bluuebunny/crossref_metadata_2025 huggingface dataset:
A systematic search for changing-look quasars in SDSS-II using difference spectra
Authors: Potts B. , Villforth C.
Published: April 2021

Context. ‘Changing-look quasars’ (CLQs) are active galactic nuclei (AGN) showing extreme variability that results in a transition from type 1 to type 2 AGN. The short timescales of these transitions present a challenge to the unified model of AGN and the physical processes causing these transitions remain poorly understood. CLQs also provide interesting samples for the study of AGN host galaxies since the central emission disappears almost entirely.

Aims. Previous searches for CLQs have utilised photometric variability or SDSS classification changes to systematically identify CLQs; this approach may miss lower luminosity CLQs. In this paper, we aim to use spectroscopic data to asses if analysis difference spectra can be used to detect further CLQs that have been missed by photometric searches.

Methods. We searched SDSS-II DR 7 repeat spectra for sources that exhibit either a disappearance or appearance of both broad line emission and accretion disc continuum emission by directly analysing the difference spectrum between two epochs of observation.

Results. From a sample of 24 782 objects with difference spectra, our search yielded six CLQs within the redshift range 0.1 ⩽ z ≤ 0.3, including four newly identified sources. Spectral analysis indicates that changes in the accretion rate can explain the changing-look behaviour. While a change in dust extinction fits the changes in the spectral shape, the timescales of the changes observed are too short for obscuration from torus clouds.

Conclusions. Using difference spectra was shown to be an effective and sensitive way to detect CLQs. We recover CLQs an order of magnitude lower in luminosities than those found by photometric searches and achieve higher completeness than spectroscopic searches relying on pipeline classification.
Homogeneous model for the TRAPPIST-1e planet with an icy layer
Authors: Gevorgyan Yeva
Published: April 2021

In this work, we investigate whether a multilayered planet can be approximated as a homogeneous planet, and in particular how well the dissipation rate of a multilayered planet can be reproduced with a homogeneous rheology. We study the case of a stratified body with an icy crust that, according to recent studies, displays a double peak feature in the tidal response that cannot be reproduced with a homogeneous planet with an Andrade rheology. We revisit the problem with a slightly more complex rheology for the homogeneous body, the Sundberg–Cooper rheology, which naturally has a double peak feature, and apply the model to the TRAPPIST-1e planet. Our results compare very well with the results obtained when employing a multilayered model, showing that it is possible to approximate the behavior of a multilayer icy planet with a homogeneous planet using the Sundberg–Cooper rheology. This highlights the fact that we do not need the complexity of the multilayer planet model in order to estimate the tidal dissipation of an icy planet.
Pure hydrocarbon cycles in TMC-1: Discovery of ethynyl cyclopropenylidene, cyclopentadiene, and indene
Authors: Cernicharo J. , Agúndez M. , Cabezas C. , Tercero B. , Marcelino N. , Pardo J. R. , de Vicente P.
Published: April 2021

We report the detection for the first time in space of three new pure hydrocarbon cycles in TMC-1: c-C3HCCH (ethynyl cyclopropenylidene), c-C5H6 (cyclopentadiene), and c-C9H8 (indene). We derive a column density of 3.1 × 1011 cm−2 for the first cycle and similar values, in the range (1−2) × 1013 cm−2, for the second and third. This means that cyclopentadiene and indene, in spite of their large size, are exceptionally abundant, only a factor of five less abundant than the ubiquitous cyclic hydrocarbon c-C3H2. The high abundance found for these two hydrocarbon cycles together with the high abundance previously found for the propargyl radical (CH2CCH) and other hydrocarbons, such as vinyl and allenyl acetylene (Agúndez et al. 2021, A&A, 647, L10; Cernicharo et al. 2021a, A&A, 647, L2; Cernicharo et al. 2021b, A&A, 647, L3), start to allow us to quantify the abundant content of hydrocarbon rings in cold dark clouds and to identify the intermediate species that are probably behind the in situ bottom-up synthesis of aromatic cycles in these environments. While c-C3HCCH is most likely formed through the reaction between the radical CCH and c-C3H2, the high observed abundances of cyclopentadiene and indene are difficult to explain through currently proposed chemical mechanisms. Further studies are needed to identify how five- and six-membered rings are formed under the cold conditions of a cloud such as TMC-1.
Predicted hexagonal titanium nitride monolayer as an intrinsic ferromagnetic semiconductor
Authors: Li Jun , Huang Yuhong , Yuan Hongkuan , Chen Hong
Published: April 2021

Two-dimensional (2D) magnetic semiconductors have great promising for energy-efficient ultracompact spintronics due to the low-dimensional ferromagnetic and semiconducting behavior. Here, we predict hexagonal titanium nitride monolayer (h-TiN) to be a ferromagnetic semiconductor by investigating stability, magnetism, and carrier transport of h-TiN using the first-principles calculations. The thermodynamical stability of h-TiN is revealed by phonon dispersion, molecular dynamics simulation and formation energy. The energy band structure shows that h-TiN is a ferromagnetic semiconductor with medium magnetic anisotropy, the magnetic moment of 1μB and the band gaps of 1.33 and 4.42 eV for spin-up and -down channels, respectively. The Curie temperature of h-TiN is estimated to be about 205 K by mean-field theory and not enhanced by the compressive and tensile strains. Higher carrier mobility, in-plane stiffness and conductivity indicate that h-TiN has favorable transport performance. The ferromagnetic semiconducting behavior is robust against the external strains, indicating that h-TiN could be a rare candidate for nanoscale spintronic devices.
Theory and experimental research on spiral bevel gear by double-side milling method
Authors: Geng Longlong , Deng Xiaozhong , Zhang Hua , Nie Shaowu , Jiang Chuang
Published: April 2021

In this paper, a double-side milling method on spiral bevel gear is proposed. First, according to the tooth taper processed by double-side milling method, the influence of dedendum angle on the tooth taper was researched. Taking cut parameters into comprehensive consideration, the geometric parameters were designed through the inclination of root line and modified mean point in which machine setting parameters calculated was selected. Only the modified mean point met the meshing equation, and the error of pressure angle would increase as far away from the modified mean point in tooth line. The error would lead to bias in contact. A helical correction motion was introduced and the influence of helical motion coefficient on tooth surface topology was studied. Based on the meshing performance, a suitable coefficient was calculated. Finally, an example was illustrated. The experimental results were consistent with the theoretical analysis. The validity of the proposed method is verified.
Optimal location of electronic charity boxes in charity NGOs by proposing a combined mathematical model
Authors: Omrani Meisam , Naji-Azimi Zahra , Pooya Alireza , Salari Majid
Published: April 2021

The topic of collecting public donations has always attracted the attention of charity Non-Governmental Organizations as their basic policy; nevertheless, despite its importance, not much scientific research has been conducted on the issue. The optimal location of electronic charity boxes is effective in optimizing the obtained benefits. In this paper, for the first time in the literature, a location problem is defined with the aim of maximizing people’s motivation for money donation. We propose a new model to find the optimal location of e-charity boxes across the city with an aim to maximize the total amount of received benefits, as well as the total amount of donation motivation. To reach this aim, the effective criteria on the amount of gathered donation in each district and in each location type are investigated separately. Then, considering some constraints of the problem, a new mathematical model is proposed in order to determine the optimal location of e-charity boxes. We solve the model using LP-Metric, SAW, and TOPSIS methods, as a combination of Multi-Objective and Multi-Attributes Decision Making methods. Besides, we run the model in a real case study and 80 final locations are specified as the optimal locations in the studied city.
High-risk motor vehicle drivers engage in more risk behaviors than motorcyclists
Authors: Rankin Kelsey A. , Zaki Theodore , Ou Derek , Kim Chang-Yeon , Averbukh Leon , Maisano Julianna R. , Leslie Michael P. , Wiznia Daniel H.
Published: April 2021

Objective: The purpose of this study was to characterize and compare risk behaviors between motorcyclists and motor vehicle drivers who were involved in accidents and required hospitalization. The study focused on patients who were recently involved in motorcycle collisions (MCCs) and motor vehicle collisions (MVCs). Methods: We identified 63 patients involved in MCCs and 39 patients involved in MVCs who were admitted to our level-1 trauma center from April 2014 to September 2015. These 102 patients completed a questionnaire designed to evaluate risky driving behaviors. Pearson’s chi-squared tests and unpaired two-tailed t-tests were used to evaluate categorical and normally distributed continuous variables, respectively. Multivariable linear regression was used to analyze predictors of risk behavior. Significance was set at p < 0.05. Results: When compared to patients involved in an MCC, patients involved in MVCs were more likely to be female (p = 0.007), drive more frequently (p < 0.001), and never perceive the risk of an accident (p = 0.036). MVC patients were more likely to have admitted to substance use on the day of the accident (p = 0.030), historically drive under the influence of drugs (p = 0.031), drive while tired (p < 0.001), drive while text messaging (p < 0.001), and speed while overtaking vehicles (p = 0.011). Overall, MVC patients engaged in more risk behaviors (3.3 ± 1.3 vs. 2.0 ± 1.5; p < 0.001) and were more likely to engage in multiple risk behaviors (p < 0.001). MVCs were associated with increased risk behavior, even after controlling for protective behaviors, driving history, and demographics (p = 0.045). Conclusions: Within our cohort of trauma patients at our institution, motor vehicle drivers were more likely than motorcyclists to engage in any one risk behavior and engage in a higher number of risk behaviors. In addition, motor vehicle drivers perceived their risk of a potential accident as lower than riding a motorcycle. Education initiatives should focus on motor vehicle driver safety interventions that reduce risk behaviors.
Seltene Erkrankungen der Nase, der Nasennebenhöhlen und der vorderen Schädelbasis
Authors: Sommer Fabian
Published: April 2021

Seltene Erkrankungen der Nase, der Nasennebenhöhlen und der vorderen Schädelbasis stellen aufgrund der niedrigen Inzidenz und den daraus resultierend eingeschränkten diagnostischen Kriterien sowie therapeutischen Optionen eine Herausforderung dar. Der Schwellenwert, ab dem eine Erkrankung als selten zu werten ist, liegt bei höchstens 5 Betroffenen pro 10 000 Personen. Innerhalb dieser Erkrankungen gibt es allerdings extreme Schwankungen. So gehören einige seltene Erkrankungen, wie z.B. das invertierte Papillom, zu den regelmäßig diagnostizierten und therapierten Krankheitsbildern einer größeren Klinik für Hals-Nasen-Ohrenheilkunde. Andererseits liegen bei anderen seltenen Erkrankungen und Fehlbildungen weltweit deutlich unter 100 Fallberichte vor, was die Notwendigkeit einer Bündelung der verfügbaren Erfahrung zu Diagnostik und Therapie unterstreicht.

Die vorliegende Arbeit gibt eine Übersicht zu seltenen Erkrankungen der Nase, der Nasennebenhöhlen und der vorderen Schädelbasis aus den übergeordneten Bereichen Erkrankungen / Syndrome des olfaktorischen Systems, Fehlbildungen der Nase und Nasennebenhöhlen, Belüftungs- und Funktionsstörungen sowie benigne und maligne Tumore. Die Einordnung sowie Angaben zu Diagnostik und Therapiemöglichkeiten wurden unter Berücksichtigung der aktuellen Literatur erstellt.
Seltene Erkrankungen der Mundhöhle, des Halses und des Pharynx
Authors: Reichel Christoph A.
Published: April 2021

Erkrankungen, welche mit einer Häufigkeit von weniger als 1–10 Fällen pro 10 000 Personen in der Bevölkerung auftreten, gelten als selten. Derzeit sind zwischen 5000 und 8000 seltene Krankheiten bekannt, jedes Jahr werden etwa 250 seltene Krankheitsbilder neu beschrieben. Eine Vielzahl dieser Pathologien betrifft den Kopf-Halsbereich. Für die Diagnosestellung einer seltenen Erkrankung bedarf es oftmals langer Zeit. Das Leben betroffener Patientinnen und Patienten ist häufig von Arztbesuchen und Krankenhausaufenthalten geprägt. Die meisten seltenen Krankheiten besitzen eine genetische Ursache und sind trotz des medizinischen Fortschritts bis heute unheilbar. In den letzten Jahren sind jedoch die Wahrnehmung und das Wissen von bzw. zu seltenen Krankheitsbildern unter anderem durch die Schaffung von öffentlich zugänglichen Datenbanken gestiegen, die Etablierung von Selbsthilfegruppen hat zudem die Mündigkeit Betroffener gestärkt. Seit kurzem erlauben nun neuartige technische Errungenschaften im biomedizinischen Bereich genetische Ursachen seltener Erkrankungen bei einzelnen Patientinnen und Patienten individuell zu charakterisieren. Auf Grundlage dessen sollte es in naher Zukunft möglich werden, im Sinne der translationalen und personalisierten Medizin maßgeschneiderte Behandlungskonzepte für Patientinnen und Patienten mit seltenen Krankheiten zu erarbeiten. Mit dem vorliegenden Referat, welches sich mit seltenen Erkrankungen von Lippe, Mundhöhle, Pharynx und Halsweichteilen beschäftigt, soll ein Beitrag zu diesen Entwicklungen geleistet werden. Den Leserinnen und Lesern wird dabei ein kompakter Überblick zu einer Auswahl diesen anatomischen Bereich betreffender Krankheitsbilder gegeben. Verweise auf weiterführende Informationen für das medizinische Fachpersonal und betroffene Patientinnen und Patienten unterstützen die weitere Vertiefung ihres Wissens und führen gezielt zum aktuellen Kenntnisstand in diesem hoch-dynamischen Themengebiet.
Embryologie, Fehlbildungen und seltene Erkrankungen der
Cochlea
Authors: Warnecke Athanasia , Giesemann Anja
Published: April 2021

Auch wenn die einzelnen Krankheitsbilder selten sind, stellen seltene
Erkrankungen der Cochlea in ihrer Gänze eine doch gehäufte
Entität dar, die zu Hörstörungen führt.
Ein/Das Ziel des vorliegenden Referates war es, unter
Berücksichtigung der Embryonalentwicklung der Hörschnecke
und einer systematischen Zusammenfassung eine übersichtliche
Darstellung der seltenen cochleären Erkrankungen zu
ermöglichen. Auch wenn rapide biotechnologische und bioinformatische
Fortschritte die Diagnose einer seltenen Erkrankung erleichtern, so kann oft
nur im interdisziplinären Austausch der Verdacht einer seltenen
Erkrankung erhoben werden. Trotz gleicher zugrunde liegender Mutationen kann
der Phänotyp nicht nur bei den genetisch bedingten
Hörstörungen sondern auch bei den syndromalen Erkrankungen
stark variieren. Schließlich wird deutlich, dass der
Phänotyp der einzelnen seltenen Erkrankungen nicht
ausschließlich durch die klassische Genetik bestimmt werden
kann.
The Lucerne Protocol for the Production of Autologous Serum Eyedrops
Authors: Sanak Frantisek , Baenninger Philipp , Kaufmann Claude , Iselin Katja , Bachmann Lucas , Buhl Daniela , Thiel Michael
Published: April 2021

Background There are a variety of protocols for manufacturing autologous serum (AS) eye drops. The Lucerne protocol for the production of AS eye drops uses a slightly reduced gravitational (g)-force and time for the centrifugation process (2500 × g for 10 minutes), compared to previously published optimised protocols, to obtain high levels of epitheliotropic growth factors (3000 × g for 15 minutes). The goal of this study was to compare the concentrations of growth factors, albumin and lysozyme in autologous serum eye drops manufactured with these protocols.

Material and Methods Blood from 5 healthy volunteers was placed in plastic tubes without an anticoagulant. Tubes from each donor were left in a vertical position for 2 hours at room temperature to facilitate coagulation, followed by centrifugation at either 2500 × g for 10 minutes or at 3000 × g for 15 minutes at room temperature. The serum levels of beta nerve growth factor (β-NGF), transforming growth factor β1 (TGF-β1), epidermal growth factor (EGF), hepatocyte growth factor (HGF), platelet-derived growth factor BB (PDGF-BB) and vascular endothelial growth factor A (VEGF-A) were measured in triplicate with a multi-analyte Simple Plex platform. The Simple Plex cartridge allows each sample to be run in triplicate for each analyte and prevents any interaction between the antibody components for each biomarker. The serum level of albumin was measured by turbidimetric immunoassay Tina-quant and of lysozyme by single radial immunodiffusion assay.

Results For all analytes, the reduced g-force and centrifugation time did not result in a significant difference in serum levels.

Conclusions The Lucerne protocol for the production of autologous serum eye drops with reduced g-force and a shorter centrifugation time does not affect the concentrations of the main epitheliotropic growth factors, albumin and lysozyme, in AS eye drops.
Copper-Catalyzed Oxydifluoroalkylation of β,γ-Unsaturated Oximes for the Construction of Isoxazolines with a Difluoroalkyl Side Chain
Authors: Wang Guangwei , Wang Lianxin , Chen Hongtai , Zhao Wentao
Published: April 2021

A copper-catalyzed oxydifluoroalkylation of β,γ-unsaturated oximes has been developed. This reaction proceeded through a cascade of difluoroalkylation of alkene followed by a nucleophilic attack of the hydroxyl group of oximes. This protocol features mild reaction conditions, low-cost catalyst, and broad substrate scope, which provides a facile method to synthesize isoxazolines with a fluorinated side chain
Pseudoaneurysm following Surgical Resection of Craniopharyngioma: What Is the Best Management?
Authors: del Pont Francisco Marco , Villalonga Juan Francisco , Sáenz Amparo , Caffaratti Guido , Alcorta Santiago Condomi , Cervio Andrés
Published: April 2021

Craniopharyngiomas are benign tumors of the sellar and parasellar region for which surgical resection remains the treatment of choice. There are many publications on the most frequent postoperative complications, but few reports on subclinical lesions affecting the arteries of the circle of Willis, despite their high morbidity and mortality rate. Trauma-induced aneurysms are infrequent, representing less than 1% of intracranial aneurysms. Iatrogenic intracranial pseudoaneurysms are a subtype of surgically induced aneurysms developed as a result of direct injury to the arterial wall or after dissection of tumors adherent to the vessel adventitia. The natural history of these lesions is not well known because their incidence is extremely low. We report two cases of postoperative aneurysms of the internal carotid artery after craniopharyngioma resection and a brief review on the management of such lesions.
Perioperative Practices and Outcome of Neurosurgery during the COVID-19 Pandemic: Institutional Experience and Retrospective Observational Analysis
Authors: Khurana Priyanka , Ganjoo Pragati , Duggal Sakshi , Kiro Kiran Lata , Dhanwani Lavina , Tandon Monica S. , Singh Daljit , Jagetia Anita
Published: April 2021

Introduction Surgery during the coronavirus disease 2019 (COVID-19) pandemic is a major concern due to possibility of infection transmission among health care workers (HCWs) and patients, and a worsened surgical outcome; most surgeries are thus being deferred. However, we continued with emergency neurosurgeries using our own Neurosurgical Standard Operating Procedures (NS-SOPs). We describe here our institutional neurosurgical experience and observations of a retrospective analysis done to determine the incidence of workplace-acquired COVID infection among the HCWs, and the outcome of neurosurgery performed during the early phase of the on-going pandemic.

Methods Our NS-SOPs included a Screening Proforma, and protocols for the conduct of neurosurgery, starting from the preoperative period till death or postdischarge follow-up of the patients. Protocols to ensure safety and mental well-being of the HCWs were also implemented. Patient and HCW data from April 1 to August 31, 2020 was collected and analyzed for the postsurgical patient outcome and for determining the level of workplace-transmitted COVID infection.

Results Neurosurgeries were performed on 169 patients during this 5-month period. We observed a cumulative mortality of 17/169 (10.1%), with 5 patients having unexplained postoperative respiratory manifestations and rapid deterioration suggestive of COVID illness. Nineteen HCWs (8.83%), mostly nurses, were infected, but only 3 (16.7%) had workplace-acquired infection. The infections were sporadic with no cluster of infections observed.

Conclusion Implementation of standard perioperative protocols and their continuous scrutiny, evaluation, and modification is important to contain infection in HCWs and to improve the neurosurgical outcome during this pandemic.
Diagnostic Value of MRI and Radiographs of the Knee to Identify Osteochondral Lesions in Acute Patellar Instability
Authors: Baker Hayden , Dickherber Jason , Reddy Manoj , Rizzi Andrew , Kahn Adam , Athiviraham Aravind
Published: April 2021

The purpose of this study was to define the diagnostic value of magnetic resonance imaging (MRI) and plain radiographs (X-ray [XR]) in identifying an osteochondral defect or loose body in patients undergoing operative treatment for patellar instability. A total of 87 patients treated operatively for patellar instability with medial patellofemoral ligament (MPFL) reconstruction between 2015 and 2019 were identified. Inclusion criteria were evidence of clinical patellar instability, preoperative XR and MRI studies, and concomitant diagnostic knee arthroscopy and MPFL reconstruction performed to address patellar instability. Patients were excluded if they had a history of prior procedure for patellar instability on the surgical knee, underwent MPFL reconstruction without concomitant diagnostic knee arthroscopy, or had an anterior cruciate ligament or posterior cruciate ligament deficient knee. Operative notes and arthroscopic images were reviewed to identify osteochondral or chondral injuries and loose bodies noted during diagnostic arthroscopy. The primary outcome was the identification of intra-articular loose bodies, chondral injury, or osteochondral defect on preoperative plain radiographs and MRI in patients with patellar instability. All MRIs were performed on a 3T MRI. The sensitivity and specificity of identifying loose bodies on MRI were 0.52 and 0.92 and on XR were 0.23 and 0.98, respectively. The sensitivity and specificity of identifying osteochondral lesions on MRI were 0.43 and 0.81 and on XR were 0.08 and 0.97, respectively. Of the 87 available reports, 45 (51%) described performing chondroplasty for Outerbridge grade II/III chondral lesions on diagnostic arthroscopy. In conclusion, MRI and XR are poorly sensitive at identifying loose bodies or osteochondral defects after patellar dislocations. The poor sensitivity of imaging studies must be considered when determining whether or not to recommend operative management to a patient with patellar instability. This is a Level IV, diagnostic study.
Mechanotransduction assays for neural regeneration strategies: A focus on glial cells
Authors: Marinval Nicolas , Chew Sing Yian
Published: April 2021

Glial cells are mechanosensitive, and thus, engineered systems have taken a step forward to design mechanotransduction platforms in order to impart diverse mechanical stresses to cells. Mechanical strain encountered in the central nervous system can arise from diverse mechanisms, such as tissue reorganization, fluid flow, and axon growth, as well as pathological events including axon swelling or mechanical trauma. Biomechanical relevance of the in vitro mechanical testing requires to be placed in line with the physiological and mechanical changes in central nervous tissues that occur during the progression of neurodegenerative diseases. Mechanotransduction signaling utilized by glial cells and the recent approaches intended to model altered microenvironment adapted to pathological context are discussed in this review. New insights in systems merging substrate's stiffness and topography should be considered for further glial mechanotransduction studies, while testing platforms for drug discoveries promise great advancements in pharmacotherapy. Potential leads and strategies for clinical outcomes are expected to be developed following the exploration of these glial mechanosensitive signaling pathways.
Void containing AlN layer grown on AlN nanorods fabricated by polarity selective epitaxy and etching method
Authors: So Byeongchan , Lee Junchae , Cheon Changheon , Lee Joohyung , Choi Uiho , Kim Minho , Song Jindong , Chang Joonyeon , Nam Okhyun
Published: April 2021

Creating voids between thin films is a very effective method to improve thin film crystal quality. However, for AlN material systems, the AlN layer growth, including voids, is challenging because of the very high Al atom sticking coefficient. In this study, we demonstrated an AlN template with many voids grown on AlN nanorods made by polarity selective epitaxy and etching methods. We introduced a low V/III ratio and NH3 pulsed growth method to demonstrate high-quality coalesced AlN templates grown on AlN nanorods in a metal organic chemical vapor deposition reactor. The crystal quality and residual strain of AlN were enhanced by the void formations. It is expected that this growth method can contribute to the demonstration of high-performance deep UV LEDs and transistors.
Influences of thickness and gamma-ray irradiation on the frictional and electronic properties of WSe2 nanosheets
Authors: Wu Xiongli , Zheng Xuejun , Zhang Guangbiao , Dong Hui , Chen Xinnan
Published: April 2021

The nanoscale characteristics of semiconducting transition metal dichalcogenides (TMDCs) are largely determined by their photonic, mechanical, magnetic, thermal, and electronic properties, which can be modulated by adjusting thickness and radiation treatments. In this paper, gamma-rays were applied to irradiate the materials with one to six layers, based on which a comparison was drawn of the frictional and electrical properties before and after irradiation. The changes on a few-layer WSe2 were investigated using Raman spectroscopy, photoluminescence spectroscopy, scanning electron microscopy, transmission electron microscopy, force friction microscopy, and Kelvin probe force microscopy. Under the context of irradiation, there was a phenomenon found different than previously reported. The friction force of WSe2 nano-flakes increased from monolayer to bilayer, decreased at tri-layer, and then increased on a continued basis with thickness. It is suggested that the gamma-ray irradiation treatment could be effective in improving frictional and electronic properties. The range of change to the surface contact potential difference (CPD) was narrowed, and the stability of the device surface potential was enhanced. The continuum mechanics theory was applied to explore the friction force variation between different thickness layers. Based on the puckering effect of tip-flake adhesion, the friction force was determined by bending stiffness. The thermal treatment of WSe2 nanoflakes had a significant impact on the CPD between the sample and the test tip. After thermal treatment, the surface potential increased from one to five layers with thickness. These phenomena were explained in detail. The research contributes to enriching nanotribology and electrical theory in addition to promoting the use of semiconducting TMDCs for nano-components’ design.
Recent advances in flexible thermoelectrics
Authors: Shang Hongjing , Gu Hongwei , Ding Fazhu , Ren Zhifeng
Published: April 2021

Recently, flexible thermoelectric (TE) materials and devices have attracted extensive attention due to their capability to convert heat into electricity directly and their conformal contact with arbitrarily shaped heat sources, demonstrating great promise for application in self-powered portable/wearable low power consuming electronics. Here, we review the state of the art in the development of flexible TEs, including TE modules and materials themselves. The remaining challenges that limit the practical application of flexible TE devices are discussed, and possible solutions and suggestions to guide future development are also provided in this perspective.
A direct link between active matter and sheared granular systems
Authors: Morse Peter K. , Roy Sudeshna , Agoritsas Elisabeth , Stanifer Ethan , Corwin Eric I. , Manning M. Lisa
Published: April 2021

Significance

There is not yet a robust theoretical framework predicting the dynamics of dense active matter, where energy is injected at the scale of constituent particles. Previous work has shown that some features of dense active matter are similar to those in dense disordered materials that are sheared globally from the boundaries. Using analytic and computational tools, we show that there is a direct correspondence between active matter and applied shear strain, which can in turn be used to help predict the behavior of dense active matter.
Counterpossible Reasoning in Physics
Authors: Wilson Alastair
Published: April 2021

This article explores three ways in which physics may involve counterpossible reasoning. The first way arises when evaluating false theories: to say what the world would be like if the theory were true, we need to evaluate counterfactuals with physically impossible antecedents. The second way relates to the role of counterfactuals in characterizing causal structure: to say what causes what in physics, we need to make reference to physically impossible scenarios. The third way is novel: to model metaphysical dependence in physics, we need to consider counterfactual consequences of metaphysical impossibilities. Physics accordingly bears substantial and surprising counterpossible commitments.
Interferometric visibility in curved spacetimes
Authors: Basso Marcos L W , Maziero Jonas
Published: April 2021

In (Zych et al 2011 Nat. Commun.
2 505), the authors predicted that the interferometric visibility is affected by a gravitational field in way that cannot be explained without the general relativistic notion of proper time. In this work, we take a different route and start deriving the same effect using the unitary representation of the local Lorentz transformation in the Newtonian limit. In addition, we show that the effect on the interferometric visibility due to gravity persists in different spacetime geometries. However, the influence is not necessarily due to the notion of proper time. For instance, by constructing a ‘astronomical’ Mach–Zehnder interferometer in the Schwarzschild spacetime, the influence on the interferometric visibility can be due to another general relativistic effect, the geodetic precession. Besides, by using the unitary representation of the local Lorentz transformation, we show that this behavior of the interferometric visibility is general for an arbitrary spacetime, provided that we restrict the motion of the quanton to a two-dimensional spacial plane.
Quantitative experiments in a distance lab: studying blackbody radiation with a smartphone
Authors: Onorato Pasquale , Rosi Tommaso , Tufino Eugenio , Caprara Caterina , Malgieri Massimiliano
Published: April 2021

In this paper we present an experiment aimed at investigating the thermal radiation law. The spectrum of a filament light bulb is acquired at different temperatures using a low-cost grating spectrometer based on a smartphone camera, while the measurement of filament temperature is obtained indirectly from the temperature dependence of the filament resistance. Two different methods for measuring the light intensity are tested: one is based on the use of the ambient light sensor of a smartphone, the other on a home-made grating spectrometer coupled with the smartphone camera. We observe a good agreement of the experimental data with the theoretical predictions of the Planck distribution in the limit of the Wien approximation restricted to the wavelength range characterizing the response of the smartphone light sensor and camera.
A review on fabrication of blazed gratings
Authors: Gao Jian , Chen Peng , Wu Lei , Yu Bingjun , Qian Linmao
Published: April 2021

Ultra-precision manufacturing plays a critical role in the successful development of various technological fields and has a significant influence on the processes conducted in human society. Blazed gratings with periodically inclined structures exhibit satisfactory characteristics, concentrating most of the diffracted light to a single, non-zero order. In addition to their high diffraction efficiency, blazed gratings can also significantly improve the sensitivity, resolution, and measurement range of grating measurement systems; they are also core functional components for improving ultra-precision manufacturing. Significant research and industrial attention have been devoted toward the manufacturing of blazed gratings. This review describes the physical principles of blazed gratings, the specific approaches used, and the achievements of typical processing methods, including mechanical ruling, holographic ion beam etching, electron beam lithography, and wet etching. The advantages and disadvantages of these fabrication methods were addressed, and prospective approaches were proposed to improve the manufacturing of blazed gratings.
Vibrational CARS measurements in a near-atmospheric pressure plasma jet in nitrogen: I. Measurement procedure and results
Authors: Kuhfeld J , Lepikhin N D , Luggenhölscher D , Czarnetzki U
Published: April 2021

The non-equilibrium ro-vibrational distribution functions of molecules in a plasma can heavily influence the discharge operation and the plasma-chemistry. A convenient method for measuring the distribution function is coherent anti-Stokes Raman scattering (CARS). CARS spectra are measured in a ns-pulsed plasma between two parallel, 1 mm spaced molybdenum electrodes in nitrogen at 200 mbar with pulse durations of 200 ns/250 ns and a repetition rate of 1 kHz. The CARS spectra are analyzed by a fitting routine to extract information about the vibrational excitation of the nitrogen molecules in the plasma. It is found that during the discharge the vibrational distribution for

v
≲
7

can be described by a vibrational two-temperature distribution function. Additionally, the electric field is measured by the electric field induced second harmonic generation method during the discharge pulse. It is found to be constant in time after the initial ionization wave with values close to 81 Td for the investigated conditions. During the afterglow between two discharge pulses a more general fitting approach is used to obtain the population differences of two neighboring vibrational states. This allows to capture the more complex vibrational dynamics in that time period. The measurement results are discussed in more detail and compared to simple plasma models in a companion paper Kuhfeld et al (2021 J. Phys. D: Appl. Phys.
54 305205).
Doping tuned spin reorientation and spin switching in praseodymium–samarium orthoferrite single crystals
Authors: Luo Xiong , Li Rubin , Ma Xiaoxuan , Chen Yunke , Kang Baojuan , Zhang Jincang , Ren Wei , Feng Zhenjie , Cao Shixun
Published: April 2021

We investigate the detailed analysis of the magnetic properties in a series of Pr1–x
Sm
x
FeO3 single crystals from x = 0 to 1 with an interval of 0.1. Doping controlled spin reorientation transition temperature T
SR Γ4 (G

x
, A

y
, F

z
) to Γ2 (F

x
, C

y
, G

z
) covers a wide temperature range including room temperature. A ‘butterfly’-shape type-I spin switching with 180° magnetization reversal occurs below and above the magnetization compensation points in x = 0.4 to 0.8 compounds. Interestingly, in Pr0.6Sm0.4FeO3 single crystal, we find an inadequate spin reorientation transition accompanied by uncompleted type-I spin switching in the temperature region from 138 to 174 K. Furthermore, a type-II spin switching appears at 23 K, as evidenced from the magnetization curve in field-cooled-cooling (FCC) mode initially bifurcate from zero-field-cooled (ZFC) magnetization curve at 40 K and finally drops back to coincide the ZFC magnetization value at 23 K. Our current research reveals a strong and complex competition between Pr3+–Fe3+ and Sm3+–Fe3+ exchange interactions and more importantly renders a window to design spintronic device materials for future potential applications.
Rigorous 3D modeling of confocal microscopy on 2D surface topographies
Authors: Pahl Tobias , Hagemeier Sebastian , Bischoff Jörg , Manske Eberhard , Lehmann Peter
Published: April 2021

Although optical 3D topography measurement instruments are widespread, measured profiles suffer from systematic deviations occurring due to the wave characteristics of light. These deviations can be analyzed by numerical simulations. We present a 3D modeling of the image formation of confocal microscopes. For this, the light-surface interaction is simulated using two different rigorous methods, the finite element method and the rigorous coupled-wave analysis. The image formation in the confocal microscope is simulated using a Fourier optics approach. The model provides high accuracy and advantages with respect to the computational effort as a full 3D model is applied to 2D structures and the lateral scanning process of the confocal microscope is considered without repeating the time consuming rigorous simulation of the scattering process. The accuracy of the model is proved considering different deterministic surface structures, which usually cause strong systematic deviations in measurement results. Further, the influences of apodization and a finite pinhole size are demonstrated.
Electronic properties of atomically coherent square PbSe nanocrystal superlattice resolved by Scanning Tunneling Spectroscopy
Authors: Capiod Pierre , van der Sluijs Maaike , de Boer Jeroen , Delerue Christophe , Swart Ingmar , Vanmaekelbergh Daniel
Published: April 2021

Rock-salt lead selenide nanocrystals can be used as building blocks for large scale square superlattices via two-dimensional assembly of nanocrystals at a liquid-air interface followed by oriented attachment. Here we report Scanning Tunneling Spectroscopy measurements of the local density of states of an atomically coherent superlattice with square geometry made from PbSe nanocrystals. Controlled annealing of the sample permits the imaging of a clean structure and to reproducibly probe the band gap and the valence hole and conduction electron states. The measured band gap and peak positions are compared to the results of optical spectroscopy and atomistic tight-binding calculations of the square superlattice band structure. In spite of the crystalline connections between nanocrystals that induce significant electronic couplings, the electronic structure of the superlattices remains very strongly influenced by the effects of disorder and variability.
Controllable high-performance memristors based on 2D Fe2GeTe3 oxide for biological synapse imitation
Authors: Zeng Xiangyu , Huang Shuyi , Ye Qikai , Rajagopalan Pandey , Li Wei , Kuang Haoze , Ye Ge , Chen Chufan , Li Menglu , Liu Yulu , Shi Lin , Guo Yuzheng , Lu Xin , Shi Wenhua , Luo Jikui , Wang Xiaozhi
Published: April 2021

Memristors are an important component of the next-generation artificial neural network, high computing systems, etc. In the past, two-dimensional materials based memristors have achieved a high performance and low power consumption, though one at the cost of the other. Furthermore, their performance can not be modulated frequently once their structures are fixed, which remains the bottleneck in the development. Herein, a series of forming free memristors are fabricated with the same Cu/Fe3GeTe2 oxide/Fe3GeTe2/Al structure, yet the On/Off ratio and set voltage is modulated continuously by varying the oxidation time during fabrication. With an optimal oxidation time, a large On/Off ratio (1.58 × 103) and low set voltage (0.74 V) is achieved in a single device. The formation and rapture of Al conductive filaments are found to be responsible for the memristors, and the filaments density and the cross-section area increase with the increase of current compliance, which achieves a higher On/Off ratio. The memristor can imitate basic biological synaptic functions using voltage pulses, demonstrating the potential for low-power consuming neuromorphic computing applications.
Nonlinear localized waves for a (2+1)-dimensional Heisenberg ferromagnetic spin chain equation
Authors: Du Xia-Xia , Tian Bo , Zhang Chen-Rong , Chen Su-Su
Published: April 2021

We focus on the spin dynamics of the nonlinear localized waves for a (2+1)-dimensional Heisenberg ferromagnetic spin chain equation. Based on the technique for the nonlinearization of spectral problem, we derive the values of the spectral parameter and periodic eigenfunction of the Lax pair associated with dn which is the Jacobian elliptic function of the third kind. According to the Darboux transformation, we take the seed solutions expressed by the Jacobian elliptic function and construct the semirational solutions. Such solutions are used for describing the eye-shaped lumps and line rogue waves on the dn-periodic backgrounds. Besides, the lump and mixed lump-soliton solutions are deduced through the semirational solutions.
Entropy and stochastic properties in catalysis at nanoscale
Authors: Castellanos-Jaramillo Juan Miguel , Castellanos-Moreno Arnulfo
Published: April 2021

This work approaches the Michaelis-Menten model for enzymatic reactions at a nanoscale, where we focus on the quasi-stationary state of the process. The entropy and the kinetics of the stochastic fluctuations are studied to obtain new understanding about the catalytic reaction. The treatment of this problem begins with a state space describing an initial amount of substrate and enzyme-substrate complex molecules. Using the van Kampen expansion, this state space is split into a deterministic one for the mean concentrations involved, and a stochastic one for the fluctuations of these concentrations. The probability density in the fluctuation space displays a behavior that can be described as a rotation, which can be better understood using the formalism of stochastic velocities. The key idea is to consider an ensemble of physical systems that can be handled as if they were a purely conceptual gas in the fluctuation space. The entropy of the system increases when the reaction starts and slightly diminishes once it is over, suggesting: 1. The existence of a rearrangement process during the reaction. 2. According to the second law of thermodynamics, the presence of an external energy source that causes the vibrations of the structure of the enzyme to vibrate, helping the catalytic process. For the sake of completeness and for a uniform notation throughout this work and the ones referenced, the initial sections are dedicated to a short examination of the master equation and the van Kampen method for the separation of the problem into a deterministic and stochastic parts. A Fokker-Planck equation (FPE) is obtained in the latter part, which is then used as grounds to discuss the formalism of stochastic velocities and the entropy of the system. The results are discussed based on the references cited in this work.
Ultra-slow-roll inflation with quantum diffusion
Authors: Pattison Chris , Vennin Vincent , Wands David , Assadullahi Hooshyar
Published: April 2021

We consider the effect of quantum diffusion on the dynamics of the inflaton during a period of ultra-slow-roll inflation. We extend the stochastic-δ𝒩 formalism to the ultra-slow-roll regime and show how this system can be solved analytically in both the classical-drift and quantum-diffusion dominated limits.
By deriving the characteristic function, we are able to construct the full probability distribution function for the primordial density field. In the diffusion-dominated limit, we recover an exponential tail for the probability distribution, as found previously in slow-roll inflation.
To complement these analytical techniques, we present numerical results found both by very large numbers of simulations of the Langevin equations, and through a new, more efficient approach based on iterative Volterra integrals.
We illustrate these techniques with two examples of potentials that exhibit an ultra-slow-roll phase leading to the possible production of primordial black holes.
deep21: a deep learning method for 21 cm foreground removal
Authors: Makinen T. Lucas , Lancaster Lachlan , Villaescusa-Navarro Francisco , Melchior Peter , Ho Shirley , Perreault-Levasseur Laurence , Spergel David N.
Published: April 2021

We seek to remove foreground contaminants from 21 cm intensity mapping observations. We demonstrate that a deep convolutional neural network (CNN) with a UNet architecture and three-dimensional convolutions, trained on simulated observations, can effectively separate frequency and spatial patterns of the cosmic neutral hydrogen (HI) signal from foregrounds in the presence of noise. Cleaned maps recover cosmological clustering amplitude and phase within 20% at all relevant angular scales and frequencies. This amounts to a reduction in prediction variance of over an order of magnitude across angular scales, and improved accuracy for intermediate radial scales (0.025 < k∥
< 0.075 h Mpc-1) compared to standard Principal Component Analysis (PCA) methods. We estimate epistemic confidence intervals for the network's prediction by training an ensemble of UNets. Our approach demonstrates the feasibility of analyzing 21 cm intensity maps, as opposed to derived summary statistics, for upcoming radio experiments, as long as the simulated foreground model is sufficiently realistic.
We provide the code used for this analysis on GitHub , as well as a browser-based tutorial for the experiment and UNet model via the accompanying Colab notebook .
A novel family of rotating black hole mimickers
Authors: Mazza Jacopo , Franzin Edgardo , Liberati Stefano
Published: April 2021

The recent opening of gravitational wave astronomy has shifted the debate about black hole mimickers from a purely theoretical arena to a phenomenological one. In this respect, missing a definitive quantum gravity theory, the possibility to have simple, meta-geometries describing in a compact way alternative phenomenologically viable scenarios is potentially very appealing. A recently proposed metric by Simpson and Visser is exactly an example of such meta-geometry describing, for different values of a single parameter, different non-rotating black hole mimickers.
Here, we employ the Newman-Janis procedure to construct a rotating generalisation of such geometry. We obtain a stationary, axially symmetric metric that depends on mass, spin and an additional real parameter ℓ. According to the value of such parameter, the metric may represent a rotating traversable wormhole, a rotating regular black hole with one or two horizons, or three more limiting cases. By studying the internal and external rich structure of such solutions, we show that the obtained metric describes a family of interesting and simple regular geometries providing viable Kerr black hole mimickers for future phenomenological studies.