bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulatory T-cells and cAMP suppress effector T-cells independently of PKA–CREM/ICER: a potential role for Epac
Authors: Vang Amanda G. , Housley William , Dong Hongli , Basole Chaitali , Ben-Sasson Shlomo Z. , Kream Barbara E. , Epstein Paul M. , Clark Robert B. , Brocke Stefan
Published: September 2013

cAMP signalling is both a major pathway as well as a key therapeutic target for inducing immune tolerance and is involved in Treg cell (regulatory T-cell) function. To achieve potent immunoregulation, cAMP can act through several downstream effectors. One proposed mechanism is that cAMP-mediated suppression, including immunosuppression by Treg cells, results from activation of PKA (protein kinase A) leading to the induction of the transcription factor ICER (inducible cAMP early repressor). In the present study, we examined CD4+CD25− Teff cell (effector T-cell) and CD4+CD25+ Treg cell immune responses in Crem (cAMP-response-element modulator) gene-deficient mice which lack ICER (Crem−/−/ICER-deficient mice). ICER deficiency did not significantly alter the frequency or number of Treg cells and Teff cells. Treg cells or a pharmacological increase in cAMP suppressed Teff cells from Crem+/+ and Crem−/−/ICER-deficient mice to an equivalent degree, demonstrating that ICER is dispensable in these functions. Additionally, activating the cAMP effector Epac (exchange protein directly activated by cAMP) suppressed Teff cells. Treg cells expressed low levels of all cyclic nucleotide Pde (phosphodiesterase) genes tested, but high levels of Epac. These data identify ICER as a redundant mediator of Treg cells and cAMP action on Teff cells and suggest that Epac may function as an alternative effector to promote cAMP-dependent Teff cell suppression.
A density‐based enhancement to dominant sets clustering
Authors: Hou Jian , Xu E , Liu Wei‐Xue , Xia Qi , Qi Nai‐Ming
Published: September 2013

Although there is no shortage of clustering algorithms, existing algorithms are often afflicted by problems of one kind or another. Dominant sets clustering is a graph‐theoretic approach to clustering and exhibits significant potential in various applications. However, the authors' work indicates that this approach suffers from two major problems, namely over‐segmentation tendency and sensitiveness to distance measures. In order to overcome these two problems, the authors present a density‐based enhancement to dominant sets clustering where a cluster merging step is used to fuse adjacent clusters close enough from the original dominant sets clustering. Experiments on various datasets validate the effectiveness of the proposed method.
Analytical estimation of short circuit axial and radial forces on power transformers windings
Authors: Ebrahimi Bashir Mahdi , Fereidunian Alireza , Saffari Saeed , Faiz Jawad
Published: September 2013

In this study, an analytical method is proposed to calculate exerted axial and radial forces on the high and low voltage (LV) windings in core type power transformers. Hence, an analytical modelling approach is proposed to compute short circuit currents in the transient mode and steady state. The proposed model includes non‐linear characteristics of the core materials, eddy currents effects, symmetrical and asymmetrical hysteresis loops of the used laminates. Then, exerted axial and radial forces on the high and LV windings are analytically computed in the transient mode and steady state. In order to certify obtained analytical results, the two‐dimensional (2D) time stepping finite element method (TSFEM) is utilised to determine aforementioned forces. In this modelling approach, the geometrical, electrical and magnetic characteristics of the core type transformer under short circuit fault are taken into account. Furthermore, three‐dimensional TSFEM is employed to verify the analytical and 2D TSFEMs results.
Integrated dual‐grating inteferometric detection with polymer microbeams for bio‐chemical sensing in liquid environment
Authors: Feng Jin‐yang , Ye Xiong‐ying , Shang Yuan‐fang , Wu Kang , Chen Feng
Published: September 2013

An interferometric displacement detection method of polymer microbeams based on integrated dual‐grating was developed for bio‐chemical sensing in a liquid environment. Sensing microstructures made of polyimide (PI) with four symmetrically arranged L‐shaped beams suspending a central plate were designed and fabricated on a glass substrate using a surface micromachining process. With these structures, deflection changes of the microbeams were transduced to out‐of‐plane movements of the central plate, which were then measured from the interference of light spots diffracted from the integrated gratings using a charge coupled device image measurement setup. To extend the displacement detection range, two adjacent metal gratings corresponding to a microbeam were formed inside and outside a groove with a depth of 55 nm, respectively, to achieve a phase shift of about π/2 in liquid. The detected noise of aluminium (Al) microcantilevers in ethanol slightly increased compared with that in air, and the noise of PI microbeams in phosphate‐buffered saline was about three times larger than that of Al cantilevers in ethanol. The preliminary experimental results in ethanol show that the detection method based on polymer microbeams integrated with dual‐gratings is feasible in a liquid environment. Antibody–antigen binding detection was also conducted with a rabbit immunoglobulin G (IgG) immobilised chip in 100 μg/ml goat anti‐rabbit IgG solution.
Silver selenide nanoparticles: synthesis, characterisation and effect of preparation conditions under ultrasound radiation
Authors: Jafari Maryam , Salavati‐Niasari Masoud , Sobhani Azam
Published: September 2013

A convenient sonochemical process for the preparation of silver selenide (Ag2Se) nanoparticles by using different complexing agents [NH3, citric acid, potassium thiocyanate (KSCN)] and hydrazine as reductant agent is developed. It was found that pure Ag2Se nanoparticles were prepared in the presence of KSCN after 90 minutes of sonication. The products were characterised by X‐ray diffraction, scanning electron microscopy and energy‐dispersive X‐ray spectroscopy analysis. Photoluminescence was used to study the optical properties of Ag2Se samples.
Communication: Evidence of structural phase transitions in silicalite-1 by infrared spectroscopy
Authors: Ballandras Anthony , Weber Guy , Paulin Christian , Bellat Jean-Pierre , Rotger Maud
Published: September 2013

The adsorption of trichloroethylene, perchloroethylene, and p-xylene on a MFI (Mobile-FIve) zeolite is studied using in situ FTIR spectroscopy at 298 K. Spectra of self-supported zeolites in contact with increasing pressures of pure gas were recorded at equilibrium in the mid-infrared domain. Analysis of the evolution of the shape and location of vibrational bands of the zeolite as a function of the amount adsorbed allowed the observation of structural modifications of the adsorbent for the first time by infrared spectroscopy.
The importance of wall-normal Reynolds stress in turbulent rough channel flows
Authors: Orlandi P.
Published: September 2013

In this paper, it is demonstrated by DNS of turbulent rough channels that a proportionality between \documentclass[12pt]{minimal}\begin{document}$\widetilde{u}_2^\prime |_w$\end{document}ũ2′|w (the wall-normal Reynolds stress \documentclass[12pt]{minimal}\begin{document}$\widetilde{u}_2^\prime =\langle u_2^{\prime 2} \rangle ^{1/2}$\end{document}ũ2′=⟨u2′2⟩1/2 at the top of the roughness elements) and the roughness function does exist. This observation confirmed by experiments allows the derivation of a simple expression for the velocity profile in the log-region. This parameterization of rough walls through \documentclass[12pt]{minimal}\begin{document}$\widetilde{u}_2^\prime |_w$\end{document}ũ2′|w is suggested by the direct link between wall structures and \documentclass[12pt]{minimal}\begin{document}$\frac{\partial ^2 \widetilde{u_2^{\prime }}^2}{\partial x^2_{2}}$\end{document}∂2u2′̃2∂x22. Identification of the wall structures, near smooth and different kinds of rough surfaces, demonstrates flow isotropization near rough walls, corroborated by profiles of \documentclass[12pt]{minimal}\begin{document}$\frac{\partial ^2 \widetilde{u_2^{\prime }}^2}{\partial x^2_{2}}$\end{document}∂2u2′̃2∂x22, is depicted by visualizations of ∇2p. The relationship between the roughness function and \documentclass[12pt]{minimal}\begin{document}$\widetilde{u}_2^\prime |_w$\end{document}ũ2′|w allows the derivation of a new kind of Moody diagram, useful in the prediction of friction factors of rough flows at high Reynolds numbers.
Quasi-steady stages in the process of premixed flame acceleration in narrow channels
Authors: Valiev D. M. , Bychkov V. , Akkerman V. , Eriksson L.-E. , Law C. K.
Published: September 2013

The present paper addresses the phenomenon of spontaneous acceleration of a premixed flame front propagating in micro-channels, with subsequent deflagration-to-detonation transition. It has recently been shown experimentally [M. Wu, M. Burke, S. Son, and R. Yetter, Proc. Combust. Inst. 31, 2429 (2007)]10.1016/j.proci.2006.08.098, computationally [D. Valiev, V. Bychkov, V. Akkerman, and L.-E. Eriksson, Phys. Rev. E 80, 036317 (2009)]10.1103/PhysRevE.80.036317, and analytically [V. Bychkov, V. Akkerman, D. Valiev, and C. K. Law, Phys. Rev. E 81, 026309 (2010)]10.1103/PhysRevE.81.026309 that the flame acceleration undergoes different stages, from an initial exponential regime to quasi-steady fast deflagration with saturated velocity. The present work focuses on the final saturation stages in the process of flame acceleration, when the flame propagates with supersonic velocity with respect to the channel walls. It is shown that an intermediate stage may occur during acceleration with quasi-steady velocity, noticeably below the Chapman-Jouguet deflagration speed. The intermediate stage is followed by additional flame acceleration and subsequent saturation to the Chapman-Jouguet deflagration regime. We elucidate the intermediate stage by the joint effect of gas pre-compression ahead of the flame front and the hydraulic resistance. The additional acceleration is related to viscous heating at the channel walls, being of key importance at the final stages. The possibility of explosion triggering is also demonstrated.
Endohedral and exohedral complexes of substituted benzenes with carbon nanotubes and graphene
Authors: Munusamy Elango , Wheeler Steven E.
Published: September 2013

Non-covalent complexes of cyclohexane and a series of substituted benzenes with short carbon nanotube (CNT) models are investigated primarily at the B97-D3/TZV(2d,2p) level of theory. Understanding non-covalent interactions of arenes with CNTs is vital for the development of next-generation organic electronic materials and for harnessing CNTs as nano-reactors and vehicles for drug delivery. The interaction of benzene and cyclohexane with the interior and exterior of CNTs depends on the nanotube diameter, particularly for endohedral complexes. Both benzene and cyclohexane interact more strongly with the interior of CNTs than the outside, with benzene exhibiting stronger interactions than cyclohexane for CNTs larger than (8,8). Studies of two benzenes inside of CNTs predict the formation of one-dimensional sandwich and parallel-displaced stacks of benzenes within certain sized CNTs, which could have interesting optoelectronic properties. Concerning the impact of substituents on the interaction of benzene with CNTs, we find that electrostatic interactions do not control substituent effects. That is, the electron-donating or -withdrawing character of the substituents is not correlated with the predicted interaction energies. Moreover, substituent effects are the same for both endohedral and exohedral complexes, despite the different electronic character of the interior and exterior CNT walls. Ultimately, substituent effects in π-stacking interactions with CNTs and graphene are explained by differences in dispersion interactions between the substituents and CNT walls or graphene surface.
Exact solution to the Landau-Lifshitz equation in a constant electromagnetic field
Authors: Yaremko Yurij
Published: September 2013

We are interested in the motion of a classical charge acted upon an external constant electromagnetic field where the back reaction of the particle's own field is taken into account. The Landau-Lifshitz approximation to the Lorentz-Abraham-Dirac equation is solved exactly and in closed form. It is shown that the ultrarelativistic limit of the Landau-Lifshitz equation for a radiating charge is the equation for eigenvalues and eigenvectors of the external electromagnetic field tensor.
Subwavelength imaging through spoof surface acoustic waves on a two-dimensional structured rigid surface
Authors: Jia Han , Lu Minghui , Wang Qingcui , Bao Ming , Li Xiaodong
Published: September 2013

We demonstrate that acoustic subwavelength imaging can be realized through the spoof surface acoustic waves on the surface phononic crystal which is composed of borehole arrays with square lattice in a rigid plate. The dispersion property of the spoof surface acoustic waves on the two-dimensional textured rigid plate is analyzed theoretically. By utilizing the broad flat equifrequency contour of the spoof surface acoustic waves, a subwavelength image with full width at half maximum of 0.14 λ has been obtained both numerically and experimentally. We believe that such work can bring potential applications in the design of acoustic imaging and focusing devices.
Effect of secondary flows on dispersion in finite-length channels at high Peclet numbers
Authors: Adrover Alessandra
Published: September 2013

We investigate the effects of secondary (transverse) flows on convection-dominated dispersion of pressure driven, open column laminar flow in a conduit with rectangular cross-section. We show that secondary flows significantly reduce dispersion (enhancing transverse diffusion) in Taylor-Aris regime [H. Zhao and H. H. Bau, “Effect of secondary flows on Taylor-Aris dispersion,” Anal. Chem. 79, 7792–7798 (2007)], as well as in convection-controlled regime. In the convection-controlled dispersion regime (i.e., laminar dispersion in finite-length channel with axial flow at high Peclet numbers) the properties of the dispersion boundary layer and the values of the scaling exponents controlling the dependence of the moment hierarchy on the Peclet number \documentclass[12pt]{minimal}\begin{document}$m^{(n)}_{\rm out} \sim Pe_{\rm eff}^{\theta _n}$\end{document}m out (n)∼Pe eff θn are determined by the local near-wall behaviour of the axial velocity. The presence of transverse flows strongly modify the localization properties of the dispersion boundary layer and consequently the moment scaling exponents. Different secondary flows, electrokinetically induced and independent of the primary axial flow are considered. A complete scaling theory is presented for the nth order moment of the outlet chromatogram as a function of the axial Peclet number, the secondary flow's pattern and intensity. We show that some secondary flows (the corotating and the counter-rotating cavity flows) significantly reduce dispersion and \documentclass[12pt]{minimal}\begin{document}$m^{(n)}_{\rm out} \sim Pe_{\rm eff}^{(n-1)/3}$\end{document}m out (n)∼Pe eff (n−1)/3. No significant dispersion reduction is obtained with the cavity cross-flow \documentclass[12pt]{minimal}\begin{document}$m^{(n)}_{\rm out} \sim Pe_{\rm eff}^{(n-1)/2}$\end{document}m out (n)∼Pe eff (n−1)/2. The best result is obtained with the two full-motion counter-rotating cross-flows because \documentclass[12pt]{minimal}\begin{document}$m^{(n)}_{\rm out}$\end{document}m out (n) saturates towards a constant value. Theoretical results from scaling theory are strongly supported by numerical results obtained by Finite Element Method.
Molecular dynamic simulation of tip-polymer interaction in tapping-mode atomic force microscopy
Authors: Onofrio N. , Venturini G. N. , Strachan A.
Published: September 2013

We present a molecular dynamic study of the interaction between an amorphous silica tip (SiO2) and an amorphous poly-(methyl-methacrylate) substrate under conditions relevant for tapping-mode atomic force microscopy. To capture the actual dynamics of the tip, we use the dynamic contact simulation method [Kim et al., J. Appl. Phys. 112, 094325 (2012)]. We obtain force-displacement relationships both for neat polymer substrates and a sample with a sub-surface nanotube and extract the local stiffness and energy dissipation per cycle. The simulations capture non-trivial aspects of the interaction that originate from the viscoelastic nature of the polymer including an increase in repulsive interaction force during approach with tip velocity and an increase in adhesion during retraction with decreasing tip velocity. Scans of local stiffness and dissipation over the samples reveal intrinsic variability in the amorphous polymer but also the effect of local surface topography on the extracted properties as well as the ability of the method to detect a sub-surface nanotube. This insight and quantitative data should be valuable to interpret the results of atomic force microscopy studies.
Time-resolved and temperature-dependent photoluminescence of ternary and quaternary nanocrystals of CuInS2 with ZnS capping and cation exchange
Authors: Seo Jaetae , Raut Sangram , Abdel-Fattah Mahmoud , Rice Quinton , Tabibi Bagher , Rich Ryan , Fudala Rafal , Gryczynski Ignacy , Gryczynski Zygmunt , Kim Wan-Joong , Jung Sungsoo , Hyun Ruh
Published: September 2013

Time-resolved and temperature-dependent photoluminescence (PL) spectroscopy of ternary compound copper indium disulfide (CuInS2, or CIS) core materials, CIS/ZnS coreshells, and quaternary compound ZnCuInS2 (ZnCIS) revealed their optical properties with spectral, temporal, and thermal characteristics, which were closely linked to surface-related recombination, and shallow or deep defect-related donor-acceptor transitions. The PL peaks of semiconductor nanocrystals (SNCs) with sizes near Bohr radius displayed at ∼775 nm for CIS, ∼605 nm for CIS/ZnS, and ∼611 nm for ZnCIS. The spectral blue shift and spectral narrowing with CIS/ZnS and ZnCIS are assigned to the increased spatial confinement and surface regularity with the etching of core materials. Both the shorter lifetime at surface-trapped states or interface states and the longer lifetime at intrinsic defect-related states of CIS, CIS/ZnS, and ZnCIS SNCs were widely distributed across the entire PL spectral region. The surface or interface-trapped electrons were thermally active even at low temperatures, but the electrons at intrinsic defect-related states were relatively stable, which was attributable to the strong Coulomb energy between the charge carriers.
Time-dependent conduction current in lithium niobate crystals with charged domain walls
Authors: Ya. Shur V. , Baturin I. S. , Akhmatkhanov A. R. , Chezganov D. S. , Esin A. A.
Published: September 2013

We present the experimental study of the increase and decrease of the abnormal conduction current appeared during polarization reversal at elevated temperatures (120–250 °C) in stoichiometric and MgO doped lithium niobate single crystals. It is shown that the conduction current is caused by existence of the through charged domain walls. The time dependence of the conduction current has been measured in low electric field immediately after partial switching. The maximal value of the conduction current in crystal with through charged domain walls is of 4–5 orders of magnitude higher than in initial single domain state. The activation energy is 1.1 eV.
Efficient red electroluminescence from diketopyrrolopyrrole copolymerised with a polyfluorene
Authors: Fenwick O. , Fusco S. , Baig T. N. , Di Stasio F. , Steckler T. T. , Henriksson P. , Fléchon C. , Andersson M. R. , Cacialli F.
Published: September 2013

We report the synthesis, characterization, and device incorporation of copolymers based on a common green-emitting polyfluorene but containing a small proportion of a low energy gap donor-acceptor-donor unit for red emission in photo- and electro-luminescence. At just 1%–3% random incorporation, the low-gap unit is not present on all chains, yet we demonstrate that efficient charge and energy transfer can yield electroluminescent devices with 1% quantum efficiency and a color that can be tuned by adjusting the density of low-gap units to achieve primary red (National Television System Committee). The high current density tail off in the efficiency is reduced by replacing the hole-injection layer with a photochemically cross-linked electron‑blocking layer.
A differential spin current detection scheme
Authors: Hemingway Bryan , Appelbaum Ian
Published: September 2013

We provide detailed calculations for modeling an alternative scheme to detect spin polarization of conduction electrons injected into a nonmagnetic metal or degeneratively doped semiconductor using transport to two oppositely polarized ferromagnetic metal contacts. We show that, as in the well-known spin injection problem, detection efficiency can be amplified by the addition of spin-selective tunneling barriers. Considering the appropriate geometry and achievable injection rates, we estimate that the differential current can be as high as 1-10 nA for reasonable design parameters.
Low temperature crystal structure and large lattice discontinuity at Tc in superconducting FeTeOx films
Authors: Narangammana L. K. , Liu X. , Nie Y. F. , Rueckert F. J. , Budnick J. I. , Hines W. A. , Gu G. , Wells B. O.
Published: September 2013

We report a high resolution x-ray diffraction study of the crystal structure of superconducting FeTeOx films. The crystal symmetry of FeTeOx matches the parent FeTe, unlike most iron-based superconductors. However, at the superconducting transition there is a large change in the c-axis lattice parameter. Such a discontinuity in the thermal expansion is known in normal-to-superconducting phase transitions, but here the effect is far larger than for other iron-based superconductors. Following the typical analysis of such a discontinuity in thermal expansion using the Ehrenfest-relation leads to a prediction of a large enhancement of Tc in strained FeTeOx films.
Electronic structure, morphology and emission polarization of enhanced symmetry InAs quantum-dot-like structures grown on InP substrates by molecular beam epitaxy
Authors: Maryński A. , Sęk G. , Musiał A. , Andrzejewski J. , Misiewicz J. , Gilfert C. , Reithmaier J. P. , Capua A. , Karni O. , Gready D. , Eisenstein G. , Atiya G. , Kaplan W. D. , Kölling S.
Published: September 2013

The optical and structural properties of a new kind of InAs/InGaAlAs/InP quantum dot (QD)-like objects grown by molecular beam epitaxy have been investigated. These nanostructures were found to have significantly more symmetrical shapes compared to the commonly obtained dash-like geometries typical of this material system. The enhanced symmetry has been achieved due to the use of an As2 source and the consequent shorter migration length of the indium atoms. Structural studies based on a combination of scanning transmission electron microscopy (STEM) and atom probe tomography (APT) provided detailed information on both the structure and composition distribution within an individual nanostructure. However, it was not possible to determine the lateral aspect ratio from STEM or APT. To verify the in-plane geometry, electronic structure calculations, including the energy levels and transition oscillator strength for the QDs have been performed using an eight-band k·p model and realistic system parameters. The results of calculations were compared to measured polarization-resolved photoluminescence data. On the basis of measured degree of linear polarization of the surface emission, the in-plane shape of the QDs has been assessed proving a substantial increase in lateral symmetry. This results in quantum-dot rather than quantum-dash like properties, consistent with expectations based on the growth conditions and the structural data.
Shock compression of pyrolytic graphite to 18 GPa: Role of orientational order
Authors: Lucas Marcel , Winey J. M. , Gupta Y. M.
Published: September 2013

Shock wave response of highly-oriented pyrolytic graphite (HOPG) compressed to stresses above the phase transformation onset (∼20 GPa) depends strongly on the HOPG orientational order [Erskine and Nellis, Nature 349, 317 (1991)]. To gain insight into this finding, which is not understood, and because corresponding results do not exist at stresses below the transition stress, the shock compression responses of three grades of pyrolytic graphite, differing in their orientational order, were examined at peak stresses below ∼20 GPa. Measured wave profiles and the corresponding end states reveal significant differences in the shock wave response of highly oriented ZYB-grade HOPG, less oriented ZYH-grade HOPG, and as-deposited pyrolytic graphite (PG). For peak stresses above 9 GPa, ZYB-grade HOPG exhibits a two-wave structure (elastic-inelastic response); the large elastic wave amplitudes for ZYB-grade increase linearly with peak stress, reaching 16 GPa for a peak stress of 18 GPa. In contrast, ZYH-grade HOPG and PG exhibit single (overdriven) wave profiles, due to considerably smaller elastic limits, at all peak stresses. Measured peak states show that PG is more compressible than ZYB- and ZYH-grade HOPG. Our results show that orientational order plays a significant role in the shock wave response of pyrolytic graphite over a broad range of stresses below the transition stress (∼20 GPa). This finding agrees well with the orientational order effects observed above the phase transition onset. The ZYB-grade HOPG, the only pyrolytic graphite that showed a clear phase transition response above ∼20 GPa in the work by Erskine and Nellis, is also the only pyrolytic graphite that displayed a large elastic limit which increases with peak stress. The latter finding suggests that the rapid phase change observed in shocked ZYB-grade HOPG may be a consequence of the large elastic compression observed for this orientational order.
Structural, electronic, and optical properties of hydrogenated few-layer silicene: Size and stacking effects
Authors: Liu Yang , Shu Haibo , Liang Pei , Cao Dan , Chen Xiaoshuang , Lu Wei
Published: September 2013

The size and stacking effects on the structural, electronic, and optical properties of hydrogenated few-layer silicenes (HFLSs) are investigated systematically by the first-principle calculations within density functional theory. It is found that both the formation energies and band gaps of HFLSs increases with the reduction of layer thickness. The high formation energies imply the relatively lower structural stability in the thinner HFLSs due to their high surface/volume ratio. With the reduction of layer thickness, the increasing band gaps lead to an obvious blue shift of optical absorption edge in the HFLSs. Among three different stacking HFLSs with the same thickness, the ABC-stacking one has the lowest formation energy and the largest band gap due to the strong interactions of Si layers. Moreover, the structural transition of HFLSs from the ABC-stacking sequence to the AA-stacking one will cause a relative red shift of optical absorption peaks. The results indicate that the electronic and optical properties of HFLSs strongly depend on their size and stacking modes.
Triple band polarization-independent metamaterial absorber with bandwidth enhancement at X-band
Authors: Bhattacharyya Somak , Ghosh Saptarshi , Vaibhav Srivastava Kumar
Published: September 2013

In this paper, we propose a triple band polarization-independent metamaterial absorber using square-shaped closed ring resonators over wide angle of incidence. The unit cell consisting of various square loops is designed by using the parametric analysis so that it exhibits a triple band absorption response with two bands lying in C-band and one in X-band for airborne and surveillance radar signal absorption applications. Furthermore, in X-band, the absorber exhibits a broadband response with full width at half maxima bandwidth of 940 MHz (9.43%). The structure exhibits bandwidth enhanced properties for any angle of polarization under normal incidence. It also shows high absorption for wide angle of incidence up to 60°. The proposed structure is fabricated and experimental results show proper matching with the simulated responses.
Emission dynamics of an expanding ultrafast-laser produced Zn plasma under different ambient pressures
Authors: Smijesh N. , Philip Reji
Published: September 2013

We report time and space resolved spectral measurements of neutral Zn emission from an ultrafast laser produced plasma, generated by the irradiation of a Zn target with laser pulses of 100 femtoseconds duration, carried out in a broad ambient pressure range of 0.05 to 100 Torr. The measurement is done for three different axial positions in the expanding plume. The spectra are rich in neutral Zn (Zn I) emissions at 334.5 nm, 468 nm, 472 nm, 481 nm, and 636 nm, respectively, depicting the characteristic triplet structure of Zn. Fast as well as slow peaks are observed in the time of flight data of 481 nm emission, which arise from recombination and atomic contributions, respectively, occurring at different time scales. Average speeds of the fast atomic species do not change appreciably with ambient pressure. The plasma parameters (electron temperature and number density) are evaluated from the measured optical emission spectra. The rates of ionization and recombination can be enhanced by a double-pulse excitation configuration in which optical energy is coupled to the ultrafast plasma through a delayed laser pulse.
Brillouin scattering and x-ray diffraction of solid argon to 65 GPa and 700 K: Shear strength of argon at HP/HT
Authors: Marquardt H. , Speziale S. , Gleason A. , Sinogeikin S. , Kantor I. , Prakapenka V. B.
Published: September 2013

We performed simultaneous Brillouin scattering and x-ray diffraction measurements on solid argon at high pressures and high temperatures (HP/HT) in an externally heated diamond-anvil cell. From the measured acoustic velocities and densities, we derive the bulk elastic properties of solid argon up to 700 K at above 60 GPa. Our measured acoustic velocity results at room temperature are in agreement with previous Brillouin scattering results. However, the derived aggregate elastic moduli differ from previous studies. In particular, the shear modulus is significantly lower. Our HP-/HT-data show that the bulk modulus is almost insensitive to an increase of temperature (within the P-T-range of our study), whereas the shear modulus G measurably decreases with increasing temperature. We find that G(P,T) can be described by a polynomial of the form: G (P,T) = 5.8(9) GPa + 1.45(12)*(P − P0) – 0.007(2) GPa−1*(P − P0)2 – 0.01(.3) GPaK−1*(T − T0) – 0.0006(2) K−1*(P − P0)*(T − T0) (where the reference P/T-conditions are 4.3 GPa and 300 K). We use our results to estimate the shear strength of argon at HP/HT, which we find to be 0.8 GPa at 65 GPa, substantially lower than found in a previous study. Increasing temperature to 700 K reduces the shear strength to 0.5 GPa at 65 GPa.
Stability analysis of current-driven domain wall in the presence of spin Hall effect
Authors: He Peng-Bin , Zhou Zi-Dong , Wang Ri-Xing , Li Zai-Dong , Cai Meng-Qiu , Pan An-Lian
Published: September 2013

We investigate theoretically the current-driven domain wall dynamics in heavy-metal-ferromagnet bilayers. Within Lagrangian formalism, the influence of spin Hall effect on the behavior and stability of Walker's profile is analyzed. We find that in the high-current regime, although the spin Hall current alters the wall mobility slightly, the Walker breakdown is removed. In the low-current regime, the spin Hall effect makes the wall motion dependant on the polarity. The static Néel wall can be transformed into Bloch one and the polarity of Bloch wall can be switched. Especially, for proper initial polarity and current, the wall propagates along the current direction.
Simulation ensemble for a laser–driven shear experiment
Authors: Haines Brian M. , Grinstein Fernando F. , Welser–Sherrill Leslie , Fincke James R. , Doss Forrest W.
Published: September 2013

We perform an ensemble of simulations of a laser-driven shear experiment [L. Welser-Sherrill et al., “Two laser-driven mix experiments to study reshock and shear,” High Energy Density Phys. J. 9(3), 496–499 (2013)] in the strong-shock high energy-density regime to better understand material mixing driven by the Kelvin–Helmholtz instability. Each simulation uses a different realization of random initial interface perturbations based on data from targets used in experiments. Validation of the simulations is based on direct comparison of simulation and radiographic data. Simulations are also compared with published direct numerical simulation and the theory of homogeneous isotropic turbulence. Despite the fact that the flow is neither homogeneous, isotropic, nor fully turbulent, there are local regions in which the flow demonstrates characteristics of homogeneous isotropic turbulence. Our analysis shows characteristics consistent with those of incompressible isotropic turbulence. Our results show that turbulent features are present both near the shock front and in a separated region in the wake of the shock. These features develop and decay at different rates. Finally, we use the ensemble of three-dimensional simulations to test the performance of two-dimensional Reynolds-averaged Navier-Stokes simulations. In this context, we also test a presumed probability density function turbulent mixing model extensively used in combustion applications.
A standing wave linear ultrasonic motor operating in face-diagonal-bending mode
Authors: Ci Penghong , Liu Guoxi , Chen Zhijiang , Dong Shuxiang
Published: September 2013

We report a piezoelectric standing wave linear ultrasonic motor with double driving tips for generating precision motion. The motor's piezoelectric actuator was made of a simple Pb(Zr,Ti)O3 square-plate (15 × 15 × 2 mm3) operating in a single face-diagonal-bending standing wave mode to produce symmetric, bi-directional linear motion. The motor generated a driving force of 3.0 N and a moving speed of up to 165 mm/s under a relatively low applied electric field of 75 Vpp/mm at a resonance frequency of 141.5 kHz. This motor is superior to those previously reported because of the double friction-tip standing wave driving mechanism and the operating mode.
Transport coefficients in Lorentz plasmas with the power-law kappa-distribution
Authors: Jiulin Du
Published: September 2013

Transport coefficients in Lorentz plasma with the power-law κ-distribution are studied by means of using the transport equation and macroscopic laws of Lorentz plasma without magnetic field. Expressions of electric conductivity, thermoelectric coefficient, and thermal conductivity for the power-law κ-distribution are accurately derived. It is shown that these transport coefficients are significantly modified by the κ-parameter, and in the limit of the parameter κ →∞ they are reduced to the standard forms for a Maxwellian distribution.
Effects of alpha beam on the parametric decay of a parallel propagating circularly polarized Alfven wave: Hybrid simulations
Authors: Gao Xinliang , Lu Quanming , Tao Xin , Hao Yufei , Wang Shui
Published: September 2013

Alfven waves with a finite amplitude are found to be unstable to a parametric decay in low beta plasmas. In this paper, the parametric decay of a circularly polarized Alfven wave in a proton-electron-alpha plasma system is investigated with one-dimensional (1-D) hybrid simulations. In cases without alpha particles, with the increase of the wave number of the pump Alfven wave, the growth rate of the decay instability increases and the saturation amplitude of the density fluctuations slightly decrease. However, when alpha particles with a sufficiently large bulk velocity along the ambient magnetic field are included, at a definite range of the wave numbers of the pump wave, both the growth rate and the saturation amplitude of the parametric decay become much smaller and the parametric decay is heavily suppressed. At these wave numbers, the resonant condition between the alpha particles and the daughter Alfven waves is satisfied, therefore, their resonant interactions might play an important role in the suppression of the parametric decay instability.
Articulating Upgrading: Island Developing States and Canned Tuna Production
Authors: Havice Elizabeth , Campling Liam
Published: September 2013

Recently, researchers have drawn attention to an inclusionary bias in commodity chain research and proposed a ‘dis/articulations’ project aimed at drawing out how things included in, as well as excluded or expulsed from, production processes mutually, and often simultaneously, constitute commodity chains. The purpose of this paper is to situate the dis/articulations project in debates and policy proposals that identify ‘upgrading’ within a commodity chain as a pathway to development. We draw on foundational uses of the term ‘articulation’ in historical materialism to complicate linear notions of ‘upgrading as development’ before developing a framework for capturing the nonlinear dynamics of upgrading in a particular commodity chain. Our case study explains how small states that interact with the tuna commodity chain rise and fall (individually and in relation to each other), and have remained surprisingly relevant, though often at high cost, in competitive standardized manufacture. We suggest that, with careful attention to method in concept building, researchers can develop the dis/articulations project to create space for systematic assessment of the inclusionary bias in upgrading debates and policy formulations.
The Impact of Intangible Assets on Regional Productivity Disparities in Great Britain
Authors: Melachroinos Konstantinos A , Spence Nigel
Published: September 2013

During the past few years there has been a growing consensus in the literature that intangible assets represent a major source of productivity growth. Intangibles facilitate the accumulation of knowledge and information via learning and innovation, allowing, in this way, modern economies to improve the efficiency with which they utilise their resources. Nonetheless, despite the proliferation of studies that investigate the territorial impact of intangibles (variously defined), the full effect of these assets on regional productivity dynamics remains elusive. National Accounts still treat most of what can be considered intangibles as intermediate expenditure entailing that they are largely excluded from conventional measures of gross value added (GVA) and investment. The present paper attempts to tackle this shortcoming not only by including intangibles as capital in the aggregate production function, but also by employing GVA data that are adjusted for intangibles as output. The aim is to investigate the role of intangible assets on the evolution of regional productivity disparities in Great Britain during the period 1995–2004. The analysis considers the spatial effects of intangibles on both partial productivity measures and total factor productivity levels, while the regional figures are also scrutinised for the possible presence of σ-convergence and β-convergence trends during this time.
Hydrological manipulation to assist spawning of a threatened galaxiid fish in a highland lake system
Authors: Hardie Scott A.
Published: September 2013

Hydrological alterations threaten freshwater fishes globally, with infrastructure-related modification of inland waterways (e.g. dams, water diversions) having profound impacts on many species. Adapting existing water-management systems can provide opportunities for undertaking hydrological manipulations to assist management of threatened fishes. The present study conducted two hydrological manipulations in an impounded highland lake system in Tasmania, Australia, under differing hydrological conditions in 2007 and 2009, to assist recovery of an endemic species, Galaxias auratus, following a prolonged drought. Monitoring at egg, larvae, juvenile and adult life stages revealed a positive response by G. auratus in Lake Crescent (recipient of water release), with no adverse impact on the species in Lake Sorell (source of water release). In both years, reproductive constraints imposed by water level-related availability of sediment-free rocky substrata delayed spawning (~1 month) of G. auratus in Lake Crescent. Despite this, spawning and recruitment occurred in 2007 (drought year) and 2009 (drought-breaking year), and the 2007 manipulation resulted in a two-fold increase in the seasonal density of larvae in Lake Crescent and an abundant cohort of YOY fish. Given knowledge of life histories and eco-hydrological relationships, manipulating (or re-instating) hydrologic conditions is a powerful tool for assisting recovery of threatened lacustrine fishes.
Spatial and temporal variability of guinea grass (Megathyrsus maximus) fuel loads and moisture on Oahu, Hawaii
Authors: Ellsworth Lisa M. , Litton Creighton M. , Taylor Andrew D. , Kauffman J. Boone
Published: September 2013

Frequent wildfires in tropical landscapes dominated by non-native invasive grasses threaten surrounding ecosystems and developed areas. To better manage fire, accurate estimates of the spatial and temporal variability in fuels are urgently needed. We quantified the spatial variability in live and dead fine fuel loads and moistures at four guinea grass (Megathyrsus maximus) dominated sites. To assess temporal variability, we sampled these four sites each summer for 3 years (2008–2010) and also sampled fuel loads, moistures and weather variables biweekly at three sites for 1 year. Live and dead fine fuel loads ranged spatially from 0.85 to 8.66 and 1.50 to 25.74Mgha–1 respectively, and did not vary by site or year. Biweekly live and dead fuel moistures varied by 250 and 54% respectively, and were closely correlated (P<0.05) with soil moisture, relative humidity, air temperature and precipitation. Overall, fine fuels and moistures exhibited tremendous variability, highlighting the importance of real-time, site-specific data for fire prevention and management. However, tight correlations with commonly quantified weather variables demonstrates the capacity to accurately predict fuel variables across large landscapes to better inform management and research on fire potential in guinea grass ecosystems in Hawaii and throughout the tropics.
A comparison of targeted and systematic fire-scar sampling for estimating historical fire frequency in south-western ponderosa pine forests
Authors: Farris Calvin A. , Baisan Christopher H. , Falk Donald A. , Van Horne Megan L. , Fulé Peter Z. , Swetnam Thomas W.
Published: September 2013

Fire history researchers employ various forms of search-based sampling to target specimens that contain visible evidence of well preserved fire scars. Targeted sampling is considered to be the most efficient way to increase the completeness and length of the fire-scar record, but the accuracy of this method for estimating landscape-scale fire frequency parameters compared with probabilistic (i.e. systematic and random) sampling is poorly understood. In this study we compared metrics of temporal and spatial fire occurrence reconstructed independently from targeted and probabilistic fire-scar sampling to identify potential differences in parameter estimation in south-western ponderosa pine forests. Data were analysed for three case studies spanning a broad geographic range of ponderosa pine ecosystems across the US Southwest at multiple spatial scales: Centennial Forest in northern Arizona (100ha); Monument Canyon Research Natural Area (RNA) in central New Mexico (256ha); and Mica Mountain in southern Arizona (2780ha). We found that the percentage of available samples that recorded individual fire years (i.e. fire-scar synchrony) was correlated strongly between targeted and probabilistic datasets at all three study areas (r=0.85, 0.96 and 0.91 respectively). These strong positive correlations resulted predictably in similar estimates of commonly used statistical measures of fire frequency and cumulative area burned, including Mean Fire Return Interval (MFI) and Natural Fire Rotation (NFR). Consistent with theoretical expectations, targeted fire-scar sampling resulted in greater overall sampling efficiency and lower rates of sample attrition. Our findings demonstrate that targeted sampling in these systems can produce accurate estimates of landscape-scale fire frequency parameters relative to intensive probabilistic sampling.
Oxygen isotope anomaly observed in water vapor from Alert, Canada and the implication for the stratosphere
Authors: Lin Ying , Clayton Robert N. , Huang Lin , Nakamura Noboru , Lyons James R.
Published: September 2013

To identify the possible anomalous oxygen isotope signature in stratospheric water predicted by model studies, 25 water vapor samples were collected in 2003−2005 at Alert station, Canada (82°30′N), where there is downward transport of stratospheric air to the polar troposphere, and were analyzed for δ
17
O and δ
18
O relative to Chicago local precipitation (CLP). The latter was chosen as a reference because the relatively large evaporative moisture source should erase any possible oxygen isotope anomaly from the stratosphere. A mass-dependent fractionation coefficient for meteoric waters, λ
MDF
(H
2
O) = 0.529 ± 0.003 [2σ standard error (SE)], was determined from 27 CLP samples collected in 2003−2005. An oxygen isotopic anomaly of Δ
17
O = 76 ± 16 ppm (2σ SE) was found in water vapor samples from Alert relative to CLP. We propose that the positive oxygen isotope anomalies observed at Alert originated from stratospheric ozone, were transferred to water in the stratosphere, and subsequently mixed with tropospheric water at high latitudes as the stratospheric air descended into the troposphere. On the basis of this ground signal, the average Δ
17
O in stratospheric water vapor predicted by a steady-state box model is ∼40‰. Seven ice core samples (1930−1991) from Dasuopu glacier (Himalayas, China) and Standard Light Antarctic Precipitation did not show an obvious oxygen isotope anomaly, and Vienna Standard Mean Ocean Water exhibited a negative Δ
17
O relative to CLP. Six Alert snow samples collected in March 2011 and measured at Laboratoire des Sciences du Climat et de l'Environnement, Gif sur Yvette, France, had
17
O
excess
of 45 ± 5 ppm (2σ SE) relative to Vienna Standard Mean Ocean Water.