bluuebunny/crossref_metadata_2025 huggingface dataset:
Stellar age gradients and inside-out star formation quenching in galaxy bulges
Authors: Breda Iris , Papaderos Polychronis , Gomes Jean Michel , Vílchez José Manuel , Ziegler Bodo L. , Hirschmann Michaela , Cardoso Leandro S. M. , Lagos Patricio , Buitrago Fernando
Published: February 2020

Radial age gradients hold the cumulative record for the multitude of physical processes driving the build-up of stellar populations and the ensuing star formation (SF) quenching process in galaxy bulges and, therefore, potentially sensitive discriminators between competing theoretical concepts on bulge formation and evolution. Based on spectral modeling of integral field spectroscopy (IFS) data from the CALIFA survey, we derived mass- and light-weighted stellar age gradients (∇(t⋆, B)ℒ, ℳ) within the photometrically determined bulge radius (RB) of a representative sample of local face-on late-type galaxies that span 2.6 dex in stellar mass (8.9 ≤ log ℳ⋆, T ≤ 11.5). Our analysis documents a trend of decreasing ∇(t⋆, B)ℒ, ℳ with increasing ℳ⋆, T, with high-mass bulges predominantly showing negative age gradients and vice versa. The inversion from positive to negative ∇(t⋆, B)ℒ, ℳ occurs at log ℳ⋆, T ≃ 10, which roughly coincides with the transition from lower-mass bulges whose gas excitation is powered by SF to bulges classified as composite, LINER, or Seyfert. We discuss two simple limiting cases for the origin of radial age gradients in massive late-type galaxy bulges. The first one assumes that the stellar age in the bulge is initially spatially uniform (∇(t⋆, B)ℒ, ℳ ≈ 0), thus the observed age gradients (∼ − 3 Gyr/RB) arise from an inside-out SF quenching (ioSFQ) front that is radially expanding with a mean velocity vq. In this case, the age gradients for massive bulges translate into a slow (vq ∼1–2 km s−1) ioSFQ that lasts until z ∼ 2, suggesting mild negative feedback by SF or an active galactic nucleus (AGN). If, on the other hand, negative age gradients in massive bulges are not due to ioSFQ but primarily due to their inside-out formation process, then the standard hypothesis of quasi-monolithic bulge formation has to be discarded in favor of another scenario. This would involve a gradual buildup of stellar mass over 2–3 Gyr through, for instance, inside-out SF and inward migration of SF clumps from the disk. In this case, rapid (≪1 Gyr) AGN-driven ioSFQ cannot be ruled out. While the ℳ⋆, T versus ∇(t⋆, B)ℒ, ℳ relation suggests that the assembly history of bulges is primarily regulated by galaxy mass, its large scatter (∼1.7 Gyr/RB) reflects a considerable diversity. This calls for an in-depth examination of the role of various processes (e.g., negative and positive AGN feedback, bar-driven gas inflows) with higher-quality IFS data in conjunction with advanced spectral modeling codes.
Radial velocity constraints on the long-period transiting planet Kepler-1625 b with CARMENES
Authors: Timmermann Anina , Heller René , Reiners Ansgar , Zechmeister Mathias
Published: February 2020

Context. The star Kepler-1625 recently attracted considerable attention when an analysis of the stellar photometric time series from the Kepler mission was interpreted as showing evidence of a large exomoon around the transiting Jupiter-sized planet candidate Kepler-1625 b. However, the mass of Kepler-1625 b has not been determined independently and its planetary nature has not been formally validated. Moreover, Kepler’s long-period Jupiter-sized planet candidates, like Kepler-1625 b with an orbital period of about 287 d, are known to have a high false-alarm probability. An independent confirmation of Kepler-1625 b is therefore particularly important.

Aims. We aim to detect the radial velocity (RV) signal imposed by Kepler-1625 b (and its putative moon) on the host star, or, as the case may be, determine an upper limit on the mass of the transiting object (or the combined mass of the two objects).

Methods. We took a total of 22 spectra of Kepler-1625 using CARMENES, 20 of which were useful. Observations were spread over a total of seven nights between October 2017 and October 2018, covering 125% of one full orbit of Kepler-1625 b. We used the automatic Spectral Radial Velocity Analyser pipeline to deduce the stellar RVs and uncertainties. We then fitted the RV curve model of a single planet on a Keplerian orbit to the observed RVs using a χ2 minimisation procedure.

Results. We derive upper limits on the mass of Kepler-1625 b under the assumption of a single planet on a circular orbit. In this scenario, the 1σ, 2σ, and 3σ confidence upper limits for the mass of Kepler-1625 b are 2.90 MJ, 7.15 MJ, and 11.60 MJ, respectively (MJ being Jupiter’s mass). An RV fit that includes the orbital eccentricity and orientation of periastron as free parameters also suggests a planetary mass but is statistically less robust.

Conclusions. We present strong evidence for the planetary nature of Kepler-1625 b, making it the (confirmed) planet with the tenth longest period known today. Our data do not allow us to make any form conclusions regarding a second, possibly shorter period planet that could be responsible for the observed transit timing variation of Kepler-1625 b.
Synthesis of 4-Nitroisoxazoles via NO/NO2-Mediated Heterocyclization of Aryl-Substituted α,β-Unsaturated Ketones
Authors: Averina Elena B. , Vasilenko Dmitry A. , Sadovnikov Kirill S. , Sedenkova Kseniya N. , Kurova Anastasiya V. , Grishin Yuri K. , Kuznetsova Tamara S. , Rybakov Victor B. , Volkova Yulia A.
Published: February 2020

A straightforward approach for the synthesis of 4-nitroisoxazoles has been developed via heterocyclization of aryl/hetaryl-substituted α,β-unsaturated ketones upon treatment with tetranitromethane-triethylamine (TNM-TEA) complex or t-BuONO. This strategy features high efficiency and wide substrate tolerance under simple reaction conditions.
A Decade with Dötz Benzannulation in the Synthesis of Natural Products
Authors: Fernandes Rodney A. , Kumari Anupama , Pathare Ramdas S.
Published: February 2020

The Dötz benzannulation is a named reaction that utilizes Fischer chromium carbenes in a formal [3+2+1] cycloaddition with an alkyne and CO to produce the corresponding benzannulated product. Since its development in the 1970s, this reaction has been extensively used in the synthesis of natural products and various molecular architectures. Although the reaction sometimes suffers from the formation of other competing side products, the rapid construction of naphthol structures with a 1,4-dihydroxy unit makes it the most appropriate reaction for the synthesis of p-naphthoquinones. This review focuses on our group’s efforts over the past decade on the extensive use of this annulation reaction along with the contributions of others on the synthesis of different natural products.

1 Introduction

2 General Description and Mechanism of the Dötz Benzannulation Reaction

3 Applications of the Dötz Benzannulation in Natural Product Synthesis over the Last Decade

4 Conclusion
Total Synthesis of Natural Products Using Intramolecular Nozaki–Hiyama–Takai–Kishi Reactions
Authors: Takao Ken-ichi , Ogura Akihiro , Yoshida Keisuke , Simizu Siro
Published: February 2020

In this Account, we describe our studies on the total synthesis of several natural products using intramolecular Nozaki–Hiyama–Takai–Kishi (NHTK) reactions. In each synthesis, an NHTK reaction is used to efficiently construct a medium-sized ring. These examples demonstrate the utility of the intramolecular NHTK reaction in natural product synthesis.

1 Introduction

2 Total Synthesis of (+)-Pestalotiopsin A

3 Total Synthesis of (+)-Cytosporolide A

4 Total Synthesis of (+)-Vibsanin A

5 Total Syntheses of (+)-Aquatolide and Related Humulanolides

6 Conclusion
Quantifying the Risks and Benefits of Continuing Labor Induction: Data for Shared Decision-Making
Authors: Teal Elizabeth Nicole , Lewkowitz Adam K. , Koser Sarah L.P. , Tran Carol B.N. , Gaw Stephanie L.
Published: February 2020

Objective This study aimed to quantify the relative maternal and fetal risks and benefits of continuing labor induction.

Study Design This retrospective cohort study included nulliparous women with nonanomalous, singleton, vertex, term pregnancies undergoing labor induction with intact membranes at a tertiary-care academic hospital from January 2015 to April 2017. The primary outcome was mode of delivery. Secondary outcomes included hemorrhage, transfusion, infection, and composite neonatal morbidity. The data were analyzed using chi-square and Fisher's exact tests. Multivariable regression was used to control for potential confounders.

Results A total of 955 patients met the inclusion criteria. The median induction duration was 32.3 hours (interquartile range: 20.4–41 hours) and the vaginal delivery rate was 70.5% (n = 673). The chance of vaginal delivery at 12, 24, 36, 48, 60, and ≥60 hours was 76, 83, 77, 74, 72, and 48%, respectively. After controlling for confounders, there was a 20% decrease in chance of vaginal delivery with induction ≥ 24 hours compared with induction < 24 hours. The adjusted relative risks of hemorrhage, transfusion, and infection with induction ≥ 24 hours compared with induction < 24 hours were 1.9, 2.2, and 2.7, respectively (95% confidence interval [CI] of 1.4–2.5, 1.1–3.9, and 1.8–4.0, respectively). The relative risk for these outcomes remained stable or decreased at each subsequent time point. The increasing risks of hemorrhage and infection were primarily among patients who underwent cesarean delivery. There was no association between induction duration and neonatal morbidity.

Conclusion In this cohort, the chance of vaginal delivery remained nearly 50% even when induction extended beyond 60 hours. Risks of hemorrhage and maternal infection rose modestly over time, but primarily in patients who underwent cesarean delivery. There was no difference in the risk of transfusion beyond 24 hours and no association between induction duration and neonatal morbidity. These findings may be useful when engaging patients in shared decision-making during labor induction.
Poland Syndrome with Atypical Malformations Associated to a de novo 1.5 Mb Xp22.31 Duplication
Authors: Massimino Carmela R. , Smilari Pierluigi , Greco Filippo , Marino Silvia , Vecchio Davide , Bartuli Andrea , Parisi Pasquale , Cho Sung Y. , Pavone Piero
Published: February 2020

Poland's syndrome (PS; OMIM 173800) is a rare congenital syndrome which consists of absence or hypoplasia of the pectoralis muscle. Other features can be variably associated, including rib defects. On the affected side other features (such as of breast and nipple anomalies, lack of subcutaneous tissue and skin annexes, hand anomalies, visceral, and vertebral malformation) have been variably documented. To date, association of PS with central nervous system malformation has been rarely reported remaining poorly understood and characterized. We report a left-sided PS patient carrying a de novo 1.5 Mb Xp22.31 duplication diagnosed in addiction to strabismus, optic nerves and chiasm hypoplasia, corpus callosum abnormalities, ectopic neurohypophysis, pyelic ectasia, and neurodevelopmental delay. Since, to our knowledge, this features' association has not been previously reported, we argue that this case may contribute to further widening of the variability of PS phenotype.
Older Patients May Have More Frequent Seizures among Children Diagnosed as Benign Convulsions with Mild Gastroenteritis
Authors: You Su Jeong
Published: February 2020

Purpose Benign convulsions with mild gastroenteritis (CwG) is a condition that does not usually require treatment. However, when the patient experiences multiple seizures or prolonged seizures, anticonvulsant treatment may be required. We investigated this study to identify the factors that may influence on the number or duration of seizures at CwG.

Methods We retrospectively analyzed the medical records of CwG patients who were admitted to the Department of Pediatrics at Sanggye Paik Hospital.

Results A total of 105 children with CwG were enrolled. The mean age was 19.59 ± 7.09 months. The mean duration of seizure was 2.79 ± 5.51 minutes and mean number of seizure was 2.33 ± 1.70. Sixty-nine children had seizures less than twice, whereas 36 experienced three times or more. These groups differed significantly according to age in CwG (18.16 ± 7.08, vs. 22.33 ± 6.34 months, p < 0.05). When patients were divided into two groups based on age in CwG using a cut-off of 20 months, we found significant differences in seizure number (1.91 ± 1.27 vs. 3.11 ± 2.10, p < 0.05). There was also a positive correlation between patient age and frequency of seizures (R = 0.316, p = 0.001). Patients who received anticonvulsants were older (17.60 ± 6.87 vs. 22.04 ± 6.63 months, p < 0.05) and had more frequent (1.59 ± 1.37 vs. 3.26 ± 1.63, p < 0.05) and longer seizures (1.76 ± 2.75 vs. 4.07 ± 7.49 minutes, p < 0.05).

Conclusion As the number of seizure in CwG was associated with age, treatment in older children may be required in acute stage.
Local well-posedness and blow-up criteria for a three-component Camassa–Holm type equation
Authors: Li Zhigang , Hu Yuxi
Published: February 2020

Considered herein is a three-component Camassa–Holm type equation that admits a bi-Hamiltonian structure and infinitely many conserved quantities. In this paper, we establish the local well-posedness of this system in Bp,rs. We also deduce two blow-up criteria for this system.
Perspectives, frontiers, and new horizons for plasma-based space electric propulsion
Authors: Levchenko I. , Xu S. , Mazouffre S. , Lev D. , Pedrini D. , Goebel D. , Garrigues L. , Taccogna F. , Bazaka K.
Published: February 2020

There are a number of pressing problems mankind is facing today that could, at least in part, be resolved by space systems. These include capabilities for fast and far-reaching telecommunication, surveying of resources and climate, and sustaining global information networks, to name but a few. Not surprisingly, increasing efforts are now devoted to building a strong near-Earth satellite infrastructure, with plans to extend the sphere of active life to orbital space and, later, to the Moon and Mars if not further. The realization of these aspirations demands novel and more efficient means of propulsion. At present, it is not only the heavy launch systems that are fully reliant on thermodynamic principles for propulsion. Satellites and spacecraft still widely use gas-based thrusters or chemical engines as their primary means of propulsion. Nonetheless, similar to other transportation systems where the use of electrical platforms has expanded rapidly, space propulsion technologies are also experiencing a shift toward electric thrusters that do not feature the many limitations intrinsic to the thermodynamic systems. Most importantly, electric and plasma thrusters have a theoretical capacity to deliver virtually any impulse, the latter being ultimately limited by the speed of light. Rapid progress in the field driven by consolidated efforts from industry and academia has brought all-electric space systems closer to reality, yet there are still obstacles that need addressing before we can take full advantage of this promising family of propulsion technologies. In this paper, we briefly outline the most recent successes in the development of plasma-based space propulsion systems and present our view of future trends, opportunities, and challenges in this rapidly growing field.
Locality and renormalization: Universal properties and integrals on trees
Authors: Clavier Pierre , Guo Li , Paycha Sylvie , Zhang Bin
Published: February 2020

The purpose of this paper is to build an algebraic framework suited to regularize branched structures emanating from rooted forests and which encodes the locality principle. This is achieved by means of the universal properties in the locality framework of properly decorated rooted forests. These universal properties are then applied to derive the multivariate regularization of integrals indexed by rooted forests. We study their renormalization, along the lines of Kreimer’s toy model for Feynman integrals.
Incomplete symmetric orthogonal polynomials of finite type generated by a generalized Sturm–Liouville theorem
Authors: Masjed-Jamei Mohammad , Moalemi Zahra , Saad Nasser
Published: February 2020

In a classical case, orthogonal polynomial sequences are in such a way that the nth polynomial has the exact degree n. Such sequences are complete and form a basis of the space for any arbitrary polynomial. In this paper, we introduce some incomplete sets of finite orthogonal polynomials that do not contain all degrees, but they are solutions of some symmetric generalized Sturm–Liouville problems. Although such polynomials do not possess all properties as in classical cases, they can be applied to functions approximation theory as we will compute their explicit norm square values.
Terahertz radiation enhanced by target ablation during the interaction of high intensity laser pulse and micron-thickness metal foil
Authors: Zhang Siyuan , Yu Jinqing , Shou Yinren , Gong Zheng , Li Dongyu , Geng Yixing , Wang Weimin , Yan Xueqing , Lin Chen
Published: February 2020

When an ultra-intense relativistic laser is irradiated on a solid target, terahertz (THz) pulses can be generated by coherent transition radiation when the laser-driven electron beams cross the rear surface of the target. The radiation energy depends on the number and energy of the electrons. By introducing a milli-joule picosecond ablation laser pulse, an underdense preplasma with a scale length of micrometers is generated at the front surface of the target. Electron beams with more charge and higher energy can be produced during the interaction between the following main laser pulse and the preplasma, which enhance the THz radiation and affect the radiation angle. Two dimensional particle-in-cell simulations demonstrate the improvement of electron beams and a nearly tenfold enhancement of THz radiation energy is observed.
The injected plasma triggered breakdown of the trigatron spark gap
Authors: Chen Li , Yang Weihong , Fan Hao , Li Xinwen , Li Ying
Published: February 2020

This paper presents experimental results on a trigatron spark gap breakdown process induced by different densities of the injected plasma. The results show that the shape of the injected plasma has a great influence on the electric field distribution. The decrease in the curvature radius of the injected plasma front can induce a breakdown during the dissipation of the injected plasma. This process is significant in explaining the sharp increase in the breakdown delay and jitter observed under very low working coefficients. The inception and propagation of the streamer are studied in detail. Due to the high intensity illumination, direct ionization between the injected plasma front and the head of the streamer can occur during the propagation of the streamer. This differs from the conventional streamer breakdown process under a uniform electric field. An explanation of the streamer inception and the direct ionization between the front of the injected plasma and the streamer head is presented. Using the Meek criterion, the effects of electric field distortion and photoionization induced by the injected plasma are analyzed. The results indicate that the effect of the photoionization changes significantly with the density and duration of the plasma injection. Combining this effect with the electric field distortion, a breakdown can occur under a very low working coefficient.
Initial stage of beam-generated plasma with evaporating electrode
Authors: Levko Dmitry
Published: February 2020

The initial stage of a beam-generated plasma with an evaporating electrode is analyzed for the conditions of Zolotukhin et al., Phys. Plasmas 26, 053512 (2019). The analysis is performed using the Particle-in-Cell model for charged species coupled with the Euler equations for neutral species. It is shown that the metal wall evaporation significantly influences the plasma parameters. This is due to a much larger ionization and elastic scattering cross sections of the metal vapors than the background gas. The influence of the metal evaporation on the electron energy distribution function is also analyzed.
Mutual synchronization of two flame-driven thermoacoustic oscillators: Dissipative and time-delayed coupling effects
Authors: Moon Kihun , Guan Yu , Li Larry K. B. , Kim Kyu Tae
Published: February 2020

Low-emissions can-annular gas turbines are prone to develop low-frequency self-excited thermoacoustic oscillations. Such oscillations arise from the coupling between adjacent combustors and can increase wear and thermal stresses. In this experimental study, we explore the mutual synchronization of two thermoacoustic oscillators (i.e., two model combustors) interacting via dissipative and time-delayed coupling, as introduced via a cross-talk section. Unlike most previous studies, our study makes use of a turbulent lean-premixed flame in each combustor, bringing the system configuration closer to that of practical gas turbines. Using stationary and transient measurements, we examine the effect of the cross-talk diameter and length so as to gain insight into the effect of dissipative and time-delayed coupling. We find that strengthening the dissipative coupling promotes mutual synchronization, but that weakening the dissipative coupling leads to weakly coupled or desynchronized oscillations. On operating the two combustors at different conditions, we find a significant reduction in their overall oscillation amplitude for some coupling conditions. On varying the combustor length and examining the transient response, we find elaborate changes in the pressure−heat-release-rate coupling, spontaneous mode transitions between coupled thermoacoustic modes, and the emergence of a rhomboid structure in the phase plane owing to the coexistence of in-phase and out-of-phase synchronization. In the combustion community, these two types of synchronization are known to be associated with push–push modes and push–pull modes. These findings offer new insight into the mutual synchronization of low-frequency, self-excited thermoacoustic oscillations in can-annular gas turbines, paving the way for the development of improved control strategies.
Numerical simulation of experimental tests performed on ZAO® non-evaporable-getter pump designed for neutral beam injector applications
Authors: Siragusa M. , Sartori E. , Mura M. , Siviero F.
Published: February 2020

Vacuum systems of neutral beam injectors have very demanding requirements in terms of pumping speed, throughput, and capacity. Due to their high affinity to hydrogenic species, porous sintered Non-Evaporable Getters (NEG) are a possible candidate for deployment in giant hydrogen ion sources and neutral beam injectors for fusion. This paper presents the numerical interpretation of experimental tests on a recently developed NEG cartridge, that is part of a modular pump under development for neutral beam injectors. The cartridge is composed of six stacks of ZAO® porous sintered NEG disks and a heater. It was tested under hydrogen loads relevant for neutral beam injectors, namely, at constant pressure or constant flow, such that the hydrogen pressure was in the range of 20 mPa–40 mPa. The result of the sorption test was reproduced by a three dimensional flow simulation in molecular regime to determine the actual pumping speed, the effective sticking coefficient, and the uniformity of the gas load on the various NEG disks. The procedure developed and the results obtained provide the basic understanding for interpreting the large-scale tests on the modular pump, consisting of 34 of these cartridges.
Capture of high energy orbit of Duffing oscillator with time-varying parameters
Authors: Yu Liuding , Tang Lihua , Xiong Liuyang , Yang Tiejun
Published: February 2020

This work investigates the time response of a Duffing oscillator with time-varying parameters (excitation frequency, linear stiffness, and mass) by approximate analytical and numerical methods. When the excitation frequency sweep covers the multisolution range, the characteristics of the response (maximum response, jump-up frequency, and jump-down frequency) mainly depend on the frequency sweep rate. If the frequency sweep is ended in the multisolution range, the sweep rate determines the energy orbit that the final response will capture. The results can be explained by comparing the state spaces of the oscillator with the change of basin of attraction of the high-energy orbit during the sweep. Furthermore, if the excitation is fixed at a specific frequency in the multisolution range, a method of natural frequency temporary modulation is proposed for the capture of the high-energy orbit. For practical realization, this method is completed by two ways, that is, the linear stiffness temporary modulation and mass temporary modulation. The modulation schedules of time-varying linear stiffness and mass are determined quantitatively, and it is proved that they could help capture the high-energy orbit similar to the excitation frequency sweep. The developed methods and results of this work can provide the guidelines to design nonlinear systems to work on preferred energy orbit.
Simulations of electromagnetic effects in large-area high-frequency capacitively coupled plasmas with symmetric electrodes: Different axial plasma density profiles
Authors: Liu Jian-Kai , Zhang Yu-Ru , Zhao Kai , Wen De-Qi , Wang You-Nian
Published: February 2020

In this paper, the electromagnetic effects are investigated in large-area high-frequency symmetric capacitive discharges by solving the Maxwell equations under two different axial plasma density profiles, i.e., the spatially uniform and the axial non-uniform density profiles. Simulation results show that the spatially uniform density profile underestimates the standing wave effect and overestimates the skin effect. Moreover, the electromagnetic effects are significantly affected by the frequency, sheath width, electron-neutral momentum transfer frequency, and plasma density. As the frequency increases, the surface wavelength is significantly reduced, and the standing wave effect becomes pronounced. An opposite result is obtained by increasing the sheath width. As the electron-neutral momentum transfer frequency increases, the radial damping of surface waves when they propagate from the radial edge to the center becomes prominent. As the plasma density increases, the discharge is dominated by the skin effect instead of the standing wave effect, due to the reduced skin depth.
Origin of depressed fill factor in organic solar cells due to S-shape current–voltage characteristics
Authors: Rana Aniket , Kumar Amit , Vashistha Nikita , Garg Kuldeep K. , Chand Suresh , Singh Rajiv K.
Published: February 2020

Often, a depressed fill factor is observed in organic solar cells (OSCs), which is usually known as S-shaped current-voltage (J−V) characteristics. To investigate the origin of the depressed fill factor further, a poly[N-9-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)]:[6,6]-phenyl C71 butyric acid methyl ester based OSC has been characterized through impedance spectroscopy. In addition, the photocurrent vs the applied effective bias plot reveals that the S-shaped J−V characteristics primarily reduce the diffusion current of the device. The present study shows that the diffusion current dominated section of photocurrent reduces with a slope of 2 in the depressed fill factor section given that the slope may further increase as per the impact of the S-shape. The reduction in the diffusion constant (Dn) in the S-shaped region supports the decrease in the diffusion current, which is observed through the photocurrent analysis. It is observed that, in the S-shaped section of the current-voltage characteristics, the transport time for free carriers increases up to 443 μs. The larger Urbach energy for the active layer of an S-shaped device demonstrates higher subbandgap disorder. Therefore, it is concluded that the accumulation of the charge carriers within the device and disorder in the active layer leads to the S-shaped current–voltage characteristics as well as poor carrier extraction.
Wettability of ultra-small pores of carbon electrodes by size-asymmetric ionic fluids
Authors: Liu Kun , Wu Jianzhong
Published: February 2020

Recently, we studied the phase behavior of ionic fluids under confinement using the classical density functional theory within the framework of the restricted primitive model. The theoretical results indicate that narrowing the pore size may lead to a drastic reduction in the electric double layer capacitance, while increasing the surface electrical potential would improve the ionic accessibility of micropores. In this work, we extend the theoretical investigation to systems containing size-asymmetric electrolytes that may exhibit a vapor-liquid like phase transition in the bulk phase. The effects of pore size and surface electric potential on the phase diagram and microscopic structures of the confined electrolytes were studied over a broad range of parameters. We found that decreasing the pore size or increasing the surface potential could destabilize the liquid phase in micropores, and capillary evaporation could occur regardless of the size asymmetry between cations and anions. Compared to that in a symmetric ionic system, the vapor-liquid phase separation is more likely to take place as the size asymmetry becomes more pronounced. The phase transition would alter the “accessibility” of ions to micropores and lead to coexisting micropores with different surface charge densities as identified by Monte Carlo simulation.
Coexistence of firing patterns and its control in two neurons coupled through an asymmetric electrical synapse
Authors: Tabekoueng Njitacke Z. , Sami Doubla Isaac , Kengne J. , Cheukem A.
Published: February 2020

In this paper, the effects of asymmetry in an electrical synaptic connection between two neuronal oscillators with a small discrepancy are studied in a 2D Hindmarsh–Rose model. We have found that the introduced model possesses a unique unstable equilibrium point. We equally demonstrate that the asymmetric electrical couplings as well as external stimulus induce the coexistence of bifurcations and multiple firing patterns in the coupled neural oscillators. The coexistence of at least two firing patterns including chaotic and periodic ones for some discrete values of coupling strengths and external stimulus is demonstrated using time series, phase portraits, bifurcation diagrams, maximum Lyapunov exponent graphs, and basins of attraction. The PSpice results with an analog electronic circuit are in good agreement with the results of theoretical analyses. Of most/particular interest, multistability observed in the coupled neuronal model is further controlled based on the linear augmentation scheme. Numerical results show the effectiveness of the control strategy through annihilation of the periodic coexisting firing pattern. For higher values of the coupling strength, only a chaotic firing pattern survives. To the best of the authors' knowledge, the results of this work represent the first report on the phenomenon of coexistence of multiple firing patterns and its control ever present in a 2D Hindmarsh–Rose model connected to another one through an asymmetric electrical coupling and, thus, deserves dissemination.
Study of material ablation and plasma radiation in double-pulse laser induced breakdown spectroscopy at different delay times: Modeling and numerical simulation
Authors: Nosrati Y. , Tavassoli S. H. , Hassanimatin M. M. , Safi A.
Published: February 2020

A one-dimensional numerical model is presented on a copper sample to investigate double-pulse laser induced breakdown spectroscopy (DP-LIBS). The effect of the inter-pulse delay time on the material ablation, plasma homogeneity, and signal enhancement is examined. The dynamics of laser ablation, plume expansion, plasma formation, and plasma radiation of the ionized and neutral atoms in the presence of helium background gas at a pressure of 1 atm are studied. A heat conduction equation is solved in the sample and is coupled to the fluid dynamic equations through the Knudsen layer relations. Saha-Eggert equations are utilized to investigate the plasma formation. The influence of plasma shielding, due to the photoionization and inverse bremsstrahlung processes, is considered. Continuous radiation, bremsstrahlung and recombination radiations, and spectral emissions of the plasma are examined. The optimum inter-pulse delay time for maximizing the neutral and ionized spectral emissions is determined. The results reveal that the ablation rate in DP-LIBS is significantly higher than that of single pulse laser induced breakdown spectroscopy (SP-LIBS) and reaches its maximum at an optimum inter-pulse delay time due to the decrease in the recondensation of the ablated plume. Furthermore, it is demonstrated that in DP-LIBS, the ablation profile is smoother and its continuous radiation decreases much earlier than that of SP-LIBS. Although the double-pulse mode improves the signal to background ratio, it leads to more inhomogeneity in the plasma.
Electric-field-induced phase transition in 2D layered perovskite (BA)2PbI4 microplate crystals
Authors: Wang Jiaqi , Shen Hongzhi , Li Junze , Li Wancai , Fang Chen , Ma Jiaqi , Cheng Xue , Li Dehui
Published: February 2020

Two-dimensional (2D) lead halide perovskite materials are solution-processable semiconductor materials, which would find promising applications in optoelectronic devices. The fundamental understanding of the structural phase transition in two-dimensional perovskites is of great importance for fully exploiting their potential applications in electronic and optoelectronic devices. Here, we report on how the external electric field affects the structural phase transition in 2D perovskite (BA)2PbI4 microplates via temperature-dependent photoluminescence spectroscopy. A high-temperature phase and a low-temperature phase can coexist in a wider range of temperatures. The external electric field would enhance the phase transition to the dominant phase depending on the surrounding temperature. This field-induced phase transition might be ascribed to the release of strain in the perovskite microplate induced by the applied electric field, leading to the change in the structural phase transition temperature. Our findings are of great significance not only to the fundamental understanding of phase transition but also to the design and optimization of two-dimensional perovskite based electronic and optoelectronic devices.
Sound absorption of acoustic resonators with oblique perforations
Authors: Carbajo J. , Ghaffari Mosanenzadeh S. , Kim S. , Fang N. X.
Published: February 2020

Low-frequency airborne noise reduction is an issue of major concern in most practical cases due to the limiting space constraints. The applicability of acoustic resonators that not only work in this frequency range but can also be tuned is of great interest in many noise control applications such as muffler devices, noise barriers, or building isolation walls. This Letter studies the acoustic behavior of perforated panel absorbers with oblique perforations. Unlike more complex devices, the proposed absorber uses a simple concept that relies on the increase in the effective length of the panel by using perforations aligned obliquely with respect to the panel surface. In doing so, a shift of the resonance frequency toward low frequencies along with an increase in the sound absorption can be achieved provided that the geometrical characteristics of the absorber are properly chosen. A simple predictive model that relies on the fluid-equivalent theory was developed to investigate the acoustic properties of these absorbers, measurements in an impedance tube over additive manufactured samples serving to confirm the previous assertions. Preliminary results show the potential of these absorbers and encourage their further development for practical purposes.
Acoustic and double elastic shock waves in single-crystal graphene
Authors: Long X. J. , Cai Y. , Jian W. R. , Wang L. , Luo S. N.
Published: February 2020

Double elastic shock waves are rarely observed in two-dimensional (2D) materials and normally unexpected for elastically isotropic 2D crystals such as graphene. With large-scale molecular dynamics simulations, we show that in single-crystal graphene shock-loaded along nonzigzag and nonarmchair directions, double elastic shock waves (quasilongitudinal and quasitransverse) can emerge. Quantitative acoustic wave equation analysis reveals that shock-induced symmetry reduction in lattice, as well as in elastic stiffness tensor, gives rise to the normally unexpected quasitransverse wave following the quasilongitudinal wave.
GLIDER—A pulsed-current generator for laboratory astrophysics x-ray absorption experiments
Authors: Gissis I. , Behar E. , Fisher A. , Aricha S. , Yeger E. , Avni U. , Schnitzer I.
Published: February 2020

In the field of pulse-power, there has always been an interest on small and medium size pulsed-current generators (≤2 MA) which are affordable and of low maintenance. We developed the GLIDER, a compact and modular generator, that drives a gas-puff z-pinch load as a soft x-ray source (0.1–1 keV) for laboratory astrophysics absorption experiments. It comprises 48 bricks, tightly packed in a 1.7 m × 3.5 m × 0.8 m transformer oil container. Its compactness and reliability was enabled owing to unique multilayered oil-soaked insulators, and more than 100 post-hole convolutes. Its stripline includes interchangeable tiles for ease of construction and maintenance. Six triggering units enable current pulse shaping. The GLIDER was tested up to ±60 kV (34 kJ) and produced 2 MA in 450 ns rise time on a 5 nH load. We present grating spectra of K-shell absorption of neutral O and N proving the experimental concept and demonstrating column density and ionization measurements.
Terahertz electron paramagnetic resonance spectroscopy using continuous-wave frequency-tunable photomixers based on photoconductive antennae
Authors: Ohmichi Eiji , Fujimoto Tatsuya , Minato Keisuke , Ohta Hitoshi
Published: February 2020

In this article, we demonstrate terahertz (THz) electron paramagnetic resonance (EPR) spectroscopy using a frequency-tunable photomixing source/detection system to investigate the electronic structure of solid-state samples in a microscopic manner. Fiber-coupled photoconductive antennae were used to generate and detect continuous THz waves obtained as the beat signals from two laser beams with different wavelengths. We will show some examples of EPR spectroscopy obtained by multi-frequency EPR measurements at room temperature. The technique reported here has several advantages, including high spectral resolution, wide frequency-range operation, high dynamic range, owing to the continuous-wave (cw) and tunable generation/detection of THz waves.
On the E to H mode transition in a dual frequency (2 and 13.56 MHz) inductively coupled plasma
Authors: Kim Ju-Ho , Chung Chin-Wook
Published: February 2020

The E to H transition is investigated in 2 MHz, 13.56 MHz, and dual frequency (2 MHz + 13.56 MHz) inductively coupled plasmas (ICPs). At argon gas pressures of 1 mTorr and 10 mTorr, the E to H transition power of 2 MHz ICP is the lowest and the transition power of 13.56 MHz ICP is the highest. However, at pressures of 25 mTorr and 50 mTorr, the transition power of 13.56 MHz ICP decreases and the transition power of 2 MHz ICP significantly increases. Interestingly, despite these changes, the E to H transition in the dual frequency operation occurs at the power between the 2 MHz and the 13.56 MHz transition power. The measurement shows that the plasma density in dual frequency operation is from about 1.1 to 11.7 times higher than that in single frequency operation, but this is changed with the pressure. For quantitative analysis, a global model including the capacitive coupling and the inductive coupling in the solenoidal ICP was developed and the E to H transition powers were calculated. It turns out that the results at various pressures and frequencies agree well with the experimental measurements and the relevant physical mechanism is also presented.
The search for the most conductive metal for narrow interconnect lines
Authors: Gall Daniel
Published: February 2020

A major challenge for the continued downscaling of integrated circuits is the resistivity increase of Cu interconnect lines with decreasing dimensions. Alternative metals have the potential to mitigate this resistivity bottleneck by either (a) facilitating specular electron interface scattering and negligible grain boundary reflection or (b) a low bulk mean free path that renders resistivity scaling negligible. Recent research suggests that specular electron scattering at the interface between the interconnect metal and the liner layer requires a low density of states at the interface and in the liner (i.e., an insulating liner) and either a smooth epitaxial metal-liner interface or only weak van der Waals bonding as typical for 2D liner materials. The grain boundary contribution to the room-temperature resistivity becomes negligible if the grain size is large (>200 nm or ten times the linewidth for wide or narrow conductors, respectively) or if the electron reflection coefficient is small due to low-energy boundaries and electronic state matching of neighboring grains. First-principles calculations provide a list of metals (Rh, Pt, Ir, Nb, Ru, Ni, etc.) with a small product of the bulk resistivity times the bulk electron mean free path ρo × λ, which is an indicator for suppressed resistivity scaling. However, resistivity measurements on epitaxial layers indicate considerably larger experimental ρo × λ values for many metals, indicating the breakdown of the classical transport models at small (<10 nm) dimensions and suggesting that Ir is the most promising elemental metal for narrow high-conductivity interconnects, followed by Ru and Rh.
Low resistance at LiNi1/3Mn1/3Co1/3O2 and Li3PO4 interfaces
Authors: Nishio Kazunori , Nakamura Naoto , Horiba Koji , Kitamura Miho , Kumigashira Hiroshi , Shimizu Ryota , Hitosugi Taro
Published: February 2020

We report the low resistance observed at the interface of LiNi1/3Mn1/3Co1/3O2 (NMC) and Li3PO4. First, we show the deposition of high-quality single-phase NMC (001) epitaxial thin films on Al2O3 (0001) substrates using pulsed laser deposition. Controlling the oxidation states of the three transition metals in NMC films is crucial for stable battery operation. However, in general, it is very difficult to simultaneously control the oxidation states of three elements in vacuum deposition processes. Tuning the oxygen partial pressure and temperature during deposition led to the growth of NMC thin films with ideal oxidation states (Ni2+, Mn4+, and Co3+), as confirmed using bulk-sensitive x-ray excited optical luminescence. Next, using the NMC epitaxial thin films, we prepared solid-state batteries that demonstrated stable operation and very low resistance at the solid electrolyte/electrode interfaces. These results provide insight into the fabrication of multi-transition-metal electrode thin film materials, which are important for investigating the mechanisms of lithium battery operation. Furthermore, the low interface resistance indicates that Li3PO4 and oxide electrode materials form very stable low-resistance interfaces.
Time-domain characterization and correction of on-chip distortion of control pulses in a quantum processor
Authors: Rol M. A. , Ciorciaro L. , Malinowski F. K. , Tarasinski B. M. , Sagastizabal R. E. , Bultink C. C. , Salathe Y. , Haandbaek N. , Sedivy J. , DiCarlo L.
Published: February 2020

We introduce Cryoscope, a method for sampling on-chip baseband pulses used to dynamically control qubit frequency in a quantum processor. We specifically use Cryoscope to measure the step response of the dedicated flux control lines of two-junction transmon qubits in circuit QED processors with the temporal resolution of the room-temperature arbitrary waveform generator producing the control pulses. As a first application, we iteratively improve this step response using optimized real-time digital filters to counter the linear-dynamical distortion in the control line, as needed for high-fidelity repeatable one- and two-qubit gates based on dynamical control of qubit frequency.
Out-of-plane electromechanical coupling in transition metal dichalcogenides
Authors: Brennan Christopher J. , Koul Kalhan , Lu Nanshu , Yu Edward T.
Published: February 2020

Monolayer transition metal dichalcogenides (TMDs) are intrinsically piezoelectric within the plane of their atoms, but out-of-plane piezoelectric response should not occur due to the symmetry of the crystal structure. Recently, however, MoS2 was shown to exhibit out-of-plane electromechanical coupling consistent with the flexoelectric effect. In this study, MoSe2, WS2, and WSe2 are investigated to determine the existence and strength of out-of-plane electromechanical coupling in other monolayer TMD semiconductor materials. Piezoresponse force microscopy measurements show that monolayer MoS2, MoSe2, WS2, and WSe2 all exhibit out-of-plane electromechanical response. The relative magnitudes of their out-of-plane electromechanical couplings are calculated and compared with one another and to predictions made from a simple model of flexoelectricity. This simple model correctly predicts the magnitude of out-of-plane electromechanical response in these materials, and the measured values provide useful guidance for both more detailed understanding of flexoelectric response in monolayer TMDs, and assessment of their consequences in devices incorporating these materials.
Magnetocaloric effect in 2D-alkylammonium copper halides layered inorganic-organic systems
Authors: Bochalya Madhu , Kumar Sunil
Published: February 2020

Two-dimensional inorganic–organic hybrids are important due to tunable physical properties and their suitability in the data storage, memory devices, low-temperature magnetic refrigeration technology, energy storage, and other applications. The significance of such lead-free layered hybrids is in the ease of synthesis and material stability against heat, humidity, temperature, and other environmental conditions. Here, we report the magnetic properties of (C12H25NH3)2Cu(Br1 – xClx)4 and (C6H9C2H4NH3)2Cu(Br1 – xClx)4 systems that are self-assembled layered structures formed by solution processing. The systems exhibit paramagnetic to ferromagnetic transition with the Curie temperature and amount of magnetization both controllable by halogen content in the stoichiometric composition. Magnetocaloric properties have been investigated to find out the suitability of highly stable (C12H25NH3)2CuCl4 in environment friendly low-temperature magnetic refrigeration technology. A large magnetic entropy change varying from ∼0.6 J kg−1 K−1 to larger than 2.0 J kg−1 K−1 is measured from isothermal magnetization data around the Curie temperature at field variations 0–10 kOe and 0–60 kOe, respectively. Characteristic critical exponents from the field-dependent magnetic entropy changes have been determined, which show excellent agreement with the three-dimensional Heisenberg model.