1,458 research outputs found
The Atacama Cosmology Telescope: Lensing of CMB Temperature and Polarization Derived from Cosmic Infrared Background Cross-Correlation
We present a measurement of the gravitational lensing of the Cosmic Microwave Background (CMB) temperature and polarization fields obtained by cross-correlating the reconstructed convergence signal from the first season of Atacama Cosmology Telescope Polarimeter data at 146 GHz with Cosmic Infrared Background (CIB) fluctuations measured using the Planck satellite. Using an effective overlap area of 92.7 square degrees, we detect gravitational lensing of the CMB polarization by large-scale structure at a statistical significance of 4.5 sigma. Combining both CMB temperature and polarization data gives a lensing detection at 9.1 sigma significance. A B-mode polarization lensing signal is present with a significance of 3.2 sigma. We also present the first measurement of CMB lensing-CIB correlation at small scales corresponding to l \u3e 2000. Null tests and systematic checks show that our results are not significantly biased by astrophysical or instrumental systematic effects, including Galactic dust. Fitting our measurements to the best-fit lensing-CIB cross-power spectrum measured in Planck data, scaled by an amplitude A, gives A = 1.02(-0.08)(+0.12)(stat.) +/- 0.06(syst.), consistent with the Planck results
Determining the Hubble Constant without the Sound Horizon: A Constraint on from Galaxy Surveys, CMB Lensing and Supernovae
Many theoretical resolutions to the so-called "Hubble tension" rely on
modifying the sound horizon at recombination, , and thus the acoustic
scale used as a standard ruler in the cosmic microwave background (CMB) and
large scale structure (LSS) datasets. As shown in a number of recent works,
these observables can also be used to compute -independent constraints on
by making use of the horizon scale at matter-radiation equality, , which has different sensitivity to high redshift physics than . In
this work, we present the tightest -based constraints on the
expansion rate from current data, finding at 68 CL
from a combination of BOSS galaxy power spectra, Planck CMB lensing, and the
newly released Pantheon+ supernova constraints, as well as physical priors on
the baryon density, neutrino mass, and spectral index (in
units). The BOSS and Planck
measurements have different degeneracy directions, leading to the improved
combined constraints, with a bound of
() from BOSS (Planck) alone. The results show some
dependence on the neutrino mass bounds, with the constraint broadening to if we instead impose a weak prior on from
terrestrial experiments rather than assuming , or
shifting to if the neutrino mass is fixed to its minimal
value. Even without any dependence on the sound horizon, our results are in
tension with those obtained from the Cepheid-calibrated
distance ladder, providing evidence against new physics models that vary
by changing acoustic physics or the expansion history immediately prior to
recombination.Comment: 11 pages, 3 figures, submitted to Phys. Rev.
Stability of Projection Methods for Incompressible Flows Using High Order Pressure-Velocity Pairs of Same Degree: Continuous and Discontinuous Galerkin Formulations
Abstract. This paper presents limits for stability of projection type schemes when using high order pressure-velocity pairs of same degree. Two high order h/p varia-tional methods encompassing continuous and discontinuous Galerkin formulations are used to explain previously observed lower limits on the time step for projection type schemes to be stable [18], when h- or p-refinement strategies are considered. In addition, the analysis included in this work shows that these stability limits do not depend only on the time step but on the product of the latter and the kinematic vis-cosity, which is of particular importance in the study of high Reynolds number flows. We show that high order methods prove advantageous in stabilising the simulations when small time steps and low kinematic viscosities are used. Drawing upon this analysis, we demonstrate how the effects of this instability can be reduced in the discontinuous scheme by introducing a stabilisation term into the global system. Finally, we show that these lower limits are compatible with Courant-Friedrichs-Lewy (CFL) type restrictions, given that a sufficiently high polynomial or
Making the user more efficient: Design for sustainable behaviour
User behaviour is a significant determinant of a product’s environmental impact; while engineering advances permit increased efficiency of product operation, the user’s decisions and habits ultimately have a major effect on the energy or other resources used by the product. There is thus a need to change users’ behaviour. A range of design techniques developed in diverse contexts suggest opportunities for engineers, designers and other stakeholders working in the field of sustainable innovation to affect users’ behaviour at the point of interaction with the product or system, in effect ‘making the user more efficient’. Approaches to changing users’ behaviour from a number of fields are reviewed and discussed, including: strategic design of affordances and behaviour-shaping constraints to control or affect energyor other resource-using interactions; the use of different kinds of feedback and persuasive technology techniques to encourage or guide users to reduce their environmental impact; and context-based systems which use feedback to adjust their behaviour to run at optimum efficiency and reduce the opportunity for user-affected inefficiency. Example implementations in the sustainable engineering and ecodesign field are suggested and discussed
Transient growth analysis of the flow past a circular cylinder
We apply direct transient growth analysis in complex geometries to investigate its role in the primary and secondary bifurcation/transition process of the flow past a circular cylinder. The methodology is based on the singular value decomposition of the Navier-Stokes evolution operator linearized about a two-dimensional steady or periodic state which leads to the optimal growth modes. Linearly stable and unstable steady flow at Re=45 and 50 is considered first, where the analysis demonstrates that strong two-dimensional transient growth is observed with energy amplifications of order of 10(3) at U-infinity tau/D approximate to 30. Transient growth at Re=50 promotes the linear instability which ultimately saturates into the well known von-Kaacutermaacuten street. Subsequently we consider the transient growth upon the time-periodic base state corresponding to the von-Kaacutermaacuten street at Re=200 and 300. Depending upon the spanwise wavenumber the flow at these Reynolds numbers are linearly unstable due to the so-called mode A and B instabilities. Once again energy amplifications of order of 10(3) are observed over a time interval of tau/T=2, where T is the time period of the base flow shedding. In all cases the maximum energy of the optimal initial conditions are located within a diameter of the cylinder in contrast to the spatial distribution of the unstable eigenmodes which extend far into the downstream wake. It is therefore reasonable to consider the analysis as presenting an accelerator to the existing modal mechanism. The rapid amplification of the optimal growth modes highlights their importance in the transition process for flow past circular cylinder, particularly when comparing with experimental results where these types of convective instability mechanisms are likely to be activated. The spatial localization, close to the cylinder, of the optimal initial condition may be significant when considering strategies to promote or control shedding
Spin-based quantum information processing with semiconductor quantum dots and cavity QED
A quantum information processing scheme is proposed with semiconductor
quantum dots located in a high-Q single mode QED cavity. The spin degrees of
freedom of one excess conduction electron of the quantum dots are employed as
qubits. Excitonic states, which can be produced ultrafastly with optical
operation, are used as auxiliary states in the realization of quantum gates. We
show how properly tailored ultrafast laser pulses and Pauli-blocking effects,
can be used to achieve a universal encoded quantum computing.Comment: RevTex, 2 figure
Detecting and quantifying methane emissions from oil and gas production: algorithm development with ground-truth calibration based on Sentinel-2 satellite imagery
Sentinel-2 satellite imagery has been shown by studies to be
capable of detecting and quantifying methane emissions from oil and gas
production. However, current methods lack performance calibration with
ground-truth testing. This study developed a multi-band–multi-pass–multi-comparison-date methane retrieval algorithm that enhances Sentinel-2 sensitivity to methane plumes. The method was calibrated
using data from a large-scale controlled-release test in Ehrenberg, Arizona,
in fall 2021, with three algorithm parameters tuned based on the true
emission rates. Tuned parameters are the pixel-level concentration upper-bound threshold during extreme value removal, the number of comparison
dates, and the pixel-level methane concentration percentage threshold when
determining the spatial extent of a plume. We found that a low value of the
upper-bound threshold during extreme value removal can result in false
negatives. A high number of comparison dates helps enhance the algorithm
sensitivity to the plumes in the target date, but values in excess of
12 d are neither necessary nor computationally efficient. A high percentage
threshold when determining the spatial extent of a plume helps enhance the
quantification accuracy, but it may harm the yes/no detection accuracy. We
found that there is a trade-off between quantification accuracy and
detection accuracy. In a scenario with the highest quantification accuracy,
we achieved the lowest quantification error and had zero false-positive
detections; however, the algorithm missed three true plumes, which reduced the
yes/no detection accuracy. In contrast, all of the true plumes were
detected in the highest detection accuracy scenario, but the emission rate
quantification had higher errors. We illustrated a two-step method that
updates the emission rate estimates in an interim step, which improves
quantification accuracy while keeping high yes/no detection accuracy. We
also validated the algorithm's ability to detect true positives and true
negatives in two application studies.</p
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