531 research outputs found
Density Profiles of Collapsed Rotating Massive Stars Favor Long Gamma-Ray Bursts
Long-duration gamma-ray bursts (lGRBs) originate in relativistic collimated
outflows -- jets -- that drill their way out of collapsing massive stars.
Accurately modeling this process requires realistic stellar profiles for the
jets to propagate through and break out of. Most previous studies have used
simple power laws or pre-collapse models for massive stars. However, the
relevant stellar profile for lGRB models is in fact that of a star after its
core has collapsed to form a compact object. To self-consistently compute such
a stellar profile, we use the open-source code GR1D to simulate the
core-collapse process for a suite of low-metallicity, rotating, massive stellar
progenitors that have undergone chemically homogeneous evolution. Our models
span a range of zero-age main sequence (ZAMS) masses: , and . All of these models, at the onset of
core-collapse, feature steep density profiles, with
, which would result in jets that are inconsistent with lGRB
observables. We follow the collapse of four out of our seven models until they
form BHs and the other three proto-neutron stars (PNSs). We find, across all
models, that the density profile outside of the newly-formed BH or PNS is
well-represented by a flatter power law with . Such
flat density profiles are conducive to successful formation and breakout of
BH-powered jets and, in fact, required to reproduce observable properties of
lGRBs. Future models of lGRBs should be initialized with shallower
\textit{post-collapse} stellar profiles like those presented here instead of
the much steeper pre-collapse profiles that are typically used.Comment: 9 pages, 4 figures+1 table, submitted to ApJL, comments welcom
Public welfare or sectarianism: A new challenge for planning
Introduction
Theoretical background
Methodology
The Haredi in Jerusalem
Kiryat-Ha'Yovel
âTerrain of interestsâ between Haredi and secular in Kiryat-Ha'Yovel
Organisation in housing
Potential for influencing planning decisions
Conclusions: failure of liberalism or all-you-can-grab planning?
Full Article Figures & data References Citations Metrics Reprints & Permissions PDF
Abstract
This article examines the weaknesses of liberal planning institutions when dealing with organised group action. The case under review, the Kiryat-Ha'Yovel neighbourhood in Jerusalem, was considered as secular for many years. In 2000 the neighbourhood became attractive to the nearby Haredi (ultra-orthodox Jews) group of the âKol-Torahâ community. Differences in lifestyle led to a collision between the group of âKol-Torahâ, who began âHaredificationâ processes to change the character of the area to be suitable to Haredim, and the veteran population, who tried to prevent it. Identifying the main engines of organised neighbourhood change and evaluating the difficulties of liberalism dealing with non-autonomous individuals in the housing market sheds light on similar processes occurring in other city centres with diverse population groups
Simple Encrypted Arithmetic Library - SEAL v2.1
Achieving fully homomorphic encryption was a longstanding open problem in cryptography until it was resolved by Gentry in 2009. Soon after, several homomorphic encryption schemes were proposed. The early homomorphic encryption schemes were extremely impractical, but recently new implementations, new data encoding techniques, and a better understanding of the applications have started to change the situation. In this paper we introduce the most recent version (v2.1) of Simple Encrypted Arithmetic Library - SEAL, a homomorphic encryption library developed by Microsoft Research, and describe some of its core functionality
The weak password problem: chaos, criticality, and encrypted p-CAPTCHAs
Vulnerabilities related to weak passwords are a pressing global economic and
security issue. We report a novel, simple, and effective approach to address
the weak password problem. Building upon chaotic dynamics, criticality at phase
transitions, CAPTCHA recognition, and computational round-off errors we design
an algorithm that strengthens security of passwords. The core idea of our
method is to split a long and secure password into two components. The first
component is memorized by the user. The second component is transformed into a
CAPTCHA image and then protected using evolution of a two-dimensional dynamical
system close to a phase transition, in such a way that standard brute-force
attacks become ineffective. We expect our approach to have wide applications
for authentication and encryption technologies.Comment: 5 pages, 6 figer
Reexamination of Quantum Bit Commitment: the Possible and the Impossible
Bit commitment protocols whose security is based on the laws of quantum
mechanics alone are generally held to be impossible. In this paper we give a
strengthened and explicit proof of this result. We extend its scope to a much
larger variety of protocols, which may have an arbitrary number of rounds, in
which both classical and quantum information is exchanged, and which may
include aborts and resets. Moreover, we do not consider the receiver to be
bound to a fixed "honest" strategy, so that "anonymous state protocols", which
were recently suggested as a possible way to beat the known no-go results are
also covered. We show that any concealing protocol allows the sender to find a
cheating strategy, which is universal in the sense that it works against any
strategy of the receiver. Moreover, if the concealing property holds only
approximately, the cheat goes undetected with a high probability, which we
explicitly estimate. The proof uses an explicit formalization of general two
party protocols, which is applicable to more general situations, and a new
estimate about the continuity of the Stinespring dilation of a general quantum
channel. The result also provides a natural characterization of protocols that
fall outside the standard setting of unlimited available technology, and thus
may allow secure bit commitment. We present a new such protocol whose security,
perhaps surprisingly, relies on decoherence in the receiver's lab.Comment: v1: 26 pages, 4 eps figures. v2: 31 pages, 5 eps figures; replaced
with published version; title changed to comply with puzzling Phys. Rev.
regulations; impossibility proof extended to protocols with infinitely many
rounds or a continuous communication tree; security proof of decoherence
monster protocol expanded; presentation clarifie
Theoretical analysis of the focusing of acoustic waves by two-dimensional sonic crystals
Motivated by a recent experiment on acoustic lenses, we perform numerical
calculations based on a multiple scattering technique to investigate the
focusing of acoustic waves with sonic crystals formed by rigid cylinders in
air. The focusing effects for crystals of various shapes are examined. The
dependance of the focusing length on the filling factor is also studied. It is
observed that both the shape and filling factor play a crucial role in
controlling the focusing. Furthermore, the robustness of the focusing against
disorders is studied. The results show that the sensitivity of the focusing
behavior depends on the strength of positional disorders. The theoretical
results compare favorably with the experimental observations, reported by
Cervera, et al. (Phys. Rev. Lett. 88, 023902 (2002)).Comment: 8 figure
A Discrete and Bounded Envy-free Cake Cutting Protocol for Four Agents
We consider the well-studied cake cutting problem in which the goal is to
identify a fair allocation based on a minimal number of queries from the
agents. The problem has attracted considerable attention within various
branches of computer science, mathematics, and economics. Although, the elegant
Selfridge-Conway envy-free protocol for three agents has been known since 1960,
it has been a major open problem for the last fifty years to obtain a bounded
envy-free protocol for more than three agents. We propose a discrete and
bounded envy-free protocol for four agents
Secure Multiparty Computation from SGX
International audienceIsolated Execution Environments (IEE) offered by novel commodity hardware such as Intel's SGX deployed in Skylake processors permit executing software in a protected environment that shields it from a malicious operating system; it also permits a remote user to obtain strong interactive attestation guarantees on both the code running in an IEE and its input/output behaviour. In this paper we show how IEEs provide a new path to constructing general secure multiparty computation (MPC) protocols. Our protocol is intuitive and elegant: it uses code within an IEE to play the role of a trusted third party (TTP), and the attestation guarantees of SGX to bootstrap secure communications between participants and the TTP. In our protocol the load of communications and computations on participants only depends on the size of each party's inputs and outputs and is thus small and independent from the intricacy of the functionality to be computed. The remaining computational load-essentially that of computing the functionality-is moved to an untrusted party running an IEE-enabled machine, an appealing feature for Cloud-based scenarios. However, as often the case even with the simplest cryptographic protocols, we found that there is a large gap between this intuitively appealing solution and a protocol with rigorous security guarantees. We bridge this gap through a comprehensive set of results that include: i. a detailed construction of a protocol for secure computation for arbitrary functionalities; ii. formal security definitions for the security of the overall protocol and that of its components; and iii. a modular security analysis of our protocol that relies on a novel notion of labeled attested computation. We implemented and extensively evaluated our solution on SGX-enabled hardware, providing detailed measurements of our protocol as well as comparisons with software-only MPC solutions. Furthermore, we show the cost induced by using constant-time, i.e., timing side channel resilient, code in our implementation
Foundations for Esports Curricula in Higher Education
Esports has generated an industry of increasing economic and cultural importance. In recent years, universities and other higher education institutions have responded to its growth by establishing programmes of study which aim to satisfy the needs of innovators operating in the area. However, there is not yet consensus on what an esports curriculum should include. Despite being a technology-driven sector with ethical and professional dimensions that intersect computing, current ACM and IEEE curricula do not mention esports. Furthermore, existing courses tend to provide teaching and training on a wide variety of topics aside from those traditionally in computer science. These include: live events management; psychological research; sports science; marketing; public relations; video (livestream) production; and community management; in addition to coaching and communication. This working group examined the requirements for developing esports studies at universities with a focus on understanding career prospects in esports and on the challenges presented by its interdisciplinary complexity. Thereby, paving the way for a framework to support the design of esports curricula in higher education
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