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INSIGHT INTO THE GROWTH MECHANISM OF WS2 NANOTUBES IN THE SCALED-UP FLUIDIZED-BED REACTOR
R. TENNE,A. ZAK,L. SALLACAN-ECKER,A. MARGOLIN,M. GENUT 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2009 NANO Vol.4 No.2
The growth mechanism of WS2 nanotubes in the large-scale fluidized-bed reactor is studied in greater detail. This study and careful parameterization of the conditions within the reactor lead to the synthesis of large amounts (50–100 g/batch) of pure nanotubes, which appear as a fluffy powder, and (400–500 g/batch) of nanotubes/nanoplatelets mixture (50:50), where nanotubes usually coming in bundles. The two products are obtained simultaneously in the same reaction but are collected in different zones of the reactor, in a reproducible fashion. The characterization of the nanotubes, which grow catalyst-free, by a number of analytical techniques is reported. The majority of the nanotubes range from 10 to 50 micron in length and 20–180 nm in diameter. The nanotubes reveal highly crystalline order, suggesting very good mechanical behavior with numerous applications.
Yoel TENNE 한국항공우주학회 2009 한국항공우주학회 학술발표회 논문집 Vol.2009 No.4
Modern engineering design optimization uses computer simulation s and as such it requires optimizing expensive black-box functions. To efficiently handle such challenging optimization problems we have proposed an algorithm which uses several approaches such as global-local search, modelling and model selection and an efficient trust-region search. Performance analysis with both mathematical test functions and a real-world application show the proposed algorithm outperforms a reference algorithm representative of many existing algorithms.
Online Ensemble Topology Selection in Expensive Optimization Problems
Yoel Tenne 제어·로봇·시스템학회 2020 International Journal of Control, Automation, and Vol.18 No.4
Simulation-driven optimization problems are often computationally-expensive, an aspect which has motivated the use of metamodels as they provide approximate function values more economically. To further improve the prediction accuracy the use of ensembles has been explored in which predictions from multiple metamodels are combined. However, the optimal ensemble topology, namely, which types of metamodels it includes, is typically not known, while using a fixed topology may degrade the prediction accuracy and search effectiveness. To address this issue this paper proposes a metamodel-assisted algorithm which autonomously adapts the ensemble topology online during the search such that an optimal topology is used throughout. An extensive performance analysis shows the effectiveness of the proposed algorithm and approach.
MoS2 FULLERENE-LIKE NANOPARTICLES AND NANOTUBES USING GAS-PHASE REACTION WITH MoCl5
F. L. DEEPAK,MAYA BAR-SADAN,RESHEF TENNE,ALEXANDER MARGOLIN,INNA WIESEL,RONIT POPOVITZ-BIRO 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2006 NANO Vol.1 No.2
Inorganic fullerene-like (IF) nanoparticles of MoS2 were synthesized using gas-phase reaction starting from MoCl5 and H2S. The IF-MoS2 nanoparticles are spherical and in some cases faceted with diameters in general ranging between 20 and 80 nm. The IF-MoS2 nanoparticles have large hollow cores, filled in some cases with amorphous material. Various parameters have been investigated to understand the growth and formation of the IF-MoS2 nanoparticles. The parameters that have been studied include flow rates of the various carrier gases, temperature at which the reaction was carried out, time of the reaction and heating of the precursor material. The best set of conditions wherein maximum yields of the IF-MoS2 nanoparticles are obtained have been identified. Additionally, annealing the as-obtained samples or heating them in a mixture of H2 along with H2S improves the crystallinity and reduces the amorphous material filling in the core. Apart from the fullerene-like nanoparticles under certain experimental conditions nanotubes of MoS2 have also been obtained nonetheless in small yields.
Synthesis and Characterization of Pb@GaS Core–Shell Fullerene-Like Nanoparticles and Nanotubes
Olga Brontvein,Lothar Houben,RONIT POPOVITZ-BIRO,Moshe Levy,Daniel Feuermann,RESHEF TENNE,Jeffrey M. Gordon 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2017 NANO Vol.12 No.3
New types of core–shell nanoparticles are reported: Pb@GaS fullerene-like and nanotubular structures, achieved via the continuously high reactor temperatures and ultra-hot stronggradient annealing environments created by highly concentrated sunlight. Structural and chemical characterizations suggest a formation mechanism where vaporized Pb condenses into nanoparticles that are stabilized as they become covered by molten GaS, the ensuing crystallization of which creates the outer layers. Hollow-core GaS fullerene-like nanoparticles and nanotubes were also observed among the products, demonstrating that a single solar procedure can generate a variety of core–shell and hollow nanostructures. The proposed formation mechanisms can account for their relative abundance and the characterization data.
CHROMIUM-RICH COATINGS WITH WS_2 NANOPARTICLES CONTAINING FULLERENE-LIKE STRUCTURE
O. EIDELMAN,H. FRIEDMAN,R. ROSENTSVEIG,A. MOSHKOVITH,V. PERFILIEV,S. R. COHEN,Y. FELDMAN,L. RAPOPORT,R. TENNE 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2011 NANO Vol.6 No.4
In this work chromium-rich coatings impregnated with fullerene-like (IF)-WS2 nanoparticles were deposited on stainless steel substrates. The coatings were obtained from a trivalent chromium bath at pH 2 by galvanostatic electrodeposition. Zinc and cobalt salts were added to the aqueous solution in small amounts serving as cationic growth promoters. Photodeposition of tin-palladium nanoparticles was used as seeding enhancer for the co-deposition of the fullerene-like nanoparticles. The coatings were characterized by a number of techniques and were found to show a decreasing gradient of the IF nanoparticles towards the film-substrate interface. Tribological tests showed that in contrast to the substrate and the pure metal coating, the IF-containing films exhibit low friction and wear.
Emergence of room-temperature ferroelectricity at reduced dimensions
Lee, D.,Lu, H.,Gu, Y.,Choi, S.-Y.,Li, S.-D.,Ryu, S.,Paudel, T. R.,Song, K.,Mikheev, E.,Lee, S.,Stemmer, S.,Tenne, D. A.,Oh, S. H.,Tsymbal, E. Y.,Wu, X.,Chen, L.-Q.,Gruverman, A.,Eom, C. B. American Association for the Advancement of Scienc 2015 Science Vol.349 No.6254
<P><B>Thinning films induces ferroelectricity</B></P><P>Thin ferroelectric films are needed in computers and medical devices. However, traditional ferroelectric films typically become less and less polarized the thinner the films become. Instead of using a good ferroelectric and making it thinner, Lee <I>et al.</I> started with SrTiO<SUP>3</SUP>, which in its bulk form is not ferroelectric. This material does have naturally occurring nanosized polarized regions. and when the thickness of the SrTiO<SUB>3</SUB> films reaches the typical size of these regions, the whole film aligns and becomes ferroelectric.</P><P><I>Science</I>, this issue p. 1314</P><P>The enhancement of the functional properties of materials at reduced dimensions is crucial for continuous advancements in nanoelectronic applications. Here, we report that the scale reduction leads to the emergence of an important functional property, ferroelectricity, challenging the long-standing notion that ferroelectricity is inevitably suppressed at the scale of a few nanometers. A combination of theoretical calculations, electrical measurements, and structural analyses provides evidence of room-temperature ferroelectricity in strain-free epitaxial nanometer-thick films of otherwise nonferroelectric strontium titanate (SrTiO<SUB>3</SUB>). We show that electrically induced alignment of naturally existing polar nanoregions is responsible for the appearance of a stable net ferroelectric polarization in these films. This finding can be useful for the development of low-dimensional material systems with enhanced functional properties relevant to emerging nanoelectronic devices.</P>
Isostructural metal-insulator transition in VO<sub>2</sub>
Lee, D.,Chung, B.,Shi, Y.,Kim, G.-Y.,Campbell, N.,Xue, F.,Song, K.,Choi, S.-Y.,Podkaminer, J. P.,Kim, T. H.,Ryan, P. J.,Kim, J.-W.,Paudel, T. R.,Kang, J.-H.,Spinuzzi, J. W.,Tenne, D. A.,Tsymbal, E. Y. American Association for the Advancement of Scienc 2018 Science Vol.362 No.6418
<P><B>Separating structure and electrons in VO<SUB>2</SUB></B></P><P>Above 341 kelvin—not far from room temperature—bulk vanadium dioxide (VO<SUB>2</SUB>) is a metal. But as soon as the material is cooled below 341 kelvin, VO<SUB>2</SUB> turns into an insulator and, at the same time, changes its crystal structure from rutile to monoclinic. Lee <I>et al.</I> studied the peculiar behavior of a heterostructure consisting of a layer of VO<SUB>2</SUB> placed underneath a layer of the same material that has a bit less oxygen. In the VO<SUB>2</SUB> layer, the structural transition occurred at a higher temperature than the metal-insulator transition. In between those two temperatures, VO<SUB>2</SUB> was a metal with a monoclinic structure—a combination that does not occur in the absence of the adjoining oxygen-poor layer.</P><P><I>Science</I>, this issue p. 1037</P><P>The metal-insulator transition in correlated materials is usually coupled to a symmetry-lowering structural phase transition. This coupling not only complicates the understanding of the basic mechanism of this phenomenon but also limits the speed and endurance of prospective electronic devices. We demonstrate an isostructural, purely electronically driven metal-insulator transition in epitaxial heterostructures of an archetypal correlated material, vanadium dioxide. A combination of thin-film synthesis, structural and electrical characterizations, and theoretical modeling reveals that an interface interaction suppresses the electronic correlations without changing the crystal structure in this otherwise correlated insulator. This interaction stabilizes a nonequilibrium metallic phase and leads to an isostructural metal-insulator transition. This discovery will provide insights into phase transitions of correlated materials and may aid the design of device functionalities.</P>
Systematic Analysis of Clinical Outcomes Following Stereotactic Radiosurgery for Central Neurocytoma
( Timothy T. Bui ),( Carlito Lagman ),( Lawrance K. Chung ),( Stephen Tenn ),( Percy Lee ),( Robert K. Chin ),( Tania Kaprealian ),( Isaac Yang ) 대한뇌종양학회 대한신경종양학회 2017 Brain Tumor Research and Treatment Vol.5 No.1
Central neurocytoma (CN) typically presents as an intraventricular mass causing obstructive hydrocephalus. The first line of treatment is surgical resection with adjuvant conventional radiotherapy. Stereotactic radiosurgery (SRS) was proposed as an alternative therapy for CN because of its lower risk profile. The objective of this systematic analysis is to assess the efficacy of SRS for CN. A systematic analysis for CN treated with SRS was conducted in PubMed. Baseline patient characteristics and outcomes data were extracted. Heterogeneity and publication bias were also assessed. Univariate and multivariate linear regressions were used to test for correlations to the primary outcome: local control (LC). The estimated cumulative rate of LC was 92.2% (95% confidence interval: 86.5-95.7%, p<0.001). Mean follow-up time was 62.4 months (range 3-149 months). Heterogeneity and publication bias were insignificant. The univariate linear regression models for both mean tumor volume and mean dose were significantly correlated with improved LC (p<0.001). Our data suggests that SRS may be an effective and safe therapy for CN. However, the rarity of CN still limits the efficacy of a quantitative analysis. Future multi-institutional, randomized trials of CN patients should be considered to further elucidate this therapy.