bluuebunny/crossref_metadata_2025 huggingface dataset:
Uncorrelated multiple conductive filament nucleation and rupture in ultra-thin high-κ dielectric based resistive random access memory
Authors: Wu Xing , Li Kun , Raghavan Nagarajan , Bosman Michel , Wang Qing-Xiao , Cha Dongkyu , Zhang Xi-Xiang , Pey Kin-Leong
Published: August 2011

Resistive switching in transition metal oxides could form the basis for next-generation non-volatile memory (NVM). It has been reported that the current in the high-conductivity state of several technologically relevant oxide materials flows through localized filaments, but these filaments have been characterized only individually, limiting our understanding of the possibility of multiple conductive filaments nucleation and rupture and the correlation kinetics of their evolution. In this study, direct visualization of uncorrelated multiple conductive filaments in ultra-thin HfO2-based high-κ dielectric resistive random access memory (RRAM) device has been achieved by high-resolution transmission electron microscopy (HRTEM), along with electron energy loss spectroscopy (EELS), for nanoscale chemical analysis. The locations of these multiple filaments are found to be spatially uncorrelated. The evolution of these microstructural changes and chemical properties of these filaments will provide a fundamental understanding of the switching mechanism for RRAM in thin oxide films and pave way for the investigation into improving the stability and scalability of switching memory devices.
Self-consistency in frozen-density embedding theory based calculations
Authors: Aquilante Francesco , Wesołowski Tomasz A.
Published: August 2011

The bi-functional for the non-electrostatic part of the exact embedding potential of frozen-density embedding theory (FDET) depends on whether the embedded part is described by means of a real interacting many-electron system or the reference system of non-interacting electrons (see [Wesolowski, Phys. Rev. A. 77, 11444 (2008)]). The difference \documentclass[12pt]{minimal}\begin{document}$\frac{\delta\Delta F^{MD}[\rho_A]}{\delta\rho_A(\vec{r})}$\end{document}δΔFMD[ρA]δρA(r⃗), where ΔFMD[ρA] is the functional bound from below by the correlation functional Ec[ρA] and from above by zero. Taking into account ΔFMD[ρA] in both the embedding potential and in energy is indispensable for assuring that all calculated quantities are self-consistent and that FDET leads to the exact energy and density in the limit of exact functionals. Since not much is known about good approximations for ΔFMD[ρA], we examine numerically the adequacy of neglecting ΔFMD[ρA] entirely. To this end, we analyze the significance of \documentclass[12pt]{minimal}\begin{document}$\frac{\delta\Delta F^{MD}[\rho_A]}{\delta\rho_A(\vec{r})}$\end{document}δΔFMD[ρA]δρA(r⃗) in the case where the magnitude of ΔFMD[ρA] is the largest, i.e., for Hartree-Fock wavefunction. In hydrogen bonded model systems, neglecting \documentclass[12pt]{minimal}\begin{document}$\frac{\delta\Delta F^{MD}[\rho_A]}{\delta\rho_A(\vec{r})}$\end{document}δΔFMD[ρA]δρA(r⃗) in the embedding potential marginally affects the total energy (less than 5% change in the interaction energy) but results in qualitative changes in the calculated hydrogen-bonding induced shifts of the orbital energies. Based on this estimation, we conclude that neglecting \documentclass[12pt]{minimal}\begin{document}$\frac{\delta\Delta F^{MD}[\rho_A]}{\delta\rho_A(\vec{r})}$\end{document}δΔFMD[ρA]δρA(r⃗) may represent a good approximation for multi-reference variational methods using adequate choice for the active space. Doing the same for single-reference perturbative methods is not recommended. Not only it leads to violation of self-consistency but might result in large effect on orbital energies. It is shown also that the errors in total energy due to neglecting \documentclass[12pt]{minimal}\begin{document}$\frac{\delta\Delta F^{MD}[\rho_A]}{\delta\rho_A(\vec{r})}$\end{document}δΔFMD[ρA]δρA(r⃗) do not cancel but rather add up to the errors due to approximation for the bi-functional of the non-additive kinetic potential.
Ultra wide band frequency characterization of integrated TiTaO-based metal–insulator–metal devices
Authors: Bertaud Thomas , Bermond Cédric , Challali Fatiha , Goullet Antoine , Vallée Christophe , Fléchet Bernard
Published: August 2011

The titanium tantalum oxide, TiTaO, was fully characterized in situ in an integrated metal–insulator–metal (MIM) configuration on a wide frequency band, from 1 mHz to 30 GHz. First, XPS and XRD analysis show that TiTaO dielectric is amorphous and presents Ti-O, Ta-O, and Ti-Ta bounds. Next, by using dedicated MIM test devices and a specific extraction procedure, both relative permittivity κ and loss tangent tanδ were extracted on the wide frequency band. The results show a dependence on both frequency and thickness. Conduction mechanism of ion impurities such as oxygen vacancies at very low frequencies (below 0.1 Hz), Maxwell-Wagner relaxations due to space charges at electrode interface (between 0.1 and 5 Hz), and dielectric grain boundaries or hopping (between 1 and 100 MHz) are underlined and studied with temperature measurements. The paper shows the usefulness of in situ wideband frequency measurements and that the dielectric permittivity of TiTaO in a 100 nm thick film is decreasing from 86 at 10 kHz to 20 at 10 GHz.
Study of spin glass and cluster ferromagnetism in RuSr2Eu1.4Ce0.6Cu2O10-δ magneto superconductor
Authors: Kumar Anuj , Tandon R. P. , Awana V. P. S.
Published: August 2011

We report DC magnetization, detailed systematic linear and nonlinear AC magnetic susceptibility and transport for a single phase RuSr2Eu1.4Ce0.6Cu2O10-δ (EuRu-1222) magneto-superconductor. The studied sample is synthesized through standard solid state reaction route, which is crystallized in single phase tetragonal structure with space group I4/mmm. DC magnetic susceptibility measurements revealed that the studied EuRu-1222 is a magneto-superconductor with Ru spins ordering at around 110 K and superconductivity in the Cu-O2 planes below ≈ 30 K. Temperature dependence of AC susceptibility with different frequency and amplitude variations confirms spin-glass behavior with cluster ferromagnetism of the system. Change in the cusp position with frequency follows the Vogel-Fulcher law, which is commonly accepted feature for a spin-glass (SG) system with ferromagnetic clusters. The third harmonic of AC susceptibility (χ3) shows that the system undergoes a spin glass transition below 80 K. Superconducting transition temperature (Tc) onset and ρ = 0 are seen at around 30 and 18 K without any applied field and the same decreases to 10 and 2 K under 130 kOe applied field. Also low fields isothermal (MH) suggests that ferromagnetic clusters are embedded in spin-glass (SG) matrix. The magnetization versus applied field (MH) loops exhibited ferromagnetic (FM) like behavior with rather small coercive fields. Detailed AC magnetic susceptibility measurements are carried out to unearth the short range magnetic correlations. These results support the spin-glass (SG) formation followed by ferromagnetic clustering effects at low temperatures. Our detailed magnetization and magneto transport results will undoubtedly contribute to current understanding of the complex magnetism of the EuRu-1222 system.
Electronic structure of the poly(3-hexylthiophene):indene-C60 bisadduct bulk heterojunction
Authors: Guan Ze-Lei , Bok Kim Jong , Loo Yueh-Lin , Kahn Antoine
Published: August 2011

The electronic structure of the poly(3-hexylthiophene):indene-C60 bisadduct (P3HT:ICBA) blend is investigated with direct and inverse photoemission spectroscopy. The energy gap between the lowest unoccupied molecular orbital (LUMO) of ICBA and the highest occupied molecular orbital (HOMO) of P3HT, which is central to the performance of photovoltaic cells made with this blend, is found equal to 1.68 eV. This value is larger than the difference between the ionization energy of the donor and the electron affinity of the acceptor, implying the existence of an interface dipole barrier between these two materials. Complementary contact potential difference measurements are done with a Kelvin probe in the dark on similar donor/acceptor pairs, e.g., P3HT:C60 and copper phthalocyanine (CuPc):C60, and confirm the existence of a dipole at these interfaces. It is estimated that a 0.3–0.4 eV ground state dipole exists at the P3HT:ICBA interface.
Comment on “Coherent states on spheres” [J. Math. Phys. 43, 1211 (2002)]
Authors: Rabeie A. , Jalilian Z.
Published: August 2011

Hall and Mitchell described a family of heat kernels (or equivalently coherent states) and an associated resolution of the identity for a quantum particle whose classical configuration space is the d-dimensional sphere Sd J. Math. Phys. 43(3), 1211 (2002). These heat kernels were chosen intelligently but in the case of d = 2, “one” of the formulas for the heat kernel must be corrected.
Structure, dynamics, and thermodynamics of a family of potentials with tunable softness
Authors: Shi Zane , Debenedetti Pablo G. , Stillinger Frank H. , Ginart Paul
Published: August 2011

We investigate numerically the structure, thermodynamics, and relaxation behavior of a family of (n, 6) Lennard-Jones-like glass-forming binary mixtures interacting via pair potentials with variable softness, fixed well depth, and fixed well depth location. These constraints give rise to progressively more negative attractive tails upon softening, for separations greater than the potential energy minimum. Over the range of conditions examined, we find only modest dependence of structure on softness. In contrast, decreasing the repulsive exponent from n = 12 to n = 7 causes the diffusivity to increase by as much as two orders of magnitude at fixed temperature and density, and produces mechanically stable packings (inherent structures) with cohesive energies that are, on average, ∼1.7 well depths per particle larger than for the corresponding Lennard-Jones (n = 12) case. The softer liquids have markedly higher entropies and lower Kauzmann temperatures than their Lennard-Jones (n = 12) counterparts, and they remain diffusive down to appreciably lower temperatures. We find that softening leads to a modest increase in fragility.
On the recursion operators for the Gerdjikov, Mikhailov, and Valchev system
Authors: Yanovski A. B.
Published: August 2011

We consider the Recursion Operator approach to the soliton equations related to an auxiliary linear system introduced recently by Gerdjikov, Mikhailov, and Valchev (GMV system). We discuss the recursion operators obtained for the GMV system and show that they are particular cases of the generating operators related to a Zakharov-Shabat type linear system on the algebra $\mbox{\rm sl\,}(3,\mathbb {C})$sl(3,C) in pole gauge.
On generalized Sethi-Vafa-Witten formulas
Authors: Fullwood James
Published: August 2011

We present a formula for computing proper pushforwards of classes in the Chow ring of a projective bundle under the projection \documentclass[12pt]{minimal}\begin{document}$\pi :{\mathbb {P}}(\mathscr{E})\rightarrow B$\end{document}π:P(E)→B, for B being a non-singular compact complex algebraic variety of any dimension. Our formula readily produces generalizations of formulas derived by Sethi, Vafa, and Witten to compute the Euler characteristic of elliptically fibered Calabi-Yau fourfolds used for F-theory compactifications of string vacua. The utility of such a formula is illustrated through applications, such as the ability to compute the Chern numbers of any non-singular complete intersection in such a projective bundle in terms of the Chern class of a line bundle on B.
Infrared multiphoton dissociation tandem charge detection-mass spectrometry of single megadalton electrosprayed ions
Authors: Doussineau Tristan , Yu Bao Cong , Clavier Christian , Dagany Xavier , Kerleroux Michel , Antoine Rodolphe , Dugourd Philippe
Published: August 2011

This work presents the implementation of tandem mass spectrometry for experiments on single electrosprayed ions from compounds of megadalton (MDa) molecular weight, using two charge detection devices. The first mass spectrometry stage (first charge detection device) combined with an ion gate allows both mass-to-charge ratio and charge selections of the megadalton ion of interest. The second stage is based on an electrostatic ion trap and consists of an image charge detection tube mounted between two ion mirrors. Single MDa ions can be stored for several dozen milliseconds. During the trapping time, single ions can be irradiated by a continuous wavelength CO2 laser. We observe stepwise changes in the charge of a single trapped ion owing to multiphoton activation. Illustration of infrared multiphoton dissociation tandem mass spectrometry are given for single megadalton ions of poly(ethylene oxide)s and DNAs.
Ionic polarization of liquid-liquid interfaces; dynamic control of the rate of electro-coalescence
Authors: Szymborski Tomasz , Korczyk Piotr M. , Hołyst Robert , Garstecki Piotr
Published: August 2011

Electrostatic forces are the strongest interactions in soft matter physics, yet they are usually screened by ions present in the solutions. Here we demonstrate that the extent of ionic polarization of liquid-liquid interfaces can be dynamically controlled via appropriate choice of the strength and frequency of the external electric field. Results of microfluidic experiments on electro-coalescence of droplets of aqueous solutions of salt provide guidelines for optimization of the process.
Enhancing single-parameter quantum charge pumping in carbon-based devices
Authors: Foa Torres Luis E. F. , Calvo Hernán L. , Rocha Claudia G. , Cuniberti Gianaurelio
Published: August 2011

We present a theoretical study of quantum charge pumping with a single ac gate applied to graphene nanoribbons and carbon nanotubes operating with low resistance contacts. By combining Floquet theory with Green’s function formalism, we show that the pumped current can be tuned and enhanced by up to two orders of magnitude by an appropriate choice of device length, gate voltage intensity, and driving frequency and amplitude. These results offer a promising alternative for enhancing the pumped currents in these carbon-based devices.
Doping of GaAs by laser ablated ZnTe
Authors: Ullrich B. , Brown G. J.
Published: August 2011

The exposure of GaAs to laser ablated ZnTe causes the formation of donor (Te)-acceptor (Zn) pair states. The photonically transferred dopants resulted in a distinct transition at 1.378 eV (FWHM ≤ 30 meV), visualized by room temperature photocurrent spectroscopy. The presence of impurity absorption in the GaAs was confirmed by transmission measurements. Notably, from the standpoint of technological applications, flipping the applied bias (±1.0 V) to the ZnTe/GaAs heterostructure switches the spectral photocurrent response between the fundamental GaAs absorption and the donor-acceptor transition peak. The results further reveal the influence of the ablating laser line on the optoelectronic device properties.
Micro-assembly using optically controlled bubble microrobots
Authors: Hu Wenqi , Ishii Kelly S. , Ohta Aaron T.
Published: August 2011

Bubbles controlled by optically induced heating were made to function as novel microrobots for micromanipulation and micro-assembly. Using light patterns generated by a commercial computer projector, bubble microrobots were controlled and used to manipulate glass microbeads and perform the micro-assembly of micro-blocks and cell-encapsulating hydrogel beads. Two manipulation modes, pulling and pushing, were used to move micro-objects into place and manipulate glass beads with a velocity of up to 350 μm/s. The simultaneous independent control of three bubble robots was also demonstrated.
Improving thermal stability of hard coating films via a concept of multicomponent alloying
Authors: Lind H. , Forsén R. , Alling B. , Ghafoor N. , Tasnádi F. , Johansson M. P. , Abrikosov I. A. , Odén M.
Published: August 2011

We propose a design route for the next generation of nitride alloys via a concept of multicomponent alloying based on self-organization on the nanoscale via a formation of metastable intermediate products during the spinodal decomposition. We predict theoretically and demonstrate experimentally that quasi-ternary (TiCrAl)N alloys decompose spinodally into (TiCr)N and (CrAl)N-rich nanometer sized regions. The spinodal decomposition results in age hardening, while the presence of Cr within the AlN phase delays the formation of a detrimental wurtzite phase leading to a substantial improvement of thermal stability compared to the quasi-binary (TiAl)N or (CrAl)N alloys.
Continuously tunable magnetic phase transitions in the DyMn1−xFexO3 system
Authors: Hong Fang , Cheng Zhenxiang , Zhao Hongyang , Kimura Hideo , Wang Xiaolin
Published: August 2011

The structure and magnetic properties of perovskite DyMn1−xFexO3 samples have been studied. Static orbital orderings are expected to exist in samples with x ≤ 0.2 due to strong Jahn-Teller distortion, which become less stable as x increases and probably disappears in samples with x > 0.5. The antiferromagnetic transition temperature increases as x increases. At the composition x > 0.5, spin reorientation starts to appear. Meanwhile, the spin reorientation temperature and the antiferromagnetic Néel temperature gradually separate and widen the temperature range of the magnetic metastable state between these two transitions. The magnetic competition is discussed based on exchange interaction and Dzyaloshinsky-Moriya interaction.
Pulsars with Strong Magnetic Fields: Polar Gaps, Bound Pair Creation and Nonthermal Luminosities
Authors: Usov VV , Melrose DB
Published: August 2011

Modifications to polar-gap models for pulsars are discussed for the case where the surface magnetic field, Bs, of the neutron star is strong. For B ~ 4 X 108 T, the curvature ,-quanta emitted tangentially to the curved force lines of the magnetic field are captured near the threshold of bound pair creation and are channelled along the magnetic field as bound electron-positron pairs (positronium). The stability of such bound pairs against ionization by the parallel electric field,. Ell' in the polar cap, and against photoionization is discussed. Unlike free pairs, bound pairs do not screen Ell near the neutron star. As a consequence, the energy flux in highly relativistic particles and high-frequency (X-ray and/or ,-ray) radiation from the polar gaps can be much greater than in the absence of positronium formation. We discuss this enhancement for (a) Arons-type models, in which particles flow freely from the surface, and find any enhancement to be modest, and (b) Ruderman-Sutherland-type models, in which particles are tightly bound to the surface, and find that the enhancement can be substantial. In the latter case we argue for a self-consistent model in which partial screening of Ell maintains it close to the threshold value for field ionization of the bound pairs, and in which a reverse flux of accelerated particles maintains the polar cap at a temperature such that thermionic emission supplies the particles needed for this screening. This model applies only in a restricted range of periods, P2 < P < PI, and it implies an energy flux in high-energy particles that can correspond to a substantial fraction of the spin-down power of the pulsar. Nonthermal, high-frequency radiation has been observed from six radio pulsars and Geming is usually included as a seventh case. The nonthermal luminosity can be higher than can be explained in terms of conventional polar-gap and outer-gap models. The self-consistent polar-gap model proposed here alleviates this difficulty, provided the magnetic field satisfies B ;G 4 X 108 T (which is so for five of these pulsars, and plausibly for the other two if a modest nondipolar component is assumed), and the surface temperature (in the absence of heating by the reverse flux) satisfies T; ;S 0 .5 X 106 K, so that thermionic emission from the surface is unimportant. It is argued that sufficient power is available to explain the observed high-frequency radiation of most of these pulsars. However, the Crab and PSR 0540-69 have periods P < P2, and we suggest that an outer-gap model is more appropriate for these. Our model implies a death line at P = PI "-J 0�5 s for B ;G 4 X 108 T, and we speculate on why, nevertheless, radio pulsars with strong fields are found at P > Pl.
Large Basis Calculation of Positron?Hydrogen Scattering at Low Energies
Authors: Mitroy Jim
Published: August 2011

Calculations of low energy positron-hydrogen scattering using the close coupling approach are reported at low energies. The channel space includes nine physical hydrogen and positronium states and in addition twelve hydrogen and positronium pseudo-states. For energies below the positronium formation threshold, phase shifts are reported for J = 0 to 6 and are believed to have an absolute accuracy of 0�0015 radian or better. Elastic scattering and positronium formation cross sections in the Ore gap for the J = 0 and J = 1 partial waves are essentially identical with previous variational calculations. Total elastic and positronium formation cross sections are reported at incident energies below the ionisation threshold. Cross sections for the excitation of the H(n=2), H(n=3) and Ps( n=2) levels are also reported over a restricted energy range, and the total reaction cross section has been computed and compared with experiment.
Studies of Cu/Ru(0001) and Cu/O/Ru(0001) Surfaces by LEIS, AES and LEED
Authors: Shen YG , Yao J , O'Connor DJ , Wandelt K , MacDonald RJ
Published: August 2011

Studies of Cu/Ru(OOOI) and Cu/O/Ru(OOOl) surfaces were made by applying low energy Li+ and He+ ion scattering with a combination of Auger electron spectroscopy, low energy electron diffraction and computer simulation. It was found that Cu grew on Ru(0001) layer-by-Iayer for the first two layers. Using Li+ ions, the results obtained by analysing the incident angle dependence associated with shadowing of Ru by Cu confirmed that the first layer Cu was in a normal registry position, i.e, there was a continuation of the hexagonal close-packed stacking sequence. The second layer Cu was determined to be in registry along the long azimuth (one of three possible domains) by analysing the shadowing features for the second layer Cu focusing onto the first layer Cu atoms. The Cu/O/Ru(0001) surface was also studied by He+ ion scattering. During deposition of Cu, the great majority of oxygen (about 70%) originally on the clean Ru(OOOl) surface was found to float out onto the top of the growing Cu overlayers. This displacement process could be observed up to Cu coverages of 10 ML, which appeared to be independent of the deposition rate, the 0 precoverage and the substrate temperature. The floating 0 atoms in the top layer have been determined to be a disordered overlayer by measuring the azimuthal scan dependence at grazing incidence.
Corrigendum: Mott?Schwinger Effect in the Elastic Scattering of Neutrons from 209Bi
Authors: Alexander N , Amos K , Berge L
Published: August 2011

The results presented in our recent paper are in error. All of the theoretical developments contained therein are correct but the Mott-Schwinger (MS) interaction was doubly counted for small radii in our computations. That had a significant effect upon the exact values of the small-f partial wave phase shifts. In fact, the correct variation of the first 20 partial wave phase shifts from purely nuclear scattering are much smaller than we presented before. Consequently the variation caused by the MS effect in predictions of the observables is smaller than previously indicated, and particularly so for scattering angles in excess of 20� for the cases of neutrons scattered from bismuth that were considered. At small angles, there are still characteristic and noticeable differences caused by the MS interaction for the scattering of 0�5, 14�5 and 24 MeV neutrons from 209Bi. With the differential cross section, the forward angle effect remains as shown previously; that is, dominated by the cot (~O) element in the scattering amplitudes due to the infinite partial wave sum of MS phase contributions. But the deviations to the higher angle cross sections reported earlier are very much reduced. The major effects of the correction, however, are with the predictions of the spin-dependent measureables and the exact results for P(O) and the two general variables, Xvar(O) and Yvar(O).
Systematics of the Electroweak Plasma at Finite Temperature II
Authors: Smith BJK , Witte NS , Hines KC
Published: August 2011

This paper extends the treatment of the polarisation tensor for the electroweak plasma to encompass all the preliminaries needed for a thorough study of its characteristics as they affect the early Universe. The detailed development of the one-loop polarisation tensor calculated in a previous paper includes the construction of the basis tensors in terms of which the polarisation tensor is most conveniently expressed. The polarisation response functions are obtained next and there follows a detailed discussion of the real and imaginary parts of the polarisation tensor. These are the essential tools for the subsequent study of the mode structure and dissipation properties of the electroweak plasma.
Laser-modified Long-range Forces Between Neutral Atoms
Authors: Lerner PB
Published: August 2011

Modification of the long-range forces between atoms by laser light has been considered by Thirunamachandran (1980). More recently, Grossel and van Labeke (1994) treated the modified interaction between a conducting surface and an atom. In the present paper we establish the formulas for laser-modified Casimir forces between neutral atoms using a semiclassical formalism. These forces appear as a result of interaction of atomic dipoles with the background vacuum, in which spectral density is modified by the laser field. In particular, the interaction potential between two neutral atoms displays non-monotonic behaviour in an external field for certain polarisations. The averaging of this result over the mutual position of the atoms coincides with Thirunamachandran's result for the laser-modified Casimir forces. We give estimates for the value of this interaction, which may dominate the Casimir force for distances comparable to the wavelength. The validity of the semi-classical method is proven by comparison with the results of second-order perturbation theory. Furthermore, the method is used to calculate the external field modification of dispersive forces between a magnetically polarisable body and an electrically polarisable one and a chiral system coupled to both electric and magnetic fields.
On compactness of the \overline{∂}-Neumann problem and Hankel operators
Authors: Çeli̇k Mehmet , Şahutoğlu Sönmez
Published: August 2011

Let

Ω
=

Ω
1

∖

Ω
¯

2

\Omega =\Omega _1\setminus \overline {\Omega }_2

, where

Ω
1

\Omega _1

and

Ω
2

\Omega _2

are two smooth bounded pseudoconvex domains in

C

n

,
n
≥
3
,

\mathbb {C}^n, n\geq 3,

such that

Ω
¯

2

⊂

Ω
1

.

\overline {\Omega }_2\subset \Omega _1.

Assume that the

∂
¯

\overline {\partial }

-Neumann operator of

Ω
1

\Omega _1

is compact and the interior of the Levi-flat points in the boundary of

Ω
2

\Omega _2

is not empty (in the relative topology). Then we show that the Hankel operator on

Ω
\Omega

with symbol

ϕ
,

H

ϕ

Ω

,

\phi , H^{\Omega }_{\phi },

is compact for every

ϕ
∈
C
(

Ω
¯

)

\phi \in C(\overline {\Omega })

but the

∂
¯

\overline {\partial }

-Neumann operator on

Ω
\Omega

is not compact.
On the influence of damping in hyperbolic equations with parabolic degeneracy
Authors: Saxton Katarzyna , Saxton Ralph
Published: August 2011

This paper examines the effect of damping on a nonstrictly hyperbolic

2
×
2

2\times 2

system. It is shown that the growth of singularities is not restricted as in the strictly hyperbolic case where dissipation can be strong enough to preserve the smoothness of small solutions globally in time. Here, irrespective of the stabilizing properties of damping, solutions are found to break down in finite time on a line where two eigenvalues coincide in state space.
Metal Mesh Foil Bearing: Effect of Motion Amplitude, Rotor Speed, Static Load, and Excitation Frequency on Force Coefficients
Authors: San Andrés Luis , Chirathadam Thomas Abraham
Published: August 2011

Metal mesh foil bearings (MMFBs), simple to construct and inexpensive, are a promising bearing technology for oil-free microturbomachinery operating at high speed and high temperature. Prior research demonstrated the near friction-free operation of a MMFB operating to 60 krpm and showing substantial mechanical energy dissipation characteristics. This paper details further experimental work and reports MMFB rotordynamic force coefficients. The test rig comprises a turbocharger driven shaft and overhung journal onto which a MMFB is installed. A soft elastic support structure akin to a squirrel cage holds the bearing, aiding to its accurate positioning relative to the journal. Two orthogonally positioned shakers excite the test element via stingers. The test bearing comprises a cartridge holding a Copper wire mesh ring, 2.7 mm thick, and a top arcuate foil. The bearing length and inner diameter are 38 mm and 36.5 mm, respectively. Experiments were conducted with no rotation and with journal spinning at 40–50 krpm, with static loads of 22 N and 36 N acting on the bearing. Dynamic load tests spanning frequencies from 150 to 450 Hz were conducted while keeping the amplitude of bearing displacements at 20 µm, 25 µm, and 30 µm. With no journal spinning, the force coefficients represent the bearing elastic structure alone because the journal and bearing are in contact. The direct stiffnesses gradually increase with frequency while the direct damping coefficients drop quickly at low frequencies (< 200 Hz) and level off above this frequency. The damping combines both viscous and material types from the gas film and mesh structure. Journal rotation induces airborne operation with a hydrodynamic gas film separating the rotor from its bearing. Hence, cross-coupled stiffness coefficients appear although with magnitudes lower than those of the direct stiffnesses. The direct stiffnesses, 0.4 to 0.6 MN/m within 200–400 Hz, are slightly lower in magnitude as those obtained without journal rotation, suggesting the air film stiffness is quite high. Bearing direct stiffnesses are inversely proportional to the bearing motion amplitudes, whereas the direct equivalent viscous damping coefficients do not show any noticeable variation. All measurements evidence a test bearing system with material loss factor (γ) ∼ 1.0, indicating significant mechanical energy dissipation ability.
Modeling of implantation and mixing damage during etching of SiO2 over Si in fluorocarbon plasmas
Authors: Wang Mingmei , Kushner Mark J.
Published: August 2011

Energetic ion bombardment during plasma etching of microelectronics devices is necessary to activate chemical process and define features through the ions’ anisotropic trajectories. These energetic fluxes can also cause damage and mixing of the constituents of crystalline lattices. These properties are likely best modeled using molecular dynamics (MD) simulations. The computational expense of these techniques makes feature scale simulations difficult, and so motivates development of approximate methods that can be used to model full features. In this regard, an implantation and mixing model has been developed and implemented into a Monte Carlo feature profile model to simulate the mixing and damage to the underlying Si during high aspect ratio (HAR) etching of SiO2 trenches. Fluxes to the surface were provided by a reactor scale model. The feature scale model was validated by comparison to the mixing produced by Ar+ bombardment of Si with and without F and CF fluxes as predicted by MD simulations. Scaling of mixing damage of underlying Si during HAR of SiO2 etching in Ar/C4F8/O2 plasmas for rf bias powers of 1–4 kW was investigated. The authors found that mixing damage at the bottom of HAR features, though increasing in magnitude with increasing ion energy, does not scale as dramatically as on flat surfaces. This is due to the reflection of ions off of sidewalls which moderate the ion energies.
Resolving axon fiber crossings at clinical b‐values: An evaluation study
Authors: Ramirez‐Manzanares Alonso , Cook Philip A. , Hall Matt , Ashtari Manzar , Gee James C.
Published: August 2011

Purpose:

Diffusion tensor magnetic resonance imaging is widely used to study the structure of the fiber pathways of brain white matter. However, the diffusion tensor cannot capture complex intravoxel fiber architecture such as fiber crossings of bifurcations. Consequently, a number of methods have been proposed to recover intravoxel fiber bundle orientations from high angular resolution diffusion imaging scans, optimized to resolve fiber crossings. It is important to improve the brain tractography by applying these multifiber methods to diffusion tensor protocols with a clinicalb‐
value (low), which are optimized on computing tensor scalar statistics. In order to characterize the variance among different methods, consequently to be able to select the most appropriate one for a particular application, it is desirable to compare them under identical experimental conditions.

Methods:

In this work, the authors study how QBall, spherical deconvolution, persistent angular structure, stick and ball, diffusion basis functions, and analytical QBall methods perform under clinically‐realistic scanning conditions, where theb‐value is typically lower (around 1000 s/mm2), and the number of diffusion encoding orientations is fewer (30–60) than in dedicated high angular resolution diffusion imaging scans. To characterize the performance of the methods, they consider the accuracy of the estimated number of fibers, the relative contribution of each fiber population to the total magnetic resonance signal, and the recovered orientation error for each fiber bundle. To this aim, they use four different sources of data: synthetic data from Gaussian mixture model, cylinder restricted model, and in vivo data from two different acquisition schemes.

Results:

Results of their experiments indicate that: (a) it is feasible to apply only a subset of these methods to clinical data sets and (b) it allows one to characterize the performance of each method. In particular, two methods are not feasible to the kind of magnetic resonance diffusion data they test. By the characterization of their systematic behavior, among other conclusions, they report the method which better performs for the estimation of the number of diffusion peaks per voxel, also the method which better estimates the diffusion orientation.

Conclusions:

The framework they propose for comparison allows one to effectively characterize and compare the performance of the most frequently used multifiber algorithms under realistic medical settings and realistic signal–to–noise ratio environments. The framework is based on several crossings with a non–orientational bias and different signal models. The results they present are relevant for medical doctors and researchers, interested in the use of the multifiber solution for tractography.
Evaluation of Acupuncture in the Management of Chemotherapy-Induced Peripheral Neuropathy
Authors: Donald Graeme K , Tobin Irene , Stringer Jacqui
Published: August 2011

Aim

To clinically evaluate the effectiveness of acupuncture when used in the management of chemotherapy-induced peripheral neuropathy (PN).

Background

During cancer treatment, certain chemotherapies can cause varying degrees of PN. Patients’ quality of life can be seriously impaired through loss of sensation, pain or mobility problems. Conventional medications routinely used to manage neuropathic symptoms have poor side-effect profiles and there is little or no evidence justifying their use to treat chemotherapy-related neurotoxicities. There are studies suggesting that acupuncture may be an effective therapy in treating PN across a number of different aetiologies.

Design

A retrospective service evaluation.

Method

Patients (n=18) were referred for acupuncture by the medical staff and/ornurse specialists or they self-referred for treatment. A course of six weekly acupuncture sessions was offered to them, and their details were recorded on an evaluation form prior to session one. Points were selected by acupuncturists, based on patient presentation, and needles remained in situ for 30–45 min. Treatments took place in outpatient clinics, chemotherapy day case ward or a drop-in clinic based in a physiotherapy gym. The evaluation form was completed at the end of session 6 by a therapist who had not been involved in patient care.

Results

82% (n=14) of patients reported an improvement in symptoms following their course of acupuncture; one patient with advanced disease died during the 6 weeks. Some patients derived additional benefits from the treatment including a reduction in analgesic use and improved sleeping patterns. The most common acupoints used were SP6 (n=18), ST36 (n=18) and LV3 (n=14).

Conclusion

Although these results are encouraging, they are uncontrolled. They suggest that acupuncture could be an option for these patients and controlled trials using validated patient-reported outcome measures are justified.
THERMODYNAMICAL DESCRIPTION OF THE INTERACTING NEW AGEGRAPHIC DARK ENERGY
Authors: SHEYKHI A. , SETARE M. R.
Published: August 2011

We describe the thermodynamical interpretation of the interaction between new agegraphic dark energy and dark matter in a non-flat universe. When new agegraphic dark energy and dark matter evolve separately, each of them remains in thermodynamic equilibrium. As soon as an interaction between them is taken into account, their thermodynamical interpretation changes by a stable thermal fluctuation. We obtain a relation between the interaction term of the dark components and this thermal fluctuation.
CUT-AND-JOIN OPERATOR REPRESENTATION FOR KONTSEVICH–WITTEN TAU-FUNCTION
Authors: ALEXANDROV A.
Published: August 2011

In this short note we construct a simple cut-and-join operator representation for Kontsevich–Witten tau-function that is the partition function of the two-dimensional topological gravity. Our derivation is based on the Virasoro constraints. Possible applications of the obtained representation are discussed.
ON THE INFLUENCE OF CURVATURE ON THE LANDAU–HE–MCKELLAR–WILKENS QUANTIZATION INDUCED BY NONINERTIAL EFFECTS
Authors: BAKKE KNUT
Published: August 2011

We consider a neutral particle with permanent electric dipole moment interacting with a field configuration induced by the noninertial effects of the Fermi–Walker reference frame in the presence of a disclination and discuss the influence of curvature on the Landau–He–McKellar–Wilkens quantization.
SUPERCONDUCTIVITY IN THE 2D ATTRACTIVE HUBBARD MODEL WITHIN A FUNCTIONAL FIELD-THEORETICAL RG
Authors: CORREA EBERTH , FREIRE HERMANN , FERRAZ ALVARO
Published: August 2011

We apply the functional field-theoretical renormalization group methodology up to two-loop order to the 2D attractive Hubbard model for weak bare interaction. Since the momentum-resolved quasiparticle weight ZΛ(p) is always close to unity in the RG flow, higher-order quantum fluctuations do not affect crucially the low-energy dynamics in this case. As a result, we observe a s-wave singlet superconducting quasi-long-range order phase as a function of doping in good agreement with other numerical methods. To assess the role played by the fluctuations we compare the critical temperature Tc in which the quasi-long-range superconducting order phase takes place within our approach with mean-field theory and quantum Monte Carlo results.
SYNERGISM IN ORDER FORMATION FROM UNSTABLE FLUCTUATIONS
Authors: SUZUKI MASUO
Published: August 2011

The present paper reviews some general aspects of the stochastic analysis performed by the author in the field of statistical physics, particularly concerning the order formation from unstable states. First, a brief review and some new results are given on the generalization of the Itô-type and Stratonovich-type stochastic integrals. Their physical meaning is also discussed form the viewpoint of symmetry. Secondly, Kubo's stochastic Liouville equation is presented from the viewpoint of separation of procedures, to give a simple derivation of the Fokker–Planck equation. Thirdly, the scaling theory of order formation from the unstable point is re-formulated by introducing here a new order parameter to characterize macroscopic order formation and to clarify the synergetic effect of the initial fluctuation, random noise and nonlinearity. Finally, some discussions are given, particularly concerning applications of the Hida calculus based on the Gelfand triplet space.
COHERENT CONTROL OF MACROSCOPIC QUANTUM TUNNELING OF SPIN-1 CONDENSATE MAGNETIZATION IN A DOUBLE-WELL POTENTIAL
Authors: ZANG XIAO-FEI , TAN LEI , HAO HUO-FAN , GU HUAI-QIANG , XU YAN
Published: August 2011

We have investigated the effect of an external periodic driving to the macroscopic quantum tunneling of spin-1 condensates in a double-well potential. By manipulating the frequencies of the external magnetic fields, a rich set of phenomena can be studied, and dynamical localization and self-trapping in spin states can be realized using time-dependent magnetic field. We have shown that a relatively high-frequency field may induce a fast oscillation of the macroscopic quantum localization. The larger the periodic magnetic field frequency is, the faster oscillation of the spin condensate magnetization goes. By applying a lower-frequency field to the spin-condensate, one can find that the dynamical properties of the magnetization appears similar behaviors to the results of the modulations of a constant external magnetic field. A possible realization in experiments is also presented.
VERIFYING JAVA OBJECT INVARIANTS AT RUNTIME
Authors: NGUYEN THU-TRANG , TRUONG NINH-THUAN , NGUYEN VIET-HA
Published: August 2011

An object invariant consisting of a set of properties that must hold for all instances of a class at any time is usually used in object-oriented design. However, verifying object invariants at runtime is always a challenging task in software verification. This paper proposes a method for verifying invariants of Java objects at runtime using AOP. Suppose that a software application is designed using UML models and its constraints are specified in OCL expressions, the software is then implemented, by default, using the UML design. They propose to construct verifiable aspects which are automatically generated from OCL constraints. These aspects can be woven into Java code to check whether object invariants are violated at runtime. Benefiting from AOP in separation of crosscutting concerns and weaving mechanisms, generated aspects can do the verification task whenever values of objects' attributes are changed. A Verification Aspect Generator (VAG) tool has been developed allowing the automatic generation of verifying aspects from the UML/OCL constraints.
APPROXIMATION OF GEODESICS IN METABELIAN GROUPS
Authors: KHARLAMPOVICH OLGA , MOHAJERI MOGHADDAM ATEFEH
Published: August 2011

It is known that the bounded Geodesic Length Problem in free metabelian groups is NP-complete [A. Myasnikov, V. Roman'kov, A. Ushakov and A. Vershik, The word and geodesic problems in free solvable groups, Trans. Amer. Math. Soc.362(9) (2010) 4655–4682] (in particular, the Geodesic Problem is NP-hard). We construct a 2-approximation polynomial time deterministic algorithm for the Geodesic Problem. We show that the Geodesic Problem in the restricted wreath product of a finitely generated non-trivial group with a finitely generated abelian group containing ℤ2 is NP-hard and there exists a Polynomial Time Approximation Scheme for this problem. We also show that the Geodesic Problem in the restricted wreath product of two finitely generated non-trivial abelian groups is NP-hard if and only if the second abelian group contains ℤ2.
INDEPENDENT SETS FROM AN ALGEBRAIC PERSPECTIVE
Authors: DICKENSTEIN ALICIA , TOBIS ENRIQUE A.
Published: August 2011

In this paper, we study the basic problem of counting independent sets in a graph and, in particular, the problem of counting antichains in a finite poset, from an algebraic perspective. We show that neither independence polynomials of bipartite Cohen–Macaulay graphs nor Hilbert series of initial ideals of radical zero-dimensional complete intersections ideals, can be evaluated in polynomial time, unless #P = P. Moreover, we present a family of radical zero-dimensional complete intersection ideals JP associated to a finite poset P, for which we describe a universal Gröbner basis. This implies that the bottleneck in computing the dimension of the quotient by JP (that is, the number of zeros of JP) using Gröbner methods lies in the description of the standard monomials.
THE ROLE OF SURFACE ENERGY COEFFICIENT IN HEAVY ION REACTIONS AND IMPROVED PROXIMITY MODEL
Authors: SALEHI M. , GHODSI O. N.
Published: August 2011

In this work we have discussed dependence of surface tension coefficient that appears in proximity potential and energy of incident nucleus. The obtained results from study of the fusion barrier heights and positions for 44 reactions with z≥8 reveal that this modification on the formalism of proximity model leads to a better agreement between computed fusion barrier heights and positions and experimental data.
DEFORMATIONS OF GALOIS REPRESENTATIONS AND THE THEOREMS OF SATO–TATE AND LANG–TROTTER
Authors: PANDE AFTAB
Published: August 2011

We construct infinitely ramified Galois representations ρ such that the al(ρ)'s have distributions in contrast to the statements of Sato–Tate, Lang–Trotter and others. Using similar methods we deform a residual Galois representation for number fields and obtain an infinitely ramified representation with very large image, generalizing a result of Ramakrishna.
HYPERGEOMETRIC FUNCTIONS OVER FINITE FIELDS AND THEIR RELATIONS TO ALGEBRAIC CURVES
Authors: VEGA M. VALENTINA
Published: August 2011

In this work we present an explicit relation between the number of points on a family of algebraic curves over 𝔽q and sums of values of certain hypergeometric functions over 𝔽q. Moreover, we show that these hypergeometric functions can be explicitly related to the roots of the zeta function of the curve over 𝔽q in some particular cases. A general conjecture relating these last two is presented and advances toward its proof are shown in the last section.
A VARIANT OF THE BARBAN–DAVENPORT– HALBERSTAM THEOREM
Authors: SMITH ETHAN
Published: August 2011

Let L/K be a Galois extension of number fields. The problem of counting the number of prime ideals 𝔭 of K with fixed Frobenius class in Gal (L/K) and norm satisfying a congruence condition is considered. We show that the square of the error term arising from the Chebotarëv Density Theorem for this problem is small "on average". The result may be viewed as a variation on the classical Barban–Davenport–Halberstam Theorem.
ON THE EXISTENCE OF MAXIMAL ORDERS
Authors: YU CHIA-FU
Published: August 2011

We generalize the existence of maximal orders in a semi-simple algebra for general ground rings. We also improve several statements in Chaps. 5 and 6 of Reiner's book [Maximal Orders, London Mathematical Society Monographs, Vol. 5 (Academic Press, London, 1975), 395 pp.] concerning separable algebras by removing the separability condition, provided the ground ring is only assumed to be Japanese, a very mild condition. Finally, we show the existence of maximal orders as endomorphism rings of abelian varieties in each isogeny class.
L-FUNCTIONS OF SYMMETRIC POWERS OF THE GENERALIZED AIRY FAMILY OF EXPONENTIAL SUMS
Authors: HAESSIG C. DOUGLAS , ROJAS-LEÓN ANTONIO
Published: August 2011

This paper looks at the L-function of the kth symmetric power of the [Formula: see text]-sheaf Ai f over the affine line [Formula: see text] associated to the generalized Airy family of exponential sums. Using ℓ-adic techniques, we compute the degree of this rational function as well as the local factors at infinity. Using p-adic techniques, we study the q-adic Newton polygon of the L-function.