Effect of initial conditions on the speed of reaction-diffusion fronts

The effect of initial conditions on the speed of propagating fronts in reaction-diffusion equations is examined in the framework of the Hamilton-Jacobi theory. We study the transition between quenched and nonquenched fronts both analytically and numerically for parabolic and hyperbolic reaction diffusion. Nonhomogeneous media are also analyzed and the effect of algebraic initial conditions is also discussed

Speed of reaction-diffusion fronts in spatially heterogeneous media

The front speed problem for nonuniform reaction rate and diffusion coefficient is studied by using singular perturbation analysis, the geometric approach of Hamilton-Jacobi dynamics, and the local speed approach. Exact and perturbed expressions for the front speed are obtained in the limit of large times. For linear and fractal heterogeneities, the analytic results have been compared with numerical results exhibiting a good agreement. Finally we reach a general expression for the speed of the front in the case of smooth and weak heterogeneities

What is the value of joint processing of pilots and data in block-fading channels?

The spectral efficiency achievable with joint processing of pilot and data symbol observations is compared with that achievable through the conventional (separate) approach of first estimating the channel on the basis of the pilot symbols alone, and subsequently detecting the datasymbols. Studied on the basis of a mutual information lower bound, joint processing is found to provide a non-negligible advantage relative to separate processing, particularly for fast fading. It is shown that, regardless of the fading rate, only a very small number of pilot symbols (at most one per transmit antenna and per channel coherence interval) shouldbe transmitted if joint processing is allowed.

Calculation of radio electrical coverage in Medium-Wave Frequencies

The aim of this project is to accomplish an application software based on Matlab to calculate the radioelectrical coverage by surface wave of broadcast radiostations in the band of Medium Wave (WM) all around the world. Also, given the location of a transmitting and a receiving station, the software should be able to calculate the electric field that the receiver should receive at that specific site. In case of several transmitters, the program should search for the existence of Inter-Symbol Interference, and calculate the field strenght accordingly. The application should ask for the configuration parameters of the transmitter radiostation within a Graphical User Interface (GUI), and bring back the resulting coverage above a map of the area under study. For the development of this project, it has been used several conductivity databases of different countries, and a high-resolution elevation database (GLOBE). Also, to calculate the field strenght due to groundwave propagation, it has been used ITU GRWAVE program, which must be integrated into a Matlab interface to be used by the application developed.

DOI: The "Big Brother" in the dissemination of scientific documentation

Rapid growth in the availability and use of digital documents has prompted the development of instruments to handle them. A most important example of these instruments are digital identifiers, which provide a codification system that allows digital items, usually up to the level of a computer file, to be singled out and located. Digital identifiers make up standardized global systems applied to specific products or areas. They are part of the very many identifiers developed to handle large numbers of items and large amounts of information for transactional purposes, which often have a global span. Digital identifiers include the ubiquitous Global Trade Item Number (GTIN), a code that unequivocally identifies trade items all around the world. The GTIN can take on several configurations depending on its application. These include: EAN-13, EAN-8, EAN-14, and UCC-12. EAN-13 is the code used for retail products in order to facilitate trade at the point of sale; its widely known symbol or graphical form is the EAN/UPC-13 bar code...

Non-constant discounting in finite horizon: The free terminal time case

This paper derives the HJB (Hamilton-Jacobi-Bellman) equation for sophisticated agents in a finite horizon dynamic optimization problem with non-constant discounting in a continuous setting, by using a dynamic programming approach. A simple example is used in order to illustrate the applicability of this HJB equation, by suggesting a method for constructing the subgame perfect equilibrium solution to the problem.Conditions for the observational equivalence with an associated problem with constantdiscounting are analyzed. Special attention is paid to the case of free terminal time. Strotz¿s model (an eating cake problem of a nonrenewable resource with non-constant discounting) is revisited.

Optimal strategies for sending information through a quantum channel

Quantum states can be used to encode the information contained in a direction, i.e., in a unit vector. We present the best encoding procedure when the quantum state is made up of N spins (qubits). We find that the quality of this optimal procedure, which we quantify in terms of the fidelity, depends solely on the dimension of the encoding space. We also investigate the use of spatial rotations on a quantum state, which provide a natural and less demanding encoding. In this case we prove that the fidelity is directly related to the largest zeros of the Legendre and Jacobi polynomials. We also discuss our results in terms of the information gain.

La ciència del bé i del mal en El jardí simbòlic

Chapter 21 of the Byzantine work known as The Symbolic Garden refers to an unidentified plant (the smilax) which symbolizes science. The author has taken this symbol from patristic literature (Athanasius of Alexandria and other patristic texts). On the other hand, a passage (p. 71, 17- 73, 1) unti1 now misinterpreted can be understood if confronted with severa1 texts by John Darnascenus and Nicetas Stethatos, who both voice the same opinions about science

Oscar Wilde. 'Camma', a severe and hedonic aesthetic correction of Plutarch's ethics

The aim of this article is to present an accurate analysis of O. Wilde's poem 'Camma' by referring it to its Greek model: that Camma both in Plutarch's Amatorius (Eroticus) and Mulierum Virtutes. It is precisely this accurate reading which permits us to verify how Plutarch's Ethics is corrected from the parameters of the hedonism which is peculiar to O. Wilde's aestheticism, thus turning Camma into a symbol of a pleasant life.

Classical predictive electrodynamics of two charges with radiation: Energy and 3. momentum balance and scattering crossections-II

We deal with a classical predictive mechanical system of two spinless charges where radiation is considered and there are no external fields. The terms (2,2)Paa of the expansion in the charges of the HamiltonJacobi momenta are calculated. Using these, together with known previous results, we can obtain the paa up to the fourth order. Then we have calculated the radiated energy and the 3-momentum in a scattering process as functions of the impact parameter and the incident energy for the former and 3-momentum for the latter. Scattering cross-sections are also calculated. Good agreement with well known results, including those of quantum electrodynamics, has been found.

De llibertat, autoritat i in/dependències (a la vida i l'obra de Maria-Mercè Marçal)

This article pays attention to two moments in the life and work (inseparably united) of Maria-Mercè Marçal. The first refers to a search of small objects presided by the moon. Taking this search as a motif, the freedom which the poet confers to the nocturnal light ¿mythical and magical symbol of femaleness- and, therefore, to that which symbolises the heavenly body, is revealed. The second moment revolves around the reflection of Marçal on the ¿female authority¿, a concept which this author, inspired by the philosophical community of Diotima, distinguishes from power. Throughout history, Maria-Mercè Marçal remarked, many women have gained strength from the free atribution of authority to other women, to their texts, to their experiences.

Non-constant discounting in finite horizon: The free terminal time case

This paper derives the HJB (Hamilton-Jacobi-Bellman) equation for sophisticated agents in a finite horizon dynamic optimization problem with non-constant discounting in a continuous setting, by using a dynamic programming approach. A simple example is used in order to illustrate the applicability of this HJB equation, by suggesting a method for constructing the subgame perfect equilibrium solution to the problem.Conditions for the observational equivalence with an associated problem with constantdiscounting are analyzed. Special attention is paid to the case of free terminal time. Strotz¿s model (an eating cake problem of a nonrenewable resource with non-constant discounting) is revisited.

De llibertat, autoritat i in/dependències (a la vida i l'obra de Maria-Mercè Marçal)

This article pays attention to two moments in the life and work (inseparably united) of Maria-Mercè Marçal. The first refers to a search of small objects presided by the moon. Taking this search as a motif, the freedom which the poet confers to the nocturnal light ¿mythical and magical symbol of femaleness- and, therefore, to that which symbolises the heavenly body, is revealed. The second moment revolves around the reflection of Marçal on the ¿female authority¿, a concept which this author, inspired by the philosophical community of Diotima, distinguishes from power. Throughout history, Maria-Mercè Marçal remarked, many women have gained strength from the free atribution of authority to other women, to their texts, to their experiences.

ML approaches to channel estimation for pilot-aided multi-rate DS/CDMA systems

This paper analyzes the asymptotic performance of maximum likelihood (ML) channel estimation algorithms in wideband code division multiple access (WCDMA) scenarios. We concentrate on systems with periodic spreading sequences (period larger than or equal to the symbol span) where the transmitted signal contains a code division multiplexed pilot for channel estimation purposes. First, the asymptotic covariances of the training-only, semi-blind conditional maximum likelihood (CML) and semi-blind Gaussian maximum likelihood (GML) channelestimators are derived. Then, these formulas are further simplified assuming randomized spreading and training sequences under the approximation of high spreading factors and high number of codes. The results provide a useful tool to describe the performance of the channel estimators as a function of basicsystem parameters such as number of codes, spreading factors, or traffic to training power ratio.

Waveform-independent frame-timing acquisition for UWB signals

In this paper, the problem of frame-level symboltiming acquisition for UWB signals is addressed. The main goalis the derivation of a frame-level timing estimator which does notrequire any prior knowledge of neither the transmitted symbolsnor the received template waveform. The independence withrespect to the received waveform is of special interest in UWBcommunication systems, where a fast and accurate estimation ofthe end-to-end channel response is a challenging and computationallydemanding task. The proposed estimator is derived under theunconditional maximum likelihood criterion, and because of thelow power of UWB signals, the low-SNR assumption is adopted. Asa result, an optimal frame-level timing estimator is derived whichoutperforms existing acquisition methods in low-SNR scenarios.