bluuebunny/crossref_metadata_2025 huggingface dataset:
Correction: Towards applications in catalysis: investigation on photocatalytic activities of a derivative family of the Keplerate type molybdenum–oxide based polyoxometalates
Authors: Zhou Yunshan , Qin Libo , Yu Chao , Xiong Tian , Zhang Lijuan , Ahmad Waqar , Han Hao
Published: February 2015

Correction for ‘Towards applications in catalysis: investigation on photocatalytic activities of a derivative family of the Keplerate type molybdenum–oxide based polyoxometalates’ by Yunshan Zhou et al., RSC Adv., 2014, 4, 54928–54935.
Dye-sensitized solar cells containing mesoporous TiO2spheres as photoanodes and methyl sulfate anion based biionic liquid electrolytes
Authors: Peng Jia-De , Lee Chuan-Pei , Velayutham D. , Suryanarayanan V. , Ho Kuo-Chuan
Published: February 2015

A quasi-solid state dye-sensitized solar cell with the photoanode film of mesoporous TiO2spheres exhibited an efficiency of 6.18% and unfailing stability for 1200 h at 50 °C.
Synthesis of highly surface-textured ZnO thin films by aerosol assisted chemical vapour deposition
Authors: Chen Shuqun , Wilson Rory M. , Binions Russell
Published: February 2015

Highly surface-textured ZnO thin films are fabricated by aerosol assisted chemical vapour deposition.
Beneficial effect of alloy disorder on the conversion efficiency of ZnO/ZnxCd1−xSe coaxial nanowire solar cells
Authors: Bhutto Waseem Ahmed , Wu Zhiming , Cao Yiyan , Wang Weiping , He Jialun , Luo Qiang , Li Shuping , Li Heng , Kang Junyong
Published: February 2015

The conversion efficiency of ZnO/ZnxCd1−xSe coaxial nanowire solar cells was improved by interfacial modification based on the alloy disorder effect.
Pilot scheduling schemes for multi‐cell massive multiple‐input–multiple‐output transmission
Authors: Jin Shi , Li Mingmei , Huang Yongming , Du Yinggang , Gao Xiqi
Published: February 2015

This study addresses the pilot scheduling problem in multiuser multi‐cell massive multiple‐input–multiple‐output (MIMO) systems, aiming at mitigating the inter‐cell interference (pilot contamination), which constitutes a bottleneck of the system performance. First, the authors investigate the pilot reuse and scheduling problem in cellular systems with unlimited number of base station antennas, only considering the large fading coefficients. Three low‐complexity pilot scheduling schemes are then proposed by maximising the system achievable sum rate, including the greedy algorithm, the tabu search (TS) algorithm and the greedy TS algorithm. Second, they investigate the pilot reuse problem among the inter‐cell user terminals (UTs) under spatially correlated channels for massive MIMO transmission, trying to distinguish UTs sharing the same time‐frequency resources from the spatial domain. A closed‐form expression of the non‐asymptotic downlink achievable rate is derived by exploiting the second‐order channel statistical information. On the basis of the degree of the UTs’ covariance matrices overlap with each other, they further propose a spatial orthogonality‐based greedy pilot scheduling algorithm. The proposed approaches can provide much better performance in the presence of pilot contamination. Theoretical analysis and numerical results both verify the effectiveness of the proposed algorithms.
V–Q sensitivity‐based index for assessment of dynamic voltage stability of power systems
Authors: Konar Srayashi , Chatterjee Dheeman , Patra Sourav
Published: February 2015

A large signal voltage stability index is proposed in this study. Although the study focuses on a wind farm connected system, the index can predict instability of any power system. The index gives an idea about the stability margin of the power system under a given operating condition and can be used to predict emergency situations following a large disturbance such as line outage. The proposed index can be used effectively for systems with static as well as dynamic loads. The proposed index is verified in standard test systems. Matrix perturbation theory is used to verify the viability of the index.
Transmission‐type negative group delay networks using coupled line doublet structure
Authors: Chaudhary Girdhari , Jeong Yongchae
Published: February 2015

This study presents a novel approach to the design and implementation of transmission‐type negative group delay (NGD) networks based on a coupled line doublet structure. To improve the reflection coefficients, a quarter‐wavelength transmission line is connected between the input and through ports of a coupled line section. For the doublet structure, two coupled line sections are arranged in a symmetrical manner by connecting them back‐to‐back with the help of the quarter‐ wavelength through line. For the experimental demonstration, two planar NGD networks (unmatched and matched doublet NGD networks) are designed, simulated and measured at a centre frequency of 2.14 GHz. From the measurement, a group delay (GD) of −5.66 ns and signal attenuation (SA) of 18.78 dB were obtained in the case of an unmatched NGD network. Similarly, for the matched NGD case, a GD of −6.33 ns, SA of 20.69 dB and input/output return losses >29 dB were obtained at the centre frequency.
Strategy for switching period selection in random pulse width modulation to shape the noise spectrum
Authors: Peyghambari Amir , Dastfan Ali , Ahmadyfard Alireza
Published: February 2015

In this study a new random pulse width modulation (RPWM) has been proposed. The aim of this method is to create a gap at selective frequency in voltage spectrum to prevent the resonant frequencies excitation. This gap can be placed in human hearing band. Hence, the proposed method can reduce acoustic noise in loads supplied by power electronic converters. Unlike conventional RPWM techniques, in this method the switching period is dependent on the duty ratio. In other words, in each switching cycle the switching period is determined as a function of duty ratio and switching periods in pervious switching cycles. The experimental results confirm the ability of the proposed method for reducing noise power at a selected frequency in voltage spectrum.
Hydrophobic hydration and the anomalous partial molar volumes in ethanol-water mixtures
Authors: Tan Ming-Liang , Miller Benjamin T. , Te Jerez , Cendagorta Joseph R. , Brooks Bernard R. , Ichiye Toshiko
Published: February 2015

The anomalous behavior in the partial molar volumes of ethanol-water mixtures at low concentrations of ethanol is studied using molecular dynamics simulations. Previous work indicates that the striking minimum in the partial molar volume of ethanol VE as a function of ethanol mole fraction XE is determined mainly by water-water interactions. These results were based on simulations that used one water model for the solute-water interactions but two different water models for the water-water interactions. This is confirmed here by using two more water models for the water-water interactions. Furthermore, the previous work indicates that the initial decrease is caused by association of the hydration shells of the hydrocarbon tails, and the minimum occurs at the concentration where all of the hydration shells are touching each other. Thus, the characteristics of the hydration of the tail that cause the decrease and the features of the water models that reproduce this type of hydration are also examined here. The results show that a single-site multipole water model with a charge distribution that mimics the large quadrupole and the p-orbital type electron density out of the molecular plane has “brittle” hydration with hydrogen bonds that break as the tails touch, which reproduces the deep minimum. However, water models with more typical site representations with partial charges lead to flexible hydration that tends to stay intact, which produces a shallow minimum. Thus, brittle hydration may play an essential role in hydrophobic association in water.
An auxiliary-field quantum Monte Carlo study of the chromium dimer
Authors: Purwanto Wirawan , Zhang Shiwei , Krakauer Henry
Published: February 2015

The chromium dimer (Cr2) presents an outstanding challenge for many-body electronic structure methods. Its complicated nature of binding, with a formal sextuple bond and an unusual potential energy curve (PEC), is emblematic of the competing tendencies and delicate balance found in many strongly correlated materials. We present an accurate calculation of the PEC and ground state properties of Cr2, using the auxiliary-field quantum Monte Carlo (AFQMC) method. Unconstrained, exact AFQMC calculations are first carried out for a medium-sized but realistic basis set. Elimination of the remaining finite-basis errors and extrapolation to the complete basis set limit are then achieved with a combination of phaseless and exact AFQMC calculations. Final results for the PEC and spectroscopic constants are in excellent agreement with experiment.
Alkali metal mediated C–C bond coupling reaction
Authors: Tachikawa Hiroto
Published: February 2015

Metal catalyzed carbon-carbon (C–C) bond formation is one of the important reactions in pharmacy and in organic chemistry. In the present study, the electron and hole capture dynamics of a lithium-benzene sandwich complex, expressed by Li(Bz)2, have been investigated by means of direct ab-initio molecular dynamics method. Following the electron capture of Li(Bz)2, the structure of [Li(Bz)2]− was drastically changed: Bz–Bz parallel form was rapidly fluctuated as a function of time, and a new C–C single bond was formed in the C1–C1′ position of Bz–Bz interaction system. In the hole capture, the intermolecular vibration between Bz–Bz rings was only enhanced. The mechanism of C–C bond formation in the electron capture was discussed on the basis of theoretical results.
Tipping point analysis of atmospheric oxygen concentration
Authors: Livina V. N. , Vaz Martins T. M. , Forbes A. B.
Published: February 2015

We apply tipping point analysis to nine observational oxygen concentration records around the globe, analyse their dynamics and perform projections under possible future scenarios, leading to oxygen deficiency in the atmosphere. The analysis is based on statistical physics framework with stochastic modelling, where we represent the observed data as a composition of deterministic and stochastic components estimated from the observed data using Bayesian and wavelet techniques.
Evidence for weakly bound electrons in non-irradiated alkane crystals: The electrons as a probe of structural differences in crystals
Authors: Pietrow M. , Gagoś M. , Misiak L. E. , Kornarzyński K. , Szurkowski J. , Rochowski P. , Grzegorczyk M.
Published: February 2015

It is generally assumed that weakly bound (trapped) electrons in organic solids come only from radiolytical (or photochemical) processes like ionization caused by an excited positron entering the sample. This paper presents evidence for the presence of these electrons in non-irradiated samples of docosane. This can be due to the triboelectrification process. We argue that these electrons can be located (trapped) either in interlamellar gaps or in spaces made by non-planar conformers. Electrons from the former ones are bound more weakly than electrons from the latter ones. The origin of Vis absorption for the samples is explained. These spectra can be used as a probe indicating differences in the solid structures of hydrocarbons.
Nonlinear ion transport in the supercooled ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide: Frequency dependence of third-order and fifth-order conductivity coefficients
Authors: Patro L. N. , Burghaus O. , Roling B.
Published: February 2015

We have carried out nonlinear ion conductivity measurements on the supercooled ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide[C6mim][NTf2] by applying ac electric fields with amplitudes up to about 200 kV/cm. At these field amplitudes, 3ω and 5ω harmonic components in the current response were detected, and the higher-order conductivity coefficients σ31,σ33,σ53, and σ55 were determined. The frequency and temperature dependence of these conductivity coefficients was analyzed in detail. The most important findings were the following: (i) The third-order spectra σ31 and σ33 exhibit very similar values in the dc plateau regime but differ considerably in the dispersive regime. The same was observed for the fifth order spectra σ53 and σ55. (ii) In the dispersive regime, the third-order spectra display a minimum, while the fifth-order spectra display a maximum. (iii) The frequencies of these minima and maxima are thermally activated with the same activation energy as the low-field dc conductivity σ1,dc, whereas the dc values of the higher-order conductivity coefficients, σ3,dc and σ5,dc, are characterized by lower activation energies.
Semiclassical limits of quantum partition functions on infinite graphs
Authors: Güneysu Batu
Published: February 2015

We prove that if H denotes the operator corresponding to the canonical Dirichlet form on a possibly locally infinite weighted graph (X, b, m), and if v : X → ℝ is such that H + v/ħ is well-defined as a form sum for all ħ > 0, then the quantum partition function tr(e−βħ(H+v/ħ)) converges to ∑x∈Xe−βv(x) as ħ → 0 +, for all β > 0, regardless of the fact whether e−βv is a priori summable or not. This fact can be interpreted as a semiclassical limit, and it allows geometric Weyl-type convergence results. We also prove natural generalizations of this semiclassical limit to a large class of covariant Schrödinger operators that act on sections in Hermitian vector bundle over (X, m, b), a result that particularly applies to magnetic Schrödinger operators that are defined on (X, m, b).
Solid optical ring interferometer for high-throughput feedback-free spectral analysis and filtering
Authors: Petrak B. , Peiris M. , Muller A.
Published: February 2015

We describe a simple and inexpensive optical ring interferometer for use in high-resolution spectral analysis and filtering. It consists of a solid cuboid, reflection-coated on two opposite sides, in which constructive interference occurs for waves in a rhombic trajectory. Due to its monolithic design, the interferometer’s resonance frequencies are insensitive to environmental disturbances over time. Additional advantages are its simplicity of alignment, high-throughput, and feedback-free operation. If desired, it can be stabilized with a secondary laser without disturbance of the primary signal. We illustrate the use of the interferometer for the measurement of the spectral Mollow triplet from a quantum dot and characterize its long-term stability for filtering applications.
Self-assembly of diblock copolymer confined in an array-structure space
Authors: He Xuehao , Zou Zhixiang , Kan Di , Liang Haojun
Published: February 2015

The combination of top-down and bottom-up technologies is an effective method to create the novel nanostructures with long range order in the field of advanced materials manufacture. In this work, we employed a polymeric self-consistent field theory to investigate the pattern formation of diblock copolymer in a 2D confinement system designed by filling pillar arrays with various 2D shapes such as squares, rectangles, and triangles. Our simulation shows that in such confinement system, the microphase structure of diblock copolymer strongly depends on the pitch, shape, size, and rotation of the pillar as well as the surface field of confinement. The array structures can not only induce the formation of new phase patterns but also control the location and orientation of pattern structures. Finally, several methods to tune the commensuration and frustration of array-structure confinement are proposed and examined.
The magnetic transition in ε-Fe2O3 nanoparticles: Magnetic properties and hyperfine interactions from Mössbauer spectroscopy
Authors: Kohout J. , Brázda P. , Závěta K. , Kubániová D. , Kmječ T. , Kubíčková L. , Klementová M. , Šantavá E. , Lančok A.
Published: February 2015

The nanoparticles of ε-Fe2O3 enriched with 57Fe isotope in amorphous silica matrix were prepared by sol-gel technique starting from a single molecular precursor for both Fe2O3 and silica. From the X-ray powder diffraction pattern ε-Fe2O3 was identified as the major phase and α-Fe2O3 and β-Fe2O3 were observed as minor iron oxide phases. Using the log-normal distribution for fitting the experimental data from the TEM micrographs, the characteristic size of particles d0 ∼ 25 nm was derived. The rather high coercivity of ∼2.1 T at room temperature was confirmed for our nanoparticle system. From the dependences of magnetization on temperature a two-step magnetic transition spread between 100 K and 153 K was indicated. From the 57Fe Mössbauer spectra measured in the temperature range of 4.2–300 K, the hyperfine parameters for one tetrahedral and three octahedral sites of ε-Fe2O3 structure were identified. The in-field spectra in the external magnetic fields up to 6 T were taken both above and below the indicated two-step magnetic transition. Their dependence on temperature and external magnetic field suggests that the first step in the temperature range of 153 K–130 K is related to the spin reorientation of the local magnetic moments in the magnetic sublattices and the second step in temperatures 130 K–100 K may be associated with the intermediate spin–high spin state transition of Fe3+ cation in the tetrahedral sublattice expressed in the change of the hyperfine magnetic field.
Effects of localization on hot carriers in InAs/AlAsxSb1–x quantum wells
Authors: Tang J. , Whiteside V. R. , Esmaielpour H. , Vijeyaragunathan S. , Mishima T. D. , Santos M. B. , Sellers I. R.
Published: February 2015

The temperature dependence of a InAs/AlAs0.84Sb0.16 multi-quantum-well sample is studied using continuous wave photoluminescence. An “s-shape” shift in peak energy is observed and attributed to low energy localization states. High incident power density photoluminescence measurements were performed to probe the nature of such localization. The results opposed the possibility of a type-II band structure and supported the idea of low energy localization states. The effect of such localization on hot carriers in our system was studied and an improvement in their stability due to hole mobility at elevated temperature is presented.
Investigation of magnetic anisotropy and magnetic moments of tetragonal distorted Fe1−xCox films on L1 FePt underlayer
Authors: Wang Bochong , Oomiya Hiroyuki , Arakawa Akira , Hasegawa Takashi , Sasaki Hiromi , Ishio Shunji
Published: February 2015

Tetragonal distorted Fe1−xCox (0 ≤ x ≤ 1) thin films are prepared on L10 ordered Fe0.6Pt0.4 underlayer. The dependences of FeCo alloy composition on magnetic anisotropy energy (MAE) are investigated. Based on the LLG simulation, the tetragonal distorted Fe1−xCox films show maximum positive magnetic anisotropy energy when the Co composition is around 60 at. %, while the MAE decreases and shifts to negative when the composition is close to pure Fe or Co. The experiment results prove that the MAE can be tuned by varying the alloy composition. Furthermore, the magnetic moments of Fe and Co in distorted Fe0.4Co0.6 films are studied by the X-ray magnetic circular dichroism spectroscopy. The enhanced orbit moments which come from the lattice distortion increase the magnetic anisotropy energy of Fe0.4Co0.6 film.
Strong electrocaloric effect in lead-free 0.65Ba(Zr0.2Ti0.8)O3-0.35(Ba0.7Ca0.3)TiO3 ceramics obtained by direct measurements
Authors: Sanlialp Mehmet , Shvartsman Vladimir V. , Acosta Matias , Dkhil Brahim , Lupascu Doru C.
Published: February 2015

Solid solutions of (1 − x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 promise to exhibit a large electrocaloric effect (ECE), because their Curie temperature and a multiphase coexistence region lie near room temperature. We report on direct measurements of the electrocaloric effect in bulk ceramics 0.65Ba(Zr0.2Ti0.8)O3-0.35(Ba0.7Ca0.3)TiO3 using a modified differential scanning calorimeter. The adiabatic temperature change reaches a value of ΔTEC = 0.33 K at ∼65 °C under an electric field of 20 kV/cm. It remains sizeable in a broad temperature interval above this temperature. Direct measurements of the ECE proved that the temperature change exceeds the indirect estimates derived from Maxwell relations by about ∼50%. The discrepancy is attributed to the relaxor character of this material.
Top-gated chemical vapor deposited MoS2 field-effect transistors on Si3N4 substrates
Authors: Sanne A. , Ghosh R. , Rai A. , Movva H. C. P. , Sharma A. , Rao R. , Mathew L. , Banerjee S. K.
Published: February 2015

We report the electrical characteristics of chemical vapor deposited (CVD) monolayer molybdenum disulfide (MoS2) top-gated field-effect transistors (FETs) on silicon nitride (Si3N4) substrates. We show that Si3N4 substrates offer comparable electrical performance to thermally grown SiO2 substrates for MoS2 FETs, offering an attractive passivating substrate for transition-metal dichalcogenides (TMD) with a smooth surface morphology. Single-crystal MoS2 grains are grown via vapor transport process using solid precursors directly on low pressure CVD Si3N4, eliminating the need for transfer processes which degrade electrical performance. Monolayer top-gated MoS2 FETs with Al2O3 gate dielectric on Si3N4 achieve a room temperature mobility of 24 cm2/V s with Ion/Ioff current ratios exceeding 107. Using HfO2 as a gate dielectric, monolayer top-gated CVD MoS2 FETs on Si3N4 achieve current densities of 55 μA/μm and a transconductance of 6.12 μS/μm at Vtg of −5 V and Vds of 2 V. We observe an increase in mobility at lower temperatures, indicating phonon scattering may dominate over charged impurity scattering in our devices. Our results show that Si3N4 is an attractive alternative to thermally grown SiO2 substrate for TMD FETs.
BiasMDP: Carrier lifetime characterization technique with applied bias voltage
Authors: Jordan Paul M. , Simon Daniel K. , Mikolajick Thomas , Dirnstorfer Ingo
Published: February 2015

A characterization method is presented, which determines fixed charge and interface defect densities in passivation layers. This method bases on a bias voltage applied to an electrode on top of the passivation layer. During a voltage sweep, the effective carrier lifetime is measured by means of microwave detected photoconductivity. When the external voltage compensates the electric field of the fixed charges, the lifetime drops to a minimum value. This minimum value correlates to the flat band voltage determined in reference impedance measurements. This correlation is measured on p-type silicon passivated by Al2O3 and Al2O3/HfO2 stacks with different fixed charge densities and layer thicknesses. Negative fixed charges with densities of 3.8 × 1012 cm−2 and 0.7 × 1012 cm−2 are determined for Al2O3 layers without and with an ultra-thin HfO2 interface, respectively. The voltage and illumination dependencies of the effective carrier lifetime are simulated with Shockley Read Hall surface recombination at continuous defects with parabolic capture cross section distributions for electrons and holes. The best match with the measured data is achieved with a very low interface defect density of 1 × 1010 eV−1 cm−2 for the Al2O3 sample with HfO2 interface.
Limitations to the room temperature mobility of two- and three-dimensional electron liquids in SrTiO3
Authors: Mikheev Evgeny , Himmetoglu Burak , Kajdos Adam P. , Moetakef Pouya , Cain Tyler A. , Van de Walle Chris G. , Stemmer Susanne
Published: February 2015

We analyze and compare the temperature dependence of the electron mobility of two- and three-dimensional electron liquids in SrTiO3. The contributions of electron-electron scattering must be taken into account to accurately describe the mobility in both cases. For uniformly doped, three-dimensional electron liquids, the room temperature mobility crosses over from longitudinal optical (LO) phonon-scattering-limited to electron-electron-scattering-limited as a function of carrier density. In high-density, two-dimensional electron liquids, LO phonon scattering is completely screened and the mobility is dominated by electron-electron scattering up to room temperature. The possible origins of the observed behavior and the consequences for approaches to improve the mobility are discussed.
Magnetic anisotropy of [Co2MnSi/Pd]n superlattice films prepared on MgO(001), (110), and (111) substrates
Authors: Matsushita Naoki , Takamura Yota , Fujino Yorinobu , Sonobe Yoshiaki , Nakagawa Shigeki
Published: February 2015

Superlattice films with full-Heusler Co2MnSi (CMS) alloy and Pd layers prepared on Pd-buffered MgO(001), (110), and (111) substrates were investigated. Crystal orientation and epitaxial relationship of Pd and CMS layers were analyzed from x-ray diffraction, pole figure measurements, and transmission electron microscope observation. Formation of the L21-ordered structure in the CMS layers was confirmed by observation of CMS(111) diffraction. Perpendicular magnetic anisotropy (PMA) was obtained in the [CMS (0.6 nm)/Pd (2 nm)]6 superlattice film formed using MgO(111) substrates although other superlattice films prepared using MgO(001) and (110) substrates showed in-plane and isotropic magnetic anisotropy, respectively. The perpendicular magnetic anisotropy energy constant K for the superlattice films prepared using MgO(111) substrate was estimated to be 2.3 Mergs/cm3, and an interfacial anisotropy constant Ki per one CMS-Pd interface in the superlattice films was estimated to be 0.16 ergs/cm2. Ki in superlattice films with various crystal orientations showed positive values, indicating that Pd/CMS interfaces had an ability to induce PMA regardless of their crystal orientation.
Magnetostriction-induced in situ strain control of superconductivity in FeSe0.5Te0.5
Authors: Wang Weike , Yang Jiyong , Li Jun , Gu Chuanchuan , Chen Xuliang , Zhang Zhitao , Zhu Xuebin , Wang Huabing , Yang Zhaorong , Tian Mingliang , Zhang Yuheng , Moshchalkov Victor V.
Published: February 2015

In the superconductor of FeSe0.5Te0.5, the superconductivity is highly sensitive to variations of microstructure. Therefore, a fine manipulation of the microstructures will be crucial not only for a better understanding of the superconductivity but also for potential applications. Here, we demonstrate an approach to control the superconductivity in-situ by using a magnetostrictive substrate ZnCr2Se4 as the strain generator. By mounting an FeSe0.5Te0.5 single crystal onto a magnetostrictive substrate, we show that the magnetoresistance of FeSe0.5Te0.5 is directly coupled to the magnetostriction of ZnCr2Se4. The strain is fine-tuned in-situ by an external magnetic field, leading to the superconductivity of FeSe0.5Te0.5 correspondingly favored by compressive strain while suppressed by tensile strain.
Precision stacking of nanoparticle laden sessile droplets to control solute deposit morphology
Authors: Kabi Prasenjit , Basu Saptarshi , Sanyal Apratim , Chaudhuri Swetaprovo
Published: February 2015

Stacking pure solvent droplets on a solid substrate is apparently impossible in the absence of an external force as the second droplet will invariably spill over the first leading to a large wetted area. However, the unique feature that emerges during the drying of a nanoparticle laden droplet is the progressively enlarging thin solid film along the evaporating sessile droplet liquid periphery. This solid interface: the edge of which we shall refer to as the agglomeration front comprises of a thin layer of nanoparticle assembly and can support a carefully dispensed second droplet thereby allowing droplet stacking. It will be shown that the growth of this agglomeration front can also be effectively controlled by the dispensing time difference and the nanoparticle concentration in the two droplets. So far, we are commonly aware of material stacking in solid phase. This letter demonstrates stacking in the liquid phase and control over the thin solid interface growth.
Lithium decoration of three dimensional boron-doped graphene frameworks for high-capacity hydrogen storage
Authors: Wang Yunhui , Meng Zhaoshun , Liu Yuzhen , You Dongsen , Wu Kai , Lv Jinchao , Wang Xuezheng , Deng Kaiming , Rao Dewei , Lu Ruifeng
Published: February 2015

Based on density functional theory and the first principles molecular dynamics simulations, a three-dimensional B-doped graphene-interconnected framework has been constructed that shows good thermal stability even after metal loading. The average binding energy of adsorbed Li atoms on the proposed material (2.64 eV) is considerably larger than the cohesive energy per atom of bulk Li metal (1.60 eV). This value is ideal for atomically dispersed Li doping in experiments. From grand canonical Monte Carlo simulations, high hydrogen storage capacities of 5.9 wt% and 52.6 g/L in the Li-decorated material are attained at 298 K and 100 bars.
Analytical expression for the current-voltage characteristics of organic bulk heterojunction solar cells
Authors: Inche Ibrahim M. L. , Ahmad Zubair , Sulaiman Khaulah
Published: February 2015

An expression to describe the current-voltage characteristics of organic bulk heterojunction (BHJ) solar cells is derived. The derivation is obtained by analytically solving the drift-diffusion model for organic BHJ solar cells with the assumption of uniform bimolecular recombination rate. The assumption of uniform bimolecular recombination rate leads to somewhat inaccurate, for example, carrier densities as functions of the position inside the device. However, we show that this assumption should still produce an expression for the current as a function of applied voltage as if the actual bimolecular recombination rate is considered in the derivation. Applying this analytical expression to experimental current-voltage data enable us to directly extract and analyze, for example, the recombination loss of an organic BHJ solar cell as a function of applied voltage.
Image contrast reversals in contact resonance atomic force microscopy
Authors: Ma Chengfu , Chen Yuhang , Wang Tian
Published: February 2015

Multiple image contrast inversions are observed along with the increase of modulation frequency for contact resonance atomic force microscopy (CR-AFM) imaging of a highly oriented pyrolytic graphite (HOPG) specimen. Analysis of the contact vibrational spectra indicates that the inversions can be attributed to structure-induced variations of tip-sample contact mechanics. Contact stiffness and damping at HOPG step edges exhibit significant increases relative to those in the flat regions. For quantitative evaluation of mechanical properties in CR-AFM, coupling effects of the surface geometry must be considered.
Fabrication of a novel quartz micromachined gyroscope
Authors: Xie Liqiang , Xing Jianchun , Wang Haoxu , Wu Xuezhong
Published: February 2015

A novel quartz micromachined gyroscope is proposed in this paper. The novel gyroscope is realized by quartz anisotropic wet etching and 3-dimensional electrodes deposition. In the quartz wet etching process, the quality of Cr/Au mask films affecting the process are studied by experiment. An excellent mask film with 100 Å Cr and 2000 Å Au is achieved by optimization of experimental parameters. Crystal facets after etching seriously affect the following sidewall electrodes deposition process and the structure’s mechanical behaviours. Removal of crystal facets is successfully implemented by increasing etching time based on etching rate ratios between facets and crystal planes. In the electrodes deposition process, an aperture mask evaporation method is employed to prepare electrodes on 3-dimensional surfaces of the gyroscope structure. The alignments among the aperture masks are realized by the ABM™ Mask Aligner System. Based on the processes described above, a z–axis quartz gyroscope is fabricated successfully.
Morphological and molecular characterisation of Twitcher mouse spermatogenesis: an update
Authors: Puggioni Erica , Governini Laura , Gori Martina , Belmonte Giuseppe , Piomboni Paola , Costantino-Ceccarini Elvira , Luddi Alice
Published: February 2015

Spermatogenesis is a complex developmental program in which interactions between different cell types are finely regulated. Mouse models in which any of the sperm maturation steps are perturbed provide major insights into the molecular control of spermatogenesis. The Twitcher mouse is a model of Krabbe disease, characterised by the deficiency of galactosylceramidase, the enzyme that hydrolyses galactosylceramide and galactosylsphingosine. Galactosyl-alkyl-acyl-glycerol, a precursor of seminolipid, the most abundant glycolipid in spermatozoa, is also a substrate for galactosylceramidase. Altered sphingolipid metabolism has been suggested to be the cause of the morphological abnormalities reported previously in the spermatogenesis of Twitcher. However, given the frequency of infertility associated with neurological impairment, we hypothesised that an unbalanced hormonal profile could contribute to male infertility in this mutant. In order to clarify this issue, we investigated potential variations in the expression of hormones and hormone receptors involved in the regulation of spermatogenesis. Our data show that, in the brain of Twitcher mouse, gonadotrophin-releasing hormone (GnRH), LH and FSH gene expression is decreased, whereas expression of androgen receptor (AR) and inhibin βA (INHβA) is increased. The changes in gene expression for the LH and FSH receptors and AR in the testes support the hypothesis that altered sphingolipid metabolism is not the only cause of Twitcher infertility.
A thermal profile of metabolic performance in the rare Australian chelid, Pseudemydura umbrina
Authors: Arnall Sophie G. , Kuchling Gerald , Mitchell Nicola J.
Published: February 2015

Thermal performance curves are useful for predicting how organisms might respond to environmental change, and are becoming increasingly applicable for ectothermic animals threatened by climate change. Here we present a thermal performance curve for the critically endangered western swamp turtle (Pseudemydura umbrina) based upon measurements of O2 consumption and CO2 production obtained by flow-through respirometry at temperatures between 15 and 30°C. Standard metabolic rate was significantly higher at 30°C (0.030 mL g–1 h–1 O2, 0.021 mL g–1 h–1 CO2) than at 20°C (0.007 mL g–1 h–1 O2, 0.006 mL g–1 h–1 CO2) and the 20−30°C Q10 for O2 and CO2 were 4.60 and 3.55 respectively. Oxygen consumption rates at 15°C and 25°C were 0.002 (±0.000) and 0.018 (±0.000) mL g–1 h–1, with a corresponding Q10 of 9.21. Beyond ~30°C there was a decline in physiological performance, which was supported by activity patterns reported for P. umbrina in the literature.
The influence of the math classroom context on students’ academic English production
Authors: Liu Kristin Kline
Published: February 2015

The case study summarized in this article relies primarily on activity theory (e.g., Engestrom, 1987), and incorporates complexity, accuracy, and fluency analyses (see Ellis & Barkhuizen, 2005) to describe real-time oral language production by four focal English language learners (ELLs) in a sheltered high school math classroom in the U.S. Further, it describes how that language use was influenced by the classroom context. Findings indicate that ELLs produced very little complex, elaborated academic language because there were a variety of contextual factors that interacted to minimize students’ need to use it. Insights gained from an activity theory perspective highlight the influence of three unresolved tensions in the classroom activity system, namely: low language expectations in the curriculum, the teacher’s lack of familiarity with L2 instructional strategies, and the students’ lack of engagement with “best” practices that included use of hands-on material. Greater administrator support and transparency about desired academic language outcomes could enhance both the teachers’ language development skills and student outcomes.
Free and fair? Citizens’ assessments of the 2013 general election in Kenya
Authors: Shah Seema
Published: February 2015

Kenya's peaceful 2013 election came as a relief to domestic and international observers, who feared a repeat of the brutal 2007––2008 post-election violence. Many observers conflated this relative peace with electoral credibility, but analysis of a post-election national opinion poll reveals a more complex picture. Most Kenyans did feel that the 2013 election was free and fair, but their conception of free and fair is rooted more in the historical context of the election than in technical electoral procedures. Personal experiences of irregularities at the level of polling stations do not play a statistically significant role in shaping voters’ opinions about electoral credibility. Instead, voters are more influenced by their ethnicities, their confidence in electoral institutions and by how highly they prioritised peace. These findings reveal the importance of local context and history in conceptions of electoral integrity on the ground.
Constraints on changes in the proton–electron mass ratio using methanol lines
Authors: Kanekar N. , Ubachs W. , Menten K. M. , Bagdonaite J. , Brunthaler A. , Henkel C. , Muller S. , Bethlem H. L. , Daprà M.
Published: February 2015

We report Karl G. Jansky Very Large Array (VLA) absorption spectroscopy in four methanol (CH3OH) lines in the z = 0.885 82 gravitational lens towards PKS1830−211. Three of the four lines have very different sensitivity coefficients Kμ to changes in the proton–electron mass ratio μ; a comparison between the line redshifts thus allows us to test for temporal evolution in μ. We obtain a stringent statistical constraint on changes in μ by comparing the redshifted 12.179 and 60.531 GHz lines, [Δμ/μ] ≤ 1.1 × 10−7 (2σ) over 0 < z ≤ 0.885 82, a factor of ≈2.5 more sensitive than the best earlier results. However, the higher signal-to-noise ratio (by a factor of ≈2) of the VLA spectrum in the 12.179 GHz transition also indicates that this line has a different shape from that of the other three CH3OH lines (at >4σ significance). The sensitivity of the above result, and that of all earlier CH3OH studies, is thus likely to be limited by unknown systematic errors, probably arising due to the frequency-dependent structure of PKS1830−211. A robust result is obtained by combining the three lines at similar frequencies, 48.372, 48.377 and 60.531 GHz, whose line profiles are found to be in good agreement. This yields the 2σ constraint [Δμ/μ] ≲ 4 × 10−7, the most stringent current constraint on changes in μ. We thus find no evidence for changes in the proton–electron mass ratio over a lookback time of ≈7.5 Gyr.
Folding of Aquaporin 1: Multiple evidence that helix 3 can shift out of the membrane core
Authors: Virkki Minttu T , Agrawal Nitin , Edsbäcker Elin , Cristobal Susana , Elofsson Arne , Kauko Anni
Published: February 2015

The folding of most integral membrane proteins follows a two-step process: Initially, individual transmembrane helices are inserted into the membrane by the Sec translocon. Thereafter, these helices fold to shape the final conformation of the protein. However, for some proteins, including Aquaporin 1 (AQP1), the folding appears to follow a more complicated path. AQP1 has been reported to first insert as a four-helical intermediate, where helix 2 and 4 are not inserted into the membrane. In a second step this intermediate is folded into a six-helical topology. During this process, the orientation of the third helix is inverted. Here, we propose a mechanism for how this reorientation could be initiated: First, helix 3 slides out from the membrane core resulting in that the preceding loop enters the membrane. The final conformation could then be formed as helix 2, 3 and 4 are inserted into the membrane and the reentrant regions come together. We find support for the first step in this process by showing that the loop preceding helix 3 can insert into the membrane. Further, hydrophobicity curves, experimentally measured insertion efficiencies and MD-simulations suggest that the barrier between these two hydrophobic regions is relatively low, supporting the idea that helix 3 can slide out of the membrane core, initiating the rearrangement process
Transcriptional profiling of macrophages derived from monocytes and iPS cells identifies a conserved response to LPS and novel alternative transcription
Authors: Alasoo Kaur , Martinez Estrada Fernando , Hale Christine , Gordon Siamon , Powrie Fiona , Dougan Gordon , Mukhopadhyay Subhankar , Gaffney Daniel
Published: February 2015

Macrophages differentiated from human induced pluripotent stem cells (IPSDMs) are a potentially valuable new tool for linking genotype to phenotype in functional studies. However, at a genome-wide level these cells have remained largely uncharacterised. Here, we compared the transcriptomes of naïve and lipopolysaccharide (LPS) stimulated monocyte-derived macrophages (MDMs) and IPSDMs using RNA-Seq. The IPSDM and MDM transcriptomes were broadly similar and exhibited a highly conserved response to LPS. However, there were also significant differences in the expression of genes associated with antigen presentation and tissue remodelling. Furthermore, genes coding for multiple chemokine involved in neutrophil recruitment were more highly expressed in IPSDMs upon LPS stimulation. Additionally, analysing individual transcript expression identified hundreds of genes undergoing alternative promoter and 3′ untranslated region usage following LPS treatment representing a previously under-appreciated level of regulation in the LPS response.
Retrieval-extinction within the memory reconsolidation window does not influence appetitive choice
Authors: Bakkour Akram , Schonberg Tom , Hover Ashleigh M. , Poldrack Russell A.
Published: February 2015

Influencing choice behavior is key to achieving behavioral change. Traditional means to influence choice behavior rely on effortful self control, which is known to be fragile under several circumstances, rendering these methods ineffectual in maintaining any change in behavior over time. Behavioral maintenance efforts are likely more effective over the long term if they target more automatic processes such as attention or memory. Memories are not set in stone and are vulnerable to change and updating under certain circumstances when retrieved. It is possible to target specific memories for updating. In two studies, we sought to update the memory for an appetitive choice by way of reversal learning following retrieval of the targeted choice behavior. We found that targeting memories of a choice behavior for updating shortly after a reminder did not significantly attenuate the renewal of the targeted choice under extinction conditions. Possible explanations and suggested future directions are discussed.
A population density and moment-based approach to modeling domain Ca2+-mediated inactivation of L-type Ca2+channels
Authors: Wang Xiao , Hardcastle Kiah , Weinberg Seth H. , Smith Gregory D.
Published: February 2015

We present a population density and moment-based description of the stochastic dynamics of domain Ca2+-mediated inactivation of L-type Ca2+channels. Our approach accounts for the effect of heterogeneity of local Ca2+signals on whole cell Ca2+currents; however, in contrast with prior work, e.g., Sherman et al. (1990), we do not assume that Ca2+domain formation and collapse are fast compared to channel gating. We demonstrate the population density and moment-based modeling approaches using a 12-state Markov chain model of an L-type Ca2+channel introduced by Greenstein and Winslow (2002). Simulated whole cell voltage clamp responses yield an inactivation function for the whole cell Ca2+current that agrees with the traditional approach when domain dynamics are fast. We analyze the voltage-dependence of Ca2+inactivation that may occur via slow heterogeneous domains. Next, we find that when channel permeability is held constant, Ca2+-mediated inactivation of L-type channel increases as the domain time constant increases, because a slow domain collapse rate leads to increased mean domain [Ca2+] near open channels; conversely, when the maximum domain [Ca2+] is held constant, inactivation decreases as the domain time constant increases. Comparison of simulation results using population densities and moment equations confirms the computational efficiency of the moment-based approach, and enables the validation of two distinct methods of truncating and closing the open system of moment equations. In general, a slow domain time constant requires higher order moment truncation for agreement between moment-based and population density simulations.
Sincell:Bioconductor package for the statistical assessment of cell-state hierarchies from single-cell RNA-seq data
Authors: Juliá Miguel , Telenti Amalio , Rausell Antonio
Published: February 2015

Cell differentiation processes are achieved through a continuum of hierarchical intermediate cell-states that might be captured by single-cell RNA seq. Existing computational approaches for the assessment of cell-state hierarchies from single-cell data might be formalized under a general framework composed of i) a metric to assess cell-to-cell similarities (combined or not with a dimensionality reduction step), and ii) a graph-building algorithm (optionally making use of a cells-clustering step).SincellR package implements a methodological toolbox allowing flexible workflows under such framework. Furthermore,Sincellcontributes new algorithms to provide cell-state hierarchies with statistical support while accounting for stochastic factors in single-cell RNA seq. Graphical representations and functional association tests are provided to interpret hierarchies.Sincellfunctionalities are illustrated in a real case study where its ability to discriminate noisy from stable cell-state hierarchies is demonstrated.

Availability and implementation

Sincellis an open-source R/Bioconductor package available athttp://bioconductor.org/packages/3.1/bioc/html/sincell.html. A detailed manual and vignette describing functions and workflows is provided with the package.

Contact:antonio.rausell@isb-sib.ch
A unique HMG-box domain of mouse Maelstrom binds structured RNA but not double stranded DNA
Authors: Genzor Pavol , Bortvin Alex
Published: February 2015

Piwi-interacting piRNAs are a major and essential class of small RNAs in the animal germ cells with a prominent role in transposon control. Efficient piRNA biogenesis and function require a cohort of proteins conserved throughout the animal kingdom. Here we studied Maelstrom (MAEL), which is essential for piRNA biogenesis and germ cell differentiation in flies and mice. MAEL contains a high mobility group (HMG)-box domain and a Maelstrom-specific domain with a presumptive RNase H-fold. We employed a combination of sequence analyses, structural and biochemical approaches to evaluate and compare nucleic acid binding of mouse MAEL HMG-box to that of canonical HMG-box domain proteins (SRY and HMGB1a). MAEL HMG-box failed to bind double-stranded (ds)DNA but bound to structured RNA. We also identified important roles of a novel cluster of arginine residues in MAEL HMG-box in these interactions. Cumulatively, our results suggest that the MAEL HMG-box domain may contribute to MAEL function in selective processing of retrotransposon RNA into piRNAs. In this regard, a cellular role of MAEL HMG-box domain is reminiscent of that of HMGB1 as a sentinel of immunogenic nucleic acids in the innate immune response.