bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of copper-catalyzed enantioselective decarboxylative aldolization for the preparation of perfluorinated 1,3,5-triols featuring supramolecular recognition properties
Authors: Sperandio Céline , Rodriguez Jean , Quintard Adrien
Published: December 2019

An enantioselective aldolization on perfluorinated aldehydes has been developed. The reaction can create in one step ketodiols, precursors of crucial perfluorinated 1,3,5-triols featuring selective chiral anion recognition ability.
Classwide Extensions of Vocabulary Intervention Improve Learning of Academic Vocabulary by Preschoolers
Authors: Seven Yagmur , Hull Katharine , Madsen Keri , Ferron John , Peters-Sanders Lindsey , Soto Xigrid , Kelley Elizabeth S. , Goldstein Howard
Published: December 2019

Purpose

Many preschoolers, especially those from low-income households, would benefit from instruction to enrich their vocabulary and language repertoires. Yet, explicit instruction of vocabulary and language skills generally occurs infrequently in early childhood education settings. This study investigated the additive effects of teacher-led, classwide review strategies to a previously studied small-group intervention on children's learning of academic vocabulary.

Method

Participants included 23 children with limited oral language skills at risk for reading difficulties enrolled in single-case experimental designs. Effects of the classroom strategies alone also were examined in 10 children with above-average language abilities from 2 classrooms.

Results

Visual analyses of the adapted alternating treatments designs showed consistent learning improvements when vocabulary instruction was extended into the classroom for 12 children, ceiling effects were evident for 3 participants regardless of condition, and inconsistent or minimal effects were demonstrated by 8 participants. Multilevel modeling used to evaluate the effects statistically revealed strong treatment effects. In addition, the 10 children with above-average language showed impressive learning of vocabulary words from books subject to teacher review strategies in comparison to words from books to which they were not exposed. Teachers varied in the extent to which they implemented review strategies in their classrooms. Nevertheless, their responses to social validity assessments were positive, supporting the feasibility of this intervention.

Conclusions

The addition of classwide review and practice opportunities is an effective means of enhancing the effects of an easy-to-implement small-group intervention that teaches challenging vocabulary words within prerecorded stories. This approach holds promise as a way to shrink the pervasive word gap that typically exists when children in high-poverty communities enter school.
Burst-induced coronal cooling in GS 1826–24
Authors: Sánchez-Fernández C. , Kajava J. J. E. , Poutanen J. , Kuulkers E. , Suleimanov V. F.
Published: December 2019

Type I X-ray bursts in GS 1826–24, and in several other systems, may induce cooling of the hot inner accretion flow that surrounds the bursting neutron star. Given that GS 1826–24 remained persistently in the hard state over the period 2003–2008 and presented regular bursting properties, we stacked the spectra of the X-ray bursts detected by INTEGRAL (JEM-X and ISGRI) and XMM-Newton (RGS) during that period to study the effect of the burst photons on the properties of the Comptonizing medium. The extended energy range provided by these instruments allows the simultaneous observation of the burst and persistent emission spectra. We detect an overall change in the shape of the persistent emission spectrum in response to the burst photon shower. For the first time, we observe simultaneously a drop in the hard X-ray emission, together with a soft X-ray excess with respect to the burst blackbody emission. The hard X-ray drop can be explained by burst-induced coronal cooling, while the bulk of the soft X-ray excess can be described by fitting the burst emission with an atmosphere model, instead of a simple blackbody model. Traditionally, the persistent emission was assumed to be invariant during X-ray bursts, and more recently to change only in normalization but not in spectral shape; the observed change in the persistent emission level during X-ray bursts may thus trigger the revision of existing neutron star mass-radius constraints, as the derived values rely on the assumption that the persistent emission does not change during X-ray bursts. The traditional burst fitting technique leads to up to a 10% overestimation of the bolometric burst flux in GS 1826–24, which significantly hampers the comparisons of the KEPLER and MESA model against this “textbook burster”.
Analysis of electromagnetic pulses generation from laser coupling with polymer targets: Effect of metal content in target
Authors: Xia Yadong , Zhang Feng , Cai Hongbo , Zhou Weimin , Tian Chao , Zhang Bo , Liu Dongxiao , Yi Tao , Xu Yilin , Wang Feng , Li Tingshuai , Zhu Shaoping
Published: December 2019

Powerful lasers interacting with solid targets can generate intense electromagnetic pulses (EMPs). In this study, EMPs produced by a pulsed laser (1 ps, 100 J) shooting at CH targets doped with different titanium (Ti) contents at the XG-III laser facility are measured and analyzed. The results demonstrate that the intensity of EMPs first increases with Ti doping content from 1% to 7% and then decreases. The electron spectra show that EMP emission is closely related to the hot electrons ejected from the target surface, which is confirmed by an analysis based on the target–holder–ground equivalent antenna model. The conclusions of this study provide a new approach to achieve tunable EMP radiation by adjusting the metal content of solid targets, and will also help in understanding the mechanism of EMP generation and ejection of hot electrons during laser coupling with targets.
From symmetry to entropy: Crystal entropy difference strongly affects early stage phase transformation
Authors: Hu C. H. , Chen Y. C. , Yu P. J. , Fung K. Y. , Hsueh Y. C. , Liaw P. K. , Yeh J. W. , Hu A.
Published: December 2019

Although the connection between symmetry and entropy is not clear, researchers calculate configurational entropy with an ideal gas mixing model all along regardless of which structure they are considering. However, it is obvious that crystalline structures have symmetry, while an ideal gas does not. Therefore, the same ideal gas mixing value should not be assigned to other structures, such as face-centered-cubic (fcc) and hexagonal-close-packed (hcp) structures. Here, we offer a precise definition for determining the configurational entropy of crystals. We calculate the difference in configurational entropy between fcc and hcp structures based on Burnside's lemma in combinatorial mathematics and crystallographic rotation-point groups.
Assessment of climate change impacts on wind resource characteristics and wind energy potential in Greece
Authors: Katopodis Theodoros , Vlachogiannis Diamando , Politi Nadia , Gounaris Nikolaos , Karozis Stelios , Sfetsos Athanasios
Published: December 2019

Wind technology is projected to play a key role in mitigating climate change effects and contributing to the reduction of CO2 emissions, but its sustainability critically depends on current and future climate conditions. In this study, the climate change impacts on wind resources and wind energy potential in Greece are assessed, yielding a wealth of information that could be used by stakeholders. A detailed evaluation of future wind characteristics over Greece is carried out using EURO-CORDEX RCA4 model data with a horizontal resolution of ∼12 km, taking into consideration future RCP scenarios for the short term decadal climatology of 2040, which is the expected end-life of installed wind turbines. The RCA4 model demonstrated accurate performance when compared to actual observational data from the HNMS network, thus allowing higher confidence in assessments of future periods. Future projections revealed changes in the mean wind speed of the order of ±5% that did not vary significantly for the different RCP scenarios, although on a monthly basis that variability could reach ±20%. Decadal changes in the mean wind potential were of the order of ±15% for the two RCPs (2.6 and 8.5). Wind gusts exceeding 52 m/s, linked to the wind turbine structural integrity and robust performance, appeared more frequently in RCP 8.5 by about 2–4 times per decade, affecting mostly the South Ionian Sea. The findings also indicate a tendency for calming of the “Etesians” winds over the Aegean Sea in future summers.
ARTEC—A furnace module for directional solidification and quenching experiments in microgravity
Authors: Balter M. , Neumann C. , Bräuer D. , Dreißigacker C. , Steinbach S.
Published: December 2019

A new experimental design for directional solidification experiments with high cooling rates under microgravity conditions is presented. The aerogel-based furnace module ARTEC (AeRogel TEchnology for Cast alloys) developed at DLR extends the earlier presented sounding rocket facility ARTEX by enabling a transition from low to high solidification velocities and a simultaneous operation of five independent furnaces in the same sounding rocket module. The furnaces for directional solidification are equipped with thermally insulating aerogels as a crucible material. Their optical transparency allows the control of the solidification parameters (velocity and temperature gradient) with optical methods in the lab. In ARTEC, a drastically increased solidification velocity is achieved by contacting the sample with a movable cooling-rod during processing. Therefore, a better theoretical understanding of the influence of a sudden change in solidification velocity on microstructure formation is obtained. Carrying out experiments in microgravity gives access to purely diffusive solidification conditions. Hence, convection free-growth can be compared with growth subject to natural (earth) and/or forced-convection (earth and space). Furthermore, alloys with high density differences in their alloy components and, hence, also between the primary solidifying phase and the surrounding liquid can be studied without the negative influence of fluid-flow or macrosegregation being present.
Stochastic self-tuning hybrid algorithm for reaction-diffusion systems
Authors: Ruiz-Martínez Á. , Bartol T. M. , Sejnowski T. J. , Tartakovsky D. M.
Published: December 2019

Many biochemical phenomena involve reactants with vastly different concentrations, some of which are amenable to continuum-level descriptions, while the others are not. We present a hybrid self-tuning algorithm to model such systems. The method combines microscopic (Brownian) dynamics for diffusion with mesoscopic (Gillespie-type) methods for reactions and remains efficient in a wide range of regimes and scenarios with large variations of concentrations. Its accuracy, robustness, and versatility are balanced by redefining propensities and optimizing the mesh size and time step. We use a bimolecular reaction to demonstrate the potential of our method in a broad spectrum of scenarios: from almost completely reaction-dominated systems to cases where reactions rarely occur or take place very slowly. The simulation results show that the number of particles present in the system does not degrade the performance of our method. This makes it an accurate and computationally efficient tool to model complex multireaction systems.
Enhanced magnetoelectric torque effect in Pb(Zr,Ti)O3/NdFeB bi-cantilever composites
Authors: Wu Gaojian , Zhang Ru
Published: December 2019

A piezoelectric/ferromagnetic bicantilever composite, constructed with a Pb(Zr,Ti)O3 beam fixed at the middle point and NdFeB magnets attached at both free ends, has been designed and exhibited a giant magnetoelectric torque (MET) effect. The low-frequency and resonant MET effect in the bicantilever composite is more than twice as much as that in the single cantilever composite with the same components and geometry dimension. As the magnet mass increases, the MET effect first increases nearly linearly and then tends to saturate while the resonant frequency decreases. When the magnets are attached asymmetrically at the tip, the MET effect is stronger than that of the symmetric attachment. Our results will give more choices for preparing the magnetoelectric device used as an ac magnetic field sensor, energy harvester, etc.
Stress relaxation in semipolar and nonpolar III-nitride heterostructures by formation of misfit dislocations of various origin
Authors: Smirnov A. M. , Young E. C. , Bougrov V. E. , Speck J. S. , Romanov A. E.
Published: December 2019

We present an analytical model describing misfit stresses relaxation in semipolar III-nitride heterostructures caused by misfit dislocations (MDs) originating from basal or prismatic slip and by sessile MDs. We analyze the critical thickness hc for the formation of MDs depending on crystal lattice mismatch and orientation of the semipolar growth plane. We explore transversely isotropic elasticity solutions to describe the relaxation processes in III-nitride semipolar heterostructures and compare the results for hc with those calculated within the isotropic elasticity approach. We find that the value of angle ϑ between the polar с-axis, and the direction of heterostructure growth has an impact on the realization of the stress relaxation mechanism by the generation of MDs originating either from basal or prismatic slip. A comparison of theoretical calculations with experimental data on the observation of MDs in the III-nitride heterostructures is provided.
Analytical proof of Schottky’s conjecture for multi-stage field emitters
Authors: de Carvalho Neto Edgar Marcelino
Published: December 2019

Schottky’s conjecture is analytically proved for multistage field emitters consisting of the superposition of rectangular or trapezoidal protrusions on a line under some specific limit. The case in which a triangular protrusion is present on the top of each emitter is also considered as an extension of the model. The results presented here are obtained via Schwarz-Christoffel conformal mapping and reinforce the validity of Schottky’s conjecture when each protrusion is much larger than the ones above it, even when an arbitrary number of stages is considered. Moreover, it is showed that it is not necessary to require self-similarity between each of the stages in order to ensure the validity of the conjecture under the appropriate limits.
A mathematical model based on unstructured mesh for ice accretion
Authors: Chen Ningli , Hu Yaping , Ji Honghu , Cao Guangzhou , Yuan Yongqing
Published: December 2019

This paper proposes a three-dimensional model to simulate ice accretion on the surface of an aircraft. The model is developed using a prism grid cell, which enables iterations with an unstructured mesh. The model assumes that the impinged water droplets on the surface can form a thin water film, and ice accretion is caused by the flow and solidification of the film. The model is developed by analyzing the conservations of mass, momentum, and energy for the thin water film on the surface. The mass and energy conservation equations of the water film are discretized on the prism grid cell, while the momentum conservation equation, which is simplified using lubrication theory, is integrated along the surface normal direction to obtain an analytical solution for the film velocity. The thicknesses of the water film and ice layer are calculated by iterating the discretized mass and energy conservation equations with the analytical solution of the film velocity. The model is verified by comparing its results with published experimental and numerical data. The results show that the model provides accurate predictions of ice accretion under different conditions, even when using an unstructured grid.
Spatial confinement effects of bubbles produced by laser ablation in liquids
Authors: Zhang Zhi , Wang Aosong , Wu Jian , Liu YanZhang , Huang Dapeng , Qiu Yan , Li Jilong
Published: December 2019

The paper deals with the influence of the spatial confinement on the evolution of laser bubbles and shock waves by means of the shadowgraphy technique. Due to the constraint of walls, the bubble center shrinks faster than the bubble edge and collapses before the edge of the bubble, splitting into left and right small bubbles that continue to shrink down. The result validates that the Bjerknes force has little effect on bubble evolution at the expansion stage but a great influence on it at the collapse stage. We study the evolution of laser bubbles with different Al-plate intervals for displaying a gradual transition from constrained conditions to unconstrained conditions. In addition, we describe the dynamics of the first bubble at the expansion stage using the Rayleigh-Plesset equation. The pressure and temperature inside laser bubbles are calculated in the meanwhile.
Parts-per-trillion sensitivity for trace-moisture detection using wavelength-meter-controlled cavity ring-down spectroscopy
Authors: Hashiguchi Koji , Lisak Daniel , Cygan Agata , Ciuryło Roman , Abe Hisashi
Published: December 2019

We introduced frequency-control and temperature-control systems in wavelength-meter-controlled cavity ring-down spectroscopy. The frequency-control system shifted the wavelength of the probe laser from 1393 nm to 696.5 nm where no strong absorption lines of water exist, and therefore, it could avoid measurement errors in laser frequency due to residual moisture in the built-in Fizeau interferometer of a wavelength meter. We verified the hypothesis that the nonuniform reflectivity of the mirror surface contributes to fluctuations in the ring-down time observed with multi-transverse-mode CRDS signals. The fluctuations due to this effect were greatly suppressed by the temperature-control system. Using this system, we could improve the minimum detectable absorption coefficient by three times on average and also improve the experimental standard deviations of the averages by nine times compared with those without the system. We measured near-infrared spectra of residual moisture in dry nitrogen at an approximately 1 nmol/mol (1 ppb) level and performed least-squares fitting of the averaged spectrum. The standard deviation of the residuals of the fitting was 6.6 × 10−12 cm−1, corresponding to a mole fraction of water of 6.3 pmol/mol (6.3 ppt).
Interplay between various active regions and the interband transition for AlGaN-based deep-ultraviolet light-emitting diodes to enable a reduced TM-polarized emission
Authors: Tian Kangkai , Chu Chunshuang , Che Jiamang , Shao Hua , Kou Jianquan , Zhang Yonghui , Zhou Xingye , Feng Zhihong , Wei Tongbo , Zhang Zi-Hui
Published: December 2019

Al-rich AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) have a low light extraction efficiency, especially when the emission wavelength is shorter than 280 nm, and this is partially because of the dominant transverse-magnetic polarized light. Our results show that the transverse-electric (TE) polarized light can be obtained even if the emission wavelength becomes even shorter by reducing the quantum well thickness. The ultrathin quantum well enables the enhanced TE-polarized emission that arises from the redistributed subbands for holes. On the contrary to the common belief, we observe a blueshift for the emission wavelength when the AlN composition in the quantum barrier increases. The internal quantum efficiency (IQE) for DUV LEDs with ultrathin quantum wells is no longer determined by the quantum-confined Stark effect, while quantum barrier with high AlN composition is vitally important to improve the electron injection efficiency and thus enhance the IQE.
The ambient wind impact on eddy current distribution in air cooling island
Authors: Wang Zhi , Liu Yali , Yan Ruiming
Published: December 2019

With increasing ambient wind speed, eddy currents appear near condenser cells, affecting the thermal-flow performance of a direct air-cooled condenser. To examine the impact of ambient wind on the eddy-current distribution of an air-cooling island, a 2 × 600 MW direct air-cooling unit in North China was studied. To compare a series of different inlet wind speeds, the temperature and pressure distribution and the mechanism of and variation in eddy currents were studied. Moreover, the effects of ambient wind speed on the inlet flow rate of an axial-flow fan cluster were examined. Numerical results show that with increasing ambient speed, the chance of hot-air plume generation increases, resulting in a reduction in heat-transfer volume and efficiency. Additionally, more negative-pressure areas are created near the condenser cells. Vortices appear in the condenser-cell flow field, gradually becoming larger. The mass-flow rate of the axial flow fan cluster exhibits a downward trend with increasing ambient speed.
Magnetic properties of anisotropic bonded NdFeB/SmCo permanent magnets
Authors: An Shizhong , Ma Zhenhui , Li Wuhui , Zhang Huifang , Yin Ting
Published: December 2019

Anisotropic bonded NdFeB permanent magnets have wide potential applications in the areas such as brushless DC motors, spindle motors, and stepping motors due to their excellent processing property and high magnetic properties. Anisotropic NdFeB bonded magnets prepared by hydrogen-disproportionation–desorption-recombination (HDDR) process have large energy product at room temperature. However, they are not stable at ∼100°C, which is the working temperature of many electric motors. In order to improve their thermal stability, we developed bonded NdFeB/SmCo magnets and investigated the effects of powder particle size and SmCo content on their magnetic properties. We proposed a model to clarify the filling effect of the powder, which played a key role in the enhanced (BH)max when reducing the SmCo particle size. As for the SmCo content, the bonded magnets showed improved (BH)max at 100°C-150°C and thermal stability with the increase of SmCo content. And through adjusting the SmCo content, the remanence temperature coefficient and coercivity temperature coefficient from 25-150°C were able to be regulated in the range of -0.14%/°C to -0.04%/°C and -0.51%/°C to -0.14%/°C, respectively. This work provides a design strategy and a facile route to improve the magnetic properties and thermal stability of the bonded magnets.
Giant magnetoimpedance effect at GHz frequencies in amorphous microwires
Authors: Zhukov A. , Gonzalez-Legarreta L. , Ipatov M. , Corte-Leon P. , Blanco J. M. , Zhukova V.
Published: December 2019

Studies of magnetic properties and GMI effect of amorphous Co-Fe rich microwires reveal that they present GMI effect at GHz frequencies. Magnetic field dependences of GMI effect are affected by the post-processing conditions. In particular, we observed that in Co-Fe rich microwires stress-annealing allows improvement of frequency dependence of GMI ratio at high frequencies. We discussed observed experimental dependences considering both different magnetic structure and the anisotropy in the bulk and near the surface and close analogy between giant magnetoimpedance and ferromagnetic resonance.
Slow magnetic relaxation in well crystallized, monodispersed, octahedral and spherical magnetite nanoparticles
Authors: Navarro Enrique , Luengo Yurena , Veintemillas Sabino , Morales Puerto , Palomares F. Javier , Urdiroz Unai , Cebollada Federico , González Jesús M.
Published: December 2019

Thermally activated relaxation over energy barriers concurrently related to local properties and interparticle interactions constitutes a major contribution to both the coercivity and the applied field frequency dependence of that quantity. We have measured the slow magnetic relaxation of magnetite nanoparticles (NPs), synthetized by using the oxidative precipitation technique, having spherical and octahedral shapes, monodispersed size distributions and similar transverse dimensions. From our relaxation data we evaluated the temperature dependencies of a) the irreversible demagnetization susceptibility, b) the fluctuation field (associated to the thermally induced demagnetization occurring during the measuring time range) and c) the activation volume (corresponding to the demagnetization produced by the fluctuation field). We conclude that i) the irreversible susceptibility peaks in both samples at ca. 135 K (Verwey transition temperature) and ii) the monotonically increasing temperature variation of the activation volume shows the same values in both samples for temperatures below ca. 135 K and at 290 K reaches values corresponding to 10 and 30 times the average particle volume of the spherical and octahedral NPs, respectively. Those large increases of the activation volume are compatible with a transition from local to collective of the thermally activated processes.
Manipulations of the coercivity and the Kerr signal of the NiFe films by a ZnO underlayer
Authors: Yu Chin-Chung , Ko Hsin-Hua , Lin Zheng-Wei , Lai Jun-Yang
Published: December 2019

In this study, Ni50Fe50 films with different thicknesses were prepared on a ZnO(0001) film that was grown on a conductive Si(100) substrate. The ZnO(0001) film was characterized to be a ferroelectric layer with a value of piezoelectric constant, d33, equal to 5.0pm/V. Monotonic decreases in the coercivity of the NiFe films can be observed while the ZnO layer exposed to an electric field. As the applied potential equal to 10V, the coercivity of the NiFe films reduced 64% and 41% for the thickness equal to 10nm and 50nm, respectively. The strength of the strain field established inside the NiFe films was strongly correlated with the decreasing ratio of the coercivity. Moreover, the Kerr signal of the NiFe films can be well modulated by the electric fields established across the ZnO layer while the potential lower than 10V. The lattice distortion and dislocation formation inside the ZnO layer controlled the highest potential that can be applied and, consequently, the reliability of the modulation of the Kerr signal.
Structural and magnetic properties of Co-V nanoparticles
Authors: Tosun O. , Ruzybayev I. , Abel F. M. , Balamurugan B. , Skomski R. , Sellmyer D. J. , Hadjipanayis G. C.
Published: December 2019

We have investigated the structural and magnetic properties of Co1-xVx nanoparticles (NPs) with composition x = 0.25 (stoichiometric) and 0.29 (under-stoichiometric) prepared by the cluster-beam deposition (CBD) technique. Our data shows that the as-made Co1-xVx NPs are a mixture of the high-temperature phase (HTP) and the low-temperature phase (LTP) of Co3V and the particles are superparamagnetic at room temperature (RT) with blocking temperatures (TB) of 90 and 137 K for x = 0.25 and 0.29, respectively. This behavior contrasts with the bulk which are paramagnetic down to 4.2 K. When the Co75V25 NPs are annealed at 573 K, they undergo a phase separation into a mixture of phases and become ferromagnetic at room temperature with Curie temperature (Tc) of 515 K.
Single-reader dual-track readback scheme for synchronized interlaced magnetic recording
Authors: Yoon S. , Hwang E.
Published: December 2019

In this study, multi-level joint-track readback scheme is proposed for interlaced magnetic recording (IMR) with write synchronization. IMR typically provides an areal density capability (ADC) gain by pre-fixing the recording orders as interlaced and customizing the write configurations for neighboring tracks, such that narrow and wide tracks are interlaced. On the other hand, due to the unbalanced track widths in IMR, readback waveforms by a single wide reader covering two adjacent tracks can be decomposed into four distinguishable levels, when tracks are recorded in a synchronous manner. By taking advantage of the four level (4L) detecting capability, the single reader based dual-track readback (SR-DTR) IMR has a potential to provide a doubled data rate (2X) retrieval. For the feasibility test of the SR-DTR IMR, numerical simulations are conducted for bit-error rate (BER) evaluations by the micro-pixelated magnetic recording channel model. Partial response equalizer and Viterbi detector are modified for 4L readback waveforms, and are investigated with cross-track read offsets under various track and linear densities. BER bathtub investigation results show the feasibility of 2X retrievals by the SR-DTR IMR approach.
Boundary conditions and Berry phase in magnetic nanostructures
Authors: Ullah A. , Balamurugan B. , Zhang W. , Sellmyer D. J. , Skomski R.
Published: December 2019

The effect of micromagnetic boundary conditions on the Berry curvature and topological Hall effect in granular nanostructures is investigated by model calculations. Both free surfaces and grain boundaries between interacting particles or grains affect the spin structure. The Dzyaloshinskii-Moriya interactions yield corrections to the Erdmann-Weierstrass boundary conditions, but the Berry curvature remains an exclusive functional of the local spin structure, which greatly simplifies the treatment of nanostructures. An explicit example is a model nanostructure with cylindrical symmetry whose spin structure is described by Bessel function and which yields a mean-field-type Hall-effect contribution that can be related to magnetic-force-microscopy images.
Transport properties on an ionically disordered surface of topological insulators: Toward high-performance thermoelectrics
Authors: Chiba Takahiro , Takahashi Saburo
Published: December 2019

Motivated by recent experiments that report a strong energy dependence of the Seebeck coefficient S, we study theoretically thermoelectric (TE) transport on a surface of a three-dimensional, gap-opened, and ionically disordered topological insulator (TI). We calculate the TE coefficients and the dimensionless figure of merit ZT by using a semiclassical transport theory, taking into account the electron scattering due to ionic disorders. The ionic disorder on the TI surface is modeled by charge impurities with randomly distributed long-range potential (Coulomb impurities) and short-range potential (normal impurity). As a result, S differs significantly between two impurities in the gapless limit. Conversely, in the presence of a surface subgap, ZT for both impurity models is as high as ∼2 below room temperature within a permissible range of impurity parameters. In addition, by comparing the results of the theoretical model with the results of recently reported experiments, we find that the contribution of Coulomb impurities to TE transport is comparable to or dominates that of normal impurities.
Dynamics of a one-dimensional Holstein polaron: The multiconfigurational Ehrenfest method
Authors: Chen Lipeng , Gelin Maxim F. , Shalashilin Dmitrii V.
Published: December 2019

We have extended the multiconfigurational Ehrenfest (MCE) approach to investigate the dynamics of a one-dimensional Holstein molecular crystal model. It has been shown that the extended MCE approach yields results in perfect agreement with benchmark calculations by the hierarchy equations of motion method. The accuracies of the MCE approach in describing the dynamical properties of the Holstein polaron over a wide range of exciton transfer integrals and exciton-phonon couplings are carefully examined by a detailed comparison with the fully variational multiple Davydov D2 ansatz. It is found that while the MCE approach and the multi-D2 ansatz produce almost exactly the same results for a small transfer integral, the results obtained by the multi-D2 ansatz start to deviate from those by the MCE approach at longer times for a large transfer integral. A large number of coherent state basis functions are required to characterize the delocalized features of the phonon wavefunction in the case of large transfer integral, which becomes computationally too demanding for the multi-D2 ansatz. The MCE approach, on the other hand, uses hundreds to thousands of trajectory guided basis functions and converges very well, thus providing an effective tool for accurate and efficient simulations of polaron dynamics.
Survey of transient process during melting of silver below the equilibrium melting point
Authors: Liu Miao , Fu Qinqin , Wang Xueliang , Xie Degang , Wang Yaping
Published: December 2019

Understanding the melting behavior of metals at the microlevel and atomic level has been experimentally challenging due to the involvement of multiple phases at ultrafast time scale. By using the confocal scanning laser high-temperature microscope, differential scanning calorimetry, and environmental transmission electron microscope, we observed the transient process during melting of silver (Ag) nanoparticles below the equilibrium melting point. The melting point of Ag nanoparticles with the diameter of 60–120 nm is found to decrease by 100–400 °C, and the melting process is accompanied by a geometrical transformation at 840 °C, from an irregular polyhedron to a nearly spherical crystallinelike liquid with smooth facets. These results indicate that the melting of metal nanoparticles is not a direct sharp transformation from crystal to liquid but a gradual process via a certain intermediate state.
Timing the recoherences of attosecond electronic charge migration by quantum control of femtosecond nuclear dynamics: A case study for HCCI+
Authors: Jia Dongming , Manz Jörn , Yang Yonggang
Published: December 2019

This work suggests an approach to a new target of laser control of charge migration in molecules or molecular ions. The target is motivated by the fact that nuclear motions can not only cause decoherence of charge migration, typically within few femtoseconds, but they may also enable the reappearance of charge migration after much longer times, typically several tens or even hundreds of femtoseconds. This phenomenon is called recoherence of charge migration, opposite to its decoherence. The details depend on the initiation of the original charge migration by an ultrashort strong intense pump laser pulse. It may reappear quasiperiodically, with reference period Tr. We show that a well-designed pump-dump laser pulse can enforce recoherences of charge migration at different target times Tc, for example, at Tc ≈ Tr/2. The approach is demonstrated by quantum dynamics simulations of the laser driven electronic and nuclear motions in the oriented linear cation HCCI+. First, the concept is explained in terms of a didactic one-dimensional (1D) model that accounts for the decisive CI stretch. The 1D results are then confirmed by a three-dimensional model for the complete set of the CH, CC, and CI stretches.
Tolman lengths and rigidity constants from free-energy functionals—General expressions and comparison of theories
Authors: Rehner P. , Aasen A. , Wilhelmsen Ø.
Published: December 2019

The leading order terms in a curvature expansion of surface tension, the Tolman length (first order), and rigidities (second order) have been shown to play an important role in the description of nucleation processes. This work presents general and rigorous expressions to compute these quantities for any nonlocal density functional theory (DFT). The expressions hold for pure fluids and mixtures and reduce to the known expressions from density gradient theory (DGT). The framework is applied to a Helmholtz energy functional based on the perturbed chain polar statistical associating fluid theory (PCP-SAFT) and is used in an extensive investigation of curvature corrections for pure fluids and mixtures. Predictions from the full DFT are compared to two simpler theories: predictive DGT, which has a density and temperature dependent influence matrix derived from DFT, and DGT, where the influence parameter reproduces the surface tension predicted from DFT. All models are based on the same equation of state and predict similar Tolman lengths and spherical rigidities for small molecules, but the deviations between DFT and DGT increase with chain length for alkanes. For all components except water, we find that DGT underpredicts the value of the Tolman length but overpredicts the value of the spherical rigidity. An important basis for the calculation is an accurate prediction of the planar surface tension. Therefore, further work is required to accurately extract Tolman lengths and rigidities of alkanols because DFT with PCP-SAFT does not accurately predict surface tensions of these fluids.
Dynamic resistance measurement in a YBCO wire under perpendicular magnetic field at various operating temperatures
Authors: Liu Yanchao , Jiang Zhenan , Sidorov G. , Bumby C. W. , Badcock R. A. , Fang Jin
Published: December 2019

Dynamic resistance plays an important role in certain high-Tc superconducting (HTS) applications where an HTS coated conductor carries a DC current exposed to an AC magnetic field. Here, we report measurements of the dynamic resistance in a 4 mm-wide YBCO coated conductor under a perpendicular AC magnetic field at 77 K, 70 K, and 65 K. Dynamic resistance was measured at three different frequencies for the reduced current, i (It/Ic0), ranging from 0.04 to 0.9, where It is the DC current level and Ic0 is the self-field critical current of the conductor at each temperature. At all three temperatures, the threshold magnetic field (Bth) values increase with reducing DC current. These results show that, for a given set of applied conditions, dynamic resistance decreases with decreasing operating temperature, which we attribute to the temperature dependent increase in the critical current of the wire. We show that measured Bth values at all three temperatures agree well with the analytical values from nonlinear Mikitik and Brandt equation for i ≤ 0.2 and with a simple linear expression that assumes a current-independent penetration field for i > 0.2. We further show the measured Bth curves at different temperatures normalized by critical current density collapse into one common curve. The above result implies that dynamic resistance in coated conductors at different temperatures under perpendicular AC magnetic fields can be scaled simply using measured Ic0 values at those temperatures and analytical equations.
Direct visualization of degradation microcompartments at the ER membrane
Authors: Albert Sahradha , Wietrzynski Wojciech , Lee Chia-Wei , Schaffer Miroslava , Beck Florian , Schuller Jan M. , Salomé Patrice A. , Plitzko Jürgen M. , Baumeister Wolfgang , Engel Benjamin D.
Published: December 2019

To promote the biochemical reactions of life, cells can compartmentalize molecular interaction partners together within separated non–membrane-bound regions. It is unknown whether this strategy is used to facilitate protein degradation at specific locations within the cell. Leveraging in situ cryo-electron tomography to image the native molecular landscape of the unicellular alga
Chlamydomonas reinhardtii
, we discovered that the cytosolic protein degradation machinery is concentrated within ∼200-nm foci that contact specialized patches of endoplasmic reticulum (ER) membrane away from the ER–Golgi interface. These non–membrane-bound microcompartments exclude ribosomes and consist of a core of densely clustered 26S proteasomes surrounded by a loose cloud of Cdc48. Active proteasomes in the microcompartments directly engage with putative substrate at the ER membrane, a function canonically assigned to Cdc48. Live-cell fluorescence microscopy revealed that the proteasome clusters are dynamic, with frequent assembly and fusion events. We propose that the microcompartments perform ER-associated degradation, colocalizing the degradation machinery at specific ER hot spots to enable efficient protein quality control.
Neurons differentiate magnitude and location of mechanical stimuli
Authors: Gaub Benjamin M. , Kasuba Krishna Chaitanya , Mace Emilie , Strittmatter Tobias , Laskowski Pawel R. , Geissler Sydney A. , Hierlemann Andreas , Fussenegger Martin , Roska Botond , Müller Daniel J.
Published: December 2019

Significance

Our study provides a quantitative and morphological framework for mechanical neuromodulation. We report that mechanical stimuli at subtraumatic forces and pressures can evoke neuronal calcium responses. Cultured cortex and hippocampus neurons respond to both global and local mechanical forces and pressures delivered by shear stress and indentation, respectively, and show either short-lived or sustained responses, depending on the magnitude and location of the applied stimulus. Chemical perturbation experiments suggest that ion channel activity is modulated by forces and pressures acting on neurons. Our insights contribute to the understanding of how neurons respond to mechanical stimuli and may guide future studies to mechanically control neurons by, for example, electromagnetic forces or ultrasound.
A rapid and label-free platform for virus capture and identification from clinical samples
Authors: Yeh Yin-Ting , Gulino Kristen , Zhang YuHe , Sabestien Aswathy , Chou Tsui-Wen , Zhou Bin , Lin Zhong , Albert Istvan , Lu Huaguang , Swaminathan Venkataraman , Ghedin Elodie , Terrones Mauricio
Published: December 2019

Emerging and reemerging viruses are responsible for a number of recent epidemic outbreaks. A crucial step in predicting and controlling outbreaks is the timely and accurate characterization of emerging virus strains. We present a portable microfluidic platform containing carbon nanotube arrays with differential filtration porosity for the rapid enrichment and optical identification of viruses. Different emerging strains (or unknown viruses) can be enriched and identified in real time through a multivirus capture component in conjunction with surface-enhanced Raman spectroscopy. More importantly, after viral capture and detection on a chip, viruses remain viable and get purified in a microdevice that permits subsequent in-depth characterizations by various conventional methods. We validated this platform using different subtypes of avian influenza A viruses and human samples with respiratory infections. This technology successfully enriched rhinovirus, influenza virus, and parainfluenza viruses, and maintained the stoichiometric viral proportions when the samples contained more than one type of virus, thus emulating coinfection. Viral capture and detection took only a few minutes with a 70-fold enrichment enhancement; detection could be achieved with as little as 10
2
EID
50
/mL (50% egg infective dose per microliter), with a virus specificity of 90%. After enrichment using the device, we demonstrated by sequencing that the abundance of viral-specific reads significantly increased from 4.1 to 31.8% for parainfluenza and from 0.08 to 0.44% for influenza virus. This enrichment method coupled to Raman virus identification constitutes an innovative system that could be used to quickly track and monitor viral outbreaks in real time.
Hybrid histidine kinase activation by cyclic di-GMP–mediated domain liberation
Authors: Dubey Badri N. , Agustoni Elia , Böhm Raphael , Kaczmarczyk Andreas , Mangia Francesca , von Arx Christoph , Jenal Urs , Hiller Sebastian , Plaza-Menacho Iván , Schirmer Tilman
Published: December 2019

Cytosolic hybrid histidine kinases (HHKs) constitute major signaling nodes that control various biological processes, but their input signals and how these are processed are largely unknown. In
Caulobacter crescentus
, the HHK ShkA is essential for accurate timing of the G1-S cell cycle transition and is regulated by the corresponding increase in the level of the second messenger c-di-GMP. Here, we use a combination of X-ray crystallography, NMR spectroscopy, functional analyses, and kinetic modeling to reveal the regulatory mechanism of ShkA. In the absence of c-di-GMP, ShkA predominantly adopts a compact domain arrangement that is catalytically inactive. C-di-GMP binds to the dedicated pseudoreceiver domain Rec1, thereby liberating the canonical Rec2 domain from its central position where it obstructs the large-scale motions required for catalysis. Thus, c-di-GMP cannot only stabilize domain interactions, but also engage in domain dissociation to allosterically invoke a downstream effect. Enzyme kinetics data are consistent with conformational selection of the ensemble of active domain constellations by the ligand and show that autophosphorylation is a reversible process.
Multimodal transcriptional control of pattern formation in embryonic development
Authors: Lammers Nicholas C. , Galstyan Vahe , Reimer Armando , Medin Sean A. , Wiggins Chris H. , Garcia Hernan G.
Published: December 2019

Predicting how interactions between transcription factors and regulatory DNA sequence dictate rates of transcription and, ultimately, drive developmental outcomes remains an open challenge in physical biology. Using stripe 2 of the
even-skipped
gene in
Drosophila
embryos as a case study, we dissect the regulatory forces underpinning a key step along the developmental decision-making cascade: the generation of cytoplasmic mRNA patterns via the control of transcription in individual cells. Using live imaging and computational approaches, we found that the transcriptional burst frequency is modulated across the stripe to control the mRNA production rate. However, we discovered that bursting alone cannot quantitatively recapitulate the formation of the stripe and that control of the window of time over which each nucleus transcribes
even-skipped
plays a critical role in stripe formation. Theoretical modeling revealed that these regulatory strategies (bursting and the time window) respond in different ways to input transcription factor concentrations, suggesting that the stripe is shaped by the interplay of 2 distinct underlying molecular processes.
Pyridoxal-5′-phosphate–dependent bifunctional enzyme catalyzed biosynthesis of indolizidine alkaloids in fungi
Authors: Dai Guang Zhi , Han Wen Bo , Mei Ya Ning , Xu Kuang , Jiao Rui Hua , Ge Hui Ming , Tan Ren Xiang
Published: December 2019

Indolizidine alkaloids such as anticancer drugs vinblastine and vincristine are exceptionally attractive due to their widespread occurrence, prominent bioactivity, complex structure, and sophisticated involvement in the chemical defense for the producing organisms. However, the versatility of the indolizidine alkaloid biosynthesis remains incompletely addressed since the knowledge about such biosynthetic machineries is only limited to several representatives. Herein, we describe the biosynthetic gene cluster (BGC) for the biosynthesis of curvulamine, a skeletally unprecedented antibacterial indolizidine alkaloid from
Curvularia
sp. IFB-Z10. The molecular architecture of curvulamine results from the functional collaboration of a highly reducing polyketide synthase (CuaA), a pyridoxal-5′-phosphate (PLP)-dependent aminotransferase (CuaB), an NADPH-dependent dehydrogenase (CuaC), and a FAD-dependent monooxygenase (CuaD), with its transportation and abundance regulated by a major facilitator superfamily permease (CuaE) and a Zn(II)Cys
6
transcription factor (CuaF), respectively. In contrast to expectations, CuaB is bifunctional and capable of catalyzing the Claisen condensation to form a new C–C bond and the α-hydroxylation of the alanine moiety in exposure to dioxygen. Inspired and guided by the distinct function of CuaB, our genome mining effort discovers bipolamines A−I (bipolamine G is more antibacterial than curvulamine), which represent a collection of previously undescribed polyketide alkaloids from a silent BGC in
Bipolaris maydis
ATCC48331. The work provides insight into nature’s arsenal for the indolizidine-coined skeletal formation and adds evidence in support of the functional versatility of PLP-dependent enzymes in fungi.
Investigation of functional core-rim composite part production by inserted powder injection moulding
Authors: Subaşi Mehmet , Koçak Harun , Safarian Asghar , Karataş Çetin
Published: December 2019

In this study, the use of Cu and Ni interlayers have been investigated for functional core-rim composite part production with WC-Co 9 wt-% feedstock/steel. For this purpose, different experiments have been performed and joining condition, shear strength and microstructure of the intermediate region have been examined. It has been found that AISI 4340 insert/WC-Co have been joined and 85.8 MPa shear strength achieved, but high speed steel insert has not joined. Moreover, it has been determined that better results are obtained with Ni interlayer. Under the same conditions, when the 40 µm Ni interlayer has been used between AISI 4340 core and WC-Co rim, shear strength has been increased approximately twice and has been 162.7 MPa.