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1. The impact of the crust equation of state on the analysis of GW170817

   https://doi.org/10.1088/1361-6382/ab5ba4  

   Gamba, R. ; Read, J. S. ; Wade, L. E. ( December 2019 , Classical and Quantum Gravity)

   The detection of GW170817, the first neutron star-neutron star merger observed by Advanced LIGO and Virgo, and its following analyses represent the first contributions of gravitational wave data to understanding dense matter. Parameterizing the high density section of the equation of state of both neutron stars through spectral decomposition, and imposing a lower limit on the maximum mass value, led to an estimate of the stars’ radii ofkm andkm (Abbottet al2018Phys. Rev. Lett.121161101). These values do not, however, take into account any uncertainty owed to the choice of the crust low-density equation of state, whichmore »was fixed to reproduce the SLy equation of state model (Douchin and Haensel 2001Astron. Astrophys.380151). We here re-analyze GW170817 data and establish that different crust models do not strongly impact the mass or tidal deformability of a neutron star—it is impossible to distinguish between low-density models with gravitational wave analysis. However, the crust does have an effect on inferred radius. We predict the systematic error due to this effect using neutron star structure equations, and compare the prediction to results from full parameter estimation runs. For GW170817, this systematic error affects the radius estimate by 0.3 km, approximatelyof the neutron stars’ radii.

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2. Plants as sensors: vegetation response to rainfall predicts root-zone water storage capacity in Mediterranean-type climates

   https://doi.org/10.1088/1748-9326/abb10b  

   Dralle, David N. ; Jesse Hahm, W. ; Rempe, Daniella M. ; Karst, Nathaniel ; Anderegg, Leander D. L. ; Thompson, Sally E. ; Dawson, Todd E. ; Dietrich, William E. ( October 2020 , Environmental Research Letters)

   In Mediterranean-type climates, asynchronicity between energy and water availability means that ecosystems rely heavily on the water-storing capacity of the subsurface to sustain plant water use over the summer dry season. The root-zone water storage capacity ($S_{\mathrm{m}\mathrm{a}\mathrm{x}}$[L]) defines the maximum volume of water that can be stored in plant accessible locations in the subsurface, but is poorly characterized and difficult to measure at large scales. Here, we develop an ecohydrological modeling framework to describe how$S_{\mathrm{m}\mathrm{a}\mathrm{x}}$mediates root zone water storage (S[L]), and thus dry season plant water use.more »The model reveals that where$S_{\mathrm{m}\mathrm{a}\mathrm{x}}$is high relative to mean annual rainfall,Sis not fully replenished in all years, and root-zone water storage and therefore plant water use are sensitive to annual rainfall. Conversely, where$S_{\mathrm{m}\mathrm{a}\mathrm{x}}$is low,Sis replenished in most years but can be depleted rapidly between storm events, increasing plant sensitivity to rainfall patterns at the end of the wet season. In contrast to both the high and low$S_{\mathrm{m}\mathrm{a}\mathrm{x}}$cases, landscapes with intermediate$S_{\mathrm{m}\mathrm{a}\mathrm{x}}$values are predicted to minimize variability in dry season evapotranspiration. These diverse plant behaviors enable a mapping between time variations in precipitation, evapotranspiration and$S_{\mathrm{m}\mathrm{a}\mathrm{x}}$, which makes it possible to estimate$S_{\mathrm{m}\mathrm{a}\mathrm{x}}$using remotely sensed vegetation data − that is, using plants as sensors. We test the model using observations of$S_{\mathrm{m}\mathrm{a}\mathrm{x}}$in soils and weathered bedrock at two sites in the Northern California Coast Ranges. Accurate model performance at these sites, which exhibit strongly contrasting weathering profiles, demonstrates the method is robust across diverse plant communities, and modes of storage and runoff generation.

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3. Coherent gravitational waveforms and memory from cosmic string loops

   https://doi.org/10.1088/1361-6382/aba28b  

   Aurrekoetxea, Josu C. ; Helfer, Thomas ; Lim, Eugene A. ( September 2020 , Classical and Quantum Gravity)

   We construct, for the first time, the time-domain gravitational wave strain waveform from the collapse of a strongly gravitating Abelian Higgs cosmic string loop in full general relativity. We show that the strain exhibits a large memory effect during merger, ending with a burst and the characteristic ringdown as a black hole is formed. Furthermore, we investigate the waveform and energy emitted as a function of string width, loop radius and string tensionGμ. We find that the mass normalized gravitational wave energy displays a strong dependence on the inverse of the string tensionE_GW/M₀∝ 1/Gμ, withstretchy='false'>)%at the percent level, for the regime whereGμ≳ 10⁻³. Conversely, we show that the efficiency is only weakly dependent on the initial string width and initial loop radii. Using these results, we argue that gravitational wave production is dominated by kinematical instead of geometrical considerations.

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4. Stratospheric contribution to the summertime high surface ozone events over the western united states

   https://doi.org/10.1088/1748-9326/abba53  

   Wang, Xinyue ; Wu, Yutian ; Randel, William ; Tilmes, Simone ( October 2020 , Environmental Research Letters)

   The stratospheric influence on summertime high surface ozone (${\mathrm{O}}_3$) events is examined using a twenty-year simulation from the Whole Atmosphere Community Climate Model. We find that${\mathrm{O}}_3$transported from the stratosphere makes a significant contribution to the surface${\mathrm{O}}_3$variability where background surface${\mathrm{O}}_3$exceeds the 95thpercentile, especially over western U.S. Maximum covariance analysis is applied to${\mathrm{O}}_3$anomalies paired with stratospheric${\mathrm{O}}_3$tracer anomalies to identify the stratospheric intrusion and the underlying dynamical mechanism. The first leading mode corresponds to deep stratospheric intrusions inmore »the western and northern tier of the U.S., and intensified northeasterlies in the mid-to-lower troposphere along the west coast, which also facilitate the transport to the eastern Pacific Ocean. The second leading mode corresponds to deep intrusions over the Intermountain Regions. Both modes are associated with eastward propagating baroclinic systems, which are amplified near the end of the North Pacific storm tracks, leading to strong descents over the western U.S.

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5. Chiral and counter-propagating Majorana fermions in a p-wave superconductor

   https://doi.org/10.1088/1367-2630/ab5cad  

   Hu, Haiping ; Satija, Indubala I. ; Zhao, Erhai ( December 2019 , New Journal of Physics)

   Chiral and helical Majorana fermions are two archetypal edge excitations in two-dimensional topological superconductors. They emerge from systems of different Altland–Zirnbauer symmetries and characterized by$\mathbb{Z}$and${\mathbb{Z}}_2$topological invariants respectively. It seems improbable to tune a pair of co-propagating chiral edge modes to counter-propagate in a single system without symmetry breaking. Here, we explore the peculiar behaviors of Majorana edge modes in topological superconductors with an additional ‘mirror’ symmetry which changes the bulk topological invariant to$\mathbb{Z}\oplus \mathbb{Z}$type. A theoretical toy model describing the proximity structure of a Chern insulator andmore »ap_x-wave superconductor is proposed and solved analytically to illustrate a direct transition between two topologically nontrivial phases. The weak pairing phase has two chiral Majorana edge modes, while the strong pairing phase is characterized by mirror-graded Chern number and hosts a pair of counter-propagating Majorana fermions protected by the mirror symmetry. The edge theory is worked out in detail, and implications to braiding of Majorana fermions are discussed.

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