bluuebunny/crossref_metadata_2025 huggingface dataset:
MHC class II‐dependent T–T interactions create a diverse, functional and immunoregulatory reaction circle
Authors: Lee You Jeong , Jung Kyeong Cheon , Park Seong Hoe
Published: November 2008

Unlike conventional T cells, innate‐like T cells such as natural killer (NK) T cells are selected by homotypic T‐cell interactions. Recently, a few reports have shown that T–T CD4+ T cells can be generated in a similar manner to that for NKT cells. These two types of cells share common functional properties such as rapid response to antigenic encounters and the potential for a panoply of cytokine secretion. However, T–T CD4+ T cells differ from NKT cells in that they are restricted by highly polymorphic major histocompatibility complex (MHC) II molecules and have a diverse T‐cell receptor repertoire. Additional example of T–T interactions was recently reported in which peripheral T cells re‐circulate to the thymus and participate in the thymocyte selection process. In this review, we dissect the cellular mechanisms underlying the production of T–T CD4+ and NKT cells, with particular emphasis on the differences between these two T‐cell prototypes. Finally, we propose that T–T CD4+ T cells serve two major functions: one as an acute‐phase reactant against viral infection and the other is the generation of anti‐ergotypic CD4+ T cells for regulatory purposes. All of these features make it possible to create a diverse set of functional cells through MHC class II‐restricted T–T interactions.
Enhancement of plasmid DNA yields during fed‐batch culture of a fruR‐knockout Escherichia coli strain
Authors: Ow Dave Siak‐Wei , Yap Miranda Gek‐Sim , Oh Steve Kah‐Weng
Published: November 2008

Well‐characterized derivatives of Escherichia coli K12 such as DH5α are the host strains commonly used for plasmid DNA production. Owing to the prospective clinical demand for large quantities of plasmid DNA for gene therapy and DNA vaccination, existing plasmid production processes need to be optimized to attain higher plasmid yields. To date, nearly all production optimization efforts are focused on media or fermentation process design. Although there has been a simple empirical evaluation of the available host strains, there is a lack of systematic effort at engineering these host strains for improved plasmid DNA production. In view of this, we engineered DH5α WT (wild‐type) cells carrying a DNA vaccine plasmid by knocking out the fruR (fructose repressor) [also known as the Cra (catabolite repressor activator)] global regulator gene and evaluated the growth and plasmid yields of these P+ (plasmid‐bearing) fruR cells (fruR‐knockout cells) during fed‐batch cultures with exponential feeding. The P+ fruR cells showed a more rapid accumulation of plasmid DNA towards the end of the fed‐batch cultures compared with the P+ WT cells. As a result, the specific plasmid yield of the P+ fruR cells was 21% higher than that of the P+ WT cells [19.2 versus 15.9 mg/g DCW (dry cell weight)]. These results demonstrate that, from an initial high‐yielding fermentation process, the knockout of the fruR global regulator gene in E. coli DH5α further improves plasmid yields during fed‐batch culture.
Viscous and inviscid spatial stability analysis of compressible swirling mixing layers
Authors: Müller Sebastian B. , Kleiser Leonhard
Published: November 2008

We examine the viscous and inviscid spatial stabilities of circular swirling mixing layers that differ in swirl intensity, Mach number, and Reynolds number. The corresponding base flows are numerical solutions of the axisymmetric boundary-layer equations in cylindrical coordinates. A high-order numerical discretization scheme based on Chebyshev collocation and a global eigenvalue search are employed to solve the corresponding stability equations. The two disturbance modes that are observed are of centrifugal (or Rayleigh) type and of shear-instability (or Kelvin–Helmholtz) type. The most amplified shear instabilities with higher azimuthal wavenumber possess a long-axial-wavelength character and are fed by the axial vorticity arising from the swirl component. Moreover, secondary and higher unstable modes corresponding to the centrifugal instability are observed. Viscosity has a slightly stabilizing effect on the shear-instability disturbances. Centrifugal-instability disturbances with short-azimuthal and short axial wavelengths are stabilized by viscous effects.
Suppressing random dopant-induced fluctuations of threshold voltages in semiconductor devices
Authors: Andrei Petru , Oniciuc Liviu
Published: November 2008

This article introduces a robust and computationally efficient technique for the design of fluctuation-resistant structures (fault-tolerant) semiconductor devices. This technique can be applied to the computation of the doping profiles that minimize the intrinsic variations in various parameters induced by random dopant fluctuations. The technique is based on the evaluation of doping sensitivity functions, which are defined as elements of the space adjoint to the space of square integrable functions generated by all possible doping variations. The optimized doping profiles are computed by minimizing the standard deviation of fluctuations of different parameters, and constraints are taken into consideration by using the Lagrange multiplier method. The technique introduced here can be applied to any semiconductor device, such as metal-oxide-semiconductor field-effect transistors (MOSFETs), silicon-on-insulator (SOI) devices, and fin field-effect transistors, and can be used in the framework of any transport model. The technique is applied to the minimization of the random dopant-induced fluctuations of threshold voltages in 25 nm channel length MOSFETs and double-gate fully depleted SOI devices. It is shown that, by carefully designing the doping profiles, random dopant-induced fluctuations can be suppressed between 16% in the case of constrained optimization and 35% in the case of unconstrained optimization for devices with channel lengths smaller than 25 nm. Analytical equations are derived for the optimum doping profiles that minimize the effects of random dopant fluctuations on the threshold voltage in MOSFETs. It is shown that, in both long-channel and short-channel devices, the size of the undoped region should be at least 14 of the width of the depletion region in order to suppress efficiently the random dopant-induced fluctuations.
Theoretical calculation of the low lying electronic states of the molecular ion RbH+ with spin-orbit effects
Authors: Korek M. , Hammoud S. , Allouche A. R. , Harb T.
Published: November 2008

The potential energy has been calculated for the 42 lowest electronic states of symmetries Ω=1∕2,3∕2,5∕2, for the molecular ion RbH+. Using an ab initio method, the calculation is based on nonempirical pseudopotentials and parametrized ℓ-dependent polarization potentials. Gaussian basis sets have been used for both atoms, and spin-orbit effects have been taken into account. The spectroscopic constants for 19 electronic states have been calculated by fitting the calculated energy values to a polynomial in terms of the internuclear distance r. The permanent dipole moment and the transition dipole moments have been calculated for the considered Ω states. Through the canonical functions approach the eigenvalue Ev, the abscissas of the corresponding turning points (rmin and rmax) and the rotational constants Bv have been calculated. The comparison of the present results with those available in literature shows a very good agreement.
Scattering theory for the Klein–Gordon equation with nondecreasing potentials
Authors: Cruz Maximino , Arredondo R. Juan H.
Published: November 2008

The Klein–Gordon equation is considered in the case of nondecreasing potentials. The energy inner product is nonpositive on a subspace of infinite dimension, not consisting entirely of eigenvectors of the associated operator. A scattering theory for this case is developed and asymptotic completeness for generalized Möller operators is proven.
All low voltage lateral junction scanning tunneling microscope with very high precision and stability
Authors: Hou Yubin , Wang Jihui , Lu Qingyou
Published: November 2008

We describe the first lateral junction and fully low voltage scanning tunneling microscope, featuring very high precision, stability, compactness, and image quality (highly oriented pyrolytic graphite atomic resolution images). In its core, the tip and sample each sit on one of two parallel-mounted piezoelectric tube scanners so that the tip-sample gap is regulated along the scanners’ pairing direction. The scanner’s large lateral deflection provides a large gap regulation range even under low voltages, allowing exclusively using only low voltage (less than ±15 V) operational amplifiers to precisely implement the coarse (inertial slider) and fine approach, feedback control, and hence the entire electronics. Because the scanners are identical and adjacent, thermal drifts are minimal.
Experimental and theoretical investigations of ionization/dissociation of cyclopentanone molecule in a femtosecond laser field
Authors: Wang Qiaoqiao , Wu Di , Jin Mingxing , Liu Fuchun , Hu Feifei , Cheng Xihui , Liu Hang , Hu Zhan , Ding Dajun , Mineo H. , Dyakov Y. A. , Mebel A. M. , Chao S. D. , Lin S. H.
Published: November 2008

The ionization/dissociation mechanism of cyclopentanone has been experimentally investigated in molecular beam by irradiating with intense 394 and 788nm laser fields with pulse duration of 90fs. The range of laser intensities varied from 3×1013to4×1014W∕cm2. For both wavelengths, the singly charged parent ion is observable while the doubly charged one cannot be found easily, although the fragmentation pattern supports its presence. Meanwhile, the extent of fragmentation at 788nm is less than that in the 394nm case. We quantitatively analyze the ionization processes of cyclopentanone in intense femtosecond laser by comparing the calculation results of ionization rate constants obtained from Ammosov-Delone-Krainov, Keldysh, and Keldysh-Faisal-Reiss (KFR) theories based on hydrogenlike atom model. We also compare the experimental and theoretical results; the generalized KFR theory is found to be useful in predicting the ionization yields of singly and doubly charged cyclopentanone ion. To interpret the dissociation patterns of the cyclopentanone ions, we have used the Rice-Ramsperger-Kassel-Marcus theory with the potential surfaces obtained from the ab initio quantum chemical calculations.
Superadiabaticity in magnetic resonance
Authors: Deschamps Michaël , Kervern Gwendal , Massiot Dominique , Pintacuda Guido , Emsley Lyndon , Grandinetti Philip J.
Published: November 2008

Adiabaticity plays a central role in modern magnetic resonance experiments, as excitations with adiabatic Hamiltonians allow precise control of the dynamics of the spin states during the course of an experiment. Surprisingly, many commonly used adiabatic processes in magnetic resonance perform well even though the adiabatic approximation does not appear to hold throughout the process. Here we show that this discrepancy can now be explained through the use of Berry’s superadiabatic formalism, which provides a framework for including the finite duration of the process in the theoretical and numerical treatments. In this approach, a slow, but finite time-dependent Hamiltonian is iteratively transformed into time-dependent diagonal frames until the most accurate adiabatic approximation is obtained. In the case of magnetic resonance, the magnetization during an adiabatic process of finite duration is not locked to the effective Hamiltonian in the conventional adiabatic frame, but rather to an effective Hamiltonian in a superadiabatic frame. Only in the superadiabatic frame can the true validity of the adiabatic approximation be evaluated, as the inertial forces acting in this frame are the true cause for deviation from adiabaticity and loss of control during the process. Here we present a brief theoretical background of superadiabaticity and illustrate the concept in the context of magnetic resonance with commonly used shaped radio-frequency pulses.
Selective calculation of high-intensity vibrations in molecular resonance Raman spectra
Authors: Kiewisch Karin , Neugebauer Johannes , Reiher Markus
Published: November 2008

We present an intensity-driven approach for the selective calculation of vibrational modes in molecular resonance Raman spectra. The method exploits the ideas of the mode-tracking algorithm [M. Reiher and J. Neugebauer, J. Chem. Phys. 118, 1634 (2003)] for the calculation of preselected molecular vibrations and of Heller’s gradient approximation [Heller et al., J. Phys. Chem. 86, 1822 (1982)] for the estimation of resonance Raman intensities. The gradient approximation allows us to construct a basis vector for the subspace iteration carried out in the mode-tracking calculation, which corresponds to an artificial collective motion of the molecule that contains the entire intensity in the resonance Raman spectrum. Subsequently, the algorithm generates new basis vectors from which normal mode approximations are obtained. It is then possible to provide estimates for (i) the accuracy of the normal mode approximations and (ii) the intensity of these modes in the final resonance Raman spectrum. This approach is tested for the examples of uracil and a structural motif from the E colicin binding immunity protein Im7, in which a few aromatic amino acids dominate the resonance Raman spectrum at wavelengths larger than 240 nm.
Influence of substrate microstructure on the high field dielectric properties of BaTiO3 films
Authors: Levi R. D. , Samantaray M. M. , Trolier-McKinstry S. , Randall C. A.
Published: November 2008

The temperature dependence of the electrical leakage current density of chemical solution deposited BaTiO3 films on high purity Ni foils was investigated as function of the underlying Ni microstructure. Depending on the Ni heat treatment prior to BaTiO3 deposition, it was found that pores in the dielectric followed the profiles of the underlying Ni grain boundary grooves. The electrical properties were then characterized on capacitors with and without the presence of Ni grain boundaries. When a Ni grain boundary from the substrate was present in the capacitor used during the electrical measurements, the loss tangent of the capacitor rose rapidly for dc biases exceeding ∼25 kV/cm. The critical bias increases to ∼100 kV/cm when no substrate grain boundaries are included in the capacitor. In addition, the capacitance-voltage curves are much more symmetric when grain boundaries are absent. This disparity in the electrical behavior was analyzed in terms of the mechanisms of charge conduction across the Ni-dielectric interface. While a reverse biased Schottky emission mechanism dominates the current in areas free of Ni grain boundaries, the barrier at the cathode is ineffective when Ni grain boundaries are present in the substrate. This, in turn, leads to a larger leakage current dominated by the forward biased Schottky barrier at the anode. The results are important to both embedded and surface mount capacitors.
Charge dynamics in ionic polymer metal composites
Authors: Porfiri Maurizio
Published: November 2008

In this paper, we study the charge dynamics in ionic polymer metal composites (IPMCs) in response to a voltage difference applied across their electrodes. We use the Poisson–Nernst–Planck equations to model the time evolution of the electric potential and the concentration of mobile counterions. We present an analytical solution of the nonlinear initial-boundary value problem by using matched asymptotic expansions. We determine the charge and electric potential distributions as functions of time in the whole IPMC region. We show that in the bulk polymer region the IPMC is approximately electroneutral; in contrast, charge distribution boundary layers arise at the polymer-electrode interfaces. Prominent charge depletion and enrichment at the polymer-electrode interface are present even at moderately low input-voltage levels. We use the proposed analytical solution to derive a physics-based circuit model of IPMCs. The equivalent circuit comprises a linear resistor in series connection with a nonlinear capacitor. We derive closed-form expressions for the resistance and the capacitance by conducting a qualitative phase-plane analysis of the inner approximation of the asymptotic expansion. The circuit conductivity is independent of the IPMC dielectric constant and is proportional to the ion diffusivity; whereas, the capacitance is proportional to the square root of the dielectric constant and is independent of the diffusivity. The conductivity depends on the polymer thickness, while the capacitance is independent of it. The capacitance nonlinearity is extremely pronounced, and dramatic capacitance reduction is observed for moderately low voltage levels. We validate the proposed analytical solution along with the derived circuit model through extensive comparisons with finite element results available in the technical literature.
The role of H bonding and dipole-dipole interactions on the electrical polarizations and charge mobilities in linear arrays of urea, thiourea, and their derivatives
Authors: Pal Shrinwantu , Manna Arun K. , Pati Swapan K.
Published: November 2008

Computational studies using density functional theory are carried out on linear chains of urea, N,N′-dimethyl urea and N,N,N′,N′-tetramethyl urea, and their sulfur analogs, viz., thiourea, N,N′-dimethyl thiourea and N,N,N′,N′-tetramethyl thiourea with varying chain length, to understand the effect of hydrogen bonding and dipolar interactions on the optoelectronic response properties of such linear aggregates. While molecules of urea, N,N′-dimethyl urea, and the corresponding sulfur analogs, thiourea, N,N′-dimethyl thiourea, are stabilized in linear chains by hydrogen bonding, the molecules of N,N,N′,N′-tetramethyl urea and N,N,N′,N′-tetramethyl thiourea in the linear chains are stabilized by purely dipolar interactions. To understand the contributions of electrostatic and polarization effects on such intermolecular interactions, we study the effect of an external electric field on the intermolecular interactions in these systems. We find that the strength of hydrogen bonding increases while that of dipolar interactions decreases with increase in external field strength. We account for such findings by decomposing the interaction terms into charge-transfer and electrostatic interaction terms. The effects of these interactions on the linear and nonlinear optical properties together with transport properties such as carrier mobilities are estimated to understand their suitability for device applications.
Nucleation in polydisperse polymer mixtures
Authors: Qi Shuanhu , Yan Dadong
Published: November 2008

The effect of polydispersity on nucleation in a metastable mixture of polydisperse polymer A and monodisperse polymer B is studied using self-consistent field theory. We adopt the continuous Schulz chain length distribution to describe the polydispersity of species A. The results show that the free energy barrier, as well as many other properties of the critical nucleus, is sensitive to the polydispersity, especially in the highly polydisperse case. This should be attributed to the fact that longer chains have stronger tendencies toward nucleation. As a result, the distribution of the volume fraction as a function of chain length in the nucleus becomes different from that in the bulk. The chain length, which corresponds to the maximum contribution to the volume fraction in the nucleus, becomes larger than the number-average chain length. Meanwhile, the interface between the critical nucleus and the parent metastable bulk phase broadens. This phenomenon is obvious when the polydispersity is high.
Electrostatic layer correction with image charges: A linear scaling method to treat slab 2D+h systems with dielectric interfaces
Authors: Tyagi Sandeep , Arnold Axel , Holm Christian
Published: November 2008

A fast algorithm for dealing with electrostatic interactions in partially periodic systems that are confined along the nonperiodic direction by two planar dielectric interfaces is presented. The method is a generalization of the electrostatic layer correction (ELC) method of Arnold et al. [J. Chem. Phys. 117, 2496 (2002)], and employs an exact relation between the 2D+h system and a three-dimensional (3D) periodic system. The terms connecting the two systems can be evaluated linearly in the number of charges. Thus, the method shows overall the scaling of the underlying method employed to handle the Coulombic 3D case. Moreover, our algorithm can accurately handle multiple polarization image charges due to the dielectric interfaces as well as all the periodic images due to the periodic boundary conditions and has full control over the errors depending on the underlying method used for the 3D periodic case.
Optical properties of Yb3+ doped Lu3Al5O12 crystal fibers grown by μ-pulling down technique
Authors: Toncelli Alessandra , Alshourbagy Mohamed , Tonelli Mauro
Published: November 2008

Yb doped Lu3Al5O12 single crystal fibers has been grown with various Yb3+ ion concentrations: 2%, 5%, 10%, 15%, and 50% Yb doping levels. The diameter of the fibers is around 3mm and their length is up to 110mm. The fibers have been annealed in air at 1400°C for 24h to remove Yb2+ produced during the growth in the fibers. Structural characterization by x-ray diffraction method has been performed to confirm the monocrystalline phase and the orientation of the fibers. Absorption measurements have been performed on different pieces of the fibers to check the homogeneity of the distribution of Yb3+ along the fiber length. The results indicate that the distribution coefficient is close to 1. The fluorescence lifetime was measured for different Yb3+ concentrations. Results are in agreement with the literature and can be interpreted as a mixture of the radiation trapping and concentration quenching effects. The emission cross section has been calculated both from absorption spectra and from emission data. The two different independent methods give similar results, but emission data suffer from strong reabsorption effects on some of the lines. On the zero phonon line at high doping levels a central dip appears that can be interpreted with a reabsorption model.
Simultaneous real-time x-ray diffraction spectroscopy, Rutherford backscattering spectrometry, and sheet resistance measurements to study thin film growth kinetics by Kissinger plots
Authors: Smeets D. , Demeulemeester J. , Deduytsche D. , Detavernier C. , Comrie C. M. , Theron C. C. , Lavoie C. , Vantomme A.
Published: November 2008

When the Kissinger method is used to investigate thin film growth kinetics, activation energies obtained are often significantly higher than those of Arrhenius plots based on isothermal studies. The reason for the higher activation energies is related to the sensitivity of the Kissinger analysis to nucleation effects. In fact, this often undesirable effect opens the possibility of studying nucleation barriers in a semiquantitative way. Furthermore, we show that these nucleation effects can be filtered out by a more careful application of the Kissinger method, and activation energies that are consistent with Arrhenius plots are then obtained.
Energy barriers at interfaces of (100)GaAs with atomic layer deposited Al2O3 and HfO2
Authors: Afanas’ev V. V. , Badylevich M. , Stesmans A. , Brammertz G. , Delabie A. , Sionke S. , O’Mahony A. , Povey I. M. , Pemble M. E. , O’Connor E. , Hurley P. K. , Newcomb S. B.
Published: November 2008

Band alignment at the interfaces of (100)GaAs with Al2O3 and HfO2 grown using atomic layer deposition is determined using internal photoemission and photoconductivity measurements. Though the inferred conduction and valence band offsets for both insulators were found to be close to or larger than 2 eV, the interlayer grown by concomitant oxidation of GaAs reduces the barrier for electrons by approximately 1 eV. The latter may pose significant problems associated with electron injection from GaAs into the oxide.
The complex influence of the oscillatory shear on the melt of linear diblock copolymers
Authors: You Li-Yan , He Yan-Dong , Zhao Ying , Lu Zhong-Yuan
Published: November 2008

The phase morphologies of symmetric linear diblock copolymers subjected to the oscillatory shear are investigated with the aid of dissipative particle dynamics simulations. The frequency dependent reorientations of the lamellar phase (LAM) have been identified. We find that the parallel orientation of LAM (i.e., the lamellar normal is parallel to the velocity gradient) appears at high shear frequency, whereas the perpendicular orientation of LAM (the lamellar normal being perpendicular to the velocity gradient) takes place at low shear frequency. In both of the cases, the reorientations undergo similar processes: the original LAM phase prepared in equilibrium breaks down rapidly, and it takes a very long time for the perfectly oriented LAM being reformed. Moreover, the shear-induced isotropic to lamellar phase transitions are observed when the oscillatory shear amplitude is large enough. It indicates that the shear amplitude plays a dominant role in the order-disorder transition. The viscosity and the modulus of the melt are found to be dependent on the shear amplitude and the shear frequency in a complex way.
High program efficiency of p-type floating gate in n-channel split-gate embedded flash memory
Authors: Shih Hung-Sheng , Fang Shang-Wei , Kang An-Chi , King Ya-Chin , Lin Chrong-Jung
Published: November 2008

This work proposes a novel p-type boron-doped floating gate for n-channel split-gate flash memory. A lower program voltage, with a programming time of 7 μs, results in five times of the conventional source-side injection programming efficiency, a 5% wider program/erase window, and more reliable endurance characteristics. Additionally, a 2 Mbit embedded flash Intellectual Property (IP) has been successfully implemented and statistically compared. The lower program voltage reduces concerns around the high-voltage decoder, the charge pump efficiency, and the array efficiency beyond 90 nm nodes. The new p-doped split-gate structure provides a very promising solution for advanced embedded split-gate flash memory beyond the 90 nm node.
Quantitative coherent diffractive imaging of an integrated circuit at a spatial resolution of 20 nm
Authors: Abbey Brian , Williams Garth J. , Pfeifer Mark A. , Clark Jesse N. , Putkunz Corey T. , Torrance Angela , McNulty Ian , Levin T. M. , Peele Andrew G. , Nugent Keith A
Published: November 2008

The complex transmission function of an integrated circuit is reconstructed at 20 nm spatial resolution using coherent diffractive imaging. A quantitative map is made of the exit surface wave emerging from void defects within the circuit interconnect. Assuming a known index of refraction for the substrate allows the volume of these voids to be estimated from the phase retardation in this region. Sample scanning and tomography of extended objects using coherent diffractive imaging is demonstrated.
Similarities in the kinetics of photocrystallization and photodarkening in a-Se
Authors: Tallman Robert E. , Reznik A. , Weinstein B. A. , Baranovskii S. D. , Rowlands J. A.
Published: November 2008

The onset time of photocrystallization (PC) as a function of temperature in a-Se films designed for avalanche photodetectors is explored using Raman scattering experiments. The PC onset time τon is compared to the time-constant τIPD for irreversible photodarkening (IPD) studied in earlier work. Both τon and τIPD exhibit activated thermal behavior mediated by an energy barrier EB∼0.7–0.95eV. We suggest that the formation kinetics of PC and IPD in a-Se are governed by the same energy surface and configuration changes, occurring via photoinduced defects during the primary stage of crystallization.
Optically driven fluid flow along arbitrary microscale patterns using thermoviscous expansion
Authors: Weinert Franz M. , Braun Dieter
Published: November 2008

We show how fluid can be moved by a laser scanning microscope. Selected parts of a fluid film are pumped along the path of a moving warm spot which is generated by the repetitive motion of an infrared laser focus. With this technique, we remotely drive arbitrary two-dimensional fluid flow patterns with a resolution of 2μm. Pump speeds of 150μm∕s are reached in water with a maximal temperature increase in the local spot of 10K. Various experiments confirm that the fluid motion results from the dynamic thermal expansion in a gradient of viscosity. The viscosity in the spot is reduced by its enhanced temperature. This leads to a broken symmetry between thermal expansion and thermal contraction in the front and the wake of the spot. As result the fluid moves opposite to the spot direction due to both the asymmetric thermal expansion in the spot front and the asymmetric thermal contraction in its wake. We derive an analytical expression for the fluid speed from the Navier–Stokes equations. Its predictions are experimentally confirmed without fitting parameters under a number of different conditions. In water, this nonlinearity leads to a fluid step of <100nm for each passage of the spot. Since the spot movement can be repeated in the kilohertz regime, fluid speeds can exceed 100μm∕s. Using this technique, we pump nanoparticles over millimeters through a gel. An all-optical creation of a dilution series of DNA and biomolecules by aliquotation and mixing is demonstrated for fluids sandwiched between untreated and unstructured, disposable microscope cover slips. The shown optical remote control of fluid flow expands the microfluidic paradigm into previously inaccessible regimes of tiny volumes, closed flow paths, fast switching between flow patterns, and remote fluid control under extreme fluid conditions.
Direct measurement of slip flows in superhydrophobic microchannels with transverse grooves
Authors: Byun Doyoung , Kim Jihoon , Ko Han Seo , Park Hoon Cheol
Published: November 2008

Slippage effects in microchannels that depend on the surface characteristics are investigated, taking into account hydrophilic, hydrophobic, and superhydrophobic wettabilities. Microscale grooves are fabricated along the vertical walls to form superhydrophobic surfaces, which enable both the visualization of the flow field near the walls and the direct measurement of the slip length. Velocity profiles are measured using microparticle image velocimetry and those in hydrophilic glass, hydrophobic polydimethylsiloxane (PDMS), and superhydrophobic PDMS microchannels are compared. For the hydrophilic glass surface, the velocity near the wall smoothly decreases to zero, which is consistent with the well-known, no-slip boundary condition. On the other hand, for the flow in the hydrophobic PDMS microchannel, the velocity profile approaches some finite value at the wall, showing a slip length of approximately 2μm. In addition, to directly measure the velocity in the superhydrophobic microchannel, transverse groove structures are fabricated along the vertical walls in the microchannel. For this surface, the velocity profile approaches a value that is larger than that for the PDMS case. Incidentally, instabilities in the velocity profile are observed at the interface with the air gap. Furthermore, the velocity profile near the wall shows a larger slip length than for any of the other experimental setups. For groove structures that are high and wide, the liquid meniscus forms curves in the cavity so that a wavy flow is created beyond the grooves. Moreover, if the pitch-to-width ratio of the groove structure increases, meniscus penetration into the cavity is observed.
Ion-acoustic solitary waves and their interaction in a weakly relativistic two-dimensional thermal plasma
Authors: Han Jiu-ning , Du Sheng-lin , Duan Wen-shan
Published: November 2008

This paper discusses the existence of ion-acoustic solitary waves and their interaction in a weakly relativistic two-dimensional thermal plasma. Two Korteweg–de Vries equations for small but finite amplitude solitary waves in both ξ and η directions are derived. The phase shifts and trajectories of two solitary waves after the collision with an arbitrary angle α are also obtained. The effects of parameters of the normalized ion temperature σ, the ratio of heat capacity δ, the relativistic factor Fγ, and the colliding angle α on the amplitudes, the widths and the phase shifts of both the colliding solitary waves are studied. The effects of these parameters on the new nonlinear wave created by the collision between two solitary waves are examined as well. The results suggest that these parameters can significantly influence the amplitude, the width of the newly formed nonlinear wave and the colliding solitary waves. The phase shifts of the colliding solitary waves strongly depend on the colliding angle α. Moreover, there are compressive solitary waves in such a system.
Pseudogap formation in the metallic state of La0.7Sr0.3MnO3 thin films
Authors: Singh Udai Raj , Gupta Anjan K. , Sheet Goutam , Chandrasekhar Venkat , Jang H. W. , Eom C. B.
Published: November 2008

We report on scanning tunneling microscopy and spectroscopy (STM/S) studies of epitaxial La0.7Sr0.3MnO3 (LSMO) thin films on a lattice matched (001) La0.3Sr0.7Al0.35Ta0.35O9 substrate for both as-grown and annealed films. In contrast to the as-grown films, the films annealed at 800 °C in air show atomic terraces with spectra that develop a gaplike structure with cooling. We show that the gap structure can be attributed to the predicted pseudogap in the manganites. Unlike several previous reports, we did not find electronic inhomogeneities in LSMO by STM/S.
Highly uniform, strongly correlated fluorinated lipid nanodomains embedded in biological membrane models
Authors: Oelke Jochen , Pasc Andreea , Wixforth Achim , Konovalov Oleg , Tanaka Motomu
Published: November 2008

Synthetic, fluorinated lipids incorporated into phospholipid membranes form highly uniform self-assembled lipid nanodomains. The size of nanodomains beyond optical resolution can quantitatively be determined using grazing-incidence x-ray diffraction. The long-range interaction can reach up to the distance that is eight times larger than the domain size, which can be interpreted within the theoretical framework of two-dimensional colloidal crystallization. Coupling of bioactive molecules to lipid head groups would allow for the creation of highly uniform and strongly correlated functional nanodomains, which can be used to study the influence of molecular confinement on the cooperative interactions in biology.
Analysis of the acoustoelectric behavior of microwave frequency, temperature-compensated AlN-based multilayer coupling configurations
Authors: Caliendo Cinzia
Published: November 2008

Piezoelectric AlN films, 1.3–6.2 μm thick, have been grown on bare and metallized Al2O3(0001) substrates by reactive radio-frequency-sputtering technique at 180 °C. The films were uniform, stress-free, highly c-axis oriented normal to the surface, and extremely adhesive to the substrates. Surface acoustic wave (SAW) delay lines, showing harmonic modes with operating frequencies up to about 2.44 GHz, were obtained just using conventional optical lithography at 7.5 μm linewidth resolution. Four interdigital transducer (IDT)/counter electrode configurations were obtained locating the IDTs either on the AlN free surface or at the Al2O3/AlN interface, with and without an Al thin metal film opposite the IDTs. The temperature induced shift of the fundamental and harmonic operating frequencies of the four configurations was measured at different temperatures in the range from −25 to 70 °C. The first order temperature coefficient of delay (TCD) of the four structures was experimentally evaluated for different film thickness values and for SAWs propagating along and normal the Al2O3 a-axis. Eight AlN thicknesses, i.e., the temperature-compensated points (TCPs), were experimentally estimated at which the TCD is equal to 0 ppm/°C. These TCPs were found to be in good agreement with those theoretically evaluated. The SAW propagation along the four coupling structures was investigated in terms of phase and group velocity, electromechanical coupling coefficient, electrical potential, and IDT capacitance and radiation resistance for different film thickness values and SAW propagation directions. The numerical simulation of the mechanical and electrical behaviors of the coupling structures showed how the electroacoustic transduction efficiency, the IDT directivity, and bandwidth can benefit from having different electrical boundary conditions. The obtained results confirm the AlN feasibility to the implementation of SAW devices for application to gigahertz range, good electromechanical coupling, thermally stable electroacoustic devices.
Texture formation in Ag thin films: Effect of W–Ti diffusion barriers
Authors: Bhagat S. K. , Alford T. L.
Published: November 2008

Pure Ag films were deposited on SiO2/Si with and without introduction of W0.7Ti0.3 barrier layers. The films were annealed in vacuum for 1 h at temperatures up to 650 °C. X-ray diffraction pole figure analysis was used to investigate the texture information in as-deposited and annealed films. After annealing, the {111} texture in Ag films increased; however, the degree of increase was significantly higher in Ag/W–Ti/SiO2. In Ag/SiO2 structures, the {200} texture also increased. In Ag/W–Ti/SiO2 structures, no significant increase in {200} texture was observed; however, {111} twin related {511} texture evolved. In as-deposited samples, {111} pole figure revealed that {111} absolute intensity was higher in Ag/SiO2 than in Ag/W–Ti/SiO2. After annealing, Ag {111} intensity was always higher in Ag/W–Ti/SiO2. Sources for the texture evolution were discussed in detail. Field emission scanning electron microscope showed the presence of twins and abnormal grain growth. After annealing at 650 °C, both the roughness and resistivity of Ag increased significantly.
Simultaneous optical excitation of Na electronic and CF4 vibrational modes in Na+CF4 collisions
Authors: Alekseev V. A. , Grosser J. , Hoffmann O. , Rebentrost F.
Published: November 2008

We report on the ultraviolet excitation of Na(3s)+CF4 collision pairs in a crossed molecular beam experiment. We observe Na(3d) collision products originating from the process Na(3s)+CF4(ν3=0)+hν→Na(3d)+CF4(ν3=1). The spectral intensity distribution of the collision products and the prevailing small angle scattering confirm a previously proposed long range dipole-dipole mechanism. We report velocity-resolved spectra and a comparison to preliminary numerical results based on collisional broadening theory. Polarization experiments suggest future potential for the observation of collision geometries.
Gallium oxide and gadolinium gallium oxide insulators on Si δ-doped GaAs/AlGaAs heterostructures
Authors: Paterson G. W. , Longo P. , Wilson J. A. , Craven A. J. , Long A. R. , Thayne I. G. , Passlack M. , Droopad R.
Published: November 2008

Test devices have been fabricated on two specially grown GaAs/AlGaAs wafers with 10 nm thick gate dielectrics composed of either Ga2O3 or a stack of Ga2O3 and Gd0.25Ga0.15O0.6. The wafers have two GaAs transport channels either side of an AlGaAs barrier containing a Si δ-doping layer. Temperature dependent capacitance-voltage (C-V) and current-voltage (I-V) studies have been performed at temperatures between 10 and 300 K. Bias cooling experiments reveal the presence of DX centers in both wafers. Both wafers show a forward bias gate leakage that is by a single activated channel at higher temperatures and by tunneling at lower temperatures. When Gd0.25Ga0.15O0.6 is included in a stack with 1 nm of Ga2O3 at the interface, the gate leakage is greatly reduced due to the larger band gap of the Gd0.25Ga0.15O0.6 layer. The different band gaps of the two oxides result in a difference in the gate voltage at the onset of leakage of ∼3 V. However, the inclusion of Gd0.25Ga0.15O0.6 in the gate insulator introduces many oxide states (≥4.70×1012 cm−2). Transmission electron microscope images of the interface region show that the growth of a Gd0.25Ga0.15O0.6 layer on Ga2O3 disturbs the well ordered Ga2O3/GaAs interface. We therefore conclude that while including Gd0.25Ga0.15O0.6 in a dielectric stack with Ga2O3 is necessary for use in device applications, the inclusion of Gd decreases the quality of the Ga2O3/GaAs interface and near interface region by introducing roughness and a large number of defect states.
Dynamic colloidal sorting on a magnetic bubble lattice
Authors: Tierno Pietro , Soba Alejandro , Johansen Tom H. , Sagués Francesc
Published: November 2008

We use a uniaxial garnet film with a magnetic bubble lattice to sort paramagnetic colloidal particles with different diameters, i.e., 1.0 and 2.8μm. We apply an external magnetic field which precesses around an axis normal to the film with a frequency Ω=62.8s−1 and intensity 3120A∕m <H<6911A∕m. By varying the component of the field Hz normal to the film, we observe that particles of one size are localized around magnetic bubbles while the others are transported through the array. We complement the experimental measurements with numerical simulations to explore the sorting capability for particles with different magnetic moments.
Solitary inertial Alfvén waves in dusty plasmas
Authors: Mahmood S. , Saleem H.
Published: November 2008

Linear and nonlinear inertial Alfvén waves are studied in the presence of positively and negatively charged dust in electron-ion plasmas. The Sagdeev potential approach is employed to obtain solitary inertial Alfvén waves in such a multicomponent plasma. It is found that electron density dips are formed in the super Alfvénic region, which has behavior similar to the case of electron-ion plasmas. The amplitude of the electron density dip structure is decreased in the presence of positively charged dust particles, while it is increased due to negatively charged dust particles in dusty plasmas. The numerical results are shown for an illustrative purpose. The results can be applicable to explain some aspects of solar wind interactions with the comets and planets containing dusty plasma environments.
High-quality quantum point contact in two-dimensional GaAs (311)A hole system
Authors: Shabani J. , Petta J. R. , Shayegan M.
Published: November 2008

We studied ballistic transport across a quantum point contact (QPC) defined in a high-quality GaAs (311)A two-dimensional hole system using shallow etching and top gating. The QPC conductance exhibits up to 11 quantized plateaus. The ballistic one-dimensional subbands are tuned by changing the lateral confinement and the Fermi energy of the holes in the QPC. We demonstrate that the positions of the plateaus (in gate voltage), the source-drain data, and the negative magnetoresistance data can be understood in a simple model that takes into account the variation, with gate bias, of the hole density and the width of the QPC conducting channel.
Polarization-selective resonant photonic crystal photodetector
Authors: Yang Jin-Kyu , Seo Min-Kyo , Hwang In-Kag , Kim Sung-Bock , Lee Yong-Hee
Published: November 2008

Resonance-assisted photonic crystal (PhC) slab photodetectors are demonstrated by utilizing six 7-nm-thick InGaAsP quantum wells. In order to encourage efficient photon coupling into the slab from the vertical direction, a coupled-dipole-cavity-array PhC structure is employed. Inheriting the characteristics of the dipole mode, this resonant detector is highly polarization selective and shows a 22-nm-wide spectral width. The maximum responsivity of 0.28A∕W, which is >20 times larger than that of the identical detector without the pattern, is observed near 1.56μm.
High order mode oscillation in a terahertz photonic-band-gap multibeam reflex klystron
Authors: Jang Kyu-Ha , Jeon Seok-Gy , Kim Jung-Il , Won Jong-Hyo , So Jin-Kyu , Bak Seung-Ho , Srivastava Anurag , Jung Sun-Shin , Park Gun-Sik
Published: November 2008

TM 330 -like higher order mode was excited in a multibeam reflex klystron oscillator employing a hybrid photonic-band-gap (PBG) cavity using a three-dimensional particle-in-cell simulation. One side of a conventional metal cavity was replaced with a dielectric photonic crystal lattice to form a hybrid PBG resonator that uses lattice band-gap effects resulting in a more uniform field of a higher order mode as well as the exclusion of some conventional-cavity-type modes, thereby reducing mode competition. Simulated reflex klystron in the hybrid PBG cavity produced an output power much higher than could be delivered in a conventional metal cavity.
Enhanced ferroelectric properties of LiNbO3 substituted Na0.5K0.5NbO3 lead-free thin films grown by chemical solution deposition
Authors: Ahn Chang Won , Jeong Euh Duck , Lee Sun Young , Lee Hai Joon , Kang Sun Hee , Kim Ill Won
Published: November 2008

We have fabricated environmental friendly lead-free ferroelectric Na0.5K0.5NbO3 (NKN) and 0.95Na0.5K0.5NbO3–0.05LiNbO3 (0.95NKN-0.05LN) thin films by chemical solution deposition using metal-organic compounds, and studied the effects of LN substitution through the dielectric and ferroelectric properties. The small amount of LN substitution for NKN thin film led to a marked improvement in leakage current properties at the high electric field region. Furthermore, the 0.95NKN-0.05LN thin film (350nm) displayed clear ferroelectricity with well saturated P-E hysteresis loop with 2Pr and 2Ec values of 19.5μC∕cm2 and 91kV∕cm, respectively. The 0.95NKN-0.05LN films will be interesting for applications in lead-free ferroelectric and piezoelectric devices.
Enhanced fluorescence from Eu3+ in low-loss silica glass-ceramic waveguides with high SnO2 content
Authors: Bhaktha S. N. B. , Beclin F. , Bouazaoui M. , Capoen B. , Chiasera A. , Ferrari M. , Kinowski C. , Righini G. C. , Robbe O. , Turrell S.
Published: November 2008

We report on the sol-gel fabrication and characterization of (100−x)SiO2–xSnO2 (x=8, 16, and 25mol%) glass-ceramic waveguides doped with 1mol% Eu3+. A suitable top-down thermal process led to the formation of SnO2 nanocrystals ∼4nm embedding Eu3+ ions. The excitation spectra evidence the role of interband electronic transition of SnO2 nanocrystals on the luminescence of Eu3+. Monitoring the D05→F27 Eu3+ emission, we observe about 15 times increase in the intensity of SnO2 absorption band, moving from x=8to25mol%. These waveguides also exhibit low losses, making them quite promising for development of high-gain integrated optical amplifiers.