bluuebunny/crossref_metadata_2025 huggingface dataset:
A novel regrowth mechanism and enhanced optical properties of Mg0.25Zn0.75O nanorods subjected to vapor-confined face-to-face annealing
Authors: Nam Giwoong , Kim Byunggu , Park Youngbin , Park Seonhee , Moon Jiyun , Kim Do Yeob , Kim Sung-O , Leem Jae-Young
Published: September 2014

We report the novel regrowth method of spin-coated Mg0.25Zn0.75O films through the use of vapor-confined face-to-face annealing (VC-FTFA).
Robust synchronisation of networked Lagrangian systems and its applications to multi‐robot teleoperation
Authors: Liu Yen‐Chen
Published: September 2014

This study studies robust synchronisation for networked Lagrangian systems under dynamic uncertainties and communication delays. Using weighted storage functions, the authors propose a robust control scheme to guarantee that networked Lagrangian systems achieve ultimately bounded solutions over strongly connected communication graphs. Since the developed control system can ensure synchronous action in the absence of a common trajectory, the robust control algorithm is applied for bilateral teleoperations with multiple remote robots. The ultimate boundedness of the solutions can enable the teleoperation system to account for the presence of uncertain dynamics when a human operator intermittently intervenes on local robots. Numerical examples of a group of two‐link non‐linear robotic systems are presented to validate the efficacy of the developed control algorithms.
Containment control for multi‐agent systems via impulsive algorithms without velocity measurements
Authors: Zhou Hong , Wang Zhen‐Hua , Liu Zhi‐Wei , Hu Wenshan , Liu Guo‐Ping
Published: September 2014

In this study, the containment control problems in second‐order multi‐agent systems for both static leaders and dynamic leaders under directed topologies are studied. The authors propose the impulsive containment control algorithms without using velocity measurements. Some necessary and sufficient conditions depending on the eigenvalues of the Laplacian matrix associated with the communication graph, the impulsive period and the gain parameters, are obtained to guarantee the containment control. Then, the containment control of multi‐agent systems with input delay using impulsive algorithms is investigated. Also, some necessary and sufficient conditions are given. Finally, some simulations are conducted to verify the effectiveness of the proposed algorithms.
Inverse error analysis and adaptive output feedback control of uncertain systems preceded with hysteresis actuators
Authors: Liu Sining , Su Chun‐Yi
Published: September 2014

The development of control approaches for systems preceded with hysteresis non‐linearities has received great attentions in recent decades. The most common approach is the construction of an inverse model as the compensator to mitigate hysteresis effects. However, most of the developed schemes are state‐based, requiring the availability of states of systems, which may not be the case for some practical systems. In this study, output control with inverse compensation will be addressed. By using the inverse as a feedforward compensator for the model described by the modified generalised Prandtl–Ishlinskii model, an corresponding analytical expression of the inverse compensation error is first obtained. Then, an observer‐based robust adaptive output feedback controller is developed. It is shown that the proposed output feedback control scheme can not only guarantee the stability of the control systems, but also can achieve the desired tracking accuracy.
Suppressing stick‐slip oscillations in underactuated multibody drill‐strings with parametric uncertainties using sliding‐mode control
Authors: Liu Yang
Published: September 2014

Stabilisation of multibody drill‐strings which exhibit stick‐slip oscillations is studied in this paper from the point of view of underactuated system. The model has one control torque input acting on the rotary table from the land surface and multi‐degree‐of‐freedom downhole parts to be controlled. Three motion regimes of the model including bit sticking, stick‐slip oscillation and rotating at a constant speed are identified and their equilibria are analysed accordingly. The control objective of the system is to avoid the undesired bit sticking and stick‐slip oscillation while tracking a desired angular velocity. Three sliding‐mode controllers are studied for the drill‐string with estimated physical parameters. The stabilities of the proposed controllers are proved by using the Lyapunov direct method ensuring that any trajectory of the system can reach and stays thereafter on the pre‐designed sliding surface where the desired equilibrium is asymptotically stable. Extensive simulation results are given to demonstrate the effectiveness of the proposed controllers and their robustness to parametric uncertainties.
Robust adaptive control of non‐linear time‐delay systems with saturation constraints
Authors: Pan Huihui , Sun Weichao , Gao Huijun , Kaynak Okyay , Alsaadi Fuad , Hayat Tasawar
Published: September 2014

In this study, a robust adaptive control strategy is presented for a class of uncertain time‐delay non‐linear systems in the presence of non‐symmetric saturation constraints. On the one hand, an auxiliary system is constructed to reduce the negative effects cased by possible saturations, and the following stability proof ensures the theoretical strictness; the unknown time delays, on the other hand, are compensated by choosing appropriate Lyapunov–Krasovskii functions. Furthermore, the hyperbolic tangent functions are employed to efficiently avoid the controller singularity problem encountered in Lyapunov synthesis, and it is proved that the proposed controller design method is able to guarantee semi‐global uniform ultimate boundedness of all the signals in the closed‐loop system. Finally, an example simulation is conducted to verify the effectiveness of theoretic results.
Consensus of multi‐agent systems via delayed and intermittent communications
Authors: Huang Na , Duan Zhisheng , Zhao Yu
Published: September 2014

This study investigates consensus problems for multi‐agent systems with second‐order dynamics under delayed and intermittent communication. A class of distributed control algorithms are proposed based on the relatively delayed and periodical intermittent information of neighbouring agents. Then, by using tools from Lyapunov approach and graph theory, it is proved that under intermittent and delayed communication, consensus can still be asymptotically achieved if some sufficient conditions are satisfied. Moreover, the relationship between time delays and communication duration over each control period is sought out. As an extension, consensus tracking problems are studied under a directed communication topology containing a spanning tree. Both the cases of partly and completely intermittent information exchange are dealt with. Finally, several simulation examples are provided to illustrate the effectiveness of the proposed theoretical analyses.
Design and analysis of a spectro-angular surface plasmon resonance biosensor operating in the visible spectrum
Authors: Filion-Côté Sandrine , Roche Philip J. R. , Foudeh Amir M. , Tabrizian Maryam , Kirk Andrew G.
Published: September 2014

Surface plasmon resonance (SPR) sensing is one of the most widely used methods to implement biosensing due to its sensitivity and capacity for label-free detection. Whilst most commercial SPR sensors operate in the angular regime, it has recently been shown that an increase in sensitivity and a greater robustness against noise can be achieved by measuring the reflectivity when varying both the angle and wavelength simultaneously, in a so-called spectro-angular SPR biosensor. A single value decomposition method is used to project the two-dimensional spectro-angular reflection signal onto a basis set and allow the image obtained from an unknown refractive index sample to be compared very accurately with a pre-calculated reference set. Herein we demonstrate that a previously reported system operated in the near infra-red has a lower detection limit when operating in the visible spectrum due to the improved spatial resolution and numerical precision of the image sensor. The SPR biosensor presented here has an experimental detection limit of 9.8 × 10−7 refractive index unit. To validate the system as a biosensor, we also performed the detection of synthetic RNA from pathogenic Legionella pneumophila with the developed biosensing platform.
Nature of acoustic nonlinear radiation stress
Authors: Rus Guillermo
Published: September 2014

When a fluid is insonified with ultrasound, a flow consequence of a net stress becomes observable, which has been described as acoustic streaming, quartz wind, acoustic radiation force, or acoustic fountain. Following Sir James Lighthill's formulation of the Reynold's streaming, these phenomena have been attributed to a cumulative viscous effect. Instead, a multiscale effect, whereby the constitutive elastic nonlinearity scales from the ultrasonic to the macroscopic time, is here proposed and formulated to explain its origin. This raises an additional term in the Navier-Stokes equation, which ultimately stems from the anharmonicity of the atomic potential. In our experimental validation, this theory is consistent in water and for a range of ultrasonic configurations, whereas the formerly established viscous theory fails by an order of magnitude. This ultrasonic-fluid interaction, called nonlinear mechanical radiation since it is able to remotely exert a stress field, correctly explains a wide range of industrial and biomedical active ultrasonic uses including jet engines, acoustic tweezers, cyanobacteria propulsion mechanisms, nanofluidics, or acoustic radiation force elastography.
Theory of adhesion: Role of surface roughness
Authors: Persson B. N. J. , Scaraggi M.
Published: September 2014

We discuss how surface roughness influences the adhesion between elastic solids. We introduce a Tabor number which depends on the length scale or magnification, and which gives information about the nature of the adhesion at different length scales. We consider two limiting cases relevant for (a) elastically hard solids with weak (or long ranged) adhesive interaction (DMT-limit) and (b) elastically soft solids with strong (or short ranged) adhesive interaction (JKR-limit). For the former cases we study the nature of the adhesion using different adhesive force laws (F ∼ u−n, n = 1.5–4, where u is the wall-wall separation). In general, adhesion may switch from DMT-like at short length scales to JKR-like at large (macroscopic) length scale. We compare the theory predictions to results of exact numerical simulations and find good agreement between theory and simulation results.
Calculating two-dimensional THz-Raman-THz and Raman-THz-THz signals for various molecular liquids: The samplers
Authors: Ito Hironobu , Hasegawa Taisuke , Tanimura Yoshitaka
Published: September 2014

Recently, two-dimensional (2D) THz-Raman spectroscopy has been used to investigate the intermolecular modes of liquid water. We examine such 2D spectroscopy signals by means of full molecular dynamics (MD) simulations. In this way, we carry out a detailed analysis of intermolecular interactions that play an essential role in many important chemical processes. We calculate 2D Raman-THz-THz (RTT), THz-Raman-THz (TRT), and 2D Raman signals for liquid water, methanol, formamide, acetonitrile, formaldehyde, and dimethyl sulfoxide using an equilibrium-non-equilibrium hybrid MD simulation algorithm originally developed for 2D Raman spectroscopy. These signals are briefly analyzed in terms of anharmonicity and nonlinear polarizability of vibrational modes on the basis of the 2D Raman signals calculated from a Brownian oscillator model with a nonlinear system-bath interaction. We find that the anharmonic contribution is dominant in the RTT case, while the nonlinear polarizability contribution is dominant in the TRT case. For water and methanol, we observed vibrational echo peaks of librational motion in the 2D TRT signals. The predicted signal profiles and intensities that we obtained provide valuable information that can be applied to 2D spectroscopy experiments, allowing them to be carried out more efficiently.
Extremal projectors of two-parameter Kashiwara algebras
Authors: Cui Weideng
Published: September 2014

We define a two-parameter Kashiwara algebra \documentclass[12pt]{minimal}\begin{document}$B_{r,s}(\mathfrak {g})$\end{document}Br,s(g) associated to a semi-simple Lie algebra \documentclass[12pt]{minimal}\begin{document}$\mathfrak {g}$\end{document}g and its extremal projector, and study their basic properties. Applying their properties to the category \documentclass[12pt]{minimal}\begin{document}$\mathcal {O}(B_{r,s}(\mathfrak {g}))$\end{document}O(Br,s(g)), whose objects are “upper bounded” \documentclass[12pt]{minimal}\begin{document}$B_{r,s}(\mathfrak {g})$\end{document}Br,s(g)-modules, we obtain its semi-simplicity and the classification of simple modules.
Optoelectronic response of spinels CdX2O4 with X = (Al, Ga, In) through the modified Becke–Johnson functional
Authors: Boujnah M. , Dakir O. , Zaari H. , Benyoussef A. , El Kenz A.
Published: September 2014

Structural, electronic, and optical properties of CdAl2O4, CdGa2O4, and CdIn2O4 are investigated using the first principles technique based on the new potential approximation known as the Tran–Blaha modified Becke–Johnson exchange potential approximation (TB-mBJ). We discuss the improvements in the band gap determination using TB-mBJ compared to the standard generalized gradient approximation in density functional theory. The calculated equilibrium lattice parameters are in reasonable agreement with the experimental results. Electronic properties have been studied through the calculation of band structure and density of states. Based on our electronic structure obtained using the mBJ method, we have calculated various optical properties, including the complex dielectric function ε(ω), complex index of refraction n(ω), reflectivity coefficient R(ω), absorption coefficient α(ω), and the electron energy-loss function L(ω) as functions of the photon energy. We chose these three representative oxides spinel due to their potential applications in optoelectronics and optical fields.
Multiferroic Ni0.6Zn0.4Fe2O4-BaTiO3 nanostructures: Magnetoelectric coupling, dielectric, and fluorescence
Authors: Verma Kuldeep Chand , Singh Sukhdeep , Tripathi S. K. , Kotnala R. K.
Published: September 2014

Multiferroic nanostructures of Ni0.6Zn0.4Fe2O4-BaTiO3 (NZF/BT) have been prepared by two synthesis routes, i.e., chemical combustion (CNZF/BT) and hydrothermal (HNZF/BT). The synthesis of CNZF/BT results in nanoparticles of average size 4 nm at 500 °C annealing. However, the synthesis of HNZF/BT with hydrolysis temperature 180 °C/48 h shows nanowires of diameter 3 nm and length >150 nm. A growth mechanism in the fabrication of nanoparticles and wires is given. X-ray diffraction is used to identify the crystalline phase. The transmission electron microscopy shows the dimensions of NZF/BT nanostructures. The ferromagnetism, ferroelectricity, and magnetoelectric coupling show more enhancements in HNZF/BT nanowires than CNZF/BT nanoparticles. The observed polarization depends upon shape of nanostructures, tetragonal phase, and epitaxial strain. The tension induced by the surface curvature of nanowire counteracts the near-surface depolarizing effect and meanwhile leads to unusual enhancement of polarization. The ferromagnetism depends upon superficial spin canting, spin pinning of nanocomposite, and oxygen vacancy clusters. The magnetoelectric coefficient as the function of applied dc magnetizing field under ac magnetic field 5 Oe and frequency 1093 Hz is measured. The nanodimensions of NZF/BT are observed dielectric constant up to 120 MHz. The optical activity of NZF/BT nanostructures is shown by Fluorescence spectra.
Micro-strip ferromagnetic resonance study of strain-induced anisotropy in amorphous FeCuNbSiB film on flexible substrate
Authors: Zighem Fatih , El Bahoui Anouar , Moulin Johan , Faurie Damien , Belmeguenai Mohamed , Mercone Silvana , Haddadi Halim
Published: September 2014

The magnetic anisotropy of a FeCuNbSiB (Finemet®) film deposited on Kapton® has been studied by micro-strip ferromagnetic resonance technique. We have shown that the flexibility of the substrate allows a good transmission of elastic strains generated by a piezoelectric actuator. Following the resonance field angular dependence, we also demonstrate the possibility of controlling the magnetic anisotropy of the film by applying relatively small voltages to the actuator. Moreover, a suitable model taking into account the effective elastic strains measured by digital image correlation and the effective elastic coefficients measured by Brillouin light scattering, allowed to deduce the magnetostrictive coefficient. This latter was found to be positive (λ = 16 × 10−6) and consistent with the usually reported values for bulk amorphous FeCuNbSiB.
Edge-coherent-mode nature of the small edge localized modes in Experimental Advanced Superconducting Tokamak
Authors: Wang H. Q. , Xu G. S. , Guo H. Y. , Wan B. N. , Wang L. , Chen R. , Ding S. Y. , Yan N. , Gong X. Z. , Liu S. C. , Shao L. M. , Chen L. , Zhang W. , Liang Y. F. , Hu G. H. , Liu Y. L. , Li Y. L. , Zhao N.
Published: September 2014

High-confinement regime with high-frequency and low-energy-loss small edge localized modes (ELMs) was achieved in Experimental Advanced Superconducting Tokamak by using the lower hybrid current drive and ion cyclotron resonance heating with lithium wall conditioning. The small ELMs are usually accompanied with a quasi-coherent mode at frequency around 30 kHz, as detected by the Langmuir probes near the separatrix. The coherent mode, with weak magnetic perturbations different from the precursor of conventional ELMs, propagates in the electron diamagnetic drift direction in the lab frame with the poloidal wavelength λθ ∼ 14 cm, corresponding to both high poloidal and toroidal mode numbers (m > 60 and n > 12). This coherent mode, carrying high-temperature high-density filament-like plasma, drives considerable transport from the pedestal region into the scrape-off layer towards divertor region. The co-existence of small ELMs and quasi-coherent modes is beneficial for the sustainment of long pulse H-mode regime without significant confinement degradation.
Numerical analysis of drift resistive inertial ballooning modes
Authors: Tangri V. , Rafiq T. , Kritz A. H. , Pankin A. Y.
Published: September 2014

Three numerical techniques employing differentiation matrices are used to investigate the linear stability of drift-resistive-inertial ballooning mode for conditions that occur in tokamak edge plasmas. Hermite and Sinc spectral methods are applied to compute the ballooning mode eigenvalues and eigenvectors. In addition, a finite difference method is utilized to construct a differentiation matrix in order to verify results obtained using the spectral methods. It is shown that the spectral methods converge more rapidly than the finite difference method. Ballooning and strongly ballooning approximations are used to calculate the eigen-spectrum. The techniques that are utilized in this paper for calculating eigenvalues are quite general and are relevant to investigate other modes that use the ballooning mode formalism.
Linear and nonlinear response of a rotating tokamak plasma to a resonant error-field
Authors: Fitzpatrick Richard
Published: September 2014

An in-depth investigation of the effect of a resonant error-field on a rotating, quasi-cylindrical, tokamak plasma is preformed within the context of constant-ψ, resistive-magnetohydrodynamical theory. General expressions for the response of the plasma at the rational surface to the error-field are derived in both the linear and nonlinear regimes, and the extents of these regimes mapped out in parameter space. Torque-balance equations are also obtained in both regimes. These equations are used to determine the steady-state plasma rotation at the rational surface in the presence of the error-field. It is found that, provided the intrinsic plasma rotation is sufficiently large, the torque-balance equations possess dynamically stable low-rotation and high-rotation solution branches, separated by a forbidden band of dynamically unstable solutions. Moreover, bifurcations between the two stable solution branches are triggered as the amplitude of the error-field is varied. A low- to high-rotation bifurcation is invariably associated with a significant reduction in the width of the magnetic island chain driven at the rational surface, and vice versa. General expressions for the bifurcation thresholds are derived and their domains of validity mapped out in parameter space.
Effect of a thin Ti interfacial layer on the thermal resistance of Ge2Sb2Te5-TiN stack
Authors: Battaglia Jean-Luc , Kusiak Andrzej , Saci Abdelhak , Fallica Roberto , Lamperti Alessio , Wiemer Claudia
Published: September 2014

We study the dependence of the thermal resistance of TiN/Ge2Sb2Te5 stacks on Si in the presence or not of a thin Ti interfacial layer. While for TiN/Ge2Sb2Te5 almost ideal thermal properties of the interfaces are found, a different behaviour is measured for TiN/Ti/Ge2Sb2Te5. After exposure to temperatures up to 440 °C, the thermal resistance results to be lower than expected despite both the formation of the TiTe2 phase, the depletion of Te inside Ge2Sb2Te5, and the non complete development of the hexagonal structure. Those observations have been also validated on the SiO2/Ge2Sb2Te5 stack with and without Ti interfacial layer.
Electromagnetic characterization of metamaterials in the centimetric frequency band using an original adjustable height stripline
Authors: Chevalier A. , Gomez S. , Queffelec P.
Published: September 2014

We propose a broadband measurement method for measuring the electromagnetic (EM) properties of metamaterials in the 1–6 GHz frequency range. For this experimental technique, an original adjustable height strip transmission-line was developed that makes it possible to characterize metamaterials with different volumes and different numbers of unit cells. Therefore, it was possible to assess the influence of the number of unit cells in a sample on the measured constitutive parameters (complex permittivity and permeability). This study enabled us to define the criterion of the representative elementary number of cells. This criterion must be satisfied in practice in order to determine the microwave behavior for the sample under test in as close as possible to an infinite medium, whose EM properties can only be determined from simulations. Experimental and theoretical results for split ring resonator-type metamaterials are presented, compared, and discussed.
Circuit electromechanics with a non-metallized nanobeam
Authors: Pernpeintner M. , Faust T. , Hocke F. , Kotthaus J. P. , Weig E. M. , Huebl H. , Gross R.
Published: September 2014

We have realized a nano-electromechanical hybrid system consisting of a silicon nitride beam dielectrically coupled to a superconducting microwave resonator. We characterize the sample by making use of the Duffing nonlinearity of the strongly driven beam. In particular, we calibrate the amplitude spectrum of the mechanical motion and determine the electromechanical vacuum coupling. A high quality factor of 480 000 at a resonance frequency of 14 MHz is achieved at 0.5 K. The experimentally determined electromechanical vacuum coupling of 11.5 mHz is quantitatively compared with finite element based model calculations.
Towards simultaneous achievement of carrier activation and crystallinity in Ge and GeSn with heated phosphorus ion implantation: An optical study
Authors: D'Costa Vijay Richard , Wang Lanxiang , Wang Wei , Lim Sin Leng , Chan Taw Kuei , Chua Lye Hing , Henry Todd , Zou Wei , Hatem Christopher , Osipowicz Thomas , Tok Eng Soon , Yeo Yee-Chia
Published: September 2014

We have investigated the optical properties of Ge and GeSn alloys implanted with phosphorus ions at 400 °C by spectroscopic ellipsometry from far-infrared to ultraviolet. The dielectric response of heated GeSn implants displays structural and transport properties similar to those of heated Ge implants. The far-infrared dielectric function of as-implanted Ge and GeSn shows the typical free carrier response which can be described by a single Drude oscillator. Bulk Ge-like critical points E1, E1 + Δ1, E0', and E2 are observed in the visible-UV dielectric function of heated Ge and GeSn indicating single crystalline quality of the as-implanted layers. Although the implantation at 400 °C recovers crystallinity in both Ge and GeSn, an annealing step is necessary to enhance the carrier activation.
Diffusion of fluorine adatoms on doped graphene
Authors: Guzmán-Arellano R. M. , Hernández-Nieves A. D. , Balseiro C. A. , Usaj Gonzalo
Published: September 2014

We calculate the diffusion barrier of fluorine adatoms on doped graphene in the diluted limit using Density Functional Theory. We found that the barrier Δ strongly depends on the magnitude and character of the graphene's doping (δn): it increases for hole doping (δn < 0) and decreases for electron doping (δn > 0). Near the neutrality point the functional dependence can be approximately by Δ = Δ0 – αδn, where α ≃ 6 × 10−12 meV cm2. This effect leads to significant changes of the diffusion constant with doping even at room temperature and could also affect the low temperature diffusion dynamics due to the presence of substrate induced charge puddles. In addition, this might open up the possibility to engineer the F dynamics on graphene by using local gates.
Polarization resolved spatial near-field mapping of optical modes in an on-chip rolled-up bottle microcavity
Authors: Böttner Stefan , Li Shilong , Jorgensen Matthew R. , Schmidt Oliver G.
Published: September 2014

A detailed optical near-field mapping of the spatial distribution of two sets of linearly polarized modes in a vertically rolled-up bottle microcavity is presented. We find different effective axial potential widths depending on the polarization state by coupling a tapered fiber to the on-chip microcavity and show that we can selectively excite modes out of a rich axial mode spectrum. Our results are supported by a theoretical model and help to promote future applications of rolled-up bottle microcavities in on-chip integrated optical networks, where these tube cavities can, in principle, be used to transfer signals horizontally along the tube axis or vertically between stacked photonic layers.
Regulation of cell migration and osteogenic differentiation in mesenchymal stem cells under extremely low fluidic shear stress
Authors: Gao Xinghua , Zhang Xu , Xu Hui , Zhou Bingpu , Wen Weijia , Qin Jianhua
Published: September 2014

Mesenchymal stem cells (MSCs) are multipotent stem cells predominantly obtained from bone marrow, which are sensitive to mechanical loadings in physiological microenvironment. However, how the MSCs sense and respond to extremely low fluidic shear stress analogous to interstitial flow in vivo is poorly understood. In this work, we present a functional microfluidic device to examine the migration and differentiation behaviors of MSCs in response to multiple orders of physiologically relevant interstitial flow levels. The different magnitudes of fluid flow-induced shear stress were produced by a hydraulic resistance-based microfluidic perfusion system consisting of a microchannel network and a parallel of uniform cell culture chambers. By changing the length and width of the flow-in channels, the multiple magnitudes of low shear stresses could be generated ranging from ∼10−5 to ∼10−2 dyne/cm2. We demonstrated enhanced significant F-actin expression and cell migration in MSCs under applied fluidic shear stress at ∼10−2 dyne/cm2. We also demonstrated a significant osteogenic differentiation under this interstitial level of slow flows from ∼10−2 to ∼10−4 dyne/cm2 in MSCs by analyzing alkaline phosphatase activity and osteopontin staining. Moreover, cytochalasin D and Rho-inhibitor Y-27632 significantly reduced the cytoskeleton F-actin expression and osteogenic differentiation in MSCs, indicating the mediated mechanical responses of MSCs under extremely low fluidic shear stress, possibly as a consequence of Rho-associated kinase pathway. The established microfluidic perfusion system with multiple shear-flow capabilities is simple and easy to operate, providing a flexible platform for studying the responses of diverse types of cells to the multiple interstitial flow levels in a single assay.
Reduced stability of copper interconnects due to wrinkles and steps on hexagonal boron nitride substrates
Authors: Gao Jian , Chow Philippe K. , Thomas Abhay V. , Lu Toh-Ming , Borca-Tasciuc Theodorian , Koratkar Nikhil
Published: September 2014

There is great scientific and technological interest in the use of chemical-vapor-deposition grown hexagonal boron nitride dielectric substrates for microelectronics applications. This interest stems from its superior heat spreading capability compared to silicon dioxide as well as the lack of surface dangling bonds or charge traps in hexagonal boron nitride which results in superior performance for graphene based electronics devices. However, surface heterogeneities, such as wrinkles or steps, are ubiquitous in such devices due to the fabrication and processing of chemical vapor deposition grown hexagonal boron nitride. In this study, we characterize the effect of such surface heterogeneities on the stability of copper interconnects used in microelectronics devices. Based on the theoretical thermo-physical properties of the constituent thin film layers, our simulations predict that copper interconnects deposited on hexagonal boron nitride can withstand ∼1.9 times more power than on a silicon dioxide substrate, due to its superior in-plane thermal conductivity. However, our electrical measurements reveal that copper wires melt and fail at consistently lower current densities on hexagonal boron nitride than on silicon dioxide. This was verified by testing in air as well as under vacuum. Scanning electron microscopy and atomic force microscopy characterization of the hexagonal boron nitride surface indicates that this contradictory result is due to nanoscale surface non-uniformities (i.e., wrinkles and steps) which are omnipresent in chemical-vapor-deposition grown and transferred hexagonal boron nitride films. Our results highlight the critical need for improved processing methods before large-scale microelectronics applications of chemical vapor deposition grown hexagonal boron nitride can be realized.
Influence of semiconducting properties of nanoparticle coating on the electrochemical actuation of liquid metal marble
Authors: Sivan Vijay , Tang Shi-Yang , O'Mullane Anthony P. , Petersen Phred , Kalantar-zadeh Kourosh , Khoshmanesh Khashayar , Mitchell Arnan
Published: September 2014

Semiconducting properties of nanoparticle coating on liquid metal marbles can present opportunities for an additional dimension of control on these soft objects with functional surfaces in aqueous environments. We show the unique differences in the electrochemical actuation mechanisms of liquid metal marbles with n- and p-type semiconducting nanomaterial coating. A systematic study on such liquid metal marbles shows voltage dependent nanoparticle cluster formation and morphological changes of the liquid metal core during electrochemical actuations and these observations are unique to p-type nanomaterial coated liquid metal marbles.
Ethics of Ethnography with Families: A Geographical Perspective
Authors: Hall Sarah Marie
Published: September 2014

This paper contributes to debates on geographies of family and intimate relations, and research ethics in ethnographic research by addressing the ethics of doing ethnography with families. Drawing on debates in human geography, anthropology, and sociology, I argue that the intimate nature of both ethnography and familial relations presents particular challenges to using an ethnographic approach to studying families. Using experiences from two years of ethnographic research with six families in the UK, the ethics of confidentiality (within and between families, and in published materials), and disengagement (following long-term involvement, transforming relationships, and staying in contact with participants) are explored. In addition, the paper sheds light on the geographical and ethical complexities of doing ‘ethnography on your doorstep’. The conclusions outline the contributions of the paper to discussions within and beyond geography, family studies, and ethnography.
The Emotional Economy of Migration Driving Mainland Chinese Transnational Sojourning across Migration Regimes
Authors: Ho Elaine Lynn-Ee
Published: September 2014

In focusing on the way emotional ideologies underpin migration regimes, this paper underlines how migrants manage their emotions in a quest towards wider economic and social integration. It compares the experiences of Mainland Chinese immigrants who are in Canada with those that returned to China temporarily but plan to remigrate to Canada eventually, thus sustaining transnational journeys. The paper suggests that the intersection of emotional and migration regimes imposes norms and sanctions that direct migrants towards what are considered appropriate emotions and emotional subjectivities. The economic logics shaping the circulation of emotions within and across geographical space during transnational sojourning is referred to here as the emotional economy of migration. The paper argues that certain emotions appreciate or depreciate in value as they are mobilised geographically during such transnational sojourning. The analysis contributes to migration scholarship by drawing out the emotional logics, circulations, and calculations that structure and prop up the political economy of migration regimes.
Engaging Cooperative Research
Authors: Hinchliffe Steve , Levidow Les , Oreszczyn Sue
Published: September 2014

Cooperative research involves upstream engagement of practitioners, introducing diverse knowledges and expertise in ways that can, in theory at least, generate new knowledge that is socially robust and publicly accountable. And yet, judging cooperative research solely in terms of accountability may underplay the transformative and nonaccountable/nonconvergent nature of research—the production, in other words, of the new when collectives are drawn together. Using examples from research that sought to provide environmental civil society organisations (CSOs) with the resources to shape cooperative research, this paper argues that cooperative research may not simply mark an extension of public engagement with science but can also seed an anticipatory and thus creative research process. For cooperative research to play this role there is a need to highlight the human and nonhuman attachments that underpin cooperative research activity. We argue that such activity might best have as its aim the empowerment, not simply of participants, but of the political situations that CSOs can help to foment.
‘Heating up’ or ‘Cooling Down’? Analysing and Performing Broadened Participation in Technoscientific Conflicts
Authors: Sundqvist Göran
Published: September 2014

Stakeholders and citizens today are often invited to deliberate in controversial processes of scientific and technological decision making. Scholars in the field of science and technology studies (STS) have long supported these initiatives to transcend strong expert–lay divides. However, despite many such contributions, there is no agreement on how such broadened participation should be performed, either in theory or in practice. The theoretical ambition of this paper is to reformulate the opposing viewpoints of Michel Callon and Harry Collins on public participation in scientific and technological decision making. It is argued that they try to ‘heat up’ (Callon) or ‘cool down’ (Collins) the issues they study: that is, that they enact them differently. The performative outcomes of these two strategies for participation are analysed. The empirical ambition is to study recent developments in participatory approaches to radioactive waste management in Belgium and Sweden and the role of social science in connection with these. Due to public criticism of earlier top-down technocratic approaches, this field has played a significant role in enacting and supporting broadened participation. Moreover, while the waste programmes in Belgium and Sweden have both been internationally recognised as taking participation seriously, they have varied considerably in terms of participatory technologies and involvement of social science. A conclusion is that social science research has influenced how participatory engagements are organised in radioactive waste programmes, and thereby has become involved in processes of ‘heating up’ and ‘cooling down’. However, social scientists, as well as all actors, need to be more aware of their own preconceptions about the issue at stake—in terms of its being “hot” or “cold”—and the consequences of these enactments.
Diversity of exotic vascular plant species on Moreton Island in subtropical Australia: increase over 100 years
Authors: Wang Jian
Published: September 2014

There have been significant increases in the richness of exotic vascular plant species over the past century on Moreton Island, Australia. In total, 120 exotic species (including eight declared plants) in 90 genera and 42 families were collected and collated through field surveys during 2008–2010 and from the Queensland Herbarium collections. One-hundred years ago, no exotic vascular plant species were recorded. Sixteen years later, 14 exotic species in 14 genera from 11 families were collected. A half century later (1973–1975), a detailed vegetation survey recorded 66 exotic species (including five declared plants) belonging to 57 genera from 30 families. This increase coincides with a history of increasingly frequent wild fires, increasing human activities and greater presence of feral animals. The most significant increase occurred after the 1973–1975 surveys, namely an increase of 54 more species, equivalent to an 81.8% increase. These latter species included 17 (31.5%) woody species, 11 (20.4%) graminoid species and 26 (48.1%) forb species. The Sorensen similarity index (ISS) of total exotic species between the surveys of 1973–1975 and 2008–2010 was intermediate (ISS = 0.62). Index for woody species (ISS = 0.60) was also intermediate. Indices for annual graminoids (ISS = 0.53) and perennial forbs (ISS = 0.40) were all relatively low between the studies. Perennial graminoids and annual forbs had high similarity indices, namely, 0.75 and 0.72, respectively. The invasiveness of these plants was also assessed and it was shown that the ‘highly invasive’ and ‘generally invasive’ species were relatively few in number. The findings highlight the rapid increase and change in exotic vascular plant species on Moreton Island and the need for a more robust understanding of the exotic species’ dynamics of the island in order to inform weed management and native vegetation protection services.
Reproductive trajectories over decadal time-spans after fire for eight obligate-seeder shrub species in south-eastern Australia
Authors: Muir Annette M. , Vesk Peter A. , Hepworth Graham
Published: September 2014

Intervals between fires are critical for the persistence of obligate-seeding shrubs, and are often used in planning fires for fuel reduction and biodiversity conservation in fire-prone ecosystems worldwide. Yet information about the trajectories of reproductive performance for such species is limited and information is often qualitative. To test existing assumptions about reproductive maturity periods for eight obligate-seeding shrubs (with both canopy and soil seedbanks) in foothill forests of south-eastern Australia, we used a chronosequence approach, with sites from 2 years to >40 years post-fire. Quantitative measurements of flowering and fruiting were used to fit models of reproductive response in relation to time-since-fire for each species. Inferred reproductive maturity for each species, based on modelled times to reach 80% of maximum flower production, varied from 5 to 18 years post-fire. For a subset of three species, models predicted 80% maximum seed production occurring 1–7 years later than flowering. Our results confirmed or extended assumptions about post-fire reproductive maturity for these species, and provided a basis for improved incorporation of plant life-history in ecological fire planning. We infer that increased fire frequency makes one of our study taxa, Banksia spinulosa var. cunninghamii (Sieber ex Rchb.) A.S.George, vulnerable to decline because of its long reproductive maturity period and serotinous seed storage.
Ultrastructure and mitochondrial numbers in pre- and postpubertal pig oocytes
Authors: Pedersen Hanne Skovsgaard , Callesen Henrik , Løvendahl Peter , Chen Fenghua , Nyengaard Jens Randel , Nikolaisen Nanett Kvist , Holm Peter , Hyttel Poul
Published: September 2014

Prepubertal pig oocytes are associated with lower developmental competence. The aim of this experiment was to conduct an exhaustive survey of oocyte ultrastructure and to use a design-unbiased stereological approach to quantify the numerical density and total number of mitochondria in oocytes with different diameters from pre- and postpubertal pigs. The ultrastructure of smaller prepubertal immature oocytes indicated active cells in close contact with cumulus cells. The postpubertal oocytes were more quiescent cell types. The small prepubertal oocytes had a lower total mitochondrial number, but no differences were observed in mitochondrial densities between groups. Mature postpubertal oocytes adhered to the following characteristics: presence of metaphase II, lack of contact between cumulus cells and oocyte, absence of rough endoplasmic reticulum and Golgi complexes, peripheral location of cortical granules and central localisation of mitochondria, vesicles and lipid droplets. Prepubertal oocytes displayed more variation. The ultrastructure of large pre- and postpubertal oocytes was compatible with higher developmental competence, whereas that of smaller prepubertal oocytes could explain their reduced capacity. The higher number of mitochondria in large pre- and postpubertal oocytes could have an influence on oocyte competence, by increasing the pool of mitochondria available for early embryonic development.
Fire and carbon management in a diversified rangelands economy: research, policy and implementation challenges for northern Australia
Authors: Walsh Dionne , Russell-Smith Jeremy , Cowley Robyn
Published: September 2014

Burning of savanna is a globally important source of greenhouse gas (GHG) emissions. In Australia, burning of savanna contributes between 2% and 4% annually of the nation’s reportable emissions. Complete removal of this source of emissions is unrealistic because fire is a ubiquitous natural process and important land-management tool. In the rangelands of northern Australia, fire is used to manage habitat for conservation, control woodland thickening, manipulate pastures for grazing and is an essential component of indigenous cultural and land-management practice. There has been a concerted attempt in recent times to move away from complete fire suppression and its consequence: frequent, extensive and high intensity wildfires occurring late in the dry season. In fire-adapted vegetation types, prescribed early dry season fires help reduce the incidence of late season wildfires and consequently the amount of GHG emissions produced. The emergence of a carbon economy affords a potential opportunity for land managers to diversify their livelihoods by adopting fire-management practices that reduce GHG emissions and increase carbon sequestration. However, in order to realise benefits from this emerging economy, there is a need to identify and address a range of barriers affecting community participation. The papers in this Special Issue document current scientific knowledge, policy issues and pathways to participation, with particular reference to Australia’s savanna rangelands. This introductory paper outlines how northern Australia has both the opportunity and requirement to develop a diversified rangelands economy to realise multiple conservation, economic and emissions outcomes.
Aboveground and belowground carbon dynamics in response to fire regimes in the grazed rangelands of northern Australia: initial results from field studies and modelling
Authors: Hunt L. P.
Published: September 2014

The world’s rangelands are often seen as offering considerable potential as a carbon (C) sink, which could contribute to the management of atmospheric C levels, but there are often few data available to assess this potential or to inform the type of management regimes that would be necessary. This paper reports on a review of the literature, a field study and modelling of C stocks under a selection of experimental fire regimes in two plant communities in Australia’s northern rangelands. The field study on an open eucalypt savanna woodland and a savanna grassland-open shrubland suggested that fire regime had no effect or an inconsistent effect on aboveground C stocks. However, modelling using the Century model for the open woodland site showed that increasing fire frequency was associated with reduced aboveground and soil C stocks. Thus, while infrequent fires allowed C stocks to increase (10-yearly fire) or remain stable (6-yearly fire) over a modelled 58-year period, a regime of more frequent fires (4- and 2-yearly fires) reduced C stocks over time. Simulation of C dynamics over 93 years of pastoral settlement suggested that total C stocks had increased by 9.5 t ha–1, largely due to an increase in C in woody vegetation following a reduction in fire frequency associated with pastoral settlement. Frequent burning, as recommended to maintain low woody density and promote pasture production for grazing, will, therefore, reduce aboveground and to a lesser extent soil C stocks where there has been a history of infrequent fire. The opportunities for pastoralists to increase C stocks will depend on the frequency of fire and vegetation type, especially its woodiness or potential woodiness. Reducing fire frequency in woody rangelands will increase C stocks but may have adverse effects on pasture and livestock production. Reducing grazing pressure or destocking might also increase C stocks but may be relevant only when a property is overstocked or where relatively unproductive land could be taken out of livestock production. Any C gains from altering fire and grazing management are likely to be modest.