2,029 research outputs found
Light-Weight Free-Standing Carbon Nanotube-Silicon Films for Anodes of Lithium Ion Batteries
No full textSilicon is an attractive alloy-type anode material because of its highest known capacity (4200 mAh/g). However, lithium insertion into and extraction from silicon are accompanied by a huge volume change, up to 300%, which induces a strong strain on silicon and causes pulverization and rapid capacity fading due to the loss of the electrical contact between part of silicon and current collector. Si nanostructures such as nanowires, which are chemically and electrically bonded to the current collector, can overcome the pulverization problem, however, the heavy metal current collectors in these systems are larger in weight than Si active material. Herein we report a novel anode structure free of heavy metal current collectors by integrating a flexible, conductive carbon nanotube (CNT) network into a Si anode. The composite film is free-standing and has a structure similar to the steel bar reinforced concrete, where the infiltrated CNT network functions as both mechanical support and electrical conductor and Si as a high capacity anode material for Li-ion battery. Such free-standing film has a low sheet resistance of similar to 30 Ohm/sq. It shows a high specific charge storage capacity (similar to 2000 mAh/g) and a good cycling life, superior to pure sputtered-on silicon films with similar thicknesses. Scanning electron micrographs show that Si is still connected by the CNT network even when small breaking or cracks appear in the film after cycling. The film can also "ripple up" to release the strain of a large volume change during lithium intercalation. The conductive composite film can function as both anode active material and current collector. It offers similar to 10 times improvement in specific capacity compared with widely used graphite/copper anode sheets.Y
Metal current collector-free freestanding silicon-carbon 1D nanocomposites for ultralight anodes in lithium ion batteries
No full textAlthough current collectors take up more weight than active materials in most lithium ion battery cells, so far research has been focused mainly on improving gravimetric capacities of active materials. To address this issue of improving gravimetric capacities based on overall cell components, we develop freestanding nanocomposites made of carbon nanofibers (CNFs) and silicon nanowires (SiNWs) as metal current collector-free anode platforms. Intrinsically large capacities of SiNWs as active materials in conjunction with the light nature of freestanding CNF films allow the nanocomposites to achieve 3-5 times improved gravimetric capacities compared to what have been reported in the literature. Moreover, three-dimensional porous structures in the CNF films facilitate increased mass loadings of SiNWs when compared to flat substrates and result in good cycle lives over 40 cycles. This type of nanocomposite cell suggests that 3D porous platforms consisting of light nanomaterials can provide for higher gravimetric and areal capacities when compared to conventional battery cells based on flat, heavy metal substrates. (c) 2010 Elsevier B.V. All rights reserved
La corruzione in sanità: i nuovi strumenti per individuarla e contrastarla
No full textLa sanità rappresenta uno dei tipici casi in cui il miglioramento del benessere collettivo non può essere affidato soltanto all’azione del libero mercato (che non raggiunge i risultati allocativi e distributivi socialmente desiderati) e si richiede l’intervento del settore pubblico. Tuttavia, nell’interazione fra il settore pubblico e quello privato può verificarsi corruzione. L’analisi economica identifica nella corruzione un fallimento del governo, e, con riguardo alla relazione tra fallimenti del mercato e corruzione, evidenzia tre possibili approcci: uno di questi considera socialmente preferibile convivere con i fallimenti del mercato, posto che l’intervento pubblico porterebbe con sé notevoli fallimenti del governo; un secondo approccio sottolinea come chi governa si dedichi prevalentemente ai propri interessi personali, anziché al miglioramento del benessere sociale; il terzo, infine, pone in rilievo l’esistenza di un trade-off fra fallimenti di mercato e di governo, suggerendo, pertanto, di valutare in quali casi i fallimenti di mercato siano socialmente più dannosi (Acemoglu e Verdier, 2000). Nel caso della sanità, la rilevanza del fallimento del mercato porterebbe a ritenere che l’intervento pubblico sia giustificato, purché il fenomeno della corruzione sia raro (salvo verificare se la corruzione sia più dannosa quando ha origine nel settore pubblico o in quello privato
VCC-LF dataset
No full textThis is readme for VCC-LF dataset.
This dataset provides light field mat files that capture by Lytro I.
The light field resolusion is [h,w,u,v,d].
If you use these data or our toolkit code, please cite our paper properly
@inproceedings{ lirsiggraphasia2019,
title={Hierarchical and View-invariant Light Field Segmentation by Maximizing Entropy Rate on 4D Ray Graphs},
author={Li, Rui and Heidrich, Wolfgang},
booktitle={ACM Transactions on Graphics (Proc. SIGGRAPH Asia)},
year={2019},
publisher={ACM}
LF-copying without LF
No full textAbstractA copying approach to ellipsis is presented, whereby the locus of copying is not a level of derived syntactic structure (LF), but rather the derivation itself. The ban on preposition stranding in sprouting follows without further stipulation, and other, seemingly structure sensitive, empirical generalizations about elliptical constructions, including the preposition stranding generalization, follow naturally as well. Destructive operations which ‘repair’ non-identical antecedents are recast in terms of exact identity of derivations with parameters. In the context of a compositional semantic interpretation scheme, the derivational copying approach to ellipsis presented here is revealed to be a particular instance of a proform theory, thus showing that the distinctions between, and arguments about, syntactic and semantic theories of ellipsis need to be revisited
Highly Conductive Paper for Energy-Storage Devices
No full textPaper, invented more than 2,000 years ago and widely used today in our everyday lives, is explored in this study as a platform for energy-storage devices by integration with 1D nanomaterials. Here, we show that commercially available paper can be made highly conductive with a sheet resistance as low as 1 ohm per square (Ω/sq) by using simple solution processes to achieve conformal coating of single-walled carbon nanotube (CNT) and silver nanowire films. Compared with plastics, paper substrates can dramatically improve film adhesion, greatly simplify the coating process, and significantly lower the cost. Supercapacitors based on CNT-conductive paper show excellent performance. When only CNT mass is considered, a specific capacitance of 200 F/g, a specific energy of 30–47 Watt-hour/kilogram (Wh/kg), a specific power of 200,000 W/kg, and a stable cycling life over 40,000 cycles are achieved. These values are much better than those of devices on other flat substrates, such as plastics. Even in a case in which the weight of all of the dead components is considered, a specific energy of 7.5 Wh/kg is achieved. In addition, this conductive paper can be used as an excellent lightweight current collector in lithium-ion batteries to replace the existing metallic counterparts. This work suggests that our conductive paper can be a highly scalable and low-cost solution for high-performance energy storage devices
Polynomial Approximation in Ep(D) with 0 < p < 1
No full textAbstractIn this paper, we construct approximants by means of interpolation polynomialsto prove Jackson′s theorem and the Bernstein inequality in Ep(D) with 0 < p < 1
Mean Convergence of Interpolation Polynomials in a Domain with Corners
No full textAbstractIn this paper, we prove mean convergence of interpolation polynomials in a domain with some corners
Machine learning and digital twins: monitoring and control for dynamic security in power systems
No full textThe reader of the chapter will be able to connect techniques from machine learning (ML) and digital twins (DTs) to gain insights for monitoring and control of (dynamic) security for electrical power systems. DTs are validated and verified high-fidelity (hf) models providing high simulation accuracy. DTs can be used for simulation of the supervised process of system operation and are therefore able to provide synthetic studied data, where measurement data are scarce. However, for some real-time applications in monitoring and control, such high-fidelity simulation models are not appropriate due to the corresponding computational barrier. There, ML aims to create an application-specific, low-fidelity (lf) approximation of the digital twin. Such trained lf models are used in real-time applications where computational time is scarce and lf information is sufficient. The conceptual intersection of hf and lf models has been little explored and becomes increasingly complex. This chapter aims to provide a conceptual overview of how such hf and lf models can be combined. This chapter is split into two parts where the first part is to introduce ML, lf models, and digital twins, hf models, for power systems analysis, and the second chapter is to use these two types of models to form purpose-driven surrogate lf models, illustrated on the example of dynamic security assessment (DSA). In the first part, the concepts for using DTs as hf models for online power system studies and their corresponding tuning of model parameters are introduced. Subsequently, ML i.e., lf models, are introduced and their corresponding training frameworks. Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Intelligent Electrical Power Grid
Deep spectroscopic luminosity function of Abell 85 : no evidence for a steep upturn of the faint-end slope
No full textIA, AD and ALS acknowledge partial support from the INFN grant InDark and from the grant Progetti di Ateneo TO Call 2012 0011 ‘Marco Polo’ of the University of Torino.We present a new deep determination of the spectroscopic luminosity function (LF) within the virial radius of the nearby and massive Abell 85 (A85) cluster down to the dwarf regime (M* + 6) using Very Large Telescope/Visible Multi-Object Spectrograph (VLT/VIMOS) spectra for ∼2000 galaxies with mr ≤ 21 mag and 〈μe,r〉 ≤ 24 mag arcsec−2. The resulting LF from 438 cluster members is best modelled by a double Schechter function due to the presence of a statistically significant upturn at the faint end. The amplitude of this upturn (αf ~ -1.58+0.19-0.15), however, is much smaller than that of the Sloan Digital Sky Survey (SDSS) composite photometric cluster LF by Popesso et al., αf ∼ −2. The faint-end slope of the LF in A85 is consistent, within the uncertainties, with that of the field. The red galaxy population dominates the LF at low luminosities, and is the main factor responsible for the upturn. The fact that the slopes of the spectroscopic LFs in the field and in a cluster as massive as A85 are similar suggests that the cluster environment does not play a major role in determining the abundance of low-mass galaxies.Peer reviewe
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