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.

Dual-Energy X-Ray Absorptiometry for Quantification of Visceral Fat

Abstract: Obesity is the major risk factor for metabolic syndrome and through it diabetes as well as cardiovascular disease. Visceral fat (VF) rather than subcutaneous fat (SF) is the major predictor of adverse events. Currently, the reference standard for measuring VF is abdominal X-ray computed tomography (CT) or magnetic resonance imaging (MRI), requiring highly used clinical equipment. Dual-energy X-ray absorptiometry (DXA) can accurately measure body composition with high-precision, low X-ray exposure, and short-scanning time. The purpose of this study was to validate a new fully automated method whereby abdominal VF can be measured by DXA. Furthermore, we explored the association between DXA-derived abdominal VF and several other indices for obesity: BMI, waist circumference, waist-to-hip ratio, and DXA-derived total abdominal fat (AF), and SF. We studied 124 adult men and women, aged 18-90 years, representing a wide range of BMI values (18.5-40 kg/m(2)) measured with both DXA and CT in a fasting state within a one hour interval. The coefficient of determination (r(2)) for regression of CT on DXA values was 0.959 for females, 0.949 for males, and 0.957 combined. The 95% confidence interval for r was 0.968 to 0.985 for the combined data. The 95% confidence interval for the mean of the differences between CT and DXA VF volume was -96.0 to -16.3 cm(3). Bland-Altman bias was +67 cm(3) for females and +43 cm(3) for males. The 95% limits of agreement were -339 to +472 cm(3) for females and -379 to +465 cm(3) for males. Combined, the bias was +56 cm(3) with 95% limits of agreement of -355 to +468 cm(3). The correlations between DXA-derived VF and BMI, waist circumference, waist-to-hip ratio, and DXA-derived AF and SF ranged from poor to modest. We conclude that DXA can measure abdominal VF precisely in both men and women. This simple noninvasive method with virtually no radiation can therefore be used to measure VF in individual patients and help define diabetes and cardiovascular risk.

A Review of NOx Formation Under Gas-Turbine Combustion Conditions

Abstract: Gas turbines offer very high cycle efficiency, exceeding 50% in modern 250 MW-class combined-cycle units for power generation, as well as very low NOv in the lean premixed combustion mode with natural gas fuel. They also account for virtually all commercial aeropropulsion systems, in which case kerosene-based fuel is used. To meet future NOv and CO regulations, a higher level of understanding of turbulence, chemical kinetics and their interactions is required. NOv in particular has become a pacing consideration, although other constraints are present. Selected NOv data obtained at laboratory and machine conditions with gaseous fuel are reviewed here. Although the important chemical reactions cover a wide range in effective Damkohler number, the measure of turbulence-chemistry interactions, it appears that NOv is formed in a distributed zone manner. Equilibrium and superequilibrium effects can broaden the NOv-forming zones beyond the fine scales of turbulence, even in non-premixed flames. Pressure...

Transition Modelling for General Purpose CFD Codes

Abstract: The paper addresses modelling concepts based on the RANS equations for laminar-turbulent transition prediction in general-purpose CFD codes. Available models are reviewed, with emphasis on their compatibility with modern CFD methods. Requirements for engineering transition models suitable for industrial CFD codes are specified. A new concept for transition modeling is introduced. It is based on the combination of experimental correlations with locally formulated transport equations. The concept is termed LCTM – Local Correlation-based Transition Model. An LCTM model, which satisfies most of the specified requirements is described, including results for a variety of different complex applications. An incremental approach was used to validate the model, first on 2D flat plates and airfoils and then on to progressively more complicated test cases such as a three-element flap, a 3D transonic wing and a full helicopter configuration. In all cases good agreement with the available experimental data was observed. The authors believe that the current formulation is a significant step forward in engineering transition modeling, as it allows the combination of transition correlations with general purpose CFD codes. There is a strong potential that the model will allow the 1st order effects of transition to be included in everyday industrial CFD simulations.

On Moore graphs with diameters 2 and 3

Abstract: This note treats the existence of connected, undirected graphs homogeneous of degree d and of diameter k, having a number of nodes which is maximal according to a certain definition. For k = 2 unique graphs exist for d = 2, 3, 7 and possibly for d = 57 (which is undecided), but for no other degree. For k = 3 a graph exists only for d = 2. The proof exploits the characteristic roots and vectors of the adjacency matrix (and its principal submatrices) of the graph.

Real-time position monitoring of invasive devices using magnetic resonance†

Abstract: Techniques which can be used to follow the position of invasive devices in real-time using magnetic resonance (MR) are described. Tracking of an invasive device is made possible by incorporating one or more small RF coils into the device. These coils detect MR signals from only those spins near the coil. Pulse sequences which employ nonselective RF pulses to excite all nuclear spins within the field-of-view are used. Readout magnetic field gradient pulses, typically applied along one of the primary axes of the imaging system, are then used to frequency encode the position of the receive coil(s). Data are Fourier transformed and one or more peaks located to determine the position of each receiver coil in the direction of the applied field gradient. Subsequent data collected on orthogonal axes permits the localization of the receiver coil in three dimensions. The process can be repeated rapidly and the position of each coil can be displayed in real-time.