bluuebunny/crossref_metadata_2025_split huggingface dataset:
EURAMET key comparison between INRiM and UME in Vickers hardness scales (HV1 - HV30) - EURAMET.M.H-K1.b and c
Authors: Germak A , Kuzu C , Origlia C , Pelİt E 
Published: April 2021

Main text
This report describes the method and results of a bilateral EURAMET Key Comparison in Vickers hardness scales of two National Metrology Institutes (NMIs) of Italy and Turkey, INRiM and UME, respectively. The Pilot Laboratory (PL) is INRiM in the comparison in which one set of hardness reference blocks with three hardness levels for the Vickers Hardness scales of both HV1 and HV30 was used. The comparison was realized as planned in the Technical Protocol with some delay. The aim of this comparison is to link the UME measurement results to the CCM.H-K1.b.c through the PL (INRiM) as a participant of the CCM key comparison. The measurement results and uncertainty assessments declared by INRiM and UME are in consistency with each other and UME results are also in consistency with the CCM.H-K1.b.c Key Comparison Reference Values (KCRVs). The CCM.H-K1.b.c was realized during 2001 to 2003 to investigate the metrological equivalence of national standards among national metrology institutes (NMIs) within the CCM.
To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.
The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
Gravitational analog of the canonical acoustic black hole in Einstein–scalar–Gauss–Bonnet theory
Authors: Cañate Pedro , Sultana Joseph , Kazanas Demosthenes 
Published: April 2021

Abstract
In this work, in the context of modified gravity, a curved spacetime analogous to the ‘canonical acoustic black hole (CABH)’ is constructed. The source is a self-interacting scalar field which is non-minimally coupled to gravity through the Gauss–Bonnet invariant. The scalar-Gauss–Bonnet coupling function is characterized by three positive parameters: σ with units of (length), μ with units of (length)4, and a dimensionless parameter s, thus defining a three-parameter model for which the line element of CABH is a solution. The spacetime is equipped with spherical and static symmetry and has a single horizon determined in Schwarzschild coordinates by the region r = μ
1/4. The solution admits a photon sphere at r = (3μ)1/4, and it is shown that in the region (3μ)1/4 ⩽ r < ∞ the scalar field satisfies the null, weak, and strong energy conditions. Nonetheless, the model with s = 1 has major physical relevance since for this case the scalar field is well defined in the entire region r ⩾ μ
1/4, while for s ≠ 1 the scalar field blows up on the horizon.
An historical account of the two-fluid theory for superfluidity
Authors: Hernández-Gómez J J , Gómez-González R W 
Published: April 2021

Abstract
In 1924, Einstein showed the theoretical possibility of the three-dimensional Bose–Einstein condensate, for mass particles. When published, his work did not attract the scientific community, until approximately ten years later, when Fritz London retook it along with Laszlo Tisza, to generate a theory able to explain the superfluidity in terms of two fluids: one formed by atoms within the condensate state, and the second formed with atoms in the normal state. Later, under the commitment of Kapitsa, Landau began the research about the superfluidity problem, with conceptually different assumptions than those of London and Tisza. Landau thought that atoms are the medium in which excitations are propagated, through a two-fluid model. The development of such theories took place in the 1930s and 1940s, when Europe was convulsed by political and social problems. In this work, we clarify the differences between both models, usually confused, and we analyse the influence of the historical reality in which the main scientific actors that gave birth to such theories were involved, elucidating why the path initiated by Einstein, ended in two different intents to describe the superfluidity phenomenon: two two-fluid theories.

April is the cruellest month...

Thomas S. Eliot
Ultra-broadband solar light wave trapping by gradient cavity-thin-film metasurface
Authors: Liao Zhefu , Liu Zhengqi , Wu Qizhao , Zhan Xuefeng , Liu Mulin , Liu Guiqiang 
Published: April 2021

Abstract
Despite the fact that solar energy has been widely used as a renewable and clean energy source for decades, when designing solar irradiation absorbers one is generally confronted with the dilemma of choosing between higher absorption but narrowband or broadband but lower absorption, which has greatly limited the development of the solar energy industry. In this work, a gradient cavity-thin-film metasurface (GCM) made up of alternating multiple layers of titanium (Ti) and silicon dioxide (SiO2) exhibits ultra-broadband strong absorption in 354–2980 nm. The operating bandwidth covers the dominating portion of the solar irradiation spectrum. The absorption spectrum can be manipulated by adjusting the structural parameters of the unit cell. It is worth noting that the spectrally weighted solar absorption efficiency reaches 98.28% under the AM 1.5G illumination. This impressive near-unity absorption could be attributed to multiple light–matter interactions including surface plasmon resonances, cavity resonance, and the intrinsic spectral responses of multi-layer refractory material. In addition, the absorption response is insensitive to the incident angle and polarization states. These high performances provide the GCM with great potential for practical applications in solar thermal energy harvesting and photothermal conversion, etc.
Enhancing infrared emission behavior of polymer coatings for radiative cooling applications
Authors: Chen Meijie , Pang Dan , Chen Xingyu , Yan Hongjie 
Published: April 2021

Abstract
Radiative cooling can cool objects on Earth without an energy input, which has drawn significant attention recently. While polymers have been widely studied for radiative cooling applications due to their promising infrared emission behaviors, ease of fabrication and low cost, the cooling performance of polymer coatings still needs to be enhanced through structure design. In this work, the effects of polymer materials, coating thicknesses and surface microstructures on the cooling performance of coatings were studied. Results showed that the PDMS coating can achieve a great radiative cooling ability with less materials consumption and the polymer coating can reach a relative high saturation value of thermal emittance (

ε
ˉ

LWIR

) in the atmosphere’s long-wave infrared transmission window (8–13

μ

m

) with a large thickness, but interface reflectance in the wavelength range from 8 to 13

μ

m

limits the further enhancement of

ε
ˉ

LWIR

. By introducing a grating-pattern microstructure, the minimal reflectance at

λ

=

8–13

μ

m

was nearly zero and the low emittance region at

λ

=

9–11

μ

m

of the bare PDMS coating was greatly enhanced. At the coating thickness of t

=

200

m

,

ε
ˉ

LWIR

and the net nighttime cooling power of the PDMS coating can reach 0.996 and 110.5 W m−2, respectively, when the ambient temperature is 298.15 K. In addition, the solar reflectance of the PDMS coating can reach 0.946 using the Ag substrate, making it attractive for radiative cooling applications.
Internal photoemission of electrons from 2D semiconductor/3D metal barrier structures
Authors: Shlyakhov I , Achra S , Bosman N , Asselberghs I , Huyghebaert C , Radu I , Chai J , Yang M , Wang S J , Bol A , Iakoubovskii K , Houssa M , Stesmans A , Afanas’ev V V 
Published: April 2021

Abstract
Understanding the energy alignment of electronic bands, which originate from ultrathin MoS2 layers and metal electrodes attached to them, is crucial for the design of MoS2-based electronic devices. We have applied internal photoemission spectroscopy (IPE) to analyze this alignment. We demonstrate that IPE can yield the barrier heights in the metal/ two-dimensional semiconductor/insulator stacks when the top metal electrode is sufficiently thin for allowing both the photoexcitation of electrons and their transport towards the insulator. The electron barrier at the interface between Al and monolayer (1ML) of MoS2 is estimated at 0.7 eV, and this value explains the experimentally observed attenuated quantum yield contribution from the aluminum. Based on the relative energies of the low-energy threshold position and the Fermi level of aluminum at the interface with the SiO2 insulator, we provide a simple explanation for the observed current photoinjection at the interface between aluminum and 1ML MoS2.
Thermal Hall and Nernst responses in ultrathin magnetic films of pyrochlore lattice
Authors: Sheikhi Bahman , Kargarian Mehdi , Langari Abdollah 
Published: April 2021

Abstract
The ultrathin films of pyrochlore lattice along [111] direction provide a fertile ground for exploring topological states in oxide materials, where the electron correlations are strong and magnetically ordered states are favored. As a result of strong interactions, most of states are magnetic insulators with strong Dzyaloshinskii–Moriya and anisotropic spin interactions. We considered three types of heterostructures, a bilayer of triangular-kagome (TK), and two trilayers of triangular-kagome-triangular (TKT) and kagome-triangular-kagome (KTK) thin films. The ground states are magnetically ordered with the low-energy excitations, the magnons, characterized by nontrivial topology. While for TK model the lowest magnon band is trivial, the lowest bands in TKT and KTK model are topological. These features have direct consequences on the thermal Hall conductivity, where we observed that the latter quantity onsets at lower temperature in multilayer models, suggesting that the thermal Hall response can be controlled by engineering lattice-driven magnetic band structure. We also introduce the thermal sublattice Nernst effect in these layers and found the corresponding response is as large as the thermal Hall response.
Decomposition mechanism on different surfaces of copper azide
Authors: Han Xiuzhen , Du Huifang , Guo Wei 
Published: April 2021

Abstract
Copper azide, a potential primary explosives that may replace traditional primers such as lead azide, mercury fulminate and silver azide, has received widespread attention, but its decomposition mechanism remains unclear. Here, based on first-principles calculations, (010)N3, (100)N3 and (001) facets with a copper/nitrogen atom ratio of 1/6 are found to be the most stable surfaces of copper azide crystal. Through transition state (TS) calculations, we find that during the decomposition process on the surface, there is a synergy effect between two Cu–N1–N2–N3 chains, where the terminal N2–N3 bonds on two chains break simultaneously, and the dissociated N3 atom bonds with another N3′ atom of adjacent chain to form a N2 molecule. Next, the Cu–N bond will rupture, and two more N2 molecules (N1–N2, N1′–N2′) desorb from the surface. The overall reaction releases above 4 eV energy at a barrier of 1.23 eV on (001) surface. Electronic structure calculations reveal that the TS of N2–N3 rupture is more stabilized than that of N1–N2. According to the above results, we propose a new decomposition mechanism based on simulations of N–N bond breaking on different surfaces of copper azide. The results underscore the surface effect in decomposition of energetic materials.
Enhancement of the accuracy of ultrasonic flowmeters by applying the PCA algorithm in predicting flow patterns
Authors: Tran Ngoctan , Wang Chi-Chuan 
Published: April 2021

Abstract
In the current study, a novel arrangement of acoustic paths with an on-off technique upon ultrasonic waves is proposed to enhance the accuracy and reduce the frequency of calibration of the ultrasonic flowmeter (USFM). In addition, a web of chord probes on the velocity profile with a novel rotating method is also proposed. Twenty velocity profiles, including 19 selected Salami asymmetric velocity profiles and a centrosymmetric developed velocity profile, are combined with the proposed chord-probe mesh to build a novel velocity database. The built database includes 2241 900 sets of 12 mean velocities, ranging from 0.1 m s−1 to 25 m s−1. Furthermore, the principal component analysis algorithm is employed and trained by the developed database to predict the flow patterns in a practically flowing measurement. The predictive ability of the developed algorithm is examined in 10 different scenarios. In all cases in this study, it is found that the proposed USFM can not only measure the volumetric flow rate of the asymmetric flows with extremely high accuracy, but can also eliminate the influences of flow regimes and the effects of the installed location.
A broadcast ephemeris design of LEO navigation augmentation satellites based on the integration-type ephemeris model
Authors: Meng Lingdong , Chen Junping , Wang Jiexian , Zhang Yize 
Published: April 2021

Abstract
Low Earth orbit (LEO) satellites are a promising type of navigation augmentation satellite for current global navigation satellite systems. Aiming at the navigation function, an effective broadcast ephemeris model needs to be designed for LEO satellites. An enhanced integration-type broadcast ephemeris model is proposed in this study. First, the short-term periodical variation characteristics of LEOs’ accelerations in the Earth-centered Earth-fixed coordinate system are analyzed. The Chebyshev polynomials and harmonic functions are then applied to represent the variation perturbation of accelerations. Tests using simulated and real data from LEO satellites at altitudes from 600 to 1400 km are conducted to evaluate the fit accuracy of the proposed models in terms of arc length, integration method, integration step length, orbital altitude, inclination, eccentricity, etc. The fit accuracy is dramatically improved compared to that of the current GLONASS integration-type broadcast model, where fit errors less than 10 cm are achieved with an arc length of 20 min.
Characterisation and effective monitoring of 4D printed structures through microgeometry analysis
Authors: Trych-Wildner Anna , Wildner Krzysztof 
Published: April 2021

Abstract
This paper presents a basic study of the possible application of roughness parameters for monitoring of the life cycle of 4D printed structures. Experiments were performed with the purpose of gaining some insight into a novel manufacturing technique that may be of future interest and to investigate measurement procedures which may be helpful in the effectively monitoring, maintenance and design of 4D structures. This article describes changes in certain roughness parameters, i.e., Ra, Rsk, RSm, and Sa during the repeated bending of 4D printed beams. The quantitative values of these parameters are also provided and discussed.
Sources of error for single-shot PMT-based phosphor thermometry in harsh conditions
Authors: Feuk Henrik , Sanned David , Richter Mattias , Aldén Marcus 
Published: April 2021

Abstract
This study investigates photomultiplier tube (PMT) nonlinearities, relevant for lifetime phosphor thermometry, at various decay times to assess and minimize the impact on temperature measurement accuracy. The focus is single-shot measurements performed in harsh environments where phosphor signal attenuation often is a concern. The sensitivity of decay time measurements to changing phosphorescence intensity is therefore investigated. The experimental results show that for the studied phosphors and detectors, shorter decay times between 20 ns and 6 µs, saturation effects in the PMTs decreased the measured decay time with increasing signal attenuation. For longer phosphorescence decay times, in the millisecond regime, nonlinearity effects led to an increase in the measured decay time with increasing signal attenuation. The specific detector nonlinearity response will vary among detectors, but the introduced methodology for detector analysis is a useful resource for assessing and improving accuracy in lifetime phosphor thermometry measurements.
Activation of buried p-GaN through nanopipes in large-size GaN-based tunnel junction LEDs
Authors: Yan Shumeng , Feng Meixin , Fan Shizhao , Zhou Rui , Tang Yongjun , Jiang Tianhao , Liu Jianxun , Zhou Yu , Sun Qian , Yang Hui 
Published: April 2021

Abstract
In GaN-based light-emitting diodes (LEDs), tunnel junctions offer a way of replacing the highly resistive p-type GaN (p-GaN) ohmic contact with a low-resistance n-GaN ohmic contact. However, the p-GaN would be re-passivated by hydrogen atoms during the subsequent growth of n-GaN in a metal-organic chemical vapor deposition (MOCVD) chamber. The n-GaN layer, acting as a hydrogen diffusion barrier, hinders the thermal activation of the underlying p-GaN. Here, we report a method to thermally activate the buried p-GaN in tunnel junction LED (TJ-LED) through vertically aligned nanopipe arrays across the top n-GaN layer, which provides a hydrogen outgassing passage. The fabrication of nanopipes is realized via inductive coupled plasma etching using a mask prepared by self-assembled nanosphere arrays. As a result, we attain large-size TJ-LED chips, exhibiting nearly equivalent p-GaN activation and superior light extraction compared to conventional LEDs. Specifically, the light extraction efficiency is boosted by 44% relative to conventional LEDs at an injection current density of 100 A cm−2.
Metasurface circular polarizer based on rotational symmetric nanoholes
Authors: Lv Haoran , Mou Zhen , Zhou Changda , Wang Shuyun , He Xiaobo , Han Zhanghua , Teng Shuyun 
Published: April 2021

Abstract
A circular polarizer is proposed based on a single layered metasurface. This metasurface circular polarizer is composed of L-shaped nanoholes etched on the silver film. The L-shaped nanoholes are rotational symmetric, and the special symmetric structure determines the polarization selection transmission of the metasurface. The theoretical analysis elaborates the design process of the metasurface circular polarizer. The proposed metasurface circular polarizers have good polarization selective transmittance, and more interestingly, they take on the opposite circular dichroism at different wavebands. The numerical simulations and experiment measurement confirm the circular dichroism of the proposed circular polarizers. The compact design, ultrathin thickness and available performance can expand the applications of the metasurface circular polarizers in the integrated optics.
Unconventional plasmonic sensitization of graphene in mid-infrared
Authors: Paria Debadrita , Vadakkumbatt Vaisakh , Ravindra Pramod , Avasthi Sushobhan , Ghosh Ambarish 
Published: April 2021

Abstract
Light–matter interaction in graphene can be engineered and substantially enhanced through plasmonic sensitization, which has led to numerous applications in photodetection, sensing, photocatalysis and spectroscopy. The majority of these designs have relied on conventional plasmonic materials such as gold, silver and aluminum. This limits the implementation of such devices to the ultraviolet and visible regimes of the electromagnetic spectrum. However, for many practical applications, including those relevant to security and defense, the development of new strategies and materials for sensing and detection of infra red (IR) light is crucial. Here we use surface enhanced Raman spectroscopy (SERS), for direct visualization and estimation of enhanced light–matter interaction in graphene in the mid-IR regime, through sensitization by an unconventional plasmonic material. Specifically, we fabricate a hybrid device consisting of a single layer graphene and a two-dimensional array of nanodiscs of aluminum doped zinc oxide (AZO), which is a highly doped semiconductor, exhibiting plasmonic resonance in the mid-IR. We find that the enhancement in the SERS signal of graphene is of similar magnitude to what has been achieved previously in the visible using conventional plasmonic materials. Our results establish the potential of such hybrid systems for graphene-based optical and optoelectronic applications in the mid-IR.
Near-field probing of dielectric screening by hexagonal boron nitride in graphene integrated on silicon photonics
Authors: Wang Binbin , Kim Sera , Zhai Tingting , Seok Jinbong , Yang Heejun , Salas-Montiel Rafael 
Published: April 2021

Abstract
Hexagonal boron nitride (hBN) is one of the most suitable 2D materials for supporting graphene in electronic devices, and it plays a fundamental role in screening out the effect of charge impurities in graphene in contrast to inhomogeneous supports such as silicon dioxide (SiO2). Although many interesting surface science techniques such as scanning tunneling microscopy (STM) revealed dielectric screening by hBN and emergent physical phenomena were observed, STM is only appropriate for graphene electronics. In this paper, we demonstrate the dielectric screening by hBN in graphene integrated on a silicon photonic waveguide from the perspective of a near-field scanning optical microscopy (NSOM) and Raman spectroscopy. We found shifts in the Raman spectra and about three times lower slope decrease in the measured electric near-field amplitude for graphene on hBN relative to that for graphene on SiO2. Based on finite-difference time-domain simulations, we confirm lower electric field slope and scattering rate in graphene on hBN, which implies dielectric screening, in agreement with the NSOM signal. Graphene on hBN integrated on silicon photonics can pave the way for high-performance hybrid graphene photonics.
Microwave thermoacoustic tomographic (MTT) imaging
Authors: Lin James C 
Published: April 2021

Abstract
Microwave thermoacoustic tomography (MTT) uses microwave pulse-induced thermoelastic pressure waves to form planar or tomographic images. Since the generation and detection of thermoelastic pressure waves depends on dielectric permittivity, specific heat, thermal expansion, and acoustic properties of tissue, microwave thermoacoustic imaging possesses the characteristic features of a dual-modality imaging system. The unique attributes of the high contrast offered by microwave absorption and the fine spatial resolution furnished by ultrasound are being explored to provide a nonionizing and noninvasive imaging modality for characterization of tissues, especially for early detection of breast cancer. This paper reviews the research being conducted in developing MTT imaging for medical diagnosis. It discusses the science of thermoelastic wave generation and propagation in biological tissues, the design of prototype MTT systems, the reconstruction of tomographic images, and the application and accomplishment of prototype MTT systems in phantom models and experimental subjects.