401 research outputs found

    LIPIcs, Volume 251, ITCS 2023, Complete Volume

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    LIPIcs, Volume 251, ITCS 2023, Complete Volum

    Astrophysics with the Laser Interferometer Space Antenna

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    The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA's first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or interme-diate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe

    Design and Fabrication of Photo-Thermal and Thermo-Electric Materials and Systems

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    Thermal energy is all around us. How to control and utilize it is an important topic in advanced manufacturing. This dissertation is focused on the design and fabrication of photo-thermal and thermo-electric materials and systems and is divided into three topics: pH-responsive Au@silica semi-shell nanoparticles (NPs), thermo-osmotic ionogel (TOI), and HClO₄-enhanced Fe(III/II) thermocells (TECs). pH-responsive photothermal therapy holds promise for non-invasive antitumor treatment, but the preparation of smart photothermal agents (PTAs) remains challenging. In the first topic (Chapter 3), a simple two-step approach was developed for the precise synthesis of anisotropic Au@silica semi-shell NPs, which were then used as pH-responsive PTAs for non-invasive antitumor therapy. In the synthesis of Au@silica semi-shell NPs, the isotropic solution-synthesized Au@silica core-shell NPs were firstly self-assembled on silicon wafers to form monolayer films by drop-casting technique. Then, Au@silica semi-shell NPs were obtained after selective and directional removal of part of the silica shell by reactive ion etching. After functionalization with pH-sensitive 4-mercaptobenzoic acid (4-MBA) molecules, the semi-shell NPs achieved pH-responsive rod-shaped assembly/disassembly in physiological saline solution, thereby exhibiting pH-responsive photothermal effects. In addition, the 4-MBA-semi-shell NPs have been successfully applied to in vitro photothermal therapy of tumor cells, showing great application potential in non-invasive antitumor therapy. Low efficiency in recovering low-grade heat remains unresolved despite decades’ attempts. In the second topic (Chapter 4), a novel thermo-osmotic ionogel (TOI) composite was designed and fabricated to recover low-grade heat to generate electric power through thermo-induced ion gradient and selective ion diffusion. The TOI composite was assembled with crystalline ionogel (polymer-confined LiNO₃-3H₂O) film, cation exchange membrane, and hydrogel film. With a 90 °C heat supply, the single TOI composite produced a high open-circuit voltage of 0.52 V, a differential thermal voltage of ~26 mV/K, a peak power density of 0.4 W/mÂČ, and a ground-breaking peak energy conversion efficiency of 11.17%. Eight pieces of such TOI composite were connected in series, demonstrating an open-circuit voltage of 3.25 volts. Such a TOI system was also demonstrated to harvest body temperature for powering a LED, opening numerous opportunities for powering wearable devices. This work opens a new door for efficient harvesting of low-grade heat by embedding thermo-osmotic conversion as an intermedia stage of thermo-electric conversion. In addition to thermo-ionic capacitors (Chapter 4), emerging thermocells (TECs) can convert a temperature gradient into electricity continuously and thus are promising for low-grade heat harvesting. However, it’s challenging to simultaneously improve the thermopower (Se, a thermodynamics parameter) and ionic conductivity (Ïƒá”ą, a kinetics parameter) of TECs due to the well-known inherent interdependence between thermodynamics and kinetics. In the third topic (Chapter 5), a simple perchloric acid (HClO₄) incorporation method has been developed to enhance the charge density of the oxidant Fe(III) ions in the state-of-the-art n-type Fe(III/II)-ClO₄ redox pair, thereby improving the Se and Ïƒá”ą simultaneously. In Fe(III/II)-ClO₄ electrolyte, the addition of HClO₄ composed of protons and weakly coordinating anions suppresses the deprotonation of [Fe(H₂O)₆]Âłâș without inducing Fe(III)-anion coordination. The n-type TEC using HClO₄-acidified Fe(III/II)-ClO₄ as electrolyte and hydrophilic carbon fiber cloth as the electrode was charactered and demonstrated a Se of 1.5 mV/K (comparable to -1.4 mV/K of benchmark p-type Fe(CN)₆³⁻/Fe(CN)₆⁎⁻ TECs) and an excellent temperature normalized power density of 1.19 mW/mÂČ/KÂČ (2.64 times higher than that of the state-of-the-art n-type TECs using carbon electrodes), overcoming barriers for practical p-n integrated TEC applications

    Time-delay interferometric ranging for LISA: Statistical analysis of bias-free ranging using laser noise minimization

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    Die Laser Interferometer Space Antenna (LISA) ist eine Mission der europĂ€ischen Weltraumagentur (ESA) zur Detektion von Gravitationswellen im Frequenzbereich zwischen 10^-4 Hz und 1 Hz. Gravitationswellen induzieren relative AbstandsĂ€nderungen, die LISA mithilfe von Laserinterferometrie mit PicometerprĂ€zision misst. Ein großes Problem hierbei ist das Frequenzrauschen der Laser. Um dieses zu unterdrĂŒcken, ist es notwendig, mithilfe eines Algorithmus namens TDI (engl. time-delay interferometry), virtuelle Interferometer mit gleichlangen Armen zu konstruieren, wie z.B. das klassische Michelson-Interferometer. In dieser Arbeit untersuchen wir die Performanz von TDI unter realistischen Bedingungen und identifizieren verschiedene Kopplungsmechanismen des Laserfrequenzrauschens. Als erstes betrachten wir die Datenverarbeitung an Bord der Satelliten, die benötigt wird, um die Abtastrate der interferometrischen Messungen zu reduzieren. HierfĂŒr sind Anti-Alias-Filter vorgesehen, die der Faltung von Laserrauschleistung in das Beobachtungsband vorbeugen. Außerdem wirkt sich die Ebenheit der Filter auf die EffektivitĂ€t von TDI aus (engl. flexing-filtering-effect). Dieser Effekt ist bereits in der Literatur beschrieben und wir demonstrieren in dieser Arbeit die Möglichkeit, ihn mithilfe von Kompensationsfiltern effektiv zu reduzieren. Als zweites betrachten wir Kopplungsmechanismen von Laserfrequenzrauschen im TDI-Algorithmus selbst. Fehler in der Interpolation der interferometrischen Messungen und Ungenauigkeiten in den absoluten Abstandsmessungen zwischen den Satelliten fĂŒhren ebenfalls zu einer unzureichenden Reduzierung des Laserfrequenzrauschens. Wir beschreiben die oben genannten Kopplungsmechanismen analytisch und validieren die zugrundeliegenden Modelle mithilfe von numerischen Simulationen. Das tiefere VerstĂ€ndnis dieser Residuen ermöglicht es uns, geeignete instrumentelle Parameter zu wĂ€hlen, die von hoher Relevanz fĂŒr das Missionsdesign von LISA sind. Des Weiteren beschĂ€ftigen wir uns in dieser Arbeit mit der möglichst genauen Bestimmung der absoluten AbstĂ€nden zwischen den Satelliten, die fĂŒr den TDI Algorithmus erforderlich sind. HierfĂŒr werden die Abstandsinformationen aus den SeitenbĂ€ndern und der PRN-Modulation (engl. pseudo-random noise) kombiniert. Wir zeigen, dass die PRN-Messung von systematischen Verzerrungen betroffen ist, die zu Laserrauschresiduen in den TDI-Variablen fĂŒhren. Um diesen Fehler zu korrigieren, schlagen wir als zusĂ€tzliche Abstandsmessung TDI-Ranging (TDI-R) vor. TDI-R ist zwar ungenauer, aber frei von systematischen Verzerrungen und kann daher zur Kalibrierung der PRN-Messungen herangezogen werden. Wir prĂ€sentieren in dieser Arbeit eine ausfĂŒhrliche statistische Studie, um die Performanz von TDI-R zu charakterisieren. DafĂŒr formulieren wir die Likelihood-Funktion der interferometrischen Messungen und berechnen die Fisher-Informationsmatrix, um die theoretisch mögliche untere Grenze der SchĂ€tzvarianz zu finden. Diese verhĂ€lt sich invers proportional zur Integrationszeit und dem VerhĂ€ltnis von SekundĂ€rrauschleistung, die die interferometrische Messung fundamental limitiert, und Laserrauschleistung. ZusĂ€tzlich validieren wir die analytische untere Grenze der SchĂ€tzvarianz mithilfe von numerischen Simulationen und zeigen damit, dass unsere Implementierung von TDI-R optimal ist. Der entwickelte TDI-R-Algorithmus wird Teil der Datenverarbeitungspipeline sein und KonsistenzprĂŒfungen und Kalibrierung der primĂ€ren Abstandsmessmethoden ermöglichen.The Laser Interferometer Space Antenna (LISA) is a future ESA-led space-based observatory to explore the gravitational universe in the frequency band between 10^-4 Hz and 1 Hz. LISA implements picometer-precise inter-satellite ranging to measure tiny ripples in spacetime induced by gravitational waves (GWs). However, the single-link measurements are dominated by laser frequency noise, which is about nine orders of magnitude larger than the GW signals. Therefore, in post-processing, the time-delay interferometry (TDI) algorithm is used to synthesize virtual equal-arm interferometers to suppress laser frequency noise. In this work we identify several laser frequency noise coupling channels that limit the performance of TDI. First, the on-board processing, which is used to decimate the sampling rate from tens of megahertz down to the telemetry rate of a few hertz, requires careful design. Appropriate anti-aliasing filters must be implemented to mitigate folding of laser noise power into the observation band. Furthermore, the flatness of these filters is important to limit the impact of the flexing-filtering effect. We demonstrate that this effect can be effectively reduced by using compensation filters on ground. Second, the post-processing delays applied in TDI are subject to interpolation and ranging errors. We study these laser and timing noise residuals analytically and perform simulations to validate the models numerically. Our findings have direct implications for the design of the LISA instrument as we identify the instrumental parameters that are essential for successful laser noise suppression and provide methods for designing appropriate filters for the on-board processing. In addition, we discuss a dedicated ranging processing pipeline that produces high-precision range estimates that are the input for TDI by combining the sideband and pseudo-random noise (PRN) ranges. We show in this thesis that biases in the PRN measurements limit the laser noise suppression performance. Therefore, we propose time-delay interferometric ranging (TDI-R) as a third ranging sensor to estimate bias-free ranges that can be used to calibrate the biases in the PRN measurements. We present a thorough statistical study of TDI-R to evaluate its performance. Therefore, we formulate the likelihood function of the interferometric data and use the Fisher information formalism to find a lower bound on the estimation variance of the inter-satellite ranges. We find that the ranging uncertainty is proportional to the inverse of the integration time and the ratio of secondary noise power, that limits the interferometric readout, to the laser noise power. To validate our findings we implement prototype TDI-R pipelines and perform numerical simulations. We show that we are able to formulate optimal estimators of the unbiased range that reach the CramĂ©r-Rao lower bound previously expressed analytically. The developed TDI-R pipeline will be integrated into the ranging processing pipeline to perform consistency checks and ensure well-calibrated inter-satellite ranges

    Cosmology with the Laser Interferometer Space Antenna

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    The Laser Interferometer Space Antenna (LISA) has two scientific objectives of cosmological focus: to probe the expansion rate of the universe, and to understand stochastic gravitational-wave backgrounds and their implications for early universe and particle physics, from the MeV to the Planck scale. However, the range of potential cosmological applications of gravitational-wave observations extends well beyond these two objectives. This publication presents a summary of the state of the art in LISA cosmology, theory and methods, and identifies new opportunities to use gravitational-wave observations by LISA to probe the universe

    LIPIcs, Volume 261, ICALP 2023, Complete Volume

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    LIPIcs, Volume 261, ICALP 2023, Complete Volum

    Fair Allocation of goods and chores -- Tutorial and Survey of Recent Results

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    Fair resource allocation is an important problem in many real-world scenarios, where resources such as goods and chores must be allocated among agents. In this survey, we delve into the intricacies of fair allocation, focusing specifically on the challenges associated with indivisible resources. We define fairness and efficiency within this context and thoroughly survey existential results, algorithms, and approximations that satisfy various fairness criteria, including envyfreeness, proportionality, MMS, and their relaxations. Additionally, we discuss algorithms that achieve fairness and efficiency, such as Pareto Optimality and Utilitarian Welfare. We also study the computational complexity of these algorithms, the likelihood of finding fair allocations, and the price of fairness for each fairness notion. We also cover mixed instances of indivisible and divisible items and investigate different valuation and allocation settings. By summarizing the state-of-the-art research, this survey provides valuable insights into fair resource allocation of indivisible goods and chores, highlighting computational complexities, fairness guarantees, and trade-offs between fairness and efficiency. It serves as a foundation for future advancements in this vital field

    Astrophysics with the Laser Interferometer Space Antenna

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    The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA’s first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or interme-diate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe

    Primordial black holes and their gravitational-wave signatures

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    In the recent years, primordial black holes (PBHs) have emerged as one of the most interesting and hotly debated topics in cosmology. Among other possibilities, PBHs could explain both some of the signals from binary black hole mergers observed in gravitational wave detectors and an important component of the dark matter in the Universe. Significant progress has been achieved both on the theory side and from the point of view of observations, including new models and more accurate calculations of PBH formation, evolution, clustering, merger rates, as well as new astrophysical and cosmological probes. In this work, we review, analyse and combine the latest developments in order to perform end-to-end calculations of the various gravitational wave signatures of PBHs. Different ways to distinguish PBHs from stellar black holes are emphasized. Finally, we discuss their detectability with LISA, the first planned gravitational-wave observatory in space.Comment: 161 pages, 47 figures, comments welcom

    Hitting Subgraphs in Sparse Graphs and Geometric Intersection Graphs

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    We investigate a fundamental vertex-deletion problem called (Induced) Subgraph Hitting: given a graph GG and a set F\mathcal{F} of forbidden graphs, the goal is to compute a minimum-sized set SS of vertices of GG such that G−SG-S does not contain any graph in F\mathcal{F} as an (induced) subgraph. This is a generic problem that encompasses many well-known problems that were extensively studied on their own, particularly (but not only) from the perspectives of both approximation and parameterization. We focus on the design of efficient approximation schemes, i.e., with running time f(Δ,F)⋅nO(1)f(\varepsilon,\mathcal{F}) \cdot n^{O(1)}, which are also of significant interest to both communities. Technically, our main contribution is a linear-time approximation-preserving reduction from (Induced) Subgraph Hitting on any graph class G\mathcal{G} of bounded expansion to the same problem on bounded degree graphs within G\mathcal{G}. This yields a novel algorithmic technique to design (efficient) approximation schemes for the problem on very broad graph classes, well beyond the state-of-the-art. Specifically, applying this reduction, we derive approximation schemes with (almost) linear running time for the problem on any graph classes that have strongly sublinear separators and many important classes of geometric intersection graphs (such as fat-object graphs, pseudo-disk graphs, etc.). Our proofs introduce novel concepts and combinatorial observations that may be of independent interest (and, which we believe, will find other uses) for studies of approximation algorithms, parameterized complexity, sparse graph classes, and geometric intersection graphs. As a byproduct, we also obtain the first robust algorithm for kk-Subgraph Isomorphism on intersection graphs of fat objects and pseudo-disks, with running time f(k)⋅nlog⁥n+O(m)f(k) \cdot n \log n + O(m).Comment: 60 pages, abstract shortened to fulfill the length limi
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