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This is a copy of the slides presented at the meeting but not formally written up for the volume.
Reflection high-energy electron diffraction (RHEED) is one of the most robust and widespread techniques used for in-situ monitoring during molecular beam epitaxy (MBE) growth. Thus, all MBE systems have an electron gun allowing additional electron-beam stimulated in-situ characterizations. At WVU we are developing two such techniques, spectral analysis of cathodoluminescence (CL) in wide bandgap semiconductors and reflection high-energy electron diffraction-total reflection angle x-ray spectroscopy (RHEED-TRAXS) for in-situ composition monitoring and control.A pressing issue remaining for epitaxial growth is real-time compositional control to a high level of accuracy. For many materials, such as multi-element nitrides and oxides with unity sticking coefficients, it would be extremely beneficial to monitor the composition to a fraction of a monolayer. This technique needs to be both element-specific and surface-sensitive. RHEED-TRAXS is a leading contender as such a technique. The electron beam from a RHEED gun impinges on the sample at a small angle of incidence approximately equal to the critical angle for x-ray reflection. This geometry ensures that the measurement is extremely surface sensitive. This technique can be used to obtain both structural information, via RHEED, and chemical information, via x-ray detection. We are currently developing a compact RHEED-TRAXS using a state-of-the-art Si P-intrinsic-N (PIN) photodiode technology. We have used this system to investigate Ga and In coverage during the growth of GaN, and have observed Ga bi-layer evolution during growth, Mg destabilization of the Ga wetting layer, and significant In surface segregation. We are also investigating the in-situ, real-time composition measurements in complex oxide systems such as YMnO3 with promising initial results.In-situ cathodoluminescence (CL) occurring during RHEED is a strong candidate to determine the growth temperature and alloy composition for wide bandgap semiconductors. CL is easily detected up to and beyond typical growth temperatures for GaN and InGaN, accurately and reproducibly determining sample temperature during growth. Room CL measurement at room temperature can also be used as a means to check the quality of the substrate by comparing intensities of the GaN band edge energy peak and defect peaks. We have performed a detailed study of the factors influencing high temperature CL, and find the reproducibility of CL data and ability for fast CL scanning provide strong advantages for use in the growth of GaN films. CL could also be observed during growth using a ccd camera. This could be used to see temperature inhomogenaities, and potentially to map alloy composition fluctuations. Using tunable narrow bandpass optical filters, we can obtain a spatial/spectral map of sample CL. We will present CL images of samples at differing temperatures.This work was supported by the AFOSR MURI F49620-03-1-0330 and by ONR Grant N00014-02-1-0974.
In a series of interviews with Irina Nikolska late in his life, Witold Lutosławski claimed a distance from the political events of the Stalinist era, stating: ‘The very thought that many people believed me to have collaborated with the regime is bitterly painful to me … I've never been disposed to make a compromise.’ How do we make sense of this statement, given that around 1950 Lutosławski composed a number of political mass songs, two ideology-infused cantatas, and several folk-based works that fit comfortably within the concept of socialist realism? This article will explore Lutosławski's entanglement with socialist realism and the political structures of that time, and will present a picture rather at odds from the popular and scholarly understanding of the composer that exists, one or two notable challenges excepted, both in Poland and elsewhere. Lutosławski seemed supportive of at least aspects of the program of Polish communists in the years around 1950, but then grew increasingly frustrated and disillusioned. I argue that his initial cooperation with many communist goals was representative for Polish composers as a whole, and not surprising given both the consensus about the postwar rebuilding of Polish culture and also the appreciation for significant party support for new compositions and for expanded performance opportunities. The Lutosławski described in this article is not a transcendent musical genius who somehow remained untouched by the realities of Stalinist Poland, but is rather an engaged participant in contemporary professional and artistic activities and debates, just like the overwhelming majority of his composer colleagues. The article will grapple with this complex, understudied, and formative phase in Lutosławski's development as a composer, and situate his compositional and political activities within the larger context of Stalinist Poland.
Lutosławski's involvement with socialist realism and Stalinist politics can usefully be divided into two periods, with 1952 as a turning point. Like nearly all Polish composers in the late 1940s and early 1950s, Lutosławski was broadly receptive to the communist project and, as this essay will demonstrate, his compositional choices reflect that. Beginning in 1947, communists and their allies turned to the cultural world and began to assert increased control over artistic production.
Reflection high-energy electron diffraction total-reflection-angle x-ray spectroscopy (RHEED-TRAXS) uses high-energy electrons from RHEED to excite x-ray fluorescence. Monitoring characteristic x-rays of selected elements thus allows study of surface coverage of materials. In this study, surface coverage of Ga and In during growth of GaN and InGaN was probed using this technique. Evolution of the surface layer of Ga on GaN during growth and deposition of Ga on static GaN at room temperature were studied. RHEED-TRAXS measurements were performed during growth of InGaN by measuring the ratio of the In Lα to Ga Kα intensity. A significant surface coverage of In was observed at all temperatures investigated regardless of actual In incorporation.
To determine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization among older residents of care homes in Leeds, United Kingdom, and to identify resident and care home risk factors for carriage.
We conducted a cross-sectional prevalence survey of 715 residents from 39 care homes. All participants were tested for nasal colonization with S. aureus, including MRSA. A short questionnaire was completed about each participant and each care home. A multivariable model was used to determine which risk factors were independently associated with MRSA colonization.
Care homes for older residents in Leeds, United Kingdom.
All residents in participating homes who were able to give informed consent.
A total of 159 of 715 residents tested positive for MRSA, for a prevalence of 22% (95% confidence interval, 18%—27%) The resultant multivariate model showed that residence in a home with a low ratio of nurses to beds, residence in a care home in a deprived area, male sex, presence of an invasive device, and a hospitalization duration of more than 10 days during the previous 2 years were independently associated with MRSA colonization.
This study found a large reservoir of MRSA within the care home population. Control strategies need to be coordinated between care homes and hospitals. Increasing the ratio of nurses to beds, reducing the duration of hospitalization, and improving the management of invasive devices could help reduce the prevalence of MRSA colonization. Further research is required to ascertain the potential health benefits of reducing the rate of MRSA colonization among care home residents.
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