rates derived from omega plots using either high-resolution CEST NMR data or CEST data obtained by imaging agree favorably with exchange rates measured by the more commonly used Bloch fitting and line-width methods. Thus, this new method potentially allows access to a direct measure of exchange rates in vivo, where the agent concentration is typically unknown.

The influence of patient centering on CT dose and image noise.

Abstract: Although x-ray intensity shaping filters (bowtie filters) have been used since the introduction of some of the earliest CT scanner models, the clinical implications on dose and noise are not well understood. To achieve the intended dose and noise advantage requires the patient to be centered in the scan field of view. In this study we explore the implications of patient centering in clinical practice. We scanned various size and shape phantoms on a GE LightSpeed VCT scanner using each available source filter with the phantom centers positioned at 0, 3, and 6 cm below the center of rotation (isocenter). Surface doses were measured along with image noise over a large image region. Regression models of surface dose and noise were generated as a function of phantom size and centering error. Methods were also developed to determine the amount of miscentering using a scout scan projection radiograph (SPR). These models were then used to retrospectively evaluate 273 adult body patients for clinical implications. When miscentered by 3 and 6 cm, the surface dose on a 32 cm CTDI phantom increased by 18% and 41% while image noise also increased by 6% and 22%. The retrospective analysis of adult body scout SPR scans shows that 46% of patients were miscentered in elevation by 20-60 mm with a mean position 23 mm below the center of rotation (isocenter). The analysis indicated a surface dose penalty of up to 140% with a mean dose penalty of 33% assuming that tube current is increased to compensate for the increased noise due to miscentering. Clinical image quality and dose efficiency can be improved on scanners with bowtie filters if care is exercised when positioning patients. Automatically providing patient specific centering and scan parameter selection information can help the technologist improve workflow, achieve more consistent image quality and reduce patient dose.