The Power of Two Choices in Distributed Voting

Distributed voting is a fundamental topic in distributed computing. In pull voting, in each step every vertex chooses a neighbour uniformly at random, and adopts its opinion. The voting is completed when all vertices hold the same opinion. On many graph classes including regular graphs, pull voting requires $\Theta(n)$ expected steps to complete, even if initially there are only two distinct opinions. In this paper we consider a related process which we call two-sample voting: every vertex chooses two random neighbours in each step. If the opinions of these neighbours coincide, then the vertex revises its opinion according to the chosen sample. Otherwise, it keeps its own opinion. We consider the performance of this process in the case where two different opinions reside on vertices of some (arbitrary) sets $A$ and $B$, respectively. Here, $|A| + |B| = n$ is the number of vertices of the graph. We show that there is a constant $K$ such that if the initial imbalance between the two opinions is ?$\nu_0 = (|A| - |B|)/n \geq K \sqrt{(1/d) + (d/n)}$, then with high probability two sample voting completes in a random $d$ regular graph in $O(\log n)$ steps and the initial majority opinion wins. We also show the same performance for any regular graph, if $\nu_0 \geq K \lambda_2$ where $\lambda_2$ is the second largest eigenvalue of the transition matrix. In the graphs we consider, standard pull voting requires $\Omega(n)$ steps, and the minority can still win with probability $|B|/n$.Comment: 22 page

Extended Quantum Dimer Model and novel valence-bond phases

We extend the quantum dimer model (QDM) introduced by Rokhsar and Kivelson so as to construct a concrete example of the model which exhibits the first-order phase transition between different valence-bond solids suggested recently by Batista and Trugman and look for the possibility of other exotic dimer states. We show that our model contains three exotic valence-bond phases (herringbone, checkerboard and dimer smectic) in the ground-state phase diagram and that it realizes the phase transition from the staggered valence-bond solid to the herringbone one. The checkerboard phase has four-fold rotational symmetry, while the dimer smectic, in the absence of quantum fluctuations, has massive degeneracy originating from partial ordering only in one of the two spatial directions. A resonance process involving three dimers resolves this massive degeneracy and dimer smectic gets ordered (order from disorder).Comment: 20 pages, 13 figures, accepted for publication in J. Stat. Mec

Evaluation of the Northern Territory Library's Libraries and Knowledge Centres Model

Evaluation of the Northern Territory Library's model for Libraries and Knowledge Centres in Indigenous communities

(Pseudo) Random Quantum States with Binary Phase

We prove a quantum information-theoretic conjecture due to Ji, Liu and Song (CRYPTO 2018) which suggested that a uniform superposition with random \emph{binary} phase is statistically indistinguishable from a Haar random state. That is, any polynomial number of copies of the aforementioned state is within exponentially small trace distance from the same number of copies of a Haar random state. As a consequence, we get a provable elementary construction of \emph{pseudorandom} quantum states from post-quantum pseudorandom functions. Generating pseduorandom quantum states is desirable for physical applications as well as for computational tasks such as quantum money. We observe that replacing the pseudorandom function with a $(2t)$-wise independent function (either in our construction or in previous work), results in an explicit construction for \emph{quantum state $t$-designs} for all $t$. In fact, we show that the circuit complexity (in terms of both circuit size and depth) of constructing $t$-designs is bounded by that of $(2t)$-wise independent functions. Explicitly, while in prior literature $t$-designs required linear depth (for $t > 2$), this observation shows that polylogarithmic depth suffices for all $t$. We note that our constructions yield pseudorandom states and state designs with only real-valued amplitudes, which was not previously known. Furthermore, generating these states require quantum circuit of restricted form: applying one layer of Hadamard gates, followed by a sequence of Toffoli gates. This structure may be useful for efficiency and simplicity of implementation

The effectiveness of crowdsourcing in knowledge-based industries: the moderating role of transformational leadership and organisational learning

[EN] Crowdsourcing provides an opportunity for SMEs to exploit collective knowledge that is located outside the organisation. Crowdsourcing allows organisations to keep pace with a fast-changing environment by solving business problems, supporting R&D activities, and fostering innovation cheaply, flexibly, and dynamically. Nevertheless, managing crowdsourcing is difficult, and positive outcomes are not guaranteed. Drawing on the Resource-based View, we study transformational leadership and organisational learning capability as complementary assets to help SMEs deploy crowdsourcing. An empirical study of Spanish telecommunications and biotechnology companies confirmed the moderating effect of organisational learning on the relationship between crowdsourcing and organisational performance.Devece Carañana, CA.; Palacios Marqués, D.; Ribeiro-Navarrete, B. (2019). 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Geometria urbana e ilha de calor noturna : análise baseada em um modelo numérico

A geometria urbana é uma das causas do fenômeno da ilha de calor, pois provoca alteração do balanço energético nas cidades. Essa pesquisa visa identificar um raio de abrangência adequado para a determinação da influência térmica da geometria urbana. Para isso explora ferramentas de um Sistema de Informações Geográficas, aplicando um modelo numérico (o modelo de Oke), que relaciona a geometria urbana e a intensidade da ilha de calor. Dados térmicos reais são comparados a dados simulados para diferentes raios de abrangência. Os resultados apontaram que o raio de 30 m é o que em média permite maior aproximação entre dados reais e dados simulados. Além disso, verificou-se que o modelo aplicado demonstra comportamento diferenciado, conforme o grau de homogeneidade das alturas das edificações

Uma ferramenta para cálculo da máxima intensidade da ilha de calor noturna

O objetivo deste artigo é verificar a influência da geometria urbana na intensidade de ilhas de calor noturnas com uso de uma ferramenta computacional desenvolvida como extensão de um SIG. O método deste trabalho está dividido em três principais etapas: desenvolvimento da ferramenta, calibração do modelo e simulação de cenários hipotéticos com diferentes geometrias urbanas. Um modelo simplificado que relaciona as intensidades máximas de ilha de calor urbana (ICUmáx) com a geometria urbana foi incorporado à subrotina de cálculo e, posteriormente, adaptado para fornecer resultados mais aproximados à realidade de duas cidades brasileiras, as quais serviram de base para a calibração do modelo. A comparação entre dados reais e simulados mostraram uma diferença no aumento da ICUmáx em função da relação H/W e da faixa de comprimento de rugosidade (Z0). Com a ferramenta já calibrada, foi realizada uma simulação de diferentes cenários urbanos, demonstrando que o modelo simplificado original subestima valores de ICUmáx para as configurações de cânions urbanos de Z0 < 2,0 e superestima valores de ICUmáx para as configurações de cânions urbanos de Z0 ≥ 2,0. Além disso, este estudo traz como contribuição à verificação de que cânions urbanos com maiores áreas de fachadas e com alturas de edificações mais heterogêneas resultam em ICUmáx menores em relação aos cânions mais homogêneos e com maiores áreas médias ocupadas pelas edificações, para um mesmo valor de relação H/W. Essa diferença pode ser explicada pelos diferentes efeitos na turbulência dos ventos e nas áreas sombreadas provocados pela geometria urbana.The aim of this paper is to verify the influence of urban geometry in the intensity of nocturnal heat islands using a computational tool developed as an extension of a GIS. The method is divided into three main stages: development of the tool, calibration of the model, and simulation of hypothetical scenarios with different urban geometries. A simplified model that relates the maximum intensities of urban heat island (ICUmáx) with urban geometry was incorporated into the sub-routine and subsequently adapted to provide reliable results in relation to two Brazilian cities, which were the basis for the model calibration. A comparison between real and simulated data show a difference in the growth of the ICUmáx as a function of H/W ratio and of the roughness length range (Z0). With the previously calibrated tool, a simulation of different urban settings was performed, demonstrating that the original simplified model underestimates ICUmáx values for urban canyons settings of Z0 < 2,0 and overestimates ICUmáx values for urban canyons settings of Z0 ≥ 2,0. In addition, this study brings a contribution to finding that urban canyons with larger areas of facades and more heterogeneous heights of buildings result in lower ICUmáx in relation to more homogeneous canyons with highest average areas occupied by the buildings, for the same H/W ratio. This difference can be explained by the different effects on the turbulence of the wind and the shaded areas caused by urban geometry

A mobile antineutrino detector with plastic scintillators

We propose a new type segmented antineutrino detector made of plastic scintillators for the nuclear safeguard application. A small prototype was built and tested to measure background events. A satisfactory unmanned field operation of the detector system was demonstrated. Besides, a detailed Monte Carlo simulation code was developed to estimate the antineutrino detection efficiency of the detector.Comment: 23 pages, 11 figures; accepted for publication in Nuclear Instruments and Methods in Physics Research