bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical study of extreme-ultraviolet nanoflares in the quiet-Sun transition region
Authors: Fludra A.
Published: May 2023

Aims. We carried out a large statistical study of ubiquitous small-scale extreme-ultraviolet (EUV) brightenings in the nanoflare energy range in the quiet-Sun transition region to derive their properties, estimate their contribution to the heating of the solar atmosphere, and compare their numbers to the coronal events published in the literature. This is the first study of this magnitude at temperatures of about 2 × 105 K.

Methods. We applied a numerical method for detecting small-scale transient events in long 1D image time series. We used data recorded by the SOHO Coronal Diagnostic Spectrometer (CDS) in the transition region line O V 62.97 nm (220 000 K) and analysed 702 h of sit-and-stare time series obtained with a cadence of 15.6 s and 50 h with a cadence of 20.5 s in different quiet-Sun areas at a fixed slit position. These data span from 1996 to 2011. This analysis used a different method and a vastly larger number of data than the previous high-cadence CDS study of small events.

Results. We derive histograms of event durations, of the rise and decay time, of the peak intensity and thermal energy, and we obtain a continuous spectrum of their distributions for 117 000 events, spanning the nanoflare energy range with a linear spatial extent of 2−10 arcsec and with durations between 45 s and 40 min. The event peak intensity varied by a factor of 60. We demonstrated that all categories of small-scale events in the transition region are part of a continuum of activity. We obtain a total event rate of 460 s−1 on the entire surface of the Sun. This is more than four times greater than the coronal rate. The maximum value of the duration distribution occurs at 235 s, which is twice the duration of the coronal events. The decay time and rise time difference seen from the shortest to the longest events is symmetrical. We find two event populations: the power law of the smallest events that are confined to one pixel is far steeper for the peak count rates (index of −4.1) and thermal energy (index of −7) than the power law for combined larger events that extend over two or more pixels along the slit (thermal energy power-law index from −2.1 to −3.4).

Conclusions. The power law of the thermal energy of the smallest events, extrapolated to lower energies (picoflares), may provide a huge amount of energy for heating the entire transition region plasma at temperatures of about 220 000 K. An extrapolation of only the flatter power law of the larger events can also account for the entire observed emission.
Observing the onset of the accretion wake in Vela X-1
Authors: Diez C. M. , Grinberg V. , Fürst F. , El Mellah I. , Zhou M. , Santangelo A. , Martínez-Núñez S. , Amato R. , Hell N. , Kretschmar P.
Published: May 2023

High-mass X-ray binaries (HMXBs) offer a unique opportunity to investigate accretion onto compact objects and the wind structure in massive stars. A key source for such studies is the bright neutron star HMXB Vela X-1 whose convenient physical and orbital parameters facilitate analyses and in particular enable studies of the wind structure in HMXBs. Here, we analyse simultaneous XMM-Newton and NuSTAR observations at ϕorb ≈ 0.36–0.52 and perform time-resolved spectral analysis down to the pulse period of the neutron star based on our previous NuSTAR-only results. For the first time, we are able to trace the onset of the wakes in a broad 0.5–78 keV range with a high-time resolution of ~283 s and compare our results with theoretical predictions. We observe a clear rise in the absorption column density of the stellar wind NH,1 starting at orbital phase ~0.44, corresponding to the wake structure entering our line of sight towards the neutron star, together with local extrema throughout the observation, which are possibly associated with clumps or other structures in the wind. Periods of high absorption reveal the presence of multiple fluorescent emission lines of highly ionised species, mainly in the soft-X-ray band between 0.5 and 4 keV, indicating photoionisation of the wind.
Upstream proton cyclotron waves at Mars during the passage of solar wind stream interaction regions
Authors: Zhao Dan , Guo Jianpeng , Lin Haibo , Meng Weiduo , He Linxia , Chen Yan , Wei Yong , Liu Libo
Published: May 2023

Proton cyclotron waves (PCWs) upstream from Mars are generated by ion–ion instabilities due to the interaction between the solar wind and the pickup protons that originate from the extended hydrogen (H) exosphere of Mars, indicating a loss of H to interplanetary space. Their occurrences and properties associated with nominal solar wind conditions have been widely studied, but relatively little is known about PCW activity under extreme solar wind conditions. In this work we characterize the upstream PCWs during the passage of solar wind stream interaction regions (SIRs) utilizing in situ observations by the Mars Atmosphere and Volatile EvolutioN spacecraft from October 2014 to August 2021. The 46 analyzed SIR events are a subset of the events that occurred in the perihelion season of Martian years 32–35. We find that the PCW occurrence rate is increased by a factor of about 1.8 during the SIR phase relative to the pre-SIR and post-SIR phases. Furthermore, the PCW activity tends to occur more frequently in the leading portion of the SIR. The PCWs detected during the SIR phase have more pronounced wave characteristics, namely larger wave amplitudes, smaller propagation angles with respect to the background magnetic field, and closer-to-circular polarization.
Temperature and density dependence of line profiles of sodium perturbed by helium
Authors: Allard N. F. , Myneni K. , Blakely J. N. , Guillon G.
Published: May 2023

Context. Ultracool stellar atmospheres and hot exoplanets show absorption by alkali resonance lines severely broadened by collisions with neutral perturbers. In the coolest and densest atmospheres, such as those of T dwarfs, Na I and K I broadened by molecular hydrogen and helium can come to dominate the entire optical spectrum. The effects of Na–He collision broadening are also central to understanding the opacity of cool DZ white dwarf stars.

Aims. In order to be able to construct synthetic spectra of brown dwarfs and cool DZ white dwarfs, where helium density can reach several 1021 cm−3, Na–He line profiles of the resonance lines have been computed over a wide range of densities and temperatures.

Methods. Unified line profiles that are valid from the core to the far wings at high densities are calculated in the semiclassical approach using up-to-date molecular data including electronic spin-orbit coupling from the sodium atom. Far wings are extended to more than 4000 cm−1 from the line center when the helium density can reach 1021 cm−3 at 5000 K.

Results. We present a comprehensive study of Na–He collisional profiles at high density, and temperatures from 5000 K, which is the temperature prevailing in the atmosphere of ultra-cool DZ white dwarf stars, down to 1 K, which is the temperature in liquid helium clusters. Collision broadening and shift parameters within the impact approximation obtained in the semiclassical and quantum theory using our new accurate molecular data are presented.
Supermassive black hole wake or bulgeless edge-on galaxy?
Authors: Almeida Jorge Sánchez , Montes Mireia , Trujillo Ignacio
Published: May 2023

A recent paper reported the serendipitous discovery of a thin linear object interpreted as the trail of star-forming regions left behind by a runaway supermassive black hole (SMBH) kicked out from the center of a galaxy. Despite the undeniable interest in the idea, the actual physical interpretation is not devoid of difficulty. The wake of a SMBH produces only small perturbations in the external medium, which has to be in exceptional physical conditions to collapse gravitationally and form a long (40 kpc) massive (3 × 109 M⊙) stellar trace in only 39 Myr. Here we offer a more conventional explanation: the stellar trail is a bulgeless galaxy viewed edge-on. This interpretation is supported by the fact that its position–velocity curve resembles a rotation curve, which, together with its stellar mass, puts the object exactly on the Tully–Fisher relation characteristic of disk galaxies. Moreover, the rotation curve (Vmax ∼ 110 km s−1), stellar mass, extension, width (z0 ∼ 1.2 kpc), and surface brightness profile of the object are very much like those of IC 5249, a well-known local bulgeless edge-on galaxy. These observational facts are difficult to interpret within the SMBH wake scenario. We discuss in detail the pros and cons of the two options.
Optimal regulation of microgrid considering electro-hydrogen coupling
Authors: Zhang Yabo , Qifen Li
Published: May 2023

Aiming at the problem of large access to renewable energy and insufficient regulation capacity of microgrid systems, this paper introduces electro-hydrogen coupling to improve the flexible regulation capacity of microgrid systems. A mathematical model for power regulation of microgrid including renewable energy equipment and electro-hydrogen coupling equipment is analyzed and established. Based on this, a flexibility margin model for the system is established. Taking the total profit and flexibility margin over the entire life cycle as optimization objectives, a daily optimal scheduling model for microgrid is established. In order to reflect the optimization and adjustment ability of electro-hydrogen coupling, this paper develops a variety of scenarios for comparison, and uses an improved particle optimization algorithm to solve the scheduling plans for different scenarios. The analysis of a numerical example shows that the regulation and optimization ability of the electro-hydrogen coupling is much higher than that of traditional energy storage.
Flexible Control of Wet Desulphurization Process Based on Frequency Retrofit
Authors: Zhan Zhuo-Xuan , Zhao Gang , Su Zhi-Gang
Published: May 2023

To assist in the absorption of renewable energy, coal-fired power plants need to operate over a wide range of loads, which exacerbates the challenge of the time delay in the wet desulphurization process. Therefore, this paper proposes a new control structure based on frequency retrofit and a corresponding model predictive controller to change the traditional idea of wet desulphurization control. This structure provides faster control actions, thus reducing time delay directly. And it makes the original discrete control variable continuous, enabling most control methods. The field application to the wet flue gas desulphurization system reveals the practical prospects of the proposed control structure and simulations have been conducted to verify the merits of the proposed control scheme based on data collected from a 1000 MW power plant.
Treatment of ultra high-pressure brine overflow by drainage brine with controlling pressure technology
Authors: Wei Gao , Shuanggui Li , Guohe Xu , Wei Luo , Jiaxue Li
Published: May 2023

Overflow of high -pressure brine causes stratification and sedimentation of drilling fluid, which damages the performance of drilling fluid and lead to serious accidents such as sticking. In the face of saltwater overflow, the common practice is to increase the density of drilling fluid to prevent and deal with it. However, increasing the density will lead to serious lost circulation in the thief layer, thus aggravating the saltwater overflow. In order to solve this problem, this paper puts forward a method of drainage brine with controlling pressure to deal with the overflow of high -pressure brine layer. Through laboratory experiments, the pollution capacity limit of high -pressure brine on oil-based drilling fluid was determined, and the drainage brine with controlling pressure technology was systematically proposed. The controlled pressure water drainage treatment technology has been successful applied in 4 Wells drilling in ultra- deep salt paste formation in Tarim Basin.
Study on properties of zinc ferrite, titanium dioxide and their composites
Authors: Yang Jinlin , Huo Xingnan , Li Zongyu , Ma Shaojian
Published: May 2023

In this paper, the methods of sulfuric acid leaching and chemical coprecipitation were used to prepare products such as purified zinc ferrite, synthetic zinc ferrite, synthetic titanium dioxide and its complex with purified zinc ferrite. The morphology and microstructure of the above samples were characterized and analyzed by XRD and SEM. The results showed that the purified zinc ferrite contained a small amount of ZnO, SiO2, Al2O3 and PbSO4. Its particle size was the largest and the crystallinity was the best, but the surface was not smooth, the particle size distribution was not uniform and there was agglomeration phenomenon. The purchased zinc ferrite had high purity, the smallest particle size and the worst crystallinity. Its surface was smooth, particle size distribution was uniform, and it was loose and porous. The synthetic zinc ferrite had high purity, smooth surface, uniform particle size distribution and obvious agglomeration. The prepared titanium dioxide had no other impurities, good crystallinity, smooth surface and certain agglomeration phenomenon. For the zinc ferrite/titanium dioxide composite, adding a small amount of purified zinc ferrite would change the crystallinity of titanium dioxide, but it had little effect on the grain size of titanium dioxide. The surface was rough, the particle size distribution was not uniform, and there was agglomeration phenomenon.
Research of characterization of zinc ferrite, titanium dioxide and their composites
Authors: Yang Jinlin , Huo Xingnan , Li Zongyu , Ma Shaojian
Published: May 2023

In this paper, zinc calcines, sulfuric acid, ferric nitrate nine-hydrate, zinc nitrate hexahydrate, titanium oxide sulfate, sodium hydroxide and ammonia water were selected as raw materials, and the methods of sulfuric acid leaching and chemical coprecipitation were used to prepare purified zinc ferrite, synthetic zinc ferrite, synthetic titanium dioxide and its composite with purified zinc ferrite. And characterized by BET, UVVis and FTIR. The results showed that: SO42- existed in purified zinc ferrite. Purified zinc ferrite, synthetic zinc ferrite and purchased had different specific surface area, pore volume and average pore size. The specific surface area of synthetic zinc ferrite decreased with the increase of calcination temperature. The three kinds of zinc ferrite had good absorption of ultraviolet light and visible light. Purchased ferric acid had the strongest absorption of UV light and synthetic zinc ferrite had the strongest absorption of visible light, and purified zinc ferrite had the absorption of UV light and visible light between the two. The specific surface area of titanium dioxide prepared by chemical coprecipitation method was greatly affected by calcination temperature. With the increase of calcination temperature, the specific surface area decreased from 123.633 to 28.036m2·g-1, and the average pore diameter was less affected by calcination temperature. For the zinc ferrite/titanium dioxide composite prepared by chemical coprecipitation method, a certain amount of purified zinc ferrite was added to facilitate the absorption of visible light by titanium dioxide.
Therapie der eosinophilen Ösophagitis - Fortschritte und Perspektiven
Authors: Miehlke Stephan , Arnim Ulrike von , Schlag Christoph , Labenz Joachim , Madisch Ahmed
Published: May 2023

In jüngster Zeit wurden in der Therapie der eosinophilen Ösophagitis (EoE) und insbesondere im Bereich der topischen Corticosteroide erhebliche Fortschritte erreicht. Neue EoE-spezifische Darreichungsformen wurden entwickelt und haben in Form der orodispersiblen Budesonid-Tablette zu der ersten in Deutschland und anderen europäischen und außereuropäischen Ländern zugelassenen Therapie der EoE bei Erwachsenen geführt. In den USA steht eine EoE-spezifische orale Budesonid-Suspension kurz vor der Zulassung. Dagegen bleibt die wissenschaftliche Datenlage zur Wirksamkeit von Protonenpumpeninhibtoren weiterhin limitiert. Auch im Bereich der Biologika konnten nach langer Zeit Substanzen identifiziert werden, die erstmals in Phase 2 sehr vielversprechende Ergebnisse gezeigt haben und sich derzeit in klinischen Prüfungen der Phase 3 befinden. In diesem Artikel sollen die aktuellen Fortschritte und Perspektiven in der Therapie der EoE dargestellt und diskutiert werden.
Behandlung extremer maxillärer Retrognathien
Authors: Handschel Jörg , Nienkemper Manuel
Published: May 2023

Extreme maxilläre Retrognathien die häufig eingebettet sind in eine Mittelgesichtshypoplasie stellen ganz besondere Herausforderungen an mögliche Therapieverfahren. Neben den eher seltenen syndromalen Formen der Hypoplasie (z.B. M. Crouzon) stellen die Retrognathien bei Patienten mit Lippen-Kiefer-Gaumenspalten (LKG) sicherlich die häufigste Gruppe dar.
Digitales Design und Herstellung gedruckter Titan-Platten für die kieferorthopädische Therapie: CAD/CAM Mentoplate
Authors: Küffer Maximilian , Wilmes Benedict , Drescher Dieter
Published: May 2023

Die Knochenmorphologie jedes Menschen weist einzigartige Strukturen auf. Deshalb lassen sich Mini-Platten, wie beispielsweise die Mentoplate, nur in stark vereinfachter Form konfektioniert herstellen. Konfektionierte Platten benötigen deshalb eine zeitaufwendige intraoperative Anpassung, um annähernd den knöchernen Strukturen zu entsprechen. Durch Intraoralscans und dreidimensionale Bildgebung lässt sich die anatomische Situation so präzise wiedergeben, dass im CAD/CAM-Verfahren individualisierte Mini-Platten und kieferorthopädische Apparaturen hergestellt werden können. Dies reduziert Risiken und Komplikationen, die mit der Insertion einer Mini-Platte einhergehen können. Da die Mini-Platten zudem mithilfe einer Einsetzhilfe (Insertions-Guide) eingesetzt werden, ermöglicht dies eine präzise Umsetzung geplanter Zahnbewegungen und verringert die Operationsdauer bei der Insertion deutlich. Der vorliegende Artikel beschreibt mögliche digitale Herstellungsverfahren zur Anfertigung individuell gedruckter Mini-Platten und der auf diesen verankerten kieferorthopädischen Apparaturen.
A Case Report of COVID-19-Related Dactylitis Combined with
Chilblain-Like Acral Lesions
Authors: Kulyk Myroslava , Novytska Anna , Potemka Ruslana , Ivashkivskyi Oleksiy , Karasevska Tetyana , Mostbauer Halyna , Dzhus Marta
Published: May 2023

This case report describes the occurrence of symmetrical dactylitis of toes
combined with chilblain-like acral lesions in a 32-year-old female patient 19
days after a mild coronavirus infection. The article addresses existing problems
of managing patients after COVID-19 in daily clinical practice. Scientific
evidence is pointing to a growing number of cases of articular and skin
involvement associated with COVID-19. However, it remains unclear what
approaches to use in the treatment of such patients.
Reduction in Seroma Rate Following Deep Inferior Epigastric Perforator Flap with Umbilectomy Utilizing Progressive Tension Sutures
Authors: Lakatta Alexis C. , Steppe Cyrus , Teotia Sumeet S. , Haddock Nicholas T.
Published: May 2023

Background Umbilectomy has been implemented in both abdominoplasties and deep inferior epigastric perforator (DIEP) flaps to improve abdominal wound healing and better control the location of the neoumbilicus; however, seroma rates are increased. The objective of this study is to compare the seroma rate following DIEP flap reconstruction with umbilectomy when progressive tension sutures (PTS) are implemented.

Methods A retrospective chart review was performed to evaluate postoperative seroma rates in patients undergoing DIEP flap breast reconstruction at a single academic institution between January 2015 and September 2022. All procedures were performed by two senior surgeons. Patients were included if their umbilicus was removed intraoperatively. PTS were utilized in all abdominal closures beginning in late February 2022. Demographics, comorbidities, and postoperative complications were evaluated.

Results A total of 241 patients underwent DIEP flap breast reconstruction with intraoperative umbilectomy. Forty-three consecutive patients received PTS. Overall complications were significantly lower in those who received PTS (p = 0.007). There were no abdominal seromas (0%) in patients who received PTS, whereas 14 (7.1%) occurred without PTS. The use of PTS conferred a decreased likelihood of abdominal seroma (5.687× lower risk, p = 0.017). Additionally, wound formation was significantly lower in those who received PTS (p = 0.031).

Conclusion The use of PTS in the abdominal closure during DIEP flap reconstruction addresses the previously seen rise in seroma rates when concomitant umbilectomy is performed. Decrease in both donor-site wounds and now seroma rates reaffirm the efficacy of removing the umbilicus to improve patient outcomes.
Treatment of Rat Lymphedema by Propeller Lymphatic Tissue Flap Combined with Nanofibrillar Collagen Scaffolds
Authors: Dionyssiou Dimitrios , Nguyen Dung , Topalis Anastasios , Deptula Peter , Paukshto Michael , Zaitseva Tatiana , Demiri Efterpi , Cheva Angeliki , Rockson Stanley
Published: May 2023

Background The aim of our study was to evaluate a new propeller vascularized lymphatic tissue flap (pVLNT) combined with aligned nanofibrillar collagen scaffolds (CS) (BioBridge) in reducing lymphedema in the rat lymphedema model.

Methods Unilateral left hindlimb lymphedema was created in 15 female Sprague–Dawley rats following inguinal and popliteal lymph nodes (LN) resection and radiation. An inguinal pVLNT was elevated from the contralateral groin and transferred through a skin tunnel to the affected groin. Four collagen threads were attached to the flap and inserted in the hindlimb at the subcutaneous level in a fan shape. The three study groups consisted of group A (control), group B (pVLNT), and group C (pVLNT + CS). Volumetric analysis of both hindlimbs was performed using micro-computed tomography imaging before the surgery (at initial time point) and then at 1 and 4 months, postoperatively, and the relative volume difference (excess volume) was measured for each animal. Lymphatic drainage was assessed by indocyanine green (ICG) fluoroscopy for number and morphology of new collectors and the time required for ICG to move from injection point to the midline.

Results Four months after the induction of lymphedema, an increased relative volume difference remained in group A (5.32 ± 4.74%), while there was a significant relative volume reduction in group B (−13.39 ± 8.55%) and an even greater reduction in group C (−14.56 ± 5.04%). ICG fluoroscopy proved the functional restoration of lymphatic vessels and viability of pVLNT in both B and C groups. Notably, only group C demonstrated statistically significant improvements in lymphatic pattern/morphology and in the number of lymphatic collectors as compared with the control group A.

Conclusion The pedicle lymphatic tissue flap combined with SC is an effective procedure for the treatment of lymphedema in rats. It can be easily translated into treatment of humans' lower and upper limb lymphedema and further clinical studies are warranted.
Continuous-Flow Synthesis of Cyclobutenes Using LED Technology
Authors: Baumann Marcus , Smyth Megan , Moody Thomas S. , Wharry Scott
Published: May 2023

Cyclobutenes are highly strained ring systems of considerable synthetic interest that can be accessed via cycloaddition reactions between alkenes and alkynes. However, their traditional preparation relies on photochemical [2+2] cycloadditions that exploit low-wavelength UV radiation emitted from inefficient medium-pressure Hg lamps. This paper reports on the development of a modern approach using a high-power LED set-up emitting at the boundary of UV-A and visible light in conjunction with a continuous-flow reactor. The resulting flow process renders a series of cyclobutenes from maleimides and various commercial alkynes. This provides a more energy-efficient approach that is readily scalable to access multigram quantities of cyclobutenes in high chemical yields and short residence times. The value of these products is exemplified by flow-based hydrogenations yielding highly substituted cyclobutanes which represent sought after building blocks in modern medicinal chemistry programs.
Enantioselective Formal Synthesis of (–)-Catharanthine through Enzyme-Catalyzed Desymmetrization of a meso-Azabicyclo [2.2.2]octane
Authors: Harada Shingo , Gröger Harald , Nemoto Tetsuhiro , Ikeda Kotaro , Hashimoto Yoshinori , Homma Haruka , Kono Masato , Zumbrägel Nadine
Published: May 2023

Iboga-type indole alkaloids are a promising compound group of potentially effective drugs. The common indole-fused pentacyclic skeleton is composed of an isoquinuclidine, and both enantiomers of this architecture are naturally present. In this study, we used enzymatic desymmetrization to obtain an optically active isoquinuclidine possessing four chiral carbon centers from a prochiral diester in one step. In addition, we synthesized a pentacyclic intermediate for catharanthine in an enantioenriched form through the late-stage construction of the common Iboga scaffold.
Synthesis of Trifunctional Thiazole-Fused Anthranilonitrile and Anthranilic Acid Derivatives
Authors: Besson Thierry , Broudic Nathan , Pacheco-Benichou Alexandra , Fruit Corinne
Published: May 2023

The synthesis of trifunctional isomeric benzothiazoles derived from nitroanthranilic acids and their corresponding anthranilonitrile analogues is studied. Compared to previous work, the reaction sequence affords convenient access to hitherto undescribed 2-cyanobenzothiazoles. For further synthetic applications of these polyfunctional compounds, a hydrolysis–decarboxylation sequence is performed in an acidic medium (HCl or HBr), leading to an enlarged array of relevant building blocks.
Perfusion Changes in Perforator-Based Propeller Flaps
Authors: Bernuth Silvia , Vater Adrian , Fuchs Konrad F. , Meffert Rainer H. , Jakubietz Rafael G.
Published: May 2023

Background To cover soft tissue defects, the perforator-based propeller flap offers the option to rotate healthy tissue into complex wounds. By rotating the flap, the perforator is torqued. As a result, perfusion changes are possible.

Methods A retrospective data analysis of patients was done, who received a propeller flap to cover soft tissue defects of the lower extremity as well as a peri- and postoperative perfusion monitoring with a laser-Doppler-spectrophotometry system. Additionally, patient-specific data were collected.

Results Seven patients were identified. Four patients experienced early complications, two epidermolysis of the distal flap areas, three wound healing disorders, and one partial flap necrosis. Intraoperative perfusion monitoring showed a decline of blood flow after incision of the flap, especially at distal flap site. In case of complications, there were prolonged blood flow declines up to the first postoperative day.

Conclusion Torqueing the perforator by rotating the flap can cause an impairment in inflow and outflow. If the impairment is prolonged, perfusion-associated complications are possible. The identification of a viable perforator is particularly important. In addition, a conservative postoperative mobilization is necessary to compensate for the impaired and adapting outflow.
Recent Applications of Ammonium Ylide Based [2,3]-Sigmatropic and [1,2]-Stevens Rearrangements To Transform Amines into Natural Products
Authors: Schwartz Zachary , Valiton Chelsea , Lovasz Myles , Roberts Andrew G.
Published: May 2023

Ammonium ylide based [2,3]-sigmatropic and [1,2]-Stevens rearrangements enable the transformation of tertiary amines into rearranged and functionalized intermediates en route to many polycyclic natural product targets. Herein, we summarize recent applications of these rearrangement reactions in formal and total synthesis endeavors while highlighting innovative improvements to these transforms.

1 Introduction

2 Ammonium Ylide Based [2,3]-Sigmatropic Rearrangements in Natural Product Synthesis

2.1 (–)-Cephalotaxine

2.2 (±)-Amathaspiramide F

2.3 (–)-Cephalezomine G and Its C3 Epimer

2.4 (±)-Strictamine

2.5 (–)-Doxycycline

3 [1,2]-Stevens Rearrangements Toward Natural Products

3.1 Ring-Expanding [1,2]-Stevens Rearrangements en route to (±)-Tylophorine, (±)-7-Methoxycryptopleurine, and (±)-Xylopinine

3.2 Enantioselective Synthesis of Iboga Alkaloids and (+)-Vinblastine

4 Selected Methodology

4.1 Ammonium Ylide Based [2,3]-Sigmatropic Rearrangements To Form Natural Product Cores

4.2 Cascade Reactions Involving [1,2]-Stevens Rearrangement/ Hofmann-Type Elimination Events

5 Conclusions
Imaging Recommendations for Diagnosis, Staging, and Management of Bone Tumors
Authors: Janu Amit , Patra Anurima , Kumar Mahesh , Gulia Ashish , Kulkarni Suyash , Shetty Nitin Sudhakar , Puri Ajay , Nayak Prakash , Pruthi Manish
Published: May 2023

Primary bone sarcomas account for less than 1% of diagnosed cancers each year. In this era of multiplanar and functional imaging, the approach to the radiographic diagnosis of bone cancers goes much beyond traditional radiography. Radiographs are still the most pertinent part of the initial diagnosis of bone tumors. Multimodal imaging, such as computed tomography (CT) and magnetic resonance imaging (MRI), can help with issues such as complex anatomy, marrow assessment, soft assessment, and better local staging. The emerging imaging modality such as positron emission tomography (PET)-CT/PET-MRI has further transformed the imaging of bone malignancies. Radiologist plays an important role in the workup, staging, and management of bone tumors. The purpose of this article is to review imaging recommendations for better diagnosis, staging, and management of bone tumors.
Hepatic Encephalopathy after Transjugular Intrahepatic Portosystemic Shunt Creation
Authors: Trivedi Surbhi , Lam Katie , Ganesh Ashwin , Hasnain Yasir , Hassan Wassim , Herren Josi , Gaba Ron C.
Published: May 2023

Transjugular intrahepatic portosystemic shunt (TIPS) creation is effective in treating the sequelae of decompensated liver cirrhosis—including medically refractory ascites and variceal bleeding—by decompressing the portal venous system through a manmade portosystemic conduit within the liver. However, the altered physiology in which splenomesenteric blood bypasses intrahepatic portal venous perfusion can precipitate varying degrees of hepatic encephalopathy (HE). While the majority of post-TIPS HE cases can be treated medically, some require escalated management strategies, including endovascular interventions to modify the indwelling TIPS and/or occlude competitive physiologic spontaneous portosystemic shunts. This review article details the epidemiology, risk factors, diagnosis, classification, and treatment of post-TIPS HE.
A Comprehensive Review of Transjugular Intrahepatic Portosystemic Shunt–Related Complications
Authors: Lopera Jorge E.
Published: May 2023

Transjugular intrahepatic portosystemic shunt (TIPS) is one of the most technically complex procedures in interventional radiology, the need to connect two veins with variable anatomy, located in two different planes in hard and many times small cirrhotic livers using a needle, can be quite challenging. Despite more than 30 years of performing TIPS, the complex hemodynamics of the portal system are not fully understood, and sometimes unpredictable alterations of the portal flow can lead to serious unexpected complications. The best strategies to prevent TIPS complications are optimal patient selection, meticulous technique, operator experience, and immediate correction of identified adverse events. The purpose of this article is to review the technical complications with TIPS, the unique complications related to the use of stent grafts, and the late complications after the procedure, with emphasis on ways to prevent and treat them.
How nursing students’ risk perception affected their professional commitment during the COVID-19 pandemic: the mediating effects of negative emotions and moderating effects of psychological capital
Authors: Li Junlong , Huang Changping , Yang Yili , Liu Jie , Lin Xiaojun , Pan Jay
Published: May 2023

Nurses play a pivotal role in the delivery of medical services. Professional commitment is crucial for nursing professionals’ long-term, healthy, and sustainable development. However, nursing students’ professional commitment levels are currently unsatisfactory in China, especially given that the COVID-19 pandemic has posed unprecedented challenges to the profession. Therefore, studies investigating the professional commitment levels of nursing students and the underlying influencing factors are urgently required. This study explored how nursing students’ risk perceptions, negative emotions, and psychological capital affected their professional commitment during the COVID-19 pandemic. A cross-sectional study was conducted among nursing students using risk perception, professional commitment, negative emotions, and psychological capital scales. An analysis of 1142 Chinese nursing students suggested that nursing students’ risk perception positively impacted professional commitment and that negative emotions mediated this association. Importantly, psychological capital moderates the mediating effect of negative emotions and can buffer the negative emotions caused by risk perception. This study demonstrated that effective intervention strategies should be implemented in multiple dimensions such as education, individual, public and society to improve the professional commitment of nursing students.
Single ferroelectric memristor shows synaptic plasticity and habituation
Authors: Johnson-Groh Mara
Published: May 2023

The device mimics habituation behaviors, opening the door to more efficient artificial neural computing.
The three-dimensional multi-parameters controllable auto-focusing-type chiral optical light
Authors: Lin Danping , Tao Shaohua
Published: May 2023

Beams with auto-focusing property and a controllable number of wave lobes are of special significance. In this work, based on the helical phase-tuning and the Airy beam, we generate a chiral optical light, which focuses with both radial and angular self-accelerations. The light using the three-dimensional (3D) velocity to control the propagation dimension and the auto-rotating property of intensity peak for the two transverse dimensions is termed as 3D auto-focusing-type chiral optical light (ACOL), which can be controlled by multi-parameters theoretically and experimentally for possessing the characteristics of chiral, focusing, acceleration, rotation, etc. Owing to these characteristics, the ACOL has promising applications in optical micro-manipulation and super-resolution imaging.
Glass transition of amorphous polymeric materials informed by machine learning
Authors: Hu Anwen , Huang Yongdi , Chen Qionghai , Huang Wanhui , Wu Xiaohui , Cui Lihong , Dong Yining , Liu Jun
Published: May 2023

The glass transition temperature (Tg) is used to determine thermophysical properties of polymer materials and is often considered one of the most important descriptors. Methods for predicting various physical properties of materials based on machine learning algorithms and key molecular descriptors are efficient and accurate. However, it still needs improvements because an overly complex model is less practical and difficult to generalize. In addition, obtaining a large number of samples to achieve accurate predictions remains a challenge due to the complex and lengthy experimental process. In this work, based on Tg of 100 polymers, we use a feature selection algorithm combining FeatureWiz and the least absolute shrinkage and selection operator to quickly select molecular descriptors that are minimally redundant and maximally relevant to Tg. The processed dataset is interpolated from the original dataset using the nearest neighbor interpolation algorithm to solve the data deficiency problem. Finally, the synthetic minority oversampling technique algorithm is used to solve the data imbalance problem. The augmented dataset is used to construct the extreme gradient boosting prediction model to achieve good prediction accuracy. The experimental results demonstrate the robustness of the proposed model and the accuracy of its prediction results.
High-efficient and gate-tunable spin transport in GaN thin film at room temperature
Authors: Wu Qipeng , Lin Di , Chen Mingyu , Li Jin'an , Hu Weilin , Wu Xuefeng , Xu Feiya , Zhang Chunmiao , Cao Yiyan , Li Xu , Wu Yaping , Wu Zhiming , Kang Junyong
Published: May 2023

The emerging semiconductor spintronics has offered a practical routine for developing high-speed and energy-efficient electronic and optoelectronic devices. GaN holds broad prospects for room-temperature spintronic applications due to its weak spin scattering and moderate spin–orbit coupling. However, the development of GaN-based spintronic devices is still hindered by the relatively low spin injection efficiency and gate controllability. In this study, gate-modulated spin transport was achieved in a highly spin-polarized GaN-based non-local spin valve. A maximum spin diffusion length of 510 nm and a high spin polarization of 14.1% was obtained with the CoFeB/MgO tunnel spin injector. By applying gate voltages from −3 to +3 V, the spin-dependent magnetoresistance can be tuned in the range of 1.6–3.9 Ω. The modulation is attributed to the controllable spin relaxation of electrons by the gate electric field. This work has demonstrated high spin polarization and exceptional electric controllability in GaN, pushing forward the research in spin field-effect transistors.
Invariant representations in deep learning for optoacoustic imaging
Authors: Vera M. , González M. G. , Vega L. Rey
Published: May 2023

Image reconstruction in optoacoustic tomography (OAT) is a trending learning task highly dependent on measured physical magnitudes present at sensing time. A large number of different settings and also the presence of uncertainties or partial knowledge of parameters can lead to reconstruction algorithms that are specifically tailored and designed to a particular configuration, which could not be the one that will ultimately be faced in a final practical situation. Being able to learn reconstruction algorithms that are robust to different environments (e.g., the different OAT image reconstruction settings) or invariant to such environments is highly valuable because it allows us to focus on what truly matters for the application at hand and discard what are considered spurious features. In this work, we explore the use of deep learning algorithms based on learning invariant and robust representations for the OAT inverse problem. In particular, we consider the application of the ANDMask scheme due to its easy adaptation to the OAT problem. Numerical experiments are conducted showing that when out-of-distribution generalization (against variations in parameters such as the location of the sensors) is imposed, there is no degradation of the performance and, in some cases, it is even possible to achieve improvements with respect to standard deep learning approaches where invariance robustness is not explicitly considered.
Mimicking bacterial learning and memory in tungsten based two-sided single layers of WSeO, WSeS, WSeSe, and WSeTe
Authors: Turfanda Aykut , Ünlü Hilmi
Published: May 2023

We mimic bacterial learning and memory abilities in tungsten based two-sided single layers of WSeO, WSeS, WSeSe, and WSeTe, where the thickness of the material represents the growth in time. We aim to create a quantum memristor like system to show learning and memory abilities of bacteria with time while it grows. Its governing equation is derived, and it was found to be similar to the gene regulatory response model of the bacteria. Polarization is calculated from the Berry phase theory to plot its relation with the degauss parameter in time, which leads to bow-tie like memory switches similar to phase-change memories. We attribute this behavior to a specific bacteria, that is, Geobacter metallireducens. Mimicking bacteria’s learning and memory abilities will open a way to merge physical intelligence with quantum computing computationally.
An apparatus for probing multipactor in X-band waveguide components
Authors: Gregory A. , Wright D. , Spencer H. , Mankowski J. J. , Dickens J. C. , Stephens J. , Neuber A. A.
Published: May 2023

Rectangular waveguides are susceptible to avalanche-style breakdown via the multipactor phenomenon. The growth in secondary electron density produced via multipactor can damage and destroy RF components. A pulse-adjustable, hard-switched modulator powering an X-band magnetron was utilized to drive a modular experimental setup that enables testing different surface geometries and coatings. Power measurements, taken via diodes, and phase measurements, facilitated via a double-balanced mixer, were integrated into the overall apparatus enabling multipactor detection with high sensitivity and nanosecond temporal resolution. The utilized 150 kW peak microwave source with 2.5 μs pulse width and 100 Hz repetition frequency allows for threshold testing without the need for initial electron seeding. This paper includes the initial results of surface conditioning of the test multipactor gap via electron bombardment.
Effect of nonlinearity and persistence on multiscale irreversibility, non-stationarity, and complexity of time series—Case of data generated by the modified Langevin model
Authors: Petelczyc Monika , Czechowski Zbigniew
Published: May 2023

Stochastic models of a time series can take the form of a nonlinear equation and have a built-in memory mechanism. Generated time series can be characterized by measures of certain features, e.g., non-stationarity, irreversibility, irregularity, multifractality, and short/long-tail distribution. Knowledge of the relationship between the form of the model and features of data seems to be the key to model time series. The paper presents a systematic analysis of the multiscale behavior of selected measures of irreversibility, irregularity, and non-stationarity vs degree of nonlinearity and persistence. As a time series generator, the modified nonlinear Langevin equation with built-in persistence is adopted. The modes of nonlinearity are determined by one parameter and do not change the half-Gaussian form of the marginal distribution function. The expected direct dependencies (sometimes non-trivial) were found and explained using the simplicity of the model. It has been shown that the change in nonlinearity, although subjected to a strong constraint (the same marginal distribution), causes significant changes in the tested markers of irregularity and non-stationarity. However, a synergy of non-linearity and persistence is needed to induce greater changes in irreversibility.
Investigation of free convection flow around near horizontal surfaces using particle image velocimetry
Authors: Jha A. K. , Shukla P. , Ghosh Pradyumna
Published: May 2023

In this work, an analysis of free convection fluid flow characteristics around a flat heated surface, slightly inclined to the horizontal, has been carried out with the help of particle image velocimetry technique. Experiments were performed on a plate immersed in water and subjected to a uniform heat flux. The influence of different inclinations of the plate and heat fluxes on the flow characteristics has been analyzed. Based on the flow characteristics, different regimes—attached, transition, and buoyant plume regime—have been identified. It is observed that the onset of transition increases with the inclination angle and decreases with the heat flux. On the other hand, the length of the transition regime increases with an increase in the inclination angle and heat flux. The plume width or plume regime is found to first decrease due to necking and then increase in the vertical direction due to horizontal diffusion. Also, an increase in heat flux and inclination angle causes an increase in plume width at a particular height from the plate. It is observed that the inner velocity boundary layer thickness decreases in the laminar regime and increases in the transition regime along the length of the plate.
Scalar Breit interaction for molecular calculations
Authors: Sun Shichao , Ehrman Jordan , Zhang Tianyuan , Sun Qiming , Dyall Kenneth G. , Li Xiaosong
Published: May 2023

Variational treatment of the Dirac–Coulomb–Gaunt or Dirac–Coulomb–Breit two-electron interaction at the Dirac–Hartree–Fock level is the starting point of high-accuracy four-component calculations of atomic and molecular systems. In this work, we introduce, for the first time, the scalar Hamiltonians derived from the Dirac–Coulomb–Gaunt and Dirac–Coulomb–Breit operators based on spin separation in the Pauli quaternion basis. While the widely used spin-free Dirac–Coulomb Hamiltonian includes only the direct Coulomb and exchange terms that resemble nonrelativistic two-electron interactions, the scalar Gaunt operator adds a scalar spin–spin term. The spin separation of the gauge operator gives rise to an additional scalar orbit-orbit interaction in the scalar Breit Hamiltonian. Benchmark calculations of Aun (n = 2–8) show that the scalar Dirac–Coulomb–Breit Hamiltonian can capture 99.99% of the total energy with only 10% of the computational cost when real-valued arithmetic is used, compared to the full Dirac–Coulomb–Breit Hamiltonian. The scalar relativistic formulation developed in this work lays the theoretical foundation for the development of high-accuracy, low-cost correlated variational relativistic many-body theory.
Flow patterns and heat transfer in a dielectric liquid inside a planar capacitor under microgravity conditions
Authors: Barry Elhadj B. , Kang Changwoo , Yoshikawa Harunori N. , Mutabazi Innocent
Published: May 2023

Heat transfer in a planar capacitor containing a dielectric liquid subject to an increasing high-frequency voltage and a fixed temperature gradient under microgravity is investigated using direct numerical simulations. When the intensity of the applied voltage exceeds a critical value, the dielectrophoretic force induces thermoelectric convection in the form of stationary vortices. The increase in the voltage leads to different types of convective patterns and to the increase in the heat transfer coefficient between the electrodes of the capacitor.
Nernst–Ettingshausen effect in thin Pt and W films at low temperatures
Authors: Luo Renjie , Legvold Tanner J. , Chen Liyang , Natelson Douglas
Published: May 2023

As spin caloritronic measurements become increasingly common techniques for characterizing material properties, it is important to quantify potentially confounding effects. We report measurements of the Nernst–Ettingshausen response from room temperature to 5 K in thin film wires of Pt and W, metals commonly used as inverse spin Hall detectors in spin Seebeck characterization. Johnson–Nyquist noise thermometry is used to assess the temperature change in the metals with heater power at low temperatures, and the thermal path is analyzed via finite-element modeling. The Nernst–Ettingshausen response of W is found to be approximately temperature-independent, while the response of Pt increases at low temperatures. These results are discussed in the context of theoretical expectations and the possible role of magnetic impurities in Pt.