2,978 research outputs found
Interface optical phonons in spheroidal dots: Raman selection rules
The contribution of interface phonons to the first order Raman scattering in
nanocrystals with non spherical geometry is analyzed. Interface optical phonons
in the spheroidal geometry are discussed and the corresponding Frohlich-like
electron-phonon interaction is reported in the framework of the dielectric
continuum approach. It is shown that the interface phonon modes are strongly
dependent on the nanocrystal geometry, particularly on the ellipsoid's
semi-axis ratio. The new Raman selection rules have revealed that solely
interface phonon modes with even angular momentum are allowed to contribute to
the first order phonon-assisted scattering of light. On this basis we are able
to give an explanation for the observed low frequency shoulders present in the
Raman cross-section of several II-VI semiconductor nanostructures.Comment: 8 pages, 2 figure
The night-sky at the Calar Alto Observatory II: The sky at the near infrared
We present here the characterization of the night sky-brightness at the
near-infrared, the telescope seeing, and the fraction of useful time at the
Calar Alto observatory. For this study we have collected a large dataset
comprising 7311 near-infrared images taken regularly along the last four years
for the ALHAMBRA survey (J, H and Ks-bands), together with a more reduced
dataset of additional near-infrared images taken for the current study. In
addition we collected the information derived by the meteorological station at
the observatory during the last 10 years, together with the results from the
cloud sensor for the last ~2 years. We analyze the dependency of the
near-infrared night sky-brightness with the airmass and the seasons, studying
its origins and proposing a zenithal correction. A strong correlation is found
between the night sky-brightness in the Ks-band and the air temperature, with a
gradient of ~ -0.08 mag per 1 C degree. The typical (darkest) night
sky-brightness in the J, H and Ks-band are 15.95 mag (16.95 mag), 13.99 mag
(14.98 mag) and 12.39 mag (13.55 mag), respectively. These values show that
Calar Alto is as dark in the near-infrared as most of the other astronomical
astronomical sites in the world that we could compare with. Only Mauna Kea is
clearly darker in the Ks-band. The typical telescope seeing at the 3.5m is
~1.0" when converted to the V-band, being only slightly larger than the
atmospheric seeing measured at the same time by the seeing monitor, ~0.9".
Finally we estimate the fraction of useful time based on the relative humidity,
gust wind speed and presence of clouds. This fraction, ~72%, is very similar to
the one derived in Paper I, based on the fraction of time when the extinction
monitor is working.Comment: 15 pages, 6 figures, accepted to be published in PAS
A Tentative Modeling Study of the Effect of Wall Reactions on Oxidation Phenomena
This paper gives details of a tentative modeling study that investigates the
inhibiting effect of internal reactor walls treated with acid..
Engineering molecular chains in carbon nanotubes
A range of mono- and bis-functionalised fullerenes have been synthesised and inserted into single-walled carbon nanotubes. The effect of the size and shape of the functional groups of the fullerenes on the resultant 1D arrays formed within the nanotubes was investigated by high resolution transmission electron microscopy and X-ray diffraction. The addition of non-planar, sterically bulky chains to the fullerene cage results in highly ordered 1D structures in which the fullerenes are evenly spaced along the internal nanotube cavity. Theoretical calculations reveal that the functional groups interact with neighbouring fullerene cages to space the fullerenes evenly within the confines of the nanotube. The addition of two functional groups to opposite sides of the fullerene cages results in a further increase in the separation of the fullerene cages within the nanotubes at the cost of lower nanotube filling rates.This work was financially supported by FWF project I83-N20 (ESF IMPrESS), the Royal Society, the European Research Council (ERC), "Fundacao para a Ciencia ea Tecnologia" through the program Ciencia 2008, the project SeARCH (Services and Advanced Research Computing with HTC/HPC clusters) and Nottingham Nanoscience and Nanotechnology Centre (NNNC)
A fast and long-lived outflow from the supermassive black hole in NGC 5548
Supermassive black holes in the nuclei of active galaxies expel large amounts
of matter through powerful winds of ionized gas. The archetypal active galaxy
NGC 5548 has been studied for decades, and high-resolution X-ray and UV
observations have previously shown a persistent ionized outflow. An observing
campaign in 2013 with six space observatories shows the nucleus to be obscured
by a long-lasting, clumpy stream of ionized gas never seen before. It blocks
90% of the soft X-ray emission and causes simultaneous deep, broad UV
absorption troughs. The outflow velocities of this gas are up to five times
faster than those in the persistent outflow, and at a distance of only a few
light days from the nucleus, it may likely originate from the accretion disk.Comment: 25 pages, 8 figures. This is the author's version of the work. It is
posted here by permission of the AAAS for personal use, not for
redistribution. The definitive version was published in Science,
electronically available at Science Express (June 19, 2014). For a brief
video explaining the key results of this paper, please visit
http://www.issibern.ch/teams/ngc5548/?page_id=2
Multi-phonon Raman scattering in semiconductor nanocrystals: importance of non-adiabatic transitions
Multi-phonon Raman scattering in semiconductor nanocrystals is treated taking
into account both adiabatic and non-adiabatic phonon-assisted optical
transitions. Because phonons of various symmetries are involved in scattering
processes, there is a considerable enhancement of intensities of multi-phonon
peaks in nanocrystal Raman spectra. Cases of strong and weak band mixing are
considered in detail. In the first case, fundamental scattering takes place via
internal electron-hole states and is participated by s- and d-phonons, while in
the second case, when the intensity of the one-phonon Raman peak is strongly
influenced by the interaction of an electron and of a hole with interface
imperfections (e. g., with trapped charge), p-phonons are most active.
Calculations of Raman scattering spectra for CdSe and PbS nanocrystals give a
good quantitative agreement with recent experimental results.Comment: 16 pages, 2 figures, E-mail addresses: [email protected],
[email protected], [email protected], accepted for publication in
Physical Review
The Role of Local Therapy in Multi-focal Epithelioid Haemangioendothelioma
Contains fulltext :
208930.pdf (publisher's version ) (Open Access)BACKGROUND/AIM: Epithelioid haemangioendothelioma (EHE) is a rare tumor with a wide spectrum of clinical behavior. There is no consensus on the role of local therapy in symptomatic, multi-focal disease. PATIENTS AND METHODS: A retrospective review of patients presenting to the Royal Marsden Hospital between January 2000 and December 2017 was conducted. RESULTS: Fifty-three patients with EHE were identified, of which 18 patients (34.0%) received local therapy, and 11 patients (20.8%) underwent active surveillance. A variety of local treatment modalities were used with few toxicities, and local recurrence was managed with other local treatments or systemic therapy. Distal disease progression was infrequent (n=4, 7.5%). Patients who developed pleural effusion (n=5, 9.4%) had poor outcome irrespective of treatment. CONCLUSION: Local therapy has a role in a selected patient group managed in a multidisciplinary setting, including patients with indolent disease, and patients with a solitary area of progression/symptomatic disease
The acquisition of Sign Language: The impact of phonetic complexity on phonology
Research into the effect of phonetic complexity on phonological acquisition has a long history in spoken languages. This paper considers the effect of phonetics on phonological development in a signed language. We report on an experiment in which nonword-repetition methodology was adapted so as to examine in a systematic way how phonetic complexity in two phonological parameters of signed languages — handshape and movement — affects the perception and articulation of signs. Ninety-one Deaf children aged 3–11 acquiring British Sign Language (BSL) and 46 hearing nonsigners aged 6–11 repeated a set of 40 nonsense signs. For Deaf children, repetition accuracy improved with age, correlated with wider BSL abilities, and was lowest for signs that were phonetically complex. Repetition accuracy was correlated with fine motor skills for the youngest children. Despite their lower repetition accuracy, the hearing group were similarly affected by phonetic complexity, suggesting that common visual and motoric factors are at play when processing linguistic information in the visuo-gestural modality
The Occupational Wellbeing of People Experiencing Homelessness
This paper reports findings of a study that utilised an occupational perspective to explore how wellbeing was achieved and sustained by the occupations of people experiencing homelessness in Australia. Thirty three in-depth qualitative interviews were conducted with homeless individuals in a regional city in Australia. Data from the interviews were thematically analysed to understand the relationship between wellbeing, as defined by the individual, and the occupations engaged in by people experiencing homelessness. The findings are reported here as three collective narratives that illustrate the experiences of diverse groups within the homelessness population explored in this study. The study demonstrates how occupations go beyond the individual experience and choice; to explore the social and cultural value of occupations as a means to wellbeing. The findings are discussed in relation to three key themes that emerged from the study: survival, self-identity and social connectedness. These three interconnected concepts complement the existing occupational science literature, and offer a preliminary framework for understanding and improving wellbeing for disadvantaged and marginalised people where occupations are restricted by societal forces. The findings support the urgent need to redirect services to support occupational opportunities that are socially and culturally valued and enhance survival, self-identity and connectedness of homeless people
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