996 research outputs found
Transmission electron microscopy investigation of segregation and critical floating-layer content of indium for island formation in InGaAs
We have investigated InGaAs layers grown by molecular-beam epitaxy on
GaAs(001) by transmission electron microscopy (TEM) and photoluminescence
spectroscopy. InGaAs layers with In-concentrations of 16, 25 and 28 % and
respective thicknesses of 20, 22 and 23 monolayers were deposited at 535 C. The
parameters were chosen to grow layers slightly above and below the transition
between the two- and three-dimensional growth mode. In-concentration profiles
were obtained from high-resolution TEM images by composition evaluation by
lattice fringe analysis. The measured profiles can be well described applying
the segregation model of Muraki et al. [Appl. Phys. Lett. 61 (1992) 557].
Calculated photoluminescence peak positions on the basis of the measured
concentration profiles are in good agreement with the experimental ones.
Evaluating experimental In-concentration profiles it is found that the
transition from the two-dimensional to the three-dimensional growth mode occurs
if the indium content in the In-floating layer exceeds 1.1+/-0.2 monolayers.
The measured exponential decrease of the In-concentration within the cap layer
on top of the islands reveals that the In-floating layer is not consumed during
island formation. The segregation efficiency above the islands is increased
compared to the quantum wells which is explained tentatively by
strain-dependent lattice-site selection of In. In addition, In0.25Ga0.75As
quantum wells were grown at different temperatures between 500 oC and 550 oC.
The evaluation of concentration profiles shows that the segregation efficiency
increases from R=0.65 to R=0.83.Comment: 16 pages, 6 figures, 1 table, sbmitted in Phys. Rev.
Unusual features in the nonlinear microwave surface impedance of Y-Ba-Cu-O thin films
Striking features have been found in the nonlinear microwave (8 GHz) surface
impedance of high-quality YBaCuO thin films with comparable
low power characteristics [ and ]. The surface resistance is found to increase,
decrease, or remain independent of the microwave field (up to 60 mT)
at different temperatures and for different samples. However, the surface
reactance always follows the same functional form. Mechanisms which may
be responsible for the observed variations in and are briefly
discussed.Comment: 4 pages, 4 figure
The Serums Tool-Chain:Ensuring Security and Privacy of Medical Data in Smart Patient-Centric Healthcare Systems
Digital technology is permeating all aspects of human society and life. This leads to humans becoming highly dependent on digital devices, including upon digital: assistance, intelligence, and decisions. A major concern of this digital dependence is the lack of human oversight or intervention in many of the ways humans use this technology. This dependence and reliance on digital technology raises concerns in how humans trust such systems, and how to ensure digital technology behaves appropriately. This works considers recent developments and projects that combine digital technology and artificial intelligence with human society. The focus is on critical scenarios where failure of digital technology can lead to significant harm or even death. We explore how to build trust for users of digital technology in such scenarios and considering many different challenges for digital technology. The approaches applied and proposed here address user trust along many dimensions and aim to build collaborative and empowering use of digital technologies in critical aspects of human society
Depinning transition in type-II superconductors
The surface impedance Z(f) of conventional isotropic materials has been
carefully measured for frequencies f ranging from 1 kHz to 3 MHz, allowing a
detailed investigation of the depinning transition. Our results exhibit the
irrelevance of classical ideas to the dynamics of vortex pinning. We propose a
new picture, where the linear ac response is entirely governed by disordered
boundary conditions of a rough surface, whereas in the bulk vortices respond
freely. The universal law for Z(f) thus predicted is in remarkable agreement
with experiment, and tentatively applies to microwave data in YBaCuO films.Comment: 4 pages, 4 figures, 14 reference
Materializing digital collecting: an extended view of digital materiality
If digital objects are abundant and ubiquitous, why should consumers pay for, much less collect them? The qualities of digital code present numerous challenges for collecting, yet digital collecting can and does occur. We explore the role of companies in constructing digital consumption objects that encourage and support collecting behaviours, identifying material configuration techniques that materialise these objects as elusive and authentic. Such techniques, we argue, may facilitate those pleasures of collecting otherwise absent in the digital realm. We extend theories of collecting by highlighting the role of objects and the companies that construct them in materialising digital collecting. More broadly, we extend theories of digital materiality by highlighting processes of digital material configuration that occur in the pre-objectification phase of materialisation, acknowledging the role of marketing and design in shaping the qualities exhibited by digital consumption objects and consequently related consumption behaviours and experiences
Family memories in the home: contrasting physical and digital mementos
We carried out fieldwork to characterise and compare physical and digital mementos in the home. Physical mementos are highly valued, heterogeneous and support different types of recollection. Contrary to expectations, we found physical mementos are not purely representational, and can involve appropriating common objects and more idiosyncratic forms. In contrast, digital mementos were initially perceived as less valuable, although participants later reconsidered this. Digital mementos were somewhat limited in function and expression, largely involving representational photos and videos, and infrequently accessed. We explain these digital limitations and conclude with design guidelines for digital mementos, including better techniques for accessing and integrating these into everyday life, allowing them to acquire the symbolic associations and lasting value that characterise their physical counterparts
Cis interactions in the Irf8 locus regulate stage-dependent enhancer activation
Individual elements within a superenhancer can act in a cooperative or temporal manner, but the underlying mechanisms remain obscure. We recently identified a
Electrodynamics of a Clean Vortex Lattice
We report on a microscopic evaluation of electrodynamic response for the
vortex lattice state of a model s-wave superconductor. Our calculation accounts
self-consistently for both quasiparticle and order parameter response and
establishes the collective nature of linear response in the clean limit. We
discuss the effects of homogeneous and inhomogeneous pinning on the optical
conductivity and the penetration depth, and comment on the relationship between
macroscopic and local penetration depths. We find unexpected relationships
between pinning arrangements and conductivity due to the strongly non-local
response.Comment: 4 pages, 2 figure
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