bluuebunny/crossref_metadata_2025 huggingface dataset:
Lattice-matched epitaxial ternary PrxY2−xO3 films on SrO-passivated Si (001): Interface engineering and crystallography tailoring
Authors: Niu G. , Zaumseil P. , Schubert M. A. , Zoellner M. H. , Dabrowski J. , Schroeder T.
Published: January 2013

Rare earth bixbyite oxides (Re2O3) crystallize on Si (001) in 110-orientation due to either lattice mismatch or oxide/Si interface conditions. In this letter, a 1/2 monolayer (ML) SrO layer was employed as an interface engineering approach to achieve epitaxial ternary oxide PrxY2−xO3 (x = 0–2) films on Si (001) with a sharp oxide/Si (001) interface. The passivation layer is stable up to 780 °C. A fully lattice-matched Pr0.9Y1.1O3 film was obtained, which still has 110-orientation on Si (001). This allows us to clarify the decisive impact of the interface conditions-rather than lattice mismatch-on the growth orientation of Re2O3 films on Si (001).
Potential energy curves and spin-orbit coupling of light alkali-heavy rare gas molecules
Authors: Galbis E. , Douady J. , Jacquet E. , Giglio E. , Gervais B.
Published: January 2013

The potential energy curves of the X, A, and B states of alkali-rare gas diatomic molecules, MKr and MXe, are investigated for M = Li, Na, K. The molecular spin-orbit coefficients \documentclass[12pt]{minimal}\begin{document}$a(R)\break = \langle ^2\Pi _{\frac{1}{2}} | \hat{H}_{\rm SO} | ^2\Pi _{\frac{1}{2}} \rangle $\end{document}a(R)=⟨2Π12|Ĥ SO |2Π12⟩ and \documentclass[12pt]{minimal}\begin{document}$b(R) = \langle ^2\Pi _{-\frac{1}{2}} | \hat{H}_{\rm SO} | ^2\Sigma _{\frac{1}{2}} \rangle $\end{document}b(R)=⟨2Π−12|Ĥ SO |2Σ12⟩ are calculated as a function the interatomic distance R. We show that a(R) increases and b(R) decreases as R decreases. This effect becomes less and less important as the mass of the alkali increases. A comparison of the rovibrational properties deduced from our calculations with experimental measurements recorded for NaKr and NaXe shows the quality of the calculations.
Electron paramagnetic resonance in positively charged Au25 molecular nanoclusters
Authors: Akbari-Sharbaf Arash , Hesari Mahdi , Workentin Mark S. , Fanchini Giovanni
Published: January 2013

In this study, we investigated the unpaired electrons and singly occupied molecular orbitals (SOMO) of positively charged Au25 molecular clusters using solid-state electron paramagnetic resonance (EPR). The EPR powder spectra of the positively charged (Au25+) and neutral (Au250) species of Au25 are discussed and compared. Our study demonstrates that Au25+ is paramagnetic with a SOMO that is mostly localized about the central gold atom in the core of the molecule and possesses a strong p-type atomic character. The unpaired electron spin is demonstrated to strongly interact with the nuclear spins from other 197Au nuclei in the core of Au25+ molecules and the hyperfine tensor describing such interaction was extracted from the comparison of the EPR spectra with quantum mechanical simulations assuming an anisotropic structure of the core. Our simulations suggest that the core of Au25+ molecular clusters is more distorted than in the corresponding neutral counterpart. They also confirm previous hypotheses suggesting that the icosahedral core of Au25+ experiences contraction with decreasing temperature.
Non-Hermitian oscillator and $\cal {R}$R-deformed Heisenberg algebra
Authors: Roychoudhury R. , Roy B. , Dube P. P.
Published: January 2013

A non-Hermitian generalized oscillator model, generally known as the Swanson model, has been studied in the framework of \documentclass[12pt]{minimal}\begin{document}$\cal {R}$\end{document}R-deformed Heisenberg algebra. The non-Hermitian Hamiltonian is diagonalized by generalized Bogoliubov transformation. A set of deformed creation annihilation operators is introduced whose algebra shows that the transformed Hamiltonian has conformal symmetry. The spectrum is obtained using algebraic technique. The superconformal structure of the system is also worked out in detail. An anomaly related to the spectrum of the Hermitian counterpart of the non-Hermitian Hamiltonian with generalized ladder operators is shown to occur and is discussed in position dependent mass scenario.
Cluster characterization in supersonic nozzles using semi-empirical modeling of non-equilibrium condensation flow
Authors: Takahashi Kazumasa , Nakajima Mitsuo , Hasegawa Jun , Horioka Kazuhiko
Published: January 2013

A fundamental understanding of nucleation and condensation kinetics in non-equilibrium expanding flow is required for the formation of controllable and high-flux cluster beams. To obtain these microscopic data for the nucleation and condensation processes and also to establish a numerical modeling for the condensation flow, an experiment was performed based on parametric measurements of pressure distribution in supersonic argon flows. A method to predict the cluster properties was proposed based on the semi-empirical fitting of the condensation and surface tension coefficients to the pressure measurements of the condensation flow.
Microwave-enhanced dephasing time in a HgCdTe film
Authors: Wei L. M. , Gao K. H. , Liu X. Z. , Yu G. , Wang Q. W. , Lin T. , Guo S. L. , Wei Y. F. , Yang J. R. , He L. , Dai N. , Chu J. H. , Austing D. G.
Published: January 2013

The antilocalization effect in a compensated HgCdTe film is observed. With an applied microwave field, both the zero-magnetic-field conductance and the dephasing time are enhanced nonlinearly with microwave power. The observation concerning the dephasing time is inconsistent with a heating mechanism. Such behavior is also in contrast to the microwave-induced suppression of weak-antilocalization and dephasing time seen for a two-dimensional electron gas of the anodic-oxidized HgCdTe. The nonlinear increase in zero-magnetic-field conductance is consistent with a microwave-assisted-hopping mechanism. The increased dephasing time can be explained qualitatively by the microwave-assisted-hopping mechanism and a microwave-induced increase in the electron density.
Effect of acoustic coupling on power-law flame acceleration in spherical confinement
Authors: Akkerman V’yacheslav , Law Chung K.
Published: January 2013

A model describing acoustically-generated parametric instability in a spherical chamber is developed for quasi-one-dimensional, low-Mach number flames. We demonstrate how sound waves generated by a centrally-ignited, outwardly-propagating accelerating flamefront can be incorporated into an existing theory of self-similar flame acceleration in free space [V. Akkerman, C. K. Law, and V. Bychkov, “Self-similar accelerative propagation of expanding wrinkled flames and explosion triggering,” Phys. Rev. E 83, 026305 (2011)]10.1103/PhysRevE.83.026305. Being reflected from the chamber wall, flame-generated acoustics interact with the flamefront and the attendant hydrodynamic flamefront cellular instability. This in turn affects the subsequent flame morphology and propagation speed. It is shown that the acoustics modify the power-law flame acceleration, concomitantly facilitating or inhibiting the transition to detonation in confinement, which allows reconciliation of a discrepancy in experimental measurements of different groups.
Local elastic response measured near the colloidal glass transition
Authors: Anderson D. , Schaar D. , Hentschel H. G. E. , Hay J. , Habdas Piotr , Weeks Eric R.
Published: January 2013

We examine the response of a dense colloidal suspension to a local force applied by a small magnetic bead. For small forces, we find a linear relationship between the force and the displacement, suggesting the medium is elastic, even though our colloidal samples macroscopically behave as fluids. We interpret this as a measure of the strength of colloidal caging, reflecting the proximity of the samples' volume fractions to the colloidal glass transition. The strain field of the colloidal particles surrounding the magnetic probe appears similar to that of an isotropic homogeneous elastic medium. When the applied force is removed, the strain relaxes as a stretched exponential in time. We introduce a model that suggests this behavior is due to the diffusive relaxation of strain in the colloidal sample.
Solutions of perturbed p-Laplacian equations with critical nonlinearity
Authors: Wang Chunhua , Wang Jiangtao
Published: January 2013

In this paper, we study a perturbed p-Laplacian equation. Under some given conditions on V(x), we prove that the equation has at least one positive solution provided that \documentclass[12pt]{minimal}\begin{document}$\epsilon \le \mathcal {E};$\end{document}ε≤E; for any \documentclass[12pt]{minimal}\begin{document}$n^{*}\in \mathbb {N},$\end{document}n*∈N, it has at least n* pairs solutions if \documentclass[12pt]{minimal}\begin{document}$\epsilon \le \mathcal {E}_{n^{*}}$\end{document}ε≤En*; and suppose there exists an orthogonal involution \documentclass[12pt]{minimal}\begin{document}$T:\mathbb {R}^{N}\rightarrow \mathbb {R}^{N}$\end{document}T:RN→RN such that V(x), P(x), and K(x) are T-invariant, then it has at least one pair of solutions, which change sign exactly once provided that \documentclass[12pt]{minimal}\begin{document}$\epsilon \le \mathcal {E}$\end{document}ε≤E, where \documentclass[12pt]{minimal}\begin{document}$\mathcal {E}$\end{document}E and \documentclass[12pt]{minimal}\begin{document}$\mathcal {E}_{n^{*}}$\end{document}En* are sufficiently small positive numbers. Moreover, these solutions uε → 0 in \documentclass[12pt]{minimal}\begin{document}$W^{1,p}(\mathbb {R}^{N})$\end{document}W1,p(RN) as ε → 0.
Thermal annealing effect on material characterizations of β-Ga2O3 epilayer grown by metal organic chemical vapor deposition
Authors: Huang Chiung-Yi , Horng Ray-Hua , Wuu Dong-Sing , Tu Li-Wei , Kao Hsiang-Shun
Published: January 2013

In this work, a single-crystalline β-Ga2O3 epilayer was grown on (0001) sapphire at low temperature by low-pressure metal organic chemical vapor deposition. The optimized parameters for the chamber pressure, oxygen flow, and growth temperature were 15 Torr, 200 sccm, and 500 °C, respectively. The β-Ga2O3 epilayer was fabricated as a metal-semiconductor-metal solar-blind deep ultraviolet photodetector. Due to the gallium oxide grown at low temperature, the as-grown β-Ga2O3 epilayer was annealed at 800 °C in atmosphere or in a nitrogen environment. The effects of defects of the β-Ga2O3 epilayer before and after N2 annealing were studied using x-ray diffraction system, cathodoluminescence at differential temperature, and Hall measurement. The β-Ga2O3 epilayer that was N2 annealed for 15 min presented better photodetector performance than the as-grown β-Ga2O3 epilayer. The annealed epilayer exhibited a dark current of 1.6 × 10−13 A under 5 V bias.
A local chemical environment effect in site-specific Auger spectra of ethyl trifluoroacetate
Authors: Iwayama H. , Sisourat N. , Lablanquie P. , Penent F. , Palaudoux J. , Andric L. , Eland J. H. D. , Bučar K. , Žitnik M. , Velkov Y. , Hikosaka Y. , Nakano M. , Shigemasa E.
Published: January 2013

We have investigated a local chemical environment effect on Auger spectra of ethyl trifluoroacetate (C4H5F3O2), using multi-electron coincidence spectroscopy and high-resolution electron spectroscopy. Site-specific KVV Auger spectra for each carbon atom, and for the fluorine and oxygen atoms are presented. The extent of hole localization in the final dicationic states was investigated with the help of theoretical calculations based on a two-hole population analysis. The Auger spectra have been simulated using a statistical approach. It is found that all Auger decays populate mainly localized dicationic states, with the two holes located either on the same fluorine atom or on adjacent fluorine atoms. While the decay of the F 1s hole populates exclusively the former states, the latter class of states is also populated by the decay of the C and O 1s holes.
Luminescent LaF3:Ce-doped organically modified nanoporous silica xerogels
Authors: Yao Mingzhen , Hall Ryan , Chen Wei , Mohite Dhairyashil P. , Leventis Nicholas , Lu Ning , Wang Jinguo , Kim Moon J. , Luo Huiyang , Lu Hongbing
Published: January 2013

Organically modified silica compounds (ORMOSILs) were synthesized by a sol-gel method from amine-functionalized 3-aminopropyl triethoxylsilane and tetramethylorthosilicate and were doped in situ with LaF3:Ce nanoparticles, which in turn were prepared either in water or in ethanol. Doped ORMOSILs display strong photoluminescence either by UV or X-ray excitation and maintain good transparency up to a loading level of 15.66% w/w. The TEM observations demonstrate that ORMOSILs remain nanoporous with pore diameters in the 5–10 nm range. LaF3:Ce nanoparticles doped into the ORMOSILs are rod-like, 5 nm in diameter and 10–15 nm in length. Compression testing indicates that the nanocomposites have very good strength, without significant lateral dilatation and buckling under quasi-static compression. LaF3:Ce nanoparticle-doped ORMOSILs have potential for applications in radiation detection and solid state lighting.
First-principles based multiscale model of piezoelectric nanowires with surface effects
Authors: Hoang M.-T. , Yvonnet J. , Mitrushchenkov A. , Chambaud G.
Published: January 2013

A continuum model of nanowires incorporating surface piezoelectricity is proposed which extends the electric enthalpy energy with surface terms. The corresponding equations are solved by a numerical method using finite elements technique. A methodology is introduced to compute the surface piezoelectric coefficients by first-principles calculations through the Berry phase theory. We provide the e33s, e31s, and e15s piezoelectric coefficients of (101¯0) surfaces for hexagonal wurtzite nanowires made of GaN, ZnO, and AlN. The effective piezoelectric coefficient along the axis of the nanowire is found to increase when the diameter decreases, for the three studied materials. Finally, the solution of the continuum model is compared with large-size first-principles calculations on piezoelectric nanowires.
Effects of strain relaxation on bare surface barrier height and two-dimensional electron gas in AlxGa1−xN/GaN heterostructures
Authors: Goyal Nitin , Fjeldly Tor A.
Published: January 2013

A physics based analytical model is presented to describe the bare surface barrier height and the two-dimensional electron gas density in AlGaN/GaN heterostructures versus barrier layer thickness and Al content. Details of the model rely on the extraction of the critical thickness for strain relaxation based on the identification of a signature cusp in experimentally obtained bare surface barrier heights. This information is used to obtain the residual strain and total effective polarization when strain relaxation takes place. The model, which covers both unrelaxed and relaxed barriers, shows good agreement with reported experimental results and promises to become a useful tool in advanced design and characterization of GaN based heterostructures.
Negative refraction and subwavelength imaging in a hexagonal two-dimensional annular photonic crystal
Authors: Xia Feng , Yun Maojin , Liu Meiling , Liang Jian , Kong Weijin , Tan Huiyue , Lv Wei
Published: January 2013

Negative refraction in a hexagonal two-dimensional (2D) annular photonic crystal (APC) has been studied. The photonic band structure and equal frequency contours of the designed APC are analyzed using the plane wave expansion method, and the subwavelength imaging is simulated using finite-difference time-domain method. Numerical simulation results indicate that negative refraction and subwavelength imaging can be realized in the designed APC. The resolution of the designed APC slab is better than the radiation wavelength.
Terahertz filters based on frequency selective surfaces for high-speed terahertz switch
Authors: Zhang Xiaoyu , Tan Renbing , Zheng ZhongXin , Li Xinxing , Zhang Zhipeng , Sun Jiandong , Zhou Yu , Lü Li , Zhang Baoshun , Qin Hua
Published: January 2013

We design and fabricate two terahertz (THz) filters based on frequency selective surfaces' structures (FSSs) on single crystal sapphire substrate, which show high and low transmissivities to THz electromagnetic waves, respectively. The difference of THz transmissivity between two filters reaches up to 72% at the resonance frequency of 1.35 THz. The THz filtering effect is due to the resonant coupling between THz wave and periodic metallic elements and the filter operating frequency can be tuned systematically by the geometry of FSSs. The good agreement between experiments and finite difference time domain simulation indicates that a high-speed THz switch could be realized for THz active devices based on the FSSs.
Electric-field-induced thermally assisted switching of monodomain magnetic bits
Authors: Khalili Amiri P. , Upadhyaya P. , Alzate J. G. , Wang K. L.
Published: January 2013

We present a study of the electric-field-induced switching of magnetic memory bits exhibiting interfacial voltage-controlled magnetic anisotropy (VCMA). Switching is analyzed in the single-domain approximation and in the thermally activated regime. The effects of external magnetic fields, magnitudes of the perpendicular anisotropy and VCMA effect, and voltage pulse width on the switching voltage are discussed. Both in-plane and perpendicular magnetic memory bits are considered. Experimental results are presented and compared to the theoretical model.
Structural studies of aromatic carboxylic acids via computational chemistry and microwave spectroscopy
Authors: Godfrey Peter D. , McNaughton Don
Published: January 2013

The structures of three simple aromatic carboxylic acids: benzoic, isophthalic, and terephthalic have been investigated using a combination of theoretical high-level quantum chemical calculations and experimental millimeter-wave Stark-modulated free-jet absorption spectroscopy. Rotational and centrifugal distortion constants have been measured for one conformer of each of the species and for its –COOD isotopologue, leading to the experimental determination of the coordinates of the carboxyl hydrogen atom. Consideration of the observed inertial defect is consistent with a planar equilibrium structure for each species. Calculated structures, relative energies, and electric dipole moments, using ab initio methods at the MP2/cc-pVTZ level, are reported for all the lower-energy conformers of each species. The theoretical calculations lead to the unambiguous identification of the conformers involved in the observed microwave spectra. The match between theoretical and spectroscopic measurements was used to gauge the reliability of the quantum chemical structure optimization calculations.
In situ investigation of vapor-deposited glasses of toluene and ethylbenzene via alternating current chip-nanocalorimetry
Authors: Ahrenberg M. , Chua Y. Z. , Whitaker K. R. , Huth H. , Ediger M. D. , Schick C.
Published: January 2013

Vapor-deposited glasses of toluene and ethylbenzene have been characterized by in situ ac chip-nanocalorimetry. The high sensitivity of this method allows the detection of small changes in the heat capacity of nanogram size samples. We observe that vapor-deposited glasses have up to 4% lower heat capacities than the ordinary glass. The largest heat capacity decrease and the most kinetically stable glasses of toluene and ethylbenzene are observed in a range of deposition temperatures between 0.75 Tg and 0.96 Tg. Compared to larger molecules, deposition rate has a minor influence on the kinetic stability of these glasses. For both toluene and ethylbenzene, the kinetic stability is strongly correlated with the heat capacity decrease for deposition temperatures above 0.8 Tg. In addition, ac-nanocalorimetry was used to follow the isothermal transformation of the stable glasses into the supercooled liquid at temperatures slightly above Tg. Toluene and ethylbenzene stable glasses exhibit a constant transformation rate which is consistent with the growth front mechanism recently demonstrated for tris-naphthylbenzene and indomethacin. The kinetic stability of the most stable toluene and ethylbenzene glasses is comparable to that observed for other stable glasses formed by vapor deposition.
Direct measurements of field-induced strain at magnetoelectric interfaces by grazing incidence x-ray diffraction
Authors: Abes M. , Koops C. T. , Hrkac S. B. , Greve H. , Quandt E. , Collins S. P. , Murphy B. M. , Magnussen O. M.
Published: January 2013

The magnetic field induced strain at the interface of a magnetoelectric composite, consisting of a ZnO(001) piezoelectric substrate and an amorphous (Fe90Co10)78Si12B10 magnetostrictive layer, was directly determined by grazing incidence X-ray diffraction. Upon applying a magnetic field along the [110] direction, the ZnO single crystal is under tensile strain in [110] direction and compressive strain in [1-10] direction, in agreement with the magnetostriction in the (Fe90Co10)78Si12B10 layer. At room temperature, the saturation strain along [1-10] of about 3 × 10−5 is close to the saturation magnetostriction of the film measured with the cantilever bending technique.
Variation in glass transition temperature of polymer nanocomposite films driven by morphological transitions
Authors: Chandran Sivasurender , Basu J. K. , Mukhopadhyay M. K.
Published: January 2013

We report the variation of glass transition temperature in supported thin films of polymer nanocomposites, consisting of polymer grafted nanoparticles embedded in a homopolymer matrix. We observe a systematic variation of the estimated glass transition temperature Tg, with the volume fraction of added polymer grafted nanoparticles. We have correlated the observed Tg variation with the underlying morphological transitions of the nanoparticle dispersion in the films. Our data also suggest the possibility of formation of a low-mobility glass or gel-like layer of nanoparticles at the interface, which could play a significant role in determining Tg of the films provided.
X-ray small-angle scattering from sputtered CeO2/C bilayers
Authors: Haviar S. , Dubau M. , Khalakhan I. , Vorokhta M. , Matolínová I. , Matolín V. , Valeš V. , Endres J. , Holý V. , Buljan M. , Bernstorff S.
Published: January 2013

Surface and interface morphology of cerium oxide/carbon bilayers used as thin-film catalysts is studied by grazing-incidence small-angle x-ray scattering, scanning electron microscopy, and atomic-force microscopy, and the dependence of the structural parameters on the thicknesses of the constituting layers is investigated. The applicability of x-ray scattering and its advantages over standard analytical methods are discussed.
Magnetic properties of copper hexadecaphthalocyanine (F16CuPc) thin films and powders
Authors: Wu Wei , Rochford L. A. , Felton S. , Wu Zhenlin , Yang J. L. , Heutz S. , Aeppli G. , Jones T. S. , Harrison N. M. , Fisher A. J.
Published: January 2013

The structural and magnetic properties of F16CuPc thin films and powder, including x-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometry, and theoretical modelling of exchange interactions are reported. Analysis of XRD from films, with thickness ranging between 100 and 160 nm, deposited onto Kapton and a perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) interlayer shows that the stacking angle (defined in the text) of the film is independent of the thickness, but that the texture is modified by both film thickness and substrate chemistry. The SQUID measurements suggest that all samples are paramagnetic, a result that is confirmed by our theoretical modelling including density functional theory calculations of one-dimensional molecular chains and Green's function perturbation theory calculations for a molecular dimer. By investigating theoretically a range of different geometries, we predict that the maximum possible exchange interaction between F16CuPc molecules is twice as large as that in unfluorinated copper-phthalocyanine (CuPc). This difference arises from the smaller intermolecular spacing in F16CuPc. Our density functional theory calculation for isolated F16CuPc molecule also shows that the energy levels of Kohn-Sham orbitals are rigidly shifted ∼1 eV lower in F16CuPc compared to CuPc without a significant modification of the intra-molecular spin physics, and that therefore the two molecules provide a suitable platform for independently varying magnetism and charge transport.
The 4νCH overtone of 12C2H2: Sub-MHz precision spectrum reveals perturbations
Authors: Liu A.-W. , Li X.-F. , Wang J. , Lu Y. , Cheng C.-F. , Sun Y. R. , Hu S.-M.
Published: January 2013

The third CH stretching vibration overtone (4νCH) of the acetylene molecule has been a prototype for intra-molecular dynamics studies. Using a sensitive cavity ring-down spectrometer calibrated with precise atomic transitions, the absolute line frequencies of 50 lines of this band have been determined with sub-MHz accuracy, or relatively 2 × 10−9. The accuracy is also confirmed by the combination differences between the transitions sharing the same upper level. The improved accuracy, two orders of magnitude better than previous studies, allows us to reveal finer ro-vibrational couplings. Fitting of the rotational energies indicates that the J-dependent interactions take place after J > 7. The precise line positions present useful confinements to the models of the intra-molecular interactions of the acetylene molecule.
Microstructure-reactivity relationship of Ti + C reactive nanomaterials
Authors: Manukyan Khachatur V. , Lin Ya-Cheng , Rouvimov Sergei , McGinn Paul J. , Mukasyan Alexander S.
Published: January 2013

The influence of short-term (≤10 min) high energy ball milling (HEBM) on the microstructure and reactivity of a titanium-carbon powder mixture is reported. It is proved that the mechanism of microstructural transformation in a Ti-C mixture during HEBM defines the reaction mechanism in the produced Ti/C structural energetic materials. More specifically, it is shown that after the first two minutes of dry milling (DM) in an inert (argon) atmosphere the initially crystalline graphite flakes were almost completely amorphized and uniformly distributed on the surface of the deformed titanium particles. A subsequent “cold-welding” leads to formation of Ti-(C-rich/Ti)-Ti agglomerates. TEM studies reveal that the (C-rich/Ti) composite layers consist of nano-size (20 nm) Ti particles distributed in the matrix of the amorphous carbon and thus are characterized by extremely high surface area contacts between the reagents. A rapid self-ignition of the material during DM occurs just after 9.5 min of mechanical treatment, resulting in formation of pure cubic TiC. Wet grinding (WG) of a Ti-C mixture in hexane, under otherwise identical parameters, provides more “soft” conditions, which do not allow the rapid amorphization of carbon during the first stage of grinding. As a result graphite and titanium form sandwich-like Ti/C composite particles, in which the reagents contact primarily along the boundaries of the layers. Such particles gradually transform to the TiC phase without a spontaneous reaction during the HEBM process. The reactivity, i.e., self-ignition temperature and ignition delay time, of different milling-induced microstructures, were also studied. It was found that the ignition temperature in Ti-C structural energetic material prepared under optimized HEBM conditions is ∼600 K, which is more than three times lower than that of the initial reaction mixture (Tig ∼ 1900 K). A significant decrease of the effective activation energy for interaction in the Ti-C system is observed (from 95 kcal/mol to ∼56 kcal/mol). It is explained by the fact that solely solid-state reactions are responsible for the ignition phenomenon in the produced structural energetic materials, whereas the dissolution of carbon in a melt is responsible for the reaction in non-mechanically treated mixtures. Analysis of the milling-induced microstructures and reaction kinetics of the Ti/C composite particles suggests that a combination of several factors is responsible for enhancement of their reactivity, with the carbon amophization on the first stage of HEBM playing a key role through formation of layers that provide intimate high surface area contacts between the reagents.
High Faraday effect of antiferromagnetic/ion-crystal photonic crystals in far infrared region
Authors: Wang Xuan-Zhang , Zhao Yan
Published: January 2013

The Faraday effect of one-dimensional antiferromagnetic/ion-crystal photonic crystals (AF/IC PCs) is investigated. In numerical calculation, AF layers are FeF2 and IC layers are of IV-VI semiconductor. A valuable geometry with higher Faraday effect is found, where an incident electromagnetic wave normally illuminates the lateral surface of such a PC and the external field and AF anisotropy axis both are pointed along the wave-vector. From the numerical results based on several relevant PCs, we conclude that the FeF2/PbSe PC possesses the highest Faraday effect. Although the effect originates from AF layers and is influenced by the PC anisotropy, the rotation angle is the largest at a finite AF filling ratio (fa=0.6), reaching 22.5°μm−1 and about 20 times that of FeF2. We also discuss the wave attenuation in the PCs, and consequently find that the attenuation is lower and the transmission is better in this geometry.
Magneto-elastic behaviour of thin type-II superconducting strip with field-dependent critical current
Authors: Xue Cun , He An , Yong Huadong , Zhou Youhe
Published: January 2013

The magneto-elastic behavior of thin superconducting strip in perpendicular magnetic field with field-dependent critical current is studied. We calculate numerically the body force, strain, displacement, and thickness changes in the strip for the Bean model and Kim model during the field ascent and descent. The differences in magnetostriction between the Bean model and the Kim model are analyzed. The magnetostriction during one full cycle of the applied field for both models is presented. The results show that magnetostriction loops are different in these models, and at low temperatures Kim model is in better agreement with experiment than Bean model.
Formation and upper critical fields of the two distinct A15 phases in the subelements of powder-in-tube Nb3Sn wires
Authors: Senatore Carmine , Flükiger René
Published: January 2013

It is well known that the A15 layer in the subelements of a powder-in-tube (PIT) Nb3Sn wire exhibits two different grain morphologies: a region with fine grains (∼200 nm in size) representing about 60% of the total A15 area and one with large grains (1–2 μm in size). By means of high field specific heat and magnetization measurements, we have shown that these two A15 phases correspond to two distinctly different Tc distributions, the large grains region exhibiting a higher Tc and a lower Bc2, the fine grains region a lower Tc and a higher Bc2. We report here the values of the superconducting parameters (Tc, Bc2) of the two A15 phases, as determined from an original model to fit the experimental Tc distribution. After a prolonged reaction treatment (625 °C/320 h), an increase of the fine grain region was observed at the expenses of the large grain region, the Bc2(0 K) value of the former being raised from 28.8 to 31.7 T. These changes explain the marked increase of Jc to 2700 A/cm2 at 4.2 K/12 T, the highest value measured so far in PIT wires.
The luminescence characteristics of CsI(Na) crystal under α and X/γ excitation
Authors: Liu Jinliang , Liu Fang , Ouyang Xiaoping , Liu Bin , Chen Liang , Ruan Jinlu , Zhang Zhongbing , Liu Jun
Published: January 2013

In this paper, we study the effective decay time characteristic of CsI(Na) crystal under 239Pu alpha particle and 137Cs gamma-ray excitation using a single photon counting decay time measurement system. The measurement system employs a silicon optical fiber to couple and transit single photon. The slow decay time component of CsI(Na) crystal is 460–550 ns. We observe a 15 ns fast decay component under alpha particle excitation. In addition, we find that the primary stage of the falling edge in the decay time curve is non-exponential and drops rapidly when CsI(Na) crystal is excited by 239Pu alpha particles. Since the high density of self-trapped-excitons (STEs) is produced in alpha particle excitation process, we propose that the fast falling edge is corresponding to the quenching process of STEs which transit with non-radiation in the case of high excitation density. To prove this proposal, we excited the CsI(Na) crystal with sub-nanosecond intensive pulsed X-ray radiation. Our X-ray impinging results show that the fast falling edge also exists under low energy (average 100 keV) bremsstrahlung X-ray excitation.
A nanoscale transmission system with novel-structured carbon nanotubes
Authors: Kan Biao , Ding Jianning , Zhang Yongbin , Zhang Zhongqiang , Cheng Guanggui
Published: January 2013

We present a prototype of nanoscale transmission system consisted of three novel-structured carbon nanotubes, namely, the “T,” “I,” and “Ω” type nanotubes. Double-walled carbon nanotubes (DWCNTs) serve as joints and linear bearings in this system. Molecular dynamics simulations were carried out to investigate the transmission properties. The obtained results show that this system can work at ultrahigh rotation speeds ∼109 rps with a broad temperature range 10–1000 K. The maximum variations of the output displacement in the stroke and lateral directions caused by the vibration are, respectively, 2.3–2.6 Å and 0.27–0.95 Å, which are 6.1%–7.0% and 0.7%–2.5% of the stroke length, respectively. Moreover, the displacement precision can be effectively improved by decreasing the input rotation speed or the temperature. The small change of the van der Waals potential energy in the DWCNTs indicates ultra low frictions in the joints, which contributes to the smooth transmission motion of the system. These results may suggest a new approach to the design of nanoscale electromechanical systems by taking different types of novel-structured carbon nanotubes.
Experiment of low resistance joints for the ITER correction coil
Authors: Huajun Liu , Yu Wu , Weiyue Wu , Bo Liu , Yi Shi , Shuai Guo
Published: January 2013

A test method was designed and performed to measure joint resistance of the ITER correction coil (CC) in liquid helium (LHe) temperature. A 10 kA superconducting transformer was manufactured to provide the joints current. The transformer consisted of two concentric layer-wound superconducting solenoids. NbTi superconducting wire was wound in the primary coil and the ITER CC conductor was wound in the secondary coil. The primary and the secondary coils were both immersed in liquid helium of a 300 mm useful bore diameter cryostat. Two ITER CC joints were assembled in the secondary loop and tested. The current of the secondary loop was ramped to 9 kA in several steps. The two joint resistances were measured to be 1.2 nΩ and 1.65 nΩ, respectively.
Spectral response tuning using an optical spacer in broad-band organic solar cells
Authors: Zhang Yuliang , Pandey Ajay K. , Tao Chen , Fang Yuan , Jin Hui , Burn Paul L. , Meredith Paul
Published: January 2013

The effect of a zinc oxide optical spacer layer in broad-band polymer-fullerene solar cells is presented. The complimentary absorption in the donor and acceptor components allows photocurrent generation through photoinduced electron and hole-transfer mechanisms. Simulations of the optical-field distribution reveal that an optical spacer can be used to tune the spectral response to favor one photocurrent generation pathway via enhanced absorption in either the acceptor or donor component. Experimental results confirm these simulations, and the spacer is shown to enhance overall photocurrent in devices with thin active layers (<60 nm), with much less effect in thicker junctions (>90 nm).
Buffer layer induced band gap and surface low energy optical phonon scattering in epitaxial graphene on SiC(0001)
Authors: Yu C. , Li J. , Liu Q. B. , Dun S. B. , He Z. Z. , Zhang X. W. , Cai S. J. , Feng Z. H.
Published: January 2013

The temperature dependent electrical properties of epitaxial graphene grown on Si-face and C-face SiC substrates were investigated by Hall measurements, respectively. Quasi-free-standing epitaxial graphene by H2 intercalation was adopted as the control. Due to a ∼200 meV band gap, the electrical conductivities of graphene on Si-face SiC showed a great increase at temperatures above 350 K compared to the other two. The opened band gap was found attributed to the existent buffer layer. The fitting results of Hall mobility indicates that the buffer layer also limits the carrier transportation of graphene grown on Si-face SiC, as it introduced low energy optical phonon scattering to its epilayer.
Label-free chemiresistive biosensor for mercury (II) based on single-walled carbon nanotubes and structure-switching DNA
Authors: Gong Ji-Lai , Sarkar Tapan , Badhulika Sushmee , Mulchandani Ashok
Published: January 2013

Herein, we present a sensitive, selective, and facile label-free DNA functionalized single-walled carbon nanotube (SWNT)-based chemiresistive biosensor for the detection of Hg2+. SWNTs were functionalized with Hg2+ binding 15-bases long polyT oligonucleotide through covalent attachment using a bilinker molecule. The polyT was further hybridized with polyA to form a polyT-polyA duplex. When exposed to Hg2+ the polyT-polyA duplex was dehybridized combined with switching of polyT structure, leading to change in resistance/conductance of the SWNT chemiresistor device. The device provided a significant response within 100 to 1000 nM of Hg2+ concentration with a 6.72 × 10−3 nM−1 sensitivity.
Spectral coarse graining for random walks in bipartite networks
Authors: Wang Yang , Zeng An , Di Zengru , Fan Ying
Published: January 2013

Many real-world networks display a natural bipartite structure, yet analyzing and visualizing large bipartite networks is one of the open challenges in complex network research. A practical approach to this problem would be to reduce the complexity of the bipartite system while at the same time preserve its functionality. However, we find that existing coarse graining methods for monopartite networks usually fail for bipartite networks. In this paper, we use spectral analysis to design a coarse graining scheme specific for bipartite networks, which keeps their random walk properties unchanged. Numerical analysis on both artificial and real-world networks indicates that our coarse graining can better preserve most of the relevant spectral properties of the network. We validate our coarse graining method by directly comparing the mean first passage time of the walker in the original network and the reduced one.
Accurate alignment of a photonic crystal nanocavity with an embedded quantum dot based on optical microscopic photoluminescence imaging
Authors: Kojima T. , Kojima K. , Asano T. , Noda S.
Published: January 2013

We have developed a technique to align a two-dimensional photonic-crystal nanocavity (PCNC) with an indium arsenide/gallium arsenide self-assembled quantum dot (QD), using microscopic photoluminescence (μ-PL) spectroscopy to image a wafer with a low-density of QDs and pre-formed positioning marks. Individual QD emission wavelengths were evaluated from μ-PL spectra, and positions relative to the marks were determined. The wavelength detuning between the QD-emission peak and the PCNC resonant frequency was < 4 nm, and the alignment standard deviation was < 50 nm. The emission peaks of a single QD and a PCNC aligned by this technique showed anti-crossing, implying high accuracy.
Unique topological characterization of braided magnetic fields
Authors: Yeates A. R. , Hornig G.
Published: January 2013

We introduce a topological flux function to quantify the topology of magnetic braids: non-zero, line-tied magnetic fields whose field lines all connect between two boundaries. This scalar function is an ideal invariant defined on a cross-section of the magnetic field, and measures the average poloidal magnetic flux around any given field line, or the average pairwise crossing number between a given field line and all others. Moreover, its integral over the cross-section yields the relative magnetic helicity. Using the fact that the flux function is also an action in the Hamiltonian formulation of the field line equations, we prove that it uniquely characterizes the field line mapping and hence the magnetic topology.
Influence of wall thickness on the stability of the resistive wall mode in tokamak plasmas
Authors: Fitzpatrick Richard
Published: January 2013

The influence of finite wall thickness on the stability of the resistive wall mode (RWM) in a tokamak is determined using a simple cylindrical plasma model in which the dissipation required to stabilize the mode is provided by neoclassical parallel ion viscosity. For present-day tokamaks, which possess relatively thin walls, finite wall thickness effects are found to have relatively little influence on the RWM stability boundaries, which are almost the same as those calculated in the thin-wall limit. On the other hand, for next-step devices, which are likely to possess much thicker walls than present-day tokamaks, finite wall thickness effects are found to significantly impede the ability of plasma rotation to stabilize the RWM all the way to the perfect-wall stability limit.
Perspective: Nanomotors without moving parts that propel themselves in solution
Authors: Kapral Raymond
Published: January 2013

Self-propelled nanomotors use chemical energy to produce directed motion. Like many molecular motors they suffer strong perturbations from the environment in which they move as a result of thermal fluctuations and do not rely on inertia for their propulsion. Such tiny motors are the subject of considerable research because of their potential applications, and a variety of synthetic motors have been made and are being studied for this purpose. Chemically powered self-propelled nanomotors without moving parts that rely on asymmetric chemical reactions to effect directed motion are the focus of this article. The mechanisms they use for propulsion, how size and fuel sources influence their motion, how they cope with strong molecular fluctuations, and how they behave collectively are described. The practical applications of such nanomotors are largely unrealized and the subject of speculation. Since molecular motors are ubiquitous in biology and perform a myriad of complex tasks, the hope is that synthetic motors might be able to perform analogous tasks. They may have the potential to change our perspective on how chemical dynamics takes place in complex systems.
Consistently low subthreshold swing in carbon nanotube transistors using lanthanum oxide
Authors: Franklin Aaron D. , Bojarczuk Nestor A. , Copel Matthew
Published: January 2013

While a few singular reports have demonstrated carbon nanotube (CNT) transistors with subthreshold swings (SS) close to the theoretical limit (60 mV/decade), the majority of devices have more than double the target swing. Here, we show that a low temperature lanthanum oxide dielectric is able to yield a consistently and reproducibly low SS, with an average of 73 mV/decade and a low of 63 mV/decade. This LaOx film is characterized using medium energy ion scattering and shown to be scalable down to 3.5 nm with minimal leakage and a variation in swing of only ±13%. With interface traps playing a dominant role in the switching behavior of CNT transistors, these results reveal the existence of dielectrics with more favorable interfacial characteristics for nanotubes that yield low SS devices.
Note: A very simple circuit for piezo actuator pseudo-tracking for continuous-wave cavity ring-down spectroscopy
Authors: Földes T.
Published: January 2013

A very simple circuit for pseudo-tracking of the piezo actuator for continuous-wave cavity ring-down spectroscopy (cw-CRDS) is presented. The circuit is based on an ordinary positive-edge trigger D-type flip flop integrated circuit, has a low parts count, and can be easily assembled using only off the shelf components. The circuit can be straightforwardly incorporated into most cw-CRDS setups and, thanks to the increased ring-down event rate, higher sensitivity or lower data acquisition time can be achieved.
A general theory for gauge-free lifting
Authors: Morrison P. J.
Published: January 2013

A theory for lifting equations of motion for charged particle dynamics, subject to given electromagnetic like forces, up to a gauge-free system of coupled Hamiltonian Vlasov-Maxwell like equations is given. The theory provides very general expressions for the polarization and magnetization vector fields in terms of the particle dynamics description of matter. Thus, as is common in plasma physics, the particle dynamics replaces conventional constitutive relations for matter. Several examples are considered including the usual Vlasov-Maxwell theory, a guiding center kinetic theory, Vlasov-Maxwell theory with the inclusion of spin, and a Vlasov-Maxwell theory with the inclusion of Dirac's magnetic monopoles. All are shown to be Hamiltonian field theories and the Jacobi identity is proven directly.
Towards a complete parametrization of the ordinary-mode electromagnetic instability in counterstreaming plasmas. I. Minimizing ion dynamics
Authors: Ibscher D. , Lazar M. , Michno M. J. , Schlickeiser R.
Published: January 2013

The ordinary mode instability can be driven by drifting bi-Maxwellian plasma particle distributions with and without temperature anisotropy. Here, the linear instability analysis is generalized for realistic settings, when the plasma streams are magnetized and hot enough. The new parametrization proposed in this study enables a better understanding of the interplay of counterstreaming and temperature anisotropy, providing the derivation of new regimes of the ordinary mode instability. Accurate analytical forms are derived for the instability conditions for general values of the temperature anisotropy, the streaming velocity, and the parallel plasma beta. To keep the analysis straightforward, the role of ions is minimized.
Biomimetic tumor microenvironment on a microfluidic platform
Authors: Ma Huipeng , Xu Hui , Qin Jianhua
Published: January 2013

Tumor microenvironment is a highly complex system consisting of non-cancerous cells, soluble factors, signaling molecules, extracellular matrix, and mechanical cues, which provides tumor cells with integrated biochemical and biophysical cues. It has been recognized as a significant regulator in cancer initiation, progression, metastasis, and drug resistance, which is becoming a crucial component of cancer biology. Modeling microenvironmental conditions of such complexity in vitro are particularly difficult and technically challenging. Significant advances in microfluidic technologies have offered an unprecedented opportunity to closely mimic the physiological microenvironment that is normally encountered by cancer cells in vivo. This review highlights the recent advances of microfluidic platform in recapitulating many aspects of tumor microenvironment from biochemical and biophysical regulations. The major events relevant in tumorigenesis, angiogenesis, and spread of cancer cells dependent on specific combinations of cell types and soluble factors present in microenvironmental niche are summarized. The questions and challenges that lie ahead if this field is expected to transform the future cancer research are addressed as well.
Note: Focus error detection device for thermal expansion-recovery microscopy (ThERM)
Authors: Domené E. A. , Martínez O. E.
Published: January 2013

An innovative focus error detection method is presented that is only sensitive to surface curvature variations, canceling both thermoreflectance and photodefelection effects. The detection scheme consists of an astigmatic probe laser and a four-quadrant detector. Nonlinear curve fitting of the defocusing signal allows the retrieval of a cutoff frequency, which only depends on the thermal diffusivity of the sample and the pump beam size. Therefore, a straightforward retrieval of the thermal diffusivity of the sample is possible with microscopic lateral resolution and high axial resolution (∼100 pm).