Direct observation of dynamic surface acoustic wave controlled carrier injection into single quantum posts using phase-resolved optical spectroscopy

A versatile stroboscopic technique based on active phase-locking of a surface acoustic wave to picosecond laser pulses is used to monitor dynamic acoustoelectric effects. Time-integrated multi-channel detection is applied to probe the modulation of the emission of a quantum well for different frequencies of the surface acoustic wave. For quantum posts we resolve dynamically controlled generation of neutral and charged excitons and preferential injection of holes into localized states within the nanostructure.Comment: 10 pages, 4 figure

The Lived Experiences Of Older African Americans Residing In Urban Nursing Homes

As huge numbers of baby boomers reach old age, an increased need for nursing home care in the future is inevitable. Older people face more complex health issues that often lead to debilitation or disability and thus the need for long-term care. The numbers of consumers needing long-term care services will more than triple during the next 30 years. African Americans compose less than 10% of nursing home residents and even at age 84 and older, when the likelihood of nursing home placement is higher, proportionately fewer African Americans live in nursing homes. The underrepresentation of ethnic minorities groups in nursing homes appears to reflect cultural differences in the willingness to institutionalize older persons, greater availability of family supports, or institutionalized discrimination implicit in admission policies against older adults of color. Using a phenomenological approach, this study examines the lived experiences of African American residents in urban area nursing homes. The information gained by interviewing older, African American adults and allowing them to give an oral history of life events leading to living in a nursing home would possibly add to the knowledge base of gerontological studies and services of nursing homes which will provide a richer, thicker insight regarding the older adult lived experiences. Hence, providing a realistic service base that more closely meets the needs of African Americans in a nursing home setting

En sedelärande historia: Om Änglapottans väg från idé till produkt

Rapporten utgar fran en speciell produkt, anglapottan, och analyserar dennas 10-ariga vag fran idé till tillganglig produkt.. Slutsatsen ar att det — utöver ett verkligt behov och en god lösning — behövs antingen en engagerad entreprenör, som agnar sig

Nucleotide exchange and excision technology (NExT) DNA shuffling: a robust method for DNA fragmentation and directed evolution

DNA shuffling is widely used for optimizing complex properties contained within DNA and proteins. Demonstrated here is the amplification of a gene library by PCR using uridine triphosphate (dUTP) as a fragmentation defining exchange nucleotide with thymidine, together with the three other nucleotides. The incorporated uracil bases were excised using uracil-DNA-glycosylase and the DNA backbone subsequently cleaved with piperidine. These end-point reactions required no adjustments. Polyacrylamide urea gels demonstrated adjustable fragmentation size over a wide range. The oligonucleotide pool was reassembled by internal primer extension to full length with a proofreading polymerase to improve yield over Taq. We present a computer program that accurately predicts the fragmentation pattern and yields all possible fragment sequences with their respective likelihood of occurrence, taking the guesswork out of the fragmentation. The technique has been demonstrated by shuffling chloramphenicol acetyltransferase gene libraries. A 33% dUTP PCR resulted in shuffled clones with an average parental fragment size of 86 bases even without employment of a fragment size separation, and revealed a low mutation rate (0.1%). NExT DNA fragmentation is rational, easily executed and reproducible, making it superior to other techniques. Additionally, NExT could feasibly be applied to several other nucleotide analogs

Structure and Stability of Si(114)-(2x1)

We describe a recently discovered stable planar surface of silicon, Si(114). This high-index surface, oriented 19.5 degrees away from (001) toward (111), undergoes a 2x1 reconstruction. We propose a complete model for the reconstructed surface based on scanning tunneling microscopy images and first-principles total-energy calculations. The structure and stability of Si(114)-(2x1) arises from a balance between surface dangling bond reduction and surface stress relief, and provides a key to understanding the morphology of a family of surfaces oriented between (001) and (114).Comment: REVTeX, 4 pages + 3 figures. A preprint with high-resolution figures is available at http://cst-www.nrl.navy.mil/papers/si114.ps . To be published in Phys. Rev. Let

Surface acoustic wave controlled carrier injection into self-assembled quantum dots and quantum posts

We report on recent progress in the acousto-electrical control of self-assembled quantum dot and quantum post using radio frequency surface acoustic waves (SAWs). We show that the occupancy state of these optically active nanostructures can be controlled via the SAW-induced dissociation of photogenerated excitons and the resulting sequential bipolar carrier injection which strongly favors the formation of neutral excitons for quantum posts in contrast to conventional quantum dots. We demonstrate high fidelity preparation of the neutral biexciton which makes this approach suitable for deterministic entangled photon pair generation. The SAW driven acoustic charge conveyance is found to be highly efficient within the wide quantum well surrounding the quantum posts. Finally we present the direct observation of acoustically triggered carrier injection into remotely positioned, individual quantum posts which is required for a low-jitter SAW-triggered single photon source.Comment: Proceedings of ISCS 2011; to appear in physics status solidi (c