593 research outputs found
Observing the earliest moments of supernovae using strong gravitational lenses
We determine the viability of exploiting lensing time delays to observe
strongly gravitationally lensed supernovae (gLSNe) from first light. Assuming a
plausible discovery strategy, the Legacy Survey of Space and Time (LSST) and
the Zwicky Transient Facility (ZTF) will discover 110 and 1
systems per year before the supernova (SN) explosion in the final image
respectively. Systems will be identified days before the
final explosion. We then explore the possibility of performing early-time
observations for Type IIP and Type Ia SNe in LSST-discovered systems. Using a
simulated Type IIP explosion, we predict that the shock breakout in one
trailing image per year will peak at 24.1 mag ( 23.3) in
the -band (), however evolving over a timescale of 30 minutes.
Using an analytic model of Type Ia companion interaction, we find that in the
-band we should observe at least one shock cooling emission event per year
that peaks at 26.3 mag ( 29.6) assuming all Type Ia gLSNe
have a 1 M red giant (main sequence) companion. We perform Bayesian
analysis to investigate how well deep observations with 1 hour exposures on the
European Extremely Large Telescope would discriminate between Type Ia
progenitor populations. We find that if all Type Ia SNe evolved from the
double-degenerate channel, then observations of the lack of early blue flux in
10 (50) trailing images would rule out more than 27% (19%) of the population
having 1 M main sequence companions at 95% confidence.Comment: 17 pages, 15 figures (including appendices). Accepted by MNRAS 3rd
May 202
Boom and Bust Carbon-Nitrogen Dynamics during Reforestation
Legacies of historical land use strongly shape contemporary ecosystem dynamics. In old-field secondary forests, tree growth embodies a legacy of soil changes affected by previous cultivation. Three patterns of biomass accumulation during reforestation have been hypothesized previously, including monotonic to steady state, non-monotonic with a single peak then decay to steady state, and multiple oscillations around the steady state. In this paper, the conditions leading to the emergence of these patterns is analyzed. Using observations and models, we demonstrate that divergent reforestation patterns can be explained by contrasting time-scales in ecosystem carbon-nitrogen cycles that are influenced by land use legacies. Model analyses characterize non-monotonic plant-soil trajectories as either single peaks or multiple oscillations during an initial transient phase controlled by soil carbon-nitrogen conditions at the time of planting. Oscillations in plant and soil pools appear in modeled systems with rapid tree growth and low initial soil nitrogen, which stimulate nitrogen competition between trees and decomposers and lead the forest into a state of acute nitrogen deficiency. High initial soil nitrogen dampens oscillations, but enhances the magnitude of the tree biomass peak. These model results are supported by data derived from the long-running Calhoun Long-Term Soil-Ecosystem Experiment from 1957 to 2007. Observed carbon and nitrogen pools reveal distinct tree growth and decay phases, coincident with soil nitrogen depletion and partial re-accumulation. Further, contemporary tree biomass loss decreases with the legacy soil C:N ratio. These results support the idea that non-monotonic reforestation trajectories may result from initial transients in the plant-soil system affected by initial conditions derived from soil changes associated with land-use history
Few-body spin couplings and their implications for universal quantum computation
Electron spins in semiconductor quantum dots are promising candidates for the
experimental realization of solid-state qubits. We analyze the dynamics of a
system of three qubits arranged in a linear geometry and a system of four
qubits arranged in a square geometry. Calculations are performed for several
quantum dot confining potentials. In the three-qubit case, three-body effects
are identified that have an important quantitative influence upon quantum
computation. In the four-qubit case, the full Hamiltonian is found to include
both three-body and four-body interactions that significantly influence the
dynamics in physically relevant parameter regimes. We consider the implications
of these results for the encoded universality paradigm applied to the
four-electron qubit code; in particular, we consider what is required to
circumvent the four-body effects in an encoded system (four spins per encoded
qubit) by the appropriate tuning of experimental parameters.Comment: 1st version: 33 pages, 25 figures. Described at APS March Meeting in
2004 (P36.010) and 2005 (B17.00009). Most figures made uglier here to reduce
file size. 2nd version: 19 pages, 9 figures. Much mathematical detail chopped
away after hearing from journal referee; a few typos correcte
Crown ether helical peptides are preferentially inserted in lipid bilayers as a transmembrane ion channels
Oriented circular dichroism was used to study the alignment crown ether-modified peptides. The influence of different N- and C-functionalities was assessed using at variable peptide:lipid ratios from 1:20 to 1:200. Neither the functionalities nor the concentration had any major effect on the orientation. The alignment of the 21-mer peptides was also examined with lipid membranes of different bilayer thickness. The use of synchrotron radiation as light source allowed the study of peptide:lipid molar ratios from 1:20 to 1:1000. For all conditions studied, the peptides were found to be predominantly incorporated as a transmembrane helix into the membrane, especially at low peptide concentration, but started to aggregate on the membrane surface at higher peptide:lipid ratios. The structural information on the preferred trans-bilayer alignment of the crown ether functional groups explains their ion conductivity and is useful for the further development of membrane-active nanochemotherapeutics
The Impact of Microlensing on the Standardisation of Strongly Lensed Type Ia Supernovae
We investigate the effect of microlensing on the standardisation of strongly
lensed Type Ia supernovae (GLSNe Ia). We present predictions for the amount of
scatter induced by microlensing across a range of plausible strong lens
macromodels. We find that lensed images in regions of low convergence, shear
and stellar density are standardisable, where the microlensing scatter is <
0.15 magnitudes, comparable to the intrinsic dispersion of for a typical SN Ia.
These standardisable configurations correspond to asymmetric lenses with an
image located far outside the Einstein radius of the lens. Symmetric and small
Einstein radius lenses (< 0.5 arcsec) are not standardisable. We apply our
model to the recently discovered GLSN Ia iPTF16geu and find that the large
discrepancy between the observed flux and the macromodel predictions from More
et al. (2017) cannot be explained by microlensing alone. Using the mock GLSNe
Ia catalogue of Goldstein et al. (2017), we predict that ~ 22% of GLSNe Ia
discovered by LSST will be standardisable, with a median Einstein radius of 0.9
arcseconds and a median time-delay of 41 days. By breaking the mass-sheet
degeneracy the full LSST GLSNe Ia sample will be able to detect systematics in
H0 at the 0.5% level.Comment: 11 pages, 8 Figures. Accepted by MNRAS May 17 201
Exchange Interaction Between Three and Four Coupled Quantum Dots: Theory and Applications to Quantum Computing
Several prominent proposals have suggested that spins of localized electrons
could serve as quantum computer qubits. The exchange interaction has been
invoked as a means of implementing two qubit gates. In this paper, we analyze
the strength and form of the exchange interaction under relevant conditions. We
find that, when several spins are engaged in mutual interactions, the
quantitative strengths or even qualitative forms of the interactions can
change. It is shown that the changes can be dramatic within a Heitler-London
model. Hund-Mulliken calculations are also presented, and support the
qualititative conclusions from the Heitler-London model. The effects need to be
considered in spin-based quantum computer designs, either as a source of gate
error to be overcome or a new interaction to be exploited.Comment: 16 pages, 16 figures. v3: Added Hund-Mulliken calculations in 3-dots
case. A few small corrections. This version submitted to PR
Self-Calibration Technique for 3-point Intrinsic Alignment Correlations in Weak Lensing Surveys
The intrinsic alignment (IA) of galaxies has been shown to be a significant
barrier to precision cosmic shear measurements. (Zhang, 2010, ApJ, 720, 1090)
proposed a self-calibration technique for the power spectrum to calculate the
induced gravitational shear-galaxy intrinsic ellipticity correlation (GI) in
weak lensing surveys with photo-z measurements which is expected to reduce the
IA contamination by at least a factor of 10 for currently proposed surveys. We
confirm this using an independent analysis and propose an expansion to the
self-calibration technique for the bispectrum in order to calculate the
dominant IA gravitational shear-gravitational shear-intrinsic ellipticity
correlation (GGI) contamination. We first establish an estimator to extract the
galaxy density-density-intrinsic ellipticity (ggI) correlation from the galaxy
ellipticity-density-density measurement for a photo-z galaxy sample. We then
develop a relation between the GGI and ggI bispectra, which allows for the
estimation and removal of the GGI correlation from the cosmic shear signal. We
explore the performance of these two methods, compare to other possible sources
of error, and show that the GGI self-calibration technique can potentially
reduce the IA contamination by up to a factor of 5-10 for all but a few bin
choices, thus reducing the contamination to the percent level. The
self-calibration is less accurate for adjacent bins, but still allows for a
factor of three reduction in the IA contamination. The self-calibration thus
promises to be an efficient technique to isolate both the 2-point and 3-point
intrinsic alignment signals from weak lensing measurements.Comment: 22 pages, 5 figures, matches version published in MNRAS. Published
online December 5, 201
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