Internal Heating of Old Neutron Stars: Contrasting Different Mechanisms

The thermal emission detected from the millisecond pulsar J0437-4715 is not explained by standard cooling models of neutron stars without a heating mechanism. We investigated three heating mechanisms controlled by the rotational braking of the pulsar: breaking of the solid crust, superfluid vortex creep, and non-equilibrium reactions ('rotochemical heating'). We find that the crust cracking mechanism does not produce detectable heating. Given the dependence of the heating mechanisms on spin-down parameters, which leads to different temperatures for different pulsars, we study the thermal evolution for two types of pulsars: young, slowly rotating 'classical' pulsars and old, fast rotating millisecond pulsars (MSPs). We find that the rotochemical heating and vortex creep mechanism can be important both for classical pulsars and MSPs.Comment: VIII Symposium in Nuclear Physics and Applications: Nuclear and Particle Astrophysics. Appearing in the American Institute of Physics (AIP) conference proceeding

Non-modal analysis of spectral element methods: Towards accurate and robust large-eddy simulations

We introduce a \textit{non-modal} analysis technique that characterizes the diffusion properties of spectral element methods for linear convection-diffusion systems. While strictly speaking only valid for linear problems, the analysis is devised so that it can give critical insights on two questions: (i) Why do spectral element methods suffer from stability issues in under-resolved computations of nonlinear problems? And, (ii) why do they successfully predict under-resolved turbulent flows even without a subgrid-scale model? The answer to these two questions can in turn provide crucial guidelines to construct more robust and accurate schemes for complex under-resolved flows, commonly found in industrial applications. For illustration purposes, this analysis technique is applied to the hybridized discontinuous Galerkin methods as representatives of spectral element methods. The effect of the polynomial order, the upwinding parameter and the P\'eclet number on the so-called \textit{short-term diffusion} of the scheme are investigated. From a purely non-modal analysis point of view, polynomial orders between $2$ and $4$ with standard upwinding are well suited for under-resolved turbulence simulations. For lower polynomial orders, diffusion is introduced in scales that are much larger than the grid resolution. For higher polynomial orders, as well as for strong under/over-upwinding, robustness issues can be expected. The non-modal analysis results are then tested against under-resolved turbulence simulations of the Burgers, Euler and Navier-Stokes equations. While devised in the linear setting, our non-modal analysis succeeds to predict the behavior of the scheme in the nonlinear problems considered

大河川流域の水文学的機能と気候変動に対する応答特性の比較分析

防災学プログラム / Disaster Management Program政策研究大学院大学 / National Graduate Institute for Policy Studies論文審査委員: 佐山 敬洋 (主査), 竹内 邦良, 小池 俊雄, 安藤 尚一, 園部 哲史, 花崎 直太 (国立環境研究所地球環境研究センター

Temporal dynamics and pathophysiology of the edematous response after acute myocardial infarction: a translational journey

Post-myocardial infarction tissue composition is highly dynamic and can be characterized by cardiac magnetic resonance, which has been used to assess surrogate outcomes and efficacy endpoints in many experimental and clinical studies. However, there is a paucity of studies tracking the temporal dynamics of these processes and analyzing their pathophysiology in a comprehensive manner. The experimental and clinical work contained in this dissertation shows that the degree and extent of post-myocardial infarction tissue composition changes (mainly edema; but also necrosis, hemorrhage and microvascular obstruction) as assessed by cardiac magnetic resonance are variable according to the time from infarction, duration of ischemia, cardioprotective strategies, and the interplay between them. These dynamic changes should be taken into consideration when performing image acquisition. Comparative studies should be performed at similar timings to avoid the bias of these dynamic changes. Thus, and in contrast to the accepted view, it is shown for the first time that myocardial edema in the week after ischemia/reperfusion is a bimodal phenomenon, both in pigs and humans. The initial wave of edema, appearing abruptly upon reperfusion and which is significantly attenuated at 24 hours, is due to the reperfusion process itself. The deferred wave of edema, appearing progressively days after ischemia/reperfusion and reaching a plateau between days 4 to 7, is mainly caused by the tissue healing processes. These findings highlight the need for standardizing experimental and clinical protocols for post-myocardial infarction tissue characterization aiming to quantify edema, myocardial area at risk, infarct size, myocardial salvage, intramyocardial hemorrhage and microvascular obstruction. The timeframe between day 4 and 7 post-infarction seems a good compromise solution according to translational data here presented. However, further studies and expert consensus are needed to stablish more precise recommendations

Monte Carlo Neutrino Transport Through Remnant Disks from Neutron Star Mergers

We present Sedonu, a new open source, steady-state, special relativistic Monte Carlo (MC) neutrino transport code, available at bitbucket.org/srichers/sedonu. The code calculates the energy- and angle-dependent neutrino distribution function on fluid backgrounds of any number of spatial dimensions, calculates the rates of change of fluid internal energy and electron fraction, and solves for the equilibrium fluid temperature and electron fraction. We apply this method to snapshots from two-dimensional simulations of accretion disks left behind by binary neutron star mergers, varying the input physics and comparing to the results obtained with a leakage scheme for the case of a central black hole and a central hypermassive neutron star. Neutrinos are guided away from the densest regions of the disk and escape preferentially around 45 degrees from the equatorial plane. Neutrino heating is strengthened by MC transport a few scale heights above the disk midplane near the innermost stable circular orbit, potentially leading to a stronger neutrino-driven wind. Neutrino cooling in the dense midplane of the disk is stronger when using MC transport, leading to a globally higher cooling rate by a factor of a few and a larger leptonization rate by an order of magnitude. We calculate neutrino pair annihilation rates and estimate that an energy of 2.8e46 erg is deposited within 45 degrees of the symmetry axis over 300 ms when a central BH is present. Similarly, 1.9e48 erg is deposited over 3 s when an HMNS sits at the center, but neither estimate is likely to be sufficient to drive a GRB jet.Comment: 23 pages, 16 figures, Accepted to The Astrophysical Journa

Robust and Sustainable Energy Pathways to Reach Mexico’s Climate Goals

As countries set climate change goals for adaptation and mitigation efforts, there are many questions regarding to how to reach these targets. These efforts will necessitate the transition of our electricity infrastructure from relying on conventional electricity generation technologies including natural gas, coal and oil, to clean energy generation with renewables. Through the three essays presented in this dissertation, we explore various pathways of development for the electricity system to reach long term climate change goals. We are interested in identifying: Is there a unique optimal development option or are there various? How do different mixes of electricity generation technologies affect the development of the electricity grid, transmission infrastructure, secondary infrastructure and sustainability? The goal of the dissertation is to present new insight to decision makers trying to develop future energy policy, to help facilitate reaching climate change goals and sustainable development. While this dissertation is focused on the Mexican electrical grid and climate change goals, the methodologies presented here can be applied more broadly to other electricity systems. In the first essay, we use a multi-model approach to study a series of development pathways to reach Mexico’s 2050 climate change goals. We create expansion plans for the various development pathways with the use of a detailed model of the Mexican electrical grid. In the second essay, we develop optimal carbon capture and storage networks for each expansion plan that was presented in the first essay. We identify whether robust options exist within the carbon capture and storage network and what potential impacts the development of these networks could have on local communities. The third essay uses the results obtained from the previous essays to perform a comprehensive sustainability and equity analysis, with seven criteria, on the various development pathways for the electricity system. This analysis allows us to better understand the tradeoffs between the different development options and how they can impact questions of equity

Rotochemical Heating of Neutron Stars: Rigorous Formalism with Electrostatic Potential Perturbations

The electrostatic potential that keeps approximate charge neutrality in neutron star matter is self-consistently introduced into the formalism for rotochemical heating presented in a previous paper by Fernandez and Reisenegger. Although the new formalism is more rigorous, we show that its observable consequences are indistinguishable from those of the previous one, leaving the conclusions of the previous paper unchanged.Comment: 14 pages, including 4 eps figures. Accepted for publication in The Astrophysical Journa

Über die Kalziumleitfähigkeit von Kanalrhodopsinen

Kanalrhodopsine (ChRs) sind eine Gruppe von lichtgesteuerten Ionenkanälen, die ursprünglich aus motilen Algen stammen. In ihren nativen Organismus vermitteln sie die Bewegung zu optimalen Lichtbedingungen. In der biologischen Forschung hingegen werden ChRs eingesetzt, um die Erregbarkeit spezifischer Zellen mit hoher räumlicher und zeitlicher Auflösung optisch zu steuern, ein Forschungsfeld, was als Optogenetik bezeichnet wird. Es wurden zahlreiche ChRs mit unterschiedlichen Eigenschaften charakterisiert und entwickelt, darunter solche, die selektiv für H+, Na+, K+ und Anionen sind. Im Gegensatz dazu sind bisher keine Ca2+-selektiven ChRs bekannt. In Anbetracht der Dominanz der von Kalzium in zellulären Signalwegen in allen Reichen des Lebens, würde ein Ca2+-leitendes ChR präzise Photokontrolle einer Vielzahl von zellulären Prozessen ermöglichen. In dieser Arbeit wurden Chlamydomonas reinhardtii channelrhodopsin 2 (CrChR2) Mutanten, die mit einer Erhöhung der Ca2+-Leitfähigkeit einhergehen, elektrophysiologisch charakterisiert und systematisch verglichen. Von den getesteten Varianten zeigten diejenigen, die eine Erhöhung der negativen Ladung am Selektivitätsfilter des Kanals, dem zentralen Tor, verursachen, erhebliche Auswirkungen auf die Leitfähigkeit für Ca2+ bei negativen Membranspannungen. Daraufhin wurden gezielt homologe Mutationen an mehreren verwandten ChRs eingeführt wodurch erfolgreich zwei Kalzium-durchlässige Kanalrhodopsine (CapChR1 und 2) erzeugt werden konnten. Die erweiterte Charakterisierung der CapChRs ergab eine unterdrückte Na+-Leitfähigkeit und eine erhöhte Ca2+-Durchlässigkeit bei negativen Spannungen. Bei niedrigen extrazellulären Konzentrationen des zweiwertigen Kations zeigten Kalzium-Imaging Experimente die Überlegenheit von CapChR2 bei der Vermittlung des durch Licht ausgelösten Ca2+-Einstroms in kultivierten Zellen.Channelrhodopsins (ChRs) constitute a group of light-gated ion channels originating from motile algae. In their native organisms, they mediate movement towards optimal light conditions. In biological research, ChRs are employed to optically control excitability of specific cells with a high spatiotemporal resolution in a field commonly referred to as optogenetics. Numerous ChRs with varying properties have been characterized and engineered, including members that are selective for H+, Na+, K+ or anions. In contrast, no Ca2+-selective ChRs have been reported to date. Given the dominance of calcium signaling across the kingdoms of life, a Ca2+-conducting ChRs would enable precise photocontrol of a multitude of cellular processes. In this work, mutants of Chlamydomonas reinhardtii channelrhodopsin 2 (CrChR2) associated with an increase in Ca2+-conductance were characterized via electrophysiology and compared systematically. Out of the tested variants, those increasing the negative electric charge at the selectivity filter of the channel, the central gate, were found to have substantial effects on the conductance for Ca2+ at negative membrane voltages. Subsequently, targeted mutations on several related ChRs were introduced in order to produce two calcium-permeable channelrhodopsins (CapChR1 and 2). Extended characterization of the engineered CapChRs revealed suppressed Na+ conductance and increased Ca2+ permeation at negative voltages. At low extracellular concentrations of the divalent cation, calcium imaging experiments demonstrated the superiority of CapChR2 in mediating light-triggered Ca2+-influx in cultured cells

The Sustainability Of Decarbonizing The Grid: A Multi-Model Decision Analysis Applied To Mexico

Mexico recognizes its vulnerability to the effects of climate change, including sea level rise, increasing average temperatures, more frequent extreme weather events and changes to the hydrological cycle. Because of these concerns Mexico has a vested interest in developing sustainable strategies for mitigating climate change as it develops its electricity grid. In this study, we use a set of sustainability criteria to evaluate a number of model-derived pathways for the electricity grid aimed at meeting Mexico\u27s climate goals. We use a multi-step approach, combining pathways from multiple large scale global models with a detailed electricity model to leverage geographic information into our multi-criteria sustainability analysis. We summarize the overall ranking of each expansion plan with the use of the weighted sum method. We find that the expansion plans with more than 20% of energy coming from carbon capture and storage (CCS) technologies tend to be less sustainable. While CCS technologies have low GHG emissions, they have high air pollution and water-use and require the development of extensive pipeline networks. In particular, these CCS characteristics pose concerns from an environmental justice perspective as high air pollution and water-use can significantly effect local communities: the plan with the most CCS has an extra 14 kg/GWh of weighted air pollution emissions and 199,000 liters/GWh of weighted water use compared to the plan with the most renewables. This analysis provides novel insights on tradeoffs that decisions makers must consider when looking at different sustainable development options to reach long term climate goals