Reconstruction of Zeff profiles at TEXTOR through Bayasian source separation

The understanding of the behaviour of impurities is a critical issue in tokamak physics. The ion effective charge Zeff provides a measure for impurity concentration. On the TEXTOR tokamak (Julich, Germany), we run a diagnostic to determine Zeff from the bremsstrahlung emissivity E. From radial profiles of E, electron density ne and temperature Te, profiles for Zeff can be reconstructed. However, their interpretation is difficult outside the plasma centre, because of various uncertainties in E, ne and Te at the edge, which render the radial matching of the different profiles problematic. Conversely, if it were possible to obtain a set of line-integrated values for Zeff directly from the line-integrated measurements of E, ne and Te, then these problems would be avoided. Now, recent advances in the field of statistical signal processing allow the extraction of an unknown signal from a signal mixture. In particular, we describe a procedure for the single-channel Bayesian source separation of a line-integrated Zeff signal from a line-integrated emissivity source, using as a forward model a linearized version of the known functional dependence of Zeff on E, ne and Te. Here, a line-integral over a traditionally obtained Zeff profile may serve as a prior for the line-integrated Zeff signal. In this way, precise information on the electron density and temperature may even become superfluous for the determination of Zeff.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Low-Latency Short-Packet Transmissions: Fixed Length or HARQ?

We study short-packet communications, subject to latency and reliability constraints, under the premises of limited frequency diversity and no time diversity. The question addressed is whether, and when, hybrid automatic repeat request (HARQ) outperforms fixed-blocklength schemes with no feedback (FBL-NF) in such a setting. We derive an achievability bound for HARQ, under the assumption of a limited number of transmissions. The bound relies on pilot-assisted transmission to estimate the fading channel and scaled nearest-neighbor decoding at the receiver. We compare our achievability bound for HARQ to stateof-the-art achievability bounds for FBL-NF communications and show that for a given latency, reliability, number of information bits, and number of diversity branches, HARQ may significantly outperform FBL-NF. For example, for an average latency of 1 ms, a target error probability of 10^-3, 30 information bits, and 3 diversity branches, the gain in energy per bit is about 4 dB.Comment: 6 pages, 5 figures, accepted to GLOBECOM 201

Analysis of pavement condition survey data for effective implementation of a network level pavement management program for Kazakhstan

Pavement roads and transportation systems are crucial assets for promoting political stability, as well as economic and sustainable growth in developing countries. However, pavement maintenance backlogs and the high capital costs of road rehabilitation require the use of pavement evaluation tools to assure the best value of the investment. This research presents a methodology for analyzing the collected pavement data for the implementation of a network level pavement management program in Kazakhstan. This methodology, which could also be suitable in other developing countries’ road networks, focuses on the survey data processing to determine cost-effective maintenance treatments for each road section. The proposed methodology aims to support a decision-making process for the application of a strategic level business planning analysis, by extracting information from the survey data

Punctured Haag duality in locally covariant quantum field theories

We investigate a new property of nets of local algebras over 4-dimensional globally hyperbolic spacetimes, called punctured Haag duality. This property consists in the usual Haag duality for the restriction of the net to the causal complement of a point $p$ of the spacetime. Punctured Haag duality implies Haag duality and local definiteness. Our main result is that, if the theory is locally covariant in the sense of Brunetti, Fredenhagen and Verch, then also the converse holds. The free Klein-Gordon field provides an example in which this property is verified.Comment: Accepted for publication in Commun. Math. Phy

Blockchain Inefficiency in the Bitcoin Peers Network

We investigate Bitcoin network monitoring the dynamics of blocks and transactions. We unveil that 43\% of the transactions are still not included in the Blockchain after 1h from the first time they were seen in the network and 20\% of the transactions are still not included in the Blockchain after 30 days, revealing therefore great inefficiency in the Bitcoin system. However, we observe that most of these `forgotten' transactions have low values and in terms of transferred value the system is less inefficient with 93\% of the transactions value being included into the Blockchain within 3h. The fact that a sizeable fraction of transactions is not processed timely casts serious doubts on the usability of the Bitcoin Blockchain for reliable time-stamping purposes and calls for a debate about the right systems of incentives which a peer-to-peer unintermediated system should introduce to promote efficient transaction recording.Comment: 15 pages, 8 figures, 3 table

Development of a HGV FEM for road safety analysis

In the last years roadside safety design, in particular for passive systems, was greatly improved with the possibility to use computational mechanics. Computational mechanics is based on the use of complex finite element codes, that allows the virtual reproduction of real world problems. Regarding roadside safety, the design phase was, until now, based on the use of simplified analysis, unable to describe accurately the complexity of vehicle impacts against safety hardware. To build a FE model for an impact problem many elements are necessary: • Model geometry. • Constitutive laws of the materials. • Links (rigid, cinematic, etc.) between bodies or part of them. • Definition and characterization of contact surfaces. This set of information is needed for each different body involved in the event; making the development of a complete model very much demanding, but once a part (subset) of the entire model has been accurately validated by the comparison with real experimental data, it can be used again and again in other analogous models. Our goal was to build and validate a FE model of a Heavy Goods Vehicle (HGV). We chose this kind of vehicle because it wasn't available and because it was useful to test the containment of the barriers, and to study the dynamic interactions between vehicle and road pavement. In particular, this vehicle can be used to test the safety barriers according to EN 1317 standard, for the H4a class of containment. It reproduces a FIAT-IVECO F180 truck, a vehicle with 4 axles and a mass of 10.5 ton (30 with the full load). The model (12337 elements and 11470 nodes) was built for and is ready to use with LS Dyna FE code from Livermore Software Technology Corporation

Capacity bounds for MIMO microwave backhaul links affected by phase noise

We present bounds and a closed-form high-SNR expression for the capacity of multiple-antenna systems affected by Wiener phase noise. Our results are developed for the scenario where a single oscillator drives all the radio-frequency circuitries at each transceiver (common oscillator setup), the input signal is subject to a peak-power constraint, and the channel matrix is deterministic. This scenario is relevant for line-of-sight multiple-antenna microwave backhaul links with sufficiently small antenna spacing at the transceivers. For the 2 by 2 multiple-antenna case, for a Wiener phase-noise process with standard deviation equal to 6 degrees, and at the medium/high SNR values at which microwave backhaul links operate, the upper bound reported in the paper exhibits a 3 dB gap from a lower bound obtained using 64-QAM. Furthermore, in this SNR regime the closed-form high-SNR expression is shown to be accurate.Comment: 10 pages, 2 figures, to appear in IEEE Transactions on Communication

Reliable Transmission of Short Packets through Queues and Noisy Channels under Latency and Peak-Age Violation Guarantees

This work investigates the probability that the delay and the peak-age of information exceed a desired threshold in a point-to-point communication system with short information packets. The packets are generated according to a stationary memoryless Bernoulli process, placed in a single-server queue and then transmitted over a wireless channel. A variable-length stop-feedback coding scheme---a general strategy that encompasses simple automatic repetition request (ARQ) and more sophisticated hybrid ARQ techniques as special cases---is used by the transmitter to convey the information packets to the receiver. By leveraging finite-blocklength results, the delay violation and the peak-age violation probabilities are characterized without resorting to approximations based on large-deviation theory as in previous literature. Numerical results illuminate the dependence of delay and peak-age violation probability on system parameters such as the frame size and the undetected error probability, and on the chosen packet-management policy. The guidelines provided by our analysis are particularly useful for the design of low-latency ultra-reliable communication systems.Comment: To appear in IEEE journal on selected areas of communication (IEEE JSAC