bluuebunny/crossref_metadata_2025 huggingface dataset:
Bioactive and porous-structured nanocomposite microspheres effective for cell delivery: a feasibility study for bone tissue engineering
Authors: Park Jeong-Hui , Kim Mi-Kyung , El-Fiqi Ahmed , Seo Seog-Jin , Lee Eun-Jung , Kim Joong-Hyun , Kim Hae-Won
Published: May 2014

A novel nanocomposite microspherical cell-carrier system was developed to populate stem cells and to stimulate their osteogenesis for bone tissue engineering.
Effects of iron or manganese doping of ZnO nanoparticles on their dissolution, ROS generation and cytotoxicity
Authors: Yin Hong , Casey Philip S.
Published: May 2014

Cytotoxicity and its possible mechanisms, such as particle dissolution and intracellular ROS generation were investigated using Fe-doped, Mn-doped and undoped ZnO nanoparticles.
Application of cobalt oxide nanostructured modified aluminium electrode for electrocatalytic oxidation of guanine and single-strand DNA
Authors: Raj Vairamuthu , Silambarasan Jayachandran , Rajakumar Panchanathan
Published: May 2014

The electrocatalytic oxidation of guanine in ssDNA at cobalt oxide nanoflower-modified aluminium electrode.
Effect of an electrolyte additive hexamethylenetetramine on electrochemical behaviors of the Mg–11Li–3.5Al–2Zn–1.5Re–0.5Zr electrode
Authors: Lv Yan-zhuo , Li Yan-feng , Wang Li , Cao Dian-xue , Wang Gui-ling , Feng Jing , Ren Yueming , Zhang Milin
Published: May 2014

The current–time curves measured at different potentials for the Mg–11Li–3.5Al–2Zn–1.5Re–0.5Zr electrode in a 0.7 mol L−1 NaCl solution containing 0.10 mmol L−1 of C6H12N4.
Characterization of NTCDI supra-molecular networks on Au(111); combining STM, IR and DFT calculations
Authors: Seydou Mahamadou , Teyssandier Joan , Battaglini Nicolas , Kenfack Ghislain Tsague , Lang Philippe , Tielens Frederik , Maurel François , Diawara Boubakar
Published: May 2014

In this paper, we investigate the self-organization of NTCDI molecules on Au(111) surface by combining Density Functional Theory (DFT) and experiments based on scanning tunneling microscopy (STM) and infrared spectroscopy measurements.
Methodology for quantitative determination of the carbohydrate composition of brown seaweeds (Laminariaceae)
Authors: Manns D. , Deutschle A. L. , Saake B. , Meyer A. S.
Published: May 2014

The monosaccharide composition of four different samples of brown seaweeds Laminaria digitata and Saccharina latissima were compared by different high performance anion exchange chromatography (HPAEC) methods after different acid hydrolysis treatments or a cellulase treatment.
Protein kinase inhibitor β enhances the constitutive activity of G-protein-coupled zinc receptor GPR39
Authors: Kovacs Zsuzsa , Schacht Teresa , Herrmann Ann-Kathrin , Albrecht Philipp , Lefkimmiatis Konstantinos , Methner Axel
Published: May 2014

GPR39 is a G-protein-coupled zinc receptor that protects against diverse effectors of cell death. Its protective activity is mediated via constitutive activation of Gα13 and the RhoA pathway, leading to increased SRE (serum-response element)-dependent transcription; the zinc-dependent immediate activation of GPR39 involves Gq-mediated increases in cytosolic Ca2+ and Gs coupling leading to increased cAMP levels. We used the cytosolic and soluble C-terminus of GPR39 in a Y2H (yeast-2-hybrid) screen for interacting proteins, thus identifying PKIB (protein kinase A inhibitor β). Co-expression of GPR39 with PKIB increased the protective activity of GPR39 via the constitutive, but not the ligand-mediated, pathway. PKIB inhibits protein kinase A by direct interaction with its pseudosubstrate domain; mutation of this domain abolished the inhibitory activity of PKIB on protein kinase A activity, but had no effect on the interaction with GPR39, cell protection and induction of SRE-dependent transcription. Zinc caused dissociation of PKIB from GPR39, thereby liberating it to associate with protein kinase A and inhibit its activity, which would result in a negative-feedback loop with the ability to limit activation of the Gs pathway by zinc.
Imatinib mesylate stimulates low-density lipoprotein receptor-related protein 1-mediated ERK phosphorylation in insulin-producing cells
Authors: Fred Rikard G. , Boddeti Santosh Kumar , Lundberg Marcus , Welsh Nils
Published: May 2014

Low-density lipoprotein receptor-related protein 1 (LRP1) is an endocytic and multi-functional type I cell surface membrane protein, which is known to be phosphorylated by the activated platelet-derived growth factor receptor (PDGFR). The tyrosine kinase inhibitor imatinib, which inhibits PDGFR and c-Abl, and which has previously been reported to counteract β-cell death and diabetes, has been suggested to reduce atherosclerosis by inhibiting PDGFR-induced LRP1 phosphorylation. The aim of the present study was to study LRP1 function in β-cells and to what extent imatinib modulates LRP1 activity. LRP1 and c-Abl gene knockdown was performed by RNAi using rat INS-1 832/13 and human EndoC1-βH1 cells. LRP1 was also antagonized by treatment with the antagonist low-density lipoprotein receptor-related protein associated protein 1 (LRPAP1). We have used PDGF-BB, a PDGFR agonist, and apolipoprotein E (ApoE), an LRP1 agonist, to stimulate the activities of PDGFR and LRP1 respectively. Knockdown or inhibition of LRP1 resulted in increased hydrogen peroxide (H2O2)- or cytokine-induced cell death, and glucose-induced insulin release was lowered in LRP1-silenced cells. These results indicate that LRP1 function is necessary for β-cell function and that LRP1 is adversely affected by challenges to β-cell health. PDGF-BB, or the combination of PDGF-BB+ApoE, induced phosphorylation of extracellular-signal-regulated kinase (ERK), Akt and LRP1. LRP1 silencing blocked this event. Imatinib blocked phosphorylation of LRP1 by PDGFR activation but induced phosphorylation of ERK. LRP1 silencing blocked imatinib-induced phosphorylation of ERK. Sunitinib also blocked LRP1 phosphorylation in response to PDGF-BB and induced phosphorylation of ERK, but this latter event was not affected by LRP1 knockdown. siRNA-mediated knockdown of the imatinib target c-Abl resulted in an increased ERK phosphorylation at basal conditions, with no further increase in response to imatinib. Imatinib-induced cell survival of tunicamycin-treated cells was partially mediated by ERK activation. We have concluded that imatinib promotes LRP1-dependent ERK activation, possibly via inhibition of c-Abl, and that this could contribute to the pro-survival effects of imatinib on β-cells.
The Bioenergetic Health Index: a new concept in mitochondrial translational research
Authors: Chacko Balu K. , Kramer Philip A. , Ravi Saranya , Benavides Gloria A. , Mitchell Tanecia , Dranka Brian P. , Ferrick David , Singal Ashwani K. , Ballinger Scott W. , Bailey Shannon M. , Hardy Robert W. , Zhang Jianhua , Zhi Degui , Darley-Usmar Victor M.
Published: May 2014

Bioenergetics has become central to our understanding of pathological mechanisms, the development of new therapeutic strategies and as a biomarker for disease progression in neurodegeneration, diabetes, cancer and cardiovascular disease. A key concept is that the mitochondrion can act as the ‘canary in the coal mine’ by serving as an early warning of bioenergetic crisis in patient populations. We propose that new clinical tests to monitor changes in bioenergetics in patient populations are needed to take advantage of the early and sensitive ability of bioenergetics to determine severity and progression in complex and multifactorial diseases. With the recent development of high-throughput assays to measure cellular energetic function in the small number of cells that can be isolated from human blood these clinical tests are now feasible. We have shown that the sequential addition of well-characterized inhibitors of oxidative phosphorylation allows a bioenergetic profile to be measured in cells isolated from normal or pathological samples. From these data we propose that a single value–the Bioenergetic Health Index (BHI)–can be calculated to represent the patient's composite mitochondrial profile for a selected cell type. In the present Hypothesis paper, we discuss how BHI could serve as a dynamic index of bioenergetic health and how it can be measured in platelets and leucocytes. We propose that, ultimately, BHI has the potential to be a new biomarker for assessing patient health with both prognostic and diagnostic value.
Dopingless super‐steep impact ionisation MOS (dopingless‐IMOS) based on work‐function engineering
Authors: Singh S. , Kondekar P.N.
Published: May 2014

A unique approach is proposed to realise dopingless impact‐ionisation MOS (dopingless‐IMOS) using work‐function engineering of electrodes to form charge plasma as a substitute for doping. Using appropriate work‐function difference between metal electrodes and intrinsic silicon film with thickness less than the intrinsic Debye length (LD) leads to charge plasma formation, in turn this charge plasma induces uniform p‐type source and n‐type drain. The proposed dopingless‐IMOS is simulated using two‐dimensional technology computer‐aided design (TCAD) Sentaurus to compare its electrical characteristics with conventional IMOS having identical device dimensions and bias conditions. Dopingless‐IMOS (DL‐IMOS) offers a simple fabrication process flow as it avoids the need for ion implantation, photo masking and complicated thermal budget. Hence, it is highly immune to process variations, doping control issues and random dopant fluctuations and it retains the inherent distinctive advantages of IMOS.
Stability of cooperative teleoperation using haptic devices with complementary degrees of freedom
Authors: Li Jian , Tavakoli Mahdi , Huang Qi
Published: May 2014

In bilateral teleoperation of a dexterous task, to take full advantage of the human's intelligence, experience and sensory inputs, a possibility is to engage multiple human arms through multiple masters (haptic devices) in controlling a single‐slave robot with high degrees‐of‐freedom (DOF); the total DOFs of the masters will be equal to the DOFs of the slave. A multi‐master/single‐slave cooperative haptic teleoperation system with w DOFs can be modelled as a two‐port network where each port (terminal) connects to a termination defined by w inputs and w outputs. The stability analysis of such a system is not trivial because of dynamic coupling across the different DOFs of the robots, the human operators and the physical or virtual environments. The unknown dynamics of the users and the environments exacerbate the problem. The authors present a novel, straightforward and convenient frequency‐domain method for stability analysis of this system. As a case study, two 1‐DOF and 2‐DOF master haptic devices are considered to teleoperate a 3‐DOF slave robot. It is qualitatively discussed how such a trilateral haptic teleoperation system may result in better task performance by splitting the various DOFs of a dexterous task between two arms of a human or two humans. Simulation and experimental results demonstrate the validity of the stability analysis framework.
Asynchronous consensus‐based time synchronisation in wireless sensor networks using unreliable communication links
Authors: Ahmed Salman , Xiao Feng , Chen Tongwen
Published: May 2014

Time synchronisation is required for a variety of distributed control applications in wireless sensor networks (WSNs). In this study, a consensus‐based time synchronisation protocol is presented. The proposed protocol considers asynchronous framework where the sensor nodes can have different time‐periods, starting times and input update times. The communication links are assumed to be unreliable. The clocks in a WSN are modelled by a time‐varying system with time‐delay terms. The objective is to design local control inputs to achieve time synchronisation by processing the information received from available neighbour nodes. By employing tools from non‐negative matrix and graph theories, the convergence analysis is presented. Numerical examples are given to demonstrate the effectiveness of the proposed protocol.
Bi‐level thresholding for binarisation of handwritten and printed documents
Authors: Jennifer Ranjani J.
Published: May 2014

Document image binarisation algorithms have been available in the literature for decades. However, most of the state‐of‐the‐art methods address specific image degradation or characteristics. Moreover, they require one or more parameters to be tuned manually so as to present a significant binary image. In this study, a hybrid approach for document binarisation is presented. In the pre‐processing stage, the degradation in the background image is smoothed using the L0‐gradient minimisation algorithm and the foreground is enhanced using the local contrast feature. A divide and conquer based recursive auto‐thresholding algorithm is then utilised to binarise the enhanced image. The proposed algorithm is evaluated objectively using the evaluation metrics such as F‐measure, peak signal‐to‐noise ratio, negative rate metric. The extensive experiments over the different datasets including the Document Image Binarization Contest (DIBCO) 2009, Handwritten Document Image Binarization Competition (H‐DIBCO) 2010, DIBCO 2011 and H‐DIBCO 2012 show that the proposed hybrid binarisation algorithm outperforms most of the state‐of‐the‐art algorithms significantly.
Probabilistic approach for optimal placement and tuning of power system supplementary damping controllers
Authors: Rueda José Luis , Cepeda Jaime Cristóbal , Erlich István
Published: May 2014

This study presents a comprehensive approach to tackle the problem of optimal placement and coordinated tuning of power system supplementary damping controllers (OPCTSDC). The approach uses a recursive framework comprising probabilistic eigenanalysis (PE), a scenario selection technique (SST) and a new variant of mean‐variance mapping optimisation algorithm (MVMO‐SM). Based on probabilistic models used to sample a wide range of operating conditions, PE is applied to determine the instability risk because of poorly‐damped oscillatory modes. Next, the insights gathered from PE are exploited by SST, which combines principal component analysis and fuzzy c‐means clustering algorithm to extract a reduced subset of representative scenarios. The multi‐scenario formulation of OPCTSDC is then solved by MVMO‐SM. A case study on the New England test system, which includes performance comparisons between different modern heuristic optimisation algorithms, illustrates the feasibility and effectiveness of the proposed approach.
Simultaneous impact of unified power flow controller and off‐shore wind penetration on distance relay characteristics
Authors: Dubey Rahul , Samantaray Subhransu Ranjan , Panigrahi Bijay Ketan
Published: May 2014

This study presents an analytical approach for finding the possible impacts of flexible AC transmission system (FACTS) devices such as unified power flow controller (UPFC) and off‐shore wind penetration on distance relay characteristics. Generating relay tripping characteristics is one of the challenging issues for transmission line distance relays as the present day transmission systems is subjected to a more stressed environment with respect to power system operation. Moreover, inclusion of FACTS devices such as UPFC in the transmission system seriously impacts the performance of the distance relays as the apparent impedance changes. Furthermore, the reach setting of the relay is significantly affected as the relay end voltage fluctuates continuously when off‐shore wind‐farms are connected to power transmission systems. Thus, generating tripping characteristics for appropriate operating conditions is a demanding concern and the same has been addressed in the proposed research work. Extensive testing is carried out in generating relay tripping characteristics with possible variations under the operating conditions of UPFC and wind‐farm and it is observed that the characteristics are significantly affected for different operating conditions. Furthermore, the performance of the derived relay characteristics is validated on possible transmission line fault events and is found to work effectively.
Competition between photodetachment and autodetachment of the $\bm {2^1\pi \pi ^*}$21ππ* state of the green fluorescent protein chromophore anion
Authors: Mooney Ciarán R. S. , Parkes Michael A. , Zhang Lijuan , Hailes Helen C. , Simperler Alexandra , Bearpark Michael J. , Fielding Helen H.
Published: May 2014

Using a combination of photoelectron spectroscopy measurements and quantum chemistry calculations, we have identified competing electron emission processes that contribute to the 350–315 nm photoelectron spectra of the deprotonated green fluorescent protein chromophore anion, p-hydroxybenzylidene-2,3-dimethylimidazolinone. As well as direct electron detachment from S0, we observe resonant excitation of the 21ππ* state of the anion followed by autodetachment. The experimental photoelectron spectra are found to be significantly broader than photoelectron spectrum calculated using the Franck-Condon method and we attribute this to rapid (∼10 fs) vibrational decoherence, or intramolecular vibrational energy redistribution, within the neutral radical.
Oscillations in probability distributions for stochastic gene expression
Authors: Petrosyan K. G. , Hu Chin-Kun
Published: May 2014

The phenomenon of oscillations in probability distribution functions of number of components is found for a model of stochastic gene expression. It takes place in cases of low levels of molecules or strong intracellular noise. The oscillations distinguish between more probable even and less probable odd number of particles. The even-odd symmetry restores as the number of molecules increases with the probability distribution function tending to Poisson distribution. We discuss the possibility of observation of the phenomenon in gene, protein, and mRNA expression experiments.
Ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer
Authors: Yang Weiquan , Becker Jacob , Liu Shi , Kuo Ying-Shen , Li Jing-Jing , Landini Barbara , Campman Ken , Zhang Yong-Hang
Published: May 2014

This paper reports the proposal, design, and demonstration of ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer to optimize light management and minimize non-radiative recombination. According to our recently developed semi-analytical model, this design offers one of the highest potential achievable efficiencies for GaAs solar cells possessing typical non-radiative recombination rates found among commercially available III-V arsenide and phosphide materials. The structure of the demonstrated solar cells consists of an In0.49Ga0.51P/GaAs/In0.49Ga0.51P double-heterostructure PN junction with an ultra-thin 300 nm thick GaAs absorber, combined with a 5 μm thick Al0.52In0.48P layer with a textured as-grown surface coated with Au used as a reflective back scattering layer. The final devices were fabricated using a substrate-removal and flip-chip bonding process. Solar cells with a top metal contact coverage of 9.7%, and a MgF2/ZnS anti-reflective coating demonstrated open-circuit voltages (Voc) up to 1.00 V, short-circuit current densities (Jsc) up to 24.5 mA/cm2, and power conversion efficiencies up to 19.1%; demonstrating the feasibility of this design approach. If a commonly used 2% metal grid coverage is assumed, the anticipated Jsc and conversion efficiency of these devices are expected to reach 26.6 mA/cm2 and 20.7%, respectively.
Vortex and structural dynamics of a flexible cylinder in cross-flow
Authors: Shang Jessica K. , Stone Howard A. , Smits Alexander J.
Published: May 2014

A low-density, flexible cantilevered cylinder was permitted to vibrate freely under the influence of vortex shedding in the laminar flow regime. We find that the vortex-induced vibrations (VIV) of a flexible cantilever depart from those of a flexible cylinder that is fixed at both ends. In particular, we find discontinuous regions of VIV behavior – here called states – as a function of the reduced velocity U*. These states are demarcated by discrete changes in the dominant eigenmodes of the structural response as the cylinder vibrates in progressively higher structural modes with increasing U*. The contribution of structural modes can be identified readily by a modal projection of the cylinder oscillation onto known cantilever beam modes. Oscillation frequencies do not monotonically increase with U*. The wake response between different states is also found to have distinct characteristics; of particular note is the occurrence of a P+S wake over one of these regions, which is associated with a high-amplitude vibration of the cylinder that is due to the constructive interference of contributing eigenmodes.
Collective vibrations of water-solvated hydroxide ions investigated with broadband 2DIR spectroscopy
Authors: Mandal Aritra , Ramasesha Krupa , De Marco Luigi , Tokmakoff Andrei
Published: May 2014

The infrared spectra of aqueous solutions of NaOH and other strong bases exhibit a broad continuum absorption for frequencies between 800 and 3500 cm−1, which is attributed to the strong interactions of the OH− ion with its solvating water molecules. To provide molecular insight into the origin of the broad continuum absorption feature, we have performed ultrafast transient absorption and 2DIR experiments on aqueous NaOH by exciting the O–H stretch vibrations and probing the response from 1350 to 3800 cm−1 using a newly developed sub-70 fs broadband mid-infrared source. These experiments, in conjunction with harmonic vibrational analysis of OH−(H2O)n (n = 17) clusters, reveal that O–H stretch vibrations of aqueous hydroxides arise from coupled vibrations of multiple water molecules solvating the ion. We classify the vibrations of the hydroxide complex by symmetry defined by the relative phase of vibrations of the O–H bonds hydrogen bonded to the ion. Although broad and overlapping spectral features are observed for 3- and 4-coordinate ion complexes, we find a resolvable splitting between asymmetric and symmetric stretch vibrations, and assign the 2850 cm−1 peak infrared spectra of aqueous hydroxides to asymmetric stretch vibrations.
String model for the dynamics of glass-forming liquids
Authors: Pazmiño Betancourt Beatriz A. , Douglas Jack F. , Starr Francis W.
Published: May 2014

We test the applicability of a living polymerization theory to describe cooperative string-like particle rearrangement clusters (strings) observed in simulations of a coarse-grained polymer melt. The theory quantitatively describes the interrelation between the average string length L, configurational entropy Sconf, and the order parameter for string assembly Φ without free parameters. Combining this theory with the Adam-Gibbs model allows us to predict the relaxation time τ in a lower temperature T range than accessible by current simulations. In particular, the combined theories suggest a return to Arrhenius behavior near Tg and a low T residual entropy, thus avoiding a Kauzmann “entropy crisis.”
Electron-stimulated reactions in layered CO/H2O films: Hydrogen atom diffusion and the sequential hydrogenation of CO to methanol
Authors: Petrik Nikolay G. , Monckton Rhiannon J. , Koehler Sven P. K. , Kimmel Greg A.
Published: May 2014

Low-energy (100 eV) electron-stimulated reactions in layered H2O/CO/H2O ices are investigated. For CO layers buried in amorphous solid water (ASW) films at depths of 50 monolayers (ML) or less from the vacuum interface, both oxidation and reduction reactions are observed. However, for CO buried more deeply in ASW films, only the reduction of CO to methanol is observed. Experiments with layered films of H2O and D2O show that the hydrogen atoms participating in the reduction of the buried CO originate in the region that is 10–50 ML below the surface of the ASW films and subsequently diffuse through the film. For deeply buried CO layers, the CO reduction reactions quickly increase with temperature above ∼60 K. We present a simple chemical kinetic model that treats the diffusion of hydrogen atoms in the ASW and sequential hydrogenation of the CO to methanol to account for the observations.
Modeling delay in genetic networks: From delay birth-death processes to delay stochastic differential equations
Authors: Gupta Chinmaya , López José Manuel , Azencott Robert , Bennett Matthew R. , Josić Krešimir , Ott William
Published: May 2014

Delay is an important and ubiquitous aspect of many biochemical processes. For example, delay plays a central role in the dynamics of genetic regulatory networks as it stems from the sequential assembly of first mRNA and then protein. Genetic regulatory networks are therefore frequently modeled as stochastic birth-death processes with delay. Here, we examine the relationship between delay birth-death processes and their appropriate approximating delay chemical Langevin equations. We prove a quantitative bound on the error between the pathwise realizations of these two processes. Our results hold for both fixed delay and distributed delay. Simulations demonstrate that the delay chemical Langevin approximation is accurate even at moderate system sizes. It captures dynamical features such as the oscillatory behavior in negative feedback circuits, cross-correlations between nodes in a network, and spatial and temporal information in two commonly studied motifs of metastability in biochemical systems. Overall, these results provide a foundation for using delay stochastic differential equations to approximate the dynamics of birth-death processes with delay.
A theoretical and experimental study of pressure broadening of the oxygen A-band by helium
Authors: Grimminck Dennis L. A. G. , Spiering Frans R. , Janssen Liesbeth M. C. , van der Avoird Ad , van der Zande Wim J. , Groenenboom Gerrit C.
Published: May 2014

The rotationally resolved magnetic dipole absorption spectrum of the oxygen A-band \documentclass[12pt]{minimal}\begin{document}$b{^1\Sigma _g^+}\mathrm{(v\!=\!0)}\break \leftarrow \!X{^3\Sigma _g^-}\mathrm{(v\!=\!0)}$\end{document}b1Σg+(v=0)←X3Σg−(v=0) perturbed by collisions with helium was studied theoretically using the impact approximation. To calculate the relaxation matrix, scattering calculations were performed on a newly computed helium-oxygen (\documentclass[12pt]{minimal}\begin{document}$b{^1\Sigma _g^+}$\end{document}b1Σg+) interaction potential as well as on a helium-oxygen (\documentclass[12pt]{minimal}\begin{document}$X{^3\Sigma _g^-}$\end{document}X3Σg−) interaction potential from the literature. The calculated integrated line cross sections and broadening coefficients are in good agreement with experimental results from the literature. Additionally, cavity ring-down experiments were performed in the wings of the spectral lines for a quantitative study of line-mixing, i.e., the redistribution of rotational line intensities by helium-oxygen collisions. It is shown that inclusion of line-mixing in the theory is required to reproduce the experimentally determined absolute absorption strengths as a function of the density of the helium gas.
The vibrational spectrum of FeO2+ isomers—Theoretical benchmark and experiment
Authors: Maier Toni M. , Boese A. Daniel , Sauer Joachim , Wende Torsten , Fagiani Matias , Asmis Knut R.
Published: May 2014

Infrared photodissociation is used to record the vibrational spectrum of FeO2+(He)2–4 which shows three bands at 1035, 980, and 506 cm−1. Quantum chemical multi-reference configuration interaction calculations (MRCISD) of structures and harmonic frequencies show that these bands are due to two different isomers, an inserted dioxo complex with Fe in the +V oxidation state and a side-on superoxo complex with Fe in the +II oxidation state. These two are separated by a substantial barrier, 53 kJ/mol, whereas the third isomer, an end-on complex between Fe+ and an O2 molecule, is easily converted into the side-on complex. For all three isomers, states of different spin multiplicity have been considered. Our best energies are computed at the MRCISD+Q level, including corrections for complete active space and basis set extension, core-valence correlation, relativistic effects, and zero-point vibrational energy. The average coupled pair functional (ACPF) yields very similar energies. Density functional theory (DFT) differs significantly from our best estimates for this system, with the TPSS functional yielding the best results. The other functionals tested are BP86, PBE, B3LYP, TPSSh, and B2PLYP. Complete active space second order perturbation theory (CASPT2) performs better than DFT, but less good than ACPF.
Rotating non-Oberbeck–Boussinesq Rayleigh–Bénard convection in water
Authors: Horn Susanne , Shishkina Olga
Published: May 2014

Rotating Rayleigh–Bénard convection in water is studied in direct numerical simulations, where the temperature dependence of the viscosity, the thermal conductivity, and the density within the buoyancy term is taken into account. In all simulations, the arithmetic mean of the lowest and highest temperature in the system equals 40 °C, corresponding to a Prandtl number of Pr = 4.38. In the non-rotational case, the Rayleigh number Ra ranges from 107 to 1.16 × 109 and temperature differences Δ up to 70 K are considered, whereas in the rotational case the inverse Rossby number range from 0.07 ⩽ 1/Ro ⩽ 14.1 is studied for Δ = 40 K with the focus on Ra = 108. The non-Oberbeck–Boussinesq (NOB) effects in water are reflected in an up to 5.5 K enhancement of the center temperature and in an up to 5% reduction of the Nusselt number. The top thermal and viscous boundary layer thicknesses increase and the bottom ones decrease, while the sum of the corresponding top and bottom thicknesses remains as in the classical Oberbeck–Boussinesq (OB) case. Rotation applied to NOB thermal convection reduces the central temperature enhancement. Under NOB conditions the top (bottom) thermal and viscous boundary layers become equal for a slightly larger (smaller) inverse Rossby number than in the OB case. Furthermore, for rapid rotation the thermal bottom boundary layers become thicker than the top ones. The Nusselt number normalized by that in the non-rotating case depends similarly on 1/Ro  in both, the NOB and the OB cases. The deviation between the Nusselt number under OB and NOB conditions is minimal when the thermal and viscous boundary layers are equal.
Phase separation in solutions with specific and nonspecific interactions
Authors: Jacobs William M. , Oxtoby David W. , Frenkel Daan
Published: May 2014

Protein solutions, which tend to be thermodynamically stable under physiological conditions, can demix into protein-enriched and protein-depleted phases when stressed. Using a lattice-gas model of proteins with both isotropic and specific, directional interactions, we calculate the critical conditions for phase separation for model proteins with up to four patches via Monte Carlo simulations and statistical associating fluid theory. Given a fixed specific interaction strength, the critical value of the isotropic energy, which accounts for dispersion forces and nonspecific interactions, measures the stability of the solution with respect to nonspecific interactions. Phase separation is suppressed by the formation of protein complexes, which effectively passivate the strongly associating sites on the monomers. Nevertheless, we find that protein models with three or more patches can form extended aggregates that phase separate despite the assembly of passivated complexes, even in the absence of nonspecific interactions. We present a unified view of the critical behavior of model fluids with anisotropic interactions, and we discuss the implications of these results for the thermodynamic stability of protein solutions.
Photo-assisted etching of silicon in chlorine- and bromine-containing plasmas
Authors: Zhu Weiye , Sridhar Shyam , Liu Lei , Hernandez Eduardo , Donnelly Vincent M. , Economou Demetre J.
Published: May 2014

Cl2, Br2, HBr, Br2/Cl2, and HBr/Cl2 feed gases diluted in Ar (50%–50% by volume) were used to study etching of p-type Si(100) in a rf inductively coupled, Faraday-shielded plasma, with a focus on the photo-assisted etching component. Etching rates were measured as a function of ion energy. Etching at ion energies below the threshold for ion-assisted etching was observed in all cases, with Br2/Ar and HBr/Cl2/Ar plasmas having the lowest and highest sub-threshold etching rates, respectively. Sub-threshold etching rates scaled with the product of surface halogen coverage (measured by X-ray photoelectron spectroscopy) and Ar emission intensity (7504 Å). Etching rates measured under MgF2, quartz, and opaque windows showed that sub-threshold etching is due to photon-stimulated processes on the surface, with vacuum ultraviolet photons being much more effective than longer wavelengths. Scanning electron and atomic force microscopy revealed that photo-etched surfaces were very rough, quite likely due to the inability of the photo-assisted process to remove contaminants from the surface. Photo-assisted etching in Cl2/Ar plasmas resulted in the formation of 4-sided pyramidal features with bases that formed an angle of 45° with respect to ⟨110⟩ cleavage planes, suggesting that photo-assisted etching can be sensitive to crystal orientation.
Modeling the nanoscale linear response of superconducting thin films measured by a scanning probe microwave microscope
Authors: Tai Tamin , Ghamsari B. G. , Anlage Steven M.
Published: May 2014

A localized and strong RF magnetic field, created by a magnetic write head, is used to examine the linear electrodynamic properties of a Nb superconducting film. The complex reflection coefficient of the write head held in close proximity to the films is measured as a function of sample temperature. A model combining a magnetic circuit (magnetic write head inductively coupled to the sample) and transmission line (microwave circuit) is given to interpret the linear response measurement. Additionally, this reflection linear response measurement can be used to determine the temperature dependence of the magnetic penetration depth on a variety of superconductors.
Low bias stress and reduced operating voltage in SnCl2Pc based n-type organic field-effect transistors
Authors: Md. Obaidulla SK. , Goswami D. K. , Giri P. K.
Published: May 2014

Vacuum deposited tin (IV) phthalocyanine dichloride (SnCl2Pc) field-effect transistors were fabricated on polymethylmethacrylate/aluminum oxide (PMMA/Al2O3) bilayer gate dielectric, with reduced operating voltage and low contact resistance. The devices with top contact Ag electrodes exhibit excellent n-channel behavior with electron mobility values of 0.01 cm2/Vs, low threshold voltages ∼4 V, current on/off ratio ∼104 with an operating voltage of 10 V. Bias stress instability effects are investigated during long term operation using thin film devices under vacuum. We find that the amount of bias stress of SnCl2Pc based thin film transistor is extremely small with characteristic relaxation time >105 s obtained using stretched exponential model. Stressing the SnCl2Pc devices by applying 10 V to the gate for half an hour results in a decrease of the source drain current, IDS of only ∼10% under low vacuum. These devices show highly stable electrical behavior under multiple scans and low threshold voltage instability under electrical dc bias stress (VDS = VGS = 10 V, for 2 h) even after 40 days.
Vortex dynamics around pitching plates
Authors: Jantzen Ryan T. , Taira Kunihiko , Granlund Kenneth O. , Ol Michael V.
Published: May 2014

Vortex dynamics of wakes generated by rectangular aspect-ratio 2 and 4 and two-dimensional pitching flat plates in free stream are examined with direct numerical simulation and water tunnel experiments. Evolution of wake vortices comprised of tip, leading-edge, and trailing-edge vortices is compared with force history for a range of pitch rates. The plate pivots about its leading edge with reduced frequency from π/8 to π/48, which corresponds to pitching over 1 to 6 chord lengths of travel. Computations have reasonable agreement with experiments, despite large differences in Reynolds number. Computations show that the tip effects are confined initially near the wing tips, but begin to strongly affect the leading-edge vortex as the motion of the plate proceeds, with concomitant effects on lift and drag history. Scaling relations based on reduced frequency are shown to collapse aerodynamic force history for the various pitch rates.
Residual entropy of ices and clathrates from Monte Carlo simulation
Authors: Kolafa Jiří
Published: May 2014

We calculated the residual entropy of ices (Ih, Ic, III, V, VI) and clathrates (I, II, H), assuming the same energy of all configurations satisfying the Bernal–Fowler ice rules. The Metropolis Monte Carlo simulations in the range of temperatures from infinity to a size-dependent threshold were followed by the thermodynamic integration. Convergence of the simulation and the finite-size effects were analyzed using the quasichemical approximation and the Debye–Hückel theory applied to the Bjerrum defects. The leading finite-size error terms, ln N/N, 1/N, and for the two-dimensional square ice model also 1/N3/2, were used for an extrapolation to the thermodynamic limit. Finally, we discuss the influence of unequal energies of proton configurations.
Percolation in polydisperse systems of aligned rods: A lattice-based analysis
Authors: Chatterjee Avik P.
Published: May 2014

A model is developed for percolation in polydisperse systems of oriented cylinders that integrates excluded volume arguments with an analogy to site percolation on a modified Bethe lattice. Results from this treatment are presented for the volume fraction at the percolation threshold (denoted ϕc) as a function of the degree of polydispersity, mixture composition, and degree of orientational ordering. For monodisperse systems, ϕc is found to be a monotonically increasing function of the traditional orientational order parameter that quantifies degree of alignment. The presence of a fraction of isotropically oriented rods of small aspect ratio is shown to lower the percolation threshold for systems in which the longer rods are strongly aligned.
Plane shear flows of frictionless spheres: Kinetic theory and 3D soft-sphere discrete element method simulations
Authors: Vescovi D. , Berzi D. , Richard P. , Brodu N.
Published: May 2014

We use existing 3D Discrete Element simulations of simple shear flows of spheres to evaluate the radial distribution function at contact that enables kinetic theory to correctly predict the pressure and the shear stress, for different values of the collisional coefficient of restitution. Then, we perform 3D Discrete Element simulations of plane flows of frictionless, inelastic spheres, sheared between walls made bumpy by gluing particles in a regular array, at fixed average volume fraction and distance between the walls. The results of the numerical simulations are used to derive boundary conditions appropriated in the cases of large and small bumpiness. Those boundary conditions are, then, employed to numerically integrate the differential equations of Extended Kinetic Theory, where the breaking of the molecular chaos assumption at volume fraction larger than 0.49 is taken into account in the expression of the dissipation rate. We show that the Extended Kinetic Theory is in very good agreement with the numerical simulations, even for coefficients of restitution as low as 0.50. When the bumpiness is increased, we observe that some of the flowing particles are stuck in the gaps between the wall spheres. As a consequence, the walls are more dissipative than expected, and the flows resemble simple shear flows, i.e., flows of rather constant volume fraction and granular temperature.
Density-shear instability in electron magneto-hydrodynamics
Authors: Wood T. S. , Hollerbach R. , Lyutikov M.
Published: May 2014

We discuss a novel instability in inertia-less electron magneto-hydrodynamics (EMHD), which arises from a combination of electron velocity shear and electron density gradients. The unstable modes have a lengthscale longer than the transverse density scale, and a growth-rate of the order of the inverse Hall timescale. We suggest that this density-shear instability may be of importance in magnetic reconnection regions on scales smaller than the ion skin depth, and in neutron star crusts. We demonstrate that the so-called Hall drift instability, previously argued to be relevant in neutron star crusts, is a resistive tearing instability rather than an instability of the Hall term itself. We argue that the density-shear instability is of greater significance in neutron stars than the tearing instability, because it generally has a faster growth-rate and is less sensitive to geometry and boundary conditions. We prove that, for uniform electron density, EMHD is “at least as stable” as regular, incompressible MHD, in the sense that any field configuration that is stable in MHD is also stable in EMHD. We present a connection between the density-shear instability in EMHD and the magneto-buoyancy instability in anelastic MHD.
Canonical transformation for trapped/passing guiding-center orbits in axisymmetric tokamak geometry
Authors: Brizard Alain J. , Duthoit François-Xavier
Published: May 2014

The generating function for the canonical transformation from the parallel canonical coordinates (s,p||) to the action-angle coordinates (ζ, J) for trapped/passing guiding-center orbits in axisymmetric tokamak geometry is presented. Drawing on the analogy between the phase-space portraits of the librating/rotating pendulum and the trapped/passing guiding-center orbits, the generating function is expressed in terms of the Jacobi zeta function, which can then readily be used to obtain an explicit expression for the bounce-center transformation for trapped/passing-particle guiding-center orbits in axisymmetric tokamak geometry.
Temperature-dependent ultrafast carrier and phonon dynamics of topological insulator Bi1.5Sb0.5Te1.8Se1.2
Authors: Cheng Liang , La-o-vorakiat Chan , Tang Chi Sin , Nair Saritha K. , Xia Bin , Wang Lan , Zhu Jian-Xin , Chia Elbert E. M.
Published: May 2014

Using ultrafast optical pump-probe technique, we studied the temperature-dependent carrier and phonon dynamics of the topological insulator Bi1.5Sb0.5Te1.8Se1.2 single-crystal from 10 K to 300 K. Two relaxation processes of carriers and coherent optical/acoustic phonons have been observed. By using the two-temperature model, we are able to attribute the fast (∼ps) relaxation component to carrier-phonon coupling involving carriers in the conduction band. We also studied the temperature dependence of the dephasing time and frequency of optical phonon, and the optical penetration depth of Bi1.5Sb0.5Te1.8Se1.2.
Dynamic rectification in a thermal diode based on fluid-solid interfaces: Contrasting behavior of soft materials and fluids
Authors: Murad Sohail , Puri Ishwar K.
Published: May 2014

We have used molecular dynamics simulations to demonstrate that significant rectification is possible in nano-devices by manipulating solid-fluid interfaces between a thin solid wall and a soft material. In addition, the nature of the rectification is opposite to that for a solid wall and a simpler polar fluid (e.g., water). This thus opens the possibilities of reversing the direction of rectification in a nano-device which could lead to more precise control of heat transfer rates. Our simulations also show that surface modifications of the type introduced here can lead to over six fold increase in heat transfer rates in nano-devices. Dissipating heat from increasingly miniaturized semi-conductors of the future will become increasingly important since size limitations are often dictated by heat dissipation rates. These results also point to some other exciting practical applications. If the outside wall of a house were made hydrophilic, during hot summer days when the intent is to reduce heat transfer from the ambient (Ta > Tin), a small polar fluid like water could be introduced between the two walls. During nights, in order to cool the house (when Tin > Ta) water could be replaced by a less volatile soft material to enhance heat transfer. Thus, the same wall would demonstrate significant rectification in both cases but with different fluids.
Ultracompact plasmonic switch based on graphene-silica metamaterial
Authors: Yang Longzhi , Pei Chongyang , Shen Ao , Zhao Changyun , Li Yan , Dai Tingge , Yu Hui , Li Yubo , Jiang Xiaoqing , Yang Jianyi
Published: May 2014

Controlling the light transmission in the epsilon-near-zero channel, which is covered by the perfect-electric-conductor (PEC) walls, has been demonstrated in [L. Yang, T. Hu, A. Shen, C. Pei, B. Yang, T. Dai, H. Yu, Y. Li, X. Jiang, and J. Yang, Opt. Lett. 39, 1909 (2014)]. In this work, we investigate the possibility of replacing the PEC by some practical metal materials. Based on it, an ultracompact plasmonic switch with the length of 15 nm is presented. Its highest extinction ratio is more than 13 dB, while the 3-dB extinction ratio is obtained with a 0.41 V gate voltage.
Amorphous vs crystalline exciton blocking layers at the anode interface in planar and planar-mixed heterojunction organic solar cells
Authors: Grob Stefan , Gruber Mark , Bartynski Andrew N. , Hörmann Ulrich , Linderl Theresa , Thompson Mark E. , Brütting Wolfgang
Published: May 2014

We compare the gain in power conversion efficiency (PCE) achieved by inserting either amorphous or crystalline exciton blocking layers at the anode interface for planar (PHJ) and planar-mixed heterojunction (PM-HJ) organic solar cells based on Tetraphenyldibenzoperiflanthene and fullerenes. For PHJ devices, there is a gain of more than 37% for both types of blocking layers, mainly due to an increase in photocurrent, indicating that this gain can be solely ascribed to the exciton blocking effect. A templating effect as proposed in literature for crystalline blocking layers cannot be affirmed. On the contrary, it is shown that there is a connection between the choice of acceptor (C60/C70) and the blocking effect on the anode side. Moreover, we can show that also for PM-HJ devices a remarkable efficiency enhancement is possible. The insertion of suitable blocking layers at the anode interface can alter the effective work function and thus the open-circuit voltage, leading to a maximum PCE of 5.8% in single junction cells.
Correlation of anomalous write error rates and ferromagnetic resonance spectrum in spin-transfer-torque-magnetic-random-access-memory devices containing in-plane free layers
Authors: Evarts Eric R. , Heindl Ranko , Rippard William H. , Pufall Matthew R.
Published: May 2014

In a small fraction of magnetic-tunnel-junction-based magnetic random-access memory devices with in-plane free layers, the write-error rates (WERs) are higher than expected on the basis of the macrospin or quasi-uniform magnetization reversal models. In devices with increased WERs, the product of effective resistance and area, tunneling magnetoresistance, and coercivity do not deviate from typical device properties. However, the field-swept, spin-torque, ferromagnetic resonance (FS-ST-FMR) spectra with an applied DC bias current deviate significantly for such devices. With a DC bias of 300 mV (producing 9.9 × 106 A/cm2) or greater, these anomalous devices show an increase in the fraction of the power present in FS-ST-FMR modes corresponding to higher-order excitations of the free-layer magnetization. As much as 70% of the power is contained in higher-order modes compared to ≈20% in typical devices. Additionally, a shift in the uniform-mode resonant field that is correlated with the magnitude of the WER anomaly is detected at DC biases greater than 300 mV. These differences in the anomalous devices indicate a change in the micromagnetic resonant mode structure at high applied bias.