bluuebunny/crossref_metadata_2025 huggingface dataset:
Synchronization of chimera states in a multiplex system of phase oscillators with adaptive couplings
Authors: Kasatkin D. V. , Nekorkin V. I.
Published: September 2018

We study the interaction of chimera states in multiplex two-layer systems, where each layer represents a network of interacting phase oscillators with adaptive couplings. A feature of this study is the consideration of synchronization processes for a wide range of chimeras with essentially different properties, which are achieved due to the use of different types of coupling adaptation within isolated layers. We study the effect of forced synchronization of chimera states under unidirectional action between layers. This process is accompanied not only by changes in the frequency characteristics of the oscillators, but also by the transformation of the structure of interactions within the slave layer that become close to the properties of the master layer of the system. We show that synchronization close to identical is possible, even in the case of interaction of chimeras with essentially different structural properties (number and size of coherent clusters) formed by means of a relatively large parameter mismatch between the layers. In the case of mutual action of the layers in chimera states, we found a number of new scenarios of the multiplex system behavior along with those already known, when identical or different chimeras appear in both layers. In particular, we have shown that a fairly weak interlayer coupling can lead to suppression of the chimera state when one or both layers of the system demonstrate an incoherent state. On the contrary, a strong interlayer coupling provides a complete synchronization of the layer dynamics, accompanied by the appearance of multicluster states in the system’s layers.
Integrate-and-fire neuron circuit using positive feedback field effect transistor for low power operation
Authors: Kwon Min-Woo , Baek Myung-Hyun , Hwang Sungmin , Park Kyungchul , Jang Tejin , Kim Taehyung , Lee Junil , Cho Seongjae , Park Byung-Gook
Published: September 2018

In this work, we fabricated a dual gate positive feedback field-effect transistor (FBFET) integrated with CMOS. We investigated the DC and transient characteristics of the FBFET. The fabricated FBFET has an extremely low sub-threshold slope of less than 2.3 mV/dec and low off-current. We also propose an analog integrated-and-fire neuron circuit incorporating a FBFET, which significantly reduces the power dissipation of hardware neural networks. In a conventional neuron circuit using a membrane capacitor to integrate input pulses, most of the energy is consumed by the first inverter stage connected to the capacitor. Since the membrane capacitor is charged slowly compared to digital logic, a large amount of short-circuit current flows between Vdd and ground in the first inverter during this period. In the proposed neuron circuit, the short-circuit current is significantly suppressed by adopting a FBFET in the inverter. Through TCAD mixed mode simulation of the device and the circuit, we compare the energy consumption of a conventional and the proposed neuron circuits. In a single neuron circuit with microsecond duration pulses, 58% of the energy consumption is reduced by incorporating a FBFET. We performed SPICE compact modeling of FBFET, and its parameters were fitted to match the measurement results of the fabricated FBFET. Then, we conducted a circuit simulation to verify the operating neural networks. We implemented a single layer spiking neural network (SNN) that had resistive synaptic devices. In the SNN simulation, approximately 94% of the average power consumption of all output neurons was reduced.
Tuning LaAlO3 lattice structure by growth rate at the picometer scale in LaAlO3/SrTiO3 heterostructures
Authors: Wang Zhicheng , Zhai Xiaofang , Fu Zhengping , Lu Yalin
Published: September 2018

Here, we report an abnormal lattice reconstruction of LaAlO3 in the LaAlO3/SrTiO3 two-dimensional electron liquid heterostructure using the layer-by-layer pulsed laser deposition. We found that the lattice structure change of the top LaAlO3 layer is at the picometer level and is mainly controlled by the oxygen vacancies with an abnormal dependence on the oxygen background pressure. The lattice of the LaAlO3 film expands with more oxygen vacancies grown with high oxygen pressure and collapses with less oxygen vacancies grown with low oxygen pressure. The in situ monitoring of reflective high energy electron diffraction shows the lattice change coincident to the layer-by-layer deposition period change, revealing a non-equilibrium correlation between the lattice and the deposition environment, instead of the commonly assumed equilibrium correlation.
Suppress variations of analog resistive memory for neuromorphic computing by localizing Vo formation
Authors: Wu Wei , Wu Huaqiang , Gao Bin , Deng Ning , Qian He
Published: September 2018

Reducing device to device variations of filamentary analog resistive random access memory (RRAM) is crucial for neuromorphic computing. Larger variations decrease the computing accuracy of the neuromorphic network. One of the main factors for the variations of filamentary RRAM is the random nature of filament formation. This work presents a defect engineering approach using the atomic layer deposition method to localize the oxygen vacancies (Vo) formation uniformly, which results in uniform multi-weak-filaments formed in RRAM devices. The variation of linearity and dynamic ON/OFF ratio in different devices can be suppressed using the proposed method. Besides the variation control in this work, the retention and read disturbance are also optimized by increasing the Vo migration barrier, which are also important for neuromorphic network. The analog RRAM array is demonstrated with good uniformity of analog switching behavior, fast speed, long retention, small read disturbance, which shows tremendous potential in developing large-scale RRAM based neural networks.
Potential uses and cementing mechanism of bio-carbonate cement and bio-phosphate cement
Authors: Qian Chunxiang , Yu Xiaoniu , Wang Xin
Published: September 2018

Bio-cement, based on microbial-induced mineralization, can consolidate the loose particles and be applied to foundation reinforcement, dust control, desert settlement, repair cementitious materials crack, and other fields. In the paper, two kinds of bio-cement, such as bio-carbonate cement and bio-phosphate cement, were discussed as novel binders. The calcium carbonate (calcite), induced precipitation via Sporosarcina pasteurii, could cement between loose sandy soil particles. A series of sand-cemented experiments were conducted to confirm the cemented properties, and a numerical model based on the distribution of the concentration of Sporosarcina pasteurii was established to further analyze bio-grouting process. The evolution law of microstructure was revealed by X-ray computed tomography (X-CT) technique. The atomic binding energy of C-O bond in calcium carbonate, Si-O bond and Si in sand analysis showed that microbial-induced calcium carbonate interacted with surface of loose sand particles formed the intermolecular hydrogen bond. The other kind of bacteria (Bacillus subtilis) could hydrolyze organic phosphate monoester and released PO43-, which could react with different metal cations formed bio-phosphate minerals. The bio-phosphate cement can be used as treatment of sandy soil foundation, functional materials, remediation of heavy metals in contaminated soil, and so on.
A numerical model of superspreading surfactants on hydrophobic surface
Authors: Badra Ali Talha , Zahaf Hanane , Alla Hocine , Roques-Carmes Thibault
Published: September 2018

Many contributions significantly on experimental and mathematical studies are made to understand the mechanism of superspreading. Only few numerical methods have been proposed which solve the system of equations with soluble and insoluble surfactants. Among them, we propose a computational fluid dynamics model, based on the volume of fluid technique, with the piecewise linear interface calculation method. Interface reconstruction is applied to simulate the time evolution of the dynamics of drop spreading of surfactants on a thin water layer. We have allowed the occurrence of both the regimes relating to a series of trisiloxane (M(D′EnOH)M), sodium dodecyl sulphate, and Tergitol NP10 surfactants drop on a thin water layer with the influence of Marangoni stress. The numerical data seem consistent with those experimental for both regimes. It validates predictions for the spreading exponent in which the law of the radius of the circular area covered by the surfactant grows as tα, where 0 < α < 1. The comparison of the numerical and experimental predictions by Lee et al. [“Spreading of trisiloxanes over thin aqueous layers,” Colloid J. 71, 365–369 (2009)] is well represented in both regimes. The numerical study confirms that the spreading rates during the first stage increase as the solubility increases. This finding suggests that the model is adequate for describing the spreading of surfactants on thin fluid layers.
Overcoming device unreliability with continuous learning in a population coding based computing system
Authors: Mizrahi Alice , Grollier Julie , Querlioz Damien , Stiles M. D.
Published: September 2018

The brain, which uses redundancy and continuous learning to overcome the unreliability of its components, provides a promising path to building computing systems that are robust to the unreliability of their constituent nanodevices. In this work, we illustrate this path by a computing system based on population coding with magnetic tunnel junctions that implement both neurons and synaptic weights. We show that equipping such a system with continuous learning enables it to recover from the loss of neurons and makes it possible to use unreliable synaptic weights (i.e., low energy barrier magnetic memories). There is a trade-off between power consumption and precision because low energy barrier memories consume less energy than high barrier ones. For a given precision, there is an optimal number of neurons and an optimal energy barrier for the weights that leads to minimum power consumption.
Tracking fluid interfaces in primary cementing of surface casing
Authors: Maleki Amir , Frigaard Ian A.
Published: September 2018

We present a new method to track the interface between two fluids in an annular displacement flow typical of setting surface casing in the primary cementing of oil and gas wells. The main idea is to exploit the density difference between successive fluids pumped in order to design a tracer particle to sit at the interface. Although apparently trivial, such particles must overcome viscous drag and strong secondary flows in order to reach and remain at the interface. We explore the underlying physics through both a simple toy model and using a full annular displacement simulation. The study provides a proof of concept that the method can work, but also exposes some limitations in terms of cementing parameters and particle properties. As well as demonstrating feasibility, we explore how some of these limitations might be overcome.
Electrically tunable localized states in sub-band of bilayer graphene nanoribbon
Authors: Wang Zhongwang , Sun Jian , Muruganathan Manoharan , Mizuta Hiroshi
Published: September 2018

Multiple sub-band transport in bilayer graphene nanoribbons (GNRs) with localized charge states has not been experimentally investigated owing to the difficulty of accessing into the upper sub-band. In this letter, we utilize current annealing to heavily p-dope graphene from a capping hydrogen-silsesquioxane layer. As a result, Fermi energy can be tuned into the upper sub-valence band with reasonably small gate voltage. Owing to the localized charge states, quantum dot-like characteristics are measured in bilayer GNRs, as a result of the tunnelling transport of holes in the upper sub-band through these charge puddles. In contrast to monolayer GNRs, this phenomenon appears in a considerable conductive regime since the carrier transport in the lower sub-band is still diffusive. Moreover, by electrically tuning the Fermi energy, the localized charge puddles in the upper sub-band can be resized and isolated from each other.
Self-consistent description of the tangential-discontinuity-type current sheet, using the particle trajectory method and angular variables
Authors: Sasunov Yu. L. , Khodachenko M. L. , Alexeev I. I. , Belenkaya E. S. , Gubchenko V. M. , Dwivedi N. , Hanslmeier A.
Published: September 2018

The description of the dynamics of charged-particles in an inhomogeneous magnetic field is a fundamental problem in space plasma physics. Since, this dynamics has a character of a nonlinear oscillator, the traditionally used approaches involve certain limiting conditions regarding the scales of magnetic field, particle motion, and the assumptions about conservation of specific invariants (e.g., the magnetic momentum, integrals of action, etc.). Such approaches naturally restrict the detailization the considered particle dynamics which is described in terms of the integral characteristics and averaged parameters of motion. However, in some regions the precise account of the particle trajectory details and the motion features (e.g., the phase of gyration) are of crucial importance. In this paper, we present a method for the description of particle dynamics, based on a new system of differential equations for the particle pitch-angle θ and phase of rotation ϕ, which are derived from the analysis of the particle trajectory in a given magnetic field. It enables an easy and comprehensive description of a number of elementary problems, which form the basis for more complex natural cases in space physics. The developed method admits generalization to the case of the particle ensemble, which makes it possible to find a set of the self-consistent solutions for tangential current sheets within the frame of the kinetic approach.
Optimization of electrical treatment strategy for surface roughness reduction in conducting thin films
Authors: Du Lin , Maroudas Dimitrios
Published: September 2018

The surface roughness of deposited conducting thin films is responsible for various materials reliability problems in nanoelectronics and nanofabrication technologies. Here, we report a modeling and simulation study that aims at optimizing the electrical surface treatment of deposited conducting thin films as a physical processing strategy for their surface roughness reduction. Our study is based on a continuum model of film surface morphological evolution that accounts for the residual stress in the deposited conducting thin film, the film’s wetting of the substrate layer that it is deposited on, film texture and surface diffusional anisotropy, and surface electromigration. Through systematic linear stability analysis and dynamical simulation protocols, we examine in detail the effects of film surface crystallographic orientation and applied electric field direction toward minimizing the electric field strength required for film surface smoothening. We find that the critical electric field strength requirement for surface roughness reduction on {110}, {100}, and {111} surfaces of face-centered cubic crystalline conducting thin films exhibits a very strong dependence on the applied electric field direction, expressed as the electric field misalignment with respect to the principal residual stress directions in the film and the fast surface diffusion directions. Based on these findings, we optimize the electrical treatment strategy for surface roughness reduction of conducting thin films with respect to all relevant processing and material parameters.
On the pitfalls of applying isotropic mobility spectrum analysis to conductors with weak anisotropy
Authors: Stephenson K. S. , Bazaliy Ya. B.
Published: September 2018

It is shown that applying isotropic quantitative mobility analysis to anisotropic materials can lead to drastic qualitative errors, even in the case of modest anisotropy. The procedure may provide not only wrong values for carrier mobilities and concentrations but even a wrong number of carrier species.
Yttrium zinc tin oxide high voltage thin film transistors
Authors: Marette Alexis , Shea Herbert R. , Briand Danick
Published: September 2018

We demonstrate that doping the semiconductor zinc tin oxide (ZTO) with yttrium leads to a high-voltage thin film transistor (HVTFT) with enhanced switching performance. Adding 5% yttrium leads to an increase in the on-off ratio from 40 to 1000 at an operating voltage of 500 V and to a drop of the subthreshold swing from 65 to 35 V/dec. The performance is improved because of the reduction of the saturation voltage and because of a decrease in the off-current from several μA for undoped ZTO HVTFTs to 100 nA for Y5%ZTO. The decrease in saturation voltage and off-current can be attributed to a lower trap concentration leading to enhanced space-charge limited current and to a decrease in the background charge carrier concentration. At a 500 V bias voltage, an inverter circuit with a yttrium-doped ZTO HVTFT can control the output voltage between 50 V and 500 V, while the undoped ZTO HVTFT can only control the output voltage between 150 V and 450 V. The improvement in high voltage performance of yttrium-doped ZTO HVTFTs is important for future work related to high voltage thin film transistors made of amorphous oxide semiconductors as it demonstrates that this technology enables HVTFTs with simultaneously high operation voltage, high on-current, and high on-off ratio.
Photoluminescence characterization of Cu2Sn1-xGexS3 bulk single crystals
Authors: Aihara Naoya , Tanaka Kunihiko
Published: September 2018

Cu2Sn1-xGexS3 (CTGS) which is composed of earth-abundant and non-toxic elements is a promising material for the absorber layer of thin-film solar cells. In this study, the optical properties of CTGS bulk single crystals with varying germanium content were investigated by temperature and excitation power dependent photoluminescence (PL) measurements. At low-temperature, excitons and broad defect-related bands were observed in the PL spectra from all samples. These PL bands indicate a blue-shift with an increase in the germanium content, which suggested the formation of solid-solutions in CTGS. The broad band was dominated by donor-acceptor pair (DAP) recombination luminescence. The DAP bands were due to the transition of carriers between shallow acceptors and relatively deep donors for any alloy composition. Band-to-band (BB) recombination luminescence was also observed from all samples at room temperature. The band gap energies were varied from 0.933 to 1.544 eV with an increase in the germanium content, which was determined by spectral fitting of the BB bands. In addition, a small optical bowing parameter b, of ca. 0.1 eV was determined, which indicates that the band gap energy of CTGS can be controlled almost linearly by varying the alloy composition. Therefore, the optimum band gap energy for single-junction solar cells can be achieved by control of the CTGS alloy composition.
Effect of heat treatment process on mechanical properties and microstructure of FeAlCoCrNiTi0.5 alloy
Authors: Xiao Maohua , Chen Jingwen , Kang Jingjing , Chen Ke , Wu Dan , Gao Nong
Published: September 2018

In order to study the effects of different sintering processes on the properties of the alloy, including the microstructure, hardness, friction and wear properties of the alloy, the optimum sintering method and process parameters were selected. A series of FeAlCoCrNiTi0.5 high-entropy alloy blocks were prepared by mechanical alloying using inert alloy sintering technology. XRD pattern showed that when the sintering temperature was 1000°C and the holding time was 3h, the phase structure would be a simple body-centered cubic BCC2 phase and a face-centered cubic FCC phase. SEM observation showed that the microstructure is denser, and the grain refinement of the high entropy alloy is remarkably better. The evaluation of hardness, friction and wear properties showed that the high-entropy alloy had the best overall performance.
Hund's rule in the (1s2s)1,3S states of the two-electron Debye atom
Authors: Katriel Jacob , Montgomery H. E. , Sen K. D.
Published: September 2018

We present an investigation of the (1s2s)1,3S excited states of the two-electron atom immersed in a plasma modeled by the Debye or screened Coulomb potential. Three variants of the Debye atom are considered. The validity of Hund's multiplicity rule is confirmed, and the contribution of the interparticle repulsion energy to the singlet-triplet splitting is examined. The feature that this system shares with the unscreened two-electron atom as well as with the confined two-electron atom and the two-electron quantum dot is that the triplet wave function is contracted relative to that of the singlet. This feature affects both the behavior of the 2s-electron ionization energies and the relative magnitudes of the interparticle repulsion energies in the singlet vs. the triplet. Debye screening of the one-body attraction effectively reduces the nuclear charge, enhancing the reversal of the relative magnitudes of the triplet vs. singlet interparticle repulsion energies. Debye screening of the interparticle repulsion acts in an opposite way.
Electrons in regions of high phase density exhibit uncanny traits in the study of linear and nonlinear drift waves in spatially non-uniform magnetoplasmas
Authors: Masood W. , Aziz Tahir , Shah H. A.
Published: September 2018

Linear and nonlinear waves are examined on the ion time scale in a spatially inhomogeneous plasma having electrons that follow product bi (r,q) distribution. It has been shown that the linear dispersion relation for product bi (r,q) distribution undergoes appreciable changes as opposed to the one for the Maxwellian electrons. It has been found that the drift wave frequency is highest for flat-topped distribution, whereas it is lowest for the spiky distribution. It has been found that the drift solitary wave with flat-topped distribution (i.e., r > 0) is one of a kind and exhibits peculiar characteristics. It has been shown that Maxwellian and kappa-like electrons cannot alter the nature of the electrostatic drift waves under consideration; however, the spiky electrons can. The results obtained here are general and can be applied to many regions of space plasmas where the satellite missions have reported the presence of electron distribution functions that show deviation from the Gaussian behavior.
New magnetic, electric and anisotropic features of ammonium nickel formate revealed
Authors: Liebendorfer Adam
Published: September 2018

Characterizing key features of the little-understood 2-D metal-formate perovskite opens up new paths for studying its intermediate incommensurate structure.
Optimal initialization of a quantum system for an efficient coherent energy transfer
Authors: Gong Zhi-hao , Tang Zhou-fei , Cao Jian-shu , Wu Jianlan
Published: September 2018

For an energy transfer network, the irreversible depletion of excited electron energy occurs through either an efficient flow into an outer energy sink or an inefficient decay. With a small decay rate, the energy transfer efficiency is quantitatively reflected by the average life time of excitation energy before being trapped in the sink where the decay process is omitted. In the weak dissipation regime, the trapping time is analyzed within the exciton population subspace based on the secular Redfield equation. The requirement of the noise-enhanced energy transfer is obtained, where the trapping time follows an exact or approximate 1/Γ-scaling of the dissipation strength Γ. On the opposite side, optimal initial system states are conceptually constructed to suppress the 1/Γ-scaling of the trapping time and maximize the coherent transfer efficiency. Our theory is numerically testified in four models, including a biased two-site system, a symmetric three-site branching system, a homogeneous one-dimensional chain, and an 8-chromophore FMO protein complex.
Ultraviolet photodissociation dynamics of 1-pentyl radical
Authors: Sun Ge , Song Yu , Zhang Jingsong
Published: September 2018

The ultraviolet (UV) photodissociation of jet-cooled 1-pentyl radical is investigated in the wavelength region of 236−254 nm using the high-n Rydberg-atom time-of-flight (HRTOF) technique. The H-atom photofragment yield spectrum of the 1-pentyl radical shows a broad UV absorption feature peaking near 245 nm, similar to the 2pz →3s absorption bands of ethyl and n-propyl. The center-of-mass translational energy distribution, P (ET), of the H+C5H10 product channel is bimodal, with a slow peak at ~5 kcal/mol and a fast peak at ~50 kcal/mol. The fraction of the average translational energy release in the total available energy, ⟨fT⟩, is 0.30, with those of the slow and fast components being 0.13 and 0.58, respectively. The slow component has an isotropic product angular distribution, while the fast component is anisotropic with an anisotropy parameter ~0.4. The bimodal translational energy and angular distributions of the H+C5H10 products indicate two H-atom elimination channels in the photodissociation of 1-pentyl: (i) a direct, prompt dissociation from the electronic excited state and/or the repulsive part of the ground electronic state potential energy surface; and (ii) a unimolecular dissociation of internally hot radical in the ground electronic state after internal conversion from the electronic excited state.
Magnetic-Bottle and velocity-map imaging photoelectron spectroscopy of APS− (A=C14H10 or anthracene): Electron structure, spin-orbit coupling of APS•, and dipole-bound state of APS−
Authors: Yuan Qin-qin , Yang Zheng , Li Ren-zhong , Transue Wesley J. , Li Zhi-peng , Jiang Ling , Govind Niranjan , Cummins Christopher C. , Wang Xue-Bin
Published: September 2018

Gaseous dibenzo-7-phosphanorbornadiene P-sulfide anions APS− (A=C14H10 or anthracene) were generated via electrospray ionization, and characterized by magnetic-bottle photoelectron spectroscopy, velocity-map imaging (VMI) photoelectron spectroscopy, and quantum chemical calculations. The electron affinity (EA) and spin-orbit (SO) splitting of the APS• radical are determined from the photoelectron spectra and Franck-Condon factor simulations to be EA=(2.62±0.05) eV and SO splitting=(43±7) meV. VMI photoelectron images show strong and sharp peaks near the detachment threshold with an identical electron kinetic energy (eKE) of 17.9 meV at three different detachment wavelengths, which are therefore assigned to autodetachment from dipole-bound anion states. The B3LYP/6-31++G(d,p) calculations indicate APS• has a dipole moment of 3.31 Debye, large enough to support a dipole-bound electron.
Theoretical study of adsorption and dehydrogenation of C2H4 on Cu(410)
Authors: Sun Yangyunli , Zhang Shuo , Zhang Wen-hua , Li Zhen-yu
Published: September 2018

Adsorption and dehydrogenation of ethylene on Cu(410) surface are investigated with first-principles calculations and micro-kinetics analysis. Ethylene dehydrogenation is found to start from the most stable π-bonded state instead of the previously proposed di-σ-bonded state. Our vibrational frequencies calculations verify the π-bonded adsorption at step sites at low coverage and low surface temperature and di-σ-bonded ethylene on C−C dimer (C2H4-CC) is proposed to be the species contributing to the vibrational peaks experimentally observed at high coverage at 193 K. The presence of C2H4-CC indicates that the dehydrogenation of ethylene on Cu(410) can proceed at temperature as low as 193 K.
Accurate calculation of equilibrium reduced density matrix for the system-bath model: A multilayer multiconfiguration time-dependent Hartree approach and its comparison to a multi-electronic-state path integral molecular dynamics approach
Authors: Wang Haobin , Liu Xinzijian , Liu Jian
Published: September 2018

An efficient and accurate method for computing the equilibrium reduced density matrix is presented for treating open quantum systems characterized by the system-bath model. The method employs the multilayer multiconfiguration time-dependent Hartree theory for imaginary time propagation and an importance sampling procedure for calculating the quantum mechanical trace. The method is applied to the spin-boson Hamiltonian, which leads to accurate results in agreement with those produced by the multi-electronic-state path integral molecular dynamics method.
Quantum chemical study of potential energy surface in the formation of atmospheric sulfuric acid
Authors: Tao Emily L. , Li Jessica Y. , Soriano Samantha , Tao Fu-Ming
Published: September 2018

A new potential energy surface (PES) for the atmospheric formation of sulfuric acid from OH+SO2 is investigated using density functional theory and high-level ab initio molecular orbital theory. A pathway focused on the new PES assumes the reaction to take place between the radical complex SO3·HO2 and H2O. The unusual stability of SO3·HO2 is the principal basis of the new pathway, which has the same final outcome as the current reaction mechanism in the literature but it avoids the production and complete release of SO3. The entire reaction pathway is composed of three consecutive elementary steps: (1) HOSO2+O2→SO3·HO2, (2) SO3·HO2+H2O→SO3·H2O·HO2, (3) SO3·H2O·HO2→H2SO4+HO2. All three steps have small energy barriers, under 10 kcal/mol, and are exothermic, and the new pathway is therefore favorable both kinetically and thermodynamically. As a key step of the reactions, step (3), HO2 serves as a bridge molecule for low-barrier hydrogen transfer in the hydrolysis of SO3. Two significant atmospheric implications are expected from the present study. First, SO3 is not released from the oxidation of SO2 by OH radical in the atmosphere. Second, the conversion of SO2 into sulfuric acid is weakly dependent on the humidity of air.
Tailoring oxygen vacancy on Co3O4 nanosheets with high surface area for oxygen evolution reaction
Authors: Zhang Gong , Li Jing-hong
Published: September 2018

Electrochemical water splitting requires efficient water oxidation catalysts to accelerate the sluggish kinetics of water oxidation reaction. Here, we designed an efficient Co3O4 electrocatalyst using a pyrolysis strategy for oxygen evolution reaction (OER). Morphological characterization confirmed the ultra-thin structure of nanosheet. Further, the existence of oxygen vacancies was obviously evidenced by the X-ray photoelectron spectroscopy and electron spin resonance spectroscopy. The increased surface area of Co3O4 ensures more exposed sites, whereas generated oxygen vacancies on Co3O4 surface create more active defects. The two scenarios were beneficial for accelerating the OER across the interface between the anode and electrolyte. As expected, the optimized Co3O4 nanosheets can catalyze the OER efficiently with a low overpotential of 310 mV at current density of 10 mA/cm2 and remarkable long-term stability in 1.0 mol/L KOH.
Real-Time observation of protein transport across membranes by femtosecond sum frequency generation vibrational spectroscopy
Authors: Tan Junjun , Li Chuanzhao , Zhang Jiahui , Ye Shuji
Published: September 2018

Characterization of conformation kinetics of proteins at the interfaces is crucial for understanding the biomolecular functions and the mechanisms of interfacial biological action. But it requires to capture the dynamic structures of proteins at the interfaces with sufficient structural and temporal resolutions. Here, we demonstrate that a femtosecond sum frequency generation vibrational spectroscopy (SFG-VS) system developed by our group provides a powerful tool for monitoring the real-time peptide transport across the membranes with time resolution of less than one second. By probing the real-time SFG signals in the amide I and amide A bands as WALP23 interacts with DMPG lipid bilayer, it is found that WALP23 is initially absorbed at the gel-phase DMPG bilayer with a random coil structure. The absorption of WALP23 on the surface leads to the surface charge reversal and thus changes the orientation of membrane-bound water. As the DMPG bilayer changes from gel phase into fluid phase, WALP23 inserts into the fluid-phase bilayer with its N-terminal end moving across the membrane, which causes the membrane dehydration and the transition of WALP23 conformation from random coil to mixed helix/loop structure and then to pure α-helical structure. The established system is ready to be employed in characterizing other interfacial fast processes, which will be certainly helpful for providing a clear physical picture of the interfacial phenomena.
Exploring the low-temperature oxidation chemistry of cyclohexane in a jet-stirred reactor: An experimental and kinetic modeling study
Authors: Zou Jia-biao , Li Wei , Ye Li-li , Zhang Xiao-yuan , Li Yu-yang , Yang Jiu-zhong , Qi Fei
Published: September 2018

We report the investigation on the low-temperature oxidation of cyclohexane in a jet-stirred reactor over 500−742 K. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was used for identifying and quantifying the oxidation species. Major products, cyclic olefins, and oxygenated products including reactive hydroperoxides and high oxygen compounds were detected. Compared with n-alkanes, a narrow low-temperature window (∼80 K) was observed in the low-temperature oxidation of cyclohexane. Besides, a kinetic model for cyclohexane oxidation was developed based on the CNRS model [Combust. Flame 160, 2319 (2013)], which can better capture the experimental results than previous models. Based on the modeling analysis, the 1,5-H shift dominates the crucial isomerization steps of the first and second O2 addition products in the low-temperature chain branching process of cyclohexane. The negative temperature coefficient behavior of cyclohexane oxidation results from the reduced chain branching due to the competition from chain inhibition and propagation reactions, i.e. the reaction between cyclohexyl radical and O2 and the decomposition of cyclohexylperoxy radical, both producing cyclohexene and HO2 radical, as well as the decomposition of cyclohexylhydroperoxy radical producing hex-5-en-1-al and OH radical.
Quantum entanglement of parallel-coupled double quantum dots: A theoretical study using the hierarchical equations of motion approach
Authors: Gong Hong , Ullah Arif , Ye LvZhou , Zheng Xiao , Yan YiJing
Published: September 2018

Quantum dots comprise a type of quantum impurity system. The entanglement and coherence of quantum states are significantly influenced by the strong electron-electron interactions among impurities and their dissipative coupling with the surrounding environment. Competition between many-body effects and transfer couplings plays an important role in determining the entanglement among localized impurity spins. In this work, we employ the hierarchical-equations-of-motion approach to explore the entanglement of a strongly correlated double quantum dots system. The relation between the total system entropy and those of subsystems is also investigated.
Rotational mechanism of ammonium ion in water and methanol
Authors: Zhang Qiang , Du Yang , Chen Chen , Zhuang Wei
Published: September 2018

Dynamics of ammonium and ammonia in solutions is closely related to the metabolism of ammoniac compounds, therefore plays an important role in various biological processes. NMR measurements indicated that the reorientation dynamics of NH4+ is faster in its aqueous solution than in methanol, which deviates from the Stokes-Einstein-Debye rule since water has higher viscosity than methanol. To address this intriguing issue, we herein study the reorientation dynamics of ammonium ion in both solutions using numerical simulation and an extended cyclic Markov chain model. An evident decoupling between translation and rotation of methanol is observed in simulation, which results in the deviation of reorientation from the Stokes-Einstein-Debye rule. Slower hydrogen bond (HB) switchings of ammonium with methanol comparing to that with water, due to the steric effect of the methyl group, remarkably retards the jump rotation of ammonium. The observations herein provide useful insights into the dynamic behavior of ammonium in the heterogeneous environments including the protein surface or protein channels.
Chemical physics in living cells — Using light to visualize and control intracellular signal transduction
Authors: Krishnamurthy Vishnu V. , Zhang Kai
Published: September 2018

Cells are crowded microenvironments filled with macromolecules undergoing constant physical and chemical interactions. The physicochemical makeup of the cells affects various cellular responses, determines cell-cell interactions and influences cell decisions. Chemical and physical properties differ between cells and within cells. Moreover, these properties are subject to dynamic changes in response to environmental signals, which often demand adjustments in the chemical or physical states of intracellular molecules. Indeed, cellular responses such as gene expression rely on the faithful relay of information from the outside to the inside of the cell, a process termed signal transduction. The signal often traverses a complex path across subcellular spaces with variable physical chemistry, sometimes even influencing it. Understanding the molecular states of such signaling molecules and their intracellular environments is vital to our understanding of the cell. Exploring such intricate spaces is possible today largely because of experimental and theoretical tools. Here, we focus on one tool that is commonly used in chemical physics studies — light. We summarize recent work which uses light to both visualize the cellular environment and also control intracellular processes along the axis of signal transduction. We highlight recent accomplishments in optical microscopy and optogenetics, an emerging experimental strategy which utilizes light to control the molecular processes in live cells. We believe that optogenetics lends unprecedented spatiotemporal precision to the manipulation of physicochemical properties in biological contexts. We hope to use this work to demonstrate new opportunities for chemical physicists who are interested in pursuing biological and biomedical questions.
Resilience of benthic diatom communities in Mediterranean streams: role of endangered species
Authors: Falasco E. , Piano E. , Doretto A. , Fenoglio S. , Bona F.
Published: September 2018

The extent of drought in Mediterranean streams has been intensifying recently, and the mean annual discharge is expected to experience a decreasing trend in coming years, with significant effects on aquatic ecosystems. The aim of this study was to analyse colonisation patterns of diatom communities that differed in terms of taxonomic composition and percentage of endangered taxa exploring the possible development of resistance mechanisms. To this end, we selected three Mediterranean streams comparable in terms of water quality, but different in terms of surrounding land use, and we performed two experimental treatments. The first treatment consisted in artificially drying and cleaning of substrates (cobbles) to analyse the post-drought recolonisation process that is only driven by drift and immigration. In the second treatment cobbles coming from a site experiencing a seasonal drought were transplanted upstream in a perennial stretch to explore the possible development of resistance mechanisms within diatom communities periodically exposed to droughts. We observed that stream identity played an important role in determining diatom assemblage composition. Highly natural stretches had a high abundance of endangered species, which were less resilient to drought than assemblages composed of general and widespread taxa. Moreover, according to our results, resistance mechanisms did not play a significant role in recovery patterns. Improving our knowledge of diatom resilience mechanisms is very important in a global climate change scenario, especially in Mediterranean streams.
Cell type-specific endometrial transcriptome changes during initial recognition of pregnancy in the mare
Authors: Scaravaggi Iside , Borel Nicole , Romer Rebekka , Imboden Isabel , Ulbrich Susanne E. , Zeng Shuqin , Bollwein Heinrich , Bauersachs Stefan
Published: September 2018

Previous endometrial gene expression studies during the time of conceptus migration did not provide final conclusions on the mechanisms of maternal recognition of pregnancy (MRP) in the mare. This called for a cell type-specific endometrial gene expression analysis in response to embryo signals to improve the understanding of gene expression regulation in the context of MRP. Laser capture microdissection was used to collect luminal epithelium (LE), glandular epithelium and stroma from endometrial biopsies from Day 12 of pregnancy and Day 12 of the oestrous cycle. RNA sequencing (RNA-Seq) showed greater expression differences between cell types than between pregnant and cyclic states; differences between the pregnant and cyclic states were mainly found in LE. Comparison with a previous RNA-Seq dataset for whole biopsy samples revealed the specific origin of gene expression differences. Furthermore, genes specifically differentially expressed (DE) in one cell type were found that were not detectable as DE in biopsies. Overall, this study revealed spatial information about endometrial gene expression during the phase of initial MRP. The conceptus induced changes in the expression of genes involved in blood vessel development, specific spatial regulation of the immune system, growth factors, regulation of prostaglandin synthesis, transport prostaglandin receptors, specifically prostaglandin F receptor (PTGFR) in the context of prevention of luteolysis.
Single-molecule optical absorption imaging by nanomechanical photothermal sensing
Authors: Chien Miao-Hsuan , Brameshuber Mario , Rossboth Benedikt K. , Schütz Gerhard J. , Schmid Silvan
Published: September 2018

Significance

Absorption microscopy is a promising technique that can detect single nonfluorescent molecules. However, fundamental limitations of existing optical absorption methods result in noisy detection signals for single molecules, which has hindered many anticipated applications. A promising method is to optically measure the photothermal heating of single molecules. In this paper, we present a photothermal microscopy technique where we detect the photothermal heating of single molecules mechanically with a temperature-sensitive nanomechanical drum. With our method, we achieve an unprecedented optical absorption sensitivity, enabling the detection of single molecules with large signal-to-noise ratios. This enables interesting applications such as the accurate localization of naturally occurring marker molecules or the identification of single molecules by measuring their absorption spectrum.
Symmetric coalescence of two hydraulic fractures
Authors: O’Keeffe Niall J. , Zheng Zhong , Huppert Herbert E. , Linden P. F.
Published: September 2018

Significance

We present an experimental investigation on the coalescence of hydraulic fractures in a brittle solid. Using a dual-fracturing setup, we obtain high-resolution experimental measurements on the time evolution of the fracture profiles and internal velocity field before, during, and after fracture coalescence. These measurements show an intermediate time self-similar coalescence during the dynamic interaction of two fractures. The work probes the dynamic formation of a fracture network, which is crucial to the industrial practice of energy resource recovery, compensation grouting, and the reservoir integrity of many confined systems involving fluid injection.
Strategies for robustness:Five perspectives on how policy design is done
Authors: Van der Steen Martijn , van Twist Mark
Published: September 2018

Robust policy design is an activity that is ‘done’ by policymakers; in this paper we look further into how exactly robust policy design is done. We use the literature on strategizing to distinguish various theoretical perspectives on how policy design is done in practice. Moreover, we conducted a survey-feedback study with a group of senior level policymakers to see what they do when ‘doing’ robust policy design, how they think it should be done, and what they think are challenges for doing robust policy design in the context of a public organization. The study shows that although the language of strategy and policy design is rooted in the rational-analytical ‘planning’ approach, other perspectives are in fact more suitable for designing robust policies for deeply uncertain and volatile conditions. Moreover, our study shows that practitioners are well-aware of this bias; they have developed practical ways to combine the rational-analytical approach to design that is expected from them with other approaches for doing design.
Selective Osteotomies to Correct Deviated Bony Vaults of Asian Noses
Authors: Nam Yong Seok , Baek Jong Tae , Kang Jae-Goo
Published: September 2018

Background

Standard osteotomies for the correction of deviated noses are bilateral and comprise a combination of medial and lateral osteotomy procedures. However, their uniform application to the small/delicate Asian bony vault is inappropriate and often results in suboptimal outcomes.

Objectives

This study describes how asymmetric bony pyramids were defined through 3-component analysis, which was then used to inform selective/individualized osteotomies.

Methods

Bony vault deviations were categorized after 3-component analysis in 117 patients seeking correction of a deviated nose. Selective osteotomies were applied accordingly. Pre- and postoperative photographs were compared and rated by 2 independent evaluators. Patients’ subjective evaluations were also included.

Results

Selective osteotomies were possible in 79 (68%) out of 117 patients. Among the 79 study subjects, outcome ratings were excellent in 37 (47%), acceptable in 25 (32%), unsatisfactory in 8 (10%), and unspecified in 9 (11%). Unspecified cases aside, satisfactory correction was achieved in 88% (62/70 patients). Of the 54 patients who responded to telephone interviews, patient satisfaction was excellent in 43 (80%), improved in 10 (18.2%), and unchanged in 1 (1.8%). Follow-up of the 88% of patients with satisfactory correction showed a stable long-term outcome.

Conclusions

Each bony vault in deviated noses is different, and thus, its correction must be individualized for each patient and for each side. The protocol described herein achieves a controlled correction of deviated bony vault. Restoration of bony pyramid symmetry via current techniques is best suited to short Asian bony vaults, where additional structural needs from routine nasal augmentation/lengthening are required.

Level of Evidence: 4