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.

Raman and IR absorption spectroscopic studies on α, β, and amorphous Si3N4

Abstract: Vibrational excitations of α- and β-Si 3 N 4 were studied by Raman and infrared absorption spectroscopies. Group theory was employed to interpret the observed spectra of crystalline α- and β-Si 3 N 4 . Both Raman and IR spectra of amorphous Si 3 N 4 exhibit two broad peaks centered at about 400 and 900 cm −1 . Amorphous Si 3 N 4 was found to be of the non-molecular, random-network type.

Thermal management of LEDs: package to system

Abstract: Light emitting diodes, LEDs, historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs with white light and monochromatic colors have led to a movement towards general illumination. The increased electrical currents used to drive the LEDs have focused more attention on the thermal paths in the developments of LED power packaging. The luminous efficiency of LEDs is soon expected to reach over 80 lumens/W, this is approximately 6 times the efficiency of a conventional incandescent tungsten bulb. Thermal management for the solid-state lighting applications is a key design parameter for both package and system level. Package and system level thermal management is discussed in separate sections. Effect of chip packages on junction to board thermal resistance was compared for both SiC and Sapphire chips. The higher thermal conductivity of the SiC chip provided about 2 times better thermal performance than the latter, while the under-filled Sapphire chip package can only catch the SiC chip performance. Later, system level thermal management was studied based on established numerical models for a conceptual solid-state lighting system. A conceptual LED illumination system was chosen and CFD models were created to determine the availability and limitations of passive air-cooling.

Color tunable light source

Abstract: A color tunable light source ( 10 ) includes multiple light emitting components ( 32, 34, 36 ), such as light emitting diodes (LEDs) or laser diodes (LDs) with different emission wavelengths, and multiple phosphors ( 24 ) with different excitation and emission wavelengths. The emission wavelengths of the different light emitting components are chosen to match the excitation wavelengths of the different phosphors. The light emitting components are powered by an electrical circuit ( 42, 44, 46 ), which allows separate control of the optical power output of the different wavelength LEDs/LDs. The light from the light emitting components is arranged to impinge on the combination of phosphors such that the phosphors are excited and emit light at their characteristic wavelengths. By separately adjusting the power to each LED/LD, the amount of light emitted by each phosphor, and hence, through color mixing, the color of the light emitted, is varied.

Internal Friction in Solids

Abstract: It is shown from tests on eighteen different solids, including several metals, glass, celluloid, rubber and maple wood, that the internal friction for strains below the elastic limit does not obey the liquid viscosity law, as is usually assumed, according to which the frictional force depends upon the velocity of strain, but that the internal friction is entirely independent of strain velocity, so far as can be observed. It was found to depend upon the amplitude of strain during the strain cycles and approximately to obey the law: Energy loss per cycle per unit volume equals $\ensuremath{\xi}{{f}_{m}}^{2}$. In this expression ${f}_{m}$ is the maximum value of the stress during the stress cycle and $\ensuremath{\xi}$ a proportionality factor, which may be called the internal friction constant. The method used was to measure the transverse deflections of the end of a rod, about a meter long, of the material being studied, which transverse deflections were produced during rotation of the rod when its end was deflected downwards by suitable loads on it. The experiments differ from most previous work in that relatively large masses of material were employed, tending to reduce surface effects, which are likely to enter in the case of vibration decrement experiments on wires and on thin strips. A table of the internal friction constants obtained is given, and also a table of similar internal friction constants calculated from data of previous investigators. A reasonable agreement is found.

Quantitation of respiratory motion during 4D-PET/CT acquisition

Abstract: We report on the variability of the respiratory motion during 4D-PET/CT acquisition. The respiratory motion for five lung cancer patients was monitored by tracking external markers placed on the abdomen. CT data were acquired over an entire respiratory cycle at each couch position. The x-ray tube status was recorded by the tracking system, for retrospective sorting of the CT data as a function of respiration phase. Each respiratory cycle was sampled in ten equal bins. 4D-PET data were acquired in gated mode, where each breathing cycle was divided into ten 500 ms bins. For both CT and PET acquisition, patients received audio prompting to regularize breathing. The 4D-CT and 4D-PET data were then correlated according to their respiratory phases. The respiratory periods, and average amplitude within each phase bin, acquired in both modality sessions were then analyzed. The average respiratory motion period during 4D-CT was within 18% from that in the 4D-PET sessions. This would reflect up to 1.8% fluctuation in the duration of each 4D-CT bin. This small uncertainty enabled good correlation between CT and PET data, on a phase-to-phase basis. Comparison of the average-amplitude within the respiration trace, between 4D-CT and 4D- PET, on a bin-by-bin basis show a maximum deviation of approximately 15%. This study has proved the feasibility of performing 4D-PET/CT acquisition. Respiratory motion was in most cases consistent between PET and CT sessions, thereby improving both the attenuation correction of PET images, and co-registration of PET and CT images. On the other hand, in two patients, there was an increased partial irregularity in their breathing motion, which would prevent accurately correlating the corresponding PET and CT images.