68 research outputs found
Visual discomfort from flash afterimages of riloid patterns
Op-art-based stimuli have been shown to be uncomfortable, possibly due to a combination of fixational eye movements (microsaccades) and excessive cortical responses. Efforts have been made to measure illusory phenomena arising from these stimuli in the absence of microsaccades, but there has been no attempt thus far to decouple the effects of the cortical response from the effect of fixational eye movements. This study uses flash afterimages to stablise the image on the retina and thus reduce the systematic effect of eye movements, in order to investigate the role of the brain in discomfort from op-art-based stimuli. There was a relationship between spatial frequency and the magnitude of the P300 response, showing a similar pattern to that of discomfort judgements, which suggests there might be a role of discomfort and excessive neural responses independently from the effects of microsaccades
On the limits to mobility in InAs quantum wells with nearly lattice-matched barriers
The growth and the density dependence of the low temperature mobility of a
series of two-dimensional electron systems confined to un-intentionally doped,
low extended defect density InAs quantum wells with AlGaSb
barriers are reported. The electron mobility limiting scattering mechanisms
were determined by utilizing dual-gated devices to study the dependence of
mobility on carrier density and electric field independently. Analysis of the
possible scattering mechanisms indicate the mobility was limited primarily by
rough interfaces in narrow quantum wells and a combination of alloy disorder
and interface roughness in wide wells at high carrier density within the first
occupied electronic sub-band. At low carrier density the functional dependence
of the mobility on carrier density provided evidence of coulombic scattering
from charged defects. A gate-tuned electron mobility exceeding 750,000
cm/Vs was achieved at a sample temperature of 2 K.Comment: 23 pages, 7 figures, 1 tabl
Quantized Majorana conductance
Majorana zero-modes hold great promise for topological quantum computing.
Tunnelling spectroscopy in electrical transport is the primary tool to identify
the presence of Majorana zero-modes, for instance as a zero-bias peak (ZBP) in
differential-conductance. The Majorana ZBP-height is predicted to be quantized
at the universal conductance value of 2e2/h at zero temperature. Interestingly,
this quantization is a direct consequence of the famous Majorana symmetry,
'particle equals antiparticle'. The Majorana symmetry protects the quantization
against disorder, interactions, and variations in the tunnel coupling. Previous
experiments, however, have shown ZBPs much smaller than 2e2/h, with a recent
observation of a peak-height close to 2e2/h. Here, we report a quantized
conductance plateau at 2e2/h in the zero-bias conductance measured in InSb
semiconductor nanowires covered with an Al superconducting shell. Our
ZBP-height remains constant despite changing parameters such as the magnetic
field and tunnel coupling, i.e. a quantized conductance plateau. We distinguish
this quantized Majorana peak from possible non-Majorana origins, by
investigating its robustness on electric and magnetic fields as well as its
temperature dependence. The observation of a quantized conductance plateau
strongly supports the existence of non-Abelian Majorana zero-modes in the
system, consequently paving the way for future braiding experiments.Comment: 5 figure
Visual discomfort from flash afterimages of riloid patterns
Op-art-based stimuli have been shown to be uncomfortable, possibly due to a combination of fixational eye movements (microsaccades) and excessive cortical responses. Efforts have been made to measure illusory phenomena arising from these stimuli in the absence of microsaccades, but there has been no attempt thus far to decouple the effects of the cortical response from the effect of fixational eye movements. This study uses flash afterimages to stabilise the image on the retina and thus reduce the systematic effect of eye movements, in order to investigate the role of the brain in discomfort from op-art-based stimuli. There was a relationship between spatial frequency and the magnitude of the P300 response, showing a similar pattern to that of discomfort judgements, which suggests that there might be a role of discomfort and excessive neural responses independently from the effects of microsaccades
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04-ERD-052-Final Report
Generating the sequence of the human genome represents a colossal achievement for science and mankind. The technical use for the human genome project information holds great promise to cure disease, prevent bioterror threats, as well as to learn about human origins. Yet converting the sequence data into biological meaningful information has not been immediately obvious, and we are still in the preliminary stages of understanding how the genome is organized, what are the functional building blocks and how do these sequences mediate complex biological processes. The overarching goal of this program was to develop novel methods and high throughput strategies for determining the functions of ''anonymous'' human genes that are evolutionarily deeply conserved in other vertebrates. We coupled analytical tool development and computational predictions regarding gene function with novel high throughput experimental strategies and tested biological predictions in the laboratory. The tools required for comparative genomic data-mining are fundamentally the same whether they are applied to scientific studies of related microbes or the search for functions of novel human genes. For this reason the tools, conceptual framework and the coupled informatics-experimental biology paradigm we developed in this LDRD has many potential scientific applications relevant to LLNL multidisciplinary research in bio-defense, bioengineering, bionanosciences and microbial and environmental genomics
Selective-area chemical beam epitaxy of in-plane InAs one-dimensional channels grown on InP(001), InP(111)B, and InP(110) surfaces
We report on the selective-area chemical beam epitaxial growth of InAs
in-plane, one-dimensional (1-D) channels using patterned SiO-coated
InP(001), InP(111)B, and InP(110) substrates to establish a scalable platform
for topological superconductor networks. Top-view scanning electron micrographs
show excellent surface selectivity and dependence of major facet planes on the
substrate orientations and ridge directions, and the ratios of the surface
energies of the major facet planes were estimated. Detailed structural
properties and defects in the InAs nanowires (NWs) were characterized by
transmission electron microscopic analysis of cross-sections perpendicular to
the NW ridge direction and along the NW ridge direction. Electrical transport
properties of the InAs NWs were investigated using Hall bars, a field effect
mobility device, a quantum dot, and an Aharonov-Bohm loop device, which reflect
the strong spin-orbit interaction and phase-coherent transport characteristic
in the selectively grown InAs systems. This study demonstrates that
selective-area chemical beam epitaxy is a scalable approach to realize
semiconductor 1-D channel networks with the excellent surface selectivity and
this material system is suitable for quantum transport studies
Transcriptional network orchestrating regional patterning of cortical progenitors
We uncovered a transcription factor (TF) network that regulates cortical regional patterning in radial glial stem cells. Screening the expression of hundreds of TFs in the developing mouse cortex identified 38 TFs that are expressed in gradients in the ventricular zone (VZ). We tested whether their cortical expression was altered in mutant mice with known patterning defects (Emx2, Nr2f1, and Pax6), which enabled us to define a cortical regionalization TF network (CRTFN). To identify genomic programming underlying this network, we performed TF ChIP-seq and chromatin-looping conformation to identify enhancer–gene interactions. To map enhancers involved in regional patterning of cortical progenitors, we performed assays for epigenomic marks and DNA accessibility in VZ cells purified from wild-type and patterning mutant mice. This integrated approach has identified a CRTFN and VZ enhancers involved in cortical regional patterning in the mouse
Identifying factors influencing contraceptive use in Bangladesh: evidence from BDHS 2014 data
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