132 research outputs found

    LIPIcs, Volume 251, ITCS 2023, Complete Volume

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    LIPIcs, Volume 251, ITCS 2023, Complete Volum

    Certified Hardness vs. Randomness for Log-Space

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    Let L\mathcal{L} be a language that can be decided in linear space and let ϵ>0\epsilon >0 be any constant. Let A\mathcal{A} be the exponential hardness assumption that for every nn, membership in L\mathcal{L} for inputs of length~nn cannot be decided by circuits of size smaller than 2ϵn2^{\epsilon n}. We prove that for every function f:{0,1}{0,1}f :\{0,1\}^* \rightarrow \{0,1\}, computable by a randomized logspace algorithm RR, there exists a deterministic logspace algorithm DD (attempting to compute ff), such that on every input xx of length nn, the algorithm DD outputs one of the following: 1: The correct value f(x)f(x). 2: The string: ``I am unable to compute f(x)f(x) because the hardness assumption A\mathcal{A} is false'', followed by a (provenly correct) circuit of size smaller than 2ϵn2^{\epsilon n'} for membership in L\mathcal{L} for inputs of length~nn', for some n=Θ(logn)n' = \Theta (\log n); that is, a circuit that refutes A\mathcal{A}. Our next result is a universal derandomizer for BPLBPL: We give a deterministic algorithm UU that takes as an input a randomized logspace algorithm RR and an input xx and simulates the computation of RR on xx, deteriministically. Under the widely believed assumption BPL=LBPL=L, the space used by UU is at most CRlognC_R \cdot \log n (where CRC_R is a constant depending on~RR). Moreover, for every constant c1c \geq 1, if BPLSPACE[(log(n))c]BPL\subseteq SPACE[(\log(n))^{c}] then the space used by UU is at most CR(log(n))cC_R \cdot (\log(n))^{c}. Finally, we prove that if optimal hitting sets for ordered branching programs exist then there is a deterministic logspace algorithm that, given a black-box access to an ordered branching program BB of size nn, estimates the probability that BB accepts on a uniformly random input. This extends the result of (Cheng and Hoza CCC 2020), who proved that an optimal hitting set implies a white-box two-sided derandomization.Comment: Abstract shortened to fit arXiv requirement

    LIPIcs, Volume 261, ICALP 2023, Complete Volume

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    LIPIcs, Volume 261, ICALP 2023, Complete Volum

    Multi-laser powder bed fusion using 808 nm sources

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    Laser Powder Bed Fusion (LPBF) is a disruptive manufacturing technique widely used in aerospace, automotive, and energy industries, enabling the creation of intricate structures from various metallic alloys with minimal waste. However, LPBF systems face limitations in processing efficiency, scalability, and thermal control. The main constraint is single-fibre laser productivity, hindering large-scale adoption due to galvo-scanning method limitations. Multi-laser integration shows potential but presents challenges in design and control complexity. Innovations are sought to effectively incorporate multiple lasers while ensuring efficiency and scalability. LPBF systems use high-power fibre lasers at 1064 nm wavelength, but their low material-specific absorption efficiency (<60%) demands high laser power, resulting in challenges in processing high-performance alloys with limited weldability and high crack susceptibility. Enhanced thermal management with in-situ control and slower cooling rates are necessary to mitigate these issues, although they increase production costs and time. On the other hand, low-power diode lasers are emerging as a promising alternative. They are compact, energy-efficient, and durable and emit shorter wavelengths ranging from 450 nm to 3300 nm, making them suitable for various industrial processes. Research efforts are currently focused on developing Diode Area Melting (DAM) systems where multiple diode lasers selectively melt powder beds, offering a high-resolution and energy-efficient solution. However, challenges still exist in beam quality, power output, and system design. Integrating multi-fibre coupled diode lasers as a 2D array in LPBF can offer significant advantages, including improved productivity, enhanced material absorption, and reduced energy consumption. The ability to individually control each laser allows for customized intensity distributions, enabling the fabrication of complex parts. Further research is needed to optimize system design, increase power output, and explore scalability to larger write areas suitable for production environments. The use of fibre-coupled diode laser and optical systems can potentially create efficient and scalable LPBF systems that can enhance the microstructure of final parts. This, in turn, can significantly improve the mechanical properties at an industrial level without incurring excessive costs or time investment. This research investigates the influence of laser wavelength on the efficiency and scalability of the Powder Bed Fusion (PBF) process using a 2D array head comprising a scalable, low-power (4.5 W) 808 nm fibre-coupled diode laser. The individual control of multiple short wavelengths (808 nm) diode lasers enhances absorption and processing efficiency, enabling the fabrication of intricate parts with better thermal control. The research delves into how beam profiles, laser power, scanning speed, and wavelength affect microstructure, mechanical properties, and melt pool morphology when manufacturing three-dimensional Ti6Al4V parts. The study reveals that low-power diode lasers generate energy densities comparable to traditional selective laser melting due to shorter laser wavelengths, increasing metallic powder absorption, and enhancing processing efficiency. Moreover, the investigation highlights the impact of laser wavelength on keyhole formation, melt pool characteristics, and microstructural evolution. The 2D array laser head produces parts with mechanical properties akin to those manufactured using selective laser melting systems, indicating the potential of this technique to optimize PBF manufacturing efficiency. These findings are valuable to researchers and industry professionals seeking to enhance the quality, scalability, and cost-effectiveness of the PBF process

    LIPIcs, Volume 274, ESA 2023, Complete Volume

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    LIPIcs, Volume 274, ESA 2023, Complete Volum

    Engineering of reconfigurable integrated photonics for quantum computation protocols

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    Over the last decade, integrated optics has emerged as one of the main technologies for quantum optics and more generally quantum computation, quantum cryptography and communication. In particular, it is fundamental for the construction of reconfigurable interferometers with a high number of optical modes. In this thesis we present, on the one hand, the development of a new geometry for the creation of integrated reconfigurable devices with a high number of modes and, on the other hand, the development of quantum computation protocols to be realized in integrated photonic chips. In the first part, two algorithms are proposed for the characterization of integrated circuits in terms of implemented unitary matrix. The first uses a so-called Black Box approach, i.e. one that makes no assumptions about the internal structure of the device under consideration, and it is based on second-order correlation measurements with coherent light. The second is specific to a planar rectangular geometry, first proposed by Clements et al., which has a variety of applications in the literature and is also employed in this thesis. Subsequently, we present the realization of a new 32-mode reconfigurable integrated photonic device with a continuously coupled three-dimensional geometry. Its potential in terms of reconfigurability is tested and a Boson sampling experiment with three and four photons is carried out to show its potential in the field of quantum computation. In the second part, we propose the application of integrated photonic devices to two quantum computation protocols. The first was recently proposed and is the quantum extension of a problem called Bernoulli factory. It consists in the construction of a qubit from nn qubits in the same unknown state so that there is a predetermined exact relation between the output and input states. In the thesis, we theoretically analyze the computational complexity of the problem in terms of the qubits used and the success probability of the problem. Furthermore, a photonic implementation is proposed and experimentally tested for correctness and resilience to experimental noise. The second application consists of the experimental implementation of a quantum metrology protocol in which three distinct phases are estimated simultaneously, showing that the use of indistinguishable photons leads to an advantage in terms of the variance of the estimates

    Environmental Governance in Indonesia

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    Indonesia is one of the countries with the fastest-growing economies in Asia and one of the most biologically diverse countries in the world. With ecosystems ranging from terrestrial to marine and teemed with unique life forms, Indonesia is rich in natural resources. Unfortunately, Indonesia also suffers from overexploitation and environmental threats exacerbated by climate and human pressures. Along with the growing global ambitions for achieving sustainable development and increasing its capacity to adapt to climate change and extreme events, Indonesia is also increasing its commitments to balance development while safeguarding environmental and social sustainability. However, challenges remain, especially on how to effectively govern the responses to environmental issues. Against this background, this book will present state-of-the-art environmental governance research and practices in Indonesia. It offers a wide scope, covering different themes and sectors (e.g., climate change, disaster risk, forestry, mining, etc.), diverse physical and societal landscapes (e.g., urban, rural, deltas, coastal areas, etc.), and multiscalar perspectives (from national to local level). This book has the ambition to incorporate more knowledge to indicate research gaps and future directions for environmental governance research. Our intention is also to reflect a vision to make the national and global environmental governance research agenda to be more diverse, inclusive, interdisciplinary, and transdisciplinary. We hope that this book will be useful for researchers, students, practitioners, and policymakers who are interested in the field of environmental governance, especially in Indonesia as a megadiversity country that encompasses the world’s largest archipelago

    Annals of Scientific Society for Assembly, Handling and Industrial Robotics 2021

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    This Open Access proceedings presents a good overview of the current research landscape of assembly, handling and industrial robotics. The objective of MHI Colloquium is the successful networking at both academic and management level. Thereby, the colloquium focuses an academic exchange at a high level in order to distribute the obtained research results, to determine synergy effects and trends, to connect the actors in person and in conclusion, to strengthen the research field as well as the MHI community. In addition, there is the possibility to become acquatined with the organizing institute. Primary audience is formed by members of the scientific society for assembly, handling and industrial robotics (WGMHI)

    Gravitational waves search for generic transient of intermediate duration in future interferometes network using coherentWave Burst algorithm

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    openSearches for generic transient Gravitational Waves (GW) target the widest possible range of different astrophysical sources, using no or minimal assumption on the morphology of the signal; in particular different astrophysical phenomena are foreseen to emit GW signals with long duration (by few sec. to hundreds of sec.), among those: fallback, newborn neutron , accretion disk instabilities, non axisymmetric deformation in magnetars. Coherent Wave Burst (cWB) is the flagship algorithm, in the LIGO- Virgo collaboration, used for the generic transient analysis without assumption morphology or arrival direction of GW signal. This project contributes to improve and optimize cWB algorithm for long duration generic gravitational waves search in the LHV (LIGO-Virgo) interferometers network. In particular the project aims to test possible algorithm configurations for next data taking of LHV (O4 is foreseen to start by the beginning of the next year), through a reanalysis and simulations campaign of public data of last data taking (O3b - November 2019 to March 2020). Specifically the project reanalyses the O3b data giving attention to the efficiency of the algorithm in reconstructing the signals. The first purpose of the project was developing codes and analysis to characterize the parameters of the signals like frequency, length etc. Also the capability of the algorithm in reassembling correctly the injected signal, considering the number of segments in which is divided the trigger obtained by the pipeline have been held specially into account, since this parameter qualifies the effectiveness of the algorithm in regaining the signal through clustering process. Statistical studies of this characteristic have been taken into attention, studying the segmentation process among different morphologies of gravitiational waves signal expected for astrophysical processes. The waveforms have been chosen in order to cover a wide spectrum of morphologies, duration and frequency. Furthermore, the network with expected sensitivity for post-O4 data taking has been studied, considering a scaled strain sensitivity curve of the detectors obtained from the O3b data, and performing injection of the same Gravitational Wave signals used in O3b analysis. In particular efficiency and background analysis have been taken into account, especially in LHV network configuration due to the additional noisy behavior of the Virgo interferometer. Two different configurations of the algorithm have been studied in order to classify properly the case of non coaligned three interferometer detector networks, as LHV. Finally in this project the test of the machine learning algorithm already introduced in other cWB searches will be performed for the long search. This algorithm is supposed to help us in noise-signal discharge analysis, distinguishing the Gravitational Waves signals from the noise background and it has already been used for other research. In particular different astrophysical phenomena are foreseen to emit GW signals with long duration (by few sec. to hundreds of sec.)

    Understanding Quantum Technologies 2022

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    Understanding Quantum Technologies 2022 is a creative-commons ebook that provides a unique 360 degrees overview of quantum technologies from science and technology to geopolitical and societal issues. It covers quantum physics history, quantum physics 101, gate-based quantum computing, quantum computing engineering (including quantum error corrections and quantum computing energetics), quantum computing hardware (all qubit types, including quantum annealing and quantum simulation paradigms, history, science, research, implementation and vendors), quantum enabling technologies (cryogenics, control electronics, photonics, components fabs, raw materials), quantum computing algorithms, software development tools and use cases, unconventional computing (potential alternatives to quantum and classical computing), quantum telecommunications and cryptography, quantum sensing, quantum technologies around the world, quantum technologies societal impact and even quantum fake sciences. The main audience are computer science engineers, developers and IT specialists as well as quantum scientists and students who want to acquire a global view of how quantum technologies work, and particularly quantum computing. This version is an extensive update to the 2021 edition published in October 2021.Comment: 1132 pages, 920 figures, Letter forma
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