2,136 research outputs found
Microlensing Characterization of Wide-Separation Planets
With their excellent photometric precision and dramatic increase in
monitoring frequency, future microlensing survey experiments are expected to be
sensitive to very short time-scale, isolated events caused by free-floating and
wide-separation planets with mass as low as a few lunar masses. We estimate the
probability of measuring the Einstein radius \theta_E for bound and
free-floating planets. We carry out detailed simulations of the planetary
events expected in next-generation surveys and estimate the resulting
uncertainty in \theta_E for these events. We show that, for main-sequence
sources and Jupiter-mass planets, the caustic structure of wide-separation
planets with projected separations of < 20 AU substantially increases the
probability of measuring the dimensionless source size and thus determining
\theta_E compared to the case of unbound planets. In this limit where the
source is much smaller than the caustic, the effective cross-section to measure
\theta_E to 10% is ~25% larger than the full width of the caustic. Measurement
of the lens parallax is possible for low-mass planetary events by combined
observations from the ground and a satellite located in an L2 orbit; this would
complete the mass measurements for such wide-separation planets. Finally,
short-duration events caused by bound planets can be routinely distinguished
from those caused by free-floating planets for planet-star separations < 20 AU
from either the deviations due to the planetary caustic or (more often) the
low-amplitude bump from the magnification due to the parent star.Comment: 10 pages including 7 figures. ApJ, in pres
Pb-free Semiconductor Ferroelectrics: A Theoretical Study of Pd-substituted Ba(Ti\u3csub\u3e1-\u3cem\u3ex\u3c/em\u3e\u3c/sub\u3eCe\u3csub\u3e\u3cem\u3ex\u3c/em\u3e\u3c/sub\u3e)O\u3csub\u3e3\u3c/sub\u3e Solid Solutions
We use first-principles density-functional-theory calculations to investigate the ground state structures of Ba(Ti1âxCex)O3 solid solutions containing Pd. Previous studies have shown that the properties of BaTiO3, a Pb-free ferroelectric ABO3 perovskite, can be tailored via B-site substitution. In the present study, we substitute Ce for Ti to increase the overall volume of the perovskite, to then accommodate an O-vacancy-stabilized Pd substitution. Using the LDA+U method, we predict that these proposed materials will display a decreased band gap compared to BaTiO3 while maintaining polarization. These features, combined with their environmentally friendly characteristics make these materials promising candidates for use as semiconducting ferroelectrics in solar-energy conversion devices
Pb-free Ferroelectrics Investigated with Density Functional Theory: SnAl\u3csub\u3e½\u3c/sub\u3eNb\u3csub\u3e½\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e Perovskites
Interest in Pb-free ferroelectrics has intensified as the search for less toxic Pb replacements continues. Since Sn is isoelectronic with Pb, it has generated great interest. Most of this effort has focused on SnTiO3. Even though it shows impressive ferroelectricity in calculations, synthesis has proved elusive.We therefore use density-functional theory (DFT) to investigate B-site alternatives that involve smaller size to promote perovskite phase stability. In this paper, Sn(Al½Nb½)O3 (SAN) is investigated. We demonstrate that SAN is likely to be synthesizable, will be ferroelectric, and perhaps a good piezoelectric material as well. We discuss how cation displacements and their interactions affect the polarization of the solid solution.We also explore the electronic properties of the SAN solid solution and correlate them to the structural findings
Systematic Analysis of 22 Microlensing Parallax Candidates
We attempt to identify all microlensing parallax events for which the
parallax fit improves \Delta\chi^2 > 100 relative to a standard microlensing
model. We outline a procedure to identify three types of discrete degeneracies
(including a new one that we dub the ``ecliptic degeneracy'') and find many new
degenerate solutions in 16 previously published and 6 unpublished events. Only
four events have one unique solution and the other 18 events have a total of 44
solutions. Our sample includes three previously identified black-hole (BH)
candidates. We consider the newly discovered degenerate solutions and determine
the relative likelihood that each of these is a BH. We find the lens of event
MACHO-99-BLG-22 is a strong BH candidate (78%), event MACHO-96-BLG-5 is a
marginal BH candidate (37%), and MACHO-98-BLG-6 is a weak BH candidate (2.2%).
The lens of event OGLE-2003-BLG-84 may be a Jupiter-mass free-floating planet
candidate based on a weak 3 sigma detection of finite-source effects. We find
that event MACHO-179-A is a brown dwarf candidate within ~100 pc of the Sun,
mostly due to its very small projected Einstein radius, \tilde r_E = 0.23+-0.05
AU. As expected, these microlensing parallax events are biased toward lenses
that are heavier and closer than average. These events were examined for
xallarap (or binary-source motion), which can mimic parallax. We find that 23%
of these events are strongly affected by xallarap.Comment: 69 Pages, 10 Figures, 24 Tables, Submitted to Ap
Intrinsic Optical Transition Energies in Carbon Nanotubes
Intrinsic optical transition energies for isolated and individual single wall
carbon nanotubes grown over trenches are measured using tunable resonant Raman
scattering. Previously measured E22_S optical transitions from nanotubes in
surfactants are blue shifted 70-90 meV with respect to our measurements of
nanotubes in air. This large shift in the exciton energy is attributed to a
larger change of the exciton binding energy than the band-gap renormalization
as the surrounding dielectric constant increases.Comment: Due to a mistake, a different paper was submitted as "revised v2".
This is a re-submission of the origional version in order to correct the
mistak
Defects and disorder in metal organic frameworks.
The wide-ranging properties of metal organic frameworks (MOFs) rely in many cases on the presence of defects within their structures and the disorder that is inevitably associated with such defects. In the present work we review several aspects of defects in MOFs, ranging from simple substitutional defects at metal cation or ligand positions, to correlated defects on a larger length scale and the extreme case of disorder associated with amorphous MOFs. We consider both porous and dense MOFs, and focus particularly on the way in which defects and disorder can be used to tune physical properties such as gas adsorption, catalysis, photoluminescence, and electronic and mechanical properties.The authors would like to thank Ras Al Khaimah Center for Advanced Materials (AKC, TDB), Trinity Hall (TDB), and the ERC (ALG, Grant 279705).This is the author accepted manuscript. The final version is available from RSC via http://dx.doi.org/10.1039/C5DT04392
Videoconference Fatigue Exploring Changes in Fatigue after Videoconference Meetings during COVID-19
In response to the COVID-19 global health pandemic, many employees transitioned to remote work, which included remote meetings. With this sudden shift, workers and the media began discussing videoconference fatigue, a potentially new phenomenon of feeling tired and exhausted attributed to a videoconference. In the present study, we examine the nature of videoconference fatigue, when this phenomenon occurs, and what videoconference characteristics are associated with fatigue using a mixed methods approach. Thematic analysis of qualitative responses indicates that videoconference fatigue exists, often in near temporal proximity to the videoconference, and is affected by various videoconference characteristics. Quantitative data was collected each hour during five workdays from 55 employees who were working remotely because of the COVID-19 pandemic. Latent growth modeling results suggest that videoconferences at different times of the day are related to deviations in employee fatigue beyond what is expected based on typical fatigue trajectories. Results from multilevel modeling of 279 videoconference meetings indicate that turning off the microphone and having higher feelings of group belongingness are related to lower post-videoconference fatigue. Additional analyses suggest that higher levels of group belongingness are the most consistent protective factor against videoconference fatigue. Such findings have immediate practical implications for workers and organizations as they continue to navigate the still relatively new terrain of remote work
HLA class I-redirected anti-tumour CD4+T-cells require a higher TCR binding affinity for optimal activity than CD8+T-cells
CD4+ T helper cells are a valuable component of the immune response towards cancer. Unfortunately, natural tumour-specific CD4+ T-cells occur in low frequency, express relatively low affinity T-cell receptors (TCRs) and show poor reactivity towards cognate antigen. In addition, the lack of human leukocyte antigen (HLA) class II expression on most cancers dictates that these cells are often unable to respond to tumour cells directly. These deficiencies can be overcome by transducing primary CD4+ T-cells with tumour-specific HLA class I-restricted TCRs prior to adoptive transfer. The lack of help from the coreceptor CD8 glycoprotein in CD4+ cells might result in these cells requiring a different optimal TCR binding affinity. Here we compared primary CD4+ and CD8+ T-cells expressing wildtype and a range of affinity-enhanced TCRs specific for the HLA A*0201-restricted NY-ESO-1- and gp100 tumour antigens. Our major findings are: (i) redirected primary CD4+ T-cells expressing TCRs of sufficiently high affinity exhibit a wide range of effector functions, including cytotoxicity, in response to cognate peptide; and, (ii) optimal TCR binding affinity is higher in CD4+ T-cells than CD8+ T-cells. These results indicate that the CD4+ T-cell component of current adoptive therapies using TCRs optimised for CD8+ T-cells is below par and that there is room for substantial improvement. This article is protected by copyright. All rights reserved
Photometric Confirmation of MACHO Large Magellanic Cloud Microlensing Events
We present previously unpublished photometry of three Large Magellanic Cloud
(LMC) microlensing events and show that the new photometry confirms the
microlensing interpretation of these events. These events were discovered by
the MACHO Project alert system and were also recovered by the analysis of the
5.7 year MACHO data set. This new photometry provides a substantial increase in
the signal-to-noise ratio over the previously published photometry and in all
three cases, the gravitational microlensing interpretation of these events is
strengthened. The new data consist of MACHO-Global Microlensing Alert Network
(GMAN) follow-up images from the CTIO 0.9 telescope plus difference imaging
photometry of the original MACHO data from the 1.3m "Great Melbourne" telescope
at Mt. Stromlo. We also combine microlensing light curve fitting with
photometry from high resolution HST images of the source stars to provide
further confirmation of these events and to show that the microlensing
interpretation of event MACHO-LMC-23 is questionable. Finally, we compare our
results with the analysis of Belokurov, Evans & Le Du who have attempted to
classify candidate microlensing events with a neural network method, and we
find that their results are contradicted by the new data and more powerful
light curve fitting analysis for each of the four events considered in this
paper. The failure of the Belokurov, Evans & Le Du method is likely to be due
to their use of a set of insensitive statistics to feed their neural networks.Comment: 29 pages with 8 included postscript figures, accepted by the
Astrophysical Journa
High speed quantum gates with cavity quantum electrodynamics
Cavity quantum electrodynamic schemes for quantum gates are amongst the
earliest quantum computing proposals. Despite continued progress, and the
dramatic recent demonstration of photon blockade, there are still issues with
optimal coupling and gate operation involving high-quality cavities. Here we
show dynamic control techniques that allow scalable cavity-QED based quantum
gates, that use the full bandwidth of the cavities. When applied to quantum
gates, these techniques allow an order of magnitude increase in operating
speed, and two orders of magnitude reduction in cavity Q, over passive
cavity-QED architectures. Our methods exploit Stark shift based Q-switching,
and are ideally suited to solid-state integrated optical approaches to quantum
computing.Comment: 4 pages, 3 figures, minor revision
- âŚ