New promising bulk thermoelectrics: intermetallics,pnictides and chalcogenides

The need of alternative “green” energy sources has recently renewed the interest in thermoelectric (TE) materials, which can directly convert heat to electricity or, conversely, electric current to cooling. The thermoelectric performance of a material can be estimated by the so-called figure of merit, zT = σ α ² T/λ (α the Seebeck coefficient, σ α ² the power factor, σ and λ the electrical and thermal conductivity, respectively), that depends only on the material. In the middle 1990s the “phonon glass and electron crystal” concept was developed, which, together with a better understanding of the parameters that affect zT and the use of new synthesis methods and characterization techniques, has led to the discovery of improved bulk thermoelectric materials that start being implemented in applications. During last decades, special focus has been made on skutterudites, clathrates, half-Heusler alloys, Si_1?x Ge _x-, Bi₂Te_3- and PbTe-based materials. However, many other materials, in particular based on intermetallics, pnictides, chalcogenides, oxides, etc. are now emerging as potential advanced bulk thermoelectrics. Herein we discuss the current understanding in this field, with special emphasis on the strategies to reduce the lattice part of the thermal conductivity and maximize the power factor, and review those new potential thermoelectric bulk materials, in particular based on intermetallics, pnictides and chalcogenides. A final chapter, discussing different shaping techniques leading to bulk materials (eventually from nanostructured TE materials), is also included.     

Femtosecond optical vortices in air

We examine the robustness of ultrashort optical vortices propagating freely in the atmosphere. We first approximate the stability regions of femtosecond spinning pulses as a function of their topological charge. Next, we numerically demonstrate that atmospheric optical vortices are capable of conveying high power levels in air over hundreds of meters before they break up into filaments.     

Search for Randall-Sundrum gravitons in dilepton and diphoton final states

We report the first direct search for the Kaluza-Klein (KK) modes of Randall-Sundrum gravitons using dielectron, dimuon, and diphoton events observed with the D0 detector operating at the Fermilab Tevatron pp(-) Collider at sqrt[s]=1.96 TeV. No evidence for resonant production of gravitons has been found in the data corresponding to an integrated luminosity of approximately equal to 260 pb(-1). Lower limits on the mass of the first KK mode at the 95% C.L. have been set between 250 and 785 GeV, depending on its coupling to standard model particles.     

Rains of solitons in a figure-of-eight passively mode-locked fiber laser

We report experimental observation of rains of solitons in figure-of-eight fiber laser passively mode-locked through nonlinear optical loop mirror. Soliton pulses are created from an extended noisy background and drift until they reach a condensed phase comprising several tens of aggregated solitons. The observation of this dynamics tends to strengthen the idea of the universality of the collective behavior of solitons.     

Investigation of 2-aminoethanethiol as corrosion inhibitor for steel using response surface methodology (RSM)

The inhibition efficiency of 2-aminoethanethiol (2-AEE) has been investigated against steel corrosion in 0.1 M HCl solution. The effect of temperature, pH, and concentration were studied with the help of potentiodynamic measurement, electrochemical impedance spectroscopy, scanning electron microscopy, and atomic absorption spectroscopy techniques. The potential of zero charge (E_pzc) studies showed that the adsorption occurs via ?SH group; the metal surface is positively charged in corrosive test solution. The adsorptive interaction is evaluated, and best correlation was obtained with Langmuir isotherm. 2-AEE was shown to have significant inhibition efficiency against steel corrosion. The response surface methodology was employed to explain the relation between pH, inhibitor concentration, and the efficiency. The regression analysis was realized for development of an equation between independent variables and the output. The success of fitting model was tested with basic statistical arguments, residual and variance analysis, T and F tests, and R ² value. The statistical evaluations showed that the obtained polynomial equation can be successfully used for optimization of applications involving the use of 2-AEE as inhibitor.     

Evidence for spin correlation in t ̅t production

We present a measurement of the ratio of events with correlated t and t ?t spins to the total number of t ?t events. This ratio f is evaluated using a matrix-element-based approach in 729 t ?t candidate events with a single lepton ? (electron or muon) and at least four jets. The analyzed p ?p collisions data correspond to an integrated luminosity of 5.3 fb(-1) and were collected with the D0 detector at the Fermilab Tevatron collider operating at a center-of-mass energy √s=1.96 TeV. Combining this result with a recent measurement of f in dileptonic final states, we find f in agreement with the standard model. In addition, the combination provides evidence for the presence of spin correlation in t ?t events with a significance of more than 3 standard deviations.     

Dynamical coupling between gradients and transport in fusion plasmas

The dynamical coupling between density gradients and particle transport has been investigated using similar experimental tools in the plasma boundary of different tokamak (JET, ISTTOK) and stellarator (TJ-II) devices, showing that the size of turbulent events is minimum in the proximity of the most probable density gradient. Experimental results were found to be consistent with results from two very different models of plasma turbulence and transport. The present findings, common to several plasma devices, suggest the importance of self-regulation mechanisms between plasma transport and gradients in fusion devices.     

Linear parameter varying control design for rotating systems supported by journal bearings

Linear parameter varying (LPV) control is a model-based control technique that takes into account time-varying parameters of the plant. In the case of rotating systems supported by lubricated bearings, the dynamic characteristics of the bearings change in time as a function of the rotating speed. Hence, LPV control can tackle the problem of run-up and run-down operational conditions when dynamic characteristics of the rotating system change significantly in time due to the bearings and high vibration levels occur. In this work, the LPV control design for a flexible shaft supported by plain journal bearings is presented. The model used in the LPV control design is updated from unbalance response experimental results and dynamic coefficients for the entire range of rotating speeds are obtained by numerical optimization. Experimental implementation of the designed LPV control resulted in strong reduction of vibration amplitudes when crossing the critical speed, without affecting system behavior in sub- or super-critical speeds.     

Tri-polarized spectrum sensing based on an experimental outdoor-to-indoor cognitive-radio scenario

Compared to classical spatially separated multiple antenna system, cross-polarized co-located antenna systems are an interesting way to reduce equipment size while reducing the inter-antenna correlation. In this paper the spectrum sensing of a Cognitive Radio (CR) system taking advantage of polarization diversity under Rayleigh fading is investigated and compared to an equivalent system using spatial diversity. This analysis is based on a theoretical formulation applied to a real-world scenario. For this purpose, an outdoor-to-indoor measurement campaign at a frequency of 3.5 GHz is realized, where an indoor secondary user senses the signals received from an outdoor primary base station. The signals received at each antenna are first combined and then applied to an energy detector. The theoretical expressions are simulated in the measurement context. The detection probability behavior as a function of distance between the Primary Transmitter (PTx) and the Secondary Terminal (STE) and the inter-antenna correlation effect on the sensing performance are studied.     

An indirect hybrid sound transmission loss controller

The control of sound transmission through panels is an important noise control problem in the aerospace, aeronautical, and automotive industries. The trend towards using lightweight composite materials that have lower sound insulation performance is a negative factor regarding low frequency transmission loss. Double-panel partitions with the gap filled with sound absorption materials are often employed to improve the sound insulation performance with reduced added weight penalty. However, in the low frequency range, the strong coupling between the panels through the air cavity and mechanical paths may greatly reduce the sound transmission performance, making it even lower than the performance of a single panel in some frequency ranges. In this work, an experimental investigation of a new kind of hybrid (active/passive) acoustic actuator is presented. The idea consists of replacing the acoustic absorption material by a hybrid actuator aiming at improving the transmission loss at low frequencies without altering the passive attenuation. A prototype of the system is tested in a plane wave acoustic tube setup. Different kinds of SISO feedforward control implementations were used to attenuate the sound power transmitted through the hybrid active–passive panel using an error microphone or a particle velocity sensor placed downstream with respect to the sample panel. Measurement results of the transmission loss with active and hybrid attenuation are presented and discussed.