Micro-Raman scattering of selenium-filled double-walled carbon nanotubes: Temperature study

Selenium-filled double-walled carbon nanotubes Se@DWNT have been studied by high resolution transmission electron microscopy HRTEM and micro-Raman spectroscopy in the temperature interval from 80 to 600 K employing 785 nm excitation wavelength. The temperature dependences of the dominant bands G-band and G-band are analyzed in terms of the model developed by Klemens Phys. Rev. 148, 845 1966, Hart et al. Phys. Rev. B 1, 638 1970, Cowley J. Phys. France 26, 659 1965 and extended by Balkanski et al. Phys. Rev. B 26, 1928 1983 for anharmonic decay of optical phonons. The findings were compared to analogous study for empty double-walled carbon nanotubes DWNTs. The DWNT interatomic force constant modification as a result of the presence of the Se atoms inside the tubes is revealed through larger anharmonicity constants describing the temperature dependences of the G-band and the inner tube tangential modes G-ban

On least-cost path for realistic simulation of human motion

We are interested in "human-like" automatic motion simulation with applications in ergonomics. The apparent redundancy of the humanoid wrt its explicit tasks leads to the problem of choosing a plausible movement in the framework of redundant kinematics. Some results have been obtained in the human motion literature for reach motion that involves the position of the hands. We discuss these results and a motion generation scheme associated. When orientation is also explicitly required, very few works are available and even the methods for analysis are not defined. We discuss the choice for metrics adapted to the orientation, and also the problems encountered in defining a proper metric in both position and orientation. Motion capture and simulations are provided in both cases. The main goals of this paper are: to provide a survey on human motion features at task level for both position and orientation, to propose a kinematic control scheme based on these features, to define properly the error between motion capture and automatic motion simulation

Thermionic-enhanced near-field thermophotovoltaics

Solid-state heat-to-electrical power converters are thermodynamic engines that use fundamental particles, such as electrons or photons, as working fluids. Virtually all commercially available devices are thermoelectric generators, in which electrons flow through a solid driven by a temperature difference. Thermophotovoltaics and thermionics are highly efficient alternatives relying on the direct emission of photons and electrons. However, the low energy flux carried by the emitted particles significantly limits their generated electrical power density potential. Creating nanoscale vacuum gaps between the emitter and the receiver in thermionic and thermophotovoltaic devices enables a significant enhancement of the electron and photon energy fluxes, respectively, which in turn results in an increase of the generated electrical power density. Here we propose a thermionic-enhanced near-field thermophotovoltaic device that exploits the simultaneous emission of photons and electrons through nanoscale vacuum gaps. We present the theoretical analysis of a device in which photons and electrons travel from a hot LaB6-coated tungsten emitter to a closely spaced BaF2-coated InGaAs photovoltaic cell. Photon tunnelling and space charge removal across the nanoscale vacuum gap produce a drastic increase in flux of electrons and photons, and subsequently, of the generated electrical power density. We show that conversion efficiencies and electrical power densities of 30% and 70W/cm2 are achievable at 2000K for a practicable gap distance of 100nm, and thus greatly enhance the performances of stand-alone near-field thermophotovoltaic devices (10% and 10W/cm2). A key practical advantage of this nanoscale energy conversion device is the use of grid-less cell designs, eliminating the issue of series resistance and shadowing losses, which are unavoidable in conventional near-field thermophotovoltaic devices.Comment: Nano Energy (2019

Chemical analysis of a single basic cell of porous anodic aluminium oxide templates

We prepared anodic aluminium oxide (AAO) templates with “honeycomb” geometry, i.e. hexagonally ordered circular pores. The structures were extensively studied and characterized by EPMA coupled with FEG-SEM and FEG-TEM coupled with EDX at meso and nanoscopic scales, in other words, at the scale of a single basic cell making up the highly ordered porous anodic film. The analyses allowed the identification of the chemical compounds present and the evaluation of their levels in the different parts of each cell. Of note was the absence of phosphates inside the “skeleton” and their high content in the “internal part”. Various models of porous anodic film growth are discussed on the basis of the results, contributing to a better understanding of AAO template preparation and selfnanostructuring phenomena

An SVD approach to reaching tasks based on cartesian geodesics

We are interested in human motion characterization and automatic motion simulation. The apparent redundancy of the humanoid w.r.t its explicit tasks lead to the problem of choosing a plausible movement in the framework of redundant kinematics. This work explores the intrinsic relationships between singular value decomposition at kinematic level and optimization principles at task level and joint level. The ideas are tested on sitting reach motions, for both translations and rotations task components

On geodesic paths and least-cost motions for human-like tasks

We are interested in ”human-like” automatic mo- tion generation. The apparent redundancy of the humanoid wrt its explicit tasks lead to the problem of choosing a plausible movement in the framework of redundant kinematics. Some results have been obtained in the human motion literature for reach motion that involves the position of the hands. We discuss these results and a motion generation scheme associated. When orientation is also explicitly required, very few works are available and even the methods for analysis are not defined. We discuss the choice for metrics adapted to the orientation, and also the problems encountered in defining a proper metric in both position and orientation. Motion capture and simulations are provided in both cases. The main goals of this paper are : - to provide a survey on human motion features at task level for both position and orientation, - to propose a kinematic control scheme based on these features - to define properly the error between motion capture and automatic motion simulation

Copper Nanoparticles Prepared fromOxalic Precursors

The synthesis of nanoparticles of copper metal via a soft chemistry route is presented in this paper. The method is based on the thermal decomposition under nitrogen or hydrogen of oxalic precursors with a well-controlled morphology and particle size. The precipitation of the copper oxalates in a water-alcohol medium allows the submicron size of the precursor grains to be controlled and, consequently, the nanometric size of the metallic copper particles to be determined, as required, between 3.5 and 40 nm. The majority of the final particles are made of pure copper metal although some present a superficial layer of cuprous oxide (Cu2O)

Optimum semiconductor bandgaps in single junction and multijunction thermophotovoltaic converters

The choice of the optimum semiconductor for manufacturing thermophotovoltaic (TPV) cells is not straightforward. In contrast to conventional solar photovoltaics (PV) where the optimum semiconductor bandgap is determined solely by the spectrum (and eventually the irradiance) of the incident solar light, in a TPV converter it depends on the emitter temperature and on the spectral control elements determining the net spectral power flux between the TPV cell and the emitter. Additionally, in TPV converters there is a tradeoff between power density and conversion efficiency that does not exist in conventional solar PV systems. Thus, the choice of the proper semiconductor compound in TPV converters requires a thorough analysis that has not been presented so far. This paper presents the optimum semiconductor bandgaps leading to the maximum efficiency and power density in TPV converters using both single junction and multijunction TPV cells. These results were obtained within the framework of the detailed balance theory and assuming only radiative recombination. Optimal bandgaps are provided as a function of the emitter and cell temperature, as well as the degree of spectral control. I show that multijunction TPV cells are excellent candidates to maximize both the efficiency and the power density simultaneously, eliminating the historical tradeoff between efficiency and power density of TPV converters. Finally, multijunction TPV cells are less sensitive to photon recycling losses, which suggest that they can be combined with relatively simple cut-off spectral control systems to provide practically-viable high performing TPV devices

On singular values decomposition and patterns for human motion analysis and simulation

We are interested in human motion characterization and automatic motion simulation. The apparent redun- dancy of the humanoid w.r.t its explicit tasks lead to the problem of choosing a plausible movement in the framework of redun- dant kinematics. This work explores the intrinsic relationships between singular value decomposition at kinematic level and optimization principles at task level and joint level. Two task- based schemes devoted to simulation of human motion are then proposed and analyzed. These results are illustrated by motion captures, analyses and task-based simulations. Pattern of singular values serve as a basis for a discussion concerning the similarity of simulated and real motions