20,547 research outputs found
Quantitative model checking of continuous-time Markov chains against timed automata specifications
We study the following problem: given a continuous-time Markov chain (CTMC) C, and a linear real-time property provided as a deterministic timed automaton (DTA) A, what is the probability of the set of paths of C that are\ud
accepted by A (C satisfies A)? It is shown that this set of paths is measurable and computing its probability can be reduced to computing the reachability probability in a piecewise deterministic Markov process (PDP). The reachability probability is characterized as the least solution of a system of integral equations and is shown to be approximated by solving a system of partial differential equations. For the special case of single-clock DTA, the system of integral equations can be transformed into a system of linear equations where the coefficients are solutions of ordinary differential equations
Mean reversion in stock index futures markets: a nonlinear analysis
Several stylized theoretical models of futures basis behavior under nonzero transactions costs predict nonlinear mean reversion of the futures basis towards its equilibrium value. Nonlinearly mean-reverting models are employed to characterize the basis of the SandP 500 and the FTSE 100 indices over the post-1987 crash period, capturing empirically these theoretical predictions and examining the view that the degree of mean reversion in the basis is a function of the size of the deviation from equilibrium. The estimated half lives of basis shocks, obtained using Monte Carlo integration methods, suggest that for smaller shocks to the basis level the basis displays substantial persistence, while for larger shocks the basis exhibits highly nonlinear mean reversion towards its equilibrium value. © 2002 Wiley Periodicals, Inc
Dynamic Ethnic Fractionalization and Economic Growth in the Transition Economies from 1989 to 2007
In their survey of the literature on ethnic fractionalization and economic performance, Alesina and La Ferrara (JEL 2005) identify two main directions for future research. One is to improve the measurement of diversity and the other to treat diversity as an endogenous variable. This paper tries to address these two issues: it investigates the effects of ethnic fractionalization on economic growth across countries using unique time-varying measures. We first replicate the finding of a weak effect of exogenous diversity on growth and then we show that accounting for how diversity changes over time and treating it as an endogenous variable makes a difference. Once diversity is instrumented (with lagged diversity and latitude), it shows a significant negative impact on economic growth which is robust to different specifications, polarization measures, econometric estimators, as well as to the use of an index of ethnic-religious-linguistic fractionalization.ethnic diversity, fractionalization, polarization, growth
Deterministic Timed Finite State Machines: Equivalence Checking and Expressive Power
There has been a growing interest in defining models of automata enriched
with time. For instance, timed automata were introduced as automata extended
with clocks. In this paper, we study models of timed finite state machines
(TFSMs), i.e., FSMs enriched with time, which accept timed input words and
generate timed output words. Here we discuss some models of TFSMs with a single
clock: TFSMs with timed guards, TFSMs with timeouts, and TFSMs with both timed
guards and timeouts. We solve the problem of equivalence checking for all three
models, and we compare their expressive power, characterizing subclasses of
TFSMs with timed guards and of TFSMs with timeouts that are equivalent to each
other.Comment: In Proceedings GandALF 2014, arXiv:1408.556
A Tamper and Leakage Resilient von Neumann Architecture
We present a universal framework for tamper and leakage resilient computation on a von
Neumann Random Access Architecture (RAM in short). The RAM has one CPU that accesses
a storage, which we call the disk. The disk is subject to leakage and tampering. So is the bus
connecting the CPU to the disk. We assume that the CPU is leakage and tamper-free. For
a fixed value of the security parameter, the CPU has constant size. Therefore the code of the
program to be executed is stored on the disk, i.e., we consider a von Neumann architecture. The
most prominent consequence of this is that the code of the program executed will be subject to
tampering.
We construct a compiler for this architecture which transforms any keyed primitive into a
RAM program where the key is encoded and stored on the disk along with the program to
evaluate the primitive on that key. Our compiler only assumes the existence of a so-called
continuous non-malleable code, and it only needs black-box access to such a code. No further
(cryptographic) assumptions are needed. This in particular means that given an information
theoretic code, the overall construction is information theoretic secure.
Although it is required that the CPU is tamper and leakage proof, its design is independent
of the actual primitive being computed and its internal storage is non-persistent, i.e., all secret
registers are reset between invocations. Hence, our result can be interpreted as reducing the
problem of shielding arbitrary complex computations to protecting a single, simple yet universal
component
Timed Runtime Monitoring for Multiparty Conversations
We propose a dynamic verification framework for protocols in real-time distributed systems. The framework is based on Scribble, a tool-chain for design and verification of choreographies based on multiparty session types, developed with our industrial partners. Drawing from recent work on multiparty session types for real-time interactions, we extend Scribble with clocks, resets, and clock predicates constraining the times in which interactions should occur. We present a timed API for Python to program distributed implementations of Scribble specifications. A dynamic verification framework ensures the safe execution of applications written with our timed API: we have implemented dedicated runtime monitors that check that each interaction occurs at a correct timing with respect to the corresponding Scribble specification. The performance of our implementation and its practicability are analysed via benchmarking
Digital integrated control of a Mach 2.5 mixed-compression supersonic inlet and an augmented mixed-flow turbofan engine
A digitally implemented integrated inlet-engine control system was designed and tested on a mixed-compression, axisymmetric, Mach 2.5, supersonic inlet with 45 percent internal supersonic area contraction and a TF30-P-3 augmented turbofan engine. The control matched engine airflow to available inlet airflow. By monitoring inlet terminal shock position and over-board bypass door command, the control adjusted engine speed so that in steady state, the shock would be at the desired location and the overboard bypass doors would be closed. During engine-induced transients, such as augmentor light-off and cutoff, the inlet operating point was momentarily changed to a more supercritical point to minimize unstarts. The digital control also provided automatic inlet restart. A variable inlet throat bleed control, based on throat Mach number, provided additional inlet stability margin
Dynamic Ethnic Fractionalization and Economic Growth
In their survey of the literature on ethnic fractionalization and economic performance, Alesina and La Ferrara (JEL 2005) identify two main directions for future research. One is to improve the measurement of diversity and the other to treat diversity as an endogenous variable. This paper tries to address these two issues. We study the effects of ethnic fractionalization on economic growth using unique time-varying measures across countries, for 26 transition economies from 1989 to 2007. Our main conclusion is that we can replicate the most recent results from the literature and show that static (exogenous) diversity is not robustly related to growth. However, when we account empirically for how ethnic diversity changes over time and treat it as an endogenous variable, our estimates show that it is negatively related to growth an effect which is robust to different estimators, specifications, and fractionalization measures. --ethnic diversity,fractionalization,polarization,growth
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