The performance of the TrueBeam Linac model was shown to be consistent based on automated analysis of trajectory log files and EPID images acquired during delivery of a standardized test suite. The results can be compared directly to tolerance thresholds. In addition, sharing of results from standard tests across institutions can facilitate the identification of QA process and Linac changes. These reference values are presented along with the standard deviation for common tests so that the test suite can be used by other centers to evaluate their Linac performance against those in this consortium.

Coherent time-domain optical experiments on GaAs-AlAs superlattices reveal the existence of an unusually long-lived acoustic mode at ~ 0.6 THz, which couples weakly to the environment by evading the sample boundaries. Classical as well as quantum states that steer clear of surfaces are generally shown to occur in the spectrum of periodic structures, for most boundary conditions. These surface-avoiding waves are associated with frequencies outside forbidden gaps and wavevectors in the vicinity of the center and edge of the Brillouin zone. Possible consequences for surface science and resonant cavity applications are discussed.PACS numbers: 43.35.+d, 78.67.Pt, 63.20.-e -1-

Electric-field-induced heating is studied using noise measurements in n-type GaN grown on sapphire substrates. The measured electron temperature is found to be an order of magnitude higher than what is expected based on calculations of electron-phonon coupling via acoustic deformation potential scattering processes in GaN. The discrepancy may be explained by a large thermal boundary resistance between the GaN film and the sapphire substrate.

The authors introduce a novel approach to study the propagation of high frequency acoustic phonons in which the generation and detection involves two spatially separated superlattices ∼ 1 µm apart. Propagating modes of frequencies up to ∼ 1 THz escape from the superlattice where they are generated and reach the second superlattice where they are detected. The measured frequency spectrum reveals finite size effects, which can be accounted for by a continuum elastic model.

Based on the success of four-telescope imaging with the Michigan Infrared Combiner (MIRC) on the CHARA Array, our Michigan-based group will now upgrade our system to combine all six CHARA telescope simultaneously. In order to make this observationally efficient, we have had to improve a number of subsystems and commission new ones, including the new CHAMP fringe tracker, the introduction of photometric channels, the upgrading of the realtime operating systems, and the obvious hardware and software upgrades of the control system and the data pipeline. Here we will discuss the advantages of six-telescope operation, outline our upgrade plans and discuss our current progress.

We report results of an investigation of electric field induced heating at low temperature in GaN 3-dimensional electron gas films grown on sapphire substrates. The excess noise of the electron gas in a patterned GaN film, while the substrate is held at low temperature, is used to determine the electron temperature. We calculate the rate of power dissipation and compare our results with a calculation of acoustic deformation potential scattering processes in GaN. We discuss the existence of a thermal boundary resistance between the GaN film and the sapphire substrate.

InAs quantum wells (QWs) have been used as weak links in many recent studies of novel superconductor-normal metal–superconductor junctions. The degree of coupling between the superconducting electrodes depends sensitively on both the superconductor/InAs interface and the QW material in the weak link, factors that are difficult to separate in dc transport studies. Here we used midinfrared spectroscopy to investigate the superconductor/semiconductor contact region. The remnant intersubband absorption we observe in Nb-clad InAs shows that the superconductor/InAs interface produced some confinement of electrons in the InAs. This confinement is, however, consistent with phase coherent transport in the InAs. We find no evidence for charge transfer from the superconductor to the InAs on cooling below the critical temperature of Nb.

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