Fermi surface renormalization in Hubbard ladders

We derive the one-loop renormalization equations for the shift in the Fermi-wavevectors for one-dimensional interacting models with four Fermi-points (two left and two right movers) and two Fermi velocities v_1 and v_2. We find the shift to be proportional to (v_1-v_2)U^2, where U is the Hubbard-U. Our results apply to the Hubbard ladder and to the t_1-t_2 Hubbard model. The Fermi-sea with fewer particles tends to empty. The stability of a saddle point due to shifts of the Fermi-energy and the shift of the Fermi-wavevector at the Mott-Hubbard transition are discussed.Comment: 5 pages, 4 Postscript figure

The role of spatial and temporal radiation deposition in inertial fusion chambers: the case of HiPER¿

The first wall armour for the reactor chamber of HiPER will have to face short energy pulses of 5 to 20 MJ mostly in the form of x-rays and charged particles at a repetition rate of 5–10 Hz. Armour material and chamber dimensions have to be chosen to avoid/minimize damage to the chamber, ensuring the proper functioning of the facility during its planned lifetime. The maximum energy fluence that the armour can withstand without risk of failure, is determined by temporal and spatial deposition of the radiation energy inside the material. In this paper, simulations on the thermal effect of the radiation–armour interaction are carried out with an increasing definition of the temporal and spatial deposition of energy to prove their influence on the final results. These calculations will lead us to present the first values of the thermo-mechanical behaviour of the tungsten armour designed for the HiPER project under a shock ignition target of 48 MJ. The results will show that only the crossing of the plasticity limit in the first few micrometres might be a threat after thousands of shots for the survivability of the armour

Real-Time Hardware-in-the-Loop Simulation of Permanent Magnet Synchronous Motor Drives under Stator Faults

Hardware-in-the-loop (HIL) testing methods can facilitate the development of control strategies in a safe and inexpensive environment particularly when extreme operating conditions such as faults are considered. HIL methods rely on accurate real-time emulation of the equipment under investigation. However, no validated tools for real-time emulation of electrical drives under fault conditions are available. This paper describes the implementation of a high-fidelity real-time emulator of a Permanent Magnet Synchronous Motor (PMSM) drive in a platform suitable for HIL tests. The emulator is capable of representing the drive operation under both healthy conditions and during inter-turn stator winding faults. Nonlinearities due to saturation, higher order harmonics, slotting effects, etc. are accounted for using fourdimensional look-up tables obtained by finite element analysis (FEA). The proposed model is computationally efficient and capable of running in real-time in a FPGA platform and is validated against simulations and experimental results in a wide range of operating conditions. Potential applications of the proposed emulation environment to the development of drive control, fault detection and diagnostic algorithms are proposed

Impaired modulation of the cardiac L-type Ca2+ channel activity by ahnak-1 after myocardial infarction

Introduction: The L-type cardiac Ca2+ channel (Cav 1.2) is an important determinant of cardiac repolarization and the main source of activator Ca2+ during excitation-contraction coupling in cardiac cells. Its defective regulation is a major cause of arrhythmias and contractile dysfunction. We have recently shown that the cytoskeletal protein ahnak-1 modulates Ca2+ current through Cav 1.2 channels (ICaL) by interacting with the regulatory beta-subunit of the Cav 1.2 channel and that the genetic variant of ahnak-1 I5483T (previously Ile5236Thr), interferes with the beta-adrenergic stimulation of ICaL. Objective: To extend our study of the I5483T variant to ventricular cardiomyocytes dissociated from remodelled infarcted rat hearts (PMI). Methods: The patch-clamp technique was used to record ICaL from enzymatically dissociated ventricular cardiomyocytes from young (2-month-old) and six-month-old sham-operated and PMI rats. Results: Basal ICaL was increased from 11 ± 0.5 A/F in young cardiomyocytes to 14.6 ± 1.1 A/F and 15.7 ± 1 A/F in sham and PMI cardiomyocytes respectively, while isoprenaline (ISO, 1 µmol/L) further increased ICaL by 101 ± 6%, 109 ± 10% and 104 ± 12% respectively. When cells were intracellularly perfused with a peptide containing the mutated ahnak-1 sequence (10 µmol/L) basal ICaL was increased to 20 ± 1 A/F, 22 ± 2 A/F and 21 ± 2 A/F in young, sham and PMI cardiomyocytes respectively. In these cells ISO increased ICaL by 11 ± 4%, 33 ± 6% and 79 ± 12% respectively. Conclusion: Modulation of ICaL by ahnak-1is impaired by myocardial ischemia and remodelling. Since ahnak-1 and Cav 1.2 channels co-localize in the transverse T-tubule system, remodelling of T-tubules could affect the interaction of ahnak-1 with the regulatory beta subunit of these channels

Modelización de las distribuciones diamétricas en masas de Betula alba L. en el noroeste de España con la función Weibull biparamétrica

The diameter distributions of 125 permanent plots installed in birch dominated (Betula alba L.) stands in Galicia were modelled with the two-parameter Weibull distribution. Four different fitting methods were used: that based on percentiles of the distribution, non linear regression, maximum likelihood and the method of moments. The most accurate fit was obtained with the non linear regression (NLR) approach, considering the following statistics in the comparison: bias, mean absolute error (MAE), mean square error (MSE) and number of plots rejected by the Kolmogoroff-Smirnoff (KS) test. The scale parameter (b) and the shape parameter (c) obtained with the most accurate method (non linear regression), were first modelled with simple linear models and then related to commonly measured prediction variables (quadratic mean diameter, dominant height and stand density) with the parameter prediction model (PPM). The parameters fitted with the method of moments were recovered with the parameter recovery model (PRM) from the first and the second moments of the distribution (mean diameter and variance, respectively). Results indicated that both methods were successful in predicting the diameter frequency distributions. The PRM was more accurate than the PPM method.Las distribuciones diamétricas de 125 parcelas permanentes instaladas en masas puras de abedul (Betula alba L.) en Galicia fueron modelizadas con la distribución Weibull de dos parámetros. Se emplearon cuatro métodos de ajuste: basados en percentiles de la distribución, regresión no lineal, máxima verosimilitud y el método de los momentos. Los ajustes más precisos fueron obtenidos con regresión no lineal, considerando los siguientes estadísticos en la comparación de los resultados: sesgo, error medio absoluto, error medio cuadrático y número de parcelas rechazadas por el test de Kolmogoroff-Smirnoff. El parámetro de escala (b) y el parámetro de forma (c) obtenidos con el método más preciso (regresión no lineal), fueron relacionados con variables de masa de frecuente medición (diámetro medio cuadrático, altura dominante y densidad) mediante modelos lineales sencillos aplicando la metodología de predicción de parámetros. Los parámetros ajustados con el método de los momentos fueron recuperados con modelos de recuperación de parámetros a partir del primer y del segundo momento de la distribución (diámetro medio y varianza, respectivamente). Los resultados indicaron que ambos métodos fueron satisfactorios para predecir las distribuciones de frecuencias de diámetros. El método de recuperación de parámetros fue más preciso que el método de predicción de parámetros