9,397 research outputs found

    Cycling Through the Pandemic : Tactical Urbanism and the Implementation of Pop-Up Bike Lanes in the Time of COVID-19

    Get PDF
    Provides an international overview on how tactical urbanism was implemented to give more space to cycling Demonstrates the conceptual framework surrounding tactical urbanism and how it plays out theoretically Proposes new methodological insights to understand the effects of tactical urbanism intervention

    A study of BPS and near-BPS black holes via AdS/CFT

    Get PDF
    In the settings of various AdS/CFT dual pairs, we use results from supersymmetric localiza tion to gain insights into the physics of asymptotically-AdS, BPS black holes in 5 dimensions, and near-BPS black holes in 4 dimensions. We first begin with BPS black holes embedded in the known examples of AdS5/CFT4 dualities. Using the Bethe Ansatz formulation, we compute the superconformal index at large N with arbitrary chemical potentials for all charges and angular momenta, for general N = 1 four-dimensional conformal theories with a holographic dual. We conjecture and bring some evidence that a particular universal contribution to the sum over Bethe vacua dominates the index at large N. For N = 4 SYM, this contribution correctly leads to the entropy of BPS Kerr-Newman black holes in AdS5 × S 5 for arbitrary values of the conserved charges, thus completing the microscopic derivation of their microstates. We also consider theories dual to AdS5 × SE5, where SE5 is a Sasaki-Einstein manifold. We first check our results against the so-called universal black hole. We then explicitly construct the near-horizon geometry of BPS Kerr-Newman black holes in AdS5 × T 1,1 , charged under the baryonic symmetry of the conifold theory and with equal angular momenta. We compute the entropy of these black holes using the attractor mechanism and find complete agreement with field theory predictions. Next, we consider the 3d Chern-Simons matter theory that is holographically dual to massive Type IIA string theory on AdS4 × S 6 . By Kaluza-Klein reducing on S 2 with a background that is dual to the asymptotics of static dyonic BPS black holes in AdS4, we construct a N = 2 supersymmetric gauged quantum mechanics whose ground-state degener acy reproduces the entropy of BPS black holes. We expect its low-lying spectrum to contain information about near-extremal horizons. Interestingly, the model has a large number of statistically-distributed couplings, reminiscent of SYK models

    Uniform hyperbolicity of a class of scattering maps

    Full text link
    In recent years fractal Weyl laws and related quantum eigenfunction hypothesis have been studied in a plethora of numerical model systems, called quantum maps. In some models studied there one can easily prove uniform hyperbolicity. Yet, a numerically sound method for computing quantum resonance states, did not exist. To address this challenge, we recently introduced a new class of quantum maps. For these quantum maps, we showed that, quantum resonance states can numerically be computed using theoretically grounded methods such as complex scaling or weak absorbing potentials. However, proving uniform hyperbolicty for this class of quantum maps was not straight forward. Going beyond that work this article generalizes the class of scattering maps and provides mathematical proofs for their uniform hyperbolicity. In particular, we show that the suggested class of two-dimensional symplectic scattering maps satisfies the topological horseshoe condition and uniform hyperbolicity. In order to prove these properties, we follow the procedure developed in the paper by Devaney and Nitecki. Specifically, uniform hyperbolicity is shown by identifying a proper region in which the non-wandering set satisfies a sufficient condition to have the so-called sector bundle or cone field. Since no quantum map is known where both a proof of uniform hyperbolicity and a methodologically sound method for numerically computing quantum resonance states exist simultaneously, the present result should be valuable to further test fractal Weyl laws and related topics such as chaotic eigenfunction hypothesis.Comment: 50 pages, 23 figure

    Benchmarking highly entangled states on a 60-atom analog quantum simulator

    Full text link
    Quantum systems have entered a competitive regime where classical computers must make approximations to represent highly entangled quantum states. However, in this beyond-classically-exact regime, fidelity comparisons between quantum and classical systems have so far been limited to digital quantum devices, and it remains unsolved how to estimate the actual entanglement content of experiments. Here we perform fidelity benchmarking and mixed-state entanglement estimation with a 60-atom analog Rydberg quantum simulator, reaching a high entanglement entropy regime where exact classical simulation becomes impractical. Our benchmarking protocol involves extrapolation from comparisons against many approximate classical algorithms with varying entanglement limits. We then develop and demonstrate an estimator of the experimental mixed-state entanglement, finding our experiment is competitive with state-of-the-art digital quantum devices performing random circuit evolution. Finally, we compare the experimental fidelity against that achieved by various approximate classical algorithms, and find that only one, which we introduce here, is able to keep pace with the experiment on the classical hardware we employ. Our results enable a new paradigm for evaluating the performance of both analog and digital quantum devices in the beyond-classically-exact regime, and highlight the evolving divide between quantum and classical systems.Comment: ALS, ZC, and JC contributed equall

    Tradition and Innovation in Construction Project Management

    Get PDF
    This book is a reprint of the Special Issue 'Tradition and Innovation in Construction Project Management' that was published in the journal Buildings

    Exact Thermodynamics and Transport in the Classical Sine-Gordon Model

    Full text link
    We revisit the exact thermodynamic description of the classical sine-Gordon field theory, a notorious integrable model. We found that existing results in the literature based on the soliton-gas picture did not correctly take into account light, but extended, solitons and thus led to incorrect results. This issue is regularized upon requantization: we derive the correct thermodynamics by taking the semiclassical limit of the quantum model. Our results are then extended to transport settings by means of Generalized Hydrodynamics.Comment: 33 pages, 4 figure

    Fermion masses, critical behavior and universality

    Full text link
    We look for signals of critical behavior in the Yukawa sector. By reviewing a set of models for the fermion masses, we select those where a symmetry-breaking order parameter sits at a transition point between a disordered phase and an ordered one. Many models based on ordinary flavor symmetries are formulated in terms of small corrections to a symmetric limit, which can hardly be interpreted unambiguously as a sign of near-criticality. Different is the case of nonlinearly realized flavor symmetries when the system is always in the broken phase. By inspecting a large number of modular and CP invariant models of lepton masses, we find that most of them cluster around the fixed point τ=i\tau= i, where the system enjoys enhanced symmetry. Since a priori all values of the modulus τ\tau are equally acceptable to describe the fermion spectrum, we regard this preference as a hint of near-criticality. We analyze in detail these models in the vicinity of all fixed points, showing that only one possibility provides a good description of neutrino masses and mixing angles. Near the fixed points the models exhibit a universal behavior. Mass ratios and mixing angles scale with appropriate powers of the order parameter, independently of the details of the theory, a feature reminiscent of systems belonging to the same universality class in second-order phase transitions. The observations of this work are inspired by the role near-criticality might play in solving the naturalness problem and are motivated by the fascinating possibility that most of the free parameters of the Standard Model could find a common explanation

    Breastfeeding, motherhood and employment: the experience of breastfeeding mothers returning to work in Qatar

    Get PDF
    Participation of women in employment in Qatar has increased significantly over the past 10 years, from 12.4% in 2011 to 37% in 2020, with 64.1% of working women also being married (Planning and Statistics Authority, Qatar). Their professional commitments notwithstanding, most of these women are also mothers, with many breastfeeding. The Quran demands that mothers breastfeed their children for the first two years of their lives. This thesis explores this tension between a rapid increase in mothers entering the labour market, and the specific historic, cultural and religious expectations upon mothers in Qatar, which create challenges for mothers, employers and policy makers that are different from those of working mothers in the Global North and need further consideration. This thesis employed a qualitative research methodology in which a total of 50 breastfeeding, professional, working mothers in the public and private sectors of Qatar were interviewed. The thesis adopts a multifaceted theoretical framing. First, matricentric feminism (O’Reilly, 2016) and Hay’s concept of intensive mothering are considered in terms of their applicability, and expanded upon in seeking to make sense of the tensions and challenges the women experienced as they returned to work following birth and a relatively short maternity leave of only 50 and 60 days, in the private and public sectors respectively, within this particular context in the Global South. Second, the theory of the gendered institution, as proposed by Acker in 1990, posits that breastfeeding mothers cannot embody the ‘ideal worker’ construct due to considerations such as the roles they can handle, interpersonal interactions, self-efficacy, and culture. Third, under maternal bodies at work theory by Gatrell, Cooper and Kossek's (2017), breastfeeding mothers are perceived as social pollutants. According to this theory, women's experiences are influenced by the perspective that maternal bodies belong in the private sphere and that their presence in the workplace is repugnant to other workers. Finally, the experiences of breastfeeding women are analysed from the perspective of their embeddedness in multiple layers of contexts, in line with the theorisation of Lewis and Den Dulk (2008). There are four layers of contexts taken into account the global, national/regional and institutional layers. Under this theoretical position, the thesis appreciates the reality that different factors interact to produce magnified or suppressed effects. Through the lens of this multifaceted theoretical framework, the findings from the interviews are analysed through thematic analysis.This thesis therefore significantly contributes to the literature on working mothers through its location in an Islamic country, and through its orientation and exploration of the significance of the religious context at the intersection of gender and employment in particular, which remains underexplored. The findings show how the mothers’ return to work is complicated by the ways in which employment policies on pregnancy, maternity and breastfeeding are not aligned with Islamic doctrine on what is expected of women seeking to conform to ideas of being a ‘good Muslim mother’ In line with matricentric feminism, the findings show that Qatari women have displayed increased propensity to seek opportunities under professional employment as a way of advancing their interests as women and mothers, while also taking care of their families. The participation of women in the workplace has magnified the effects of intensive mothering, whereby women are expected to pursue professional acheivements in the workplace, while also being a good mother in accordance with the guidelines by Islam. These guidelines impose two years breastfeeding period after the birth of a baby, in addition to other domestic responsibilities. However, the novel work-related responsibilities have made fulfilling this mandate challenging for these women. The limitations arise from circumstances that can be explained through elements of the gendered organisation since most workplaces are not set up to facilitate breastfeeding. Similarly, women are found not to fit the ‘ideal worker’ image, thus limiting the extent to which they can exercise agency. It is also apparent from the resrach findings that the maternal body of the Qatari breastfeeding women in the study is perceived as a pollutant and repugnant in most workplaces and public spaces. While providing breastfeeding facilities in the workplace and accommodating breastfeeding activities could solve some of these challenges, most of the workplaces where the women interviewed work have not taken such measures. Finally, there is evidence that most breastfeeding mothers' experiences can be linked to multiple factors based on layers of contexts, starting with the global, national/regional and finally at the institutional level. The effects of the failure by Qatar to ratify the Maternity Protection Convention, 2000 (No. 183) has played a role in subsequent actions such as the provision of insufficient leave days. Furthermore, institutions have not been mandated to accommodate the interests of breastfeeding mothers by providing the necessary facilities, such as private rooms for breastfeeding or for the expression of milk. These circumstances function to cause and magnify the challenges that breastfeeding mothers experience in practice upon their return to work. It also highlights the different ways they sought to overcome these challenges. It highlights how women in Qatar find themselves in a situation in which they are compelled to adhere to religious guidelines and organisational policies that are in conflict with each other. The implications of these findings for theory, policy and practice are explored from a feminist perspective in the final discussion and conclusion. The proposal for policy changes focus on adjustments to the limited maternal leave days to provide breastfeeding mothers with more time to take care of the infant. Changes to Human Rresources policies in the workplace such as job-sharing can also provide stop-gap measures to accommodate the interests of breastfeeding mothers. For practice, it is necessary for a multi-stakeholders and multi-sector approach to developing solutions to the challenges that contribute to the negative experiences of Qatari mothers who breastfeed at work
    corecore