bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic and Magnetic Properties of Lanthanum and Strontium Doped Bismuth Ferrite: A First-Principles Study
Authors: Ghosh Ayana , Trujillo Dennis P. , Choi Hongchul , Nakhmanson S. M. , Alpay S. Pamir , Zhu Jian-Xin
Published: January 2019

While bismuth ferrite BiFeO3 (BFO) is a well studied multiferroic material, its electronic and magnetic properties in the presence of A-site dopants have not been explored widely. Here we report the results of a systematic study of the local electronic structure, spontaneous polarization, and magnetic properties of lanthanum (La) and strontium (Sr) doped rhombohedral bismuth ferrite within density functional theory. An enhanced ferroelectric polarization of 122.43 μC/cm2 is predicted in the uniformly doped BiLaFe2O6. We find that substitution of Sr in the A-site drives the system into a metallic state. The nature of magnetism arises mainly from the B-site Fe exhibiting a G-type antiferromagnetic ordering. Our study finds that upon dopant substitution, the local magnetic moment is decreased and its magnitude is dependent on the distance between the Fe and the dopant atom. The correlation between the local moment and the distance between the Fe and the dopant atom is discussed.
Universality of the DNA methylation codes in Eucaryotes
Authors: Aliaga Benoît , Bulla Ingo , Mouahid Gabriel , Duval David , Grunau Christoph
Published: January 2019

Genetics and epigenetics are tightly linked heritable information classes. Question arises if epigenetics provides just a set of environment dependent instructions, or whether it is integral part of an inheritance system. We argued that in the latter case the epigenetic code should share the universality quality of the genetic code. We focused on DNA methylation. Since availability of DNA methylation data is biased towards model organisms we developed a method that uses kernel density estimations of CpG observed/expected ratios to infer DNA methylation types in any genome. We show here that our method allows for robust prediction of mosaic and full gene body methylation with a PPV of 1 and 0.87, respectively. We used this prediction to complement experimental data, and applied hierarchical clustering to identify methylation types in ~150 eucaryotic species covering different body plans, reproduction types and living conditions. Our analysis indicates that there are only four gene body methylation types. These types do not follow phylogeny (i.e. phylogenetically distant clades can have identical methylation types) but they are consistent within clades. We conclude that the gene body DNA methylation codes have universality similar to the universality of the genetic code and should consequently be considered as part of the inheritance system.
A peptide-based four-color fluorescent polydopamine nanoprobe for multiplexed sensing and imaging of proteases in living cells
Authors: Xu Jiayao , Fang Lina , Shi Ming , Huang Yong , Yao Lifang , Zhao Shulin , Zhang Liangliang , Liang Hong
Published: January 2019

A novel peptide-based four-color fluorescent polydopamine nanoprobe has been developed for multiplexed sensing and imaging of tumor-related proteases in living cells. This nanoprobe responds rapidly and selectively, enabling accurate differentiation between cancer cells and normal cells.
Potassium perylene-tetracarboxylate with two-electron redox behaviors as a highly stable organic anode for K-ion batteries
Authors: Wang Chuan , Tang Wu , Yao Zeyi , Cao Bei , Fan Cong
Published: January 2019

A new organic compound was exploited as a highly stable organic anode for potassium-ion batteries.
Supramolecular aggregation of a redox-active copper-naphthalenediimide network with intrinsic electron conduction
Authors: Kuang Xiaofei , Chen Shanci , Meng Lingyi , Chen Jing , Wu Xiaoyuan , Zhang Guanhua , Zhong Guiming , Hu Ting , Li Yuhang , Lu Can-Zhong
Published: January 2019

A novel sextuple interpenetrated copper-naphthalenediimide network based on adamantane-like cages has been constructed and demonstrates outstanding electron transport.
Solvent driven phase transitions of acyclovir – the role of water and solvent polarity
Authors: Nartowski Karol P. , Karabin Julia , Morritt Alexander L. , Nowak Maciej , Fábián László , Karolewicz Bożena , Khimyak Yaroslav Z.
Published: January 2019

The pathways of transformations of acyclovir forms I and V induced by organic solvents and water have been identified. Significant differences in the thermal dehydration process of forms V and VI were observed.
How intermolecular interactions influence electronic absorption spectra: insights from the molecular packing of uracil in condensed phases
Authors: Fu Fangjia , Liao Kang , Ma Jing , Cheng Zheng , Zheng Dong , Gao Liuzhou , Liu Chungen , Li Shuhua , Li Wei
Published: January 2019

Intermolecular interactions in terms of molecular packing are crucial for the investigation of the absorption spectra of uracil in different environments.
Effect of surface–bulk partitioning on the heterogeneous oxidation of aqueous saccharide aerosols
Authors: Fan Hanyu , Wenyika Masaya Tadini , Goulay Fabien
Published: January 2019

Experiments and simulations are employed to discuss the effect of surface partitioning on the heterogeneous kinetics.
Ultrafast internal conversion dynamics of bilirubin bound to UnaG and its N57A mutant
Authors: Cao Xiaodan , Zhang Changcheng , Gao Ziheng , Liu Yangyi , Zhao Yuzheng , Yang Yi , Chen Jinquan , Jimenez Ralph , Xu Jianhua
Published: January 2019

High fluorescence quantum yield of BR in UnaG is due to direct hydrogen bonds to theendo-vinyl dipyrrinone moiety.
Surface faceting and compositional evolution of Pd@Au core–shell nanocrystals during in situ annealing
Authors: Wu Zhemin , Tang Min , Li Xiaoyan , Luo Sai , Yuan Wentao , Zhu Beien , Zhang Hui , Yang Hangsheng , Gao Yi , Wang Yong
Published: January 2019

A step-wise transformation process of a Pd@Au nanoparticle both structurally and compositionally was observed. Monte Carlo simulation was used to explain the results.
Transformation of silver nanoparticle consumer products during simulated usage and disposal
Authors: Potter Phillip M. , Navratilova Jana , Rogers Kim R. , Al-Abed Souhail R.
Published: January 2019

Sequential exposure of silver nanoparticle suspensions to various media gives new insight to the environmental fate of nano-enabled consumer products.
Highly fluorescent dual-emission red carbon dots and their applications in optoelectronic devices and water detection
Authors: Guan Qingwen , Su Rigu , Zhang Miaoran , Zhang Rui , Li Weijun , Wang Dong , Xu Meng , Fei Ling , Xu Quan
Published: January 2019

Synthesis of dual-emission nitrogen and sulfur co-doped (N,S)-CDs with a quantum yield up to 29.7% and their applications in white LEDs and water detection.
Correction: Comparative study of three heteropolyacids supported on carbon materials as catalysts for ethylene production from bioethanol
Authors: Almohalla M. , Rodríguez-Ramos I. , Guerrero-Ruiz A.
Published: January 2019

Correction for ‘Comparative study of three heteropolyacids supported on carbon materials as catalysts for ethylene production from bioethanol’ by M. Almohalla et al., Catal. Sci. Technol., 2017, 7, 1892–1901.
Dichotic Listening Test–Retest Reliability in Children
Authors: Kelley Kairn Stetler , Littenberg Benjamin
Published: January 2019

Purpose

The objective of the study was to compare test–retest reliability of three dichotic listening tests: SCAN–3 Competing Words Test (Words;
Keith, 2009a
,
2009b
), Double Dichotic Digits Test (Digits;
Musiek, 1983a
), and Bergen Dichotic Listening Test With Consonant–Vowel Syllables (Syllables;
Hugdahl & Hammar, 1997
).

Method

Sixty English-speaking children, 7–14 years old with normal hearing, had a single study visit during which each test was administered twice. Changes on retest were summarized by within-subject standard deviation (
S
w
), compared among tests, and compared with binomial model predictions. Correlates of variance were explored.

Results

Scores based on 40 items were more precise (
S
w
= 5%) than those based on 20–30 items (
S
w
= 6%–8%). All 3 tests had reliability within bounds predicted by binomial model. Changes on retest for Words and Digits Test were weakly associated with age, but this is confounded by the trend for older children to have higher Words and Digits scores.

Conclusions

Digits Right, Digits Left, and Words Total scores—each based on 40 items—had the best reliability among the clinically used scores. Scores based on fewer items were less precise. Poor precision may contribute to misdiagnosis in clinic and to nondifferential misclassification in research. More precise estimates of dichotic listening ability require longer tests.
Low‐complexity sparse detector for generalised space shift keying
Authors: Zhang Licheng , Zhu Sining , Zhang Lijuan , Jin Minglu
Published: January 2019

Generalised space shift keying (GSSK) technique proposed for massive multi‐input–multi‐output systems has a higher information transmission rate due to the activation of multiple antennas at the same time, and also has significant advantage in terms of hardware cost. However, the maximum likelihood detector has a very high complexity which makes it computationally intractable for large‐scale GSSK systems. In this Letter, a sparse detector is proposed by exploiting the inherent property of sparsity in GSSK. Different from the existing compressed sensing (CS)‐based detectors, the proposed detector utilises Euclidean distance instead of inner product operation for antenna matching. Moreover, it can remove erroneous antenna indices by backtracking to promote the detection performance. The simulation results show that the proposed scheme outperforms the existing CS‐based detectors while maintaining low complexity.
Three‐dimensional circular patch antenna under TM02 mode with improved impedance matching
Authors: Wang Shiyan , Zhu Lei , Wang Jianpeng , Wu Wen
Published: January 2019

A circular patch antenna under TM02 mode with improved impedance matching is proposed by adopting 3D architecture. It is known that the TM02 mode of circular patch can generate omnidirectional radiation, but its input resistance reaches maximum at centre point. In this context, impedance matching is difficult to be achieved and the feeding probe is often supposed to be placed a distance away from the centre, inevitably destroying the symmetry of radiation pattern. Without introducing pins or slots, a direct strategy is here employed where the circular patch is folded to form a concave at its centre. It is found that the input resistance can be effectively reduced with increasing depth of concave since the described concave serves as vertical electric wall in cavity and weakens the electric field in the region between centre and ground. By using electroplate technology based on plastics, a 3D antenna prototype is fabricated and measured to validate the proposed methodology.
Research on antenna for detecting the corona discharge of transmission line
Authors: Xia Yunfeng , Song Xinming , Jia Zhidong , Wang Xilin , Qi Jinfeng , Xu Zheng
Published: January 2019

Detection of corona discharge of the transmission line can reflect its health status and provide warning information for maintenance. Some existing detection methods are flawed and cannot be used widely. This study presents a new method by measuring the electromagnetic wave caused by corona discharge with RF antenna. Then a circularly polarised log‐periodic antenna was designed by making two pairs of log‐periodic antennas 90° orthogonal. Finally, this antenna was simulated and manufactured to detect electromagnetic signals, the result shows that the time domain signal of corona discharge is a high frequency oscillation wave and its fast Fourier transform main distributes between 200 and 350 MHz.
Flexible CSC‐HVDC system
Authors: Wu Haitao , Liu Yonghe , Wang Zhihe , Song Lei , Wu Fan
Published: January 2019

The current source converter (CSC)‐HVDC system is the key technology for long distance large power transmission. However, the traditional CSC‐HVDC has two serious shortcomings: (i) vulnerable to commutation failures; and (ii) not being able to control its reactive power. This study will propose a Flexible CSC topology, which is based on the dc current reinjection conversion concept. The Flexible CSC reduces the converter current waveform to zero during the commutations of valves and, thus, removes the converter dependence on line commutation. The Flexible CSC is also free to control the amplitude and phase of its output ac current. So, it can control freely active power and reactive power. Use this converter to construct a new CSC‐HVDC system. This new CSC‐HVDC system can operate in four quadrants, so as to control reactive power in wide range. In particular, it can export leading reactive power to the ac grids. This study describes the structure and control of the Flexible CSC and builds an experimental prototype. The simulation and experimental results will be shown to demonstrate the feasibility of the converter topology, the effectiveness of the active reactive power controllability, and the commutation failure elimination method.
Optimal reactive power control in a converter station during low‐power operation of HVDC
Authors: Mo Jingshan , Yan Wei , Xiao Fan , Wang Tao , Wang Hao , Zhou Youbin
Published: January 2019

When the high‐voltage DC (HVDC) system is operated in low‐power transmission, the overplus of reactive power provided by AC filters may still exist apart from satisfying the need of the converter station, restricted by the minimum number of filter banks. This will lead to a large number of surplus reactive power into AC system, affecting the safe and stable operation of power grid. Here, the impacts of the adjustment of on‐load tap changer of converter transformer and the adjustment of control angle of the converter station on reactive power consumption are analysed. Taking effects on the adjustment of control devices and the interchange of reactive power into account, a static reactive power optimisation model based on the actual control strategy of reactive power in a converter station is set up, which provides theoretical basis for an optimal control during low‐power operation. Taking Tian‐Guang HVDC project as an example, the simulation results verify its effectiveness of the proposed method.
Investigation of the correlation between radial depth of cut (RDOC) and axial depth of cut (ADOC) in NX-CAM system: Simulation Studies
Authors: Mohamad Hafiz , Zahid M.N. Osman
Published: January 2019

This paper outlines a simulation study to investigate the correlation between radial depth of cut (RDOC) and axial depth of cut (ADOC) in 4 axis machining processes. Computer-aided Manufacturing (CAM) plays a crucial role in simulating cutting operations before the real process executed. Several cutting parameters can be analysed through effective CAM program to predict the outcomes. However, an efficient program required skilled operator to develop the process planning. Besides, a standard CAM system has limited capabilities to handle repetitive simulation due to unavailable function to support the analysis. In this study, the combination of RDOC and ADOC is analyses on different parts features consist of planar surface and non-planar surface. Several set of pairing percentages between RDOC and ADOC are used in the simulation program to analyses the cutting operations. In order to perform the simulation, a customized program was developed in NX CAM system to assist the routines. It capable to generate machining data files from each simulation and assess the total volume removed. A pairing set with high volume removal is denoted as an optimum value and will be chosen as a cutting parameter in finishing operation. Generally, ADOC has a significant effect compared to RDOC in terms of total volume removed from the workpiece.
A Review on Predictive Modeling Technique for Student Academic Performance Monitoring
Authors: Asiah Mat , Nik Zulkarnaen Khidzir , Safaai Deris , Nik Nurul Hafzan Mat Yaacob , Mohd Saberi Mohamad , Siti Syuhaida Safaai
Published: January 2019

Despite of providing high quality of education, demand on predicting student academic performance become more critical to improve the quality and assisting students to achieve a great performance in their studies. The lack of existing an efficiency and accurate prediction model is one of the major issues. Predictive analytics can provide institution with intuitive and better decision making. The objective of this paper is to review current research activities related to academic analytics focusing on predicting student academic performance. Various methods have been proposed by previous researchers to develop the best performance model using variety of students data, techniques, algorithms and tools. Predictive modeling used in predicting student performance are related to several learning tasks such as classification, regression and clustering. To achieve best prediction model, a lot of variables have been chosen and tested to find most influential attributes to perform prediction. Accurate performance prediction will be helpful in order to provide guidance in learning process that will benefit to students in avoiding poor scores. The predictive model furthermore can help instructor to forecast course completion including student final grade which are directly correlated to student performance success. To harvest an effective predictive model, it requires a good input data and variables, suitable predictive method as well as powerful and robust prediction model.
Ultrasonic signal processing techniques for Pipeline: A review
Authors: Naqiuddin M. S. M , Leong M. Salman , Hee L. M. , Azrieasrie M. A. M.
Published: January 2019

Monitoring pipeline wall is an important issue in oil and gas industries. Over time, the defect can occur in the pipeline and can impact surrounding population, environment and may result in injuries or fatalities. While flaws in the pipeline could be detected by ultrasonic testing and monitoring the severity of the flaw. The limitation of ultrasonic testing is the signal contaminate with backscattering noise, which masks flaw echoes in the measured signal. Signal processing take place in the recent year to de-noising for improving signal-to-noise ratio and extract the feature for flaws classification. This paper presents a comprehensive overview of signal processing techniques used to improve ultrasonic detection method with and without intelligent classifier. Finally, the advantages and disadvantages feature extraction provided for classifications process.
The Effects of Non-uniform Distribution of Oxidizer Flow on High-Frequency Combustion Instability
Authors: Chen Peng , Nie Wansheng , Guo Kangkang , Sun Xing , Liu Yu , Wang Haiqing
Published: January 2019

The numerical calculation of three-dimensional unsteady combustion for the combustion chamber of LOX/kerosene high pressure staged combustion rocket engine was carried out. By changing the offset ratio of oxygen mass flow rate in the edge area of the injector face, computational studies were conducted to investigate the effects of non-uniform distribution of oxidizer flow on combustion instability for a liquid-propellant rocket engine. The calculation results show that the offset ratio of oxygen mass flow rate changes the distribution of heat release in the combustion chamber. Within a certain range of offset ratio, the non-uniform distribution degree of oxidizer flow enhances the coupling between the pressure and heat release. As a result, it leads to an increase in the pressure oscillation amplitude in the combustion chamber. However, if the offset ratio is too large, the oxygen-fuel ratio will be too small in some regions, which will reduce coupling between the pressure and heat release and increase the damping of combustion instability.
Online Detection and Study of Cracks in Grinding Hardening
Authors: Ping Liang , Wei Cheng , Yulong Zhao
Published: January 2019

Grind-Hardening technology is a new technology for cutting that combines grinding theory with quenching theory, and the heat produced during the grinding process has a great effect on the surface quality of the parts. This paper take advantage of method of acoustic emission testing to test the grinding hardened parts by online or scene. The wavelet packet is used to denoise the signal, then the denoising signal is analyzed to judge those grinding cracks or defects that may appear on the surface of the parts, and besides, this method is easy to do.
Reevaluating the suppression function for phonon transport in nanostructures by Monte Carlo techniques
Authors: Zeng Yuqiang , Marconnet Amy
Published: January 2019

Thermal conductivity integral models including a suppression function to account for boundary scattering have had considerable success in explaining and predicting the thermal conductivity of nanostructures. However, the suppression function is analytically defined only for some simple structures, e.g., thin films and nanowires. For arbitrary nanostructures, Monte Carlo (MC)-based methods have been developed to calculate the suppression function. Here, we focus on two main types of MC-based methods: path sampling methods and ray tracing simulations. For the path sampling method, a more computationally efficient sampling algorithm is proposed based on the analytical solution of the average distance phonons can travel before a collision. The physical meaning of the path sampling method is rigorously given for the first time by comparing to the analytical solution of the Boltzmann Transport Equation for symmetric structures. Several limitations of the path sampling method are discussed based on assumptions in the derivation. Ray tracing simulations are well defined when a converged boundary mean free path (MFP) can be found. However, convergence is not guaranteed for arbitrary structures. More generally, we propose a modified formula to approximate the full-range suppression function with a characteristic length, which is determined by fitting to the calculated suppression function at selected MFPs. Ultimately, the accuracy of each calculated suppression function is evaluated by comparing the calculated thermal conductivity accumulation function for nanostructures including thin films, nanowires, and anisotropic modulated nanostructures. Our results provide guidance for selecting the appropriate techniques for calculating the suppression function and predicting the thermal conductivity of nanostructures.
Exact coefficients for rigid dumbbell suspensions for steady shear flow material function expansions
Authors: Piette Jourdain H. , Jbara Layal M. , Saengow C. , Giacomin A. J.
Published: January 2019

From kinetic molecular theory, we can attribute the elasticity of polymeric liquids to macromolecular orientation. For a suspension of rigid dumbbells, subject to a particular flow field, we must first solve the diffusion equation for the orientation distribution function. From this distribution, we then calculate physical properties such as the steady shear flow material functions. We thus arrive at power series expansions in the shear rate for both the orientation distribution function and for the steady shear flow material functions. Analytical work on many viscoelastic material functions must be checked for consistency, in their steady shear flow limits, against these power series. For instance, for large-amplitude oscillatory shear flow, we recover the coefficients of these expansions in the limits of low test frequency. The coefficients of the steady shear viscosity and the first normal stress coefficient functions are not known exactly beyond the fourth power. In this work, for both of these functions, we arrive at exact expressions for the first 20 coefficients. We close with five worked examples illustrating uses for our new coefficients.
Sound attenuation analysis and optimal design for a duct with periodic membranes embedded in its sidewalls
Authors: Liu Yang , Du Jingtao
Published: January 2019

Ducts with membranes in their sidewalls have been used for noise control due to their remarkable ability to reflect sound waves at low frequencies. To obtain a broader attenuation band, combining several membranes is one possible way, which leads to yet another branch of engineering called phononic crystals or acoustic metamaterials. This study analyzes sound wave propagation and attenuation in a duct with periodic membranes embedded in its sidewalls. For each cell, an analytical, fully coupled vibro-acoustic model is proposed via energy formulation, and then the interference among multiple membrane cells is treated using the cell transfer matrix. Our study provides an efficient means to predict, and eventually optimize, the acoustic bandgap structure. Results from the current model fit well with those simulated using a two/three-dimensional finite element method. The 2D membrane with free lateral edges was found to perform almost as well as its 1D counterpart. Moreover, a better bandgap can be achieved via coupling of resonance and Bragg reflection. The effects of periodic distance and membrane tension force on the bandgap structure are then discussed and analyzed to determine their appropriate parameters. Some optimal designs are implemented through artificial disorder, which shows promising potential in attenuating bandwidth expansion compared with the original periodic configuration.
In-depth investigation of the charge extraction efficiency for thermally annealed inverted bulk-heterojunction solar cells
Authors: Kolb Florian , Busby Yan , Houssiau Laurent , List-Kratochvil Emil J. W.
Published: January 2019

The performance of bulk-heterojunction solar cells is significantly affected by several factors among which are the nano-morphology of the photoactive layer and the properties of interfacial layers promoting charge extraction and collection at the electrodes. In this work, we investigate the correlation between the MoOx layer thickness and the thermal annealing procedure on the device performance and on the charge extraction efficiency of inverted ITO/PEI/P3HT:PCBM/MoOx/Ag bulk heterojunction solar cells. The surface morphology of pristine and annealed P3HT:PCBM photoactive layers is examined by atomic force microscopy before and after the exposure to dichloromethane revealing that the distribution of the amorphous regions within the P3HT:PCBM layers can be related to the applied thermal annealing procedure. The chemical and molecular composition profiles in the photoactive layer and at the interfaces are investigated through depth profile analyses combining X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry showing a decreasing oxidation gradient of the MoOx and low diffusion of the MoOx species in the P3HT:PCBM layer. Additionally, we show that the voltage dependent photocurrent is significantly affected by non-geminate recombination for devices with a too thin MoOx layer thickness, while applying a non-optimal thermal annealing procedure leads to increased geminate recombination of charge carriers. The highest charge extraction efficiency and device performance is reached for devices with a MoOx layer above 5 nm while thermal annealing procedure has to be applied before the deposition of the MoOx/Ag layers.
Boundedness in the higher-dimensional Keller-Segel model with signal-dependent motility and logistic growth
Authors: Wang Jianping , Wang Mingxin
Published: January 2019

This paper concerns a higher-dimensional Keller-Segel model with signal-dependent motility and logistic growth. It is shown that the strong logistic damping can prevent blow-up in the higher dimensions.
Application of improved fifth-degree cubature Kalman filter in the nonlinear initial alignment of strapdown inertial navigation system
Authors: Zhang Tao , Wang Jian , Jin Bonan , Li Yao
Published: January 2019

This paper addresses the state estimation of the nonlinear initial alignment of the strapdown inertial navigation system (SINS), which mainly focuses on the initial alignment on the swaying base and under the in-motion condition with the measurement uncertainties. In order to achieve a higher alignment precision, stronger numerical stability, and lower computational cost for the initial alignment of SINS on the swaying base, a new discrete large azimuth misalignment error model of SINS is established, and an improved fifth-degree cubature Kalman filter (5th-CKF) algorithm is proposed, which combines the 5th-CKF and a simplified dimensionality reduction filtering algorithm. The 5th-CKF is introduced to solve the nonlinear filtering problem, a simplified dimensionality reduction algorithm is derived to reduce the large calculation values of 5th-CKF. Furthermore, under the Bayesian framework, a novel filtering approach named the fifth-degree variational Bayesian (VB) adaptive cubature Kalman filter is deduced for the in-motion alignment with a large azimuth misalignment angle and unknown and time-varying measurement noise statistics, which combines the iterative VB approach and 5th-CKF. The 5th-CKF is exploited to handle the nonlinear initial alignment model, and the VB approach is utilized to iteratively estimate the sufficient statistics of the measurement noise. Mathematical simulation, turntable, and vehicle experiments are performed to demonstrate the effectiveness and the superiority of the proposed approaches.
Phonon relaxation time reconstruction from transient thermal grating experiments and comparison with density functional theory predictions
Authors: Forghani Mojtaba , Hadjiconstantinou Nicolas G.
Published: January 2019

Phonon relaxation time and free path distributions are reconstructed from experimental measurements on a two-dimensional transient thermal grating and compared with density functional theory (DFT) results for silicon. The reconstruction is performed using the inverse problem formulation of Forghani et al. [Phys. Rev. B 94, 155439 (2016)]. The discrepancies observed between reconstructed and DFT results are analyzed in terms of the ability of each set of data to reproduce the experimental temperature relaxation profiles; the reconstructed data are found to predict temperature profiles in closer agreement with the experimental data than the DFT results, possibly due to discrepancies between the actual material and the idealized model studied in the DFT calculations. The reconstructed phonon properties accurately predict temperature relaxation profiles at grating length scales smaller than those spanned by the experimental data. This is a very important feature since in a variety of experimental setups, including the one providing the data in the present study, measurements are not available at all scales spanned by the material free paths.
Temperature dependent carrier mobility in organic field-effect transistors: The role of dielectrics
Authors: Laudari A. , Guha S.
Published: January 2019

It has been shown that the use of a ferroelectric dielectric in 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) field-effect transistors (FETs) results in a negative coefficient of carrier mobility, a signature of a band-like transport, above a certain temperature [A. Laudari and S. Guha, Phys. Rev. Appl. 6, 044007 (2016)]. Along with spontaneous polarization, polymer ferroelectric dielectrics offer a platform for tuning interfacial transport in FETs as their dielectric constant may vary nearly by an order of magnitude with temperature. In this work, we explore a variety of organic and inorganic dielectrics with varying dielectric constants on the temperature-dependent transport properties of TIPS-pentacene organic FETs to obtain a comprehensive insight into the role of energetic disorder and trap states. In particular, a high κ dielectric, Al2O3, shows an activated transport throughout the temperature regime, whereas the ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE), with comparable and even higher values of κ compared to Al2O3, above 200 K shows a very different behavior. Additionally, the external poling condition of the PVDF-TrFE dielectric plays a role. We attribute the band-like negative coefficient of carrier mobility, observed at high temperatures, in TIPS-pentacene FETs with unpoled PVDF-TrFE to a polarization fluctuation process and explore this phenomenon using the concept of transport energy.
Surface mixing and biological activity in the North-West African upwelling
Authors: El Aouni Anass , Daoudi Khalid , Yahia Hussein , Minaoui Khalid , Benazzouz Aïssa
Published: January 2019

Near-shore water along the North-West African margin is one of the world’s major upwelling regions. It is associated with physical structures of oceanic fronts which influence the biological productivity. The study of these coherent structures in connection with chlorophyll concentration data is of fundamental importance for understanding the spatial distributions of the plankton. In this work, we study the horizontal stirring and mixing in different upwelling areas using Lagrangian coherent structures (LCSs). These LCSs are calculated using the recent geodesic theory of LCSs. We use these LCSs to study the link between the chlorophyll fronts concentrations and surface mixing, based on 10 years of satellite data. These LCSs move with the flow as material lines, thus the horizontal mixing is calculated from the intersection of these LCSs with the finite time Lyapunov exponent maps. We compare our results with those of a recent study conducted over the same area, but based on finite size Lyapunov exponents (FSLEs), whose output is a plot of scalar distributions. We discuss the differences between FSLE and geodesic theory of LCS. The latter yields analytical solutions of LCSs, while FSLEs can only provide LCSs for sharp enough ridges of nearly constant height.
Development of a fused-sphere SAFT-γ Mie force field for poly(vinyl alcohol) and poly(ethylene)
Authors: Walker Christopher C. , Genzer Jan , Santiso Erik E.
Published: January 2019

SAFT-γ Mie, a group-contribution equation of state rooted in Statistical Associating Fluid Theory, provides an efficient framework for developing accurate, transferable coarse-grained force fields for molecular simulation. Building on the success of SAFT-γ Mie force fields for small molecules, we address two key issues in extending the SAFT-γ Mie coarse-graining methodology to polymers: (1) the treatment of polymer chain rigidity and (2) the disparity between the structure of linear chains of tangent spheres and the structure of the real polymers. We use Boltzmann inversion to derive effective bond-stretching and angle-bending potentials mapped from all-atom oligomer molecular dynamics (MD) simulations to the coarse-grained sites and a fused-sphere version of SAFT-γ Mie as the basis for non-bonded interactions. The introduction of an overlap parameter between Mie spheres leads to a degeneracy when fitting to monomer vapor-liquid equilibria (VLE) data, which we resolve by matching polymer density from coarse-grained MD simulation with that from all-atom simulation. The result is a chain of monomers rigorously parameterized to experimental VLE data and with structural detail consistent with all-atom simulations. We test our approach on atactic poly(vinyl alcohol) and polyethylene and compare the results for SAFT-γ Mie models with structural detail mapped from the Optimized Potentials for Liquid Simulations (OPLS) and Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) all-atom force fields.
Nanoscale thermal gradients activated by antenna-enhanced molecular absorption in the mid-infrared
Authors: Mancini Andrea , Giliberti Valeria , Alabastri Alessandro , Calandrini Eugenio , De Angelis Francesco , Garoli Denis , Ortolani Michele
Published: January 2019

We investigate local heat generation by molecules at the apex of polymer-embedded vertical antennas excited at resonant mid-infrared wavelengths, exploiting the surface enhanced infrared absorption effect. The embedding of vertical nanoantennas in a non-absorbing polymer creates thermal isolation between the apical hotspot and the heat sink represented by the substrate. Vibrational mid-infrared absorption by strongly absorbing molecules located at the antenna apex then generates nanoscale temperature gradients at the surface. We imaged the thermal gradients by using a nano-photothermal expansion microscope, and we found values up to 10 K/μm in conditions where the radiation wavelength resonates with both the molecule vibrations and the plasmonic mode of the antennas. Values up to 1000 K/μm can be foreseen at maximum quantum cascade laser power. The presented system provides a promising thermoplasmonic platform for antenna-assisted thermophoresis and resonant mid-infrared photocatalysis.
Robustness to hydrodynamic instabilities in indirectly driven layered capsule implosions
Authors: Haines Brian M. , Olson R. E. , Sweet W. , Yi S. A. , Zylstra A. B. , Bradley P. A. , Elsner F. , Huang H. , Jimenez R. , Kline J. L. , Kong C. , Kyrala G. A. , Leeper R. J. , Paguio R. , Pajoom S. , Peterson R. R. , Ratledge M. , Rice N.
Published: January 2019

We report on a high convergence ratio liquid layer capsule implosion performed on the National Ignition Facility and contrast it to two previously reported layered implosions, in order to better understand how the capsule design impacts the hydrodynamic stability properties of implosions. Three implosions were performed with similar convergence ratios, fuel entropy, in-flight aspect ratios, and unablated shell mass; these qualities are important for determining hydrodynamic stability. Nevertheless, while two of these implosions exhibited robustness to asymmetries, including our recent experiment that had abnormally large amplitude long-wavelength capsule asymmetries, and produced more than 80% or the yield predicted by one-dimensional (1D) simulations, which do not account for the impacts of hydrodynamic instabilities, the third implosion produced only 14% of the yield from a 1D simulation. We perform a detailed computational analysis of these three shots, which suggests that the combination of several large asymmetry seeds result in the significantly degraded performance: a large 30 μm fill tube, the presence of a microstructure in the high density carbon ablator, and a higher level of drive asymmetry. This indicates that while it is possible to stabilize a high convergence ratio implosion through various means, the factors that determine stability cannot be considered independently. Furthermore, when these asymmetries are combined in 2D simulations, they can exhibit destructive interference and underpredict the yield degradation compared to experiment and three-dimensional simulations.
A classical ride through a conical intersection
Authors: Schaupp Thomas , Engel Volker
Published: January 2019

Regarding the correlated electron-nuclear motion in a model system, we investigate the dynamics in the vicinity of a conical intersection (CoIn) between two excited state potential surfaces. It is documented that an ensemble of classical trajectories which move in the complete electronic-nuclear phase space tracks the quantum wave-packet motion through the CoIn which is accompanied by a non-adiabatic population transfer. On the contrary, for an adiabatic circular motion around the position of the CoIn, the quantum mechanical and classical densities deviate substantially. In the latter case, the Born-Oppenheimer classical nuclear motion on a single potential surface is able to track the quantum dynamics.
Static force characterization with Fano anti-resonance in levitated optomechanics
Authors: Timberlake Chris , Toroš Marko , Hempston David , Winstone George , Rashid Muddassar , Ulbricht Hendrik
Published: January 2019

We demonstrate a classical analogy to the Fano anti-resonance in levitated optomechanics by applying a DC electric field. Specifically, we experimentally tune the Fano parameter by applying a DC voltage from 0 kV to 10 kV on a nearby charged needle tip. We find consistent results across negative and positive needle voltages, with the Fano line-shape feature able to exist at both higher and lower frequencies than the fundamental oscillator frequency. We can use the Fano parameter to characterize our system to be sensitive to static interactions which are ever-present. Currently, we can distinguish a static Coulomb force of 2.7 ± 0.5 × 10−15 N with the Fano parameter, which is measured with 1 s of integration time. Furthermore, we are able to extract the charge to mass ratio of the trapped nanoparticle.
Transcription factor regulation of RNA polymerase’s torque generation capacity
Authors: Ma Jie , Tan Chuang , Gao Xiang , Fulbright Robert M. , Roberts Jeffrey W. , Wang Michelle D.
Published: January 2019

Significance

RNA polymerase (RNAP) carries out transcription from DNA to RNA. The double-stranded helical nature of DNA necessitates RNAP rotation of DNA during active elongation, leading to DNA supercoiling and the accumulation of torsional stress, which may ultimately stall transcription. As a torsional motor, RNAP generates and works against torsion, but it remains unclear whether and how RNAP’s torque generation capacity may be regulated. In this work, real-time single-molecule transcriptional assays revealed that, in response to increased torsion, RNAP extensively backtracks along DNA and ultimately becomes stalled. A transcription factor, GreB, can effectively increase RNAP’s stall torque by limiting RNAP backtracking. This work provides the first illustration of how a transcription factor can regulate the capacity of transcriptional torque generation.
Sequential evolution of virulence and resistance during clonal spread of community-acquired methicillin-resistant
Staphylococcus aureus
Authors: Copin Richard , Sause William E. , Fulmer Yi , Balasubramanian Divya , Dyzenhaus Sophie , Ahmed Jamil M. , Kumar Krishan , Lees John , Stachel Anna , Fisher Jason C. , Drlica Karl , Phillips Michael , Weiser Jeffrey N. , Planet Paul J. , Uhlemann Anne-Catrin , Altman Deena R. , Sebra Robert , van Bakel Harm , Lighter Jennifer , Torres Victor J. , Shopsin Bo
Published: January 2019

The past two decades have witnessed an alarming expansion of staphylococcal disease caused by community-acquired methicillin-resistant
Staphylococcus aureus
(CA-MRSA). The factors underlying the epidemic expansion of CA-MRSA lineages such as USA300, the predominant CA-MRSA clone in the United States, are largely unknown. Previously described virulence and antimicrobial resistance genes that promote the dissemination of CA-MRSA are carried by mobile genetic elements, including phages and plasmids. Here, we used high-resolution genomics and experimental infections to characterize the evolution of a USA300 variant plaguing a patient population at increased risk of infection to understand the mechanisms underlying the emergence of genetic elements that facilitate clonal spread of the pathogen. Genetic analyses provided conclusive evidence that fitness (manifest as emergence of a dominant clone) changed coincidently with the stepwise emergence of (
i
) a unique prophage and mutation of the regulator of the pyrimidine nucleotide biosynthetic operon that promoted abscess formation and colonization, respectively, thereby priming the clone for success; and (
ii
) a unique plasmid that conferred resistance to two topical microbiocides, mupirocin and chlorhexidine, frequently used for decolonization and infection prevention. The resistance plasmid evolved through successive incorporation of DNA elements from non-
S. aureus
spp. into an indigenous cryptic plasmid, suggesting a mechanism for interspecies genetic exchange that promotes antimicrobial resistance. Collectively, the data suggest that clonal spread in a vulnerable population resulted from extensive clinical intervention and intense selection pressure toward a pathogen lifestyle that involved the evolution of consequential mutations and mobile genetic elements.
A rigorous measure of genome-wide genetic shuffling that takes into account crossover positions and Mendel’s second law
Authors: Veller Carl , Kleckner Nancy , Nowak Martin A.
Published: January 2019

Comparative studies in evolutionary genetics rely critically on evaluation of the total amount of genetic shuffling that occurs during gamete production. Such studies have been hampered by the absence of a direct measure of this quantity. Existing measures consider crossing-over by simply counting the average number of crossovers per meiosis. This is qualitatively inadequate, because the positions of crossovers along a chromosome are also critical: a crossover toward the middle of a chromosome causes more shuffling than a crossover toward the tip. Moreover, traditional measures fail to consider shuffling from independent assortment of homologous chromosomes (Mendel’s second law). Here, we present a rigorous measure of genome-wide shuffling that does not suffer from these limitations. We define the parameter

r

¯

as the probability that the alleles at two randomly chosen loci are shuffled during gamete production. This measure can be decomposed into separate contributions from crossover number and position and from independent assortment. Intrinsic implications of this metric include the fact that

r

¯

is larger when crossovers are more evenly spaced, which suggests a selective advantage of crossover interference. Utilization of

r

¯

is enabled by powerful emergent methods for determining crossover positions either cytologically or by DNA sequencing. Application of our analysis to such data from human male and female reveals that (
i
)

r

¯

in humans is close to its maximum possible value of 1/2 and that (
ii
) this high level of shuffling is due almost entirely to independent assortment, the contribution of which is

∼

30 times greater than that of crossovers.
Biohybrid valveless pump-bot powered by engineered skeletal muscle
Authors: Li Zhengwei , Seo Yongbeom , Aydin Onur , Elhebeary Mohamed , Kamm Roger D. , Kong Hyunjoon , Saif M. Taher A.
Published: January 2019

Significance

Engineered living systems is a rapidly emerging field where functional biohybrid machines are built by integration of cells or tissues with engineered scaffolds for countless technological applications. Here, we present a biohybrid pumping machine or “pump-bot,” capable of generating unidirectional flow powered by engineered skeletal muscle tissue. It utilizes a bioinspired mechanism for valveless pumping and can achieve flow rates that are at least three orders of magnitude higher than previously reported biohybrid pumps. The proposed design offers several merits, including flexibility of material choices, ease of fabrication, robustness, and ability to operate without the need for valves, blades, or other moving parts. This biological pumping system can have broad utility and impact in tissue engineering, microfluidics, and biomedical devices.