574 research outputs found
Thermoelectric efficiency at maximum power in a quantum dot
We identify the operational conditions for maximum power of a
nanothermoelectric engine consisting of a single quantum level embedded between
two leads at different temperatures and chemical potentials. The corresponding
thermodynamic efficiency agrees with the Curzon-Ahlborn expression up to
quadratic terms in the gradients, supporting the thesis of universality beyond
linear response.Comment: 4 pages, 3 figure
Zone-plate focusing of Bose-Einstein condensates for atom optics and erasable high-speed lithography of quantum electronic components
We show that Fresnel zone plates, fabricated in a solid surface, can sharply
focus atomic Bose-Einstein condensates that quantum reflect from the surface or
pass through the etched holes. The focusing process compresses the condensate
by orders of magnitude despite inter-atomic repulsion. Crucially, the focusing
dynamics are insensitive to quantum fluctuations of the atom cloud and largely
preserve the condensates' coherence, suggesting applications in passive
atom-optical elements, for example zone plate lenses that focus atomic matter
waves and light at the same point to strengthen their interaction. We explore
transmission zone-plate focusing of alkali atoms as a route to erasable and
scalable lithography of quantum electronic components in two-dimensional
electron gases embedded in semiconductor nanostructures. To do this, we
calculate the density profile of a two-dimensional electron gas immediately
below a patch of alkali atoms deposited on the surface of the nanostructure by
zone-plate focusing. Our results reveal that surface-induced polarization of
only a few thousand adsorbed atoms can locally deplete the electron gas. We
show that, as a result, the focused deposition of alkali atoms by existing zone
plates can create quantum electronic components on the 50 nm scale, comparable
to that attainable by ion beam implantation but with minimal damage to either
the nanostructure or electron gas.Comment: 13 pages, 7 figure
The use of Twitter by people with young-onset dementia: A qualitative analysis of narratives and identity formation in the age of social media
A diagnosis of dementia in mid-life can be challenging, causing losses or changes in a person’s identity. Narrative provides a means of reconstructing identity and can be communicated on social media. There has been initial evidence on the value of Twitter for people with dementia, but researchers have not yet directly engaged with users’ perspectives. We employed a narrative model of identity to examine why people with dementia use Twitter and what challenges they face. Interviews were conducted with 11 younger people with dementia and analysed thematically. Participants used Twitter to counter a loss of identity through community membership and by regaining a sense of purpose. They sought to redefine dementia identities by challenging stigma and campaigning for social change. The character limit of tweets facilitated narrative through which participants preserved their identities. These findings suggest that Twitter could be an important source of post-diagnostic support for people with young-onset dementia. However, there are some risks as Twitter was sometimes a hostile environment for individuals who did not present in a ‘typical’ manner, or faced technical difficulties because of their symptoms. In the future, platform developers could work with people with dementia to make Twitter more accessible for this group
Electrochemical pore formation on InP in alkaline solutions
The surface properties of InP electrodes were examined following anodization in (NH4)2S and KOH electrolytes. In both solutions, the observation of current peaks in the cyclic voltammetric curves was attributed to selective etching of the substrate and a film formation process. AFM images of samples anodized in the sulfide solution, revealed surface pitting and TEM micrographs revealed the porous nature of the film formed on top of the pitted substrate. After anodization in the KOH electrolyte, TEM images revealed that a porous layer extending 500 nm into the substrate had been formed. Analysis of the composition of the anodic products indicates the presence of In2S3 in films grown in (NH4)2S and an In2O3 phase within the porous network formed in KOH
In-situ characterization of the Hamamatsu R5912-HQE photomultiplier tubes used in the DEAP-3600 experiment
The Hamamatsu R5912-HQE photomultiplier-tube (PMT) is a novel high-quantum
efficiency PMT. It is currently used in the DEAP-3600 dark matter detector and
is of significant interest for future dark matter and neutrino experiments
where high signal yields are needed.
We report on the methods developed for in-situ characterization and
monitoring of DEAP's 255 R5912-HQE PMTs. This includes a detailed discussion of
typical measured single-photoelectron charge distributions, correlated noise
(afterpulsing), dark noise, double, and late pulsing characteristics. The
characterization is performed during the detector commissioning phase using
laser light injected through a light diffusing sphere and during normal
detector operation using LED light injected through optical fibres
Angular power spectrum of the FastICA CMB component from BEAST data
We present the angular power spectrum of the CMB component extracted with
FastICA from the Background Emission Anisotropy Scanning Telescope (BEAST)
data. BEAST is a 2.2 meter off-axis telescope with a focal plane comprising 8
elements at Q (38-45 GHz) and Ka (26-36 GHz) bands. It operates from the UC
White Mountain Research Station at an altitude of 3800 meters. The BEAST CMB
angular power spectrum has been already calculated by O'Dwyer et.al. using only
the Q band data. With two input channels FastICA returns two possible
independent components. We found that one of these two has an unphysical
spectral behaviour while the other is a reasonable CMB component. After a
detailed calibration procedure based on Monte-Carlo (MC) simulations we
extracted the angular power spectrum for the identified CMB component and found
a very good agreement with the already published BEAST CMB angular power
spectrum and with the WMAP data.Comment: 9 pages, 5 figures. Accepted for publication in MNRA
Radon backgrounds in the DEAP-1 liquid-argon-based Dark Matter detector
The DEAP-1 \SI{7}{kg} single phase liquid argon scintillation detector was
operated underground at SNOLAB in order to test the techniques and measure the
backgrounds inherent to single phase detection, in support of the
\mbox{DEAP-3600} Dark Matter detector. Backgrounds in DEAP are controlled
through material selection, construction techniques, pulse shape discrimination
and event reconstruction. This report details the analysis of background events
observed in three iterations of the DEAP-1 detector, and the measures taken to
reduce them.
The Rn decay rate in the liquid argon was measured to be between 16
and \SI{26}{\micro\becquerel\per\kilogram}. We found that the background
spectrum near the region of interest for Dark Matter detection in the DEAP-1
detector can be described considering events from three sources: radon
daughters decaying on the surface of the active volume, the expected rate of
electromagnetic events misidentified as nuclear recoils due to inefficiencies
in the pulse shape discrimination, and leakage of events from outside the
fiducial volume due to imperfect position reconstruction. These backgrounds
statistically account for all observed events, and they will be strongly
reduced in the DEAP-3600 detector due to its higher light yield and simpler
geometry
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