99,296 research outputs found
Security Analysis of Separation Kernels Specifications and a Framework for the Verification of Concurrent Implementations
Due to the new trend of integrating safe and secure
functionalities into one separation kernel, security analysis of ARINC
653 as well as a formal specification with security proofs are thus
significant for the development and certification of Separation Kernels
(SKs). In this talk we present a specification development and security
analysis method for ARINC SKs based on refinement. We present a security
model for event-based non-Interference and a stepwise refinement
framework that will allow us to check security on sequential SKs
specifications. Moreover to be able to reason on SKs implementations
running on top of multi-core architectures it is essential to deal with
the interference of the environment between SKs instances running on
different cores. Concurrent program reasoning techniques such as
rely-guarantee can be leveraged to reason on multi-core SKs
implementations. However the source code of the programs to be verified
often involves language features such as exceptions and procedures which
are not supported by the existing mechanizations of those concurrent
reasoning techniques. CSimpl, is a rich specification language with
concurrency-oriented language features and verification techniques that
will allow reasoning on multi-core SKs implementations.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Broadening the scope of weak quantum measurements I: A single particle accurately measured yet left superposed
Weak measurement is unique in enabling measurements of non-commuting
operators as well as otherwise-undetectable peculiar phenomena predicted by the
Two-State-Vector-Formalism (TSVF). This article, the first in two parts,
explores novel applications of weak measurement. We first revisit the basic
principles of quantum measurement with the aid of the Michelson interferometer.
Weak measurement is then introduced in a simple visualized manner by a specific
choice of the reflecting mirror's position and momentum uncertainties. Having
introduced the method, we proceed to its refinement for a single particle. We
consider a photon going back and forth inside the interferometer, oscillating
between a superposed and a localized state, while subjected to alternating
strong and weak measurements. This cyclic process enables directly measuring
both the photon's position ("which-path") and momentum (interference), without
disturbing either. An alternative explanation of this result, not invoking weak
values, is thoroughly considered and shown to be at odds with the experimental
data. Finally a practical application of this experiment is demonstrated, where
a single photon measures the various transmission coefficients of a multiport
beam-splitter yet remains superposed. This method is then generalized to
measurement of the wave-function itself, performed again on a single particle.Comment: 20 pages, 5 figures. Submitted to Physical Review
1-Bit Massive MIMO Downlink Based on Constructive Interference
In this paper, we focus on the multiuser massive multiple-input single-output
(MISO) downlink with low-cost 1-bit digital-to-analog converters (DACs) for PSK
modulation, and propose a low-complexity refinement process that is applicable
to any existing 1-bit precoding approaches based on the constructive
interference (CI) formulation. With the decomposition of the signals along the
detection thresholds, we first formulate a simple symbol-scaling method as the
performance metric. The low-complexity refinement approach is subsequently
introduced, where we aim to improve the introduced symbol-scaling performance
metric by modifying the transmit signal on one antenna at a time. Numerical
results validate the effectiveness of the proposed refinement method on
existing approaches for massive MIMO with 1-bit DACs, and the performance
improvements are most significant for the low-complexity quantized zero-forcing
(ZF) method.Comment: 5 pages, EUSIPCO 201
Some Challenges of Specifying Concurrent Program Components
The purpose of this paper is to address some of the challenges of formally
specifying components of shared-memory concurrent programs. The focus is to
provide an abstract specification of a component that is suitable for use both
by clients of the component and as a starting point for refinement to an
implementation of the component. We present some approaches to devising
specifications, investigating different forms suitable for different contexts.
We examine handling atomicity of access to data structures, blocking operations
and progress properties, and transactional operations that may fail and need to
be retried.Comment: In Proceedings Refine 2018, arXiv:1810.0873
Source Broadcasting to the Masses: Separation has a Bounded Loss
This work discusses the source broadcasting problem, i.e. transmitting a
source to many receivers via a broadcast channel. The optimal rate-distortion
region for this problem is unknown. The separation approach divides the problem
into two complementary problems: source successive refinement and broadcast
channel transmission. We provide bounds on the loss incorporated by applying
time-sharing and separation in source broadcasting. If the broadcast channel is
degraded, it turns out that separation-based time-sharing achieves at least a
factor of the joint source-channel optimal rate, and this factor has a positive
limit even if the number of receivers increases to infinity. For the AWGN
broadcast channel a better bound is introduced, implying that all achievable
joint source-channel schemes have a rate within one bit of the separation-based
achievable rate region for two receivers, or within bits for
receivers
Simplifying proofs of linearisability using layers of abstraction
Linearisability has become the standard correctness criterion for concurrent
data structures, ensuring that every history of invocations and responses of
concurrent operations has a matching sequential history. Existing proofs of
linearisability require one to identify so-called linearisation points within
the operations under consideration, which are atomic statements whose execution
causes the effect of an operation to be felt. However, identification of
linearisation points is a non-trivial task, requiring a high degree of
expertise. For sophisticated algorithms such as Heller et al's lazy set, it
even is possible for an operation to be linearised by the concurrent execution
of a statement outside the operation being verified. This paper proposes an
alternative method for verifying linearisability that does not require
identification of linearisation points. Instead, using an interval-based logic,
we show that every behaviour of each concrete operation over any interval is a
possible behaviour of a corresponding abstraction that executes with
coarse-grained atomicity. This approach is applied to Heller et al's lazy set
to show that verification of linearisability is possible without having to
consider linearisation points within the program code
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