bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of laser-target parameters for the production of stable lithium beam
Authors: Cannavò A. , Takahashi K. , Okamura M. , Ceccio G. , Kanesue T. , Ikeda S.
Published: March 2020

A laser ion source coupled with a radio frequency quadrupole linac accelerator is being proposed as a suitable system for the production of a low energy, high-current stable lithium beam. In order to maximize the lithium yield, plasmas generated by laser ablation of different materials based on lithium (Li, LiOH, and LiNbO3) have been characterized by using a Faraday cup and an electrostatic ion analyzer in the time of flight configuration. A wide range of laser power density has been investigated (109–1012 W/cm2) using two Nd:YAG lasers operating at different wavelengths (1064 nm and 532 nm), pulse durations (6 ns and 17 ns), and maximum energies (1400 mJ and 210 mJ). This paper outlines the pros and cons of the investigated materials by studying how the ion energy, yields, and charge state distributions are modified when the laser power density is changed. Considerable attention has been paid to the higher charge states of oxygen, which may occur with the same mass-to-charge ratio of Li3+. The analysis has evidenced that LiNbO3 represents a valid target since it allows minimizing the O6+/7Li3+ ratio down to 2.5% by using a laser power density of 1.8 × 1010 W/cm2. For such a condition, a Li3+ current of 1.4 mA/cm2 has been measured.
Fractional order oxygen–plankton system under climate change
Authors: Ozarslan Ramazan , Sekerci Yadigar
Published: March 2020

Global climate change affects marine species including phytoplankton, which constitute the base of the marine food web, by changing the primary productivity. Global warming affects the ocean surface temperature, in turn leading to a change in the oxygen production of phytoplankton. In this work, the fractional oxygen–phytoplankton–zooplankton mathematical model is considered by the Caputo fractional operator. The production rate of photosynthesis is determined by a temperature function. The model is, therefore, based on the idea that the rate of photosynthesis changes due to the impact of global warming, while phytoplankton oxygen production increases and decreases. We analyze the model with the Caputo fractional derivative differently from the classical case of the model and we compare the results with the integer order derivative when α tends to 1. Existence and uniqueness properties of the oxygen–plankton model have been proved by means of a local Lipschitz condition. It was shown that the species are more sustainable than its corresponding classical case in the Caputo model. Our results show that the effect of global warming on the oxygen production rate has been observed to be quite severe, resulting in oxygen depletion and plankton extinction.
Experimental study on shale fracturing effect and fracture mechanism under different fracturing fluid viscosity: A case study of Guanyinqiao Member shale in Xishui, Guizhou, China
Authors: Zhang Shuhui , Li Xiao , Gao Quanchen
Published: March 2020

In this study, a series of laboratory fracturing experiments were conducted on samples mined from reservoirs of the Guanyinqiao Member shale in Xishui County, Guizhou Province, using a traditional triaxial fracturing simulation system. Based on the experimental results, the breakdown pressure and effective stimulated reservoir volume were obtained for four fracturing fluids (supercritical carbon dioxide, water, NO-sand, and sand). The fracture mechanism was then analyzed using acoustic emission monitoring data. Based on the curves of pressure vs injection time for different fracturing fluids, the breakdown pressure increased with increasing fracturing fluid viscosity. When sands with different viscosities were used as the fracturing fluid, the breakdown pressure first increased and then decreased with an increase in the sand viscosity. The distribution of the tracer or proppant was not only correlated with the fracturing effect, but also promotes the filling crack of the tracer and proppant at a certain viscosity as the best fracturing effect. During sand fracturing, the proppant mainly formed shear cracks. The results provide a valuable technical reference for shale gas mining.
Stabilization and destabilization of nonlinear systems via aperiodically intermittent stochastic noises: Average techniques and scalar functions
Authors: Li Sen , Ren Xiangnuo , Su Huan
Published: March 2020

In this paper, almost sure exponential stabilization and destabilization criteria for nonlinear systems are obtained via aperiodically intermittent stochastic noises based on average techniques and piecewise continuous scalar functions. Compared with existing results on almost sure exponential stability of stochastic systems, the requirement on the upper bound of the diffusion operator of a Lyapunov function is released. The upper bound is allowed to be a scalar function and even be unbounded. Simultaneously, by means of putting forward new concepts “average noise control rate” and “average noise control period,” assumptions on infimum of control time and supremum of rest time in the previous references about aperiodically intermittent control can be removed without implementing in the upper limit of the uncontrolled rate, which reduces the conservativeness of stabilization criteria resulting from non-uniform distribution of control time and rest time. In addition, the main results are applied to coupled and uncoupled nonlinear spring–mass–damper oscillator systems, respectively, and corresponding numerical simulations are carried out to demonstrate the validity of the theoretical analysis.
Superior growth, yield, repeatability, and switching performance in GaN-based resonant tunneling diodes
Authors: Growden Tyler A. , Storm David F. , Cornuelle Evan M. , Brown Elliott R. , Zhang Weidong , Downey Brian P. , Roussos Jason A , Cronk Nicholas , Ruppalt Laura B. , Champlain James G. , Berger Paul R. , Meyer David J.
Published: March 2020

We report the direct measurement of record fast switching speeds in GaN/AlN resonant tunneling diodes (RTDs). The devices, grown by plasma-assisted molecular-beam epitaxy, displayed three repeatable negative differential resistance (NDR) regions below a bias of +6 V. A room temperature peak-to-valley current ratio (PVCR) > 2 was observed, which represents a marked improvement over recent reports. Measurements carried out on hundreds of devices, of varying sizes, revealed a yield of ∼90%. Repeatability measurements consisting of 3000 sweeps resulted in a standard deviation, relative to the mean, of < 0.1%. Temperature dependent measurements combined with non-equilibrium Green's function based quantum transport simulations suggest the presence of both three-dimensional (3D) and two-dimensional (2D) emitters, giving rise to three NDR regions. Finally, a valley current density vs perimeter-to-area-ratio study indicates the presence of a surface leakage current mechanism, which reduces the PVCR.
Selective etching in graphene–MoS2 heterostructures for fabricating graphene-contacted MoS2 transistors
Authors: Sun Zeliang , Peng Gang , Bai Zongqi , Zhang Xiangzhe , Wei Yuehua , Deng Chuyun , Zhang Yi , Zhu Mengjian , Qin Shiqiao , Li Zheng , Luo Wei
Published: March 2020

Semiconducting molybdenum disulfide (MoS2) has drawn a lot of attention for its exceptional electronic and optoelectronic properties. Despite the potential advantages, the large contact resistance at the metal–MoS2 interfaces has been one of the biggest obstacles for the realization of ideal MoS2 transistors. One solution to improve the metal–MoS2 interfaces is to use the graphene electrodes. Here, we provide a selective etching method for fabricating graphene-contacted MoS2 transistors. It has been proved that the graphene could be totally etched with Ar+ plasma treatment, and the multilayer MoS2 flake can also be reduced layer by layer with Ar+ plasma treatment. By etching graphene selectively in graphene–MoS2 heterostructures, one can obtain graphene-contacted MoS2 transistors successfully. The transistor reported in this paper shows an on–off ratio about 106 and a carrier mobility about 42 cm2 V−1 s−1. This selective etching method would be beneficial for some other graphene-contacted electronic devices.
A scalable high-performance magnetic shield for very long baseline atom interferometry
Authors: Wodey E. , Tell D. , Rasel E. M. , Schlippert D. , Baur R. , Kissling U. , Kölliker B. , Lorenz M. , Marrer M. , Schläpfer U. , Widmer M. , Ufrecht C. , Stuiber S. , Fierlinger P.
Published: March 2020

We report on the design, construction, and characterization of a 10 m-long high-performance magnetic shield for very long baseline atom interferometry. We achieve residual fields below 4 nT and longitudinal inhomogeneities below 2.5 nT/m over 8 m along the longitudinal direction. Our modular design can be extended to longer baselines without compromising the shielding performance. Such a setup constrains biases associated with magnetic field gradients to the sub-pm/s2 level in atomic matterwave accelerometry with rubidium atoms and paves the way toward tests of the universality of free fall with atomic test masses beyond the 10−13 level.
The structure of water–DMF binary mixtures probed by linear and nonlinear vibrational spectroscopy
Authors: Tomar Deepak , Rana Bhawna , Jena Kailash C.
Published: March 2020

Attenuated total reflectance Fourier transform infrared spectroscopy and sum frequency generation (SFG) vibrational spectroscopy have been employed to probe the molecular structure of N,N-dimethylformamide (DMF) and water mixture by varying the concentration of DMF. From the bulk studies, we observed a gradual decrease in the intensity with a continuous blue shift in the OH-stretch region with the increase in the DMF concentration. In contrast, no significant blue shift in the OH-stretch region is noticed from the SFG spectra collected from the air–aqueous binary mixture interface as a function of DMF concentration. However, the impact of DMF is found to be disruptive in nature toward the existing hydrogen bonding network of the pristine water at the interfacial region. Interestingly, in the CH-stretch region, the vibrational signatures of the DMF molecule show blue shifts, as proposed in earlier studies. We have calculated the molecular tilt angle of the methyl group of the DMF molecule as a function of DMF concentration. For the case of neat DMF, the observed tilt angle is ∼17.7° with respect to the surface normal. The value of tilt angle decreases with the decrease in DMF concentration and reaches a value of ∼1.7° for a mole fraction of 0.5, and it further increases with the decrease in DMF concentration. It achieves a value of ∼20° for the dilute DMF mole fraction of 0.05 in the binary mixture. This indicates that DMF molecules at the air–binary mixture interface are placing their methyl groups more toward the normal for the intermediate DMF concentrations.
Different stages of electron-beam evaporation of ceramic target in medium vacuum
Authors: Yushkov Yury G. , Zolotukhin Denis B. , Oks Efim M. , Tyunkov Andrey V.
Published: March 2020

We present experimental results and numerical simulation of electron-beam heating, melting, and evaporation of a solid dielectric (aluminum oxide ceramic) in medium vacuum (1–100 Pa). The indicated processes occurred as a result of interaction between a powerful continuous electron beam, generated by a fore-vacuum plasma-cathode electron source, and the surface of the solid ceramic target. During the interaction with the target, the electron beam ionized a part of the evaporated material, and starting from the onset of ceramic melting up to intense evaporation, the beam plasma has been containing ions of the ceramic material. We suggest an optimal choice of ceramic evaporation regime for the purpose of coating deposition.
The use of strain and grain boundaries to tailor phonon transport properties: A first-principles study of 2H-phase CuAlO2. II
Authors: Witkoske Evan , Tong Zhen , Feng Yining , Ruan Xiulin , Lundstrom Mark , Lu Na
Published: March 2020

Transparent oxide materials, such as CuAlO2, a p-type transparent conducting oxide (TCO), have recently been studied for high temperature thermoelectric power generators and coolers for waste heat. TCO materials are generally low cost and non-toxic. The potential to engineer them through strain and nano-structuring are two promising avenues toward continuously tuning the electronic and thermal properties to achieve high zT values and low $cost/kW h devices. In this work, the strain-dependent lattice thermal conductivity of 2H CuAlO2 is computed by solving the phonon Boltzmann transport equation with interatomic force constants extracted from first-principles calculations. While the average bulk thermal conductivity is around 32 W/(m K) at room temperature, it drops to between 5 and 15 W/(m K) for typical experimental grain sizes from 3 nm to 30 nm. We find that strain can offer both an increase as well as a decrease in the thermal conductivity as expected; however, the overall inclusion of small grain sizes dictates the potential for low thermal conductivity in this material.
Gradient doping of sulfur in Sb2Se3 nanowire arrays as photoelectrochemical photocathode with a 2% half-cell solar-to-hydrogen conversion efficiency
Authors: Zhou Hongpeng , Feng Menglei , Feng Minzhen , Gong Xiangnan , Zhang Dingke , Zhou Yun , Chen Shijian
Published: March 2020

Exploring Sb2Se3 as a photoelectrochemical (PEC) photocathode for water reduction has recently attracted much attention, mainly due to its excellent photophysical properties and perfect band structure matching with water reduction potential. Whereas significant achievements have been made in improving its photocurrent density, the PEC performance remains poor mostly due to the low onset potential or low fill factor. Here, we fabricated S doped Sb2Se3 nanowire arrays with a gradient S concentration (grad-S:Sb2Se3). Gradient S doping creating a cascade valence band structure in Sb2Se3 simultaneously enhances its onset potential and fill factor. Light-trapping effects in nanowire geometry improve the light harvesting efficiency. A further deposition of a thin TiO2 layer is utilized to passivate the detrimental surface defects and form a buried junction with grad-S:Sb2Se3. By employing the prepared grad-S:Sb2Se3 nanowire arrays as the photocathode for water reduction, we achieved a high onset potential of 0.42 V vs RHE, a fill factor of 34%, and a record high half-cell solar-to-hydrogen conversion efficiency of 2% from Sb2Se3-based photocathodes.
Analytic energy gradients for the exact exchange Kohn–Sham method
Authors: Thierbach Adrian , Görling Andreas
Published: March 2020

Analytic energy gradients with respect to nuclear coordinates for an exact exchange-only (EXX) Kohn–Sham method are presented. In the underlying EXX method, the exact exchange potential is obtained as the electrostatic potential of an exchange charge density, which is determined via the optimized effective potential method. Parts of the presented calculation of analytic EXX energy gradients can be reused for analytic energy gradients in self-consistent Kohn–Sham methods treating correlation via the adiabatic-connection fluctuation–dissipation theorem, e.g., methods relying on the random phase approximation. A version of the analytic EXX energy gradients that uses density-fitting is shown to be highly efficient. The accuracy of the analytic energy gradients is tested by comparison with numerically calculated gradients.
Flow induced particle separation and collection through linear array pillar microfluidics device
Authors: Balyan Prerna , Saini Deepika , Das Supriyo , Kumar Dhirendra , Agarwal Ajay
Published: March 2020

Particle filtration and concentration have great significance in a multitude of applications. Physical filters are nearly indispensable in conventional separation processes. Similarly, microfabrication-based physical filters are gaining popularity as size-based particle sorters, separators, and prefiltration structures for microfluidics platforms. The work presented here introduces a linear combination of obstructions to provide size contrast-based particle separation. Polystyrene particles that are captured along the crossflow filters are packed in the direction of the dead-end filters. Separation of polydisperse suspension of 5 μm and 10 μm diameter polystyrene microspheres is attained with capture efficiency for larger particles as 95%. Blood suspension is used for biocharacterization of the device. A flow induced method is used to improve particle capture uniformity in a single microchannel and reduce microgap clogging to about 30%. This concept is extended to obtain semiquantification obtained by comparison of the initial particle concentration to captured-particle occupancy in a microfiltration channel.
Assessment of block size distribution in fractured rock mass and its influence on rock mass mechanical behavior
Authors: Yao Wenli , Mostafa Sharifzadeh , Yang Zhen
Published: March 2020

The response of rock mass to engineering activities related to environment greatly depends on the scale of rock mass. Therefore, the scale dependency of rock mechanical behavior under different rock mass conditions is investigated in this research. As a crucial parameter, the volume of the block provides a fundamental understanding to define the rock mass condition and possible mechanical response. In this paper, at first, a systematic approach to calculate the block size distribution (BSD) based on the natural fracture parameters using most suitable distribution functions was established with the R language. Then, the rock mass parameters were extracted from core mapping in the depth of 1500 m–2000 m and the BSD was presented in a similar manner to soil particle size distribution. Finally, the rock mass behavior under different block sizes was investigated. The results showed that Vb25 = 3.4 dm3, Vb50 = 6.4 dm3, and Vb75 = 11.2 dm3, which were the average percentages to represent the BSD. In the research area, therefore, the fractured rock mass was dominated by minor blocks. Besides, the variation of rock mass deformation vs BSD showed that the fractured rock mass was aggravated with the decrease in the block size. The results will enhance the effect of BSD on rock mass mechanical properties.
Spintronics with compensated ferrimagnets
Authors: Finley Joseph , Liu Luqiao
Published: March 2020

Magnetic information storage has been achieved by controlling and sensing the magnetic moment orientation of nanoscale ferromagnets. Recently, there has been concentrated effort to utilize materials with antiferromagnetic coupling as a storage medium to realize devices that switch faster, are more secure against external magnetic fields, and have higher storage density. Within this class of materials are ferrimagnets, whose magnetization can be reduced to zero by tuning parameters such as the chemical composition, temperature, and strain. Compared to conventional antiferromagnets, compensated ferrimagnets not only possess the aforementioned speed and density advantages but also allow the use of convenient electrical reading and writing mechanisms due to the existence of inequivalent magnetic sublattices. Recent research has demonstrated fast spin-torque switching, as well as efficient electrical reading with compensated ferrimagnets. Further material and device research using these zero-moment magnets promises a spintronic platform for fast and energy efficient information storage technology.
Realization of “single-atom ferromagnetism” in graphene by Cu–N4 moieties anchoring
Authors: Xia Baorui , Liao Zhongxin , Liu Yonggang , Chi Xiao , Xiao Wen , Ding Jun , Wang Tongtong , Gao Daqiang , Xue Desheng
Published: March 2020

Ferromagnetism in graphene-based materials has attracted much attention because of their potential applications in future spintronic devices. Here, we propose a strategy to induce “single-atom ferromagnetism” in three-dimensional graphene by Cu anchoring, wherein the Cu atoms are isolated with Cu–N4 moieties, as demonstrated by extended x-ray absorption fine structure and spherical aberration correction transmission electron microscope measurements. Superconducting quantum interference device and x-ray magnetic circular dichroism measurements reveal the clear ferromagnetism of single-atom Cu-anchored graphene with saturation magnetization of 1.15 emu/g at 2 K and 0.05 emu/g at 300 K, suggesting its promising applications in spintronics. Additionally, density functional theory (DFT) calculations prove that the Cu–N4 group can produce net magnetic moments and that the system favors the ferromagnetic stable state. More importantly, our DFT calculations show that anchoring single atoms of other transition metals can also realize single-atom ferromagnetism in graphene.
Restoring chaos using deep reinforcement learning
Authors: Vashishtha Sumit , Verma Siddhartha
Published: March 2020

A catastrophic bifurcation in non-linear dynamical systems, called crisis, often leads to their convergence to an undesirable non-chaotic state after some initial chaotic transients. Preventing such behavior has been quite challenging. We demonstrate that deep Reinforcement Learning (RL) is able to restore chaos in a transiently chaotic regime of the Lorenz system of equations. Without requiring any a priori knowledge of the underlying dynamics of the governing equations, the RL agent discovers an effective strategy for perturbing the parameters of the Lorenz system such that the chaotic trajectory is sustained. We analyze the agent’s autonomous control-decisions and identify and implement a simple control-law that successfully restores chaos in the Lorenz system. Our results demonstrate the utility of using deep RL for controlling the occurrence of catastrophes in non-linear dynamical systems.
Ultra-high piezoresponse in tantalum doped potassium sodium niobate single crystal
Authors: Meng Xiangda , Hu Chengpeng , Park Dae-Sung , Riemer Lukas , Chu Kanghyun , Zhou Zhongxiang , Damjanovic Dragan , Tian Hao
Published: March 2020

Ferroelectric materials reveal an ultra-high piezoelectric effect because of their spontaneous polarization and show high potential for applications. At present, the lead-free piezoelectric materials are in a great demand because of their environmentally friendly character, but their performance needs to be improved. Generally, in order to enhance the piezoelectric coefficients, researchers could rely on a phase boundary and/or to grow single crystals. Here, a Ta-doped (K, Na)NbO3 (KNN) single crystal with the orthorhombic–tetragonal (O–T) phase boundary is grown via the top-seed solution growth method. Excellent piezoelectric coefficients (d33 ≈ 560 pC/N via the Berlincourt method and d33* ≈ 1353 pm/V derived from strain-electric field loops) are achieved in a K0.40Na0.60Ta0.41Nb0.59O3 single crystal. What is more, with the electric field rising from 0.5 kV/cm to 4 kV/cm, the converse d33 and the strain hysteresis level improve from 580 pm/V to 640 pm/V and from 0.052 to 0.104, respectively. Our results clarify that the high d33 can be attributed to the high domain density and the labyrinthine-domain structure. In addition, the electric-field-induced phase transition is also observed, which is supposed to cause the high d33*. This work not only reports the ultra-high piezoresponse of the KNN-based single crystal but also provides strong evidence for its mesoscale origin.
Study of precessional switching speed control in voltage-controlled perpendicular magnetic tunnel junction
Authors: Wu Y. C. , Kim W. , Couet S. , Garello K. , Rao S. , Van Beek S. , Kundu S. , Houshmand Sharifi S. , Crotti D. , Van Houdt J. , Groeseneken G. , Kar G. S.
Published: March 2020

We study the characteristics of the precessional switching induced by voltage control of magnetic anisotropy (VCMA) in back-end-of-line (BEOL)-compatible perpendicular magnetic tunnel junction devices. Using micromagnetic simulation, we find three operation regimes differentiated by zero excess energy, lower boundary, zero energy barrier, and upper boundary. Experimentally, the switching speed (fs) is characterized by two phases: non-precession and acceleration. Non-precession is a thermal mediated phase, where fs cannot be deduced, while in acceleration, both the higher electric field (EF) and in-plane field (Bx) increase fs progressively. We find that the intrinsic thresholds can be retrieved by linear extrapolation of fs as a function of EF. Those thresholds and experimental results are in good agreement with the simulation. In addition, we numerically calculate the characteristic switching speed of 2γ*mz*Bx and verify it experimentally. This work provides insights into the VCMA-induced precessional switching, including detailed understandings of the switching mechanism and modeling of switching speed for reliable write duration control for practical applications.
Amplification of explosive width in complex networks
Authors: Khanra Pitambar , Kundu Prosenjit , Pal Pinaki , Ji Peng , Hens Chittaranjan
Published: March 2020

We present an adaptive coupling strategy to induce hysteresis/explosive synchronization in complex networks of phase oscillators (Sakaguchi–Kuramoto model). The coupling strategy ensures explosive synchronization with significant explosive width enhancement. Results show the robustness of the strategy, and the strategy can diminish (by inducing enhanced hysteresis loop) the contrarian impact of phase frustration in the network, irrespective of the network structure or frequency distributions. Additionally, we design a set of frequency for the oscillators, which eventually ensure complete in-phase synchronization behavior among these oscillators (with enhanced explosive width) in the case of adaptive-coupling scheme. Based on a mean-field analysis, we develop a semi-analytical formalism, which can accurately predict the backward transition of the synchronization order parameter.
Large magnetic anisotropy in highly strained epitaxial MgFe2O4 thin films
Authors: Ade Ramesh , Chen Y. S. , Huang Chin-Han , Lin Jauyn Grace
Published: March 2020

In order to acquire a soft magnetic film with low conductivity and large magnetic anisotropy, the strain-modulated magnetic anisotropy is studied in epitaxial MgFe2O4 (MFO) films. The MFO films with thicknesses of 25, 48, 75, and 110 nm are grown on the MgAl2O4 (MAO) (100) substrate using a pulsed laser deposition technique. Due to the large lattice-mismatch (3.34%) between MFO and MAO substrates, the interface exhibits a large tetragonal compressive strain. The results of field-dependent magnetization suggest the soft magnetic nature of all the measured MFO films. The analysis of angular dependent ferromagnetic resonance reveals the large uniaxial magnetic anisotropy energy (Ku) of −1.62 × 106 erg/cm3 in the highly strained 25 nm film, and Ku decreases with the increasing thickness due to strain relaxation. The observed large magnetic anisotropy in these highly strained MFO thin films is larger than most of the soft ferrite thin films, which arise due to tetragonal distortion and inverse magnetostriction. The epitaxial MFO thin films with enhanced magnetic anisotropy could be one of the potential candidates for spin filters.
Decoupling of thermo-electronic effect by traveling photothermal mirror method for characterization of thermal properties of semiconductors
Authors: Dong Jingtao , Li Jianquan , Yang Lei , Zhang Tengda , Lu Rongsheng , Li Jingsong , Zhang Lei , Zhou Sheng
Published: March 2020

Interactions between super bandgap energy photons and semiconductor materials involve plasma waves in addition to thermal waves, resulting in a strong thermo-electronic coupling effect. Here, we propose an effective traveling photothermal mirror method to decouple the thermo-electronic effect for characterization of thermal properties of a semi-insulating GaAs wafer as a demonstration. A theoretical model is presented for describing the dynamic processes of the thermal and plasma waves in the sample as well as the heat coupling between the sample and the surrounding fluid under the excitation of a laser beam traveling at a constant velocity. Based on the solution to the diffusion equations, we obtain the phase shift introduced to another probe beam associated with the photothermal signal due to the thermoelastic and electronic-strain responses of the sample and the refractive index gradient of the fluid. The theoretical and experimental results reveal that the steady-state process in the laser–material interaction makes the electronic effect act as an insensitive constant background in the photothermal signal, and the thermodynamic process is governed by the thermal properties of the sample. The distinct advantage of the traveling photothermal signal being immune to the variation of the electronic transport parameters allows the thermal diffusivity of the sample to be accurately determined from the best fit to the signal, and the traveling excitation nature of the method provides a way for high-efficiency photothermal imaging to identify thermal defects.
Huprines — an insight into the synthesis and biological properties
Authors: Mezeiova Eva , Soukup Ondrej , Korabecny Jan
Published: March 2020

The overlapping of tacrine and (–)-huperzine A templates yielded a family of highly potent cholinesterase inhibitors, so-called huprines. A relatively easy access to these compounds led to the development of dozens of huprine derivatives allowing to draw structure – activity relationship mainly for acetylcholinesterase and butyrylcholinesterase enzymes, but also with application to other biological targets of interest. An extension of their pharmacological profile is commonly associated with huprine scaffold binding to some other pharmacophores that yield high-molecular-weight heterodimers. The main purpose in developing the huprine family is related to Alzheimer’s disease therapy. However, these compounds are also interesting lead structures in the treatment of other disorders, such as Myasthenia gravis, African trypanosomiasis, malaria, and prion diseases. The present review provides a rationale behind the development of huprines, detailed synthetic routes leading to different classes of huprines, and a thorough discussion of their potential pharmacological applications.

The bibliography includes 174 references.
An autoinhibitory intramolecular interaction proof-reads RNA recognition by the essential splicing factor U2AF2
Authors: Kang Hyun-Seo , Sánchez-Rico Carolina , Ebersberger Stefanie , Sutandy F. X. Reymond , Busch Anke , Welte Thomas , Stehle Ralf , Hipp Clara , Schulz Laura , Buchbender Andreas , Zarnack Kathi , König Julian , Sattler Michael
Published: March 2020

The recognition of
cis
-regulatory RNA motifs in human transcripts by RNA binding proteins (RBPs) is essential for gene regulation. The molecular features that determine RBP specificity are often poorly understood. Here, we combined NMR structural biology with high-throughput iCLIP approaches to identify a regulatory mechanism for U2AF2 RNA recognition. We found that the intrinsically disordered linker region connecting the two RNA recognition motif (RRM) domains of U2AF2 mediates autoinhibitory intramolecular interactions to reduce nonproductive binding to weak Py-tract RNAs. This proofreading favors binding of U2AF2 at stronger Py-tracts, as required to define 3′ splice sites at early stages of spliceosome assembly. Mutations that impair the linker autoinhibition enhance the affinity for weak Py-tracts result in promiscuous binding of U2AF2 along mRNAs and impact on splicing fidelity. Our findings highlight an important role of intrinsically disordered linkers to modulate RNA interactions of multidomain RBPs.
Computational design of closely related proteins that adopt two well-defined but structurally divergent folds
Authors: Wei Kathy Y. , Moschidi Danai , Bick Matthew J. , Nerli Santrupti , McShan Andrew C. , Carter Lauren P. , Huang Po-Ssu , Fletcher Daniel A. , Sgourakis Nikolaos G. , Boyken Scott E. , Baker David
Published: March 2020

The plasticity of naturally occurring protein structures, which can change shape considerably in response to changes in environmental conditions, is critical to biological function. While computational methods have been used for de novo design of proteins that fold to a single state with a deep free-energy minimum [P.-S. Huang, S. E. Boyken, D. Baker,
Nature
537, 320–327 (2016)], and to reengineer natural proteins to alter their dynamics [J. A. Davey, A. M. Damry, N. K. Goto, R. A. Chica,
Nat. Chem. Biol.
13, 1280–1285 (2017)] or fold [P. A. Alexander, Y. He, Y. Chen, J. Orban, P. N. Bryan,
Proc. Natl. Acad. Sci. U.S.A.
106, 21149–21154 (2009)], the de novo design of closely related sequences which adopt well-defined but structurally divergent structures remains an outstanding challenge. We designed closely related sequences (over 94% identity) that can adopt two very different homotrimeric helical bundle conformations—one short (∼66 Å height) and the other long (∼100 Å height)—reminiscent of the conformational transition of viral fusion proteins. Crystallographic and NMR spectroscopic characterization shows that both the short- and long-state sequences fold as designed. We sought to design bistable sequences for which both states are accessible, and obtained a single designed protein sequence that populates either the short state or the long state depending on the measurement conditions. The design of sequences which are poised to adopt two very different conformations sets the stage for creating large-scale conformational switches between structurally divergent forms.
All-nanofiber–based, ultrasensitive, gas-permeable mechanoacoustic sensors for continuous long-term heart monitoring
Authors: Nayeem Md Osman Goni , Lee Sunghoon , Jin Hanbit , Matsuhisa Naoji , Jinno Hiroaki , Miyamoto Akihito , Yokota Tomoyuki , Someya Takao
Published: March 2020

Significance

We have fabricated an all-nanofiber–based mechanoacoustic sensor that exhibits an acoustic sensitivity as high as 10,050.6 mV Pa
−1
in the frequency range of 10 to 500 Hz. The sensors are ultralightweight (total weight 5 mg or less) and gas-permeable. These superior performances enable our sensors to continuously measure the mechanoacoustic heart signals for longer periods (>10 h) with an extraordinarily high signal-to-noise ratio of 40.9 decibels.
Synthesis of phosphoramidate-linked DNA by a modified DNA polymerase
Authors: Lelyveld Victor S. , Zhang Wen , Szostak Jack W.
Published: March 2020

All known polymerases copy genetic material by catalyzing phosphodiester bond formation. This highly conserved activity proceeds by a common mechanism, such that incorporated nucleoside analogs terminate chain elongation if the resulting primer strand lacks a terminal hydroxyl group. Even conservatively substituted 3′-amino nucleotides generally act as chain terminators, and no enzymatic pathway for their polymerization has yet been found. Although 3′-amino nucleotides can be chemically coupled to yield stable oligonucleotides containing N3′→P5′ phosphoramidate (NP) bonds, no such internucleotide linkages are known to occur in nature. Here, we report that 3′-amino terminated primers are, in fact, slowly extended by the DNA polymerase from
B. stearothermophilus
in a template-directed manner. When its cofactor is Ca
2+
rather than Mg
2+
, the reaction is fivefold faster, permitting multiple turnover NP bond formation to yield NP-DNA strands from the corresponding 3′-amino-2′,3′-dideoxynucleoside 5′-triphosphates. A single active site mutation further enhances the rate of NP-DNA synthesis by an additional 21-fold. We show that DNA-dependent NP-DNA polymerase activity depends on conserved active site residues and propose a likely mechanism for this activity based on a series of crystal structures of bound complexes. Our results significantly broaden the catalytic scope of polymerase activity and suggest the feasibility of a genetic transition between native nucleic acids and NP-DNA.
Patterns of linguistic vitality
Authors: Zajícová Lenka
Published: March 2020

Language use among different generations of speakers related to an informant is a frequent query in surveys about the vitality of heritage languages. This chapter shows how self-reporting is influenced by attitudes in favor of the dominant language. I identify patterns of reported use comparing immigrant and indigenous languages, especially language use with siblings. I then analyze these patterns within family members according to the generation of informants. The patterns of reported use with children and with parents show radical disagreement, which points to the significant influence of language attitudes especially when reporting on language use with children. I conclude that reported use does not accurately reflect the actual process of losing minority languages, which is slower than reported.
Parental language attitudes and language use among Brazilian families in Japan
Authors: Shirakawa Mineko
Published: March 2020

This chapter presents the results of a survey and interviews administered to Brazilian families living in Japan aiming to capture the use of Brazilian-Portuguese (BP) and Japanese and explore this community’s attitude toward bilingualism. Most of these families come from second or third generations of Japanese emigrants to Brazil who are not familiar with the Japanese language or culture. Their children need special assistance with Japanese at school and do not communicate easily in BP at home. Parents have high expectations for their children to acquire advanced oral and literacy skills in both languages. However, the use of BP at home does not necessarily lead children to use it as much as their parents partly because of assimilative pressures at school.
Death
Authors: Barona Josep Lluis
Published: March 2020

Death is a biological event which forms an
essential part of culture. All human societies have attributed some
meaning to death in myth, religion, philosophy or science. The
various forms of art have also represented death as an essential
part of the human condition. This article discusses the cultural,
social and medical constructions of death, starting with the origin
myth and the contradiction between death and eternal life. It
explores funeral rites and parish registers, examines death as an
important social phenomenon in modern societies and considers the
meaning of civil registries as instruments of social identity and
legitimacy. Finally, it reflects on medicine’s power over death,
death’s biological dimension and attempts to objectify signs of
death.
Montaigne, the essay and the end of life
Authors: Skelton John
Published: March 2020

This study builds on previous work in the way
that death and dying are represented in writing in the Humanities by
looking principally though not exclusively at the work of Montaigne.
It is argued that while literary texts of course portray end of life
issues, it is often either focussed on the death of an individual
and the surrounding grief, or “death” is used for symbolic purposes,
for example as evidence of a society in decay. The essay form, which
was to a large extent created by Montaigne, offers the opportunity
to explore end of life questions as concepts, and to consider
through them how to die – and by extension, how to live.
What genericity reveals about the establishment of the definite
determiner in German
Authors: Petrova Svetlana
Published: March 2020

This contribution deals with the rise of the
definite determiner in generic noun phrases in German. It calls
attention to a by now neglected part of the diachronic development
of the determiner system of German and provides a special
contribution on the subject, building upon newly collected,
first-hand corpus data and its interpretation in the context of the
current semantic debate on genericity.
Weekly Vitamin D3 supplementation improves aerobic performance in combat sport athletes
Authors: Marley Andrew , Grant Marie Clare , Babraj John
Published: March 2020

Vitamin D3 supplementation can affect the strength and power of an athlete, however the effect on endurance performance remains unclear. Twenty‐seven recreational male combat athletes with at least 12 months experience within combat sports were recruited (age: 24 ± 4 years, stature: 176 ± 6 cm, weight: 77 ± 14 kg). Participants completed baseline testing for blood haemoglobin and haematocrit, upper and lower body VO2peak and upper and lower body Wingate. Following testing participants were stratified to 50,000IU (D1), 80,000IU (D2) or 110,000IU (D3) of vitamin D3 per week. They then completed a 6‐week placebo period followed by a 6‐week supplementation period. Retesting was carried out after the placebo and supplementation period. There was a significant effect for time for haemoglobin and haematocrit, upper and lower body VO2peak and upper body Wingate power (P < 0.01) but no effect for dose of vitamin D given. Performance data were normalised to vitamin D intake and there was a moderate effect size between D1 and D2 for lower body VO2peak (d = 0.6), upper body VO2peak (d = 0.13) and upper body average power (d = 0.75), with a large effect size between D1 and D2 for haemoglobin (d = 1.19), haematocrit (d = 0.93) and upper body peak power (d = 0.95). There was a large effect size for D1 compared to D3 for all variables (d > 0.8). Therefore, there is no additional benefit to increasing dose above 50,000IU vitamin D per week. Given the endurance adaptations from vitamin D supplementation and the importance of endurance for combat performance, recreational combat athletes should supplement at 50,000IU per week for six weeks.
Developmental axon regrowth and primary neuron sprouting utilize distinct actin elongation factors
Authors: Yaniv Shiri P. , Meltzer Hagar , Alyagor Idan , Schuldiner Oren
Published: March 2020

Intrinsic neurite growth potential is a key determinant of neuronal regeneration efficiency following injury. The stereotypical remodeling of Drosophila γ-neurons includes developmental regrowth of pruned axons to form adult specific connections, thereby offering a unique system to uncover growth potential regulators. Motivated by the dynamic expression in remodeling γ-neurons, we focus here on the role of actin elongation factors as potential regulators of developmental axon regrowth. We found that regrowth in vivo requires the actin elongation factors Ena and profilin, but not the formins that are expressed in γ-neurons. In contrast, primary γ-neuron sprouting in vitro requires profilin and the formin DAAM, but not Ena. Furthermore, we demonstrate that DAAM can compensate for the loss of Ena in vivo. Similarly, DAAM mutants express invariably high levels of Ena in vitro. Thus, we show that different linear actin elongation factors function in distinct contexts even within the same cell type and that they can partially compensate for each other.
Chemistry and complexity for solitons in AdS5
Authors: Andrews Shane , Hennigar Robie A , Kunduri Hari K
Published: March 2020

MinimalD= 5 supergravity admits asymptotically globally AdS5gravitational solitons (stationary, geodesically complete, horizonless spacetimes with positive mass). We show that, like asymptotically flat gravitational solitons, these solutions satisfy mass and mass variation formulas analogous to those satisfied by AdS black holes. A thermodynamic volume associated to the non-trivial topology of the spacetime plays an important role in this construction. We then consider these solitons within the holographic ‘complexity equals action’ and ‘complexity equals volume’ conjectures as simple examples of spacetimes with nontrivial rotation and topology. We find distinct behaviours for the volume and action, with the counterterm for null boundaries playing a significant role in the latter case. For large solitons we find that both proposals yield a complexity of formation proportional to a power of the thermodynamic volume,V3/4. In fact, up to numerical prefactors, the result coincides with the analogous one for large black holes.
In-plane image quality and NPWE detectability index in digital breast tomosynthesis
Authors: Monnin P , Verdun F R , Bosmans H , Marshall N W
Published: March 2020

A rigorous 2D analysis of signal and noise transfer applied to reconstructed planes in digital breast tomosynthesis (DBT) is necessary for system characterization and optimization. This work proposes a method for assessing technical image quality and system detective quantum efficiency (DQEsys) for reconstructed planes in DBT. Measurements of 2D in-plane modulation transfer function (MTF) and noise power spectrum (NPS) were made on five DBT systems using different acquisition parameters, reconstruction algorithms and plane spacing. This work develops the noise equivalent quanta (NEQ), DQEsys and detectability index (d’) calculated using a non-prewhitening model observer with eye filter (NPWE) for reconstructed DBT planes. The images required for this implementation were acquired using a homogeneous test object of thickness 40 mm poly(methyl) methacrylate plus 0.5 mm Al; 2D MTF was calculated from an Al disc of thickness 0.2 mm and diameter 50 mm positioned within the phantom. The radiant contrast of the MTF disc and the air kerma at the system input were used as normalization factors. The NPWE detectability index was then compared to the in-plane contrast-detail (c-d) threshold measured using the CDMAM phantom.

The MTF and NPS measured on the different systems showed a strong anisotropy, consistent with the cascaded models developed in the literature for DBT. Detectability indices calculated from the measured MTF and NPS successfully predicted changes in c-d detectability for details between 0.1 mm and 2.0 mm, for DBT plane spacings between 0.5 mm and 10 mm, and for air kerma values at the system input between 157 µGy and 1170 μGy. The linear Pearson correlation between the detectability index and threshold gold thickness of the CDMAM phantom was −0.996. The method implements a parametric means of assessing the technical image quality of reconstructed DBT planes, providing valuable information for optimization of DBT systems.
Alanine dosimetry in strong magnetic fields: use as a transfer standard in MRI-guided radiotherapy
Authors: Billas Ilias , Bouchard Hugo , Oelfke Uwe , Shipley David , Gouldstone Clare , Duane Simon
Published: March 2020

Reference dosimetry in the presence of a strong magnetic field is challenging. Ionisation chambers have shown to be strongly affected by magnetic fields. There is a need for robust and stable detectors in MRI-guided radiotherapy (MRIgRT). This study investigates the behaviour of the alanine dosimeter in magnetic fields and assesses its suitability to act as a reference detector in MRIgRT.

Alanine pellets were loaded in a waterproof holder, placed in an electromagnet and irradiated by 60Co and 6 MV and 8 MV linac beams over a range of magnetic flux densities. Monte Carlo simulations were performed to calculate the absorbed dose, to water and to alanine, with and without magnetic fields. Combining measurements with simulations, the effect of magnetic fields on alanine response was quantified and a correction factor for the presence of magnetic fields on alanine was determined.

This study finds that the response of alanine to ionising radiation is modified when the irradiation is in the presence of a magnetic field. The effect is energy independent and may increase the alanine/electron paramagnetic resonance (EPR) signal by 0.2% at 0.35 T and 0.7% at 1.5 T. In alanine dosimetry for MRIgRT, this effect, if left uncorrected, would lead to an overestimate of dose. Accordingly, a correction factor,

k

Q
B

,
Q

, is defined. Values are obtained for this correction as a function of magnetic flux density, with a standard uncertainty which depends on the magnetic field and is 0.6% or less.

The strong magnetic field has a measurable effect on alanine dosimetry. For alanine which is used to measure absorbed dose to water in a strong magnetic field, but which has been calibrated in the absence of a magnetic field, a small correction to the reported dose is required. With the inclusion of this correction, alanine/EPR is a suitable reference dosimeter for measurements in MRIgRT.