bluuebunny/crossref_metadata_2025_split huggingface dataset:
Visualization of flat and curved spacetimes with simple cartography tools
Authors: Scott R B 
Published: October 2020

Abstract
Well-developed tools from cartography are adapted and used to visualize curved and flat spacetime to further understanding of relativistic effects, while interpretation of these tools is aided through their application to the familiar world map. First spacetime is cut into two-dimensional subspaces that are mapped to the Minkowski or Euclidean plane using map projections. Then, exploiting the cartographic technique of map interruptions, the two-dimensional subspaces are further cut into ‘wedges’ to minimize the distortion. The mental exercise of sewing the wedges back together aids in visualizing and interpreting the geometry of the spacetime slice. Map distortion indicators alert the reader to the inevitable effects of distortion. This wedge diagram provides a simple yet powerful tool to visualize both flat and curved spacetime geometry. It is more general than the familiar embedding diagram and avoids the pitfall of confusing the space in question with the embedding space. The wedge diagram is applied first to Minkowski spacetime with the cartographers’ azimuthal equidistant map projection and, when combined with the wedge technique, provides a simple visualization of the twin paradox. The wedge diagram is then applied to the exterior Schwarzschild spacetime to visualize the physical significance of spacetime curvature. In particular it is shown how gravitational time dilation results from intrinsic curvature of a radial-time slice of spacetime. Then this diagram is applied to the Friedmann–Robertson–Walker (FRW) spacetime revealing how expansion of the Universe results from a qualitatively similar curvature of a radial-time slice, but with the roles of space and time reversed. The analogy between the two spacetimes suggests novel interpretations of the two spacetimes. We interpret the Schwarzschild spacetime as time expanding with increasing distance from the horizon. And we interpret the FRW spacetime as the Universe expanding as the influence of the big bang peters out.
A direct reconstruction algorithm for the anisotropic inverse conductivity problem based on Calderón’s method in the plane
Authors: Murthy Rashmi , Lin Yi-Hsuan , Shin Kwancheol , Mueller Jennifer L 
Published: October 2020

Abstract
A direct reconstruction algorithm based on Calderón’s linearization method for the reconstruction of isotropic conductivities is proposed for anisotropic conductivities in two-dimensions. To overcome the non-uniqueness of the anisotropic inverse conductivity problem, the entries of the unperturbed anisotropic tensors are assumed known a priori, and it remains to reconstruct the multiplicative scalar field. The quasi-conformal map in the plane facilitates the Calderón-based approach for anisotropic conductivities. The method is demonstrated on discontinuous radially symmetric conductivities of high and low contrast.
Bright, polarization-tunable high repetition rate extreme ultraviolet beamline for coincidence electron–ion imaging
Authors: Comby A , Bloch E , Beauvarlet S , Rajak D , Beaulieu S , Descamps D , Gonzalez A , Guichard F , Petit S , Zaouter Y , Blanchet V , Mairesse Y 
Published: October 2020

Abstract
After decades of supremacy of the Titanium:Sapphire technology, Ytterbium-based high-order harmonic sources are emerging as a promising alternative for experiments requiring high flux of ultrashort extreme ultraviolet (XUV) radiation. In this article we describe a versatile experimental setup delivering XUV photons in the 10–50 eV range. The use of cascaded high-order harmonic generation enables us to reach 1.9 mW of average power at 18 eV. Several spectral selection schemes are presented, to isolate a single high-harmonic or a group of them. In the perspective of circular dichroism experiments, we produce highly elliptical XUV radiation using resonant elliptical high-harmonic generation, and circularly polarized XUV by bichromatic bicircular high-harmonic generation. As an illustration of the capacities of the beamline, we focus the XUV beam in a coincidence electron–ion imaging spectrometer, where we measure the photoelectron momentum angular distributions of xenon monomers and dimers.
Analysis of Compton profile through information theory in H-like atoms inside impenetrable sphere
Authors: Mukherjee Neetik , Roy Amlan K 
Published: October 2020

Abstract
Confinement of atoms inside various cavities has been studied for nearly eight decades. However, the Compton profile (CP) for such systems has not yet been investigated. Here we construct the CP for a H atom radially confined inside a hard spherical enclosure, as well as in a free condition. Some exact analytical relations for the CP’s of circular or nodeless states of free atoms is presented. By means of a scaling idea, this has been further extended to the study of a H-like atom trapped inside an impenetrable cavity. The accuracy of these constructed CPs has been confirmed by computing various momentum moments. Apart from that, several information theoretical measures, like Shannon entropy (S) and Onicescu energy (E) have been exploited to characterize these profiles. Exact closed-form expressions are derived for S and E using the ground state CP in free H-like atoms. A detailed study reveals that, increase in confinement inhibits the rate of dissipation of kinetic energy. At a fixed ℓ, this rate diminishes with a rise in n. However, at a certain n, this rate accelerates with progress in ℓ. Similar analysis on the respective free counterpart displays an exactly opposite trend as that in a confined system. However, in both free and confined environments, the CP generally gets broadened with rise in Z. Representative calculations are done numerically for low-lying states of the confined systems, taking two forms of position-space wave functions: (a) exact (b) highly accurate eigenfunctions through a generalized pseudospectral method. In essence, CPs are reported for confined H atoms (and isoelectronic series) and investigated adopting an information-theoretic framework.
Single and multiple excitations in double-core-hole states of free water molecules
Authors: Marchenko T , Carniato S , Goldsztejn G , Travnikova O , Journel L , Guillemin R , Ismail I , Koulentianos D , Martins J , Céolin D , Püttner R , Piancastelli M N , Simon M 
Published: October 2020

Abstract
We present a combined experimental and theoretical study of the double-core-hole photoelectron spectrum obtained in isolated water molecules irradiated with hard x-rays above the oxygen K
−2 threshold. States of the type O K
−2
V and multiply excited states are created by single-photon absorption and subsequent one-electron emission. A detailed analysis enabled by high experimental resolution reveals dissociative nuclear dynamics in the K
−2
V pre-edge states. At the binding energies above the K
−2 double-ionization potential, a complex spectral pattern is observed and attributed to highly excited states involving multiple shake-up excitation processes with the aid of state-of-the-art theoretical calculations. A strong broadening due to the nuclear motion indicates a highly dissociative nature of these multiply excited states, in agreement with the theoretical analysis.
Double differential distributions of e-emission in ionization of N2 by 3, 4 and 5 keV electron impact
Authors: Chowdhury Madhusree Roy , Chauhan Dhaval , Limbachiya Chetan G , Tőkési Karoly , Champion Christophe , Weck Philippe F , Tribedi Lokesh C 
Published: October 2020

Abstract
We report the measurement of the absolute double differential cross sections (DDCS) of secondary electrons emitted due to the ionization of N2 molecule in collisions with fast electrons having energies between 3 and 5 keV. The emitted electrons with energies from 1–500 eV have been measured for different forward and backward emission angles. The measured DDCS have been compared with the state-of-the-art first Born approximation with correct boundary condition (CB1) model calculations as well as with the classical trajectory Monte Carlo (CTMC) method. From the measured DDCS, the single differential cross sections (SDCS) as a function of the emission energies have been computed and eventually the total ionization cross sections (TCS) have been derived. The TCS values are also compared with a semi-empirical calculation, namely, the CSP-ic (complex scattering potential-ionization contribution) model.
Novel repumping on 3P0
→
3D1 for Sr magneto-optical trap and Landé g factor measurement of 3D1
Authors: Zhang Shengnan , Ramchurn Preetam , Menchetti Marco , Ubaid Qasim , Jones Jonathan , Bongs Kai , Singh Yeshpal 
Published: October 2020

Abstract
We realize an experimental facility for cooling and trapping strontium (Sr) atoms and measure the Landé g factor of 3D1 of 88Sr. Thanks to a novel repumping scheme with the 3P2 → 3S1 and 3P0 → 3D1 combination and the permanent magnets based self-assembled Zeeman slower, the peak atom number in the continuously repumped blue magneto-optical trap is enhanced by a factor of 15 with respect to the non-repumping case, and reaches ∼1 billion. Furthermore, using the resolved-sideband Zeeman spectroscopy, the Landé g factor of 3D1 is measured to be 0.4995(88) showing a good agreement with the theoretical value of 0.4988. The results will have an impact on various applications including atom laser, dipolar interactions, quantum information and precision measurements.
Magnetic noise calculation of mu-metal shields at extremely low frequencies for atomic devices
Authors: Ma Danyue , Ding Ming , Lu Jixi , Zhao Junpeng , Yang Ke , Fang Xiujie , Wang Kun , Zhang Ning , Han Bangcheng 
Published: October 2020

Abstract
Mu-metal shields are widely used in atomic devices, but their magnetic noise related to loss is the key performance limit. The magnetic noise can be calculated by using complex permeability and the magnetic field intensity in the shield. In this study, Bertotti loss separation is used for the first time to accurately calculate the changes of complex permeability due to the hysteresis loss in different frequencies and magnetic field intensities, and we further consider the change in magnetic field intensity due to the induced eddy current, which also increases the accuracy of the magnetic noise calculation. For extremely low frequencies below 20 Hz, the improved noise simulation model differs from the measured results by less than 11%. If the loss separation is not considered, the difference between the measured value and the simulated value would be as high as 54%. The high agreement between the calculation and the experimental results proves the accuracy of the proposed method. Our method can be used in the design and optimization of low-noise magnetic shields to improve the sensitivity of atomic devices
Impact of thermal annealing in forming gas on the optical and electrical properties of MoS2 monolayer
Authors: Iacovella Fabrice , Koroleva Aleksandra , Rybkin Artem G , Fouskaki Maria , Chaniotakis Nikolaos , Savvidis Pavlos , Deligeorgis George 
Published: October 2020

Abstract
Technological applications involving 2D MoS2 require transfer of chemical vapor deposition (CVD) grown material from its original substrate and subsequent lithographic processes. Inevitably, those steps contaminate the surface of the 2D material with polymeric residues affecting the electronic and optical properties of the MoS2. Annealing in forming gas is considered an efficient treatment to partially remove such residues. However, hydrogen also interacts with MoS2 creating or saturating sulfur vacancies. Sulfur vacancies are known to be at the origin of n-doping evident in the majority of as-grown MoS2 samples. In this context, investigating the impact of thermal annealing in forming gas on the electronic and optical properties of MoS2 monolayer is technologically important. In order to address this topic, we have systematically studied the evolution of CVD grown MoS2 monolayer using Raman spectroscopy, photoluminescence, x-ray photoelectron spectroscopy and transport measurements through a series of thermal annealing in forming gas at temperatures up to 500 °C. Efficient removal of the polymeric residues is demonstrated at temperatures as low as 200 °C. Above this value, carrier density modulation is identified by photoluminescence, x-ray photoelectron spectroscopy and electrical characterization and is correlated to the creation of sulfur vacancies. Finally, the degradation of the MoS2 single layer is verified with annealing at or above 350 °C through Raman and photocurrent measurements.
A polynomial approach to the spectrum of Dirac–Weyl polygonal Billiards
Authors: Quintela M F C Martins , Lopes dos Santos J M B 
Published: October 2020

Abstract
The Schrödinger equation in a square or rectangle with hard walls is solved in every introductory quantum mechanics course. Solutions for other polygonal enclosures only exist in a very restricted class of polygons, and are all based on a result obtained by Lamé in 1852. Any enclosure can, of course, be addressed by finite element methods for partial differential equations. In this paper, we present a variational method to approximate the low-energy spectrum and wave-functions for arbitrary convex polygonal enclosures, developed initially for the study of vibrational modes of plates. In view of the recent interest in the spectrum of quantum dots of two dimensional materials, described by effective models with massless electrons, we extend the method to the Dirac–Weyl equation for a spin-1/2 fermion confined in a quantum billiard of polygonal shape, with different types of boundary conditions. We illustrate the method’s convergence in cases where the spectrum is known exactly, and apply it to cases where no exact solution exists.
Smart microgel-metal hybrid particles of PNIPAM-co-PAA@AgAu: synthesis, characterizations and modulated catalytic activity
Authors: Bhol Prachi , Mohanty Priti S 
Published: October 2020

Abstract
Smart pH and thermoresponsive, poly(N-isopropyl acrylamide co acrylic acid) (PNIPAM-co-PAA) microgel particles are used as microreactors to prepare hybrids of gold (Au) and silver (Ag) nanoparticles (PNIPAM-co-PAA@AgAu) using a facile two steps in situ approach. These hybrid particles are characterized using the transmission electron microscope (TEM), UV–VIS spectrometer, and dynamic light scattering (DLS). TEM directly confirms the successful loading of metal nanoparticles onto microgels and the hybrid particles have a narrow size distribution. UV–VIS spectroscopy at different concentration ratios of silver/gold chloride strongly reveals the presence of plasmon peaks of both silver and gold between 10% to 25% of gold chloride concentration. DLS studies demonstrate that these hybrid microgels exhibit both pH and thermoresponsive properties comparatively with a lesser swelling than the pure microgels without loaded nanoparticles. Further, the catalytic activities of PNIPAM-co-PAA@AgAu hybrids are studied through a reduction of 4-nitrophenol (4-NP)-to-4-aminophenol (4-AP) in the presence of sodium borohydride at different pH. Interestingly, these hybrid particles exhibit modulating catalytic activity with variation in pH. The reduction kinetics decreases with increasing pH and the corresponding apparent rate constant exhibits two linear regimes with one at pH below pKa and another at pH above pKa of acrylic acid. This pH-modulated catalytic behavior of PNIPAM-co-PAA@AgAu hybrids is discussed based on pH-induced swelling/deswelling transition, the core–shell nature of microgel particles, and its intrinsic interplay with the diffusion of nitrophenols within the microgel network. Finally, our results are compared and discussed in the context of previously studied catalytic activities in different polymer-metal hybrids.
The view of TK-SVM on the phase hierarchy in the classical kagome Heisenberg antiferromagnet
Authors: Greitemann Jonas , Liu Ke , Pollet Lode 
Published: October 2020

Abstract
We illustrate how the tensorial kernel support vector machine (TK-SVM) can probe the hidden multipolar orders and emergent local constraint in the classical kagome Heisenberg antiferromagnet. We show that TK-SVM learns the finite-temperature phase diagram in an unsupervised way. Moreover, in virtue of its strong interpretability, it identifies the tensorial quadrupolar and octupolar orders, which define a biaxial D
3h
spin nematic, and the local constraint that underlies the selection of coplanar states. We then discuss the disorder hierarchy of the phases, which can be inferred from both the analytical order parameters and an SVM bias parameter. For completeness we mention that the machine also picks up the leading

3

×

3

correlations in the dipolar channel at very low temperature, which are however weak compared to the quadrupolar and octupolar orders. Our work shows how TK-SVM can facilitate and speed up the analysis of classical frustrated magnets.
Far-field heat and angular momentum radiation of the Haldane model
Authors: Zhang Yong-Mei , Wang Jian-Sheng 
Published: October 2020

Abstract
We investigate the radiation of energy and angular momentum from 2D topological systems with broken inversion symmetry and time reversal symmetry. A general theory of far-field radiation is developed using the linear response of 2D materials to the thermal fluctuation of electric currents. Applying the theory to the Haldane model, we verify that the heat radiation complies with Planck’s law only at low temperature and deviates from it as temperature becomes high. In contrast to normal metals, angular momentum radiation is possible for this system and exhibits saturation as temperature increases. Parameters crucial to the radiation are investigated and optimized. This research enlightens the possibility of transposing the quantum information to the angular momentum degree of freedom.
Rolling bearing remaining useful life prediction via weight tracking relevance vector machine
Authors: Tang Jian , Zheng Guanhui , He Dong , Ding Xiaoxi , Huang Wenbin , Shao Yimin , Wang Liming 
Published: October 2020

Abstract
The application scenarios of rotating machinery are becoming increasingly complicated due to the rapid development of the manufacturing industry. The remaining useful life (RUL) prediction of rolling bearings has gradually been considered in many industry fields for ensuring the safety and reliability of whole systems. As an effective way to analyze data, the relevance vector machine (RVM) approach holds great potential for RUL prediction. However, the redundant features of rolling bearing vibration signals can easily lead to overfitting and low accuracy of the RVM model for RUL prediction. To conquer these issues, inspired by the idea of the boosting algorithm and ensemble learning, this paper proposes a new RVM model, called the weight-tracking relevance vector machine (WTRVM). Within the proposed WTRVM model, an adaptive sequential optimal feature selection method is designed to avoid overfitting by selecting the best features. The error between the prediction value of the RVM model and the true value is counted for the RVM model training and weight tracking. The most accurate model can be obtained when all selected features have been trained. Finally, the proposed WTRVM algorithm is experimentally demonstrated to be effective for the RUL prediction of rolling bearings.
Towards free-standing graphane: atomic hydrogen and deuterium bonding to nano-porous graphene
Authors: Abdelnabi Mahmoud Mohamed Saad , Blundo Elena , Betti Maria Grazia , Cavoto Gianluca , Placidi Ernesto , Polimeni Antonio , Ruocco Alessandro , Hu Kailong , Ito Yoshikazu , Mariani Carlo 
Published: October 2020

Abstract
Graphane is formed by bonding hydrogen (and deuterium) atoms to carbon atoms in the graphene mesh, with modification from the pure planar sp2 bonding towards an sp3 configuration. Atomic hydrogen (H) and deuterium (D) bonding with C atoms in fully free-standing nano porous graphene (NPG) is achieved, by exploiting low-energy proton (or deuteron) non-destructive irradiation, with unprecedented minimal introduction of defects, as determined by Raman spectroscopy and by the C 1s core level lineshape analysis. Evidence of the H- (or D-) NPG bond formation is obtained by bringing to light the emergence of a H- (or D-) related sp3-distorted component in the C 1s core level, clear fingerprint of H–C (or D–C) covalent bonding. The H (or D) bonding with the C atoms of free-standing graphene reaches more than 1/4 (or 1/3) at% coverage. This non-destructive H-NPG (or D-NPG) chemisorption is very stable at high temperatures up to about 800 K, as monitored by Raman and x-ray photoelectron spectroscopy, with complete healing and restoring of clean graphene above 920 K. The excellent chemical and temperature stability of H- (and D-) NPG opens the way not only towards the formation of semiconducting graphane on large-scale samples, but also to stable graphene functionalisation enabling futuristic applications in advanced detectors for the β-spectrum analysis.
Spectral control via multi-species effects in PW-class laser-ion acceleration
Authors: Huebl Axel , Rehwald Martin , Obst-Huebl Lieselotte , Ziegler Tim , Garten Marco , Widera René , Zeil Karl , Cowan Thomas E , Bussmann Michael , Schramm Ulrich , Kluge Thomas 
Published: October 2020

Abstract
Laser-ion acceleration with ultra-short pulse, petawatt-class lasers is dominated by non-thermal, intra-pulse plasma dynamics. The presence of multiple ion species or multiple charge states in targets leads to characteristic modulations and even mono-energetic features, depending on the choice of target material. As spectral signatures of generated ion beams are frequently used to characterize underlying acceleration mechanisms, thermal, multi-fluid descriptions require revision for predictive capabilities and control in next-generation particle beam sources. We present an analytical model with explicit inter-species interactions, supported by extensive ab initio simulations. This enables us to derive important ensemble properties from the spectral distribution resulting from these multi-species effects for arbitrary mixtures. We further propose a potential experimental implementation with a novel cryogenic target, delivering jets with variable mixtures of hydrogen and deuterium. Free from contaminants and without strong influence of hardly controllable processes such as ionization dynamics, this would allow a systematic realization of our predictions for the multi-species effect.