Electron emission from quasi-freestanding bilayer epitaxial graphene (QEG) on a silicon carbide substrate is reported, demonstrating emission currents as high as 8.5 µA, at ~200 °C, under 0.3 Torr ...vacuum. Given the significantly low turn-on temperature of these QEG devices, ~150°C, the electron emission is explained by phonon-assisted electron emission, where the acoustic and optical phonons of QEG causes carrier acceleration and emission. Devices of differing dimensions and shapes are fabricated via a simple and scalable fabrication procedure and tested. Variations in device morphology increase the density of dangling bonds, which can act as electron emission sites. Devices exhibit emission enhancement at increased temperatures, attributed to greater phonon densities. Devices exhibit emission under various test conditions, and a superior design and operating methodology are identified.
We analyze the behavior of the parsec-scale jet of the quasar 3C 454.3 during pronounced flaring in 2005-2008. Three major disturbances propagated down the jet along different trajectories with ...Lorentz factors {Gamma} > 10. The disturbances show a clear connection with millimeter-wave outbursts, in 2005 May/June, 2007 July, and 2007 December. High-amplitude optical events in the R-band light curve precede peaks of the millimeter-wave outbursts by 15-50 days. Each optical outburst is accompanied by an increase in X-ray activity. We associate the optical outbursts with propagation of the superluminal knots and derive the location of sites of energy dissipation in the form of radiation. The most prominent and long lasting of these, in 2005 May, occurred closer to the black hole, while the outbursts with a shorter duration in 2005 autumn and in 2007 might be connected with the passage of a disturbance through the millimeter-wave core of the jet. The optical outbursts, which coincide with the passage of superluminal radio knots through the core, are accompanied by systematic rotation of the position angle of optical linear polarization. Such rotation appears to be a common feature during the early stages of flares in blazars. We find correlations between optical variations and those at X-ray and {gamma}-ray energies. We conclude that the emergence of a superluminal knot from the core yields a series of optical and high-energy outbursts, and that the millimeter-wave core lies at the end of the jet's acceleration and collimation zone. We infer that the X-ray emission is produced via inverse Compton scattering by relativistic electrons of photons both from within the jet (synchrotron self-Compton) and external to the jet (external Compton, or EC); which one dominates depends on the physical parameters of the jet. A broken power-law model of the {gamma}-ray spectrum reflects a steepening of the synchrotron emission spectrum from near-IR to soft UV wavelengths. We propose that the {gamma}-ray emission is dominated by the EC mechanism, with the sheath of the jet supplying seed photons for {gamma}-ray events that occur near the millimeter-wave core.
Abstract Enhanced electron emission from oxide-encapsulated quasi-freestanding bilayer epitaxial graphene devices is reported, including one emission current of 9.4 µ A and successful emission even ...with oxide thicknesses of up to 1.25 µ m. The low operating temperature (215 °C), and applied electric fields under which the devices operate indicate electron emission is due to phonon-assisted electron emission, wherein forward-scattering hot phonons impart the necessary energy for the electrons to escape the graphene as an emission current. A suite of device structures and behaviors are cataloged, and various emission behaviors are demonstrated through encapsulating oxide layers. Emission current enhancement due to electron multiplication in the oxide layers is observed across multiple devices and oxide thicknesses.
Developing low-power, high-sensitivity photodetectors for the terahertz (THz) band that operate at room temperature is an important challenge in optoelectronics. In this study, we introduce a ...photothermal-electric effect detector based on quasi-free-standing bilayer graphene on a silicon carbide substrate, designed for the THz frequency range. Our detector’s performance hinges on a quasi-optical coupling scheme, which integrates an aspherical silicon lens, to optimize impedance matching between the THz antenna and the graphene p–n junction. At room temperature, we achieved a noise equivalent power of less than 300 p W / H z . Through an impedance matching analysis, we coupled a planar antenna with a graphene p–n junction, inserted in parallel to the nanogap of the antenna, via two coupling capacitors. By adjusting the capacitors and the antenna arm length, we tailored the antenna’s maximum infrared power absorption to specific frequencies. The sensitivity, spectral properties, and scalability of our material make it an ideal candidate for future development of far-infrared detectors operating at room temperature.
6-Minute Walk Test Sherwood, Jennifer; Inouye, Cathy; Anderson, Erik ...
Medicine and science in sports and exercise,
05/2016, Letnik:
48
Journal Article
Developing low-power, high-sensitivity photodetectors for the terahertz (THz) band that operate at room temperature is an important challenge in optoelectronics. In this study, we introduce a ...photo-thermal-electric (PTE) effect detector based on quasi-free standing bilayer graphene (BLG) on a silicon carbide (SiC) substrate, designed for the THz frequency range. Our detector's performance hinges on a quasi-optical coupling scheme, which integrates an aspherical silicon lens, to optimize impedance matching between the THz antenna and the graphene p-n junction. At room temperature, we achieved a noise equivalent power (NEP) of less than 300 \(pW/\sqrt{Hz}\). Through an impedance matching analysis, we coupled a planar antenna with a graphene p-n junction, inserted in parallel to the nano-gap of the antenna, via two coupling capacitors. By adjusting the capacitors and the antenna arm length, we tailored the antenna's maximum infrared power absorption to specific frequencies. The sensitivity, spectral properties, and scalability of our material make it an ideal candidate for future development of far-infrared detectors operating at room temperature.
Duodenal adenocarcinoma is a rare but aggressive malignancy. Given its rarity, previous studies have traditionally combined duodenal adenocarcinoma (DA) with either other periampullary cancers or ...small bowel adenocarcinomas, limiting the available data to guide treatment decisions. Nevertheless,management primarily involves complete surgical resection when technically feasible. Surgery may require pancreaticoduodenectomy or segmental duodenal resection; either are acceptable options as long as negative margins are achievable and an adequate lymphadenectomy can be performed. Adjuvant chemotherapy and radiation are important components of multi-modality treatment for patients at high risk of recurrence. Further research would benefit from multiinstitutional trials that do not combine DA with other periampullary or small bowel malignancies. The purpose of this article is to perform a comprehensive review of DA with special focus on the surgical management and principles.
Duodenal adenocarcinoma is a rare but aggressive malignancy. Given its rarity, previous studies have traditionally combined duodenal adenocarcinoma(DA) with either other periampullary cancers or ...small bowel adenocarcinomas, limiting the available data to guide treatment decisions. Nevertheless, management primarily involves complete surgical resection when technically feasible. Surgery may require pancreaticoduodenectomy or segmental duodenal resection; either are acceptable options as long as negative margins are achievable and an adequate lymphadenectomy can be performed. Adjuvant chemotherapy and radiation are important components of multi-modality treatment for patients at high risk of recurrence. Further research would benefit from multiinstitutional trials that do not combine DA with other periampullary or small bowel malignancies. The purpose of this article is to perform a comprehensive review of DA with special focus on the surgical management and principles.
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