bluuebunny/crossref_metadata_2025 huggingface dataset:
Geodesic motion of S2 and G2 as a test of the fermionic dark matter nature of our Galactic core
Authors: Becerra-Vergara E. A. , Argüelles C. R. , Krut A. , Rueda J. A. , Ruffini R.
Published: July 2020

The motion of S-stars around the Galactic center implies that the central gravitational potential is dominated by a compact source, Sagittarius A* (Sgr A*), which has a mass of about 4 × 106 M⊙ and is traditionally assumed to be a massive black hole (BH). The explanation of the multiyear accurate astrometric data of the S2 star around Sgr A*, including the relativistic redshift that has recently been verified, is particularly important for this hypothesis and for any alternative model. Another relevant object is G2, whose most recent observational data challenge the scenario of a massive BH: its post-pericenter radial velocity is lower than expected from a Keplerian orbit around the putative massive BH. This scenario has traditionally been reconciled by introducing a drag force on G2 by an accretion flow. As an alternative to the central BH scenario, we here demonstrate that the observed motion of both S2 and G2 is explained in terms of the dense core – diluted halo fermionic dark matter (DM) profile, obtained from the fully relativistic Ruffini-Argüelles-Rueda (RAR) model. It has previously been shown that for fermion masses 48−345 keV, the RAR-DM profile accurately fits the rotation curves of the Milky Way halo. We here show that the solely gravitational potential of such a DM profile for a fermion mass of 56 keV explains (1) all the available time-dependent data of the position (orbit) and line-of-sight radial velocity (redshift function z) of S2, (2) the combination of the special and general relativistic redshift measured for S2, (3) the currently available data on the orbit and z of G2, and (4) its post-pericenter passage deceleration without introducing a drag force. For both objects, we find that the RAR model fits the data better than the BH scenario: the mean of reduced chi-squares of the time-dependent orbit and z data are ⟨χ̄2⟩S2,RAR ≈ 3.1 and ⟨χ̄2⟩S2,BH ≈ 3.3 for S2 and ⟨χ̄2⟩G2,RAR ≈ 20 and ⟨χ̄2⟩G2,BH ≈ 41 for G2. The fit of the corresponding z data shows that while for S2 we find comparable fits, that is, χ̄2z,RAR ≈ 1.28 and χ̄2z,BH ≈ 1.04, for G2 the RAR model alone can produce an excellent fit of the data, that is, χ̄2z,RAR ≈ 1.0 and χ̄2z,BH ≈ 26. In addition, the critical mass for gravitational collapse of a degenerate 56 keV-fermion DM core into a BH is ∼ 108 M⊙. This result may provide the initial seed for the formation of the observed central supermassive BH in active galaxies, such as M 87.
Resonant absorption: Transformation of compressive motions into vortical motions
Authors: Goossens M. , Arregui I. , Soler R. , Van Doorsselaere T.
Published: July 2020

This paper investigates the changes in spatial properties when magnetohydrodynamic (MHD) waves undergo resonant damping in the Alfvén continuum. The analysis is carried out for a 1D cylindrical pressure-less plasma with a straight magnetic field. The effect of the damping on the spatial wave variables is determined by using complex frequencies that arise as a result of the resonant damping. Compression and vorticity are used to characterise the spatial evolution of the MHD wave. The most striking result is the huge spatial variation in the vorticity component parallel to the magnetic field. Parallel vorticity vanishes in the uniform part of the equilibrium. However, when the MHD wave moves into the non-uniform part, parallel vorticity explodes to values that are orders of magnitude higher than those attained by the transverse components in planes normal to the straight magnetic field. In the non-uniform part of the equilibrium plasma, the MHD wave is controlled by parallel vorticity and resembles an Alfvén wave, with the unfamiliar property that it has pressure variations even in the linear regime.
Predicting frequency changes of global-scale solar Rossby modes due to solar cycle changes in internal rotation
Authors: Goddard C. R. , Birch A. C. , Fournier D. , Gizon L.
Published: July 2020

Context. Large-scale equatorial Rossby modes have been observed on the Sun over the last two solar cycles.

Aims. We investigate the impact of the time-varying zonal flows on the frequencies of Rossby modes.

Methods. A first-order perturbation theory approach is used to obtain an expression for the expected shift in the mode frequencies due to perturbations in the internal rotation rate.

Results. Using the time-varying rotation from helioseismic inversions we predict the changes in Rossby mode frequencies with azimuthal orders from m = 1 to m = 15 over the last two solar cycles. The peak-to-peak frequency change is less than 1 nHz for the m = 1 mode, grows with m, and reaches 25 nHz for m = 15.

Conclusions. Given the observational uncertainties on mode frequencies due to the finite mode lifetimes, we find that the predicted frequency shifts are near the limit of detectability.
The efficiency analysis of the SH-25A ball drum mill when grinding industrial products of fossil fuels
Authors: Kamarova Saule , Abildinova Saule , Terziev Angel , Elemanova Aliya
Published: July 2020

The working characteristics of a laboratory ball drum mill during grinding of Karaganda coal products were studied in order to apply the results obtained to industrial installations. The performed analysis shows that the most complicated and energy-intensive stage of preparation of coal dust is the grinding of fuel. The operational characteristics of the mill productivity, consumed electric power and specific energy consumption in terms of the relative rotational speed of the drum as well as the optimal values of the relative velocity determining the qualitative grinding of the fuel have been determined. The performance of the processed drum mill reaches its maximum at a relative speed of rotation of the drum 0.71 ensuring a waterfall mode of grinding of fuel related to the high-speed mode of a coal-grinding mill. The estimated specific energy consumption for fuel grinding varies in the range from 0.11 kWh/kg up to 0.23 kWh/kg at fuel milling coefficient of Kl = 1.2.
Transforming Romanian school buildings in prosumers. An opportunity for increasing the energy efficiency in electrical networks and reducing the environmental impact of the power distribution sector
Authors: Scripcariu Mircea , Gheorghiu Cristian , Bitir-Istrate Ioan-Sevastian , Bonea Mihaela-Madalina
Published: July 2020

In the last decades, electricity systems suffer crucial transformations from integrated networks with a unidirectional flow, to decentralized, bidirectional flow networks. The stakeholders of this large-scale business have changed or improved their role. Electricity distribution companies are becoming service providers and end-users are becoming electricity producers. With the legislation issued in 2018, a new stakeholder was born on the Romanian electricity market, the prosumer. So, the decentralization reached an extreme by giving the smallest end-user the opportunity to become an electricity producer. In the first paragraph of this paper, authors summarize provisions of most recent energy strategies issued by the Romanian Government and the regulatory framework for incentivizing this market player. Given the growing interest of local administration in energy efficiency and pollution reduction, authors consider that schools can play a major role in fulfilling ambitious environmental targets. Most school buildings date from the communist regime and have a rather similar design. In their energy management programmes, municipalities consider energy efficiency in school buildings and authors present the case study of a school in the city of Ploiesti, one of the largest in southern Romania. A brief description of the electricity end-use systems is presented. Before any measure is taken on the supply-side, school’s administration needs to implement the demand-side measures. Next, these measures are investigated, and the results of the technical-economic analysis are presented. In southern Romania, photovoltaic (PV) solutions have better operating conditions and for this case study the solution for local generation with PV panels is presented. In the paper, authors are making an in-depth investigation of extending the prosumers model, with local PV generation on school buildings, over most of Romanian geographical regions. The carbon footprint is calculated, and the environmental benefits of this integrated approach are highlighted.
Theoretical considerations on the factors influencing the processing of hemp stalks
Authors: Găgeanu Paul , Olan Mihai , Găgeanu Iuliana , Zaica Alexandru
Published: July 2020

The present work is achieved based on the processing of the data accumulated over time, within the activity of research, technological engineering, and testing of machines for processing agricultural products in the last years, as well as studying the specialized literature with the latest achievements of some companies that make machinery for processing agricultural products. The compression of the hemp stalks for processing is analyzed, the main characteristics of the working rolls, the specific energy consumed are determined and an analysis of the obtained fiber length is performed. In order to develop a technical equipment for processing hemp stalks that ensures high performance, the following aspects were studied: the constructive and functional factors of a technical equipment that influence the working processes in order to choose a performance solution for processing hemp stalks. In the last part of the paper, the main technical and functional characteristics of a high-performance technical equipment for processing the hemp stalks harvested in green are established.
Research on methods, techniques and technologies of carbon sequestration in soil
Authors: Cristea Oana Diana , Vlăduţ Valentin , Ungureanu Nicoleta , Popa Diana Lorena , Isticioaia Simona , Dumitrescu Liliana , Matei Gheorghe , Apostol Livia
Published: July 2020

Soil is one of the natural reservoirs of the carbon biogeochemical cycle, incorporating approximately 6000 billion tons of carbon. Given that with the industrial development more and more carbon is emitted into the atmosphere, solutions, technologies and methods are being sought to reduce this carbon or, where appropriate, it is not eliminated into the atmosphere. The purpose of this paper is to study and identify the simplest methods to be applied in agriculture, for soil processing, by identifying the techniques, technologies and equipment to achieve this without turning the furrow, so that the carbon incorporated in the soil by plants remains sequestered there.
The energy future of Saudi Arabia
Authors: Boretti Alberto , Castelletto Stefania , Al-Kouz Wael , Nayfeh Jamal
Published: July 2020

In a recent publication, North European experts argue that “Saudi Arabia can achieve a 100% renewable energy power system by 2040 with a power sector dominated by PV single-axis tracking and battery storage”. They also say “Battery storage contributed up to 30% of the total electricity demand in 2040 and the contribution increases to 48% by 2050”. Based on considerations specific to the geography, climate conditions, and resources of Saudi Arabia, it is explained as batteries and photovoltaic solar panels are not the best choice for the country's energy sector. To cover all the total primary energy supply of Saudi Arabia by solar photovoltaic, plus battery storage to compensate for the sun's energy intermittency, unpredictability, and seasonal variability, is impracticable and inconvenient, for both the economy and the environment. Better environment and economy may be achieved by further valorizing the fossil fuel resources, through the construction of other high-efficiency plants such as the combined cycle gas turbine plants of Qurayyah, development of novel technologies for the production of clean fuels and clean electricity, including oxyfuel combustion and carbon capture and storage. Construction of nuclear power plants may also be more beneficial to the economy and the environment than photovoltaic and batteries. Regarding solar energy, enclosed trough solar thermal power systems developed along the coast have much better perspectives than solar photovoltaic, as embedded thermal energy storage is a better approach than battery storage. Further, a centralized power plant works better than distributed rooftop photovoltaic installations covered by dust and sand, rusted or cracked. Finally, pumped hydro energy storage along the coast may also have better perspectives than battery storage.
The effect of NCG on the characteristics of hydraulic cavitation
Authors: Li Qiang , Li Wei , Zhang Jian , Ming Dezhi , Xu Weiwei , Wang Zhenbo
Published: July 2020

Hydraulic cavitation, as an important and complex hydrodynamic phenomenon, has long drawn attention. In this paper, the ZGB (Zwart-Gerber-Belamri) cavitation model is improved and the effect of NCG (noncondensable gas) on cavitation in water is studied by numerical simulation. The influence of NCG on the cavity length, the temperature of the cavities and the mixed viscosity of the cavities is investigated through the improved ZGB cavitation model. In addition, experiments on hydrodynamic cavitation produced by a Venturi tube are used to validate the improved ZGB cavitation model. The results show that NCG not only shortens the length of the cavity but also reduces the volume fraction of the vapor. The existence of NCG decreases the viscosity in the cavity of the Venturi tube but increases the viscosity at the sidewall of the tube. In addition, the temperature in the cavities increases with increasing NCG. Regardless of whether air is injected, the volume fraction of the vapor in the cavities increases first and then decreases with increasing temperature. However, the transition temperature decreases somewhat after injecting air. Therefore, the influence of NCG on hydraulic cavitation is significant, and the role of NCG should be considered in industry.
Effects of process parameters on tensile strength of friction stir welded Al-Cu double-layer sheets
Authors: Tabrizi Mohammad Taghizadeh , Mostahsan Amirhossein Jabbari , Sedighi Mohammad
Published: July 2020

In this paper, friction stir welding (FSW) process was used to join double-layer sheets of pure copper and 1050 aluminum alloy produced by explosive welding (EXW). The double-layer sheets were arranged side by side to perform friction stir butt-welding. In this regard, rotary FSW tools with different geometries were used at rotational speeds of 800 and 1250 rpm and linear speeds of 8, 12, and 20 mm min‑1, in one and two number of passes. According to the results, the sample welded by a conical tool with a rotational speed of 800 rpm and a linear speed of 12 mm min‑1 in one pass offered the highest tensile strength, which was approximately equivalent to the 84% of the strength of the raw double-layer sheet. In addition, applying the second FSW pass and using a threaded tool from the aluminum side had negative effects on the tensile strength. The microstructural evaluation showed the presence of more intermetallic phases including Al4Cu9, AlCu, and Al2Cu in the sample welded by the threaded tool from the aluminum side in two number of passes, which was the responsible of the lower tensile strength and the higher microhardness.
Das Myalgie-Faszikulations-Krampus-Syndrom (MFKS)
Authors: Rollnik Jens D. , Däuper Jan
Published: July 2020

Die vorliegende Übersichtsarbeit beschäftigt sich mit dem Myalgie-Faszikulations-Krampus-Syndrom (MFKS), einer gutartigen Erkrankung, die zu den Hyperexzitabilitätssyndromen des peripheren Nervensystems gezählt wird. Der Artikel stellt die Klinik, Pathophysiologie, Differenzialdiagnostik und Therapie dar und illustriert das MFKS mit einem typischen Fallbericht.
Determinants of Cardiovascular Disease among Urban Women with Psoriasis: A Case–Control Study
Authors: Bala Sudha , Mavoori Archana , Pandve Harshal , Biswal Chinmayee , Prasanna Vijay , Jogi Suneeth
Published: July 2020

Background and Aim Psoriasis have a direct impact on development of cardiovascular risk factors leading to atherosclerosis and metabolic abnormalities. In order to prevent the complications, early and prompt identification of factors through various parameters help in primary and secondary prevention of cardiovascular diseases (CVDs) among these psoriatic patients. Therefore the aim of this study is to determine the prevalence of various determinants for cardiovascular diseases among cases and controls.

Methods A hospital based case control study at a tertiary care hospital included women from the out patient department, aged above 18 years who were known cases of psoriasis. 114 patients were recruited with 1:1 ratio between cases and controls. All patients were evaluated using semi structured interview schedule with socio demographic variables, duration of disease, family history, and usage of drugs. Severity of disease was assessed through the psoriasis area severity index (PASI). Body surface area (BSA), body mass index (BMI), waist circumference and blood pressure measurement were done using standard methods. Lipid profile, high sensitivity C-Reactive protein (HsCRP) and blood sugar through calibrated analyzers having quality control. Carotid intima media thickness (CIMT) was assessed by using carotid Doppler technique to measure atherosclerosis.

Results One hundred fourteen patients, means 57 pairs of cases and controls were analyzed in this study. Significant determinants among cases were raised such as waist circumference (p = 0.025), diastolic blood pressure (p = 0.0001), low density lipoprotein (p = 0.002) and fasting blood glucose (p = 0.004) when compared to controls. HsCRP and CIMT were also raised among cases but only CIMT was statistically significant when compared to controls (p = 0.0001). We also found raised determinants among psoriatic arthritis patients compared to psoriasis.

Conclusion Psoriasis patients had high waist circumference, diastolic blood pressure, low density lipoprotein, fasting blood glucose, and CIMT when compared to controls. Early identification of these determinants make them amenable for prevention.
Facile Synthesis of β-Bromostyrenes by Direct Bromination of Styrenes with N-Bromosuccinimide and Sodium Persulfate
Authors: Chen Xuenian , Ma Yan-Na , Jing Yi , Gao Yan , Zhao Qianyi
Published: July 2020

A new, direct, efficient, and transition-metal-free method is reported for the synthesis of β-bromostyrenes from styrenes by using N-bromosuccinimide as the brominating reagent and sodium persulfate (Na2S2O8) as the oxidant. This convenient and concise reaction is practical, operationally simple, and can be adapted for large-scale syntheses.
Total Synthesis of Stemoamide, 9a-epi-Stemoamide, and 9a,10-epi-Stemoamide: Divergent Stereochemistry of the Final Methylation Steps
Authors: Pápai Imre , Pihko Petri M. , Siitonen Juha H. , Csókás Dániel
Published: July 2020

Total syntheses of stemoamide, 9a-epi-stemoamide, and 9a,10-epi-stemoamide by a convergent A + B ring-forming strategy is reported. The synthesis required a diastereoselective late-stage methylation of the ABC stemoamide core that successfully enabled access to three of the four possible diastereomeric structures. For the natural stemoamide series, the diastereoselectivity can be rationalized both by kinetic and thermodynamic arguments, whereas for the natural 9a-epi-stemoamide series, the kinetic selectivity is explained by the prepyramidalization of the relevant enolate.
Catalyst-Free Synthesis of Chromane-Type N,O-Acetals via Intramolecular Addition of Phenols to Enamines
Authors: Osyanin Vitaly A. , Osipov Dmitry V. , Melnikova Irina V. , Korzhenko Kirill S. , Semenova Irina A. , Klimochkin Yuri N.
Published: July 2020

A new strategy to 2-aminochromanes through catalyst-free cascade reaction of 3-trifluoroacetyl-4H-chromenes and 4H-chromene-3-carbaldehydes with cyclic secondary amines is presented. The reaction proceeds through subsequent 1,4- and 1,2-additions of amine, bimolecular elimination of trifluoroacetamide or formamide, and 6-exo-trig cyclization. The latter stage is a very rare example of addition of phenols to enamines. The obtained semicyclic N,O-acetals were applied as useful precursors for the synthesis of other chromanes.
Nickel-Catalyzed Asymmetric Cross-Electrophile Coupling Reactions
Authors: Wang Chuan , Jin Youxiang
Published: July 2020

The merger of cross-electrophile coupling and asymmetric catalysis provides a novel approach to the preparation of optically active compounds. This method is often endowed with high step economy, mild conditions, and excellent tolerance of functional groups. Recent advances in the research field of nickel-catalyzed asymmetric cross-electrophile coupling reactions are highlighted in this concise Synpacts article.

1 Introduction

2 Asymmetric Cross-Electrophile Coupling Reactions between Organohalides

3 Asymmetric Electrophilic Ring-Opening Reactions

4 Asymmetric Electrophilic Difunctionalization of Alkenes

4.1 Two-Component Electrophilic Difunctionalization of Alkenes Involving Arylnickelation as an Enantiodetermining Step

4.2 Two-Component Electrophilic Difunctionalization of Alkenes Involving Carbamoylnickelation as an Enantiodetermining Step

4.3 Three-Component Electrophilic Difunctionalization of Alkenes

5 Asymmetric Electrophilic Functionalization of Carbonyl Compounds

6 Summary
Will Resting Full-Cycle Ratio Substitute Fractional Flow Reserve
Authors: Aditya M. S.
Published: July 2020

Physiological assessment of coronary artery stenosis added an element of certainty of benefit to the patient undergoing revascularization. Fractional flow reserve (FFR) was the gold standard, with good reproducibility, correlation with noninvasive inducible ischemia testing and, most importantly, clinical benefit. Increased usage also brought into focus some limitations with respect to achieving hyperemia, assessment of sequential stenoses, drift, multivessel disease, chronic total occlusion, fidelity and accuracy of measurement and, in some cases, cost of adenosine. This set the background for nonhyperemic testing which eliminates the need for drug administration and simplifies procedure vastly.
The Association between Oral Anticoagulants and Cancer Incidence among Individuals with Nonvalvular Atrial Fibrillation
Authors: Abrahami Devin , Renoux Christel , Yin Hui , Fournier Jean-Pascal , Azoulay Laurent
Published: July 2020

Objective Existing evidence on the association between vitamin K antagonists (VKAs) and direct oral anticoagulants (DOACs) and cancer is limited and contradictory. No observational studies have been conducted to simultaneously address the cancer safety of VKAs and DOACs. The objective of this study was to determine whether use of VKAs and DOACs, separately, when compared with nonuse, is associated with cancer overall and prespecified site-specific incidence.

Methods Using the United Kingdom Clinical Practice Research Datalink, we identified patients newly diagnosed with nonvalvular atrial fibrillation (NVAF) between 2011 and 2017. Using a time-varying exposure definition, each person-day of follow-up was classified as use of (1) VKAs, (2) DOACs, (3) VKAs and DOACs (drug switchers), and (4) nonuse of anticoagulants (reference). We also conducted a head-to-head comparison of new users of DOACs versus VKAs using propensity score fine stratification weighting. Hazard ratios (HRs) with 95% confidence intervals (CIs) for cancer overall and prespecified subtypes were estimated using Cox proportional hazards models.

Results Compared with nonuse, use of VKAs was not associated with cancer overall (HR: 1.05, 95% CI: 0.91–1.22) or cancer subtypes. Similarly, use of DOACs was not associated with cancer overall (HR: 1.13, 95% CI: 0.93–1.37), but an association was observed for colorectal cancer (HR: 1.73, 95% CI: 1.01–2.99), and pancreatic cancer generated an elevated, though nonsignificant HR (HR: 2.15, 95% CI: 0.72–6.44). Results were consistent in the head-to-head comparison.

Conclusion Use of oral anticoagulants is not associated with the incidence of cancer overall among patients with NVAF. Possible associations between DOACs and colorectal and pancreatic cancer warrant further study.
Unilateral Nasal Obstruction Causes Symptom Severity Scores Similar to Bilateral Nasal Obstruction
Authors: Weitzman Rachel E. , Feng Allen L. , Justicz Natalie , Gadkaree Shekhar K. , Lindsay Robin W.
Published: July 2020

The objective of this paper is to investigate the differences between unilateral and bilateral nasal obstruction with subjective symptomatology in nasal obstruction. This is a retrospective chart review of prospectively collected data of patients with nasal obstruction presenting to a facial plastic and reconstructive surgery clinic for evaluation and treatment. Patient demographics including age and gender were recorded along with nasal physical exam findings. These included internal valve narrowing (IVN), external valve narrowing, internal valve collapse, external valve collapse, and septal deviations (inferior and superior). Findings were reported for the left, the right, and both sides. Nasal valve and septal findings were recorded on 3- and 4-point Likert scales, respectively, for each side of the nose. A total of 1,646 patients were included in the study. On univariate analysis, a significant correlation was seen between Nasal Obstruction Symptom Evaluation (NOSE) scores and all individual exam findings (p < 0.001). On multiple linear regression, total, left, and right septal deviation (p < 0.001, p = 0.001, p = 0.007, respectively) and total, left, and right IVN (p < 0.001, p = 0.003, p < 0.001) were all predictive of an increased NOSE score. Patients with unilateral septal deviation or internal nasal valve narrowing have symptoms of nasal obstruction similar to those with bilateral nasal obstruction. Unilateral and bilateral septal deviation and internal nasal valve narrowing are predictive of having an increased NOSE score. Unilateral nasal obstruction should be recognized and treated as a cause for severe symptomatic nasal obstruction despite a normal contralateral nasal exam.
Trisomy 21 and Ebstein Anomaly: Diagnosis and Prognosis of a Rare Association
Authors: Brandão Gabriela Rangel , Welter Amanda Thum , Abech Gabriel Dotta , Almeida Carla Bastos da Costa , Okabayashi Caio Seiti Mestre , Gadelha Kerolainy Alves , Zen Paulo Ricardo Gazzola , Rosa Rafael Fabiano Machado
Published: July 2020

Trisomy 21 is considered the most common chromosomal aneuploidy, and congenital heart disease (CHD) is highly prevalent and relevant to the morbidity and mortality of these patients. Ebstein anomaly (EA) is a rare CHD characterized by tricuspid valve dysplasia with inferior septal leaflet displacement. Herein, we described a patient with trisomy 21 who presented with EA and discuss the association between the two conditions based on a literature review. We conclude that the concomitant occurrence of both conditions is considered to be rare. These individuals are most frequently diagnosed during birth and childhood, and they usually have a good prognosis, as observed with our patient and is typical for EA patients in general. However, it is important to be aware that electrophysiologic anomalies may also be present.
Nb3Sn multicell cavity coating system at Jefferson Lab
Authors: Eremeev G. , Clemens W. , Macha K. , Reece C. E. , Valente-Feliciano A. M. , Williams S. , Pudasaini U. , Kelley M.
Published: July 2020

Superconducting radio frequency niobium cavities are the building blocks of modern accelerators for scientific applications. Lower surface resistance, higher fields, and high operating temperatures advance the reach of the future accelerators for scientific discovery as well as potentially enabling cost-effective industrial solutions. We describe the design and performance of an Nb3Sn coating system that converts the inner surface of niobium cavities to an Nb3Sn film. The niobium surface, heated by radiation from the niobium retort, is exposed to Sn and SnCl2 vapor during the heat cycle, which results in about 2 μm Nb3Sn film on the niobium surface. Film composition and structure as well as radio frequency properties with 1-cell R&D cavities and 5-cell practical accelerator cavities are presented.
Machine-learning adsorption on binary alloy surfaces for catalyst screening
Authors: Wang Tai-ran , Li Jian-cong , Shu Wu , Hu Su-lei , Ouyang Run-hai , Li Wei-xue
Published: July 2020

Over the last few years, machine learning is gradually becoming an essential approach for the investigation of heterogeneous catalysis. As one of the important catalysts, binary alloys have attracted extensive attention for the screening of bifunctional catalysts. Here we present a holistic framework for machine learning approach to rapidly predict adsorption energies on the surfaces of metals and binary alloys. We evaluate different machine-learning methods to understand their applicability to the problem and combine a tree-ensemble method with a compressed-sensing method to construct decision trees for about 60000 adsorption data. Compared to linear scaling relations, our approach enables to make more accurate predictions lowering predictive root-mean-square error by a factor of two and more general to predict adsorption energies of various adsorbates on thousands of binary alloys surfaces, thus paving the way for the discovery of novel bimetallic catalysts.
Photo- and electro-luminescence studies of semipolar (112¯2) InxAl1−xN
Authors: Chung Roy Byung Kyu
Published: July 2020

InxAl1−xN (0.15 < x < 0.4) single layers (thickness = 300 nm) and light emitting diodes (LEDs) with InxAl1−xN (x = 0.24 or 0.28) quantum wells (QWs) were grown on (112¯2) free-standing GaN substrates by metal organic chemical vapor deposition. The emission characteristics of InxAl1−xN films and QWs were then investigated by photoluminescence (PL), cathodoluminescence (CL), and electroluminescence (EL). PL emission down at 1.87 eV (∼660 nm) was observed from In0.37Al0.63N at room temperature. However, its emission wavelength and spectral width showed almost no temperature-dependence, strongly suggesting the radiative recombination process in In0.37Al0.63N is heavily affected by the potential fluctuations associated with the defect levels such as deep donor–acceptor pairs (DAPs). For In0.23Al0.77N, the emission peaks at 3.24 and 2.4 eV were observed at 300 K but CL showed no evidence of compositional fluctuations. Given the wide spectral width and weak In clustering, PL at 3.24 eV is likely from a shallow DAP transition involving an impurity-related shallow donor and valence band. PL emission at 2.4 eV, on the other hand, behaved more like In0.37Al0.63N, suggesting significant deep DAP transitions. Both LEDs with In0.24Al0.76N and In0.28Al0.72N QWs showed a discrete blueshift of the emission peak with increasing injection current, which is very different from the gradual shift observed in InGaN LEDs. The high-energy peak was much narrower than the low-energy peak, suggesting it could be the near-band edge emission. Si doping of In0.24Al0.76N QWs lowered the injection current level at which the high-energy peak appears.
Non-diffusive nature of collisionless
α
-particle transport: Dependence on toroidal symmetry in stellarator geometries
Authors: Gogoleva A. , Tribaldos V. , Reynolds-Barredo J. M. , Sánchez R. , Alcusón J. , Bustos A.
Published: July 2020

An adequate confinement of α-particles is fundamental for the operation of future fusion powered reactors. An even more critical situation arises for stellarator devices, whose complex magnetic geometry can substantially increase α-particle losses. A traditional approach to transport evaluation is based on a diffusive paradigm; however, a growing body of literature presents a considerable amount of examples and arguments toward the validity of non-diffusive transport models for fusion plasmas, particularly in cases of turbulent driven transport [R. Sánchez and D. E. Newman, Plasma Phys. Controlled Fusion 57, 123002 (2015)]. Likewise, a recent study of collisionless α-particle transport in quasi-toroidally symmetric stellarators [A. Gogoleva et al., Nucl. Fusion 60, 056009 (2020)] puts the diffusive framework into question. In search of a better transport model, we numerically characterized and quantified the underlying nature of transport of the resulting α-particle trajectories by employing a whole set of tools, imported from the fractional transport theory. The study was carried out for a set of five configurations to establish the relation between the level of the magnetic field toroidal symmetry and the fractional transport coefficients, i.e., the Hurst H, the spatial α, and the temporal β exponents, each being a merit of non-diffusive transport. The results indicate that the α-particle ripple-enhanced transport is non-Gaussian and non-Markovian. Moreover, as the degree of quasi-toroidal symmetry increases, it becomes strongly subdiffusive, although the validity of the fractional model itself becomes doubtful in the limiting high and low symmetry cases.
Characterization and comparison of large directed networks through the spectra of the magnetic Laplacian
Authors: F. de Resende Bruno Messias , F. Costa Luciano da
Published: July 2020

In this paper, we investigated the possibility of using the magnetic Laplacian to characterize directed networks. We address the problem of characterization of network models and perform the inference of the parameters used to generate these networks under analysis. Many interesting results are obtained, including the finding that the community structure is related to rotational symmetry in the spectral measurements for a type of stochastic block model. Due the hermiticity property of the magnetic Laplacian we show here how to scale our approach to larger networks containing hundreds of thousands of nodes using the Kernel Polynomial Method (KPM), a method commonly used in condensed matter physics. Using a combination of KPM with the Wasserstein metric, we show how we can measure distances between networks, even when these networks are directed, large, and have different sizes, a hard problem that cannot be tackled by previous methods presented in the literature.
Nonlinear friction in underdamped anharmonic stochastic oscillators
Authors: Capała Karol , Dybiec Bartłomiej , Gudowska-Nowak Ewa
Published: July 2020

Non-equilibrium stationary states of overdamped anharmonic stochastic oscillators driven by Lévy noise are typically multimodal. The very same situation is recorded for an underdamped Lévy noise-driven motion in single-well potentials with linear friction. Within the current article, we relax the assumption that the friction experienced by a particle is linear. Using computer simulations, we study underdamped motions in single-well potentials in the regime of nonlinear friction. We demonstrate that it is relatively easy to observe multimodality in the velocity distribution as it is determined by the friction itself and it is the same as the multimodality in the overdamped case with the analogous deterministic force. Contrary to the velocity marginal density, it is more difficult to induce multimodality in the position. Nevertheless, for a fine-tuned nonlinear friction, the spatial multimodality can be recorded.
Chirality-dependent asymmetric vortex core structures in a harmonic excitation mode
Authors: Han Hee-Sung , Lee Sooseok , Jung Dae-Han , Kang Myeonghwan , Lee Ki-Suk
Published: July 2020

Chirality of the magnetic vortex plays an essential role in dynamic excitations of the magnetic vortex structure. In a harmonic excitation of the vortex gyrotropic motion, it has been known that the chirality determines its phase to the driving force. From our micromagnetic simulations, we find an additional role of chirality in the harmonic excitation of the vortex gyration. The shear deformation of the three-dimensional structure of the vortex core is determined by the chirality of the vortex. We confirm that this is due to the gyrotropic field. For the same vortex core motion with the same polarization but with opposite chirality, it turns out that the opposite gyrotropic field is formed at the spiral magnetization in the vicinity of the vortex core structure.
Structural characterizations and dielectric, magnetic, and optical properties of Ba2FeVO6 double perovskite ceramics
Authors: Pei Zhipeng , Zhou Xiaoxiang , Leng Kai , Xia Weiren , Wei Ying , Zhu Xinhua
Published: July 2020

Here, we present the structural characterization and physical properties of Ba2FeVO6 (BFVO) ceramics prepared by the solid-state ceramic method, which is regarded as potential Mott multiferroics. Structural studies demonstrate that the BFVO ceramic samples crystallize in a hexagonal structure with R3c symmetry. SEM images show a spherical morphology of the ceramic grains with an average composition of Bi:Fe:V close to 2.0:1.0:1.0 determined by x-ray energy dispersive spectroscopy. Infrared spectra revealed the vibrational modes of [FeO6] and [VO6] octahedrons in the ceramics, and XPS spectra confirmed the dual chemical valence states of iron (Fe2+ and Fe3+) and vanadium (V3+ and V4+) and two states of oxygen species in the BFVO ceramics, while barium was present as Ba2+. The BFVO ceramics exhibit relaxor-like dielectric behavior with an activation energy of 0.62 eV. The antiferromagnetic (AFM) nature was confirmed in the BFVO ceramics, whereas a weak magnetism was observed at 2 K. The temperature dependence of magnetizations measured with (and without) field cooling across 2 K–300 K under external magnetic fields indicates the spin glass characteristics in the present system. A strong variation of the dielectric behavior observed close to the AFM transition temperature was due to the induced dielectric polarization via the magnetostrictive effect driven by AFM transition. The bandgaps (Eg) of the investigated ceramic samples were deduced from their UV–visible spectra. The Eg values were about 1.15 eV and 1.50 eV, which were ascribed to the d–d electronic transitions of Fe 3d t2g → Fe 3d eg and 6A1g → 4T1g, respectively.
A mechanism of electric charge losses in adiabatically compressed ferroelectrics
Authors: Shkuratov Sergey I. , Baird Jason , Antipov Vladimir G. , Chase Jay B.
Published: July 2020

A ferroelectric depolarized by high strain-rates induced by the passage of adiabatic shock waves releases a high-density electric charge, initiating the generation of high voltage and megawatt power levels. Additionally, this depolarization process alters physical and mechanical properties that might cause energy and electric charge losses in the ferroelectric materials. We report, herein, the results of an experimental study of electric charge losses in Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 and Pb0.99(Zr0.52Ti0.48)0.99Nb0.01O3 ferroelectrics subjected to shock compression. We found that electric charge losses mainly occur in the compressed zone of ferroelectric elements; i.e., shock compression is an essential part of the charge loss mechanism. Based on our analysis of the experimental results, charge losses are explained by the leakage current flowing through microscopic conductive pathways (conductive channels), which are formed due to the effects of high magnitude stress and high electric fields in compressed zones of ferroelectric elements. It is shown that the Joule heating of conductive channels by the leakage current increases their temperature and conductance, eventually short-circuiting the electrodes of the shocked ferroelectric element and causing electric breakdown. The leakage current density, jleak, and breakdown delay time, tcr, can be described by the relationship, jleak2tcr=β (where β is the material dependent constant), over a wide range of delay times. The breakdown criterion we propose is based on the integral of specific current action and can be used to characterize the electric breakdown in a broad range of shock-compressed ferroelectric materials.
Organic polariton lasing with molecularly isolated perylene diimides
Authors: Sabatini Randy P. , Maasoumi Fatemeh , Prasad Shyamal K. K. , Zhang Bolong , Clark Caspar , Schmidt Timothy W. , Wong Wallace W. H. , Lakhwani Girish
Published: July 2020

A dye immersed in a polymer matrix represents a promising material class for organic polariton lasers. While polariton condensation has been established for boron-dipyrromethene blends, it has yet to be extended to other small dye blends. Here, we demonstrate polariton lasing in a molecularly isolated perylene diimide immersed in polystyrene. The emission exhibits threshold behavior, strong directionality, and slight blueshifting of organic polariton systems. We expect that continuous exploration of new dyes will allow improved performance in organic polariton lasing.
Multi-level free energy simulation with a staged transformation approach
Authors: Ito Shingo , Cui Qiang
Published: July 2020

Combining multiple levels of theory in free energy simulations to balance computational accuracy and efficiency is a promising approach for studying processes in the condensed phase. While the basic idea has been proposed and explored for quite some time, it remains challenging to achieve convergence for such multi-level free energy simulations as it requires a favorable distribution overlap between different levels of theory. Previous efforts focused on improving the distribution overlap by either altering the low-level of theory for the specific system of interest or ignoring certain degrees of freedom. Here, we propose an alternative strategy that first identifies the degrees of freedom that lead to gaps in the distributions of different levels of theory and then treats them separately with either constraints or restraints or by introducing an intermediate model that better connects the low and high levels of theory. As a result, the conversion from the low level to the high level model is done in a staged fashion that ensures a favorable distribution overlap along the way. Free energy components associated with different steps are mostly evaluated explicitly, and thus, the final result can be meaningfully compared to the rigorous free energy difference between the two levels of theory with limited and well-defined approximations. The additional free energy component calculations involve simulations at the low level of theory and therefore do not incur high computational costs. The approach is illustrated with two simple but non-trivial solution examples, and factors that dictate the reliability of the result are discussed.
Zero temperature coefficient of resistance in back-end-of-the-line compatible titanium aluminum nitride films by atomic layer deposition
Authors: Krylov Igor , Qi Yuanshen , Korchnoy Valentina , Weinfeld Kamira , Eizenberg Moshe , Yalon Eilam
Published: July 2020

Thin film resistors with near-zero temperature coefficient of resistance (TCR) are key passive elements in analog integrated circuits (ICs). State-of-the-art near-zero TCR technology is based on sputtered compounds of Si, Cr, B, and C, which require annealing at temperatures higher than 500 °C, making it incompatible with back-end-of-the-line (BEOL) processes. We report here that near-zero TCR resistors can be obtained by atomic layer deposition (ALD) of TiN-AlN nano-laminates at BEOL-compatible deposition temperature. The resistivity and the TCR can be tuned by varying the ratio between AlN (insulating) and TiN (metallic) in the TiXAl1−XN thin film. The TCR changes from positive to negative as the AlN content is increased, allowing for optimization to zero TCR. The ALD method provides ultimate control of the thickness, composition ratio, coverage, and uniformity. Microstructure analysis shows that the film consists of metallic TiN crystallites embedded in the semiconducting TiyAl1−yN amorphous matrix, suggesting that the electrical behavior is similar to that of SiCr-based compounds. These results pave the way toward BEOL-compatible near-zero TCR thin film resistors, which can significantly reduce capacitance and minimize design complexity of passive analog IC components.
Temperature dependence of nuclear quantum effects on liquid water via artificial neural network model based on SCAN meta-GGA functional
Authors: Yao Yi , Kanai Yosuke
Published: July 2020

We investigate the temperature dependence of nuclear quantum effects (NQEs) on structural and dynamic properties of liquid water by training a neural network force field using first-principles molecular dynamics (FPMD) based on the strongly constrained and appropriately normed meta-generalized gradient approximation exchange-correlation approximation. The FPMD simulation based on density functional theory has become a powerful computational approach for studying a wide range of condensed phase systems. However, its large computational cost makes it difficult to incorporate NQEs in the simulation and investigate temperature dependence of various properties. To circumvent this difficulty, we use an artificial neural network model and employ the thermostatted ring polymer MD approach for studying the temperature dependence of NQEs on various properties. The NQEs generally bring the radial distribution functions closer to the experimental measurements. Translational diffusivity and rotational dynamics of water molecules are both slowed down by the NQEs. The competing inter-molecular and intra-molecular quantum effects on hydrogen bonds, as discussed by Habershon, Markland, and Manolopoulos [J. Chem. Phys. 131(2), 024501 (2019)], can explain the observed temperature dependence of the NQEs on the dynamical properties in our simulation.
Effect of cesium for Cu(In,Ga)Se2 and Cu(In,Ga)(S,Se)2 films studied by depth-resolved XAFS
Authors: Beppu Kosuke , Hirai Yoshiaki , Kato Takuya , Ishizuka Shogo , Ina Toshiaki , Wada Takahiro
Published: July 2020

Alkali metal treatment is an indispensable technology for obtaining highly efficient CuInSe2 (CIS) solar cells. This study evaluated the structural change of Cu(In,Ga)Se2 (CIGSe) and Cu(In,Ga)(S,Se)2 (CIGSSe) films with and without the CsF post-deposition treatment (CsF-PDT) (for CIGSe) and Cs treatment (for CIGSSe) by the Se K-edge depth-resolved X-ray absorption fine structure. The CIGSe films were deposited by a three-stage process, and the CIGSSe films were deposited by the sulfurization after the selenization method. Although CsF-PDT can re-form the surface of CIGSe film, the Cs treatment cannot modify the surface of the CIGSSe film. Our result suggests that the improvement is due to not only the surface reforming but also an effect on the inside of the CIGSe and CIGSSe films. This study provides useful information for the preparation of highly efficient CIS solar cells.
Rivulet flow down a slippery substrate
Authors: Alshaikhi Abdulwahed S. , Wilson Stephen K. , Duffy Brian R.
Published: July 2020

A detailed analysis of small-scale locally unidirectional gravity-driven rivulet flow with prescribed volume flux down an inclined slippery substrate for a rivulet with either constant width (i.e., pinned contact lines) or constant contact angle is undertaken. In particular, we determine the effect of varying the Navier slip length λ (i.e., the strength of the slip at the solid–fluid interface) on the rivulet. The present analysis shows that the shape and size of the rivulet and the velocity within it depend strongly on the value of λ. Increasing the value of λ reduces the viscous resistance at the substrate and, hence, leads to a larger velocity within the rivulet, and so the prescribed flux is achieved with a smaller rivulet. In particular, in the limit of strong slip, λ → ∞, for a rivulet of a perfectly wetting fluid and a rivulet with constant width, the velocity becomes large and plug-like like O(λ1/2) ≫ 1, and the rivulet becomes shallow like O(λ−1/2) ≪ 1, while for a rivulet with positive constant contact angle, the velocity becomes large and plug-like like O(λ2/3) ≫ 1, and the rivulet becomes narrow like O(λ−1/3) ≪ 1 and shallow like O(λ−1/3) ≪ 1.