Solar Irradiance Variability is Caused by the Magnetic Activity on the Solar Surface

The variation in the radiative output of the Sun, described in terms of solar irradiance, is important to climatology. A common assumption is that solar irradiance variability is driven by its surface magnetism. Verifying this assumption has, however, been hampered by the fact that models of solar irradiance variability based on solar surface magnetism have to be calibrated to observed variability. Making use of realistic three-dimensional magnetohydrodynamic simulations of the solar atmosphere and state-of-the-art solar magnetograms from the Solar Dynamics Observatory, we present a model of total solar irradiance (TSI) that does not require any such calibration. In doing so, the modeled irradiance variability is entirely independent of the observational record. (The absolute level is calibrated to the TSI record from the Total Irradiance Monitor.) The model replicates 95% of the observed variability between April 2010 and July 2016, leaving little scope for alternative drivers of solar irradiance variability at least over the time scales examined (days to years).Comment: Supplementary Materials; https://journals.aps.org/prl/supplemental/10.1103/PhysRevLett.119.091102/supplementary_material_170801.pd

Analysis and Design of Wideband Low Noise Amplifier with Digital Control

The design issues in designing low noise amplifier (LNA) for Software-Defined-Radio (SDR) are reviewed. An inductor-less wideband low noise amplifier aiming at low frequency band (0.2-2GHz) for Software-Defined-Radio is presented. Shunt-shunt LNA with active feedback is used as the first stage which is carefully optimized for low noise and wide band applications. A digitally controlled second stage is employed to provide an additional 12dB gain control. A novel method is proposed to bypass the first stage without degrading input matching. This LNA is fabricated in a standard 0.18 um CMOS technology. The measurement result shows the proposed LNA has a gain range of 6dB-18dB at high gain mode and -12dB-0dB at low gain mode, as well as a –3dB bandwidth of 2GHz. The noise figure (NF) is 3.5-4.5dB in the high gain setting mode. It consumes 20mW from a 1.8V supply

Unsupervised Fiber Bundles Registration using Weighted Measures Geometric Demons

International audienceBrain image registration aims at reducing anatomical variability across subjects to create a common space for group analysis. Multi-modal approaches intend to minimize cortex shape variations along with internal structures, such as fiber bundles. A di ficulty is that it requires a prior identi fication of these structures, which remains a challenging task in the absence of a complete reference atlas. We propose an extension of the log-Geometric Demons for jointly registering images and fi ber bundles without the need of point or ber correspondences. By representing fi ber bundles as Weighted Measures we can register subjects with di fferent numbers of fiber bundles. The ef ficacy of our algorithm is demonstrated by registering simultaneously T1 images and between 37 and 88 ber bundles depending on each of the ten subject used. We compare results with a multi-modal T1 + Fractional Anisotropy (FA) and a tensor-based registration algorithms and obtain superior performance with our approach

Conditions for the freezing phenomena of geometric measure of quantum discord for arbitrary two-qubit X states under non-dissipative dephasing noises

We study the dynamics of geometric measure of quantum discord (GMQD) under the influences of two local phase damping noises. Consider the two qubits initially in arbitrary X-states, we find the necessary and sufficient conditions for which GMQD is unaffected for a finite period. It is further shown that such results also hold for the non-Markovian dephasing process.Comment: 4 pages, 2 figure

Joint T1 and Brain Fiber Log-Demons Registration Using Currents to Model Geometry

International audienceWe present an extension of the diffeomorphic Geometric Demons algorithm which combines the iconic registration with geometric constraints. Our algorithm works in the log-domain space, so that one can efficiently compute the deformation field of the geometry. We represent the shape of objects of interest in the space of currents which is sensitive to both location and geometric structure of objects. Currents provides a distance between geometric structures that can be defined without specifying explicit point-to-point correspondences. We demonstrate this framework by registering simultaneously T1 images and 65 fiber bundles consistently extracted in 12 subjects and compare it against non-linear T1, tensor, and multi-modal T1+ Fractional Anisotropy (FA) registration algorithms. Results show the superiority of the Log-domain Geometric Demons over their purely iconic counterparts

Life history evolution, species differences and phenotypic plasticity in hemiparasitic eyebrights (Euphrasia)

Premise of the study: Species delimitation in parasitic organisms is challenging as traits used in the identification of species are often plastic and vary depending on the host. Here, we use species from a recent radiation of generalist hemiparasitic Euphrasia to investigate trait variation and trait plasticity. We test whether Euphrasia species show reliable trait differences, investigate whether these differences correspond to life history trade-offs between growth and reproduction, and quantify plasticity in response to host species. Methods: We perform common garden experiments to evaluate trait differences between eleven Euphrasia taxa grown on a common host, document phenotypic plasticity when a single Euphrasia species is grown on eight different hosts, and relate our observations to trait differences recorded in the wild. Key results: Euphrasia exhibit variation in life history strategies; some individuals transition rapidly to flower at the expense of early season growth, while others invest in vegetative growth and delay flowering. Life history differences are present between some species, though many related taxa lack clear-cut trait differences. Species differences are further blurred by phenotypic plasticity—many traits are plastic and change with host type or between environments. Conclusions: Phenotypic plasticity in response to host and environment confounds species delimitation in Euphrasia. When grown in a common garden environment it is possible to identify some morphologically distinct taxa, though others represent morphologically similar shallow segregates. Trait differences present between some species and populations demonstrates the rapid evolution of distinct life history strategies in response to local ecological conditions."Manyhosts.csv" contains morphological measurements from one Euphrasia arctica population from North Berwick, Scotland, grown with eight hosts. "Manyspecies.csv" contains morphological measurements of five Euphrasia species and six natural Euphrasia hybrids grown on a single host, Trifolium repens. "Earlylate.csv" contains repeated growth measurements at different times of year, used in correlations of height at end of season. "Wildcommon.csv" contains Euphrasia species grown in the common garden experiment and wild collected plants for trait comparisons.Data collection is detailed in the associated manuscript. Post collection data processing can be viewed at: https://github.com/Euphrasiologist/phenotypic_plasticity_euphrasi

Reentrant Melting of Soliton Lattice Phase in Bilayer Quantum Hall System

At large parallel magnetic field $B_\parallel$, the ground state of bilayer quantum Hall system forms uniform soliton lattice phase. The soliton lattice will melt due to the proliferation of unbound dislocations at certain finite temperature leading to the Kosterlitz-Thouless (KT) melting. We calculate the KT phase boundary by numerically solving the newly developed set of Bethe ansatz equations, which fully take into account the thermal fluctuations of soliton walls. We predict that within certain ranges of $B_\parallel$, the soliton lattice will melt at $T_{\rm KT}$. Interestingly enough, as temperature decreases, it melts at certain temperature lower than $T_{\rm KT}$ exhibiting the reentrant behaviour of the soliton liquid phase.Comment: 11 pages, 2 figure

B meson wave function from the B→γlνB\to\gamma l\nu decay

We show that the leading-power $B$ meson wave function can be extracted reliably from the photon energy spectrum of the $B\to\gamma l\nu$ decay up to $O(1/m_b^2)$ and $O(\alpha_s^2)$ uncertainty, $m_b$ being the $b$ quark mass and $\alpha_s$ the strong coupling constant. The $O(1/m_b)$ corrections from heavy-quark expansion can be absorbed into a redefined leading-power $B$ meson wave function. The two-parton $O(1/m_b)$ corrections cancel exactly, and the three-parton $B$ meson wave functions turn out to contribute at $O(1/m_b^2)$. The constructive long-distance contribution through the $B\to V\to\gamma$ transition, $V$ being a vector meson, almost cancels the destructive $O(\alpha_s)$ radiative correction. Using models of the leading-power $B$ meson wave function available in the literature, we obtain the photon energy spectrum in the perturbative QCD framework, which is then compared with those from other approaches.Comment: 11 pages, 5 figures with minor correction

COVID-19 Related Mobility Reduction: Heterogenous Effects on Sleep and Physical Activity Rhythms

Mobility restrictions imposed to suppress coronavirus transmission can alter physical activity (PA) and sleep patterns. Characterization of response heterogeneity and their underlying reasons may assist in tailoring customized interventions. We obtained wearable data covering baseline, incremental movement restriction and lockdown periods from 1824 city-dwelling, working adults aged 21 to 40 years, incorporating 206,381 nights of sleep and 334,038 days of PA. Four distinct rest activity rhythms (RARs) were identified using k-means clustering of participants' temporally distributed step counts. Hierarchical clustering of the proportion of time spent in each of these RAR revealed 4 groups who expressed different mixtures of RAR profiles before and during the lockdown. Substantial but asymmetric delays in bedtime and waketime resulted in a 24 min increase in weekday sleep duration with no loss in sleep efficiency. Resting heart rate declined 2 bpm. PA dropped an average of 38%. 4 groups with different compositions of RAR profiles were found. Three were better able to maintain PA and weekday/weekend differentiation during lockdown. The least active group comprising 51 percent of the sample, were younger and predominantly singles. Habitually less active already, this group showed the greatest reduction in PA during lockdown with little weekday/weekend differences. Among different mobility restrictions, removal of habitual social cues by lockdown had the largest effect on PA and sleep. Sleep and resting heart rate unexpectedly improved. RAR evaluation uncovered heterogeneity of responses to lockdown and can identify characteristics of persons at risk of decline in health and wellbeing.Comment: 30 pages, 3 main figures, 3 tables, 4 supplementary figure