bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of uncertainties in N2O and NO fluxes from agricultural soil using a hierarchical Bayesian model
Authors: Nishina Kazuya , Akiyama Hiroko , Nishimura Seiichi , Sudo Shigeto , Yagi Kazuyuki
Published: October 2012

Agricultural soil is the major source of nitrous oxide (N2O) and nitric oxide (NO). However, N2O and NO fluxes from the soil show high spatial and temporal variability. Therefore, traditional statistical tools are insufficient for evaluating the strength of the emissions and determining the environmental and management factors affecting these fluxes. To compensate for the inherent variability of N oxide fluxes in situ, we proposed the application of a hierarchical Bayesian (HB) model based on a simple semi‐mechanistic model with a lognormal probability distribution. We applied the HB model to the daily N2O and NO fluxes from an Andosol soil field to which a chemical N fertilizer was applied. In addition, we evaluated the responses of these fluxes to environmental factors and N application. The posterior inference revealed various sensitivities to the soil temperature and water‐filled pore space (WFPS) among the N oxide gas fluxes. The N2O flux showed a higher temperature dependency compared with the NO flux. The estimated optimum WFPS of the NO flux (54.1% with credible interval (CI) 95%, from 47.1% to 79.4%) was lower than that of the N2O flux (75.8% with CI 95%, from 54.1% to 98.3%) in this soil sample. Although control plots without N fertilizer application are usually required to calculate the fertilizer‐induced emission factor (EF), our HB model could estimate EFs and their uncertainties using posterior simulations (for N2O 0.077% with CI 95% high probability density, from 0.056% to 0.191%; for NO 0.875% with CI 95% high probability density, from 0.552% to 2.05%). Our HB model can be easily applied to the observations of the N2O and NO fluxes because it requires only several explanatory variables and can be used to evaluate the flux uncertainties and responses of the nonlinear N oxide fluxes to environmental factors.
Fluid circulation and seepage in lake sediment due to propagating and trapped internal waves
Authors: Olsthoorn Jason , Stastna Marek , Soontiens Nancy
Published: October 2012

It has long been known that surface gravity waves induce significant seepage through the porous layer found at the lake bottom. Away from coastal regions, however, the pressure signature of surface waves at the lake bottom is weak. We consider fully nonlinear internal gravity waves, whose long wavelength and slow motion implies a sustained and strong pressure perturbation even in the deep regions of the lake. We argue that internal waves can induce significant seepage through the sediment layer, in regions where surface gravity waves have negligible impact. The pressure profile at the fluid–porous layer interface is computed from the “exact” Dubreil‐Jacotin‐Long theory, giving a reliable profile even for large waves. This profile is used in conjunction with Darcy's law to compute the seepage within the porous region. We find that the geometric distribution of seepage is strongly controlled by both the ratio of porous media thickness to the horizontal length of the pressure perturbation, and the bottom topography, when it is present. Based on work on the interaction of internal solitary waves with the bottom boundary layer, we develop a model to account for the changes in permeability due to wave‐induced instabilities in the bottom boundary layer and enhanced benthic turbulence. This turbulence acts to unplug the pores near the surface by lifting the detritus that clogs them. The resulting changes in permeability significantly enhance exchange between the free fluid and the porous medium on the downstream side of the wave.
Ganglioside GM3 participates in the TGF-β1-induced epithelial–mesenchymal transition of human lens epithelial cells
Authors: Kim Seok-Jo , Chung Tae-Wook , Choi Hee-Jung , Kwak Choong-Hwan , Song Kwon-Ho , Suh Seok-Jong , Kwon Kyung-Min , Chang Young-Chae , Park Young-Guk , Chang Hyeun Wook , Kim Kyoung-Sook , Kim Cheorl-Ho , Lee Young-Choon
Published: October 2012

TGF-β (transforming growth factor-β)-induced EMT (epithelial–mesenchymal transition) induces the proliferation and migration of the HLE (human lens epithelial) cells. Ganglioside GM3, simple sialic-acid-containing glycosphingolipids on mammalian cell membranes, regulates various pathological phenomena such as insulin resistance and tumour progression. However, the relationship between ganglioside GM3 and TGF-β-induced EMT in the HLE B-3 cells is poorly understood. In the present study we demonstrated that ganglioside GM3 was involved in TGF-β1-induced EMT in HLE B-3 cells. Our results indicated that the expression of ganglioside GM3 and GM3 synthase mRNA were significantly increased in TGF-β1-induced HLE B-3 cells. Reporter gene analysis also demonstrated that transcriptional activation of the GM3 synthase gene was regulated by Sp1 (specificity protein 1) in HLE B-3 cells upon TGF-β1 stimulation. Interestingly, the inhibition of ganglioside GM3 expression by d-PDMP [d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol] and GM3 synthase shRNA (short hairpin RNA) resulted significantly in the suppression of cell migration and EMT-related signalling in HLE B-3 cells stimulated by TGF-β. Furthermore, exogenous treatment of ganglioside GM3 rescued the expression of EMT molecules and cell migration suppressed by the depletion of ganglioside GM3 in TGF-β1-induced HLE B-3 cells. We also found that ganglioside GM3 interacted with TGFβRs (TGF-β receptors) in TGF-β1-induced HLE B-3 cells. Taken together, these results suggest that ganglioside GM3 induced by TGF-β1 regulates EMT by potential interaction with TGFβRs.
Translocation dynamics of freely jointed Lennard-Jones chains into adsorbing pores
Authors: Rasmussen Christopher J. , Vishnyakov Aleksey , Neimark Alexander V.
Published: October 2012

Polymer translocation into adsorbing nanopores is studied by using the Fokker-Planck equation of chain diffusion along the energy landscape calculated with Monte Carlo simulations using the incremental gauge cell method. The free energy profile of a translocating chain was found by combining two independent sub-chains, one free but tethered to a hard wall, and the other tethered inside an adsorbing pore. Translocation dynamics were revealed by application of the Fokker-Planck equation for normal diffusion. Adsorption of polymer chains into nanopores involves a competition of attractive adsorption and repulsive steric hindrance contributions to the free energy. Translocation times fell into two regimes depending on the strength of the adsorbing pore. In addition, we found a non-monotonic dependence of translocation times with increasing adsorption strength, with sharp peak associated with local free energy minima along the translocation coordinate.
Universal vertex-IRF transformation for quantum affine algebras
Authors: Buffenoir E. , Roche Ph. , Terras V.
Published: October 2012

We construct a universal solution of the generalized coboundary equation in the case of quantum affine algebras, which is an extension of our previous work to $U_q(A^{(1)}_r)$Uq(Ar(1)). This universal solution has a simple Gauss decomposition which is constructed using Sevostyanov's characters of twisted quantum Borel algebras. We show that in the evaluation representations it gives a vertex-face transformation between a vertex type solution and a face type solution of the quantum dynamical Yang-Baxter equation. In particular, in the evaluation representation of $U_q(A_1^{(1)})$Uq(A1(1)), it gives Baxter's well-known transformation between the 8-vertex model and the interaction-round-faces (IRF) height model.
Self-consistent phonons revisited. I. The role of thermal versus quantum fluctuations on structural transitions in large Lennard-Jones clusters
Authors: Georgescu Ionuţ , Mandelshtam Vladimir A.
Published: October 2012

The theory of self-consistent phonons (SCP) was originally developed to address the anharmonic effects in condensed matter systems. The method seeks a harmonic, temperature-dependent Hamiltonian that provides the “best fit” for the physical Hamiltonian, the “best fit” being defined as the one that optimizes the Helmholtz free energy at a fixed temperature. The present developments provide a scalable \documentclass[12pt]{minimal}\begin{document}$\mathcal {O}(N)$\end{document}O(N) unified framework that accounts for anharmonic effects in a many-body system, when it is probed by either thermal (ℏ → 0) or quantum fluctuations (T → 0). In these important limits, the solution of the nonlinear SCP equations can be reached in a manner that requires only the multiplication of 3N × 3N matrices, with no need of diagonalization. For short range potentials, such as Lennard-Jones, the Hessian, and other related matrices are highly sparse, so that the scaling of the matrix multiplications can be reduced from \documentclass[12pt]{minimal}\begin{document}$\mathcal {O}(N^{3})$\end{document}O(N3) to \documentclass[12pt]{minimal}\begin{document}$\sim \mathcal {O}(N)$\end{document}∼O(N). We investigate the role of quantum effects by continuously varying the de-Boer quantum delocalization parameter Λ and report the N-Λ (T = 0), and also the classical N-T (Λ = 0) phase diagrams for sizes up to N ∼ 104. Our results demonstrate that the harmonic approximation becomes inadequate already for such weakly quantum systems as neon clusters, or for classical systems much below the melting temperatures.
β-sheet propensity controls the kinetic pathways and morphologies of seeded peptide aggregation
Authors: Morriss-Andrews Alex , Bellesia Giovanni , Shea Joan-Emma
Published: October 2012

The effect of seeds in templating the morphology of peptide aggregates is examined using molecular dynamics simulations and a coarse-grained peptide representation. Varying the nature of the aggregate seed between β-sheet, amorphous, and β-barrel seeds leads to different aggregation pathways and to morphologically different aggregates. Similar effects are seen by varying the β-sheet propensity of the free peptides. For a fibrillar seed and free peptides of high β-sheet propensity, fibrillar growth occurred by means of direct attachment (without structural rearrangement) of free individual peptides and small ordered oligomers onto the seed. For a fibrillar seed and free peptides of low β-sheet propensity, fibrillar growth occurred through a dock-lock mechanism, in which the free peptides first docked onto the seed, and then locked on, extending and aligning to join the fibril. Amorphous seeds absorbed free peptides into themselves indiscriminately, with any fibrillar rearrangement subsequent to this absorption by means of a condensation-ordering transition. Although the mechanisms observed by varying peptide β-sheet propensity are diverse, the initial pathways can always be broken down into the following steps: (i) the free peptides diffuse in the bulk and attach individually to the seed; (ii) the free peptides diffuse and aggregate among themselves; (iii) the free peptide oligomers collide with the seed; and (iv) the free oligomers merge with the seed and rearrange in a manner dependent on the backbone flexibility of both the free and seed peptides. Our simulations indicate that it is possible to sequester peptides from amorphous aggregates into fibrils, and also that aggregate morphology (and thus cytoxicity) can be controlled by introducing seeds of aggregate-compatible peptides with differing β-sheet propensities into the system.
Experimental studies of Debye-like process and structural relaxation in mixtures of 2-ethyl-1-hexanol and 2-ethyl-1-hexyl bromide
Authors: Preuß M. , Gainaru C. , Hecksher T. , Bauer S. , Dyre J. C. , Richert R. , Böhmer R.
Published: October 2012

Binary solutions of 2-ethyl-1-hexanol (2E1H) with 2-ethyl-1-hexyl bromide (2E1Br) are investigated by means of dielectric, shear mechanical, near-infrared, and solvation spectroscopy as well as dielectrically monitored physical aging. For moderately diluted 2E1H the slow Debye-like process, which dominates the dielectric spectra of the neat monohydroxy alcohol, separates significantly from the α-relaxation. For example, the separation in equimolar mixtures amounts to four decades in frequency. This situation of highly resolved processes allows one to demonstrate unambiguously that physical aging is governed by the α-process, but even under these ideal conditions the Debye process remains undetectable in shear mechanical experiments. Furthermore, the solvation experiments show that under constant charge conditions the microscopic polarization fluctuations take place on the time scale of the structural process. The hydrogen-bond populations monitored via near-infrared spectroscopy indicate the presence of a critical alcohol concentration, xc ≈ 0.5–0.6, thereby confirming the dielectric data. In the pure bromide a slow dielectric process of reduced intensity is present in addition to the main relaxation. This is taken as a sign of intermolecular cooperativity probably mediated via halogen bonds.
Modified semi-classical methods for nonlinear quantum oscillations problems
Authors: Moncrief Vincent , Marini Antonella , Maitra Rachel
Published: October 2012

We develop a modified semi-classical approach to the approximate solution of Schrödinger's equation for certain nonlinear quantum oscillations problems. In our approach, at lowest order, the Hamilton-Jacobi equation of the conventional semi-classical formalism is replaced by an inverted-potential-vanishing-energy variant thereof. With suitable smoothness, convexity and coercivity properties imposed on its potential energy function, we prove, using methods drawn from the calculus of variations together with the (Banach space) implicit function theorem, the existence of a global, smooth “fundamental solution” to this equation. Higher order quantum corrections thereto, for both ground and excited states, can then be computed through the integration of associated systems of linear transport equations, derived from Schrödinger's equation, and formal expansions for the corresponding energy eigenvalues obtained therefrom by imposing the natural demand for smoothness on the (successively computed) quantum corrections to the eigenfunctions. For the special case of linear oscillators our expansions naturally truncate, reproducing the well-known exact solutions for the energy eigenfunctions and eigenvalues. As an explicit application of our methods to computable nonlinear problems, we calculate a number of terms in the corresponding expansions for the one-dimensional anharmonic oscillators of quartic, sectic, octic, and dectic types and compare the results obtained with those of conventional Rayleigh/Schrödinger perturbation theory. To the orders considered (and, conjecturally, to all orders) our eigenvalue expansions agree with those of Rayleigh/Schrödinger theory whereas our wave functions more accurately capture the more-rapid-than-gaussian decay known to hold for the exact solutions to these problems. For the quartic oscillator in particular our results strongly suggest that both the ground state energy eigenvalue expansion and its associated wave function expansion are Borel summable to yield natural candidates for the actual exact ground state solution and its energy. Our techniques for proving the existence of the crucial “fundamental solution” to the relevant (inverted-potential-vanishing-energy) Hamilton-Jacobi equation have the important property of admitting interesting infinite dimensional generalizations. In a project paralleling the present one we shall show how this basic construction can be carried out for the Yang-Mills equations in Minkowski spacetime.
In situ triaxial magnetic field compensation for the spin-exchange-relaxation-free atomic magnetometer
Authors: Fang Jiancheng , Qin Jie
Published: October 2012

The spin-exchange-relaxation-free (SERF) atomic magnetometer is an ultra-high sensitivity magnetometer, but it must be operated in a magnetic field with strength less than about 10 nT. Magnetic field compensation is an effective way to shield the magnetic field, and this paper demonstrates an in situ triaxial magnetic field compensation system for operating the SERF atomic magnetometer. The proposed hardware is based on optical pumping, which uses some part of the SERF atomic magnetometer itself, and the compensation method is implemented by analyzing the dynamics of the atomic spin. The experimental setup for this compensation system is described, and with this configuration, a residual magnetic field of strength less than 2 nT (±0.38 nT in the x axis, ±0.43 nT in the y axis, and ±1.62 nT in the z axis) has been achieved after compensation. The SERF atomic magnetometer was then used to verify that the residual triaxial magnetic fields were coincident with what were achieved by the compensation system.
Angular-dependences of giant in-plane and interlayer magnetoresistances in Bi2Te3 bulk single crystals
Authors: Yue Z. J. , Wang X. L. , Dou S. X.
Published: October 2012

Angular-dependences of in-plane and interlayer magnetotransport properties in n-type Bi2Te3 bulk single crystals have been investigated over a broad range of temperatures and magnetic fields. Giant in-plane magnetoresistances (MR) of up to 500% and interlayer MR of up to 200% were observed, respectively. The observed MR exhibits quadratic field dependences in low fields and linear field dependences in high fields. The angular dependences of the MR represent strong anisotropy and twofold oscillations. The observed angle-dependent, giant MR might result from the strong coulomb scattering of electrons as well as impurity scattering in the bulk conduction bands of n-type Bi2Te3. The strong anisotropy of the MR may be attributable to the anisotropy of electron mobility, effective mass, and relaxation time in the Fermi surface. The observed giant anisotropic MR in n-type Bi2Te3 bulk single crystals paves the way for Bi2Te3 single crystals to be useful for practical applications in magnetoelectronic devices such as disk reading heads, anisotropic magnetic sensors, and other multifunctional electromagnetic applications.
Superconductivity and magnetism in the KxMoO2−δ
Authors: Alves L. M. S. , dos Santos C. A. M. , Benaion S. S. , Machado A. J. S. , de Lima B. S. , Neumeier J. J. , Marques M. D. R. , Aguiar J. Albino , Mossanek R. J. O. , Abbate M.
Published: October 2012

Coexistence between superconductivity and magnetism is reported for the KxMoO2−δ samples. Photoemission experiments show that the presence of Mo3+ ions is responsible for the weak ferromagnetic ordering observed in the KxMoO2−δ samples. Magnetic ordering temperature and superconducting critical temperature (TC) ratio range from 7 to 18 in this compound. These are the highest ratios reported so far for a magnetic superconductor. TC decreases with increasing potassium composition (x). For the first time, TC near 10 K is reported in the K-Mo-O system.
Photofragment translational spectroscopy of CH3I at 225 nm—with the high excitation of the symmetric stretch vibration of CH3 fragment
Authors: Hu Lili , Zhou Zhimin , Dong Changwu , Zhang Lijuan , Du Yikui , Cheng Min , Zhu Qihe
Published: October 2012

The photodissociation dynamics of CH3I at 225 nm is studied on our high resolution mini-TOF photofragment translational spectrometer. The photofragment translational spectra of the I* and the I channels via parallel (∥) and perpendicular (⊥) transitions, i.e., of the four pathways 3Q0, 3Q0 ← 1Q1, 1Q1, and 1Q1 ← 3Q0, are obtained with both the symmetric stretch (ν1) and the umbrella (ν2) vibrational modes of the CH3 fragments partially resolved. The strong excitation of the symmetric stretch mode (ν1) is revealed in both the I and the I* channels. The branching fractions for the four pathways (0.09 for 3Q0, 0.03 for 3Q0 ← 1Q1, 0.34 for 1Q1, and 0.54 for 1Q1 ← 3Q0) show that the parallel transition (3Q0 ← X) is the major and the I channel is dominant in the photodissociation of CH3I at 225 nm. The curve-crossing probability is found to be 0.86 for 1Q1 ← 3Q0 but 0.08 for 3Q0 ← 1Q1.
A new method to derive electronegativity from resonant inelastic x-ray scattering
Authors: Carniato S. , Journel L. , Guillemin R. , Piancastelli M. N. , Stolte W. C. , Lindle D. W. , Simon M.
Published: October 2012

Electronegativity is a well-known property of atoms and substituent groups. Because there is no direct way to measure it, establishing a useful scale for electronegativity often entails correlating it to another chemical parameter; a wide variety of methods have been proposed over the past 80 years to do just that. This work reports a new approach that connects electronegativity to a spectroscopic parameter derived from resonant inelastic x-ray scattering. The new method is demonstrated using a series of chlorine-containing compounds, focusing on the Cl 2p−1LUMO1 electronic states reached after Cl 1s → LUMO core excitation and subsequent KL radiative decay. Based on an electron-density analysis of the LUMOs, the relative weights of the Cl 2pz atomic orbital contributing to the Cl 2p3/2 molecular spin-orbit components are shown to yield a linear electronegativity scale consistent with previous approaches.
New implementation of the configuration-based multi-reference second order perturbation theory
Authors: Lei Yibo , Wang Yubin , Han Huixian , Song Qi , Suo Bingbing , Wen Zhenyi
Published: October 2012

We present an improved version of the configuration-based multi-reference second-order perturbation approach (CB-MRPT2) according to the formulation of Lindgren on perturbation theory of a degenerate model space. This version involves a reclassification of the perturbation functions and new algorithms to calculate matrix elements in the perturber energy expressions utilizing the graphical unitary group approach and the hole-particle symmetry. The diagonalize-then-perturb (DP), including Rayleigh-Schrödinger and Brillouin-Wigner, and diagonalize-then-perturb-then-diagonalize (DPD) modes have been implemented. The new CB-MRPT2 method is applied to several typical and interesting systems: (1) the vertical excitation energies for several states of CO and N2, (2) energy comparison and timing of the ground state of C4H6, (3) the quasi-degeneracy of states in LiF, (4) the intruder state problems of AgH, and (5) the relative energies of di-copper-oxygen-ammonia complex isomers. The results indicate that the computational accuracy and efficiency of the presented methods are competitive and intruder-free. It should be emphasized that the DPD method rectifies naturally the shortcomings of LiF potential energy curves constructed by the original second order complete active space perturbation theory (CASPT2), without having to recourse to the so-called state mixture. Unlike CASPT2, the new methods give the same energy ordering for the two di-copper-oxygen-ammonia isomers as the previous multi-reference configuration interaction with single and double excitations methods. The new CB-MRPT2 method is shown to be a useful tool to study small to medium-sized systems.
Coarse-grained Brownian dynamics simulations of protein translocation through nanopores
Authors: Lee Po-Hsien , Helms Volkhard , Geyer Tihamér
Published: October 2012

A crucial process in biological cells is the translocation of newly synthesized proteins across cell membranes via integral membrane protein pores termed translocons. Recent improved techniques now allow producing artificial membranes with pores of similar dimensions of a few nm as the translocon system. For the translocon system, the protein has to be unfolded, whereas the artificial pores are wide enough so that small proteins can pass through even when folded. To study how proteins permeate through such membrane pores, we used coarse-grained Brownian dynamics simulations where the proteins were modeled as single beads or bead-spring polymers for both folded and unfolded states. The pores were modeled as cylindrical holes through the membrane with various radii and lengths. Diffusion was driven by a concentration gradient created across the porous membrane. Our results for both folded and unfolded configurations show the expected reciprocal relation between the flow rate and the pore length in agreement with an analytical solution derived by Brunn et al. [Q. J. Mech. Appl. Math. 37, 311 (1984)]10.1093/qjmam/37.2.311. Furthermore, we find that the geometric constriction by the narrow pore leads to an accumulation of proteins at the pore entrance, which in turn compensates for the reduced diffusivity of the proteins inside the pore.
Inferring bulk self-assembly properties from simulations of small systems with multiple constituent species and small systems in the grand canonical ensemble
Authors: Ouldridge Thomas E.
Published: October 2012

In this paper, we generalize a methodology [T. E. Ouldridge, A. A. Louis, and J. P. K. Doye, J. Phys.: Condens. Matter 22, 104102 (2010)] for dealing with the inference of bulk properties from small simulations of self-assembling systems of characteristic finite size. In particular, schemes for extrapolating the results of simulations of a single self-assembling object to the bulk limit are established in three cases: for assembly involving multiple particle species, for systems with one species localized in space and for simulations in the grand canonical ensemble. Furthermore, methodologies are introduced for evaluating the accuracy of these extrapolations. Example systems demonstrate that differences in cluster concentrations between simulations of a single self-assembling structure and bulk studies of the same model under identical conditions can be large, and that convergence on bulk results as system size is increased can be slow and non-trivial.
A 670 GHz gyrotron with record power and efficiency
Authors: Glyavin M. Yu. , Luchinin A. G. , Nusinovich G. S. , Rodgers J. , Kashyn D. G. , Romero-Talamas C. A. , Pu R.
Published: October 2012

A 670 GHz gyrotron with record power and efficiency has been developed in joint experiments of the Institute of Applied Physics, Russian Academy of Sciences (Nizhny Novgord, Russia), and the University of Maryland (USA) teams. The magnetic field of 27–28 T required for operation at the 670 GHz at the fundamental cyclotron resonance is produced by a pulsed solenoid. The pulse duration of the magnetic field is several milliseconds. A gyrotron is driven by a 70 kV, 15 A electron beam, so the beam power is on the order of 1 MW in 10–20 ms pulses. The ratio of the orbital to axial electron velocity components is in the range of 1.2–1.3. The gyrotron is designed to operate in the TE31,8-mode. Operation in a so high-order mode results in relatively low ohmic losses (less than 10% of the radiated power). Achieved power of the outgoing radiation (210 kW) and corresponding efficiency (about 20%) represent record numbers for high-power sources of sub-THz radiation.
Extrinsic charge traps in disordered organic materials
Authors: Lin Liang-Bih , Cheng Chi-Wen , Dai Chi-An , Lee Yuan-Pern
Published: October 2012

The effects of p-diethylaminobenzaldehyde diphenylhydrazone, a 0.22 eV trap, on the charge transport properties of disordered organic materials consisted of a mixture of N,N′-diphenyl N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine and polycarbonate are described. Trap-perturbed, trap-limited, and trap-controlled (trap-to-trap) transports were observed, where the trap is less effective at very low trap concentrations but appears to have increasing trap depth with respect to the concentration increase in the trap-limited regime. Most photocurrent transients showed non-dispersive transport behaviors; however, some were dispersive, especially at low electric fields or near the cross-over region between the trap-limited and trap-controlled transports. Field dependency of the mobilites at the trap-limited regime is higher than that of the trap-controlled regime, suggesting some type of superexchange phenomenon or field induced detrapping for the latter transport. For most known systems, charge transport reaches at a minimum mobility that is higher than anticipated from the trap depth. Analysis of the experimental results by theoretical models based on molecular crystals and disordered materials strongly suggests the influence of disorder but only gives qualitative agreements.
Hybrid pentacene/a-silicon solar cells utilizing multiple carrier generation via singlet exciton fission
Authors: Ehrler Bruno , Musselman Kevin P. , Böhm Marcus L. , Friend Richard H. , Greenham Neil C.
Published: October 2012

Silicon dominates the solar cell market because of its abundance, mature production processes, and high efficiencies, with the best solar cells approaching the Shockley-Queisser limit. Multiple exciton photogeneration provides a route to solar cells that surpass the Shockley-Queisser limit, and we report the use of pentacene, for which photogenerated singlet excitons rapidly convert into two lower-energy spin-triplet excitons. We report solar cells that couple amorphous silicon to pentacene. We show that a thin layer of nanocrystals between silicon and pentacene allows simultaneously harnessing low-energy photons absorbed in silicon and high-energy photons absorbed in pentacene, generating two excitons via singlet fission.
Analysis of Reynolds number scaling for viscous vortex reconnection
Authors: Ni Qionglin , Hussain Fazle , Wang Jianchun , Chen Shiyi
Published: October 2012

A theoretical analysis of viscous vortex reconnection is developed based on scale separation, and the Reynolds number, Re (= circulation/viscosity), scaling for the reconnection time Trec is derived. The scaling varies continuously as Re increases from $T_{rec} \sim {\mathop{\rm Re}\nolimits} ^{ - 1}$Trec∼ Re −1 to $T_{rec} \sim {\mathop{\rm Re}\nolimits} ^{ - 1/2}$Trec∼ Re −1/2. This theoretical prediction agrees well with direct numerical simulations by Garten et al. [J. Fluid Mech. 426, 1 (2001)]10.1017/S0022112000002251 and Hussain and Duraisamy [Phys. Fluids 23, 021701 (2011)]10.1063/1.3532039. Moreover, our analysis yields two Re’s, namely, a characteristic Re ${\mathop{\rm Re}\nolimits} _{0.75} \in \left[ {O\left({10^2 } \right),O\left({10^3 } \right)} \right]$ Re 0.75∈O102,O103 for the $T_{rec} \sim {\mathop{\rm Re}\nolimits} ^{ - 0.75}$Trec∼ Re −0.75 scaling given by Hussain and Duraisamy and the critical Re ${\mathop{\rm Re}\nolimits} _c \sim O\left({10^4 } \right)$ Re c∼O104 for the transition after which the first reconnection is completed. For ${\mathop{\rm Re}\nolimits} > {\mathop{\rm Re}\nolimits} _c$ Re > Re c, a quiescent state follows, and then, a second reconnection may occur.
Systematic optimization of quantum junction colloidal quantum dot solar cells
Authors: Liu Huan , Zhitomirsky David , Hoogland Sjoerd , Tang Jiang , Kramer Illan J. , Ning Zhijun , Sargent Edward H.
Published: October 2012

The recently reported quantum junction architecture represents a promising approach to building a rectifying photovoltaic device that employs colloidal quantum dot layers on each side of the p-n junction. Here, we report an optimized quantum junction solar cell that leverages an improved aluminum zinc oxide electrode for a stable contact to the n-side of the quantum junction and silver doping of the p-layer that greatly enhances the photocurrent by expanding the depletion region in the n-side of the device. These improvements result in greater stability and a power conversion efficiency of 6.1% under AM1.5 simulated solar illumination.
Blue monolithic AlInN-based vertical cavity surface emitting laser diode on free-standing GaN substrate
Authors: Cosendey Gatien , Castiglia Antonino , Rossbach Georg , Carlin Jean-François , Grandjean Nicolas
Published: October 2012

We report on III-nitride based blue vertical cavity surface emitting lasers using defect-free highly reflective AlInN/GaN distributed Bragg reflectors grown on c-plane free-standing GaN substrates. Lasing is demonstrated at room temperature under pulsed electrical injection. The high lasing threshold current density still prevents devices from continuous wave lasing because of large self-heating. The reasons for such a high threshold are discussed and we show that it mainly comes from large light absorption in the indium tin oxide current spreading layer. Properly tuning both its thickness and its position with respect to the electrical field could remarkably decrease the threshold.
Atomistic investigation of scratching-induced deformation twinning in nanocrystalline Cu
Authors: Zhang Junjie , Sun Tao , Yan Yongda , Shen Dong , Li Xiaodong
Published: October 2012

Deformation twinning is an important deformation mode of nanocrystalline metals. In current study, we investigate the scratching-induced deformation twinning in nanocrystalline Cu by means of molecular dynamics simulations. The tribological behavior, the deformation mechanisms, the formation mechanism of deformation twins, and the grain size dependence of the propensity of deformation twinning are elucidated. Simulation results demonstrate that deformation twinning plays an important role in the plastic deformation of nanocrystalline Cu under nanoscratching, in addition to dislocation activity and grain boundary-associated mechanism. The nucleation of initial twinning partial dislocations originates from the dissociation of lattice partial dislocations that emit from grain boundary triple junctions, and subsequent twin boundary migration is resulted from the glide of lattice partial dislocations emitted from twin boundary-grain boundary intersections on the twin plane. It is found that the propensity of deformation twinning in nanocrystalline Cu under scratching has strong dependence on both grain size and stress state. These findings will advance our understanding of the tribological behavior of nanocrystalline Cu and provide design and fabrication guidelines for nanocrystalline Cu based micro/nanosystems.
Optical absorption in semiconductor quantum dots coupling to dispersive phonons of infinite modes
Authors: Ding Zhiwen , Wang Qin , Zheng Hang
Published: October 2012

Optical absorption spectrum of semiconductor quantum dot is investigated by means of an analytical approach based on the Green's function for different forms of coupling strength in an unified method by using the standard model with valence and conduction band levels coupled to dispersive quantum phonons of infinite modes. The analytical expression of the optical absorption coefficient in semiconductor quantum dots is obtained and by this expression the line shape and the peak position of the absorption spectrum are procured. The relation between the properties of absorption spectrum and the forms of coupling strength is clarified, which can be referenced for choosing the proper form of the coupling strength or spectral density to control the features of absorption spectrum of quantum dot. The coupling and confinement induced energy shift and intensity decrease in the absorption spectrum are determined precisely for a wide range of parameters. The results show that the activation energy of the optical absorption is reduced by the effect of exciton-phonon coupling and photons with lower frequencies could also be absorbed in absorption process. With increase of the coupling constant, the line shape of optical absorption spectrum broadens and the peak position moves to lower photon energy with a rapid decrease in intensity at the same time. Both the coupling induced red shift and the confinement induced blue shift conduce to decrease in the intensity of absorption spectrum. Furthermore, this method may have application potential to other confined quantum systems.
Eigen-like hydrated protons traveling with a local distortion through the water nanotube in new molecular porous crystals {[MIII(H2bim)3](TMA)·20H2O}n (M = Co, Rh, Ru)
Authors: Matsui Hiroshi , Tadokoro Makoto
Published: October 2012

In molecular porous crystals {[MIII(H2bim)3](TMA)·20H2O}n (M = Co, Rh, Ru), the structural property of confined water network and the dynamics of mobile hydrated protons have been examined by the measurement of infrared spectrum and microwave conductivity. The water network undergoes first order phase transition from the ice nanotube (INT) to the water nanotube (WNT) around 200 K, while the infrared spectral features for these states are almost equivalent. Consequently, the water molecules in WNT dynamically fluctuate in the vicinity of the regulated position in INT with maintaining the O-O distance. The additional band observed around 2200 cm−1 reveals the emergence of an Eigen-like protonic hydrate, around which the O-O distance locally shrinks to ∼2.56 Å. The microwave conductivity exhibiting activation-type behavior, isotope effect and anisotropy indicates that the water nanotube is a quasi one-dimensional high proton conductor. Together with the neutron experimental results, we have clarified that the proton and protonic hole are generated by the self-dissociation in some water molecules just hydrated to the carboxylate oxygen atom of trimesic acid. The Eigen-like hydrated proton and protonic hole contribute to the intrinsic proton conduction accompanying local distortions. The carrier density dominated by the intrinsic ionic equilibrium is not large, whereas the actual mobility, which is higher than 1 × 10−2 (cm2/Vs), yields the present high proton conductivity.
Propagation and scattering of spin waves in curved magnonic waveguides
Authors: Tkachenko V. S. , Kuchko A. N. , Dvornik M. , Kruglyak V. V.
Published: October 2012

We report a continuous medium theory of dispersion and scattering of spin waves propagating in thin nanowire magnonic waveguides with curved regions. Assuming that the static magnetization is aligned along the waveguide, the curvature leads to a “geometrical” effective magnetic field term that is proportional to the square of the ratio of the exchange length to the radius of curvature of the waveguide. The term is small enough to favor the use of bended nanowire waveguides in planar magnonic data architectures. However, a stronger (multiple) winding (e.g., within helical structures) could enable design of magnonic waveguides with desired properties.
Pressure dependence of the Verwey transition in magnetite: An infrared spectroscopic point of view
Authors: Ebad-Allah J. , Baldassarre L. , Sing M. , Claessen R. , Brabers V. A. M. , Kuntscher C. A.
Published: October 2012

We investigated the electronic and vibrational properties of magnetite at temperatures from 300 K down to 10 K and for pressures up to 10 GPa by far-infrared reflectivity measurements. The Verwey transition is manifested by a drastic decrease of the overall reflectance and the splitting of the phonon modes as well as the activation of additional phonon modes. In the whole studied pressure range, the down-shift of the overall reflectance spectrum saturates and the maximum number of phonon modes is reached at a critical temperature, which sets a lower bound for the Verwey transition temperature Tv. Based on these optical results, a pressure-temperature phase diagram for magnetite is proposed.
Complementary periodic diffracting metallic nanohole and nanodipole arrays in the mid-infrared range
Authors: Ye Yong-Hong , Zhang Jia-Yu , Feng Ma Hui , Yao Jie , Wang Xudong
Published: October 2012

Metallic nanohole arrays and metallic nanodipole arrays are fabricated and experimentally characterized. A complementary response is observed in both transmission and reflection. For the metallic nanohole arrays, a peak (dip) in transmission (reflection) is observed at resonance whereas the metallic nanodipole arrays display a dip (peak) in transmission (reflection). The resonant frequency of both the metallic nanohole arrays and the nanodipole arrays depends on the dipole arm length, the incident angle, and the period. The resonant position of the nanohole arrays matches that of its complement, which means that Babinet's principle nearly holds for these structures in the mid-infrared region.
Coercivity enhancement in Pr9.5Fe83Zr2B5.5 magnetic nanomaterials
Authors: Lin Zhong , Han Jingzhi , Xing Meiying , Wan Fangming , Li Chan , Liu Shunquan , Wang Changsheng , Du Honglin , Yang Jinbo , Yang Yingchang
Published: October 2012

The coercivity of Pr2Fe14B/α-Fe magnetic nanomaterial has been drastically improved from 6.8 kOe to 26 kOe by the diffusion of the Pr68Cu32 alloy. Pr68Cu32 alloy reacts with α-Fe to form boundary phases among Pr2Fe14B grains. The boundary phases have weak magnetic properties and have a thickness comparable to the domain wall thickness of Pr2Fe14B phase. So boundary layers are very effective in pinning the motion of domain walls, leading to an increased coercivity. The coercivity of this material at 160 °C is improved from 2.7 kOe to 10 kOe by diffusion treatment.
Electronic structures of single-layer boron pnictides
Authors: Zhuang Houlong L. , Hennig Richard G.
Published: October 2012

Single-layer materials such as graphene and boron nitride promise alternative routes to electronic devices. Hybrid density functional calculations for single-layer boron pnictides boron nitride (BN), boron phosphide (BP), boron arsenide (BAs), and boron antimonide (BSb) show that these materials exhibit a direct bandgap of 6.1, 1.4, 1.2, and 0.6 eV, respectively, that originates from the energy difference of the pz orbitals of the species and is tunable by strain. The bandgap linearly decreases with strain for BN, while it increases non-linearly for BP, BAs, and BSb. The calculated natural band offsets between the various boron pnictides are all of type I.
Broadband switching functionality based on defect mode coupling in W2 photonic crystal waveguide
Authors: Cui Kaiyu , Feng Xue , Huang Yidong , Zhao Qiang , Huang Zhilei , Zhang Wei
Published: October 2012

Broadband switching functionality realized by an ultra-compact W2 photonic crystal waveguide (PCW) is demonstrated with an integrated titanium/aluminum microheater on its surface. Due to the enhanced coupling between the defect modes in W2 PCW, switching functionality with bandwidth up to 24 nm is achieved by the PCW with footprint of only 8 μm × 17.6 μm, while the extinction ratio is in excess of 15 dB over the entire bandwidth. Moreover, the switching speed is measured by alternating current modulation. Response time for this thermo-optic switch is 11.0 ± 3.0 μs for rise time and 40.3 ± 5.3 μs for fall time, respectively.
Effect of inter-bit material on the performance of directly deposited bit patterned media
Authors: Thiyagarajah Naganivetha , Duan Huigao , Song Debra L. Y. , Asbahi Mohamed , Huei Leong Siang , Yang Joel K. W. , Ng Vivian
Published: October 2012

We evaluated the effects of inter-bit material on the switching performance of bit patterned media (BPM) fabricated by direct deposition of magnetic material onto pre-patterned substrates. We performed a controlled experiment to vary the sidewall thickness and symmetry in bits with nominally identical size and pitch. Thick, asymmetric sidewalls resulted in significant broadening of the switching field distribution to 14%–20% compared to 10%–11% for bits with thin, symmetric sidewalls. These differences were attributed to changes in the intrinsic properties and dipolar interactions as supported by micromagnetic simulations. Our results highlight the importance of controlling inter-bit material to achieve high-density BPM.
Deformation behaviors of InP pillars under uniaxial compression
Authors: Jian Sheng-Rui , Sung T.-H. , Huang J. C. , Juang Jenh-Yih
Published: October 2012

We report the deformation behavior of single-crystal InP(100) micropillars, measuring about 1 μm in diameter and 2 μm in height, subjected to uniaxial compression at room temperature. The engineering stress-strain results indicated that the yield strength of InP pillar is about 2.5 GPa, and the presence of a drastic strain burst right after yielding. Cross-sectional transmission electron microscopy microstructural observations reveal the formation of extremely dense twins. The results indicate that the plastic deformation in InP micropillars is dominated by explosive generation of deformation twins under the high stress state.
Increased efficiency of light-emitting diodes incorporating anodes functionalized with fluorinated azobenzene monolayers and a green-emitting polyfluorene derivative
Authors: Lazzerini G. M. , Mian S. , Di Stasio F. , Merari Masillamani A. , Crivillers N. , Reinders F. , Mayor M. , Samorì P. , Cacialli F.
Published: October 2012

We investigate the functionalization of gold anodes with azobenzene-based self-assembled monolayers (AZO-SAM) and the influence of such functionalization on the external quantum efficiency (EQE) of polyfluorene-based light-emitting diodes (LEDs). Photoluminescence and electroluminescence measurements show that the AZO-SAMs do not modify the shape of the emission spectrum of the active layer. Instead, AZO-SAMs enhance the EQE of LEDs by an order of magnitude (from 0.018% to 0.18%) and decrease the turn-on voltage from 7.9 V to 6.2 V by reducing the injection barrier at the anode, thus promoting a better balance between hole and electron populations in the active layer.
Laser-induced quantum pumping in graphene
Authors: San-Jose Pablo , Prada Elsa , Schomerus Henning , Kohler Sigmund
Published: October 2012

We investigate non-adiabatic electron pumping in graphene generated by laser irradiation with linear polarization parallel or perpendicular to the transport direction. Transport is dominated by the spatially asymmetric excitation of electrons from evanescent into propagating modes. For a laser with parallel polarization, the pumping response exhibits a subharmonic resonant enhancement which directly probes the Fermi energy; no such enhancement occurs for perpendicular polarization. The resonance mechanism relies on the chirality of charge carriers in graphene.
Improvement of amplified spontaneous emission performance of conjugated polymer waveguides with a low loss cladding
Authors: Zhang Bo , Hou Yanbing , Lou Zhidong , Teng Feng , Liu Xiaojun , Meng Lingchuan , Shen Jingling , Wang Yongsheng
Published: October 2012

We report the improvement of the amplified spontaneous emission (ASE) performance in the optically pumped symmetric thin film waveguide glass/indium-tin oxide (ITO)/SiO2/poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene]/SiO2/Al or Ag by optimizing the thickness of SiO2 and replacing the Al electrode with Ag, where SiO2 acted as a spacer layer to prevent the ASE at 620 nm from being destructed. The results show that the SiO2/Ag cladding reduced the ASE threshold to 4 μJ/pulse compared with the SiO2/Al cladding, owing to the higher work function and reflection rate as well as lower absorption loss of the Ag electrode. No photoluminescence at 580 nm being observed makes it possible for an electric field to only modulate the ASE at 620 nm in the device with the SiO2/Ag cladding. The electric-field quenching of the ASE has been observed, which increases with the electric field. The field dependence of ASE can be attributed to field-induced dissociation of photogenerated excitons in the polymer waveguides.
Molecular dynamics prediction of interfacial strength and validation through atomic force microscopy
Authors: Galan Ulises , Sodano Henry A.
Published: October 2012

Molecular dynamics (MD) simulations are performed to calculate the interfacial energy between zinc oxide (ZnO) and graphitic carbon. The MD model consists of a ZnO slab and a single layer of graphitic carbon. The calculation was validated experimentally by atomic force microscopy (AFM) liftoff. A polishing process was applied to create a tip with a flat surface that was subsequently coated with a ZnO film allowing force displacement measurement on highly oriented pyrolitic graphite to validate the simulations. The MD simulation and AFM lift-off show good agreement with adhesive energies of 0.303 J/m2 and 0.261 ± 0.054 J/m2, respectively.