Optical frequency comb generation from a monolithic microresonator

Optical frequency combs provide equidistant frequency markers in the infrared, visible and ultra-violet and can link an unknown optical frequency to a radio or microwave frequency reference. Since their inception frequency combs have triggered major advances in optical frequency metrology and precision measurements and in applications such as broadband laser-based gas sensing8 and molecular fingerprinting. Early work generated frequency combs by intra-cavity phase modulation while to date frequency combs are generated utilizing the comb-like mode structure of mode-locked lasers, whose repetition rate and carrier envelope phase can be stabilized. Here, we report an entirely novel approach in which equally spaced frequency markers are generated from a continuous wave (CW) pump laser of a known frequency interacting with the modes of a monolithic high-Q microresonator13 via the Kerr nonlinearity. The intrinsically broadband nature of parametric gain enables the generation of discrete comb modes over a 500 nm wide span (ca. 70 THz) around 1550 nm without relying on any external spectral broadening. Optical-heterodyne-based measurements reveal that cascaded parametric interactions give rise to an optical frequency comb, overcoming passive cavity dispersion. The uniformity of the mode spacing has been verified to within a relative experimental precision of 7.3*10(-18).Comment: Manuscript and Supplementary Informatio

Phase transformation in Si from semiconducting diamond to metallic beta-Sn phase in QMC and DFT under hydrostatic and anisotropic stress

Silicon undergoes a phase transition from the semiconducting diamond phase to the metallic beta-Sn phase under pressure. We use quantum Monte Carlo calculations to predict the transformation pressure and compare the results to density functional calculations employing the LDA, PBE, PW91, WC, AM05, PBEsol and HSE06 exchange-correlation functionals. Diffusion Monte Carlo predicts a transition pressure of 14.0 +- 1.0 GPa slightly above the experimentally observed transition pressure range of 11.3 to 12.6 GPa. The HSE06 hybrid functional predicts a transition pressure of 12.4 GPa in excellent agreement with experiments. Exchange-correlation functionals using the local-density approximation and generalized-gradient approximations result in transition pressures ranging from 3.5 to 10.0 GPa, well below the experimental values. The transition pressure is sensitive to stress anisotropy. Anisotropy in the stress along any of the cubic axes of the diamond phase of silicon lowers the equilibrium transition pressure and may explain the discrepancy between the various experimental values as well as the small overestimate of the quantum Monte Carlo transition pressure

The Closest Look at 1H0707-495: X-ray Reverberation Lags with 1.3 Ms of Data

Reverberation lags in AGN were first discovered in the NLS1 galaxy, 1H0707-495. We present a follow-up analysis using 1.3 Ms of data, which allows for the closest ever look at the reverberation signature of this remarkable source. We confirm previous findings of a hard lag of ~100 seconds at frequencies v ~ [0.5 - 4] e-4 Hz, and a soft lag of ~30 seconds at higher frequencies, v ~ [0.6 - 3] e-3 Hz. These two frequency domains clearly show different energy dependences in their lag spectra. We also find evidence for a signature from the broad Fe K line in the high frequency lag spectrum. We use Monte Carlo simulations to show how the lag and coherence measurements respond to the addition of Poisson noise and to dilution by other components. With our better understanding of these effects on the lag, we show that the lag-energy spectra can be modelled with a scenario in which low frequency hard lags are produced by a compact corona responding to accretion rate fluctuations propagating through an optically thick accretion disc, and the high frequency soft lags are produced by short light-travel delay associated with reflection of coronal power-law photons off the disc.Comment: 11 pages, 10 figures. Accepted for publication in MNRA

Cochrane corner: PCSK9 monoclonal antibodies for the primary and secondary prevention of cardiovascular disease

Introduction: Drug therapies targeted at the reduction of low-density lipoproteincholesterol (LDL-C) are mainstream in the treatment of cardiovascular disease (CVD) and particularly for the prevention of coronary heart disease. In patients who do not have a sufficient response to, or who do not tolerate traditional LDL-C-lowering therapies such as statins or ezetimibe, monoclonal antibodies (mAbs) against PCSK9 (PCSK9 inhibitors) may provide an alternative treatment. Non-mAb-based PCSK9 inhibitors such as inclisiran are also emerging but currently lack robust outcome data1 and their effects are not considered in the current review. In this synopsis, we summarise findings from a recent update of a Cochrane systematic review on the efficacy and safety of PCSK9 inhibitors.2 This article focuses on the effects on outcomes (CVD and total mortality), safety, and the quality of the evidence in studies of mAb PCSK9 inhibitors alirocumab and evolocumab. Most of the available studies compared PCSK9 mAb treatment against placebo (against a background of usual care including statin and or ezetimibe), with a smaller group of studies evaluating the effects of PCSK9 mAb directly against statins and/or ezetimibe (none of the trials compared PCSK9 exclusively against statin treatment). Methods: The following databases were systematically searched for suitable randomised controlled trials (RCTs): Cochrane Central Register of Controlled Trials, MEDLINE, Embase, Web of Science, ClinicalTrials.gov and the International Clinical Trials Registry Platform. Parallel-group and factorial RCTs with at least 24 weeks of follow-up were eligible; due to discontinuation of bococizumab and RG7652, studies examining these mAbs were excluded in this update. Summary of findings The 24 selected randomised trials (60 997 participants, box 1) predominantly included high-risk patients, for example, by enrolling patients with non-optimal LDL-C concentration despite treatment with statins or ezetimibe, or with a history of CVD. The study sample included 1879 who had familial hypercholesterolaemia (FH) (22% of the alirocumab participants and 38% of the evolocumab participants who provided information on FH status), and 18 908 (31%) with a diagnosis of type 2 diabetes mellitus (T2DM) at baseline (32% in alirocumab and 34% evolocumab trials; out of participants with reported T2DM status). Of the included patients, 4590 had no history of CVD (10% of the alirocumab patients and 7% of the evolocumab participants). Alirocumab was evaluated in 18 trials and evolocumab in 6 trials. Comparisons were made against placebo in 18 trials, ezetimibe and/or statins in 6 trials. Tables 1 and 2 display the key results of the meta-analysis for both PCSK9 inhibitors compared with placebo and with statins and/or ezetimibe, respectively

Resonant X-Ray Scattering on the M-Edge Spectra from Triple-k Structure Phase in U_{0.75}Np_{0.25}O_{2} and UO_{2}

We derive an expression for the scattering amplitude of resonant x-ray scattering under the assumption that the Hamiltonian describing the intermediate state preserves spherical symmetry. On the basis of this expression, we demonstrate that the energy profile of the RXS spectra expected near U and Np M_4 edges from the triple-k antiferromagnetic ordering phase in UO_{2} and U_{0.75}Np_{0.25}O_{2} agree well with those from the experiments. We demonstrate that the spectra in the \sigma-\sigma' and \sigma-\pi' channels exhibit quadrupole and dipole natures, respectively.Comment: 3 pages, 3 figures, to be published in J. Phys. Soc. Jpn. Supp

Interactive Execution Monitoring of Agent Teams

There is an increasing need for automated support for humans monitoring the activity of distributed teams of cooperating agents, both human and machine. We characterize the domain-independent challenges posed by this problem, and describe how properties of domains influence the challenges and their solutions. We will concentrate on dynamic, data-rich domains where humans are ultimately responsible for team behavior. Thus, the automated aid should interactively support effective and timely decision making by the human. We present a domain-independent categorization of the types of alerts a plan-based monitoring system might issue to a user, where each type generally requires different monitoring techniques. We describe a monitoring framework for integrating many domain-specific and task-specific monitoring techniques and then using the concept of value of an alert to avoid operator overload. We use this framework to describe an execution monitoring approach we have used to implement Execution Assistants (EAs) in two different dynamic, data-rich, real-world domains to assist a human in monitoring team behavior. One domain (Army small unit operations) has hundreds of mobile, geographically distributed agents, a combination of humans, robots, and vehicles. The other domain (teams of unmanned ground and air vehicles) has a handful of cooperating robots. Both domains involve unpredictable adversaries in the vicinity. Our approach customizes monitoring behavior for each specific task, plan, and situation, as well as for user preferences. Our EAs alert the human controller when reported events threaten plan execution or physically threaten team members. Alerts were generated in a timely manner without inundating the user with too many alerts (less than 10 percent of alerts are unwanted, as judged by domain experts)