429 research outputs found
Besov priors for Bayesian inverse problems
We consider the inverse problem of estimating a function from noisy,
possibly nonlinear, observations. We adopt a Bayesian approach to the problem.
This approach has a long history for inversion, dating back to 1970, and has,
over the last decade, gained importance as a practical tool. However most of
the existing theory has been developed for Gaussian prior measures. Recently
Lassas, Saksman and Siltanen (Inv. Prob. Imag. 2009) showed how to construct
Besov prior measures, based on wavelet expansions with random coefficients, and
used these prior measures to study linear inverse problems. In this paper we
build on this development of Besov priors to include the case of nonlinear
measurements. In doing so a key technical tool, established here, is a
Fernique-like theorem for Besov measures. This theorem enables us to identify
appropriate conditions on the forward solution operator which, when matched to
properties of the prior Besov measure, imply the well-definedness and
well-posedness of the posterior measure. We then consider the application of
these results to the inverse problem of finding the diffusion coefficient of an
elliptic partial differential equation, given noisy measurements of its
solution.Comment: 18 page
Tunable inductive coupler for high fidelity gates between fluxonium qubits
The fluxonium qubit is a promising candidate for quantum computation due to
its long coherence times and large anharmonicity. We present a tunable coupler
that realizes strong inductive coupling between two heavy-fluxonium qubits,
each with MHz frequencies and GHz anharmonicities. The coupler
enables the qubits to have a large tuning range of coupling
strengths ( to MHz). The coupling strength is kHz
across the entire coupler bias range, and Hz at the coupler off-position.
These qualities lead to fast, high-fidelity single- and two-qubit gates. By
driving at the difference frequency of the two qubits, we realize a
gate in ns with fidelity , and by driving
at the sum frequency of the two qubits, we achieve a
gate in ns with fidelity . This latter gate is only 5 qubit
Larmor periods in length. We run cross-entropy benchmarking for over
consecutive hours and measure stable gate fidelities, with
drift () and
drift .Comment: 16 pages, 14 figure
Experimental advances with the QICK (Quantum Instrumentation Control Kit) for superconducting quantum hardware
The QICK is a standalone open source qubit controller that was first
introduced in 2022. In this follow-up work, we present recent experimental use
cases that the QICK uniquely enabled for superconducting qubit systems. These
include multiplexed signal generation and readout, mixer-free readout,
pre-distorted fast flux pulses, and phase-coherent pulses for parametric
operations, including high-fidelity parametric entangling gates. We explain in
detail how the QICK was used to enable these experiments
Environmental changes and violent conflict
This letter reviews the scientific literature on whether and how environmental changes affect the risk of violent conflict. The available evidence from qualitative case studies indicates that environmental stress can contribute to violent conflict in some specific cases. Results from quantitative large-N studies, however, strongly suggest that we should be careful in drawing general conclusions. Those large-N studies that we regard as the most sophisticated ones obtain results that are not robust to alternative model specifications and, thus, have been debated. This suggests that environmental changes may, under specific circumstances, increase the risk of violent conflict, but not necessarily in a systematic way and unconditionally. Hence there is, to date, no scientific consensus on the impact of environmental changes on violent conflict. This letter also highlights the most important challenges for further research on the subject. One of the key issues is that the effects of environmental changes on violent conflict are likely to be contingent on a set of economic and political conditions that determine adaptation capacity. In the authors' view, the most important indirect effects are likely to lead from environmental changes via economic performance and migration to violent conflict. © 2012 IOP Publishing Ltd
NEOWISE Observations of Near-Earth Objects: Preliminary Results
With the NEOWISE portion of the \emph{Wide-field Infrared Survey Explorer}
(WISE) project, we have carried out a highly uniform survey of the near-Earth
object (NEO) population at thermal infrared wavelengths ranging from 3 to 22
m, allowing us to refine estimates of their numbers, sizes, and albedos.
The NEOWISE survey detected NEOs the same way whether they were previously
known or not, subject to the availability of ground-based follow-up
observations, resulting in the discovery of more than 130 new NEOs. The
survey's uniformity in sensitivity, observing cadence, and image quality have
permitted extrapolation of the 428 near-Earth asteroids (NEAs) detected by
NEOWISE during the fully cryogenic portion of the WISE mission to the larger
population. We find that there are 98119 NEAs larger than 1 km and
20,5003000 NEAs larger than 100 m. We show that the Spaceguard goal of
detecting 90% of all 1 km NEAs has been met, and that the cumulative size
distribution is best represented by a broken power law with a slope of
1.320.14 below 1.5 km. This power law slope produces 1,900
NEAs with 140 m. Although previous studies predict another break in the
cumulative size distribution below 50-100 m, resulting in an increase in
the number of NEOs in this size range and smaller, we did not detect enough
objects to comment on this increase. The overall number for the NEA population
between 100-1000 m are lower than previous estimates. The numbers of near-Earth
comets will be the subject of future work.Comment: Accepted to Ap
Can a Code of Ethics Improve Manager Behavior and Investor Confidence? An Experimental Study
Policy makers and corporations have recently emphasized a code of ethics as an effective aspect of corporate governance. The corporate governance literature in accounting, however, provides little empirical or theoretical support for this emphasis. We address this gap between public policy and the literature by studying the effectiveness of a code of ethics in an experimental setting. Using Bicchieri\u27s (2006) model of social norm activation, we predict that a code of ethics will improve manager return behavior and investor confidence to the extent that it activates social norms that control opportunistic behavior. Further, we predict that adding a certification choice whereby the manager can publicly certify that he will adhere to the code will enhance the potential for the code of ethics to activate such norms. We find that a code of ethics only improves manager return behavior and investor confidence when the code incorporates a public certification choice by the manager. When the code is present but there is no certification choice, manager return behavior does not improve and investor confidence erodes over time because of increased expectations that are not met by managers. An analysis of individual return decisions and exit questionnaire responses supports the activation of social norms as the underlying mechanism behind our results
Response to letter on use of functional imaging by 11C-metomidate PET for primary aldosteronism subtyping
Non peer reviewe
Pharmacogenetics of Bleeding and Thromboembolic Events in Direct Oral Anticoagulant Users
Publisher Copyright: © 2021 The Authors. Clinical Pharmacology & Therapeutics published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and TherapeuticsThis study aimed to analyze associations between genetic variants and the occurrence of clinical outcomes in dabigatran, apixaban, and rivaroxaban users. This was a retrospective real-world study linking genotype data of three Finnish biobanks with national register data on drug dispensations and healthcare encounters. We investigated several single-nucleotide variants (SNVs) in the ABCG2, ABCB1, CES1, and CYP3A5 genes potentially associated with bleeding or thromboembolic events in direct oral anticoagulant (DOAC) users based on earlier research. We used Cox regression models to compare the incidence of clinical outcomes between carriers and noncarriers of the SNVs or haplotypes. In total, 1,806 patients on apixaban, dabigatran, or rivaroxaban were studied. The ABCB1 c.3435C>T (p.Ile1145=, rs1045642) SNV (hazard ratio (HR) 0.42, 95% confidence interval (CI), 0.18-0.98, P = 0.044) and 1236T-2677T-3435T (rs1128503-rs2032582-rs1045642) haplotype (HR 0.44, 95% CI, 0.20-0.95, P = 0.036) were associated with a reduced risk for thromboembolic outcomes, and the 1236C-2677G-3435C (HR 2.55, 95% CI, 1.03-6.36, P = 0.044) and 1236T-2677G-3435C (HR 5.88, 95% CI, 2.35-14.72, P A (rs4148738) SNV associated with a lower risk for bleeding events (HR 0.37, 95% CI, 0.16-0.89, P = 0.025) in apixaban users. ABCB1 variants are potential factors affecting thromboembolic events in rivaroxaban users and bleeding events in apixaban users. Studies with larger numbers of patients are warranted for comprehensive assessment of the pharmacogenetic associations of DOACs and their relevance for clinical practice.Peer reviewe
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