bluuebunny/crossref_metadata_2025 huggingface dataset:
MiR-302c inhibits tumor growth of hepatocellular carcinoma by suppressing the endothelial-mesenchymal transition of endothelial cells
Authors: Zhu Kai , Pan Qi , Jia Luo-qi , Dai Zhi , Ke Ai-wu , Zeng Hai-ying , Tang Zhao-you , Fan Jia , Zhou Jian
Published: July 2014

Endothelial cells (ECs) are critical for angiogenesis and microRNA plays important roles in this process. In this study, we investigated the function and mechanism of miR-302c in the process of endothelial-mesenchymal transition (EndMT) in ECs. When miR-302c was overexpressed in HUVECs, the motility of the HUVECs was weakened; the expression levels of EndMT markers were also changed: vascular endothelial (VE)-cadherin was up-regulated, whereas β-catenin, FSP1 and α-SMA were down-regulated. Further in vivo and in vitro experiments showed that the growth of HCC was inhibited when co-cultured or co-injected with HUVECs overexpressing miR-302c. On the contrary, when miR-302c was suppressed in HUVECs, the opposite results were observed. Reporter assays showed that miR-302c inhibited metadherin (MTDH) expression through directly binding to its 3′UTR. In addition, compared to ECs isolated from normal liver tissues of HCC patients, ECs isolated from tumor tissues expressed markedly low levels of miR-302c but high levels of MTDH. These results suggest that EC-specific miR-302c suppresses tumor growth in HCC through MTDH-mediated inhibition of EndMT. MTDH and miR-302c might provide a new strategy for anti-angiogenic therapy in HCC.
The seeded growth of graphene
Authors: Lee Jae-Kap , Lee Sohyung , Kim Yong-Il , Kim Jin-Gyu , Min Bong-Ki , Lee Kyung-Il , Park Yeseul , John Phillip
Published: July 2014

In this paper, we demonstrate the seeded growth of graphene under a plasma chemical vapor deposition condition. First, we fabricate graphene nanopowders (~5 nm) by ball-milling commercial multi-wall carbon nanotubes. The graphene nanoparticles were subsequently subject to a direct current plasma generated in a 100 Torr 10%CH4 - 90%H2 gas mixture. The plasma growth enlarged, over one hour, the nuclei to graphene sheets larger than one hundred nm2 in area. Characterization by electron and X-ray diffraction, high-resolution transmission electron microscopy images provide evidence for the presence of monolayer graphene sheets.
Preparation, optimization and application of poly(ethylene glycol)methyl ether methacrylate/urethane methacrylate as a new polar phase for stir bar sorptive extraction
Authors: Rostami Simindokht , Talebpour Zahra , Yeganeh Hamid
Published: July 2014

The aim of this paper is to discuss the determination of carbaryl in a water sample using a stir bar sorptive extraction method based on a new polar extraction phase coupled with HPLC-DAD.
Recent advances in the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides
Authors: Adrio Javier , Carretero Juan C.
Published: July 2014

The scope of the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides has been greatly expanded by the incorporation of novel types of dipolarophiles and dipole precursors. This feature article summarizes the recent development in this area.
Synthesis and kinetic resolution of N-Boc-2-arylpiperidines
Authors: Cochrane Edward J. , Leonori Daniele , Hassall Lorraine A. , Coldham Iain
Published: July 2014

An efficient kinetic resolution of 2-arylpiperidines was developed using a chiral base.
Synthesis of U3Se5 and U3Te5 type polymorphs of Ta3N5 by combining high pressure–temperature pathways with a chemical precursor approach
Authors: Salamat Ashkan , Woodhead Katherine , Shah S. Imran U. , Hector Andrew L. , McMillan Paul F.
Published: July 2014

Two new polymorphs of Ta3N5 were synthesised by high pressure, high temperature treatment of an amorphous precursor formed from pentakis(dimethylamido) tantalum and ammonia. The new phases form with the U3Se5 and U3Te5 structure types, in line with previous theoretical predictions.
Influence of substituent on equilibrium of benzoxazine synthesis from Mannich base and formaldehyde
Authors: Deng Yuyuan , Zhang Qin , Zhou Qianhao , Zhang Chengxi , Zhu Rongqi , Gu Yi
Published: July 2014

Influence of substituents on equilibrium of reaction between Mannich base and formaldehyde to form benzoxazine is the major concern.
Noble gas encapsulation: clathrate hydrates and their HF doped analogues
Authors: Mondal Sukanta , Chattaraj Pratim Kumar
Published: July 2014

The noble gas encapsulating ability of HF doped 512and 51268clathrate hydrates increases with the increase in the size of the noble gas atom and decrease in the hydrate cage radius.
Screened coulomb hybrid DFT investigation of band gap and optical absorption predictions of CuVO3, CuNbO3 and Cu5Ta11O30 materials
Authors: Harb Moussab , Masih Dilshad , Takanabe Kazuhiro
Published: July 2014

A joint theoretical and experimental investigation was conducted on the optoelectronic properties of CuVO3, CuNbO3 and Cu5Ta11O30 materials.
Rational investigations in the ring opening of cyclic carbonates by amines
Authors: Blain M. , Jean-Gérard L. , Auvergne R. , Benazet D. , Caillol S. , Andrioletti B.
Published: July 2014

Non-isocyanate polyurethanes (NIPUs) constitute a promising alternative for more classical polyurethanes (PUs) as they may display mechanical properties that can match those of PUs and their synthesis does not involve the use of toxic isocyanates.
Determination of trace elements in the Pb–Bi-eutectic system by inductively coupled plasma-quadrupole mass spectrometry after sequential removal of the matrix by precipitation
Authors: Chandrasekaran Krishnan , Karunasagar Dheram
Published: July 2014

Matrix precipitation for the sensitive determination of impurities in the Pb–Bi eutectic system by ICP-MS.
A filter paper-based microdevice for low-cost, rapid, and automated DNA extraction and amplification from diverse sample types
Authors: Gan Wupeng , Zhuang Bin , Zhang Pengfei , Han Junping , Li Cai-Xia , Liu Peng
Published: July 2014

A plastic microdevice with an embedded filter paper disc was developed for rapid DNA extraction and “in situ” PCR amplification.
A copper-responsive gene cluster is required for copper homeostasis and contributes to oxidative resistance in Deinococcus radiodurans R1
Authors: Zhao Zhongchao , Zhou Zhengfu , Li Liang , Xian Xianyi , Ke Xiubin , Chen Ming , Zhang Yuxiu
Published: July 2014

Excess copper is toxic to organisms, and therefore, copper homeostasis is important for the limitation of its cellular levels.
Aqueous room temperature synthesis of zeolitic imidazole framework 8 (ZIF-8) with various concentrations of triethylamine
Authors: Nordin N. A. H. M. , Ismail A. F. , Mustafa A. , Goh P. S. , Rana D. , Matsuura T.
Published: July 2014

The schematic illustration shows the influence of triethylamine (TEA) concentration on ZIF-8 formation.
Antiaromatic bisindeno-[n]thienoacenes with small singlet biradical characters: syntheses, structures and chain length dependent physical properties
Authors: Shi Xueliang , Burrezo Paula Mayorga , Lee Sangsu , Zhang Wenhua , Zheng Bin , Dai Gaole , Chang Jingjing , López Navarrete Juan T. , Huang Kuo-Wei , Kim Dongho , Casado Juan , Chi Chunyan
Published: July 2014

Antiaromatic bisindeno-[n]thienoacenes with small biradical character were synthesized and showed chain length dependent ground states and physical properties.
Remarkable gas adsorption by carbonized nitrogen-rich hypercrosslinked porous organic polymers
Authors: Yang Xiao , Yu Miao , Zhao Yang , Zhang Chong , Wang Xiaoyan , Jiang Jia-Xing
Published: July 2014

Carbonized materials from a nitrogen-rich hypercrosslinked porous organic polymer exhibit a high surface area of 2065 m2 g−1 and an exceptionally high carbon dioxide uptake up to 6.51 mmol g−1 (1.13 bar/273 K).
The synthesis and performance of Zr-doped and W–Zr-codoped VO2 nanoparticles and derived flexible foils
Authors: Shen Nan , Chen Shi , Chen Zhang , Liu Xinling , Cao Chuanxiang , Dong Bingrong , Luo Hongjie , Liu Jianjun , Gao Yanfeng
Published: July 2014

The effect of Zr doping on the Tc, Tlum and ΔTsol values of VO2.
Enhanced performance of plasmid DNA polyplexes stabilized by a combination of core hydrophobicity and surface PEGylation
Authors: Adolph Elizabeth J. , Nelson Christopher E. , Werfel Thomas A. , Guo Ruijing , Davidson Jeffrey M. , Guelcher Scott A. , Duvall Craig L.
Published: July 2014

Nonviral gene therapy has high potential for safely promoting tissue restoration and for treating various genetic diseases.
One-pot synthesis of CuFe2O4magnetic nanocrystal clusters for highly specific separation of histidine-rich proteins
Authors: Zheng Jiangnan , Lin Zian , Liu Wei , Wang Ling , Zhao Sen , Yang Huanghao , Zhang Lan
Published: July 2014

A facile one-pot method was developed for the synthesis of CuFe2O4magnetic nanocrystal clusters and their application in the ligand-free separation of histidine-rich proteins.
Kinetics of promoter escape by bacterial RNA polymerase: effects of promoter contacts and transcription bubble collapse
Authors: Ko Je , Heyduk Tomasz
Published: July 2014

Promoter escape by RNA polymerase, the transition between the initiation and elongation, is a critical step that defines transcription output at many promoters. In the present study we used a real-time fluorescence assay for promoter melting and escape to study the determinants of the escape. Perturbation of core promoter–polymerase contacts had opposing effects on the rates of melting and escape, demonstrating a direct role of core promoter elements sequence in setting not only the kinetics of promoter melting, but also the kinetics of promoter escape. The start of RNA synthesis is accompanied by an enlargement of the transcription bubble and pulling in of the downstream DNA into the enzyme, resulting in DNA scrunching. Promoter escape results in collapse of the enlarged bubble. To test whether the energy that could be potentially released by the collapse of the bubble plays a role in determining escape kinetics, we measured the rates of promoter escape in promoter constructs, in which the amount of this energy was perturbed by introducing sequence mismatches. We found no significant changes in the rate of promoter escape with these promoter constructs suggesting that the energy released upon bubble collapse does not play a critical role in determining the kinetics of promoter escape.
Development and operation of a high-throughput accurate-wavelength lens-based spectrometer
Authors: Bell Ronald E.
Published: July 2014

A high-throughput spectrometer for the 400–820 nm wavelength range has been developed for charge exchange recombination spectroscopy or general spectroscopy. A large 2160 mm−1 grating is matched with fast f/1.8 200 mm lenses, which provide stigmatic imaging. A precision optical encoder measures the grating angle with an accuracy ≤0.075 arc sec. A high quantum efficiency low-etaloning CCD detector allows operation at longer wavelengths. A patch panel allows input fibers to interface with interchangeable fiber holders that attach to a kinematic mount at the entrance slit. Computer-controlled hardware allows automated control of wavelength, timing, f-number, automated data collection, and wavelength calibration.
Brownian dynamics simulations of nanosheet solutions under shear
Authors: Xu Yueyi , Green Micah J.
Published: July 2014

The flow-induced conformation dynamics of nanosheets are simulated using a Brownian Dynamics (BD) formulation applied to a bead-rod sheetlike molecular model. This is the first-ever use of BD to simulate flow-induced dynamics of two-dimensional structures. Using this framework, we simulate dilute suspensions of coarse-grained nanosheets and compute conformation dynamics for simple shear flow. The data show power law scaling relationships between nanosheet parameters (such as bending moduli and molecular weight) and the resulting intrinsic viscosity and conformation. For nonzero bending moduli, an effective dimension of 2.77 at equilibrium is calculated from the scaling relationship between radius of gyration and molecular weight. We also find that intrinsic viscosity varies with molecular weight with an exponent of 2.12 ± 0.23; this dependence is significantly larger than those found for linear polymers. Weak shear thinning is observed at high Weissenberg number (Wi). This simulation method provides a computational basis for developing manufacturing processes for nanosheet-derived materials by relating flow forces and nanosheet parameters to the resulting material morphology.
A split imaging spectrometer for temporally and spatially resolved titanium absorption spectroscopy
Authors: Hager J. D. , Lanier N. E. , Kline J. L. , Flippo K. A. , Bruns H. C. , Schneider M. , Saculla M. , McCarville T.
Published: July 2014

We present a temporally and a spatially resolved spectrometer for titanium x-ray absorption spectroscopy along 2 axial symmetric lines-of-sight. Each line-of-sight of the instrument uses an elliptical crystal to acquire both the 2p and 3p Ti absorption lines on a single, time gated channel of the instrument. The 2 axial symmetric lines-of-sight allow the 2p and 3p absorption features to be measured through the same point in space using both channels of the instrument. The spatially dependent material temperature can be inferred by observing the 2p and the 3p Ti absorption features. The data are recorded on a two strip framing camera with each strip collecting data from a single line-of-sight. The design is compatible for use at both the OMEGA laser and the National Ignition Facility. The spectrometer is intended to measure the material temperature behind a Marshak wave in a radiatively driven SiO2 foam with a Ti foam tracer. In this configuration, a broad band CsI backlighter will be used for a source and the Ti absorption spectrum measured.
Fluid structure in the immediate vicinity of an equilibrium three-phase contact line and assessment of disjoining pressure models using density functional theory
Authors: Nold Andreas , Sibley David N. , Goddard Benjamin D. , Kalliadasis Serafim
Published: July 2014

We examine the nanoscale behavior of an equilibrium three-phase contact line in the presence of long-ranged intermolecular forces by employing a statistical mechanics of fluids approach, namely, density functional theory (DFT) together with fundamental measure theory (FMT). This enables us to evaluate the predictive quality of effective Hamiltonian models in the vicinity of the contact line. In particular, we compare the results for mean field effective Hamiltonians with disjoining pressures defined through (i) the adsorption isotherm for a planar liquid film, and (ii) the normal force balance at the contact line. We find that the height profile obtained using (i) shows good agreement with the adsorption film thickness of the DFT-FMT equilibrium density profile in terms of maximal curvature and the behavior at large film heights. In contrast, we observe that while the height profile obtained by using (ii) satisfies basic sum rules, it shows little agreement with the adsorption film thickness of the DFT results. The results are verified for contact angles of 20°, 40°, and 60°.
Neutron resonance spin flippers: Static coils manufactured by electrical discharge machining
Authors: Martin N. , Wagner J. N. , Dogu M. , Fuchs C. , Kredler L. , Böni P. , Häußler W.
Published: July 2014

Radiofrequency spin flippers (RFSF) are key elements of Neutron Resonance Spin Echo (NRSE) spectrometers, which allow performing controlled manipulations of the beam polarization. We report on the design and test of a new type of RFSF which originality lies in the new manufacturing technique for the static coil. The largely automated procedure ensures reproducible construction as well as an excellent homogeneity of the neutron magnetic resonance condition over the coil volume. Two salient features of this concept are the large neutron window and the closure of the coil by a μ-metal yoke which prevents field leakage outside of the coil volume. These properties are essential for working with large beams and enable new applications with coils tilted with respect to the beam axis such as neutron Larmor diffraction or the study of dispersive excitations by inelastic NRSE.
Upgrades of imaging x-ray crystal spectrometers for high-resolution and high-temperature plasma diagnostics on EAST
Authors: Lyu B. , Wang F. D. , Pan X. Y. , Chen J. , Fu J. , Li Y. Y. , Bitter M. , Hill K. W. , Delgado-Aparicio L. F. , Pablant N. , Lee S. G. , Shi Y. J. , Ye M. Y. , Wan B. N.
Published: July 2014

Upgrade of the imaging X-ray crystal spectrometers continues in order to fulfill the high-performance diagnostics requirements on EAST. For the tangential spectrometer, a new large pixelated two-dimensional detector was deployed on tokamaks for time-resolved X-ray imaging. This vacuum-compatible detector has an area of 83.8 × 325.3 mm2, a framing rate over 150 Hz, and water-cooling capability for long-pulse discharges. To effectively extend the temperature limit, a double-crystal assembly was designed to replace the previous single crystals for He-like argon line measurement. The tangential spectrometer employed two crystal slices attached to a common substrate and part of He- and H-like Ar spectra could be recorded on the same detector when crystals were chosen to have similar Bragg angles. This setup cannot only extend the measurable Te up to 10 keV in the core region, but also extend the spatial coverage since He-like argon ions will be present in the outer plasma region. Similarly, crystal slices for He-like iron and argon spectra were adopted on the poloidal spectrometer. Wavelength calibration for absolute rotation velocity measurement will be studied using cadmium characteristic L-shell X-ray lines excited by plasma radiation. A Cd foil is placed before the crystal and can be inserted and retracted for in situ wavelength calibration. The Geant4 code was used to estimate X-ray fluorescence yield and optimize the thickness of the foil.
Critical point of gas-liquid type phase transition and phase equilibrium functions in developed two-component plasma model
Authors: Butlitsky M. A. , Zelener B. B. , Zelener B. V.
Published: July 2014

A two-component plasma model, which we called a “shelf Coulomb” model has been developed in this work. A Monte Carlo study has been undertaken to calculate equations of state, pair distribution functions, internal energies, and other thermodynamics properties. A canonical NVT ensemble with periodic boundary conditions was used. The motivation behind the model is also discussed in this work. The “shelf Coulomb” model can be compared to classical two-component (electron-proton) model where charges with zero size interact via a classical Coulomb law. With important difference for interaction of opposite charges: electrons and protons interact via the Coulomb law for large distances between particles, while interaction potential is cut off on small distances. The cut off distance is defined by an arbitrary ɛ parameter, which depends on system temperature. All the thermodynamics properties of the model depend on dimensionless parameters ɛ and γ = βe2n1/3 (where β = 1/kBT, n is the particle's density, kB is the Boltzmann constant, and T is the temperature) only. In addition, it has been shown that the virial theorem works in this model. All the calculations were carried over a wide range of dimensionless ɛ and γ parameters in order to find the phase transition region, critical point, spinodal, and binodal lines of a model system. The system is observed to undergo a first order gas-liquid type phase transition with the critical point being in the vicinity of $\varepsilon _{crit} \approx 13\left( {T_{crit}^* \approx 0.076} \right),\gamma _{crit} \approx 1.8\left( {v_{crit}^* \approx 0.17} \right),P_{crit}^* \approx 0.39$ɛcrit≈13Tcrit*≈0.076,γcrit≈1.8vcrit*≈0.17,Pcrit*≈0.39, where specific volume v* = 1/γ3 and reduced temperature T* = ɛ−1.
An instrumental and numerical method to determine the hydrogenic ratio in isotopic experiments in the TJ-II stellarator
Authors: Baciero A. , Zurro B. , Martínez M.
Published: July 2014

The isotope effect is an important topic that is relevant for future D-T fusion reactors, where the use of deuterium, rather than hydrogen, may lean to improved plasma confinement. An evaluation of the ratio of hydrogen/deuterium is needed for isotope effect studies in current isotopic experiments. Here, the spectral range around Hα and Dα lines, obtained with an intensified multi-channel detector mounted to a 1-m focal length spectrometer, is analyzed using a fit function that includes several Gaussian components. The isotopic ratio evolution for a single operational day of the TJ-II stellarator is presented. The role of injected hydrogen by Neutral Beam Injection heating is also studied.
Measurements of fuel and ablator ρR in Symmetry-Capsule implosions with the Magnetic Recoil neutron Spectrometer (MRS) on the National Ignition Facility
Authors: Gatu Johnson M. , Frenje J. A. , Li C. K. , Séguin F. H. , Petrasso R. D. , Bionta R. M. , Casey D. T. , Caggiano J. A. , Hatarik R. , Khater H. Y. , Sayre D. B. , Knauer J. P. , Sangster T. C. , Herrmann H. W. , Kilkenny J. D.
Published: July 2014

The Magnetic Recoil neutron Spectrometer (MRS) on the National Ignition Facility (NIF) measures the neutron spectrum in the energy range of 4–20 MeV. This paper describes MRS measurements of DT-fuel and CH-ablator ρR in DT gas-filled symmetry-capsule implosions at the NIF. DT-fuel ρR's of 80–140 mg/cm2 and CH-ablator ρR's of 400–680 mg/cm2 are inferred from MRS data. The measurements were facilitated by an improved correction of neutron-induced background in the low-energy part of the MRS spectrum. This work demonstrates the accurate utilization of the complete MRS-measured neutron spectrum for diagnosing NIF DT implosions.
Upgrade of the neutral particle analyzers for the TJ-II stellarator
Authors: Fontdecaba J. M. , Petrov S. Ya. , Nesenevich V. G. , Ros A. , Chernyshev F. V. , McCarthy K. J. , Barcala J. M.
Published: July 2014

The TJ-II stellarator, a magnetically confined plasma device, is equipped with a broad range of diagnostics for plasma characterization. These include 4 neutral particle analyzers (NPAs), consisting of two Acord-12's, to perform poloidal measurements, plus a compact NPA, and an Acord-24, these in tangential viewing positions. The Acord-12's were originally equipped with two rows of 6 channels each, one for hydrogen neutrals and the other for deuterium neutrals but were changed to a single row of 12 detectors for hydrogen, the principal working gas in TJ-II. With this upgrade the resultant improved energy resolution spectrum has allowed more reliable ion temperature estimates to be obtained. Here we present the upgrades undertaken and present results to demonstrate the improved performance of this diagnostic.
Design of vibration compensation interferometer for Experimental Advanced Superconducting Tokamak
Authors: Yang Y. , Li G. S. , Liu H. Q. , Jie Y. X. , Ding W. X. , Brower D. L. , Zhu X. , Wang Z. X. , Zeng L. , Zou Z. Y. , Wei X. C. , Lan T.
Published: July 2014

A vibration compensation interferometer (wavelength at 0.532 μm) has been designed and tested for Experimental Advanced Superconducting Tokamak (EAST). It is designed as a sub-system for EAST far-infrared (wavelength at 432.5 μm) poloarimeter/interferometer system. Two Acoustic Optical Modulators have been applied to produce the 1 MHz intermediate frequency. The path length drift of the system is lower than 2 wavelengths within 10 min test, showing the system stability. The system sensitivity has been tested by applying a periodic vibration source on one mirror in the system. The vibration is measured and the result matches the source period. The system is expected to be installed on EAST by the end of 2014.
Analytical modeling of the radial pn junction nanowire solar cells
Authors: Ali Nouran M. , Allam Nageh K. , Abdel Haleem Ashraf M. , Rafat Nadia H.
Published: July 2014

In photovoltaic solar cells, radial p-n junctions have been considered a very promising structure to improve the carrier collection efficiency and accordingly the conversion efficiency. In the present study, the semiconductor equations, namely Poisson's and continuity equations for a cylindrical p-n junction solar cell, have been solved analytically. The analytical model is based on Green's function theory to calculate the current density, open circuit voltage, fill factor, and conversion efficiency. The model has been used to simulate p-n and p-i-n silicon radial solar cells. The validity and accuracy of the present simulator were confirmed through a comparison with previously published experimental and numerical reports.
Long-run growth rate in a random multiplicative model
Authors: Pirjol Dan
Published: July 2014

We consider the long-run growth rate of the average value of a random multiplicative process xi + 1 = aixi where the multipliers \documentclass[12pt]{minimal}\begin{document}$a_i=1+\rho \exp (\sigma W_i - \frac{1}{2}\sigma ^2 t_i)$\end{document}ai=1+ρexp(σWi−12σ2ti) have Markovian dependence given by the exponential of a standard Brownian motion Wi. The average value ⟨xn⟩ is given by the grand partition function of a one-dimensional lattice gas with two-body linear attractive interactions placed in a uniform field. We study the Lyapunov exponent \documentclass[12pt]{minimal}\begin{document}$\lambda =\lim _{n\rightarrow \infty } \frac{1}{n}\log \langle x_n\rangle$\end{document}λ=limn→∞1nlog⟨xn⟩, at fixed \documentclass[12pt]{minimal}\begin{document}$\beta = \frac{1}{2} \sigma^2 t_n n$\end{document}β=12σ2tnn, and show that it is given by the equation of state of the lattice gas in thermodynamical equilibrium. The Lyapunov exponent has discontinuous partial derivatives along a curve in the (ρ, β) plane ending at a critical point (ρC, βC) which is related to a phase transition in the equivalent lattice gas. Using the equivalence of the lattice gas with a bosonic system, we obtain the exact solution for the equation of state in the thermodynamical limit n → ∞.
An ITPA joint experiment to study runaway electron generation and suppression
Authors: Granetz R. S. , Esposito B. , Kim J. H. , Koslowski R. , Lehnen M. , Martin-Solis J. R. , Paz-Soldan C. , Rhee T. , Wesley J. C. , Zeng L. ,   ITPA MHD Group
Published: July 2014

Recent results from an ITPA joint experiment to study the onset, growth, and decay of relativistic electrons (REs) indicate that loss mechanisms other than collisional damping may play a dominant role in the dynamics of the RE population, even during the quiescent Ip flattop. Understanding the physics of RE growth and mitigation is motivated by the theoretical prediction that disruptions of full-current (15 MA) ITER discharges could generate up to 10 MA of REs with 10–20 MeV energies. The ITPA MHD group is conducting a joint experiment to measure the RE detection threshold conditions on a number of tokamaks under quasi-steady-state conditions in which Vloop, ne, and REs can be well-diagnosed and compared to collisional theory. Data from DIII-D, C-Mod, FTU, KSTAR, and TEXTOR have been obtained so far, and the consensus to date is that the threshold E-field is significantly higher than predicted by relativistic collisional theory, or conversely, the density required to damp REs is significantly less than predicted, which could have significant implications for RE mitigation on ITER.
A new developed velocity of sound measurement device for characterization of multi-component gas mixtures under elevated temperatures and pressures
Authors: Seibel C. , Suedmeyer J. , Fieback T. M.
Published: July 2014

Inline process control by measurement of velocity of sound of fluids is a direct and comprehensive technique [J. D. N. Cheeke and Z. Wang, “Acoustic wave gas sensors,” Sens. Actuators B 59, 146–153 (1999); J. W. Grate, S. J. Martin, and R. M. White, “Acoustic wave microsensors,” Anal. Chem. 65, 1868 (1993)]. Depending on the varying conditions of measuring fluid(s), temperatures and pressures, it is a challenging task to find the best possible acoustic setup. Taking this background into account, a velocity of sound measurement device for temperatures up to 475 K and pressures up to 24 MPa was designed and assembled that is to be used for testing different resonator types. Two bulk acoustic wave resonators out of the commonly used lead zirconatetitanate compound (PZT) were tested at different test fluids under temperatures up to 423.15 K and pressures up to 24 MPa [S. Gebhardt, L. Seffner, F. Schlenkirch, and A. Schönecker, “PZT thick films for sensor and actuator applications,” J. Eur. Ceram. Soc. 27, 4177–4180 (2007)]. Initially the pure gases methane, ethane, carbon dioxide, nitrogen, and helium were measured, followed by multi-component gas mixtures. Beside methane-based binary and ternary gas mixtures, a quaternary gas mixture comprising methane, ethane, carbon dioxide, and helium was analyzed. Results for all measurement fluids in a broad temperature and pressure range show a relative deviation to theoretical values derived from GERG-2008 smaller than 0.5%.
Infrared spectroscopy of the acetyl cation and its protonated ketene isomer
Authors: Mosley J. D. , Young J. W. , Duncan M. A.
Published: July 2014

[C2,H3,O]+ ions are generated with a pulsed discharge in a supersonic expansion containing methyl acetate or acetone. These ions are mass selected and their infrared spectra are recorded via laser photodissociation and the method of argon tagging. Computational chemistry is employed to investigate structural isomers and their spectra. The acetyl cation (CH3CO+) is the global minimum and protonated ketene (CH2COH+) is the next lowest energy isomer (+176.2 kJ/mol). When methyl acetate is employed as the precursor, the infrared spectrum reveals that only the acetyl cation is formed. Partially resolved rotational structure reveals rotation about the C3 axis. When acetone is used as the precursor, acetyl is still the most abundant cation, but there is also a minor component of protonated ketene. Computations reveal a significant barrier to interconversion between the two isomers (+221 kJ/mol), indicating that protonated ketene must be obtained via kinetic trapping. Both isomers may be present in interstellar environments, and their implications for astrochemistry are discussed.
Simulating the vibrational spectra of ionic liquid systems: 1-Ethyl-3-methylimidazolium acetate and its mixtures
Authors: Thomas Martin , Brehm Martin , Hollóczki Oldamur , Kelemen Zsolt , Nyulászi László , Pasinszki Tibor , Kirchner Barbara
Published: July 2014

The vibrational spectra of the ionic liquid 1-ethyl-3-methylimidazolium acetate and its mixtures with water and carbon dioxide are calculated using ab initio molecular dynamics simulations, and the results are compared to experimental data. The new implementation of a normal coordinate analysis in the trajectory analyzer TRAVIS is used to assign the experimentally observed bands to specific molecular vibrations. The applied computational approaches prove to be particularly suitable for the modeling of bulk phase effects on vibrational spectra, which are highly important for the discussion of the microscopic structure in systems with a strong dynamic network of intermolecular interactions, such as ionic liquids.
Modeling of fluorescence line-narrowed spectra in weakly coupled dimers in the presence of excitation energy transfer
Authors: Lin Chen , Reppert Mike , Feng Ximao , Jankowiak Ryszard
Published: July 2014

This work describes simple analytical formulas to describe the fluorescence line-narrowed (FLN) spectra of weakly coupled chromophores in the presence of excitation energy transfer (EET). Modeling studies for dimer systems (assuming low fluence and weak coupling) show that the FLN spectra (including absorption and emission spectra) calculated for various dimers using our model are in good agreement with spectra calculated by: (i) the simple convolution method and (ii) the more rigorous treatment using the Redfield approach [T. Renger and R. A. Marcus, J. Chem. Phys. 116, 9997 (2002)]. The calculated FLN spectra in the presence of EET of all three approaches are very similar. We argue that our approach provides a simplified and computationally more efficient description of FLN spectra in the presence of EET. This method also has been applied to FLN spectra obtained for the CP47 antenna complex of Photosystem II reported by Neupane et al. [J. Am. Chem. Soc. 132, 4214 (2010)], which indicated the presence of uncorrelated EET between pigments contributing to the two lowest energy (overlapping) exciton states, each mostly localized on a single chromophore. Calculated and experimental FLN spectra for CP47 complex show very good qualitative agreement.
Multipole plasmon excitations of C60 dimers
Authors: Moradi Afshin
Published: July 2014

We study the multipole plasmon mode frequencies of a pair of C60 molecules by means of the linearized hydrodynamic theory for electronic excitations on the each C60 surface. We apply the two-center spherical coordinate system for mathematical convenience and find an explicit form of the surface plasmon energies. Numerical result shows when approaching the two C60 molecules, the coupling between the bare plasmon modes leads to the appearance of additional modes having energies that are different from those of the isolated C60 molecules.
Surface reconstruction stability of Bi/GaSb surfaces
Authors: Duzik Adam , Millunchick Joanna M.
Published: July 2014

The phase diagram of the Bi/GaSb surface reconstructions has been established using density functional theory and cluster expansion computational methods. The predominant reconstructions in the alloy system are the same as those found for pure GaSb. That is, the (4 × 3) family of reconstructions dominate the phase diagram. However, at low Sb and Bi chemical potentials, the calculations predict a (2 × 1) structure for both GaSb and Bi/GaSb. It is found that Bi does not stabilize any additional structures, and Bi does not readily incorporate into the surface in the presence of Sb.
Axisymmetric stagnation-point flow on a spiraling disk
Authors: Weidman Patrick
Published: July 2014

Two axisymmetric stagnation-point flows impinging normal to a rotating, radially stretching disk are studied. One is the classic Homann stagnation flow and the other is the rotational Argawal stagnation flow. The combined effects of uniform rotation and linear radial stretching give a disk surface velocity in the form of a logarithmic spiral. A similarity reduction of the Navier-Stokes equations for each problem yields different coupled pairs of ordinary differential equations which are solved by a shooting technique. Parametric results for the magnitude σ and angle ϕσ of the wall shear stress are computed for selected values of spiral angle ϕ and disk speed parameter V for both stagnation flows. Leading order large-V asymptotic results for the shear stress parameters, found to be the same for both flows, are determined and sample similarity profiles are presented.
Nonlinear evolution of three-dimensional instabilities of thin and thick electron scale current sheets: Plasmoid formation and current filamentation
Authors: Jain Neeraj , Büchner Jörg
Published: July 2014

Nonlinear evolution of three dimensional electron shear flow instabilities of an electron current sheet (ECS) is studied using electron-magnetohydrodynamic simulations. The dependence of the evolution on current sheet thickness is examined. For thin current sheets (half thickness =de=c/ωpe), tearing mode instability dominates. In its nonlinear evolution, it leads to the formation of oblique current channels. Magnetic field lines form 3-D magnetic spirals. Even in the absence of initial guide field, the out-of-reconnection-plane magnetic field generated by the tearing instability itself may play the role of guide field in the growth of secondary finite-guide-field instabilities. For thicker current sheets (half thickness ∼5 de), both tearing and non-tearing modes grow. Due to the non-tearing mode, current sheet becomes corrugated in the beginning of the evolution. In this case, tearing mode lets the magnetic field reconnect in the corrugated ECS. Later thick ECS develops filamentary structures and turbulence in which reconnection occurs. This evolution of thick ECS provides an example of reconnection in self-generated turbulence. The power spectra for both the thin and thick current sheets are anisotropic with respect to the electron flow direction. The cascade towards shorter scales occurs preferentially in the direction perpendicular to the electron flow.
Heat transfer and tear film dynamics over multiple blink cycles
Authors: Deng Quan , Braun R. J. , Driscoll Tobin A.
Published: July 2014

We consider model problems for the tear film over multiple blink cycles with heat transfer from the posterior side of the tear film. A nonlinear partial differential equation governs the film thickness on a moving domain in one space dimension and time. One end of the tear film moves in order to mimic blinking in the eye. The film thickness is coupled with the diffusion of heat from the posterior of the film, where the underlying cornea and aqueous humor are modeled as a rectangular domain. The domain of the tear film is located on one edge of the rectangle. The resulting problem is solved using the method of lines with a Chebyshev spectral method in space. Evaporation is included in the model, with end fluxes specified to compensate for the evaporation from the film. The numerical results reveal a similarity to quantitative in vivo observations of the film dynamics and measured ocular surface temperature. Periodicity in the film and temperature dynamics is explored with different flux conditions and end motions, and a transition between periodic and non-periodic solutions is analyzed.
Joint measurement of current-phase relations and transport properties of hybrid junctions using a three junctions superconducting quantum interference device
Authors: Basset J. , Delagrange R. , Weil R. , Kasumov A. , Bouchiat H. , Deblock R.
Published: July 2014

We propose a scheme to measure both the current-phase relation and differential conductance dI/dV of a superconducting junction, in the normal and the superconducting states. This is done using a dc Superconducting Quantum Interference Device with two Josephson junctions in parallel with the device under investigation and three contacts. As a demonstration, we measure the current-phase relation and dI/dV of a small Josephson junction and a carbon nanotube junction. In this latter case, in a regime where the nanotube is well conducting, we show that the non-sinusoidal current phase relation we find is consistent with the theory for a weak link, using the transmission extracted from the differential conductance in the normal state. This method holds great promise for future investigations of the current-phase relation of more exotic junctions.
Substrate-supported thermometry platform for nanomaterials like graphene, nanotubes, and nanowires
Authors: Li Zuanyi , Bae Myung-Ho , Pop Eric
Published: July 2014

We demonstrate a substrate-supported thermometry platform to measure thermal conduction in nanomaterials like graphene, with no need to suspend them. We use three-dimensional simulations and careful uncertainty analysis to optimize the platform geometry and to obtain the sample thermal conductivity. The lowest thermal sheet conductance that can be sensed with <50% error is ∼25 nWK−1 at room temperature, indicating applicability of this platform to graphene or polymer thin films, nanotube or nanowire arrays, even a single Si nanowire. The platform can also be extended to plastic substrates, and could find wide applicability in circumstances where fabrication challenges and low yield associated with suspended platforms must be avoided.
Time-frequency analysis of non-stationary fusion plasma signals using an improved Hilbert-Huang transform
Authors: Liu Yangqing , Tan Yi , Xie Huiqiao , Wang Wenhao , Gao Zhe
Published: July 2014

An improved Hilbert-Huang transform method is developed to the time-frequency analysis of non-stationary signals in tokamak plasmas. Maximal overlap discrete wavelet packet transform rather than wavelet packet transform is proposed as a preprocessor to decompose a signal into various narrow-band components. Then, a correlation coefficient based selection method is utilized to eliminate the irrelevant intrinsic mode functions obtained from empirical mode decomposition of those narrow-band components. Subsequently, a time varying vector autoregressive moving average model instead of Hilbert spectral analysis is performed to compute the Hilbert spectrum, i.e., a three-dimensional time-frequency distribution of the signal. The feasibility and effectiveness of the improved Hilbert-Huang transform method is demonstrated by analyzing a non-stationary simulated signal and actual experimental signals in fusion plasmas.
Nanowire-based frequency-selective capacitive photodetector for resonant detection of infrared radiation at room temperature
Authors: Bandyopadhyay Saumil
Published: July 2014

Characteristics of a capacitive infrared photodetector that works at room temperature by registering a change in capacitance upon illumination are reported. If used in an ideal resonant inductor-resistor-capacitor circuit, it can exhibit zero dark current, zero standby power dissipation, infinite detectivity, and infinite light-to-dark contrast ratio. It is also made frequency-selective by employing semiconductor nanowires that selectively absorb photons of energies close to the nanowire's bandgap. Based on measured parameters, the normalized detectivity is estimated to be ∼3 × 107 Jones for 1.6 μm IR wavelength at room temperature.
Iron silicide formation at different layers of (Fe/Si)3 multilayered structures determined by conversion electron Mössbauer spectroscopy
Authors: Badía-Romano L. , Rubín J. , Magén C. , Bürgler D. E. , Bartolomé J.
Published: July 2014

The morphology and the quantitative composition of the Fe-Si interface layer forming at each Fe layer of a (Fe/Si)3 multilayer have been determined by means of conversion electron Mössbauer spectroscopy (CEMS) and high-resolution transmission electron microscopy (HRTEM). For the CEMS measurements, each layer was selected by depositing the Mössbauer active 57Fe isotope with 95% enrichment. Samples with Fe layers of nominal thickness dFe = 2.6 nm and Si spacers of dSi = 1.5 nm were prepared by thermal evaporation onto a GaAs(001) substrate with an intermediate Ag(001) buffer layer. HRTEM images showed that Si layers grow amorphous and the epitaxial growth of the Fe is good only for the first deposited layer. The CEMS spectra show that at all Fe/Si and Si/Fe interfaces a paramagnetic c-Fe1−xSi phase is formed, which contains 16% of the nominal Fe deposited in the Fe layer. The bottom Fe layer, which is in contact with the Ag buffer, also contains α-Fe and an Fe1−xSix alloy that cannot be attributed to a single phase. In contrast, the other two layers only comprise an Fe1−xSix alloy with a Si concentration of ≃0.15, but no α-Fe.
Carrier transport properties of nanocrystalline Er3N@C80
Authors: Sun Yong , Maeda Yuki , Sezaimaru Hiroki , Sakaino Masamichi , Kirimoto Kenta
Published: July 2014

Electrical transport properties of the nanocrystalline Er3N@C80 with fcc crystal structure were characterized by measuring both temperature-dependent d.c. conductance and a.c. impedance. The results showed that the Er3N@C80 sample has characteristics of n-type semiconductor and an electron affinity larger than work function of gold metal. The Er3N@C80/Au interface has an ohmic contact behavior and the contact resistance was very small as compared with bulk resistance of the Er3N@C80 sample. The charge carriers in the sample were thermally excited from various trapped levels and both acoustic phonon and ionic scatterings become a dominant process in different temperature regions, respectively. At temperatures below 250 K, the activation energy of the trapped carrier was estimated to be 35.5 meV, and the ionic scattering was a dominant mechanism. On the other hand, at temperatures above 350 K, the activation energy was reduced to 15.9 meV, and the acoustic phonon scattering was a dominant mechanism. In addition, a polarization effect from the charge carrier was observed at low frequencies below 2.0 MHz, and the relative intrinsic permittivity of the Er3N@C80 nanocrystalline lattice was estimated to be 4.6 at frequency of 5.0 MHz.
A reactive flow model for heavily aluminized cyclotrimethylene-trinitramine
Authors: Kim Bohoon , Park Jungsu , Lee Kyung-Cheol , Yoh Jack J.
Published: July 2014

An accurate and reliable prediction of reactive flow is a challenging task when characterizing an energetic material subjected to an external shock impact as the detonation transition time is on the order of a micro second. The present study aims at investigating the size effect behavior of a heavily aluminized cyclotrimethylene-trinitramine (RDX) which contains 35% of aluminum by using a detonation rate model that includes ignition and growth mechanisms for shock initiation and subsequent detonation. A series of unconfined rate stick tests and two-dimensional hydrodynamic simulations are conducted to construct the size effect curve which represents the relationship between detonation velocity and inverse radius of the charge. A pressure chamber test is conducted to further validate the reactive flow model for predicting the response of a heavily aluminized high explosive subjected to an external impact.
A relationship between statistical time to breakdown distributions and pre-breakdown negative differential resistance at nanometric scale
Authors: Foissac R. , Blonkowski S. , Kogelschatz M. , Delcroix P.
Published: July 2014

Using an ultra-high vacuum Conductive atomic force microscopy (C-AFM) current voltage, pre-breakdown negative differential resistance (NDR) characteristics are measured together with the time dependent dielectric breakdown (TDDB) distributions of Si/SiON (1.4 and 2.6 nm thick). Those experimental characteristics are systematically compared. The NDR effect is modelled by a conductive filament growth. It is showed that the Weibull TDDB statistic distribution scale factor is proportional to the growth rate of an individual filament and then has the same dependence on the electric field. The proportionality factor is a power law of the ratio between the surfaces of the CAFM tip and the filament's top. Moreover, it was found that, for the high fields used in those experiments, the TDDB acceleration factor as the growth rate characteristic is proportional to the Zener tunnelling probability. Those observations are discussed in the framework of possible breakdown or forming mechanism.
Graphene nanopore field effect transistors
Authors: Qiu Wanzhi , Skafidas Efstratios
Published: July 2014

Graphene holds great promise for replacing conventional Si material in field effect transistors (FETs) due to its high carrier mobility. Previously proposed graphene FETs either suffer from low ON-state current resulting from constrained channel width or require complex fabrication processes for edge-defecting or doping. Here, we propose an alternative graphene FET structure created on intrinsic metallic armchair-edged graphene nanoribbons with uniform width, where the channel region is made semiconducting by drilling a pore in the interior, and the two ends of the nanoribbon act naturally as connecting electrodes. The proposed GNP-FETs have high ON-state currents due to seamless atomic interface between the channel and electrodes and are able to be created with arbitrarily wide ribbons. In addition, the performance of GNP-FETs can be tuned by varying pore size and ribbon width. As a result, their performance and fabrication process are more predictable and controllable in comparison to schemes based on edge-defects and doping. Using first-principle transport calculations, we show that GNP-FETs can achieve competitive leakage current of ∼70 pA, subthreshold swing of ∼60 mV/decade, and significantly improved On/Off current ratios on the order of 105 as compared with other forms of graphene FETs.