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Dynamic response of an elastic bridge loaded by a moving elastic beam with a finite length
Cojocaru, Eugenia C.,Irschik, Hans Techno-Press 2010 Interaction and multiscale mechanics Vol.3 No.4
The present paper is concerned with vibrations of an elastic bridge loaded by a moving elastic beam of a finite length, which is an extension of the authors' previous study where the second beam was modeled as a semi-infinite beam. The second beam, which represents a train, moves with a constant speed along the bridge and is assumed to be connected to the bridge by the limiting case of a rigid interface such that the deflections of the bridge and the train are forced to be equal. The elastic stiffness and the mass of the train are taken into account. The differential equations are developed according to the Bernoulli-Euler theory and formulated in a non-dimensional form. A solution strategy is developed for the flexural vibrations, bending moments and shear forces in the bridge by means of symbolic computation. When the train travels across the bridge, concentrated forces and moments are found to take place at the front and back side of the train.
Schwarz, Torsten,Cojocaru-Miré,din, Oana,Mousel, Marina,Redinger, Alex,Raabe, Dierk,Choi, Pyuck-Pa Elsevier 2017 ACTA MATERIALIA Vol.132 No.-
<P>Atom probe tomography and transmission electron microscopy are used to study the formation of nano sized Cu-Sn-Se particles in Cu2ZnSnSe4 thin -films. For a Cu -rich precursor, which was deposited at 320 degrees C under Cu- and Zn-rich growth conditions, Cu2-xSe grains at the surface are detected. During annealing the precursor at 500 degrees C in a SnSe + Se atmosphere most of the Cu2-xSe is transformed to Cu2ZnSnSe4 via the consumption of excessive ZnSe and incorporation of Sn. However, atom probe tomography studies also reveal the formation of various nanometer-sized Cu-Sn-Se particles close to the CdS/Cu(2)ZnSnSe4 interface. One of those particles has a composition close to the Cu2SnSe3 compound. This phase has a smaller band gap than Cu2ZnSnSe4 and is proposed to lead to a significant drop in the open -circuit voltage and could be the main cause for a detrimental p-n junction and the zero efficiency of the final device. Possible effects of the other phases on solar cell performance and formation mechanisms are discussed as well. (C)2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.</P>
Direct Synthesis and Integration of Individual, Diameter-Controlled Single-Walled Nanotubes (SWNTs)
Bouanis, Fatima Z.,Cojocaru, Costel S.,Huc, Vincent,Norman, Evgeny,Chaigneau, Marc,Maurice, Jean-Luc,Mallah, Talal,Pribat, Didier American Chemical Society 2014 Chemistry of materials Vol.26 No.17
<P>We present a robust and versatile approach for the reproducible and controllable growth of single-walled carbon nanotubes (SWNTs) through a self-assembled monolayer (SAM) technique coupled with an atomic hydrogen (H<SUB>at</SUB>) pretreatment to control the catalytic metallic nanoparticles size and density. The nanoparticles are obtained from a self-assembled monolayer of metal complexes or salts on a SiO<SUB>2</SUB> substrate using a two-step strategy. The oxide is first functionalized by silanization with a coordinating ligand leading to the formation of an anchoring SAM on the substrate. Then, metallic complexes such as ruthenium porphyrin (RuTPP) or metallic salts (FeCl<SUB>3</SUB>, RuCl<SUB>3</SUB>) are assembled by coordination bonds on the preformed organic SAM. Pyrolysis under radical hydrogen atmosphere of the as-prepared SAM yields metallic nanoparticles whose size and density are controlled and tuned. Using the as-formed nanoparticles as catalysts, SWNTs are grown by double hot-filament-assisted chemical vapor deposition (d-HFCVD). They exhibit a remarkably good crystalline quality, with a diameter (and type) strongly dependent on the nature of the initial catalyst precursor and its preparation. Field-effect transistors (FETs) with excellent characteristics were obtained using such in-place grown SWNTs. The electronic properties of the SWNTs can be tuned: the transistors obtained from Ru(TPP) and FeCl<SUB>3</SUB> exhibit <I>I</I><SUB>ON</SUB>/<I>I</I><SUB>OFF</SUB> current ratio up to ∼10<SUP>9</SUP>, indicative of the direct growth of a high proportion of semiconducting nanotubes over than 98%. Such elevated <I>I</I><SUB>ON</SUB>/<I>I</I><SUB>OFF</SUB> values have been reported essentially for CNT-FETs devices based on individual semiconducting SWNTs, so far. By contrast, devices obtained from the RuCl<SUB>3</SUB> salt display <I>I</I><SUB>ON</SUB>/<I>I</I><SUB>OFF</SUB> current ratio well below 10<SUP>2</SUP>, indicating the direct growth of SWNTs highly enriched in metallic specimens.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2014/cmatex.2014.26.issue-17/cm502282x/production/images/medium/cm-2014-02282x_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm502282x'>ACS Electronic Supporting Info</A></P>
Zhou, Chongjian,Yu, Yuan,Lee, Yong Kyu,Cojocaru-Miré,din, Oana,Yoo, Byeongjun,Cho, Sung-Pyo,Im, Jino,Wuttig, Matthias,Hyeon, Taeghwan,Chung, In American Chemical Society 2018 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.140 No.45
<P>From a structural and economic perspective, tellurium-free PbSe can be an attractive alternative to its more expensive isostructural analogue of PbTe for intermediate temperature power generation. Here we report that PbSe<SUB>0.998</SUB>Br<SUB>0.002</SUB>-2%Cu<SUB>2</SUB>Se exhibits record high peak <I>ZT</I> 1.8 at 723 K and average <I>ZT</I> 1.1 between 300 and 823 K to date for all previously reported n- and p-type PbSe-based materials as well as tellurium-free n-type polycrystalline materials. These even rival the highest reported values for n-type PbTe-based materials. Cu<SUB>2</SUB>Se doping not only enhance charge transport properties but also depress thermal conductivity of n-type PbSe. It flattens the edge of the conduction band of PbSe, increases the effective mass of charge carriers, and enlarges the energy band gap, which collectively improve the Seebeck coefficient markedly. This is the first example of manipulating the electronic conduction band to enhance the thermoelectric properties of n-type PbSe. Concurrently, Cu<SUB>2</SUB>Se increases the carrier concentration with nearly no loss in carrier mobility, even increasing the electrical conductivity above ∼423 K. The resulting power factor is ultrahigh, reaching ∼21-26 μW cm<SUP>-1</SUP> K<SUP>-2</SUP> over a wide range of temperature from ∼423 to 723 K. Cu<SUB>2</SUB>Se doping substantially reduces the lattice thermal conductivity to ∼0.4 W m<SUP>-1</SUP> K<SUP>-1</SUP> at 773 K, approaching its theoretical amorphous limit. According to first-principles calculations, the achieved ultralow value can be attributed to remarkable acoustic phonon softening at the low-frequency region.</P> [FIG OMISSION]</BR>
Child Rights Practice among the Indigenous Communities in Bangladesh
M. Rezaul Islam,Bhabatash Nath,Stefan Cojocaru,Rabiul Islam 한국사회복지학회 2015 Asian Social Work and Policy Review Vol.9 No.3
The objective of this article was to explore the practice of child rights among the indigenous communities of Bangladesh. We used a mixed method approach to collect data from four ethnic communities in the Bandarban District of the Chittagong Division in Bangladesh. We questioned children, parents, community members, local leaders, and service providers of those communities on a number of child rights issues, for example, child education, child labor, child recreation and culture, parents’ guidance to children for capacity development, and access to child rights at home and in the community according to Convention on the Rights of the Child treaty. The results showed that while the community was aware of child rights, financial vulnerability and a lack of social support meant that these rights could not be upheld in practice. The paper urges improvement of social support, including income generation activities for indigenous communities
Synthesis of few-layered graphene by ion implantation of carbon in nickel thin films
Baraton, Laurent,He, Zhanbing,Lee, Chang Seok,Maurice, Jean-Luc,Cojocaru, Costel Sorin,Gourgues-Lorenzon, Anne-Franç,oise,Lee, Young Hee,Pribat, Didier IOP Pub 2011 Nanotechnology Vol.22 No.8
<P>The synthesis of few-layered graphene is performed by ion implantation of carbon species in thin nickel films, followed by high temperature annealing and quenching. Although ion implantation enables a precise control of the carbon content and of the uniformity of the in-plane carbon concentration in the Ni films before annealing, we observe thickness non-uniformities in the synthesized graphene layers after high temperature annealing. These non-uniformities are probably induced by the heterogeneous distribution/topography of the graphene nucleation sites on the Ni surface. Taken altogether, our results indicate that the number of graphene layers on top of Ni films is controlled by the nucleation process on the Ni surface rather than by the carbon content in the Ni film. </P>