bluuebunny/crossref_metadata_2025 huggingface dataset:
Triplet annihilation exceeding spin statistical limit in highly efficient fluorescent organic light-emitting diodes
Authors: Kondakov D. Y. , Pawlik T. D. , Hatwar T. K. , Spindler J. P.
Published: December 2009

We have demonstrated that the exemplary red fluorescent organic light-emitting diodes (OLEDs) gain as much as half of their electroluminescence from annihilation of triplet states generated by recombining charge carriers. The magnitude of triplet-triplet annihilation (TTA) contribution in combination with the remarkably high total efficiencies [>11% external quantum efficiency (EQE)] indicates that the absolute amount of electroluminescence attributable to TTA substantially exceeds the limit imposed by spin statistics, which was independently confirmed by studying magnetic field effects on delayed luminescence. We determined the value of 1.3 for the ratio of the rate constants of singlet and triplet channels of annihilation, which is indeed substantially higher than the value of 0.33 expected for a purely statistical annihilation process. It is, however, in an excellent quantitative agreement with the extent of the experimental contribution of delayed luminescence to steady-state electroluminescence. The nonstatistical branching ratio of the two annihilation channels is attributed to the favorable relationship between the energies of the excited singlet and triplet states of rubrene—emissive layer host. We surmise that, with the appropriate emissive layer materials, the fluorescent OLED devices are capable of using a considerably larger fraction of triplet states than was previously believed. In principle, the upper limit for the singlet excited state yield in the TTA process is 0.5, which makes the maximum internal quantum efficiency of fluorescent OLEDs to be 25%+0.5×75%=62.5%. The estimates of maximum EQE of the fluorescent OLEDs should be revised to at least 0.2×62.5%=12.5% and, likely, even higher to account for optical outcoupling exceeding 0.2.
Canonical and microcanonical analysis of nongrafted homopolymer adsorption by an attractive substrate
Authors: Wang Lei , Chen Tao , Lin Xiangsong , Liu Yuan , Liang Haojun
Published: December 2009

Using the off-lattice Monte Carlo simulation and replica-exchange method, we studied the behavior of nongrafted homopolymer adsorption by an attractive substrate from both the canonical and the microcanonical views. An adsorption transition is identified from the peak in canonical specific heat and compared with the conventional polymer adsorption with one end anchored on the surface of the substrate. Judging from the typical “backbending effect” and the negative specific heat in microcanonical ensemble, the transition is first-order-like when adsorption is relatively strong. However, it becomes second-order-like when the strength of adsorption becomes weak enough. Further study reveals that for a chain consisting of a limited number of monomers, the type of this transition becoming either first- or second-order-like depends not only on the interplay between monomer-monomer and monomer-substrate interaction, but also on the width of the gap in which it is confined.
Phase equilibria in polymer blend thin films: A Hamiltonian approach
Authors: Souche M. , Clarke N.
Published: December 2009

We propose a Hamiltonian formulation of the Flory–Huggins–de Gennes theory describing a polymer blend thin film. We then focus on the case of 50:50 polymer blends confined between antisymmetric walls. The different phases of the system and the transitions between them, including finite-size effects, are systematically studied through their relation with the geometry of the Hamiltonian flow in phase space. This method provides an easy and efficient way, with strong graphical insight, to infer the qualitative physical behavior of polymer blend thin films.
Strong upconversion luminescence properties of Yb3+ and Er3+ codoped Bi4Ti3O12 ferroelectric thin films
Authors: Gao Feng , Wu Guangheng , Zhou Hong , Bao Dinghua
Published: December 2009

Strong upconversion green luminescence was observed in Er3+ and Yb3+ codoped Bi4Ti3O12 ferroelectric thin films. The thin films were prepared on fused silica and Pt/TiO2/SiO2/Si substrates by chemical solution deposition method. There are two strong green emission bands centered at 524 and 545 nm and a weak red emission band centered at 667 nm in the upconversion luminescence spectra pumped by 980 nm at room temperature. They correspond to the radiative relaxation of Er3+ from H211/2, S43/2, and F49/2 levels to the ground level I415/2, respectively. Bi3.65Yb0.3Er0.05Ti3O12 thin films exhibit higher green emission intensity by a factor of about 30 compared with Bi3.95Er0.05Ti3O12 thin films. The upconversion emission mechanism of the thin films has been discussed. In addition, Bi3.65Yb0.3Er0.05Ti3O12 ferroelectric thin films on Pt/TiO2/SiO2/Si substrates also show well-defined hysteresis loops with a remnant polarization (2Pr) of 28.2 μC/cm2. This study opens the possibility of constructing new integrated photoluminescent ferroelectric thin film devices.
High-performance negative differential resistance behavior in fullerenes encapsulated double-walled carbon nanotubes
Authors: Li Y. F. , Kaneko T. , Hatakeyama R.
Published: December 2009

The authors report negative differential resistance (NDR) characteristics observed in nanodevices constructed using three types of fullerenes (C60, C70, and C84) encapsulated metallic double-walled carbon nanotubes. The NDR behavior persists from room temperature (300 K) to lower temperatures, and a significantly high on-off peak-to-valley current ratio is observed for many of the devices examined. The fullerene species exerts a strong influence on the peak voltage of the NDR, which exhibits a linear decrease with increasing fullerene size. The observed current-voltage curves are highly reproducible during measurements, and fully reversible upon change in the bias sweep direction. In addition, the peak current of the NDR is found to increase significantly under light illumination and is recoverable in the absence of light, which indicates potential for applications such as logic optoelectronic devices.
High energy x-ray diffraction/x-ray fluorescence spectroscopy for high-throughput analysis of composition spread thin films
Authors: Gregoire John M. , Dale Darren , Kazimirov Alexander , DiSalvo Francis J. , van Dover R. Bruce
Published: December 2009

High-throughput crystallography is an important tool in materials research, particularly for the rapid assessment of structure-property relationships. We present a technique for simultaneous acquisition of diffraction images and fluorescence spectra on a continuous composition spread thin film using a 60 keV x-ray source. Subsequent noninteractive data processing provides maps of the diffraction profiles, thin film fiber texture, and composition. Even for highly textured films, our diffraction technique provides detection of diffraction from each family of Bragg reflections, which affords direct comparison of the measured profiles with powder patterns of known phases. These techniques are important for high throughput combinatorial studies as they provide structure and composition maps which may be correlated with performance trends within an inorganic library.
A versatile thermoelectric temperature controller with 10 mK reproducibility and 100 mK absolute accuracy
Authors: Libbrecht K. G. , Libbrecht A. W.
Published: December 2009

We describe a general-purpose thermoelectric temperature controller with 1 mK stability, 10 mK reproducibility, and 100 mK absolute accuracy near room temperature. The controller design is relatively simple and could be readily modified for use in different experimental circumstances. We also describe a time-domain numerical model that allows one to characterize the stability and transient behavior of the system being controlled, even in the presence of elements with highly nonlinear responses.
Simple and efficient scanning tunneling luminescence detection at low-temperature
Authors: Keizer J. G. , Garleff J. K. , Koenraad P. M.
Published: December 2009

We have designed and built an optical system to collect light that is generated in the tunneling region of a low-temperature scanning tunneling microscope. The optical system consists of an in situ lens placed approximately 1.5 cm from the tunneling region and an ex situ optical lens system to analyze the emitted light, for instance, by directing the light into a spectrometer. As a demonstration, we measured tip induced photoluminescence spectra of a gold surface. Furthermore, we demonstrate that we can simultaneously record scanning tunneling microscope induced luminescence and topography of the surface both with atomic resolution.
Theoretical characteristics of the bound states of M-X complexes (M=Cu, Ag, and Au, and X=He, Ne, and Ar)
Authors: Tong Xiao-Fei , Yang Chuan-Lu , An Yi-Peng , Wang Mei-Shan , Ma Xiao-Guang , Wang De-Hua
Published: December 2009

The potential energy curves (PECs) of the bound states of M-X (M=Cu, Ag, and Au and X=He, Ne, and Ar) complexes have been calculated using the coupled cluster singles and doubles method with perturbative treatment of triple excitations. Large basis sets and bond functions, as well as the basis set superposition errors, are employed to obtain accurate PECs. The analytical potential energy functions (APEFs) are fitted using the PECs. The vibrational energy levels and the spectroscopic parameters for the complexes are determined using our APEFs and compared to the theoretical works available at present. We also find that the PECs are bound with similar van der Waals interactions, which implies that He, Ne, and Ar may be used for buffer-gas cooling; and Cu, Ag, and Au may be trapped with a similar method because Cu and Ag have been experimentally trapped with He buffer-gas cooling.
A theoretical study of the low-lying excited states of thieno[3,4-b]pyrazine
Authors: Gómez-Jiménez María D. , Pou-Amérigo Rosendo , Ortí Enrique
Published: December 2009

The low-lying electronic excited states of thieno[3,4-b]pyrazine have been studied using the multiconfigurational second-order perturbation CASPT2 theory with extended atomic natural orbital basis sets. The CASPT2 results allow for a full interpretation of the electronic absorption and emission spectra and provide valuable information for the rationalization of the experimental data. The nature, position, and intensity of the spectral bands have been analyzed in detail. A preliminary comparative study of the ground-state geometry of thieno[3,4-b]pyrazine has been performed at the coupled cluster single and doubles and density functional theory levels using a variety of correlation-consistent basis sets. Thieno[3,4-b]pyrazine exhibits a polyene-like structure in the ground state due to the bond localization in the pyrazine moiety. An aromatization of the pyrazine unit is predicted for the lowest-energy electronic excited states.
Quantum Monte Carlo study of large spin-polarized tritium clusters
Authors: Bešlić I. , Markić L. Vranješ , Boronat J.
Published: December 2009

This work expands recent investigations in the field of spin-polarized tritium (T↓) clusters. We report the results for the ground-state energy and structural properties of large T↓ clusters consisting of up to 320 atoms. All calculations have been performed with variational and diffusion Monte Carlo methods, using an accurate ab initio interatomic potential. Our results for N≤40 are in good agreement with results obtained by other groups. Using a liquid-drop expression for the energy per particle, we estimate the liquid equilibrium density, which is in good agreement with our recently obtained results for bulk T↓. In addition, the calculations of the energy for large clusters have allowed for an estimation of the surface tension. From the mean-square radius of the drop, determined using unbiased estimators, we determine the dependence of the radii on the size of the cluster and extract the unit radius of the T↓ liquid.
Hierarchical assembly of light-emitting polymer nanofibers in helical morphologies
Authors: Pagliara Stefano , Camposeo Andrea , Cingolani Roberto , Pisignano Dario
Published: December 2009

Single electrospun nanofibers of light-emitting conjugated polymers hierarchically assemble at nano- to macroscopic lengthscales in various helical morphologies. At nanoscopic lengthscales, molecular chains follow the microscopic assembly, prevalently aligning along the fiber dynamic axis, as demonstrated by polarized photoluminescence spectroscopy. The role of molecular weight in the resulting assembling and optical properties is highlighted and discussed. Nanofibers based on the heaviest polymer exhibit the most stretched helical geometries and the highest suppression of the excitonic energy migration, resulting in the most blue-shifted photoluminescence with respect to thin films.
Spectroscopic evidence for limited carrier hopping interaction in amorphous ZnO thin film
Authors: Cho Deok-Yong , Kim Jeong Hwan , Na Kwang Duk , Song Jaewon , Hwang Cheol Seong , Park Byeong-Gyu , Kim Jae-Young , Min Chul-Hee , Oh Se-Jung
Published: December 2009

The electronic structure of amorphous ZnO film (a-ZnO) was examined by O K- and Zn L3-edge x-ray absorption spectroscopy and valence band photoemission spectroscopy. Comparative studies of a-ZnO and a wurtzite ZnO (w-ZnO) revealed a decrease in Zn 4s-O 2p hybridization strength and the localization of Zn 4s band as a consequence of local structural disorder, indicating limited electron hopping interactions in a-ZnO. The 0.1 eV higher Fermi-level of a-ZnO compared to w-ZnO suggests that the electrical properties of a-ZnO are different from those in w-ZnO due to structural disorder, even in the absence of impurities or grain boundaries.
High subthreshold field-emission current due to hydrogen adsorption in single-walled carbon nanotubes: A first-principles study
Authors: Yaghoobi Parham , Alam Md. Kawsar , Walus Konrad , Nojeh Alireza
Published: December 2009

We investigate the effect of hydrogen adsorption on field-emission current from a single-walled carbon nanotube using first-principles calculations. The results show a new emission regime at field values around the field-emission threshold of bare nanotubes, with emission currents comparable to those of the high-field regime. This current enhancement can be explained with the surface dipole created as a result of the difference in electronegativity between carbon and hydrogen that contributes to electron extraction from the nanotube.
Formulation and numerical analysis of vibrationally coupled recombination of monatomic molecules using Boltzmann kinetic equation
Authors: Yano Ryosuke , Suzuki Kojiro , Kuroda Hisayasu
Published: December 2009

Monatomic molecular recombination is formulated using the Boltzmann kinetic equation. The recombination is coupled to the diatomic molecular vibrational states using the truncated harmonic oscillator model. The obtained recombination rate is equal to the modified Arrhenius rate, which is independent of the dissociation (activation) energy, when the temperature defined in the gain term on the basis of the intermediate’s collisions is much lower than that of the dissociation. The formulated model is numerically analyzed by solving the hypersonic shock layer problem with dissociation-recombination reactions. The obtained numerical results indicate that dissociated monatomic molecules behind a shock wave recombine into diatomic molecules owing to the decrease in the temperature near the wall.
Direct numerical simulation of canonical shock/turbulence interaction
Authors: Larsson Johan , Lele Sanjiva K.
Published: December 2009

A set of direct numerical simulations of isotropic turbulence passing through a nominally normal shock wave is presented. Upstream of the shock, the microscale Reynolds number is 40, the mean Mach number is 1.3–6.0, and the turbulence Mach number is 0.16–0.38. It is shown that the Kolmogorov scale decreases during the shock interaction, which implies that the grid resolution needed to resolve the viscous dissipation is finer than that used in previous studies. This leads to some qualitative differences with previous work, e.g., a rapid increase in the streamwise vorticity variance behind the shock and large anisotropy of the postshock Reynolds stresses. The instantaneous structure of the shock/turbulence interaction is examined using averages conditioned on the instantaneous shock strength. For locally strong compressions, the flow is characterized by overcompression, followed by an expansion. At points where the shock is locally weak, the profiles differ qualitatively depending on the strength of the incoming turbulence relative to the strength of the shock, as measured by the turbulence and mean Mach numbers, respectively. In the wrinkled shock regime, these profiles are discontinuous and the shock has a simple topology. In the broken shock regime, the weak interaction profiles are smooth without any discontinuity.
Molecular beam epitaxy-grown Bi4Te3 nanowires
Authors: Wang G. , Lok S. K. , Wong G. K. L. , Sou I. K.
Published: December 2009

With Au nanoparticles as the catalyst, the formation of Bi4Te3 nanowires was achieved at an optimized substrate temperature of around 330 °C. We found two growth mechanisms for the nanowires: a self-assembled growth mode through islands as the seed and a vapor-solid-solid growth mode through the assistance of Au catalyst nanoparticles, the decisive factor for which was identified as the density of the Au nanoparticles.
Dynamic contact angle effects onto the maximum drop impact spreading on solid surfaces
Authors: Vadillo D. C. , Soucemarianadin A. , Delattre C. , Roux D. C. D.
Published: December 2009

This paper reports experimental investigations of drop impacts onto chemically treated surfaces with wettability from 5° to 160°. To follow in time the drop spreading, a high speed video camera was used, and it allows us to determine precisely the expansion of the drop and the profile of the free surface at the contact line. By changing the impact velocity, between less than 0.5 and 5 m/s, and the viscosity, from 1 to 100 mPa s, at constant surface tension, a broad range of Reynolds and Weber numbers is explored. This paper is divided into two parts. In the first part, the experimental drop evolution during spreading is directly reported and compared with previous works. Secondly, the emphasis is on the importance of the apparent dynamic contact angle for the prediction of the maximum spreading diameter. This achievement is manifested at low Reynolds numbers at which the matching between the experiment and the model is improved greatly.
Comprehensive physical mechanism of two-headed biomotor myosin V
Authors: Xu Yuzhi , Wang Zhisong
Published: December 2009

Two-headed biomotor myosin V autonomously coordinates its two identical heads in fuel consumption and mechanical stepping, so that the dimerized motor as a whole gains the capability of processive, unidirectional movement along cytoskeletal filament. How the dimer-level functions like sustained direction rectification and autonomous coordination emerge out of physical principles poses an outstanding question pertinent to motor protein biology as well as the nascent field of bioinspired nanomotors. Here the comprehensive physical mechanism for myosin V motor is identified by a dimer-level free-energy analysis that is methodologically calibrated against experimental data. A hallmark of the identified mechanism is a mechanically mediated symmetry breaking that occurs at the dimer level and prevails against ubiquitous thermal fluctuations. Another character is the onset of substantial free-energy gaps between major dimer-track binding configurations. The symmetry breaking is the basis for myosin V’s directional rectification, and the energy gaps facilitate autonomous head-head coordination. The mechanism explains the experimental finding that myosin V makes ATP-independent consecutive steps under high opposing loads but not under pushing loads. Interestingly, myosin V and another major biomotor kinesin 1 are found to share essentially the same core mechanism but for distinctly different working regimes.
Lymphotactin: How a protein can adopt two folds
Authors: Camilloni Carlo , Sutto Ludovico
Published: December 2009

Metamorphic proteins such as lymphotactin are a notable exception of the empirical principle that structured natural proteins possess a unique three-dimensional structure. In particular, the human chemokine lymphotactin protein exists in two distinct conformations (one monomeric and one dimeric) under physiological conditions. In this work, we use a Cα Go¯ model to show how this very peculiar behavior can be reproduced. From the study of the thermodynamics and of the kinetics, we characterize the interconversion mechanism. In particular, this takes place through the docking of the two chains living in a third monomeric, partially unfolded, state which shows a residual structure involving a set of local contacts common to the two native conformations. The main feature of two fold proteins appears to be the sharing of a common set of local contacts between the two distinct folds as confirmed by the study of two designed two fold proteins. Metamorphic proteins may be more common than expected.
Hydroelectrical energy conversion in narrow confinements in the presence of transverse magnetic fields with electrokinetic effects
Authors: Munshi Farooque , Chakraborty Suman
Published: December 2009

In this work, we investigate the combined influences of externally applied axial pressure gradients and transverse magnetic fields on hydroelectrical energy conversion mechanisms in narrow fluidic confinements. This energy conversion is achieved through an exploitation of the electromagnetohydrodynamic effects as a result of electrical double layer formation and the consequent interfacial phenomena. Although no electrical field is externally applied, a reverse electrokinetic transport may be induced on account of the streaming potential field which is spontaneously developed due to the preferential migration of ionic charges with the fluid flow, as modulated by the pressure and the magnetic fields. We explore ranges of surface potentials beyond the traditional Debye–Hückel limits by employing nonlinear forms of the Poisson–Boltzmann equation for electrical potential distribution, yet adhering to a semianalytical formalism. Our studies quantitatively depict the explicit implications of the external magnetic field on the overall energy conversion efficiency through the pertinent nondimensional parameters. We also investigate the cases of low surface potentials and thin electrical double layers as special limits of the generalized considerations addressed in this work.
Oxidation states of graphene: Insights from computational spectroscopy
Authors: Zhang Wenhua , Carravetta Vincenzo , Li Zhenyu , Luo Yi , Yang Jinlong
Published: December 2009

When it is oxidized, graphite can be easily exfoliated forming graphene oxide (GO). GO is a critical intermediate for massive production of graphene, and it is also an important material with various application potentials. With many different oxidation species randomly distributed on the basal plane, GO has a complicated nonstoichiometric atomic structure that is still not well understood in spite of intensive studies involving many experimental techniques. Controversies often exist in experimental data interpretation. We report here a first principles study on binding energy of carbon 1s orbital in GO. The calculated results can be well used to interpret experimental x-ray photoelectron spectroscopy (XPS) data and provide a unified spectral assignment. Based on the first principles understanding of XPS, a GO structure model containing new oxidation species epoxy pair and epoxy-hydroxy pair is proposed. Our results demonstrate that first principles computational spectroscopy provides a powerful means to investigate GO structure.
Nonlinear particle behavior during cross-type optical particle separation
Authors: Kim Sang Bok , Lee Kyung Heon , Sung Hyung Jin , Kim Sang Soo
Published: December 2009

The effects of varying the ratio of the optical force to the viscous drag force, termed S, on cross-type optical particle separation were investigated experimentally to test previous theoretical predictions. The experiments were performed for various flow velocities, powers of the laser beam, and radii of the laser beam waist and the particles. The behaviors of the particles during optical separation were examined by measuring the retention distances and analyzing the particle trajectories. For small values of S, the particles move with constant velocity in the flow direction and the retention distance increases linearly with S. However, the particles accelerate and decelerate within the laser beam and the retention distance increases nonlinearly with S when S increases further.
The role of Zr and B in room temperature magnetic entropy change of FeZrB amorphous alloys
Authors: Wang Yanyan , Bi Xiaofang
Published: December 2009

Effect of Zr and B on magnetocaloric effect for Fe90−xZr10Bx (x:3∼9) and Fe93−xZr7Bx (x:0∼13) amorphous alloys is presented. A clear dependence of peak magnetic entropy change (|ΔSmpk|) on (Zr+B) total contents rather than respective contents is observed and found to be correlated with average magnetic moment per Fe atom. Temperature of |ΔSmpk| corresponding to Curie temperature (Tc) is dependent on B contents, which is discussed in terms of exchange coupling. These findings exhibit in general the importance of Zr and B in seeking for an optimal |ΔSmpk| and meanwhile tunable Tc in Fe-based amorphous alloys.
Performance of hybrid entanglement photon pair source for quantum key distribution
Authors: Fujiwara M. , Toyoshima M. , Sasaki M. , Yoshino K. , Nambu Y. , Tomita A.
Published: December 2009

We report on the experimental demonstration of a source of hybrid entanglement pairs between two different degrees of freedom, a 1550 nm time-bin qubit and an 810 nm polarization qubit. The polarization qubit at 810 nm is transformed by an asymmetric Mach–Zehnder interferometer consisted of a Glan laser prism and a polarization-maintaining fiber. We obtained visibilities of 95.8% and 88% with tolerance ±0.2% and ±1% along Z-Z and X-X axes on the Poincare sphere, respectively, with a coincidence count rate of more than 800 c/s after entanglement format transformation. These values are well above the threshold of 70.7% needed to violate a Bell inequality and allow distilling a secure key in the quantum key distribution.
Low-temperature ballistic transport in nanoscale epitaxial graphene cross junctions
Authors: Weingart S. , Bock C. , Kunze U. , Speck F. , Seyller Th. , Ley L.
Published: December 2009

We report on the observation of inertial-ballistic transport in nanoscale cross junctions fabricated from epitaxial graphene grown on SiC(0001). Ballistic transport is indicated by a negative bend resistance of R12,43≈−170 Ω, which is measured in a nonlocal, four-terminal configuration at 4.2 Κ and which vanishes as the temperature is increased above 80 K.
Direct measurements of the penetration depth in a superconducting film using magnetic force microscopy
Authors: Nazaretski E. , Thibodaux J. P. , Vekhter I. , Civale L. , Thompson J. D. , Movshovich R.
Published: December 2009

We report the local measurements of the magnetic penetration depth λ in a superconducting Nb film using magnetic force microscopy (MFM). We developed a method for quantitative extraction of the penetration depth from single-parameter simultaneous fits to the lateral and height profiles of the MFM signal, and demonstrate that the obtained value is in excellent agreement with that obtained from the bulk magnetization measurements.
Polar solvation dynamics of coumarin 153 by ultrafast time-resolved fluorescence
Authors: Eom Intae , Joo Taiha
Published: December 2009

Polar solvation dynamics of coumarin 153 in acetonitrile, methanol, and butanol are investigated by dynamic Stokes shift function, S(t). In small protic solvents, it is known that an initial ultrafast component below 50 fs constitutes more than half of the total solvation process. We use fluorescence up-conversion technique via two-photon absorption process, which can provide 40 fs time resolution for the whole emission wavelength range. Moreover, time-resolved fluorescence spectra are recorded directly without the spectral reconstruction. We observe a temporal oscillation in frequency of whole emission spectrum in the solvation curve. In the obtained S(t), initial solvation time scale is 120 fs, invariant to solvents used in this experiment, although its amplitude varies in different solvents.
Turbulent flow and organized motions over a two-dimensional rough wall
Authors: Vesely Lukas , Haigermoser Christian , Greco Davide , Onorato Michele
Published: December 2009

Particle image velocimetry measurements at relatively low Reynolds number in a turbulent boundary layer over a two-dimensional roughened surface are presented and compared to those for a smooth wall. The main goal of the study was to give a contribution to the understanding of the behavior of the turbulent organized motions, when the influence of the wall roughness on the turbulent structures may be expected to be noticeable, i.e., for relatively high roughness and relatively low Reynolds number. In addition, the flow behavior with respect to the wall similarity hypothesis in the case of moderately large values of the roughness height k and moderately low Reynolds number was tested. The behavior of the turbulent coherent motions appears to be similar for the two flows in the outer layer. Quantitative differences, observed mainly in the roughness sublayer, are enlightened comparing spatial velocity correlations and vortex population density and strength in the wall-normal-streamwise plane and in planes parallel to the wall. Mean flows expressed in velocity defect law, inner scaled streamwise Reynolds normal stress, and Reynolds shear stresses profiles show excellent agreement in the outer layer between the rough wall and the smooth surface. Wall normal Reynolds normal stress profiles, instead, show some small discrepancy, but within the measurement uncertainty.
Size-dependent hydrophobic to hydrophilic transition for nanoparticles: A molecular dynamics study
Authors: Chiu Chi-cheng , Moore Preston B. , Shinoda Wataru , Nielsen Steven O.
Published: December 2009

The physical properties of nanoscale materials often vary with their size, unlike the corresponding bulk material properties, which can only be changed by modifying the material composition. In particular, it is believed that hydration phenomena are length scale dependent. The manifestation of hydrophobicity over multiple length scales plays a crucial role in self-assembly processes such as protein folding and colloidal stability. In the case of particles composed of a bulk hydrophobic material, it is well known that the free energy of hydration monotonically increases with particle size. However, the size-dependent free energy of hydration for particles composed of a bulk hydrophilic material has not been studied. Here we show that the free energy of hydration is not a monotonic function of particle size, but rather, changes sign from positive to negative as the particle size increases. In other words, the particle is hydrophobic at small size and hydrophilic at large size. This behavior arises from a purely geometrical effect caused by the curvature of the particle-water interface. We explore the consequences of this phenomenon on colloidal stability and find that it dictates the shape of colloidal aggregates.
Design of one-dimensional optical pulse-shaping filters by time-domain topology optimization
Authors: Yang Lirong , Lavrinenko Andrei V. , Hvam Jørn M. , Sigmund Ole
Published: December 2009

Time-domain topology optimization is used here to design optical pulse-shaping filters in Si/SiO2 thin-film systems. A novel envelope objective function as well as explicit penalization are used to adapt the optimization method to this unique class of design problems.
Stress-enhancement in free-standing Si pillars through nonequilibrium dehydrogenation in SiN:H stress-liners by ultraviolet light irradiation
Authors: Tanaka Takanori , Sadoh Taizoh , Kurosawa Masashi , Tanaka Masanori , Yamaguchi Masanori , Suzuki Shinji , Kitamura Tokuhide , Miyao Masanobu
Published: December 2009

Tensile-strained Si pillars are desired to achieve three-dimensional (3D) transistors with high speed. Effects of ultraviolet (UV) light irradiation on tensile strains in Si pillars covered with SiN:H stress-liners are investigated as a function of the wavelength (172–436 nm). Tensile-stress enhancement is found at specific wavelengths (200–330 nm) under low-temperature heating (400 °C), where dehydrogenation in SiN:H is clearly detected by infrared absorption measurements. On the other hand, equilibrium dehydrogenation by high-temperature heating (>700 °C) without UV-irradiation does not cause tensile-stress enhancement. This nonequilibrium dehydrogenation at low temperatures opens up possibility of 3D transistors with high carrier mobility.
A near infrared organic photodiode with gain at low bias voltage
Authors: Campbell I. H. , Crone B. K.
Published: December 2009

We demonstrate an organic photodiode with near infrared optical response out to about 1100 nm with a gain of ∼10 at 1000 nm under 5 V reverse bias. The diodes employ a soluble naphthalocyanine with a peak absorption coefficient of ∼105 cm−1 at 1000 nm. In contrast to most organic photodiodes, no exciton dissociating material is used. At zero bias, the diodes are inefficient with an external quantum efficiency of ∼10−2. In reverse bias, large gain occurs and is linear with bias voltage above 4 V. The observed gain is consistent with a photoconductive gain mechanism.
Polychromatic beam splitting by fractional stimulated Raman adiabatic passage
Authors: Dreisow F. , Ornigotti M. , Szameit A. , Heinrich M. , Keil R. , Nolte S. , Tünnermann A. , Longhi S.
Published: December 2009

We propose and demonstrate a femtosecond laser inscribed micro-optical device for broadband beam splitting based on the interruption of the stimulated Raman adiabatic passage. For the spectral characterization waveguide fluorescence microscopy is applied by exciting nonbridging oxygen holes and exciton defects at several wavelengths. Additionally, spectrally resolved nearfield imaging shows octave spanning 50:50 beam splitting.
Optimization of back reflector for high efficiency hydrogenated nanocrystalline silicon solar cells
Authors: Yue Guozhen , Sivec Laura , Owens Jessica M. , Yan Baojie , Yang Jeffrey , Guha Subhendu
Published: December 2009

We have studied the effect of texture in Ag/ZnO back reflectors (BRs) on the performance of hydrogenated nanocrystalline silicon (nc-Si:H) solar cells. While a larger texture provides superior light trapping, it also deteriorates the nc-Si:H quality. We have used total and diffused reflection and atomic force microscopy to evaluate the BR texture. A BR with textured Ag and thin ZnO layers has been found to give the best cell performance. Using the optimized BR, we have achieved an initial active-area efficiency of 10.2% in a nc-Si:H single-junction cell and a stable total-area efficiency of 12.5% in a hydrogenated amorphous silicon/nc-Si:H/nc-Si:H triple-junction cell.
Electrical and optical properties of p-type InGaN
Authors: Pantha B. N. , Sedhain A. , Li J. , Lin J. Y. , Jiang H. X.
Published: December 2009

Mg-doped InxGa1−xN alloys were grown by metal organic chemical vapor deposition on semi-insulating c-GaN/sapphire templates. Hall effect measurements showed that Mg-doped InxGa1−xN epilayers are p-type for x up to 0.35. Mg-acceptor levels (EA) as a function of x, (x up to 0.35), were experimentally evaluated from the temperature dependent hole concentration. The observed EA in Mg-doped In0.35Ga0.65N alloys was about 43 meV, which is roughly four times smaller than that in Mg doped GaN. A room temperature resistivity as low as 0.4 Ω cm (with a hole concentration ∼5×1018 cm−3 and hole mobility ∼3 cm2/V s) was obtained in Mg-doped In0.22Ga0.78N. It was observed that the photoluminescence (PL) intensity associated with the Mg related emission line decreases exponentially with x. The Mg energy levels in InGaN alloys obtained from PL measurements are consistent with those obtained from Hall-effect measurements.
Thermally driven molecular linear motors: A molecular dynamics study
Authors: Zambrano H. A. , Walther J. H. , Jaffe R. L.
Published: December 2009

We conduct molecular dynamics simulations of a molecular linear motor consisting of coaxial carbon nanotubes with a long outer carbon nanotube confining and guiding the motion of an inner short, capsulelike nanotube. The simulations indicate that the motion of the capsule can be controlled by thermophoretic forces induced by thermal gradients. The simulations find large terminal velocities of 100–400 nm/ns for imposed thermal gradients in the range of 1–3 K/nm. Moreover, the results indicate that the thermophoretic force is velocity dependent and its magnitude decreases for increasing velocity.
Large enhancement of the vibration-rotation coupling of the ν1 and ν3 states of silane in helium droplets
Authors: Skvortsov Dmitry , Marinov Daniil , Sartakov Boris G. , Vilesov Andrey F.
Published: December 2009

Silane molecules have been embedded in helium droplets and studied via infrared laser depletion spectroscopy in the range of 2190 cm−1. We found that the R1 and Q2 lines of the ν3 band have satellites shifted by about 2.3 cm−1 towards low frequency and having similar intensity to the main lines. We assigned this perturbation in the spectrum to the coupling of the J=2 levels in ν3 and close lying ν1 vibration states. The strength of the coupling is a factor of about 50 larger in He droplets than in free molecules and have the same selection rules implied by the tetrahedral symmetry of SiH4 molecules. The perturbation, which cannot be explained within the framework of a Hamiltonian of free molecules, is evidence of strong coupling of the molecule with some He excitations in the molecular vicinity.
Design of versatile biochemical switches that respond to amplitude, duration, and spatial cues
Authors: Lipshtat Azi , Jayaraman Gomathi , He John Cijiang , Iyengar Ravi
Published: December 2009

Cells often mount ultrasensitive (switch-like) responses to stimuli. The design principles underlying many switches are not known. We computationally studied the switching behavior of GTPases, and found that this first-order kinetic system can show ultrasensitivity. Analytical solutions indicate that ultrasensitive first-order reactions can yield switches that respond to signal amplitude or duration. The three-component GTPase system is analogous to the physical fermion gas. This analogy allows for an analytical understanding of the functional capabilities of first-order ultrasensitive systems. Experiments show amplitude- and time-dependent Rap GTPase switching in response to Cannabinoid-1 receptor signal. This first-order switch arises from relative reaction rates and the concentrations ratios of the activator and deactivator of Rap. First-order ultrasensitivity is applicable to many systems where threshold for transition between states is dependent on the duration, amplitude, or location of a distal signal. We conclude that the emergence of ultrasensitivity from coupled first-order reactions provides a versatile mechanism for the design of biochemical switches.
Murine leukemia virus glycosylated Gag (gPr80

gag

) facilitates interferon-sensitive virus release through lipid rafts
Authors: Nitta Takayuki , Kuznetsov Yurii , McPherson Alexander , Fan Hung
Published: December 2009

Murine leukemia viruses encode a unique form of Gag polyprotein, gPr80

gag

or glyco-gag. Translation of this protein is initiated from full-length viral mRNA at an upstream initiation site in the same reading frame as Pr65

gag

, the precursor for internal structural (Gag) proteins. Whereas gPr80

gag

is evolutionarily conserved among gammaretroviruses, its mechanism of action has been unclear, although it facilitates virus production at a late assembly or release step. Here, it is shown that gPr80

gag

facilitates release of Moloney murine leukemia virus (M-MuLV) from cells along an IFN-sensitive pathway. In particular, gPr80

gag

-facilitated release occurs through lipid rafts, because gPr80

gag

-negative M-MuLV has a lower cholesterol content, is less sensitive to inhibition of release by the cholesterol-depleting agent MβCD, and there is less Pr65

gag

associated with detergent-resistant membranes in mutant-infected cells. gPr80

gag

can also facilitate the release of HIV-1-based vector particles from human 293T cells.
Cooperative nanomaterial system to sensitize, target, and treat tumors
Authors: Park Ji-Ho , von Maltzahn Geoffrey , Xu Mary Jue , Fogal Valentina , Kotamraju Venkata Ramana , Ruoslahti Erkki , Bhatia Sangeeta N. , Sailor Michael J.
Published: December 2009

A significant barrier to the clinical translation of systemically administered therapeutic nanoparticles is their tendency to be removed from circulation by the mononuclear phagocyte system. The addition of a targeting ligand that selectively interacts with cancer cells can improve the therapeutic efficacy of nanomaterials, although these systems have met with only limited success. Here, we present a cooperative nanosystem consisting of two discrete nanomaterials. The first component is gold nanorod (NR) “activators” that populate the porous tumor vessels and act as photothermal antennas to specify tumor heating via remote near-infrared laser irradiation. We find that local tumor heating accelerates the recruitment of the second component: a targeted nanoparticle consisting of either magnetic nanoworms (NW) or doxorubicin-loaded liposomes (LP). The targeting species employed in this work is a cyclic nine-amino acid peptide LyP-1 (Cys-Gly-Asn-Lys-Arg-Thr-Arg-Gly-Cys) that binds to the stress-related protein, p32, which we find to be upregulated on the surface of tumor-associated cells upon thermal treatment. Mice containing xenografted MDA-MB-435 tumors that are treated with the combined NR/LyP-1LP therapeutic system display significant reductions in tumor volume compared with individual nanoparticles or untargeted cooperative system.
Composite system mediates two-step DNA uptake into
Helicobacter pylori
Authors: Stingl Kerstin , Müller Stephanie , Scheidgen-Kleyboldt Gerda , Clausen Martin , Maier Berenike
Published: December 2009

The Gram-negative gastric pathogen
Helicobacter pylori
depends on natural transformation for genomic plasticity, which leads to host adaptation and spread of resistances. Here, we show that
H. pylori
takes up covalently labeled fluorescent DNA preferentially at the cell poles and that uptake is dependent on the type IV secretion system ComB. By titration of external pH and detection of accessibility of the fluorophor by protons, we localized imported fluorescent DNA in the periplasm. Single molecule analysis revealed that outer membrane DNA transport occurred at a velocity of 1.3 kbp·s
−1
and that previously imported DNA was reversibly extracted from the bacterium at pulling forces exceeding 23 pN. Thus, transport velocities were 10-fold higher than in
Bacillus subtilis
, and stalling forces were substantially lower. dsDNA stained with the intercalator YOYO-1 was transiently detected in the periplasm in wild-type
H. pylori
but was periplasmatically trapped in a mutant lacking the
B. subtilis
membrane-channel homolog ComEC. We conclude that
H. pylori
uses a two-step DNA uptake mechanism in which ComB transports dsDNA across the outer membrane at low force and poor specificity for DNA structure. Subsequently, Hp-ComEC mediates transport into the cytoplasm, leading to the release of the noncovalently bound DNA dye. Our findings fill the gap to propose a model for composite DNA uptake machineries in competent bacteria, all comprising the conserved ComEC channel for cytoplasmic membrane transport in combination with various transporters for access of external DNA to the cytoplasmic membrane.
Distinct defects in collagen microarchitecture underlie vessel-wall failure in advanced abdominal aneurysms and aneurysms in Marfan syndrome
Authors: Lindeman Jan H. N. , Ashcroft Brian A. , Beenakker Jan-Willem M. , van Es Maarten , Koekkoek Nico B. R. , Prins Frans A. , Tielemans Jarl F. , Abdul-Hussien Hazem , Bank Ruud A. , Oosterkamp Tjerk H.
Published: December 2009

An aneurysm of the aorta is a common pathology characterized by segmental weakening of the artery. Although it is generally accepted that the vessel-wall weakening is caused by an impaired collagen metabolism, a clear association has been demonstrated only for rare syndromes such as the vascular type Ehlers–Danlos syndrome. Here we show that vessel-wall failure in growing aneurysms of patients who have aortic abdominal aneurysm (AAA) or Marfan syndrome is not related to a collagen defect at the molecular level. On the contrary our findings indicate similar (Marfan) or even higher collagen concentrations (AAA) and increased collagen cross-linking in the aneurysms. Using 3D confocal imaging we show that the two conditions are associated with profound defects in collagen microarchitecture. Reconstructions of normal vessel wall show that adventitial collagen fibers are organized in a loose braiding of collagen ribbons. These ribbons encage the vessel, allowing the vessel to dilate easily but preventing overstretching. AAA and aneurysms in Marfan syndrome show dramatically altered collagen architectures with loss of the collagen knitting. Evaluations of the functional characteristics by atomic force microscopy showed that the wall has lost its ability to stretch easily and revealed a second defect: although vascular collagen in normal aortic wall behaves as a coherent network, in AAA and Marfan tissues it does not. As result, mechanical forces loaded on individual fibers are not distributed over the tissue. These studies demonstrate that the mechanical properties of tissue are strongly influenced by collagen microarchitecture and that perturbations in the collagen networks may lead to mechanical failure.
Superatom spectroscopy and the electronic state correlation between elements and isoelectronic molecular counterparts
Authors: Peppernick Samuel J. , Gunaratne K.D. Dasitha , Castleman A.W.
Published: December 2009

Detailed in the present investigation are results pertaining to the photoelectron spectroscopy of negatively charged atomic ions and their isoelectronic molecular counterparts. Experiments utilizing the photoelectron imaging technique are performed on the negative ions of the group 10 noble metal block (i.e. Ni
-
, Pd
-
, and Pt
-
) of the periodic table at a photon energy of 2.33 eV (532 nm). The accessible electronic transitions, term energies, and orbital angular momentum components of the bound electronic states in the atom are then compared with photoelectron images collected for isoelectronic early transition metal heterogeneous diatomic molecules, M-X
-
(M = Ti,Zr,W; X = O or C). A superposition principle connecting the spectroscopy between the atomic and molecular species is observed, wherein the electronic structure of the diatomic is observed to mimic that present in the isoelectronic atom. The molecular ions studied in this work, TiO
-
, ZrO
-
, and WC
-
can then be interpreted as possessing superatomic electronic structures reminiscent of the isoelectronic elements appearing on the periodic table, thereby quantifying the superatom concept.