bluuebunny/crossref_metadata_2025 huggingface dataset:
The challenge to bring personalized cancer medicine from clinical trials into routine clinical practice: The case of the Institut Gustave Roussy
Authors: Arnedos Monica , André Fabrice , Farace Françoise , Lacroix Ludovic , Besse Benjamin , Robert Caroline , Soria Jean Charles , Eggermont Alexander M.M.
Published: March 2012

Research with high throughput technologies has propitiated the segmentation of different types of tumors into very small subgroups characterized by the presence of very rare molecular alterations.

The identification of these subgroups and the apparition of new agents targeting these infrequent alterations are already affecting the way in which clinical trials are being conducted with an increased need to identify those patients harboring specific molecular alterations.

In this review we describe some of the currently ongoing and future studies at the Institut Gustave Roussy that aim for the identification of potential therapeutic targets for cancer patients with the incorporation of high throughput technologies into daily practice including aCGH, next generation sequencing and the creation of a software that allows for target identification specific for each tumor. The initial intention is to enrich clinical trials with cancer patients carrying certain molecular alterations in order to increase the possibility of demonstrating benefit from a targeted agent. Mid and long term aims are to facilitate and speed up the process of drug development as well as to implement the concept of personalized medicine.
Effect of slippage on the thermocapillary migration of a small droplet
Authors: Nguyen Huy-Bich , Chen Jyh-Chen
Published: March 2012

We conduct a numerical investigation and analytical analysis of the effect of slippage on the thermocapillary migration of a small liquid droplet on a horizontal solid surface. The finite element method is employed to solve the Navier-Stokes equations coupled with the energy equation. The effect of the slip behavior on the droplet migration is determined by using the Navier slip condition at the solid-liquid boundary. The results indicate that the dynamic contact angles and the contact angle hysteresis of the droplet are strictly correlated to the slip coefficient. The enhancement of the slip length leads to an increase in the droplet migration velocity due to the enhancement of the net momentum of thermocapillary convection vortices inside the droplet. A larger contact angle leads to an increase in the migration velocity which in turn enlarges the rate of the droplet migration velocity to the slip length. There is good agreement between the analytical and the numerical results when the dynamic contact angle utilizes in the analytical approach obtained from the results of the numerical computation, and the static contact angle is smaller than 50°.
Integrated microfluidics system using surface acoustic wave and electrowetting on dielectrics technology
Authors: Li Y. , Fu Y. Q. , Brodie S. D. , Alghane M. , Walton A. J.
Published: March 2012

This paper presents integrated microfluidic lab-on-a-chip technology combining surface acoustic wave (SAW) and electro-wetting on dielectric (EWOD). This combination has been designed to provide enhanced microfluidic functionality and the integrated devices have been fabricated using a single mask lithographic process. The integrated technology uses EWOD to guide and precisely position microdroplets which can then be actuated by SAW devices for particle concentration, acoustic streaming, mixing and ejection, as well as for sensing using a shear-horizontal wave SAW device. A SAW induced force has also been employed to enhance the EWOD droplet splitting function.
Hydrogen production from methane conversion in a gliding arc
Authors: Garduño M. , Pacheco Marquidia , Pacheco Joel , Valdivia Ricardo , Santana Alfredo , Lefort Benoîte , Estrada Nadia , Rivera-Rodríguez C.
Published: March 2012

Until now, the major problem of methane conversion is to break the very strong C-H bond. It is possible by employing some catalytic methods. However, the formation of carbon powder diminishes the catalytic performance. The use of a gliding arc, described in this work, has two objectives: the hydrogen production and other syngas such as acetylene, and the treatment of the green house gas methane. A good approximation model describing the chemical processes concerning the methane decomposition is described, first by the interaction of key radicals such as CH3 and H, followed by chemical reactions involving other hydrocarbons. Furthermore, the experimental results demonstrated the ability of the gliding arc to accelerate chemical reactions at low temperatures while decreasing energetic cost.
Handling of artificial membranes using electrowetting-actuated droplets on a microfluidic device combined with integrated pA-measurements
Authors: Martel Anne , Cross Benjamin
Published: March 2012

Artificial membranes, as a controllable environment, are an essential tool to study membrane proteins. Electrophysiology provides information about the ion transport mechanism across a membrane at the single-protein level. Unfortunately, high-throughput studies and screening are not accessible to electrophysiology because it is a set of not automated and technically delicate methods. Therefore, it is necessary to automate and parallelize electrophysiology measurement in artificial membranes. Here, we present a first step toward this goal: the fabrication and characterization of a microfluidic device integrating electrophysiology measurements and the handling of an artificial membrane which includes its formation, its displacement and the separation of its leaflets using electrowetting actuation of sub-μL droplets. To validate this device, we recorded the insertion of a model porin, α-hemolysin.
Microfluidic fabrication of water-in-water (w/w) jets and emulsions
Authors: Cheung Shum Ho , Varnell Jason , Weitz David A.
Published: March 2012

We demonstrate the generation of water-in-water (w/w) jets and emulsions by combining droplet microfluidics and aqueous two-phase systems (ATPS). The application of ATPS in microfluidics has been hampered by the low interfacial tension between typical aqueous phases. The low tension makes it difficult to form w/w droplets with conventional droplet microfluidic approaches. We show that by mechanically perturbing a stable w/w jet, w/w emulsions can be prepared in a controlled and reproducible fashion. We also characterize the encapsulation ability of w/w emulsions and demonstrate that their encapsulation efficiency can be significantly enhanced by inducing formation of precipitates and gels at the w/w interfaces. Our work suggests a biologically and environmentally friendly platform for droplet microfluidics and establishes the potential of w/w droplet microfluidics for encapsulation-related applications.
Characterization and separation of Cryptosporidium and Giardia cells using on-chip dielectrophoresis
Authors: Narayanan Unni Harikrishnan , Hartono Deny , Yue Lanry Yung Lin , Mah-Lee Ng Mary , Pueh Lee Heow , Cheong Khoo Boo , Lim Kian-Meng
Published: March 2012

Dielectrophoresis (DEP) has been shown to have significant potential for the characterization of cells and could become an efficient tool for rapid identification and assessment of microorganisms. The present work is focused on the trapping, characterization, and separation of two species of Cryptosporidium (C. parvum and C. muris) and Giardia lambia (G. lambia) using a microfluidic experimental setup. Cryptosporidium oocysts, which are 2-4 μm in size and nearly spherical in shape, are used for the preliminary stage of prototype development and testing. G. lambia cysts are 8–12 μm in size. In order to facilitate effective trapping, simulations were performed to study the effects of buffer conductivity and applied voltage on the flow and cell transport inside the DEP chip. Microscopic experiments were performed using the fabricated device and the real part of Clausius—Mossotti factor of the cells was estimated from critical voltages for particle trapping at the electrodes under steady fluid flow. The dielectric properties of the cell compartments (cytoplasm and membrane) were calculated based on a single shell model of the cells. The separation of C. muris and G. lambia is achieved successfully at a frequency of 10 MHz and a voltage of 3 Vpp (peak to peak voltage).
Development and validation of a low cost blood filtration element separating plasma from undiluted whole blood
Authors: Homsy Alexandra , van der Wal Peter D. , Doll Werner , Schaller Roland , Korsatko Stefan , Ratzer Maria , Ellmerer Martin , Pieber Thomas R. , Nicol Andreas , de Rooij Nico F.
Published: March 2012

Clinical point of care testing often needs plasma instead of whole blood. As centrifugation is labor intensive and not always accessible, filtration is a more appropriate separation technique. The complexity of whole blood is such that there is still no commercially available filtration system capable of separating small sample volumes (10-100 μl) at the point of care. The microfluidics research in blood filtration is very active but to date nobody has validated a low cost device that simultaneously filtrates small samples of whole blood and reproducibly recovers clinically relevant biomarkers, and all this in a limited amount of time with undiluted raw samples. In this paper, we show first that plasma filtration from undiluted whole blood is feasible and reproducible in a low-cost microfluidic device. This novel microfluidic blood filtration element (BFE) extracts 12 μl of plasma from 100 μl of whole blood in less than 10 min. Then, we demonstrate that our device is valid for clinical studies by measuring the adsorption of interleukins through our system. This adsorption is reproducible for interleukins IL6, IL8, and IL10 but not for TNFα. Hence, our BFE is valid for clinical diagnostics with simple calibration prior to performing any measurement.
Visualizing millisecond chaotic mixing dynamics in microdroplets: A direct comparison of experiment and simulation
Authors: Jiang Liguo , Zeng Yan , Zhou Hongbo , Qu Jianan Y. , Yao Shuhuai
Published: March 2012

In order to fully explore and utilize the advantages of droplet-based microfluidics, fast, sensitive, and quantitative measurements are indispensable for the diagnosis of biochemical reactions in microdroplets. Here, we report an optical detection technique using two-photon fluorescence lifetime imaging microscopy, with an aligning-summing and non-fitting division method, to depict two-dimensional (2D) maps of mixing dynamics by chaotic advection in microdroplets with high temporal and spatial resolution. The mixing patterns of two dye solutions inside droplets were quantitatively and accurately measured. The mixing efficiency in a serpentine droplet mixer was also quantified and compared with the simulation data. The mapped chaotic mixing dynamics agree well with the numerical simulation and theoretical prediction. This quantitative characterization is potentially applicable to the real-time kinetic study of biological and chemical reactions in droplet-based microfluidic systems.
Floating-electrode enhanced constriction dielectrophoresis for biomolecular trapping in physiological media of high conductivity
Authors: Chaurey Vasudha , Polanco Carlos , Chou Chia-Fu , Swami Nathan S.
Published: March 2012

We present an electrokinetic framework for designing insulator constriction-based dielectrophoresis devices with enhanced ability to trap nanoscale biomolecules in physiological media of high conductivity, through coupling short-range dielectrophoresis forces with long-range electrothermal flow. While a 500-fold constriction enables field focusing sufficient to trap nanoscale biomolecules by dielectrophoresis, the extent of this high-field region is enhanced through coupling the constriction to an electrically floating sensor electrode at the constriction floor. However, the enhanced localized fields due to the constriction and enhanced current within saline media of high conductivity (1 S/m) cause a rise in temperature due to Joule heating, resulting in a hotspot region midway within the channel depth at the constriction center, with temperatures of ∼8°–10°K above the ambient. While the resulting vortices from electrothermal flow are directed away from the hotspot region to oppose dielectrophoretic trapping, they also cause a downward and inward flow towards the electrode edges at the constriction floor. This assists biomolecular trapping at the sensor electrode through enabling long-range fluid sampling as well as through localized stirring by fluid circulation in its vicinity.
Efficiency curves analysis of a parabolic trough solar collector in the Yucatan Peninsula
Authors: Pech A. Jiménez , Soberanis M. A. Escalante
Published: March 2012

The application of parabolic trough collector (PTC) technology is a clean and new way to produce industrial process heat. The experimental evaluation of the efficiency of first law in a PTC as the solar angle of incidence changes around the noon is presented in this paper. A brief introduction on the PTC operating conditions is included. The efficiency was obtained under the standards of the ASHRAE norms, by means of the thermal analysis depending on the fluid inlet and outlet temperature. Finally, the characteristic curves of the collector were established, as well as its removal factor. To fulfill the previous results, the following measurements were carried out: the inlet and outlet temperatures of the working fluid in the receptor of the PTC, and the solar angle of incidence referred to the azimuthal angle, with the axis located during the noon. These data were analyzed and the angle correction factor was calculated, as well as the instantaneous optical efficiency of the PTC.
Influence of noise color on stochastic resonance in hysteretic systems
Authors: Dimian M. , Manu O. , Andrei P.
Published: March 2012

Stochastic resonance phenomena in complex hysteretic systems driven by noisy oscillatory inputs are found and analyzed emphasizing the influence of noise color on resonance characteristics. This study considers various frameworks for modeling magnetic materials such as Energetic and Preisach models, while Monte-Carlo techniques and Fast Fourier Transforms are involved in generating arbitrary colored noise. The quantity used to characterize the noise induced resonance is signal-to-noise ratio, which displays a maximum at the resonance noise strength. It is found that complex systems can exhibit stochastic resonance for sub-coercive as well as for supra-coercive field values of the sinusoid amplitude, while the increase in external oscillation may also lead to an increase in the resonant noise strength. It is also shown that the maximum of the signal-to-noise ratio decreases and moves toward large noise intensities when decreasing the power coefficient of the noise spectrum.
A new kind of non-linear distortion in hard disk drives
Authors: Nichols Mark A. , Miladinovic Nenad
Published: March 2012

This paper introduces a form of non-linear distortion (NLD) in rotating magnetic storage. This NLD is inherent to the read back process, and is caused by a non-linear field versus amplitude response in the read element. This is different than traditional NLD inherent to the write process, or non-linear “saturation” effects in the read back process. Because of these differences, standard methods of mitigating NLD performance losses do not work on magneto-resistive non-linear distortion (MR-NLD). As of today there is no method of mitigating performance losses due to MR-NLD in any shipping hard drive.
Cyclic olefin copolymer based microfluidic devices for biochip applications: Ultraviolet surface grafting using 2-methacryloyloxyethyl phosphorylcholine
Authors: Jena Rajeeb K. , Yue C. Y.
Published: March 2012

This report studies the surface modification of cyclic olefin copolymer (COC) by 2-methacryloyloxyethyl phosphorylcholine (MPC) monomer using photografting technique for the purpose of biointerface applications, which demonstrate resistance to both protein adsorption and cell adhesion in COC-based microfluidic devices. This is essential because the hydrophobic nature of COC can lead to adsorption of specific compounds from biological fluids in the microchannel, which can affect the results during fluidic analysis and cause clogging inside the microchannel. A correlation was found between the irradiation time and hydrophobicity of the modified substrate. Static water contact angle results show that the hydrophilicity property of the MPC-grafted substrate improves with increasing irradiation time. The contact angle of the modified surface decreased to 20 ± 5° from 88 ± 3° for the untreated substrate. The surface characterization of the modified surface was evaluated using x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR spectroscopy). Attenuated total reflection-FTIR and XPS results show the presence of the phosphate group (P-O) on modified COC substrates, indicating that the hydrophilic MPC monomer has successfully grafted on COC. Finally, it was demonstrated that cell adhesion and protein adsorption on the MPC modified COC specimen has reduced significantly.
Concentration dependence of magnetic moment in Ce1-xFexO2
Authors: Beausoleil Geoffrey L. , Thurber Aaron , Rao S. S. , Alanko Gordon , Hanna C. B. , Punnoose Alex
Published: March 2012

In this study, we examined the impact of iron doping on the structural, chemical, and magnetic properties of ceria (Ce1-xFexO2). Samples were produced in triplicate through a coprecipitation approach in a forced hydrolysis synthesis that yielded consistently sized nanocrystals using three different cerium precursors: cerium chloride, cerium ammonium nitrate, and cerium nitrate. Particles were characterized by x ray diffraction (XRD), x ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy, and vibrating sample magnetometry (VSM). XPS and EPR data shows iron to be in the Fe3+ state and confirms the nominal dopant concentration. The moment per Fe ion found was largest at the lowest dopant concentrations, and quickly decreased as the concentration was increased. We used XPS to estimate the Ce3+/Ce4+ ratio and observed a linear relation between the saturation magnetization and the Ce3+/Ce4+ ratio.
Graphene waveguide induced by gradually varied magnetic fields
Authors: Huang Weide , He Ying , Yang Yanfang , Li Chunfang
Published: March 2012

A different way of producing the magnetic waveguide by loading gradually varied magnetic fields on graphene is proposed. The vector potential induced by the magnetic fields is connected by two square magnetic barriers and one magnetic well with linear variation. We investigate the guided modes and probability current density distribution within the graphene waveguide. It provides channels freely propagating and enables strong confinement for the modes by the gradually varied magnetic fields. The guide modes are caused by the electron reflection at the interfaces of the magnetic barriers. At the specific incident energy of electrons, there exist stable waveguide modes analogous to those in an optical waveguide. The hierarchy of guided modes decreases with the increasing incident angles. We hope that these results may lead to the potential applications in graphene-based waveguide structure.
Theory of charging and charge transport in “intermediate” thickness dielectrics and its implications for characterization and reliability
Authors: Palit Sambit , Alam Muhammad A.
Published: March 2012

Thin film dielectrics have broad applications, and the performance degradation due to charge trapping in these thin films is an important and pervasive reliability concern. It has been presumed since the 1960s that current transport in intermediate-thickness (IT) oxides (∼10–100 nm) can be described by Frenkel-Poole (FP) conduction (originally developed for ∼mm-thick films) and algorithms based on the FP theory can be used to extract defect energy levels and charging-limited lifetime. In this paper, we review the published results to show that the presumption of FP-dominated current in IT oxides is incorrect, and therefore, the methods to extract trap-depths to predict lifetime should be revised. We generalize/adapt the bulk FP current conduction model by including additional tunneling-based current injection. Steady state characteristics are obtained by a flux balance between contacts and the IT oxide. An analytical approximation of the generalized FP model yields a steady state leakage current J ∝ exp(−B√E)(1 − C√E − D/E), where B, C, and D are material-specific constants. This reformulation provides a new algorithm for extracting defect levels to predict the corresponding charging limited device lifetime. The validity and robustness of the new algorithm are confirmed by simulations and published experimental data.
Distinguishing defect induced intermediate frequency modes from combination modes in the Raman spectrum of single walled carbon nanotubes
Authors: Singh Dilip K. , Iyer Parameswar K. , Giri P. K.
Published: March 2012

Understanding of the origin of some of the intermediate frequency modes (IFMs) in the Raman spectrum of carbon nanotubes has remained controversial in the literature. In this work, through controlled introduction and elimination of defects in carbon nanotubes, we attempt to isolate the IFMs due to structural defects from that of the combination modes in single walled carbon nanotubes (SWCNTs). Our investigations on pristine and defect engineered SWCNTs using ion-irradiation, thermal annealing, and laser processing show systematic changes in the IFMs in the range 400–1200 cm−1 and its manipulation with the processing parameters. In particular, we found that the intensity of IFM at 929 cm−1 scale up with the increasing defect concentration, while that at 668 cm−1 follows opposite behavior. New IFM peaks were observed upon the creation of a controlled amount of structural defects through 30 keV N+ ion irradiation. Elimination of defects through vacuum annealing results into reduction of intensity of some IFMs identified as defect related, while the intensity of characteristic combination modes correspondingly increases. Our results show that the IFMs observed at 709, 805, 868, 926, and 1189 cm−1 are due to structural defects in the SWCNTs, while those in the range 400–550 cm−1 and at 669 cm−1 are due to the combination modes. Our x-ray photoelectron spectroscopy analysis on ion irradiated SWCNTs supports the Raman results.
Dynamical mean-field theory for molecules and nanostructures
Authors: Turkowski Volodymyr , Kabir Alamgir , Nayyar Neha , Rahman Talat S.
Published: March 2012

Dynamical mean-field theory (DMFT) has established itself as a reliable and well-controlled approximation to study correlation effects in bulk solids and also two-dimensional systems. In combination with standard density-functional theory (DFT), it has been successfully applied to study materials in which localized electronic states play an important role. It was recently shown that this approach can also be successfully applied to study correlation effects in nanostructures. Here, we provide some details on our recently proposed DFT+DMFT approach to study the magnetic properties of nanosystems [V. Turkowski, A. Kabir, N. Nayyar, and T. S. Rahman, J. Phys.: Condens. Matter 22, 462202 (2010)] and apply it to examine the magnetic properties of small FePt clusters. We demonstrate that DMFT produces meaningful results even for such small systems. For benchmarking and better comparison with results obtained using DFT+U, we also include the case of small Fe clusters. As in the case of bulk systems, the latter approach tends to overestimate correlation effects in nanostructures. Finally, we discuss possible ways to further improve the nano-DFT+DMFT approximation and to extend its application to molecules and nanoparticles on substrates and to nonequilibrium phenomena.
Shot noise of multichannel transport in mesoscopic junction systems
Authors: Ho I. L. , Chung D. S. , Lee M. T. , Wu C. S. , Chang Y. C. , Chen C. D.
Published: March 2012

Shot noise, which accompanies the emergence of the quantization nature (discreteness) of electrons, indicates dynamic fluctuations in electrical current and further reveals underlying operations in mesoscopic applications. This work presents a multichannel junction device with which to study the shot noise of coupled-channel transports as in normal nanocircuits, and it describes the theoretical algorithms. The numerical results show that, in contrast to the indistinguishable results of average current on direct-current measurements, the shot noise related to a dynamic current definitely exhibits significant differences among devices with diverse multichannel set-ups and presents super-Poissonian behaviors associated with the splitting of tunneling states.
A transferable ab initio based force field for aqueous ions
Authors: Tazi Sami , Molina John J. , Rotenberg Benjamin , Turq Pierre , Vuilleumier Rodolphe , Salanne Mathieu
Published: March 2012

We present a new polarizable force field for aqueous ions (Li+, Na+, K+, Rb+, Cs+, Mg2 +, Ca2 +, Sr2 +, and Cl−) derived from condensed phase ab initio calculations. We use maximally localized Wannier functions together with a generalized force and dipole-matching procedure to determine the whole set of parameters. Experimental data are then used only for validation purposes and a good agreement is obtained for structural, dynamic, and thermodynamic properties. The same procedure applied to crystalline phases allows to parametrize the interaction between cations and the chloride anion. Finally, we illustrate the good transferability of the force field to other thermodynamic conditions by investigating concentrated solutions.
Coupled core-edge simulations of H-mode buildup using the Fusion Application for Core-Edge Transport Simulations (FACETS) code
Authors: Hakim A. H. , Rognlien T. D. , Groebner R. J. , Carlsson J. , Cary J. R. , Kruger S. E. , Miah M. , Pankin A. , Pletzer A. , Shasharina S. , Vadlamani S. , Cohen R. , Epperly T.
Published: March 2012

Coupled simulations of core and edge transport in the DIII-D shot number 118897, after the L-H transition but before the first edge localized mode (ELM), are presented. For the plasma core transport, a set of one dimensional transport equations are solved using the FACETS:Core solver. The fluxes in this region are calculated using the GLF23 anomalous transport model and Chang-Hinton neoclassical model. For the plasma edge transport, two-dimensional transport equations are solved using the UEDGE code. Fluxes in the edge region use static diffusivity profiles based on an interpretive analysis of the experimental profiles. Simulations are used to study the range of validity of the selected models and sensitivity to neutral fueling. It has been demonstrated that the increase of neutral influx to the level that exceeds the level of neutral influx obtained from analysis simulations with the UEDGE code by a factor of two results in increased plasma density pedestal heights and plasma density levels in the scrape-off-layer region. However, the additional neutral influx has relatively weak effect on the pedestal width and plasma density profiles in the plasma core for the DIII-D discharge studied in this research.
Strain effect analysis on the thermoelectric figure of merit in n-type Si/Ge nanocomposites
Authors: Xu Y. , Li G.
Published: March 2012

In this paper, the effect of strain on the thermoelectric figure of merit is investigated in n-type Ge nanowire-Si host nanocomposite materials. The Seebeck coefficient and electrical conductivity of the Si–Ge nanocomposites are calculated using an analytical model derived from the Boltzmann transport equation (BTE) under the relaxation-time approximation. The effect of strain is incorporated into the BTE through the strain induced energy shift and effective mass variation calculated from the deformation potential theory and a degenerate k·p method at the zone-boundary X point. The effect of strain on the phonon thermal conductivity in the nanocomposites is computed with a model combining the strain dependent lattice dynamics and the ballistic phonon BTE. The electronic thermal conductivity is computed from the electrical conductivity using the Wiedemann-Franz law. Normal and shear strains are applied in the transverse plane of the Si–Ge nanocomposites. Thermoelectric properties, including the electrical conductivity, thermal conductivity, Seebeck coefficient, and dimensionless figure of merit, are computed for Si–Ge nanocomposites under these strain conditions.
Development of a compact cylindrical reaction cavity for a microwave dielectric heating system
Authors: Kim Myungsik , Kim Kwangsoo
Published: March 2012

This paper describes a compact reaction cavity for a microwave-assisted synthesis system. The microwave dielectric heating is a key technology to improve synthesizing yield, however, the large size of the microwave generation and reaction parts in an all-in-one system is a major obstacle when applying the technique to various systems, of which the installation space is limited. For this particular problem, a compact stand-alone cylindrical reaction cavity was developed in the current study. A microwave excited from a monopole probe, which is inserted into the side of the cavity, is transferred to a reaction mixture through the upper hole of the cavity. The cavity is miniaturized by filling it with an alumina ceramic dielectric. Fine-tuning of the resonance frequency becomes available by controlling the length of the inserted screw between the probe and the upper hole. The physical properties of the cavity were simulated using high frequency structural simulator (HFSS) and the produced cavity was tested using an Agilent E8357A network analyzer. The test results show that the developed cavity is able to send enough energy to various solvents.
Magnetic enhancement across a ferroelectric–antiferroelectric phase boundary in Bi1−xNdxFeO3
Authors: Wu Yu-Jie , Chen Xiao-Kun , Zhang Jing , Chen Xiao-Jia
Published: March 2012

The structural and magnetic properties of well-prepared Bi1−xNdxFeO3 (0 ≤ x ≤ 0.2) powders are investigated by combining x-ray diffraction, Raman scattering spectra, and magnetic measurements. Structural symmetric breaking from rhombohedral R3c to orthorhombic Pnma at the substituted Nd concentration of x = 0.125–0.15, accompanying a ferroelectric-antiferroelectric phase transition, is identified from x-ray diffraction patterns and Raman scattering spectra. The magnetization enhancement of Bi1−xNdxFeO3 is observed before approaching ferroelectric-antiferroelectric phase boundary conditions (0 ≤ x ≤ 0.15). We consider that such enhancement results from the destruction of the spin cycloid accompanying the structural transition. At x > 0.15, the magnetization decreases, which is probably attributable to further degradation of the space modulated spin structure, allowing a more perfect antiferromagnetic ordering.
Terahertz generation by quantum-dot miniband superlattices in the absence of electric field domains
Authors: Wang C. , Cao J. C.
Published: March 2012

We theoretically study terahertz power generation by a quantum-dot miniband superlattice operating in the limited space-charge accumulation regime, where the growth of electric field domains is suppressed. By applying a voltage along the growth direction, the steady-state and transient electron properties are investigated using a balance equation approach. Damped Bloch oscillation is observed with an onset electric field in the order of 105 V/m. The generated terahertz power density and generation efficiency are numerically evaluated. It is shown that the generation efficiency can be as high as 35% at a moderate dc electric field. The generated power density at room temperature is in the range of one tenth microwatt per micron. Quantum-dot miniband superlattice operating in the limited space-charge accumulation regime provides a promising mechanism for the purpose of terahertz generation.
Effects of low temperature anneals on the photovoltage in Si nanocrystals
Authors: Korotchenkov O. , Podolian A. , Kuryliuk V. , Romanyuk B. , Melnik V. , Khatsevich I.
Published: March 2012

We report on the time decays of surface photovoltage (SPV) and SPV spectra for Si nanocrystals (nc-Si) embedded into a SiO2 matrix. After precipitation at 1150 °C anneal in Ar the SPV increases by a factor of ≈30 compared with the value observed in an oxidized Si substrate. An increase in the signal is accompanied by longer time decays in the SPV transients (roughly from tens to hundreds of microseconds). The separation of photoexcited electrons and holes at the nc-Si/SiO2 interface is expected to play a major role in increasing the SPV signal. We emphasize that annealing of nc-Si at 450 °C in either N2 + O2 or H2 results in a remarkable increase (up to 10-fold) in photoluminescence intensity, which is accompanied by a concomitant decrease in the SPV signal and modification of the SPV decay transients. Anneal in N2 + O2 ambient slightly accelerates the SPV decay, whereas anneal in H2 dramatically speeds it up. Employment of Fourier transform infrared absorption and x-ray photoelectron spectroscopy techniques allows us to gain insight about the nature of chemical bonds into the oxidized matrix. A hypothesis is suggested that the observed effects are attributable to different passivating abilities of H2 and N2 + O2 ambients. A simple model, which takes into account the capture of photoexcited carriers at the nc-Si/SiO2 interface and the varying passivation ability of the interface traps, is capable of explaining the observed changes in the SPV transients, even quantitatively. The results may be of interest for studying the passivation of dangling bonds at the nc-Si/SiO2 interface by SPV techniques and can be used in advancing the development of silicon based photovoltaic materials with high efficiency.
The role of contact size on the formation of Schottky barriers and ohmic contacts at nanoscale metal-semiconductor interfaces
Authors: Kraya R. A. , Kraya L. Y.
Published: March 2012

We have measured the electronic structure at Au nanoisland--niobium doped SrTiO3 interfaces over a range of contact diameters. Electron transport processes at the interface transition from thermionic emission dominated to tunneling dominated, leading to ohmic behavior at small sizes. The transition increases at a much higher rate than is generally expected, emphasizing the need for precise control of nanoscale dimensions for reproducible effects in nanoscale electronic devices.
Effects of laser energy and impact surface on the stopping distance in metal oxide targets laser ablation
Authors: Lagrange J.-F. , Wolfman J. , Motret O.
Published: March 2012

The aim of this paper is to study the effect of fluence on the propagating parameters of the plasma plume. Two complex metal oxide targets CaCu3Ti4O12 and Ba0.6Sr0.4TiO3 were studied at moderate fluences (1.1 to 2.5 J.cm−2) and at two oxygen pressures (10 and 30 Pa). From imaging data, we showed that the stopping distance is drastically modified whether the fluence is increased by raising laser energy or by reducing impact surface. Indeed, in the first case the stopping distance was increased, while in the second case the stopping distance was almost not influenced.
Electronic and optical properties of ZnO/(Mg,Zn)O quantum wells with and without a distinct quantum-confined Stark effect
Authors: Stölzel Marko , Kupper Johannes , Brandt Matthias , Müller Alexander , Benndorf Gabriele , Lorenz Michael , Grundmann Marius
Published: March 2012

The luminescence properties of polar ZnO/(Mg,Zn)O quantum wells (QWs) are determined, besides confinement effects, by a redshift caused by the Stokes shift and the quantum-confined Stark effect (QCSE). We present a comprehensive study of photoluminescence and optical transmission measurements to separate these two effects. Single QW structures have been prepared by pulsed laser deposition on a-plane sapphire exhibiting excitons with and without a distinct QCSE. The QCSE leads to a redshift of the QW luminescence maximum beneath the free exciton energy in ZnO as well as a change of the dynamics from a single exponential decay function to a non-exponential one, well described by a stretched exponential decay function. The internal electric field was evaluated to 0.66 MV/cm. In the absence of an internal electric field, the Stokes shift was determined to drop from 64 meV down to 24 meV with increasing well width. Additionally, with increasing temperature, the QCSE vanishes as the internal electric field is screened by free charge carriers, leading to a drop of the redshift above 150 K to a value comparable to the Stokes shift determined for the QWs without a distinct QCSE. The radiative decay time increases linearly at low temperatures for both types of QWs, indicating free exciton emission as the major recombination channel.
The electronic barrier height of silicon native oxides at different oxidation stages
Authors: Qin H. L. , Goh K. E. J. , Troadec C. , Bosman M. , Pey K. L.
Published: March 2012

A systematic study on silicon native oxides grown in ambient air at room temperature is carried out using ballistic electron emission microscopy. The electronic barrier height of Au/native oxide was directly measured for native oxides at different oxidation stages. While the ballistic electron transmission decreases with increasing oxidation time, the electronic barrier height remains the same, even after oxidation for 1 week. After oxidation for 26 months, the oxide layer showed the bulk-like SiO2 barrier; however, some local areas still show the same barrier height as that of an Au/n-Si device. This demonstrates the non-uniformity of native oxide growth.
Raman scattering by the E2h and A1(LO) phonons of InxGa1−xN epilayers (0.25 < x < 0.75) grown by molecular beam epitaxy
Authors: Oliva R. , Ibáñez J. , Cuscó R. , Kudrawiec R. , Serafinczuk J. , Martínez O. , Jiménez J. , Henini M. , Boney C. , Bensaoula A. , Artús L.
Published: March 2012

We use Raman scattering to investigate the composition behavior of the E2h and A1(LO) phonons of InxGa1−xN and to evaluate the role of lateral compositional fluctuations and in-depth strain/composition gradients on the frequency of the A1(LO) bands. For this purpose, we have performed visible and ultraviolet Raman measurements on a set of high-quality epilayers grown by molecular beam epitaxy with In contents over a wide composition range (0.25 < x < 0.75). While the as-measured A1(LO) frequency values strongly deviate from the linear dispersion predicted by the modified random-element isodisplacement (MREI) model, we show that the strain-corrected A1(LO) frequencies are qualitatively in good agreement with the expected linear dependence. In contrast, we find that the strain-corrected E2h frequencies exhibit a bowing in relation to the linear behavior predicted by the MREI model. Such bowing should be taken into account to evaluate the composition or the strain state of InGaN material from the E2h peak frequencies. We show that in-depth strain/composition gradients and selective resonance excitation effects have a strong impact on the frequency of the A1(LO) mode, making very difficult the use of this mode to evaluate the strain state or the composition of InGaN material.
Exchange biased CoFeB-MgO tunnel junctions at the onset of perpendicular anisotropy with in-plane/out-of-plane sensing capabilities
Authors: Teixeira J. M. , Ventura J. , Fernández-García M. P. , Araujo J. P. , Sousa J. B. , Wisniowski P. , Leitao D. C. , Freitas P. P.
Published: March 2012

We investigate the transport properties of exchange biased CoFeB-MgO tunnel junctions at the onset of perpendicular anisotropy of the CoFeB free layer. Angular dependent measurements of the tunnel conductance (varying the applied magnetic field from the in-plane to the out-of-plane direction) show linear and hysteresis-free switching under low applied magnetic fields, demonstrating a new concept for a reversible in-plane/out-of-plane magnetoresistive sensor. State-of-the-art sensitivities were achieved, and a value of 0.4% TMR/Oe is observed in the direction perpendicular to the tunnel junction plane. An analysis of the anisotropy energies at play is performed based on a Stoner--Wohlfarth like model.
A sintered nanoparticle p-n junction observed by a Seebeck microscan
Authors: Becker A. , Schierning G. , Theissmann R. , Meseth M. , Benson N. , Schmechel R. , Schwesig D. , Petermann N. , Wiggers H. , Ziolkowski P.
Published: March 2012

A nanoparticular p-n junction was realized by a field-assisted sintering process, using p-type and n-type doped silicon nanoparticles. A spatially resolved Seebeck microscan showed a broad transition from the positively doped to the negatively doped range. Overshoots on both sides are characteristic for the transition. Despite the tip size being much larger than the mean particle size, information about the dopant distribution between the particles is deduced from modeling the measured data under different assumptions, including the limited spatial resolution of the tip. The best match between measured and modeled data is achieved by the idea of doping compensation, due to the sintering process. Due to a short time at high temperature during the field-assisted sintering process, solid state diffusion is too slow to be solely responsible for the observed compensation of donors and acceptors over a wide range. Therefore, these measurements support a densification mechanism based on (partial) melting and recrystallization.
Sustainable spin current in the time-dependent Rashba system
Authors: Ho Cong Son , Jalil Mansoor B. A. , Tan Seng Ghee
Published: March 2012

The generation of spin current and spin polarization in 2DEG Rashba system is considered, in which the spin-orbital coupling (SOC) is modulated by an ac gate voltage. By using non-Abelian gauge field method, we show the presence of an additional electric field. This field induces a spin current generated even in the presence of impurity scattering and is related to the time-modulation of the Rashba SOC strength. In addition, the spin precession can be controlled by modulating the modulation frequency of the Rashba SOC strength. It is shown that at high modulation frequency, the precessional motion is suppressed so that the electron spin polarization can be sustained in the 2DEG.
Fully converged integral cross sections of collision induced dissociation, four-center, and single exchange reactions, and accuracy of the centrifugal sudden approximation in H2 + D2 reaction
Authors: Song Hongwei , Lu Yunpeng , Lee Soo-Y.
Published: March 2012

The initial state selected time-dependent wave packet method was employed to calculate the integral cross sections for the H2 + D2 reaction with and without the centrifugal sudden (CS) approximation by including all important K (the projection of the total angular momentum on the body-fixed axis) blocks. With a full-dimensional model, the first fully converged coupled-channel (CC) cross sections for different competitive processes from the ground rotational state were obtained: collision induced dissociation (CID), four-center (4C) reaction and single exchange (SE) reaction. The effect of the total angular momentum J on the reaction dynamics of H2 + D2 and the accuracy of the CS approximation have also been studied. It was found that the CID and SE processes occur in a wide range of J values while the 4C process can only take place in a narrow window of J values. For this reason, the CC cross section for the 4C channel is merely comparable to the SE channel. A comparison of the integral cross sections from CC and CS calculations showed that the CS approximation works well for the CID process but not for the 4C and SE processes, and the discrepancy between the CC and CS cross sections grows larger as the translational energy and/or the vibrational energy increase(s).
An invariant theory of marginally trapped surfaces in the four-dimensional Minkowski space
Authors: Ganchev Georgi , Milousheva Velichka
Published: March 2012

A marginally trapped surface in the four-dimensional Minkowski space is a spacelike surface whose mean curvature vector is lightlike at each point. We associate a geometrically determined moving frame field to such a surface and using the derivative formulas for this frame field we obtain seven invariant functions. Our main theorem states that these seven invariants determine the surface up to a motion in Minkowski space. We introduce meridian surfaces as one-parameter systems of meridians of a rotational hypersurface in the four-dimensional Minkowski space. We find all marginally trapped meridian surfaces.
Ion assisted growth of B4C diffusion barrier layers in Mo/Si multilayered structures
Authors: Bruijn S. , van de Kruijs R. W. E , Yakshin A. E. , Bijkerk F.
Published: March 2012

We investigated the thermal stability of e-beam deposited Mo/B4C/Si/B4C layered systems, with and without ion assistance during the growth of the B4C diffusion barrier layers. The thermal stability was investigated by in situ thermal annealing during grazing incidence X-ray reflection. By studying partially treated B4C barrier layers, we found that the improvement in thermal stability is caused by an enhanced density of the B4C layer.
Field emission from single-crystalline HfC nanowires
Authors: Yuan Jinshi , Zhang Han , Tang Jie , Shinya Norio , Nakajima Kiyomi , Qin Lu-Chang
Published: March 2012

Single HfC nanowire field emitter/electrode structures have been fabricated using nano-assembling and electron beam induced deposition. Field ion microscopy has been applied to study the atomic arrangement of facets formed on a field evaporation-modified HfC nanowire tip. Field evaporation and crystal form studies suggest that the {111} and {110} crystal planes have lower work functions, while the {100}, {210}, and {311} planes have higher work functions. Field emission measurement permits us to obtain that the work function of the {111} crystal plane is about 3.4 eV.
Chimeras in random non-complete networks of phase oscillators
Authors: Laing Carlo R. , Rajendran Karthikeyan , Kevrekidis Ioannis G.
Published: March 2012

We consider the simplest network of coupled non-identical phase oscillators capable of displaying a “chimera” state (namely, two subnetworks with strong coupling within the subnetworks and weaker coupling between them) and systematically investigate the effects of gradually removing connections within the network, in a random but systematically specified way. We average over ensembles of networks with the same random connectivity but different intrinsic oscillator frequencies and derive ordinary differential equations (ODEs), whose fixed points describe a typical chimera state in a representative network of phase oscillators. Following these fixed points as parameters are varied we find that chimera states are quite sensitive to such random removals of connections, and that oscillations of chimera states can be either created or suppressed in apparent bifurcation points, depending on exactly how the connections are gradually removed.
Tuning of mid-infrared emission of ternary PbSrTe/CdTe quantum dots
Authors: Hochreiner A. , Kriechbaumer S. , Schwarzl T. , Groiss H. , Hassan M. , Springholz G.
Published: March 2012

Tunable room-temperature mid-infrared photoluminescence emission from epitaxial PbSrTe quantum dots embedded in CdTe is demonstrated. By variation of the Sr content, the emission wavelength can be tuned over the whole 3 to 1.6 μm range. Comparing the emission of PbSrTe quantum dots, quantum wells and bulk material, a one order of magnitude increase in the emission efficiency is found for the quantum dots, contrary to the bulk behavior. Theoretical modelling of the transition energies shows that at higher Sr content, segregation of Sr into CdTe occurs. This conclusion is supported by annealing experiments.