bluuebunny/crossref_metadata_2025 huggingface dataset:
The Shear Response of Beryllium as a Function of Temperature and Strain Rate
Authors: Cady Carl M. , Liu Cheng , Trujillo Carl P. , Brown Donald W. , Gray III George T.
Published: September 2018

A new specimen design has been developed to measure the shear response of materials. This compact forced-simple-shear specimen (CFSS) has been utilized to measure the shear stress/shear strain response of other materials [1, 2]. Earlier, unpublished work on the shear response of beryllium using a split Hopkinson pressure bar (SHPB) with the shear compression specimen (SCS) [3] had limited success at higher strain rates due to compressive deformation in the web leading to tensile failure in the samples. The CFSS geometry was engineered to produce essentially “pure” simple shear, mode II in-plane shear, in a compact-sample geometry that eliminates the multi-mode loading of other sample geometries and produces direct measurements of shear deformation. The use of digital image correlation (DIC) to capture and calculate shear stress and shear strain when paired with this test geometry will be described. There are two competing mechanisms for the deformation in beryllium were observed, a brittle to ductile response due to increased temperature and a transition of the deformation mechanism from dislocation dominated slip to twin deformation as the strain rate is increased. The advantages of this specimen geometry and test results as a function of temperature and strain rate are discussed for high purity beryllium.
Strain rate jump tests on an austenitic stainless steel with a modified tensile Hopkinson split bar
Authors: Vazquez Fernandez Naiara I. , Isakov Matti , Hokka Mikko , Kuokkala Veli-Tapani
Published: September 2018

This paper presents an improved experimental setup for high strain rate testing based on the modified Tensile Hopkinson Split Bar device developed previously at TUT. The test setup can be used to study the effects of a sudden large change in the strain rate on the stress flow of the material. The setup allows deforming the sample at a low rate and at isothermal conditions before the high rate loading. During the strain rate jump, the deformation rate is rapidly increased by approximately six orders of magnitude. In this work, the low and high rate deformation of the specimen was recorded with a combination of low and high-speed digital cameras and analyzed using the Digital Image Correlation technique. The measurement provides information about the effects of the strain rate jump on the macroscopic response of the material and allows accurate observation of the deformation of the sample just before, during, and immediately after the strain rate jump, when the conditions change from isothermal to adiabatic. In this paper, we present the results for a metastable austenitic stainless steel and discuss the effects of the strain rate jump on the strain-hardening rate, compare the experimental results with numerical results from a thermomechanical model, and evaluate the effects of the preceding deformation at a low strain rate on the strain localization. We conclude that the strain rate jump results in a clear decrease in the strain-hardening rate, the deformation following the jump is uniform along the gauge section, and that the strain localization is not significantly affected by the strain rate or the amount of pre-strain in the studied conditions.
Experimental investigation of Low velocity impact response of reinforced concrete beams without stirrups
Authors: Fu Yingqian , Yu Xinlu , Dong Xinlong , Zhou Fenghua
Published: September 2018

This paper presents an experimental program of reinforced concrete beam without stirrups tested by impact three-point-bending under different initial velocity (drop height). As the results shown, for the static events, the failure mode is bending firstly, and then translates to shearing. the longitudinal reinforcements play an important role for the increasing of loading during bending stage. For the impact events, reinforced concrete beams failed in a flexural failure model at slow rates of loading and in shear failure model at high impact loading rate relatively. Moreover, the shear failure and bending failure have developed during the peak stage of Force-deflection curves. That is different with the emergence sequence of cracks under static tests. So the mechanical parameters of peak stage should be considered for the resistance of concrete beam under impact loading.
Testing of Auxetic Materials Using Hopkinson Bar and Digital Image Correlation
Authors: Fíla Tomáš , Zlámal Petr , Falta Jan , Doktor Tomáš , Koudelka Petr , Kytýř Daniel , Adorna Marcel , Luksch Jutta , NeuhäuserovTomá Michaela , Valach Jaroslav , Jiroušek Ondřej
Published: September 2018

In this paper, a split Hopkinson pressure bar (SHPB) was used for impact loading of an auxetic lattice (structure with negative Poisson’s ratio) at a given strain-rate. High strength aluminum and polymethyl methacrylate bars instrumented with foil strain-gauges were used for compression of an additively manufactured missing-rib auxetic lattice. All experiments were observed using a high-speed camera with frame-rate set to approx. 135.000 fps. High-speed images were synchronized with the strain-gauge records. Dynamic equilibrium in the specimen was analyzed and optimized pulse-shaping was introduced in the selected experiments. Longitudinal and lateral in-plane displacements and strains were evaluated using digital image correlation (DIC) technique. DIC results were compared with results obtained from strain-gauges and were found to be in good agreement. Using DIC, it was possible to analyze in-plane strain distribution in the specimens and to evaluate strain dependent Poisson’s ratio of the auxetic structure.
Nickel-titanium pseudo-elastic behavior under equi-biaxial dynamic loading conditions
Authors: Quillery Pierre , Durand Bastien , Hubert Olivier , Zhao Han
Published: September 2018

Shape memory alloys (SMA) undergo a solid-solid phase transformation called martensitic transformation, involving a "high temperature" phase (austenite) and a "low temperature" phase (martensite). The stress-strain pseudo-elastic behavior of a nickel-titanium under equi-biaxial dynamic compression is measured thanks to a new home-made impact testing set-up using split Hopkinson bars. The use of thermal and optical cameras allows strain and heating sources fields to be identified. The stress field is estimated by the combination of the strain gauges information placed on bars, and a finite element analysis of the specimen. Experimental average stress-strain behavior and thermal emission are finally compared to the results of a finite difference axisymmetric model where the constitutive law is given by a fully coupled stochastic multi scale model.
Dynamic perforation and compression tests of PMMA for a wide range of temperatures - experimental and preliminary numerical analysis
Authors: Klosak Maciej , Rusinek Alexis , Jankowiak Tomasz , Qoubba Zakaria El , Matadi Boumbimba Rodrigue , Bendarma Amine
Published: September 2018

Experimental tests were carried out on poly(Methyl Methacrylate) (PMMA) in order to define its mechanical behaviour over a wide range of temperature. To reach high strain rate, perforation tests were performed within a wide range of temperatures using a high-performance oven, from room temperature to 130 °C, above the glass transition temperature Tg. In addition, the results were confronted with compression tests previously obtained. Based on experiments, the temperature transition between fragile and ductile was defined. The material became fully ductile above 118 °C inducing no cracking and debris during the perforation process. The yield stress evolution as function of strain rate for various temperatures was modelled by using the cooperative model. The model predictions were in agreement with experimental data. Two material models developed by Richeton and Nasraoui were analysed, the latter was then implemented into the FE model to simulate perforation tests for a wide range of temperatures and strain rates. It was observed that the coupling strain rate-temperature is a key factor to predict the structure behaviour not only in terms of material behaviour but also in terms of dynamic failure.
Study of flow stress and spall strength of additively manufactured Ti-6-4 alloy
Authors: Paris Vitaly , Cohen Amitai , Gudinetsky Eli , Hevroni Refael , Samuha Shmuel , Osovsky Shmuel , Tiferet Eitan , Yosef-Hai Arnon
Published: September 2018

The use of additive manufacturing (AM) by Electron Beam Melting (EBM) or Selective Laser Melting (SLM) has extensively grown in the past few years. A major goal in AM is to manufacture materials with mechanical properties at least as good as traditionally manufactured materials. In this work we present the results of planar impact tests and Split Hopkinson Pressure Bar tests (SHPB) on Ti-6Al-4V manufactured by EBM and LSM techniques. Stress strain curves based on SHPB measurements at strain rate of about 1500 s-1 display similar plastic flow stresses for SLM and EBM processed Ti-6Al-4V alloys, and about 15% higher than reported for commercial Ti-6Al-4V alloy. Results of planar impact tests on SLM samples display slightly higher spall strength than EBM while the stress at Hugoniot elastic limit (HEL) is practically the same. Hugoniot elastic limit and spall strength estimates for EBM-and SLM-processed Ti-6Al-4V alloys are at least as high as values obtained for conventionally-processed alloys. The results of post mortem SEM analysis of the spall fracture have demonstrated significant differences in the spall fracture characteristics between the AM-processed and commercial Ti-6Al-4V alloys.
Incipience and development of spall fracture in 30KHGSA steel, α↔ε transformation, spall fracture and damage recovery
Authors: Malyugina Svetlana , Mokrushin Sergey , Mayorova Anna , Kazakov Dmitry , Kozelkov Oleg , Pavlenko Alexander , Belyaev Dmitry
Published: September 2018

Results of investigation into strength and elasto-plastic properties of 30KhGSA steel are presented. The investigation was performed with planar samples using submicrosecond shockwave length technique. Shockwave amplitude varied in the range from 4 to 26 GPa and controlled with 0.2% accuracy. Steel sample temperature varied in the range from-90 °C to 670 °C. Stress wave profiles in the samples were registered with VISAR and PDV interferometers having nanosecond time resolution and measurement error better than 0.8%. Special attention was payed to the study of spall fracture incipience and development processes as well as damage recovery (healing), and shockwave passing through the damaged region in steel samples. Relaxation characteristics of dynamic elastic limit were determined. Spall strength magnitude versus strain rate and temperature characteristics was determined. The impact of polymorphic α↔ε transition in 30KhGSA steel on spall strength was studied.
Shock-induced Martensite phase transformation and its effects of metastable near β Ti-5553 titanium alloy
Authors: Wang Lin , Liu Anjin , Dai Huaxiang , Xu Feng , Min Xinhua
Published: September 2018

In this paper, microstructure evolution and mechanic properties of metastable near β Ti-5553 alloy were investigated. SHPB, SHTB and light gas gun were employed to carry out the dynamic loadings. Microstructure evolution were characterized by OM, quantitative metallography and XRD. The experimental results demonstrated that stress-induced martensite transformation occur in metastable Ti-5553 alloy through SHPB, SHTB and plate impact loadings. In SHPB loading test, stress-induced martensite transformation is one of the methods that dissipate energy besides of adiabatic shear band, and also occur before ASB. In SHTB and SHPB+SHTB loading tests, the transformation amount of stressinduced martensite exhibit similar trend. In plate impact experiment, the content of martensite phase transformation increased with the impact velocity.
Connections between steel and aluminium using adhesive bonding combined with self-piercing riveting
Authors: Reil Matthias , Morin David , Langseth Magnus , Knoll Octavian
Published: September 2018

The multi-material design of modern car bodies requires joining technologies for dissimilar materials. Adhesive bonding in combination with self-piercing riveting is widely used for joining steel and aluminium structures. To guarantee crashworthiness and reliability of a car body, accurate and effcient numerical models of its materials and connections are required. Suitable component test setups are necessary for development and validation of such models. In this work, a novel test setup for adhesively bonded and point-wise connected components is presented. Here, load combinations comparable to a vehicle crash are introduced into the connections. The developed setup facilitates successive failure of multiple connections and enables a broad validation of numerical connection models.
Occupational Deprivation – Weit entfernt von bedeutungsvollen Betätigungen
Authors: Kranz Florence
Published: September 2018

Es gibt Menschen, die nicht die Freiheit haben, die Dinge zu tun, die ihnen wichtig sind. Zum Beispiel weil sie im Gefängnis, im Pflegeheim oder auf der Flucht sind. Demnach können es äußere Umstände erschweren, sinnstiftenden Betätigungen nachzugehen.
Schulbasierte Ergotherapie – Partizipation im inklusiven Schulalltag ermöglichen
Authors: Zillhardt Cornelie , Hasselbusch Andrea , Kaelin Vera
Published: September 2018

In den USA, Kanada oder Neuseeland sind Ergotherapeuten schon lange Teil interdisziplinärer Teams in Schulen und leisten ihren Beitrag zur schulischen Inklusion. Damit Ergotherapeuten auch bei uns eine Rolle im inklusiven Bildungsalltag spielen können, ist eine Veränderung der traditionellen Sicht- und Vorgehensweise notwendig.
Wer die Zukunft erforschen will, muss die Vergangenheit kennen
Authors: Leyendecker Christine
Published: September 2018

Seit mehr als 50 Jahren ist es Pflegenden möglich, eine Weiterbildung in speziellen Arbeitsbereichen wie der Intensivpflege zu absolvieren. Bisher wurde diese
Qualifizierungsmaßnahme nicht infrage gestellt. Allerdings entwickeln sich seit wenigen Jahren neue Qualifizierungsmöglichkeiten für diesen speziellen
Arbeitsbereich. Sie reichen von einer direkten Ausbildung zur Intensivpflegekraft bis hin zu speziellen Studiengängen. So stellt sich nun doch die Frage, ob die
Fachweiterbildung bei dieser Entwicklung bald überflüssig sein wird. Eine genaue Vorhersage in die Zukunft ist natürlich nicht möglich. Aber unter Anwendung der
kritischen Diskursanalyse lässt sich eine prognostische Aussage über die Entwicklung der Fachweiterbildung erarbeiten.
Frühzeitig wärmen
Authors: Gamon Eike
Published: September 2018

Bekanntermaßen hat das perioperative Wärmemanagement einen großen Stellenwert hinsichtlich eines möglichen Wärmeverlustes des Patienten und den daraus
resultierenden multifaktoriellen Problemen. Ziel dieser Arbeit war es, anhand einer Auswertung von perioperativen Temperaturaufzeichnungen der Anästhesiepflege
festzustellen, wie gut das von uns angewendete Wärmekonzept unter Nutzung eines Systems zur konvektiven Lufterwärmung den Wärmeerhalt beim operativen Patienten
sichern kann.
Visible-Light-Mediated ipso-Carbosulfonylation of Alkynes: Synthesis of 3-Sulfonylspiro[4,5]trienones from Propiolamides and Sulfonyl Chlorides under Transition-Metal-Free Conditions
Authors: Liu Yu , Zhou Quan , Wang Qiao-Lin , Xiong Bi-Quan , Zhang Pan-Liang , Yang Chang-An , Gong Yan-Xia , Liao Jing
Published: September 2018

An efficient and convenient strategy to synthesize diverse 3-sulfonylspiro[4,5]trienones has been developed. This ipso-carbosulfonylation of alkynes proceeds by visible-light catalysis under transition-metal-free conditions and represents a new sulfonylation and ipso-cyclization of alkynes. In this transformation, the O atom in the newly generated carbonyl is derived from H2O and it features a broad substrates scope, especially for alkyl propiolamides and aliphatic sulfonyl chlorides.
Total Syntheses of Spinosyn A
Authors: Dai Mingji , Cai Xinpei , Bai Yu
Published: September 2018

Spinosyn A is an important polycyclic natural product with impressive insecticidal activity and has been used worldwide in agriculture as the major component of Spinosad. Herein, four chemical total syntheses of spinosyn A are summarized. Its biosynthesis and a chemoenzymatic total synthesis are discussed as well.

1 Biosynthesis

2 The Evans Synthesis

3 The Paquette Synthesis

4 The Roush Synthesis

5 The Liu Synthesis

6 The Dai Synthesis

7 Conclusions
Cord Blood Erythropoietin and Hepcidin Reflect Lower Newborn Iron Stores due to Maternal Obesity during Pregnancy
Authors: Korlesky Colin , Kling Pamela , Pham Daphne , Ovasapyan Albina , Leyns Cheryl , Weber Morgan , Coe Christopher
Published: September 2018

Objective Obesity during pregnancy impedes fetal iron endowment. In adults, both iron depletion and hypoxia stimulate erythropoietin (Epo) production, while hepcidin, the primary iron regulator, is inhibited by Epo and stimulated by obesity. To understand this relationship in fetuses, we investigated obesity, inflammation, and fetal iron status on fetal Epo and hepcidin levels.

Study Design Epo, hepcidin, C-reactive protein (CRP), and ferritin levels were measured in 201 newborns of 35 to 40 weeks' gestation with historical risk factors for a low fetal iron endowment, including half with maternal obesity.

Results Epo was unrelated to fetal size, but Epo was directly related to maternal body mass index (BMI; kg/m2) (p < 0.03) and CRP (p < 0.0005) at delivery. Epo levels were twice as likely to be elevated (≥50 IU/L) while comparing the lowest quartile of ferritin with the upper three quartiles (p < 0.01). Hepcidin was directly related to ferritin (p < 0.001) and indirectly related to maternal BMI (p < 0.015), but BMI became nonsignificant when undergoing multivariate analysis. Hepcidin was unrelated to Epo.

Conclusion Although some of the fetal responses involving Epo were similar to adults, we did not find a hepcidin–Epo relationship like that of adults, where fetal liver is the site of both hepcidin and Epo production.
Improved particle swarm optimization of designing resonance fatigue tests for large-scale wind turbine blades
Authors: Zhang Jinbo , Shi Kezhong , Liao Caicai
Published: September 2018

As the sizes of wind turbine blades increase, it is becoming more difficult for designing fatigue tests to meet the requirements of blades' certification. In order to design accurate fatigue tests for large-scale wind turbine blades, this paper proposes an improved optimization based on particle swarm optimization. The advantages of this optimization algorithm are its accuracy in predicting test moments and its ability in matching distributions of test moments. The shell model, which can model some special details of large-scale blades, is used to predict test moments instead of the beam model in the optimization algorithm. Besides, removing the blade tip is introduced in to enrich test methods, which enlarges the dimensions of variables in the optimization algorithm. Furthermore, moment errors are measured in both the absolute type and the relative type. Based on the study of these two types of moment errors, the objective function and constraints are designed to guide the decrease and distribution of moment errors. At last, edge-tests of a 38-m blade (shell and beam model), a 60-m blade (beam model), and a 38.75-m blade (beam model) are designed by this improved optimization, and the optimal test moments and distributions of moment errors prove the abilities of this improved optimization. Differences of the moment errors and test durations between the results designed by the standard testing method and those designed by the improved testing method demonstrate the advantages of improved optimization.
Angular, temperature, and impurity effects on secondary electron emission from Ni(110)
Authors: Patino M. I. , Wirz R. E. , Raitses Y. , Koel B. E.
Published: September 2018

The secondary electron emission from a temperature-controlled Ni(110) sample was examined for 50–1500 eV electrons impacting at 0°–35°, 50°, and 78°. Measurements showed a non-cosine dependence on an electron incidence angle: the yield has a maximum at 0°, minima at ±12°, and increases at larger angles up to 35°. This trend in angular dependence is characteristic of single crystal materials and is due to increased secondary electron generation when primary electrons are directed along a close-packed direction. For example, compared to polycrystalline nickel, the yield for Ni(110) from primary electrons at 0° (i.e., along the [110] direction) is up to 36% larger. Additionally, secondary electron yields are highly sensitive to incident electron energy (most notably between 0 and 500 eV) and to the presence of adsorbed carbon monoxide [with an up to 25% decrease compared to clean Ni(110)]. However, yields are independent of sample temperature between 300 and 600 K and of exposure to deuterium ions leading to formation of subsurface hydrogen. These results reaffirm the unique secondary electron emission properties of single crystals materials and highlight the importance of crystal orientation. Results are important for plasma-enhanced chemistry applications that utilize Ni(110) catalysts, since larger secondary electron emission may facilitate reactions of adsorbed species.
A new elliptical-beam method based on time-domain thermoreflectance (TDTR) to measure the in-plane anisotropic thermal conductivity and its comparison with the beam-offset method
Authors: Jiang Puqing , Qian Xin , Yang Ronggui
Published: September 2018

Materials lacking in-plane symmetry are ubiquitous in a wide range of applications such as electronics, thermoelectrics, and high-temperature superconductors, in all of which the thermal properties of the materials play a critical part. However, very few experimental techniques can be used to measure in-plane anisotropic thermal conductivity. A beam-offset method based on time-domain thermoreflectance (TDTR) was previously proposed to measure in-plane anisotropic thermal conductivity. However, a detailed analysis of the beam-offset method is still lacking. Our analysis shows that uncertainties can be large if the laser spot size or the modulation frequency is not properly chosen. Here we propose an alternative approach based on TDTR to measure in-plane anisotropic thermal conductivity using a highly elliptical pump (heating) beam. The highly elliptical pump beam induces a quasi-one-dimensional temperature profile on the sample surface that has a fast decay along the short axis of the pump beam. The detected TDTR signal is exclusively sensitive to the in-plane thermal conductivity along the short axis of the elliptical beam. By conducting TDTR measurements as a function of delay time with the rotation of the elliptical pump beam to different orientations, the in-plane thermal conductivity tensor of the sample can be determined. In this work, we first conduct detailed signal sensitivity analyses for both techniques and provide guidelines in determining the optimal experimental conditions. We then compare the two techniques under their optimal experimental conditions by measuring the in-plane thermal conductivity tensor of a ZnO [11-20] sample. The accuracy and limitations of both methods are discussed.
Suppression of anomalous Hall effect by heavy-fermion in epitaxial antiperovskite Mn4-xGdxN films
Authors: Li Hongwei , Wang Gaili , Hu Ping , Li Dan , Dang Shuai , Ma Xingyuan , Dai Tian , Kang Songdan , Yu Fengmei , Zhou Xiang , Wu Shuxiang , Li Shuwei
Published: September 2018

Mn4-xGdxN films with x ranging from 0 to 0.48 have been grown by a plasma-assisted molecular beam epitaxy (PA-MBE) system. Analyses show that there is a competition between Kondo coupling and the Ruderman–Kittel–Kasuya–Yosida interaction in these films. The anomalous Hall effect (AHE) was investigated, and a multiple competing scattering mechanism was used to differentiate different contributions to the AHE. Fitting results using a multivariable scaling relation show that contribution of the skew-scattering mechanism to the AHE is suppressed and competition between different contributions is stronger in highly doped samples than that in undoped samples. Resistivity-temperature (ρ-T) curves in Gd-rich samples exhibit a typical behavior of heavy fermion (HF) materials. It shows a weak metal conducting behavior in a high temperature range, while Kondo coupling dominates the middle temperature range of 50 K–110 K. With a further decrease in the temperature to 5 K, a Fermi-liquid behavior is found in the range of 5 K–20 K. Comprehensive analyses indicate that Mn4-xGdxN with large x might be a new kind of HF material with room temperature ferromagnetism.
Fabrication of a precise ellipsoidal mirror for soft X-ray nanofocusing
Authors: Mimura Hidekazu , Takei Yoshinori , Kume Takehiro , Takeo Yoko , Motoyama Hiroto , Egawa Satoru , Matsuzawa Yusuke , Yamaguchi Gota , Senba Yasunori , Kishimoto Hikaru , Ohashi Haruhiko
Published: September 2018

In X-ray focusing, grazing incidence mirrors offer advantages of no chromatic aberration and high focusing efficiency. Although nanofocusing mirrors have been developed for the hard X-ray region, there is no mirror with nanofocusing performance in the soft X-ray region. Designing a system with the ability to focus to a beam size smaller than 100 nm at an X-ray energy of less than 1 keV requires a numerical aperture larger than 0.01. This leads to difficulties in the fabrication of a soft X-ray focusing mirror with high accuracy. Ellipsoidal mirrors enable soft X-ray focusing with a high numerical aperture. In this study, we report a production process for ellipsoidal mirrors involving mandrel fabrication and replication processes. The fabricated ellipsoidal mirror was assessed under partial illumination conditions at the soft X-ray beamline (BL25SU) of SPring-8. A focal spot size of less than 250 nm was confirmed at 300 eV. The focusing tests indicated that the proposed fabrication process is promising for X-ray mirrors that have the form of a solid of revolution, including Wolter mirrors.
The Ehrenfest method with fully quantum nuclear motion (Qu-Eh): Application to charge migration in radical cations
Authors: Jenkins Andrew J. , Spinlove K. Eryn , Vacher Morgane , Worth Graham A. , Robb Michael A.
Published: September 2018

An algorithm is described for quantum dynamics where an Ehrenfest potential is combined with fully quantum nuclear motion (Quantum-Ehrenfest, Qu-Eh). The method is related to the single-set variational multi-configuration Gaussian approach (vMCG) but has the advantage that only a single quantum chemistry computation is required at each time step since there is only a single time-dependent potential surface. Also shown is the close relationship to the “exact factorization method.” The quantum Ehrenfest method is compared with vMCG for study of electron dynamics in a modified bismethylene-adamantane cation system. Illustrative examples of electron-nuclear dynamics are presented for a distorted allene system and for HCCI+ where one has a degenerate Π system.
Looking at the dynamical heterogeneity in a supercooled polymer system through isoconfigurational ensemble
Authors: Balbuena Cristian , Gianetti Melisa M. , Soulé Ezequiel R.
Published: September 2018

The dynamic correlations that emerge in a polymer system in supercooling conditions have been studied using molecular dynamic simulations. It is known that when a glass former approaches the glass transition temperature, the dynamics of the system (in terms of the mobilities of the particles) not only significantly slows down but also becomes more heterogeneous. Several theories relate this slowing down to increasing spatial (structural) correlations, for example, through the onset of cooperative relaxation regions in the Adam-Gibbs theory. In this work, we employ Pearson’s coefficient in the isoconfigurational ensemble (ICE) which allows us to study the dynamic correlations of the monomers in the ICE and establish the relation between the structure of the monomers and its dynamic behavior. Similar to what happens with mobility, monomers with highest correlation are clustered, and the clustering increases with decreasing temperature. An interesting result is that regions with high ICE dynamic correlation are not coincident with highly mobile or immobile regions. These results represent a new approach to the study of dynamic heterogeneity that emerges in glass forming liquids, complementing the more traditional characterization in terms of mobility. The methodology proposed in this work that characterize the connected dynamic regions to structural causes can represent an alternative way to observe the cooperative relaxation regions.
Non-Markovian decoherence dynamics in nonequilibrium environments
Authors: Cai Xiangji , Zheng Yujun
Published: September 2018

We theoretically investigate the non-Markovian dynamical decoherence of a quantum system coupled to nonequilibrium environments with nonstationary statistical properties. We show the time evolution of the decoherence factor in real-imaginary space to study the environment-induced energy renormalization and backaction of coherence which are associated with the unitary and nonunitary parts of the quantum master equation, respectively. It is also shown that the nonequilibrium decoherence dynamics displays a transition between Markovian and non-Markovian and the transition boundary depends on the environmental parameters. The results are helpful for further understanding non-Markovian dynamics and coherence backaction on an open quantum system from environments.
Toward deterministic construction of low noise avalanche photodetector materials
Authors: Rockwell A. K. , Ren M. , Woodson M. , Jones A. H. , March S. D. , Tan Y. , Yuan Y. , Sun Y. , Hool R. , Maddox S. J. , Lee M. L. , Ghosh A. W. , Campbell J. C. , Bank S. R.
Published: September 2018

Over the past 40+ years, III-V materials have been intensively studied for avalanche photodetectors, driven by applications including optical communications, imaging, quantum information processing, and autonomous vehicle navigation. Unfortunately, impact ionization is a stochastic process that introduces noise, thereby limiting sensitivity and achievable bandwidths, leading to intense effort to mitigate this noise through the identification of different materials and device structures. Exploration of these materials has seen limited success as it has proceeded in a largely ad hoc fashion due to little consensus regarding which fundamental properties are important. Here, we report an exciting step toward deterministic design of low-noise avalanche photodetector materials by alternating the composition at the monolayer scale; this represents a dramatic departure from previous approaches, which have concentrated on either unconventional compounds/alloys or nanoscale band-engineering. In particular, we demonstrate how to substantially improve upon the noise characteristics of the current state-of-the art telecom avalanche multipliers, In0.52Al0.48As grown on InP substrates, by growing the structure as a strain-balanced digital alloy of InAs and AlAs layers, each only a few atomic layers thick. The effective k-factor, which has historically been considered a fundamental material property, was reduced by 6–7× from k = 0.2 for bulk In0.52Al0.48As to k = 0.05 by using the digital alloy technique. We also demonstrate that these “digital alloys” can significantly extend the photodetector cutoff wavelength well beyond those of their random alloy counterparts.
Coupled-mode analysis for two-dimensional coaxial Bragg structures with helical ripples
Authors: Lai Ying-Xin , Jiang Xiao-Min , Wang Shan-Jin , Liu Tai-Jun
Published: September 2018

Making use of field expansion and the equivalent boundary, an analytical model is set up to describe the multi-mode intercoupling in two-dimensional coaxial Bragg structures with either one or both of the conductors corrugated with helical ripples. The coupled-mode equations and the explicit formulae of the coupling coefficients for all possible mode combinations are derived, and the general mode coupling rules are discussed. Based on the analytical model, the dependence of the coupling coefficients on structural parameters of the two-dimensional coaxial Bragg structures with overmoded operation is investigated by numerical calculation. The results show that the additional conductor provides more flexibility for adjustment of coupling coefficients compared with other types of two-dimensional Bragg structures with a single conductor. Taking advantage of this feature, a two-dimensional coaxial Bragg structure can provide strong reflection with high mode purity under overmoded operation by suppressing the parasitic coupling using an optimized combination of corrugated outer and inner conductors. In this way, the structure has potential applications in the design of high-Q improved Bragg resonators for high-power microwave oscillators operating in the millimeter wave or terahertz range.
Laser cooling of thallium chloride: A theoretical investigation
Authors: Yuan Xiang , Yin Shuang , Shen Yong , Liu Yong , Lian Yi , Xu Hai-Feng , Yan Bing
Published: September 2018

The possibility of laser cooling of thallium chloride (TlCl) molecules has been investigated based on high-level ab initio calculations with the consideration of the core-valence and the spin-orbit coupling (SOC) effects. The potential energy curves of the 13 Λ-S states as well as the 24 Ω states split from them via SOC are obtained by multi-reference configuration interaction plus the Davidson correction. We show that the aΠ0+3-X1Σ0+ transition of TlCl is a possible candidate for laser cooling, which features highly diagonal Franck-Condon factors and no intermediate interacting electronic states. Based on our calculations, we propose an optical cycling scheme by utilizing four lasers at wavelengths around 320 nm with more than 104 cycles for photon absorption/emission and a sub-microkelvin temperature limit.
Modeling the effects of molecular disorder on the properties of Frenkel excitons in organic molecular semiconductors
Authors: Shi Liang , Willard Adam P.
Published: September 2018

The Frenkel exciton model provides a convenient framework for simulating electronic excitations in organic conjugated systems that are too large to address with atomistic level electronic structure methods. Parameterization of this model is typically based on analytical expressions that incompletely describe the spatial and temporal correlations that are inherent to many condensed phase molecular systems. In this manuscript, we present a general procedure for including these correlations in the Frenkel exciton model, by mapping them directly from all-atom molecular configurations, for instance from classical molecular dynamics. Regardless of system morphology, this mapping automatically captures the spatial and temporal molecular correlations that are otherwise difficult or impossible to represent in terms of low-dimensional correlation functions. We apply this procedure to study the excited state properties of condensed phase materials made up of thiophene oligomers. We show that Frenkel model parameters can be mapped from a series of single molecule electronic structure calculations, and that for these materials efficient semi-empirical methods are sufficient to accurately reproduce experimental spectral measurements. By analyzing the statistics of model parameters derived from materials with different characteristic morphologies, we highlight failures in some assumptions that are commonly applied when generating model parameters. Finally, by simulating exciton dynamics on a mapped Frenekel exciton model, we demonstrate the ability to quantify the effect of material morphology on the dynamic properties of excitons.
Influence of spatial degeneracy on rotational spectroscopy: Three-wave mixing and enantiomeric state separation of chiral molecules
Authors: Lehmann Kevin K.
Published: September 2018

Pulse flip angles are calculated for three-wave mixing, three-state cycles of chiral molecules to produce optimized free induction decay amplitudes proportional to the enantiomeric excess of a sample and to produce optimized degrees of state-specific enantiomeric separation. The calculations account for the spatial degeneracy of the levels involved and the resulting inhomogeneous distribution of transition dipole moments. Cycles of transitions that include R followed by Q followed by P branch transitions display only modest reductions of the calculated optimal signals compared to those calculated if every M component was optimally polarized. Transition cycles P–Q–R are only slightly worse, while the Q–Q–Q cycles are much worse, increasingly so, as the rotational total quantum number is increased.
Current sheet bending as destabilizing factor in magnetotail dynamics
Authors: Korovinskiy D. B. , Semenov V. S. , Erkaev N. V. , Ivanov I. B. , Kiehas S. A.
Published: September 2018

The problem of the magnetohydrodynamical stability of bent magnetotail current sheets is considered by means of 2.5-dimensional numerical simulations. This study is focused on the cross-tail transversal mode, modeling the magnetotail flapping motions, at the background of the Kan-like magnetoplasma equilibrium. It is found that in symmetrical current sheets, both stable and unstable branches of the solution may coexist; the growth rate of the unstable mode is rather small, so that the sheet may be considered as stable at the substorm timescale. With the increasing dipole tilt angle, the sheet bends and the growth rate rises. For sufficiently large tilt angles, the stable branch of the solution disappears. Thereby, the sheet destabilization timescale shortens for an order of magnitude, down to several minutes. The analysis of the background parameters has shown that stability loss is not related to buoyancy; it is controlled by the cross-sheet distribution of the total pressure.
Predicted infrared spectra in the HF stretching band of the H2–HF complex
Authors: Huang Jing , Zhou Yanzi , Xie Daiqian
Published: September 2018

The infrared spectra with hydrogen fluoride (HF) and deuterium fluoride (DF) (v2 = 1 ← 0) for eight isotropic species of H2–HF complex are predicted, based on our newly constructed high-accuracy ab initio potential energy surface [D. Yang et al., J. Chem. Phys. 148, 184301 (2018)]. The radial discrete variable representation/angular finite basis representation method and Lanczos algorithm were used to determine the ro-vibrational energy levels and wave functions for eight species of H2–HF complex (para-H2–HF, ortho-H2–HF, para-D2–HF, ortho-D2–HF, para-H2–DF, ortho-H2–DF, para-D2–DF, and ortho-D2–DF) with separating the inter- and intra-molecular vibrations. Bound states properties including their dissociation energies and rotational constants were presented. The calculated band origins are all red shifted to the isolated HF molecule and in good agreement with available experimental values. The frequencies and line intensities of ro-vibrational transitions in the HF stretching band were further calculated, and the predicted infrared spectra are consistent with available observed spectra. Among them, the spectra for three isotopic species of H2–HF (para-H2–DF, para-D2–DF, and ortho-D2–DF) were predicted for the first time.
Finite-size corrections in numerical simulation of liquid water
Authors: Belloni Luc
Published: September 2018

Monte Carlo (MC) simulations of the SPC/E liquid water model are performed at two numbers of molecules N = 100 and 512 and in canonical NVT, isobaric NPT, and grand canonical μVT ensembles. The molecular non-spherically symmetric pair distribution function g(r, Ω) (pdf) is accumulated in terms of projections gμνmnl(r) onto rotational invariants. The precisely measured differences between N values and between ensembles are in very good agreement with the theoretical predictions for the expected finite-size corrections of different origins: (1) the canonical simulation is affected by explicit corrections due to the absence of density fluctuations. Beyond the well-known shift in the long-range asymptote, all projections exhibit rich short-range contributions. These corrections vanish exactly in the isobaric ensemble provided that the pdf is constructed using the rigorous definition. (2) In the presence of dielectric discontinuity with the external medium surrounding the central box and its replica within the Ewald treatment of the Coulombic interactions, the disagreement with the prediction of the literature, already noticed recently for dipolar fluids, is confirmed in the present site-site model. (3) The implicit corrections originate from the coupling between the environment around a given particle and that around its periodic images in the neighboring cells. The recent, powerful MC/HNC mixed integral equation, which offers a complete and exact description of the molecular correlations in the whole real and Fourier spaces, enables us to quantify the observed N-dependence in the pdf projections down to the sub 10−3 levels.
Communication: Long range corrections in liquid-vapor interface simulations
Authors: Lishchuk Sergey V. , Fischer Johann
Published: September 2018

Long range corrections (lrc) for the potential energy and for the force in planar liquid-vapor interface simulations are considered for spherically symmetric interactions. First, it is stated that for the Lennard-Jones (LJ) fluid the lrc for the energy Δu of Janeček [J. Phys. Chem. B 110, 6264 (2006)] is the same as that of Lotfi et al. [Mol. Simul. 5, 233 (1990)]. Second, we present the lrc for the force ΔF for any spherically symmetric interaction as a derivative of Δu plus a surface integral over the cut-off sphere by using the extended Leibniz rule of Flanders [Am. Math. Monthly 80, 615 (1973)]. This ΔF corrects the incomplete lrc Δ1F of Lotfi et al. and agrees with the result of Janeček obtained by direct averaging of the forces. Third, we show that the molecular dynamics (MD) results for the surface tension γ of the LJ fluid with size parameter σ obtained by Werth et al. [Physica A 392, 2359 (2013)] with the lrc ΔF of Janeček and a cut-off radius rc = 3σ agree with the results of Mecke et al. [J. Chem. Phys. 107, 9264 (1997)] obtained with the lrc Δ1F of Lotfi et al. and rc = 6.5σ within −0.4% to +1.6%. Moreover, using only the MD results for γ of Werth et al., we obtain for the LJ fluid a new surface tension correlation which also represents the γ-values of Mecke et al. within ±0.7%. The critical temperature resulting from the correlation is Tc = 1.317 66 and is in very good agreement with Tc,ref = 1.32 of the reference equation of state for the LJ fluid given by Thol et al. [J. Phys. Chem. Ref. Data 45, 023101 (2016)].
Supervised machine learning looks to help researchers design collective variables
Authors: Liebendorfer Adam
Published: September 2018

A newly demonstrated automated approach defines low-dimensional representation of molecules for accelerated sampling on alanine dipeptide and Chignolin mini-protein models.
Liquid Structures and Transport Properties of Lithium Bis(fluorosulfonyl)amide/Glyme Solvate Ionic Liquids for Lithium Batteries
Authors: Terada Shoshi , Ikeda Kohei , Ueno Kazuhide , Dokko Kaoru , Watanabe Masayoshi
Published: September 2018

The liquid structures and transport properties of electrolytes composed of lithium bis(fluorosulfonyl)amide (Li[FSA]) and glyme (triglyme (G3) or tetraglyme (G4)) were investigated. Raman spectroscopy indicated that the 1:1 mixtures of Li[FSA] and glyme (G3 or G4) are solvate ionic liquids (SILs) comprising a cationic [Li(glyme)]+ complex and the [FSA]− anion. In Li[FSA]-excess liquids with Li[FSA]/glyme molar ratios greater than 1, anionic Lix[FSA]y(y–x)– complexes were formed in addition to the cationic [Li(glyme)]+ complex. Pulsed field gradient NMR measurements revealed that the self-diffusion coefficients of Li+ (DLi) and glyme (Dglyme) are identical in the Li[FSA]/glyme=1 liquid, suggesting that Li+ and glyme diffuse together and that a long-lived cationic [Li(glyme)]+ complex is formed in the SIL. The ratio of the self-diffusion coefficients of [FSA]− and Li+, DFSA/DLi, was essentially constant at ~1.1–1.3 in the Li[FSA]/glyme<1 liquid. However, DFSA/DLi increased rapidly as the amount of Li[FSA] increased in the Li[FSA]/glyme>1 liquid, indicating that the ion transport mechanism in the electrolyte changed at the composition of Li[FSA]/glyme=1. The oxidative stability of the electrolytes was enhanced as the Li[FSA] concentration increased. Furthermore, Al corrosion was suppressed in the electrolytes for which Li[FSA]/glyme>1. A battery consisting of a Li metal anode, a LiNi1/3Mn1/3Co1/3O2 cathode, and Li[FSA]/G3=2 electrolyte exhibited a discharge capacity of 105mAhg−1 at a current density of 1.3mAcm−2, regardless of its low ionic conductivity of 0.2mScm−1.
Macrocycle ring deformation as the secondary design principle for light-harvesting complexes
Authors: De Vico Luca , Anda André , Osipov Vladimir Al. , Madsen Anders Ø. , Hansen Thorsten
Published: September 2018

Significance

Bacteriochlorophyll–protein complexes, such as LH2 and LH3 from
Rhodoblastus acidophilus
, represent the core of bacterial photosynthesis. While similar in many aspects, these two prototypical complexes show different absorption wavelengths, being the latter blue-shifted ca. 30 nm in its major peak respect to the former. These systems have been intensively studied so as to understand the underlying structural mechanisms controlling the difference in absorption and, ultimately, the photosynthetic process. Through highest level computational tools, we here demonstrate that, somewhat contrary to common belief, the major device steering the absorption of bacteriochlorophylls is the direction of their macrocycle ring curvature axis. This finding could lead to the design of novel, easily, and highly tunable chromophores, for future light-harvesting artificial systems.
Structural basis for murine norovirus engagement of bile acids and the CD300lf receptor
Authors: Nelson Christopher A. , Wilen Craig B. , Dai Ya-Nan , Orchard Robert C. , Kim Arthur S. , Stegeman Roderick A. , Hsieh Leon L. , Smith Thomas J. , Virgin Herbert W. , Fremont Daved H.
Published: September 2018

Murine norovirus (MNoV) is closely related to human norovirus (HNoV), an infectious agent responsible for acute gastroenteritis worldwide. Here we report the X-ray crystal structure of the dimeric MNoV VP1 protruding (P) domain in complex with its cellular receptor CD300lf. CD300lf binds the P domain with a 2:2 stoichiometry, engaging a cleft between the AB and DE loops of the P2 subdomain at a site that overlaps the epitopes of neutralizing antibodies. We also identify that bile acids are cofactors enhancing MNoV cell-binding and infectivity. Structures of CD300lf–P domain in complex with glycochenodeoxycholic acid (GCDCA) and lithocholic acid (LCA) reveal two bile acid binding sites at the P domain dimer interface distant from receptor binding sites. The structural determinants for receptor and bile acid binding are supported by numerous biophysical assays utilizing interface residue mutations. We find that the monomeric affinity of CD300lf for the P domain is low and is divalent cation dependent. We have also determined the crystal structure of CD300lf in complex with phosphocholine, revealing that MNoV engages its receptor in a manner mimicking host ligands including similar metal coordination. Docking of the cocomplex structures onto a cryo-EM–derived model of MNoV suggests that each virion can make multiple CD300lf engagements, and thus, infection may be driven by the avidity of cell surface clustered CD300lf. These studies identify multiple potential modulators of norovirus infection that may act to regulate the interaction between the viral capsid P domain and its cognate cellular receptor.