Non-linear electronic transport and anomalous resistance fluctuations in the stripes state of La2NiO4.14La_2NiO_{4.14}

We report on electronic transport measurements in $La_2NiO_{4.14}$. Non-Ohmic and hysteretic $V(I)$ curves are measured for $T \lesssim$ 220 $K$. Large and non Gaussian resistance fluctuations can be observed, with strong cooling rate dependence. During a slow cooling, the resistance reaches plateaus and then suddenly jumps for $T \lesssim$ 100 $K$, evidencing a macroscopic freezing of the charges. Anti-correlation between time-series of orthogonal resistances is also observed. These results are discussed in the framework of the stripes state scenario.Comment: accepted in Phys Rev

Time delay between the optical and X-ray outbursts in the high mass X-ray transient A0535+26/HDE245770

The optical behaviour of the Be star in the high mass X-ray transient A0535+26/HDE245770 shows that at the periastron typically there is an enhancement in the luminosity of order 0.02 to few tenths mag, and the X-ray outburst happens about 8 days after the periastron. We construct a quantitative model of this event, basing on the a nonstationary accretion disk behavior, connected with a high ellipticity of the orbital motion. The ephemeris used in this paper -- JD$_{\rm opt-outb}$ = JD$_0$(2,444,944) $\pm$ n(111.0 $\pm$ 0.4) days are derived from the orbital period of the system P$_{\rm orb} = 111.0 \pm 0.4$ days, determined by Priedhorsky & Terrell (1983), and from the optical flare of December 5, 1981 (Giovannelli et al., 1985) (here after 811205-E; E stands for the Event occurred at that date) that triggered the subsequent X-ray outburst of December 13, 1981 (Nagase et al., 1982) (here after 811213-E). We explain the observed time delay between the peaks of the optical and X-ray outbursts in this system by the time of radial motion of the matter in the accretion disk, after an increase of the mass flux in the vicinity of a periastral point in the binary. This time is determined by the turbulent viscosity, with the parameter $\alpha=0.1-0.3$. The increase of the mass flux is a sort of flush that reaches the external part of the accretion disk around the neutron star, producing an enhancement in the optical luminosity. The consequent X-ray flare happens when the matter reaches the hot central parts of the accretion disk, and the neutron star surface.Comment: 30 pages, 15 figures, with correction in abstrac

Estimating hyperparameters and instrument parameters in regularized inversion. Illustration for SPIRE/Herschel map making

We describe regularized methods for image reconstruction and focus on the question of hyperparameter and instrument parameter estimation, i.e. unsupervised and myopic problems. We developed a Bayesian framework that is based on the \post density for all unknown quantities, given the observations. This density is explored by a Markov Chain Monte-Carlo sampling technique based on a Gibbs loop and including a Metropolis-Hastings step. The numerical evaluation relies on the SPIRE instrument of the Herschel observatory. Using simulated and real observations, we show that the hyperparameters and instrument parameters are correctly estimated, which opens up many perspectives for imaging in astrophysics

Design of an Expander for Internal Power Recovery in Cryogenic Cooling Plants

Abstract The electrical power consumption of refrigeration plants is evaluated to be in the order of 15% of the total electricity consumption worldwide. For this reason, many efforts are spent in the development of energy saving techniques to be applied to refrigeration and air conditioning systems. This paper deals with the development of a device which allows an internal recovery in cryogenic plants, reducing their power consumption. Such a device consists in a Compressor-Expander Group (CEG) developed on the basis of automotive turbocharging technology. According to the rules of the similarity theory, a preliminary CEG design has been realized modifying commercially available components. The critical CEG component is the expander. In order to address the new requirements, a turbocharger expander wheel has been strongly modified and equipped with supersonic variable nozzles, designed to have a radially inflow full admission. To verify the performance of such a machine and suggest improvements, a numerical fluid dynamic model has been set up. The commercial Ansys-CFX software has been used to perform steady-state 3D CFD simulations. In this paper all the numerical results are presented, compared with available experimental data and discussed

A simheuristic algorithm for solving an integrated resource allocation and scheduling problem

Modern companies have to face challenging configuration issues in their manufacturing chains. One of these challenges is related to the integrated allocation and scheduling of resources such as machines, workers, energy, etc. These integrated optimization problems are difficult to solve, but they can be even more challenging when real-life uncertainty is considered. In this paper, we study an integrated allocation and scheduling optimization problem with stochastic processing times. A simheuristic algorithm is proposed in order to effectively solve this integrated and stochastic problem. Our approach relies on the hybridization of simulation with a metaheuristic to deal with the stochastic version of the allocation-scheduling problem. A series of numerical experiments contribute to illustrate the efficiency of our methodology as well as their potential applications in real-life enterprise settings

high temperature cavity receiver integrated with a short term storage system for solar mgts heat transfer enhancement

Abstract Dish-Micro Gas Turbines (MGTs) can be promising systems for power production at small-scale by concentrated solar radiation. Several high-temperature solar receivers have been already designed for such plants, however, nowadays, none of them can assure the proper thermal inertia to level the effects of solar radiation fluctuations on engine performance and safety. In this paper, a solar receiver integrated with a short-term storage system based on high-temperature Phase-Change Materials (PCMs), is proposed. On the basis of a previous preliminary component design and analysis, the receiver geometry has been modified to improve storage capability and heat transfer to the working fluid, reducing temperatures on the irradiated surface making them compatible with material properties and reducing also temperature gradients inside the PCM. Six different geometries, varying length, opening and shape of a front cavity have been analyzed by means of CFD methods. All the configurations have shown a satisfactory behavior in terms of working fluid outlet temperature, storage capabilities and maximum temperatures reached on the surface and inside the receiver. In particular, among them, three geometries can be considered the most promising ones

Internal Power Recovery Systems for Cryogenic Cooling Plants: Secondary Compressor Development

Abstract Refrigeration systems consume a relevant amount of electrical power worldwide. For this reason, in the last decades, several energy saving techniques have been proposed to reduce the power demand of such plants. The present paper deals with the development of an innovative internal power recovery system for industrial cryogenic cooling plants. Such an innovative system consists in a Compressor-Expander Group (CEG) for internal power recovery. In particular, the paper is focused on the development of the CEG compressor, which has to pre-compress the refrigerant main flow before the fluid enters the main compressor. The machine has been re-designed, modifying a centrifugal compressor for automotive turbocharging. To verify the performance and suggest improvements, a numerical fluid dynamic model has been set up and the commercial Ansys-CFX software has been utilized to perform steady-state 3D simulations. Expected performance of the secondary compressor are presented and discussed in this paper