Two-step phase changes in cubic relaxor ferroelectrics

The field-driven conversion between the zero-field-cooled frozen relaxor state and a ferroelectric state of several cubic relaxors is found to occur in at least two distinct steps, after a period of creep, as a function of time. The relaxation of this state back to a relaxor state under warming in zero field also occurs via two or more sharp steps, in contrast to a one-step relaxation of the ferroelectric state formed by field-cooling. An intermediate state can be trapped by interrupting the polarization. Giant pyroelectric noise appears in some of the non-equilibrium regimes. It is suggested that two coupled types of order, one ferroelectric and the other glassy, may be required to account for these data.Comment: 27 pages with 8 figures to appear in Phys. Rev.

Performance evaluation in competitive REE models

Our basic premise is that fund managers performance is related to superior information about an asset payoff. We investigate the relationship between managerial skills and trading behavior within a two-period rational expectation equilibrium (REE) model where agents trade on private information in the first round, while a public signal arrives at the second date that makes traders revise their beliefs and retrade. The public signal can be related to the asset payoff, or to variables not related to fundamentals (noise), or both. We characterize the unique partially revealing REE and explore the drivers of price dynamics and trading behavior. Our main prediction is that good managers are contrarian traders, while bad managers are momentum traders when public news arrive to the market. Furthermore, the change in holdings of each type of trader is monotonic on the traders' skills. Based on these predictions, we propose new performance evaluation measures that rely on the manager's change in holdings around the arrival of public news rather than his past performance. A byproduct of our analysis is the proposal of a new protocol for performance evaluation and Due Diligence (DD) procedures.REE; performance evaluation; mutual fund; hedge funds; talent; informed traders; due diligence

Cluster-induced crater formation

Using molecular-dynamics simulation, we study the crater volumes induced by energetic impacts ($v= 1- 250$ km/s) of projectiles containing up to N=1000 atoms. We find that for Lennard-Jones bonded material the crater volume depends solely on the total impact energy $E$. Above a threshold \Eth, the volume rises linearly with $E$. Similar results are obtained for metallic materials. By scaling the impact energy $E$ to the target cohesive energy $U$, the crater volumes become independent of the target material. To a first approximation, the crater volume increases in proportion with the available scaled energy, $V=aE/U$. The proportionality factor $a$ is termed the cratering efficiency and assumes values of around 0.5.Comment: 9 page

Aging in the Relaxor Ferroelectric PMN/PT

The relaxor ferroelectric (PbMn$_{1/3}$Nb$_{2/3}$O$_3$)$_{1-x}$(PbTiO$_3$)$_{x}$, $x=0.1$, (PMN/PT(90/10)) is found to exhibit several regimes of complicated aging behavior. Just below the susceptibility peak there is a regime exhibiting rejuvenation but little memory. At lower temperature, there is a regime with mainly cumulative aging, expected for simple domain-growth. At still lower temperature, there is a regime with both rejuvenation and memory, reminiscent of spin glasses. PMN/PT (88/12) is also found to exhibit some of these aging regimes. This qualitative aging behavior is reminiscent of that seen in reentrant ferromagnets, which exhibit a crossover from a domain-growth ferromagnetic regime into a reentrant spin glass regime at lower temperatures. These striking parallels suggest a picture of competition in PMN/PT (90/10) between ferroelectric correlations formed in the domain-growth regime with glassy correlations formed in the spin glass regime. PMN/PT (90/10) is also found to exhibit frequency-aging time scaling of the time-dependent part of the out-of-phase susceptibility for temperatures 260 K and below. The stability of aging effects to thermal cycles and field perturbations is also reported.Comment: 8 pages RevTeX4, 11 figures; submitted to Phys. Rev.

steam turbine control valve and actuation system modeling for dynamics analysis

Abstract The paper describes a study conducted on Steam Turbine control valve and actuation systems, which rule the machine final power production and rotational speed. A dynamic model developed in the Matlab/Simulink environment is proposed to support the analysis of the operational stability of the hydro-mechanical system as well as the failure modes that it may face during operation. The model was validated through specific field tests conducted on the actuation system at a cogeneration plant in Nuovo Pignone, Florence. The proposed work also underlines the requirements that new actuation technologies should fulfil in order to meet control valve system performance criteria

Reply to Comment on "Quantum dense key distribution"

In this Reply we propose a modified security proof of the Quantum Dense Key Distribution protocol detecting also the eavesdropping attack proposed by Wojcik in his Comment.Comment: To appear on PRA with minor change

Does the thermal spike affect low-energy ion-induced interfacial mixing?

Molecular dynamics simulations have been used to obtain the three-dimensional distribution of interfacial mixing and cascade defects in Ti/Pt multilayer system due to single 1 keV $Ar^+$ impacts at grazing angle of incidence. The Ti/Pt system was chosen because of its relatively high heat of mixing in the binary alloy and therefore a suitable candidate for testing the effect of heat of mixing on ion-beam mixing. However, the calculated mixing profile is not sensitive to the heat of mixing. Therefore the thermal spike model of mixing is not fully supported under these irradiation conditions. Instead we found that the majority of mixing occurs after the thermal spike during the relaxation process. These conclusions are supported by liquid, vacancy as well as adatom analysis. The interfacial mixing is in various aspects anomalous in this system: the time evolution of mixing is leading to a phase delay for Ti mixing, and Pt exhibits an unexpected double peaked mixing evolution. The reasons to these effects are discussed.Comment: 7 pages, 12 figures, Nucl. Instr. Meth. B211, 524. (2003

Neural network based prediction of roughing and finishing times in a hot strip mill

The paper presents a model based on neural networks which is able to predict the time required to pass the different gauges of a roughing and finishing mill as function of some slab features and process parameters. The final aim of the work is to increase the rolling efficiency while avoiding collisions and queues that cause time and energy losses. Neural networks are suitable to this prediction task as they are particularly able to cope with unknown non linear relationships between input and output variables. Moreover they can learn from real industrial data and therefore do not require prior assumptions or mathematical modelling of the process and transferability is ensured by the possibility to use different databases coming from different rolling mills. In the paper, two different kinds of neural network- based models have been proposed, their performances have been discussed and compared.En este artículo se presenta un modelo basado en redes neuronales capaz de predecir el tiempo necesario para pasar las diferentes galgas de un tren desbastador y acabador en función de ciertas características del desbaste y parámetros de proceso. El objetivo final es aumentar la eficacia de la laminación evitando colisiones y colas que provoquen pérdidas de tiempo y energía. Se propone utilizar para esta tarea redes neuronales por su capacidad de predicción en aquellos casos en los que existen relaciones no lineales desconocidas entre las variables de entrada y las de salida. Además, son capaces de aprender de datos industriales reales y, por tanto, no requieren suposiciones previas o modelos matemáticos del proceso, estando la transferibilidad asegurada ya que es posible utilizar distintas bases de datos procedentes de diferentes trenes de laminación

analysis of a simplified steam turbine governor model for power system stability studies

Abstract The present study describes an analysis performed on a simplified Steam Turbine governor model, which is useful for pre-tuning the machine regulation system. A dynamic model has been implemented in two different simulation tools, namely DigSILENT PowerFactory and Matlab/Simulink, to the aim of verifying the suitability of the latter one for power system stability studies. The proposed work paves the way to the wide range of possibilities connected to the integration of the machine governor model with other simulation blocks of a Combined Cycle Plant, by enabling the opportunity for pre-commissioning of the regulation system together with the analysis of the fulfillment of grid code regulations