bluuebunny/crossref_metadata_2025 huggingface dataset:
Hybrid automatic repeat request‐based intelligent reflecting surface‐assisted communication system
Authors: Ai Yun , Mohamed Marshed , Kong Long , Al‐Saman Ahmed , Cheffena Michael
Published: January 2021

The intelligent reflecting surface (IRS) is an emerging technique to extend wireless coverage. In this letter, the performance of the hybrid automatic repeat request (hybrid ARQ) for an IRS‐assisted system is analysed. More specifically, the outage performance of the IRS‐aided system using hybrid ARQ protocol with chase combining is studied. The asymptotic analysis also shows that the outage performance is better and improves linearly by increasing the number of reflectors of the IRS‐aided system. The results also verify the potential of combining the ARQ scheme in the link layer of the IRS‐aided system and demonstrate that a very small change of path loss condition can impact the performance largely.
Cogging torque reduction based on segmented skewing magnetic poles with different combinations of pole‐arc coefficients in surface‐mounted permanent magnet synchronous motors
Authors: Xing Zezhi , Wang Xiuhe , Zhao Wenliang
Published: January 2021

The calculation and reduction of cogging torque are fundamental to the evaluation and optimisation of motor performance. Considering that the accuracy of the cogging torque calculated by analytical method (AM) is low, an accurate calculation model of the effective air‐gap length considering the actual stator slot structure and suitable for any motor is proposed, the cogging torque of 6p36s surface‐mounted permanent magnet synchronous motor (SPMSM) are calculated accurately and verified by finite element method (FEM). Furthermore, the segmented skewing magnetic poles with different combinations of pole‐arc coefficients are designed to weaken cogging torque, and the optimal combination of pole‐arc coefficients and tilting angle of the adjacent magnetic poles are summarised by AM and particle swarm optimisation (PSO) algorithm. Finally, the cogging torques of six SPMSMs with different slot‐pole combinations including 6p36s, 4p36s, 6p9s, 8p9s, 8p12s and 10p12s are analysed, and the results indicate that the cogging torque can be greatly weakened based on segmented skewing magnetic poles with different combinations of pole‐arc coefficients, and other performances of the motors are basically not affected.
Medium frequency diode rectifier unit based HVDC transmission for offshore wind farm integration
Authors: Zhang Zheren , Tang Yingjie , Xu Zheng
Published: January 2021

The offshore wind farms are the main trend of the wind power development in the future. The medium frequency diode rectifier unit based high voltage direct current transmission system is proposed here for offshore wind farm integration. Unlike conventional high voltage direct current solutions, the rated frequency of the offshore alternating current (AC) grid is increased to about 100∼400 Hz in the proposed system. Besides, a grid‐forming control scheme for the wind turbine converters is also proposed in this paper, where the machine side converter controls the direct current (DC) voltage and the grid side converter controls its output alternating current voltage in the global unified reference coordinate system. As a result, smaller and lighter passive components, such as the transformers, alternating current filters and reactive power (VAR) compensators, could be adopted in the offshore grid, which is beneficial for achieving higher economic efficiency. The small stability analysis and the time domain simulation of the proposed system are carried out based on a simplified model and power systems computer aided design/electromagnetic transients including DC (PSCAD/EMTDC) respectively, and the feasibility of the proposed schemes is verified.
Linear multi‐vector model‐based predictive control for grid side converters of renewable power plants under severe grid disturbances
Authors: Ramirez Dionisio , Castillo Rafael De Jesus , Zarei Mohammad Ebrahim , Serrano Javier
Published: January 2021

Grid side converters of renewable power plants have to be capable of dealing with severe grid disturbances, such as, grid faults and voltage sags. Model‐based predictive control provides outstanding performance to grid side converters: fast dynamic response, good tracking error and high‐quality currents. However, choosing the best set of vectors for the modulation requires assessing all the possible combinations of vectors using a cost function, which is very time consuming. Thus, the modulation is normally carried out with only 1 or 2 vectors per PWM period to save computing time, but this turns the modulation non‐linear. This lack of linearity makes it impossible to use symmetrical components in unbalanced grids. A linear multi‐vector model‐based predictive control that controls the power of both sequences using a sole cost function and analyses the effect of the transient response of several sequence decomposition systems on the model‐based predictive control predictions and dynamic response is proposed. Moreover, the proposed multi‐vector provides low THD currents while keeping the computing time low. In addition, the paper addresses the extrapolation of the proposed multi‐vector model‐based predictive control to N‐level converters. The good performance obtained is supported by the results obtained in simulations and the laboratory.
Wake‐effect aware optimal online control of wind farms: An explicit solution
Authors: Chen Kaixuan , Qiu Yiwei , Lin Jin , Liu Feng , Zhao Xiaowei , Song Yonghua
Published: January 2021

Wake effects impose significant aerodynamic interactions among wind turbines. To improve the wind farm operating performance, practical wind farm online control considering wake effects becomes very important. To achieve online optimal wind farm control while responding to grid demands, this paper proposes a novel optimal wind farm supervisory control (SC) model and its explicit solutions. From the controller modelling perspective, the two major wind farm operating modes, the maximum power point tracking mode and the set‐point tracking mode, are first analysed and unified in one optimisation model while considering wake effects. In this way, wind farm power production and rotor kinetic energy reserve can be simultaneously considered to conveniently modify the operation mode in response to different grid demands. Aside from controller modelling, the collocation method is first introduced to address the online application problem of such wake‐effect aware optimal WF control. Although a few optimisation algorithms have been proposed to find the optimum offline, online optimal control is still challenging because of the computational complexity brought by wake model non‐linearity and non‐convexity. The proposed collocation method explicitly approximates the optimal solutions to the proposed supervisory control model, through which only a direct algebraic operation is required for online optimal control instead of repeated optimisations. Case studies are carried out on different wind farms under various wind conditions, showing that the wind farm power production potential and releasable power reserve are improved compared to traditional greedy control in both modes. The accuracy of the collocation method is verified. A detailed analysis of the wind farm production capacity under different wind speeds and directions is also provided.
Ultra‐short‐term multi‐step wind power forecasting based on CNN‐LSTM
Authors: Wu Qianyu , Guan Fei , Lv Chen , Huang Yongzhang
Published: January 2021

The fluctuation and intermission of large‐scale wind power integration is a serious threat to the stability and security of the power system. Accurate prediction of wind power is of great significance to the safety of wind power grid connection. This study proposes a novel spatio‐temporal correlation model (STCM) for ultra‐short‐term wind power prediction based on convolutional neural networks‐long short‐term memory (CNN‐LSTM). The original meteorological factors at multi‐historical time points of different sites throughout the target wind farm can be reconstructed into the input window of the model, and thus a new data reconstruction method is represented. CNN is used to extract the spatial correlation feature vectors of meteorological factors of different sites and the temporal correlation vectors of the meteorological features in ultra‐short term, which are reconstructed in time series and used as the input data of LSTM. Then, LSTM extracts the temporal feature relationship between the historical time points for multi‐step wind power forecasting. The STCM based on CNN‐LSTM proposed in this study is suitable for wind farms that can collect meteorological factors at different locations. Taking the measured meteorological factors and wind power dataset of a wind farm in China as an example, four evaluation metrics of the CNN‐LSTM model, CNN and LSTM individually used for multi‐step wind power prediction, are obtained. The results show that the proposed STCM based on CNN‐LSTM has better spatial and temporal characteristics extraction ability than the traditional structure model and can forecast the power of wind farm more accurately.
Control of solar PV‐integrated battery energy storage system for rural area application
Authors: Chauhan Shubhra , Singh Bhim
Published: January 2021

The inaccessibility of a utility grid is the challenge for rural and remote areas. This work presents the application of solar photovoltaic (PV) integrated battery energy storage (BES) for rural area electrification. The addition of a BES at DC link, is realised by means of a DC–DC bidirectional converter. The BES is discharged/charged in accordance with the solar PV generation and load variations. This converter control also maintains the voltage for the maximum power point tracking (MPPT) with perturb and observe (P & O) control at the DC link. The voltage source converter (VSC) works by means of voltage control algorithm in a solar PV‐BES system. The system manages the power for the load network with frequency and voltage regulation by the non‐ideal discrete proportional and resonant controller (PR). The fundamental component from the load current, is acquired using an adaptive digital filter, which improves the power quality. The utilization of buck‐boost converter with an optimum BES rating as related to the system, when it is linked directly at the VSC DC link. The system's operations at steady state and dynamic circumstances i.e. solar insolation change and load variation, load disconnection, are authenticated with test results on a developed prototype.
A current sensor based adaptive step‐size MPPT with SEPIC converter for photovoltaic systems
Authors: Kumar Vipin , Ghosh Sandip , Naidu N. K. Swami , Kamal Shyam , Saket R. K. , Nagar S. K.
Published: January 2021

Efficient maximum power point tracking (MPPT) is an important problem for renewable power generation from photovoltaic systems. In this work, a current sensor based MPPT algorithm using an adaptive step‐size for a single ended primary inductance converter (SEPIC) based solar photovoltaic system is proposed. Due to lower sensitivity of power to current perturbation as compared to the voltage one, such a scheme is shown to yield better efficiency at steady‐state. A new adaptation scheme is also proposed for faster convergence of the MPPT technique. Hence, the proposed scheme yields better transient as well as steady‐state performance. A prototype converter is used along with digital implementation of the proposed MPPT technique to demonstrate the superiority of the proposed algorithm over the fixed step‐size and voltage based ones. Simulation and experimental results corroborates the same.
High-resolution international LOFAR observations of 4C 43.15
Authors: Sweijen F. , Morabito L. K. , Harwood J. , van Weeren R. J. , Röttgering H. J. A. , Callingham J. R. , Jackson N. , Miley G. , Moldon J.
Published: January 2021

It has long been known that radio sources with the steepest spectra are preferentially associated with the most distant galaxies, the α − z relation, but the reason for this relation is an open question. The spatial distribution of spectra in high-z radio sources can be used to study this relation, and low-frequency observations are particularly important in understanding the particle acceleration and injection mechanisms. However, the small angular sizes of high-z sources together with the inherently low resolution of low-frequency radio telescopes until now has prevented high angular resolution low-frequency observations of distant objects. Here we present subarcsecond observations of a z = 2.4 radio galaxy at frequencies between 121 and 166 MHz. We measure the spatial distribution of spectra, and discuss the implications for models of the α−z relation. We targeted 4C 43.15 with the High Band Antennas of the International LOFAR Telescope with a range of baselines up to 1300 km. At the central frequency of 143 MHz we achieve an angular resolution of ~0.3″. By complementing our data with archival Very Large Array data we study the spectral index distribution across 4C 43.15 between 55 MHz and 8.4 GHz at resolutions of 0.4″ and 0.9″. With a magnetic field strength of B = 5.2 nT and fitted injection indices of αinjnorth = −0.8 and αinjsouth = −0.6, fitting a Tribble spectral ageing model results in a spectral age of τspec = 1.1 ± 0.1 Myr. We conclude that our data on 4C 43.15 indicates that inverse Compton losses could become comparable to or exceed synchrotron losses at higher redshifts and that inverse Compton losses could be a viable explanation for the α−z relation. Statistical studies of these objects will become possible in the future when wide-area subarcsecond surveys start.
Functional Hypogonadism and Testosterone Deficiency in Aging Males With and Without HIV-infection
Authors: Postel Nils , Wolf Eva , Balogh Annamaria , Obermeier Martin , Degen Olaf , Mayr Christoph , Baumgarten Axel , Pauli Ramona , Mueck Birgit , Jaeger Hans , Noe Sebastian
Published: January 2021

Introduction HIV infection has become a chronic, well-treatable disease and the focus of caretakers has shifted to diagnosis and treatment of comorbidities. Hypogonadism in elderly men with HIV might be of particular relevance, however, little is known about its epidemiology in contrast to non-infected peers and men with other chronic medical conditions, such as type 2 diabetes. This study aimed at comparing the prevalence of testosterone deficiency and functional hypogonadism in men ≥ 50 years in these three groups.

Patients and Methods Multi-center, cross-sectional substudy of the German-wide 50/2010 study, including men aged 50 years or older with HIV-infection, type 2 diabetes, and controls.

Results Altogether, 322 men were included (mean age: 62 years (SD±7.9)). The prevalence of testosterone deficiency in men living with HIV, type 2 diabetes, and controls was 34.5, 44.9, and 35.0%, respectively; the prevalence of functional hypogonadism was 7.7, 14.3 and 3.5%, respectively. Single-factor ANOVA demonstrated significant differences between the groups for total testosterone (p<0.001), SHBG (p<0.001), as well as for free testosterone concentrations (p=0.006). Comorbidities were, however, most important single factor in multi-factor analysis.

Discussion Despite a comparable prevalence of testosterone deficiency, functional hypogonadism was more frequent in men living with HIV when compared to non-infected controls. This was the result of a higher burden of symptoms that might, however, also be secondary to other conditions. Number of comorbidities was a more important factor than belonging to one of the groups.
Hausarztzentrierte Rehabilitationsnachsorge bei chronischen Rückenschmerzen
Authors: Weier Lisa , Steinhäuser Jost , Träder Jens-Martin , Deck Ruth
Published: January 2021

Hintergrund Rückenschmerzen gehören in Deutschland zu den häufigsten und kostenintensiven Gesundheitsstörungen. Rehabilitationsmaßnahmen bei Rückenschmerzen sind oft nur kurzfristig wirksam. Das Nachsorgekonzept „Neues Credo“ hat sich bei der Steigerung der Langzeiteffekte als erfolgversprechend erwiesen. In der aktuellen Studie wurde es in Hausarztpraxen erprobt und evaluiert.

Methodik Es wurde eine prospektive Beobachtungsstudie durchgeführt. Beteiligt waren 9 orthopädische Rehabilitationseinrichtungen und N=178 Hausärzte, die die Nachsorge begleiten. Die Evaluation der Intervention erfolgte durch schriftliche Befragungen von 85 Rehabilitanden mit chronischen Rückenschmerzen zu drei Messzeitpunkten. Hauptzielkriterien waren Funktionskapazität und Teilhabe, als sekundäre Zielgrößen wurden u. a. Parameter der subjektiven Gesundheit und körperliche Aktivität herangezogen. Die Auswertung der Langzeiteffekte erfolgte mit Varianzanalysen mit Messwiederholung.

Ergebnisse Am Ende der Rehabilitation zeigen sich im primären Outcome Funktionskapazität eine signifikante Verbesserung kleiner Größenordnung, in allen sekundären Zielgrößen signifikante mittlere bis große Effekte. Im Katamnesezeitraum konnten die Teilnehmer ihre körperliche Aktivität signifikant steigern. Vor allem im Bereich Ausdauersport und Krafttraining. Zwölf Monate nach der Rehabilitation sind bei allen Outcomes immer noch signifikante Verbesserungen festzustellen, es werden Effekte kleiner Größenordnung erreicht, die im Hinblick auf ihre klinische Relevanz etwas unterhalb der üblichen Schwelle für minimal bedeutsame Unterschiede liegen.

Schlussfolgerungen Rehabilitationsnachsorge im Sinn des Neuen Credo, welche durch den Hausarzt unterstützt wird, zeigt ebenso nachhaltige Effekte, wie die Begleitung durch die Rehabilitationseinrichtung. Die Erfolge lassen 12 Monate nach der Rehabilitation zwar wieder etwas nach, bei allen erfassten Merkmalen sehen wir aber signifikante Unterschiede im Vergleich zur Ausgangslage. Die hohe Zufriedenheit von Hausärzten und Rehabilitanden sprechen für das Konzept. Da Hausärzte die unmittelbaren Ansprechpartner nach einer Rehabilitationsmaßnahme darstellen, wäre ein Transfer in die Routine vielversprechend.
Erfolge der Rehabilitation bei chronischen nichtspezifischen Rückenschmerzen in Deutschland – Metaanalysen der Verläufe von Schmerzintensität und Funktionskapazität
Authors: Höder Jürgen
Published: January 2021

Ziele Wie verändern sich Schmerzintensität und Funktionskapazität nach einer Rehabilitation wegen chronischer nichtspezifischer Rückenschmerzen? Sind die Veränderungen von praktischer Relevanz für Lebensqualität und Teilhabeprobleme? Sind sie größer als Plazeboeffekte?

Methodik Es wurden Metaanalysen von kurz-, mittel- und langfristigen Verläufen aus Rehastudien mit standardisierten Mittelwertdifferenzen und MID-Units durchgeführt, ferner Metaanalysen von Verläufen unter Scheintherapien. Außerdem wurden nicht standardisierte Effektmaße und das Ausmaß von Reliable Change bestimmt.

Ergebnisse Für Schmerzintensität ergaben sich kurzfristig mittlere, langfristig kleine Effekte, für Funktionskapazität kurzfristig kleine, langfristig keine Effekte. Die Veränderungen waren zu keinem Zeitpunkt von praktischer Relevanz. Scheinbehandlungen erzielten ähnliche Ergebnisse.

Schlussfolgerung Der typische Rehabilitand erfährt keine bedeutsamen Verbesserungen in den Bereichen Schmerzlinderung und Funktionsfähigkeit, ein kleinerer Teil erzielt Erfolge in der Größenordnung von Plazeboeffekten.
AGE–RAGE Stress and Coronary Artery Disease
Authors: Prasad Kailash
Published: January 2021

Coronary artery atherosclerosis and atherosclerotic plaque rupture cause coronary artery disease (CAD). Advanced glycation end products (AGE) and its cell receptor RAGE, and soluble receptor (sRAGE) and endogenous secretory RAGE (esRAGE) may be involved in the development of atherosclerosis. AGE and its interaction with RAGE are atherogenic, while sRAGE and esRAGE have antiatherogenic effects. AGE–RAGE stress is a ratio of AGE/sRAGE. A high AGE–RAGE stress results in development and progression of CAD and vice-versa. AGE levels in serum and skin, AGE/sRAGE in patients with CAD, and expression of RAGE in animal model of atherosclerosis were higher, while serum levels of esRAGE were lower in patients with CAD compared with controls. Serum levels of sRAGE in CAD patients were contradictory, increased or decreased. This contradictory data may be due to type of patients used, because the sRAGE levels are elevated in diabetics and end-stage renal disease. AGE/sRAGE ratio is elevated in patients with reduced or elevated levels of serum sRAGE. It is to stress that AGE, RAGE, sRAGE, or esRAGE individually cannot serve as universal biomarker. AGE and sRAGE should be measured simultaneously to assess the AGE–RAGE stress. The treatment of CAD should be targeted at reduction in AGE levels, prevention of AGE formation, degradation of AGE in vivo, suppression of RAGE expression, blockade of RAGE, elevation of sRAGE, and use of antioxidants. In conclusion, AGE–RAGE stress would initiate the development and progression of atherosclerosis. Treatment modalities would prevent, regress, and slow the progression of CAD.
Olfactory Outcomes after Resection of Tuberculum Sella and Planum Sphenoidale Meningiomas via a Transcranial Approach
Authors: Ved Ronak , Mo Matthew , Hayhurst Caroline
Published: January 2021

Objectives Controversy exists surrounding the optimal approaches to tuberculum sella meningioma (TSM) and planum meningioma (PM). Olfaction is infrequently considered within this context but is nonetheless an important quality of life measure. The evolution of olfactory outcomes following contemporary transcranial surgery remains unclear. This study reviews olfactory outcomes after supraorbital craniotomy for TSM or PM and defines temporal trends in its recovery.

Study Design A prospective study of a patients who underwent a minimally invasive supraorbital craniotomy for TSM or PM was conducted at a single neurosurgical center.

Participants & Main Outcome Measures All patients were questioned about olfaction at presentation 3 months postoperatively, 12 months postoperatively, and annually thereafter (median follow-up = 37 months). The olfactory status of patients was categorized as normosmia, anosmia, hyposmia, parosmia, (altered perception of odours), or phantosmia, (olfactory hallucinations).

Results Twenty-two patients were included in the study analysis, (range = 27–76). Precisely, 3 months after surgery, seven patients had normal olfaction (32%). Six patients were anosmic, (27%) four hyposmic, (18%), three parosmic, (14%), and two were phantosmic (9%). At 1-year follow-up, almost half of patients (10; 48%) were normosmic, while two patients (9.5%) were anosmic. There were no further improvements in olfaction between 1 year and long-term follow-up.

Conclusion Subfrontal transcranial approaches for TSM or PM appear to be associated with changes in olfaction that can improve with time; these improvements occur within the first year after surgery. Impacts upon olfaction should be considered when selecting a surgical approach and patients counseled appropriately.
Predictive modeling of religiosity, prosociality, and moralizing in 295,000 individuals from European and non-European populations
Authors: Jacquet Pierre O. , Pazhoohi Farid , Findling Charles , Mell Hugo , Chevallier Coralie , Baumard Nicolas
Published: January 2021

Why do moral religions exist? An influential psychological explanation is that religious beliefs in supernatural punishment is cultural group adaptation enhancing prosocial attitudes and thereby large-scale cooperation. An alternative explanation is that religiosity is an individual strategy that results from high level of mistrust and the need for individuals to control others’ behaviors through moralizing. Existing evidence is mixed but most works are limited by sample size and generalizability issues. The present study overcomes these limitations by applying k-fold cross-validation on multivariate modeling of data from >295,000 individuals in 108 countries of the World Values Surveys and the European Value Study. First, this methodology reveals no evidence that European and non-European religious people invest more in collective actions and are more trustful of unrelated conspecifics. Instead, the individuals’ level of religiosity is found to be weakly but positively associated with social mistrust and negatively associated with the production of behaviors, which benefit unrelated members of the large-scale community. Second, our models show that individual variation in religiosity is well explained by the interaction of increased levels of social mistrust and increased needs to moralize other people’s sexual behaviors. Finally, stratified k-fold cross-validation demonstrates that the structures of these association patterns are robust to sampling variability and reliable enough to generalize to out-of-sample data.
Mg and Ni incorporated ZnO diluted magnetic semiconductor for magnetic and photo-catalytic applications
Authors: Iqbal Tahir , Irfan M. , Ramay Shahid M. , Alhamidi Abdullah , Shaikh Hamid , Saleem Murtaza , Siddiqi Saadat A.
Published: January 2021

Zinc oxide is recently being used as a magnetic semiconductor with the introduction of mag- netic elements. In this work, we report phase pure synthesis of Mg and Ni co-substituted ZnO to explore its structure, optical, magnetic and photo-catalytic properties. X-ray diffraction analysis reveals the hexagonal wurtzite type structure having P63mc space group without any impurity phase. UV-Vis spectrophotometry demonstrates the variation in bandgap with the addition of Mg and Ni content in ZnO matrix. Magnetic measurements exhibit a clear boosted magnetization in Ni and Mg co-doped compositions with its stable value of bandgap corroborating the structural stability and magnetic tuning for its advanced applications in modern-day spintronic devices. Photo-catalytic measurements performed using methyl green degradation demonstrate an enhanced trend of activity in Mg and Ni co-doped compositions.
Impact of channel length and width for charge transportation of graphene field effect transistor
Authors: Hosen Kamal , Islam Md. Rasidul , Liu Kong
Published: January 2021

The effect of channel length and width on the large and small-signal parameters of the graphene field effect transistor have been explored using an analytical approach. In the case of faster saturation as well as extremely high transit frequency, the graphene field effect transistor shows outstanding performance. From the transfer curve, it is observed that there is a positive shift of Dirac point from the voltage of 0.15 V to 0.35 V because of reducing channel length from 440 nm to 20 nm and this curve depicts that graphene shows ambipolar behavior. Besides, it is found that because of widening channel the drain current increases and the maximum current is found approximately 2.4 mA and 6 mA for channel width 2 µm and 5 µm respectively. Furthermore, an approximate symmetrical capacitance-voltage (C-V) characteristic of the graphene field effect transistor is obtained and the capacitance reduces when the channel length decreases but the capacitance can be increased by raising the channel width. In addition, a high transconductance, that demands high-speed radio frequency (RF) applications, of 6.4 mS at channel length 20 nm and 4.45 mS at channel width 5 µm along with a high transit frequency of 3.95 THz have been found that demands high-speed radio frequency applications.
Direct measurements of the 3D plasma velocity in single-helical-axis RFP plasmas
Authors: Boguski J. , Nornberg M. D. , Gupta U. , McCollam K. J. , Almagri A. F. , Chapman B. E. , Craig D. , Nishizawa T. , Sarff J. S. , Sovinec C. R. , Terry P. W. , Xing Z. A.
Published: January 2021

The first local velocity measurements of helical equilibrium plasmas in the Reversed Field Pinch (RFP) Single Helical Axis (SHAx) state using a Charge Exchange Recombination Spectroscopy (CHERS) diagnostic are presented. Measurements show strong axisymmetric and non-axisymmetric flow, with n = 5 components of flow related to the (m,n)=(1,5) dominant magnetic mode on the order of the axisymmetric flow in certain regions of the plasma, as well as significant n > 5 flow. Flow measurements are compared with NIMROD simulations of visco-resistive, single-fluid MHD in toroidal and cylindrical geometries with limited axial periodicity. Both measurements and the simulation with toroidal geometry show stronger inboard flows relative to the outboard flows, which is attributed to the toroidal geometry of the device. In the experiment, the n = 5 component of flow is phase shifted from the reconnection-like flow pattern observed in the single-fluid simulations, possibly due to decoupling of the ion and electron fluids over much of the plasma. Finally, the strength of the helical angular flow shear relative to the critical shear necessary to disrupt nonlinear coupling between tearing modes is calculated around the helical magnetic axis. The shear in the measured flow is on the order of the theoretical critical threshold needed to nonlinearly decouple modes, but the measurement uncertainty in the gradient of the flow is large.
Imaging confined and bulk p-type/n-type carriers in (Al,Ga)N heterostructures with multiple quantum wells
Authors: Minj A. , Zhao M. , Bakeroot B. , Paredis K.
Published: January 2021

The current state of dopant assessment for the optimization of the III-nitride-based heterostructures for high frequency, high power, and light emission applications relies heavily on quantitative chemical analysis techniques. In such complex heterostructures, determination of p-type carrier density of the cap layer, control of background concentration, and assessment of polarization induced confined carriers are necessary for the realization of optimal devices. None of these can be completely inferred from chemical analysis owing to several material and growth issues including poor activation of Mg, presence of O impurities, and amphoteric nature of carbon impurities. Here, as regions of interest require nanometer resolution, especially near the interfaces featuring triangular quantum wells and exhibiting electron/hole confinement, exploitation of the behavior of the nanosize metal–semiconductor junction formed between the metallic scanning probe microscopy probe and the III-nitride surface is promising for carrier determination. By combining two techniques sensitive to local change in capacitance and rectifying characteristic of conduction at the nanoscale, the nature of free carriers originating from extrinsic n-type and p-type dopants and polarization induced confined carriers, two-dimensional electron gas and hole gas, were eventually revealed across III-nitride heterostructures.
Multi-headed loop chimera states in coupled oscillators
Authors: Dudkowski Dawid , Czołczyński Krzysztof , Kapitaniak Tomasz
Published: January 2021

In this paper, we introduce a novel type of chimera state, characterized by the geometrical distortion of the coherent ring topology of coupled oscillators. The multi-headed loop chimeras are examined for a simple network of locally coupled pendulum clocks, suspended on the vertical platform. We determine the regions of the occurrence of the observed patterns, their structure, and possible co-existence. The representative examples of behaviors are shown, exhibiting the variety of configurations that can be observed. The statistical analysis of the solutions indicates the geometrical regions of the system with the highest probability of the chimeras’ occurrence. We investigate the mechanism of the creation of the observed states, showing that the manipulation of the initial positions of chosen pendula may induce the desired patterns. Apart from the study of the isolated network, we also discuss the scenario of the movable platform, showing a possible influence of the global coupling structure on the stability of the observed states. The stability of loop chimeras is examined for varying both the amplitude and the frequency of the oscillations of the platform. We indicate the excitation parameters for which the solutions can survive as well as be destroyed. The bifurcation analysis included in the paper allows us to discuss the transitions between possible behaviors. The appearance of multi-headed loop chimeras is generalized into large networks of oscillators, showing the universal character of the observed patterns. One should expect to observe similar results also in other types of coupled oscillators, especially the mechanical ones.
On the theory of charge transport and entropic effects in solvated molecular junctions
Authors: Sowa Jakub K. , Marcus Rudolph A.
Published: January 2021

Experimental studies on single-molecule junctions are typically in need of a simple theoretical approach that can reproduce or be fitted to experimentally measured transport data. In this context, the single-level variant of the Landauer approach is most commonly used, but methods based on Marcus theory are also gaining popularity. Recently, a generalized theory unifying these two approaches has also been developed. In the present work, we extend this theory so that it includes entropic effects (which can be important when polar solvents are involved but are likely minor for solid-state systems). We investigate the temperature-dependence of the electric current and compare it to the behavior predicted by the Landauer and the conventional Marcus theory. We argue that this generalized theory provides a simple yet effective framework for understanding charge transport through molecular junctions. Furthermore, we explore the role of the entropic effects in different transport regimes and suggest experimental criteria for detecting them in solvated molecular junctions. Finally, in order to account for nuclear tunneling effects, we also demonstrate how lifetime broadening can be introduced into the Marcus–Levich–Dogonadze–Jortner-type description of electron transport.
Interaction between dual spherical particles during settling in fluid
Authors: Liu Jieqing , Zhang Pei , Xiao Yang , Wang Zhihao , Yuan Saiyu , Tang Hongwu
Published: January 2021

Settling of solid particles in the fluid is one of the most basic forms of sediment transport. However, due to the complex particle–particle and particle–fluid interactions, the mechanism of settling is not yet fully understood. This study focuses on characterizing the dynamics of dual particles settling side by side. Both settling experiments and simulations are conducted with different initial spacings between particles and Reynolds numbers (Re). The range of Re is from 30 to 300, which corresponds to the transition zone between the Stokes and the Newton regime. Particle tracking velocimetry and particle image velocimetry are used in the experiments to determine particles’ trajectories and velocity fields around particles. A new electromagnetic release device is manufactured, which ensures accurate control of the initial condition. Together with the experiments, settling processes of particles are simulated based on discrete element–lattice Boltzmann method to investigate detailed flow structures. The results show that no attraction exists between particles when released simultaneously side by side. The repulsion between the two particles is a result of the asymmetry between the inside and outside vortices, and this repulsion will vanish when the initial spacing exceeds 5 particle diameters. Depending on the repulsion between particles, the settling process can be divided into three stages. The results also demonstrate that the initial spacing of the particles and Re are the two key parameters in the determination of the final settling velocity and separation distance. Their influence can be separated into two phase regimes depending on a critical Re (≈60), which is consistent with the one for the appearance of the Karman vortex street. In regime I (Re < 60), the settling process is dominated by viscous effects, and the effect of vortex interaction starts to take dominance in regime II (Re > 60). Overall, small initial spacing and large Re lead to strong repulsion between particles.
Broadband adiabatic inversion experiments for the measurement of longitudinal relaxation time constants
Authors: Altenhof Adam R. , Jaroszewicz Michael J. , Harris Kristopher J. , Schurko Robert W.
Published: January 2021

Accurate measurements of longitudinal relaxation time constants (T1) in solid-state nuclear magnetic resonance (SSNMR) experiments are important for the study of molecular-level structure and dynamics. Such measurements are often made under magic-angle spinning conditions; however, there are numerous instances where they must be made on stationary samples, which often give rise to broad powder patterns arising from large anisotropic NMR interactions. In this work, we explore the use of wideband uniform-rate smooth-truncation pulses for the measurement of T1 constants. Two experiments are introduced: (i) BRAIN-CPT1, a modification of the BRAIN-CP (BRoadband Adiabatic-INversion-Cross Polarization) sequence, for broadband CP-based T1 measurements and (ii) WCPMG-IR, a modification of the WURST-CPMG sequence, for direct-excitation (DE) inversion-recovery experiments. A series of T1 constants are measured for spin-1/2 and quadrupolar nuclei with broad powder patterns, such as 119Sn (I = 1/2), 35Cl (I = 3/2), 2H (I = 1), and 195Pt (I = 1/2). High signal-to-noise spectra with uniform patterns can be obtained due to signal enhancements from T2eff-weighted echo trains, and in favorable cases, BRAIN-CPT1 allows for the rapid measurement of T1 in comparison to DE experiments. Protocols for spectral acquisition, processing, and analysis of relaxation data are discussed. In most cases, relaxation behavior can be modeled with either monoexponential or biexponential functions based upon measurements of integrated powder pattern intensity; however, it is also demonstrated that one must interpret such T1 values with caution, as demonstrated by measurements of T1 anisotropy in 119Sn, 2H, and 195Pt NMR spectra.
Crystalline structure and magnetic properties of pyrite FeS2
Authors: Choi Hyunkyung , Seo Jae Yeon , Uhm Young Rang , Sun Gwang Min , Kim Chul Sung
Published: January 2021

Iron pyrite (FeS2) has attracted significant attention as a promising inorganic material in various applications, such as electrode materials for high-energy batteries, medical diagnostics, semiconductor materials, and photovoltaic solar cells. In this study, we characterized the crystalline structure and magnetic properties of FeS2 using X-ray diffraction (XRD), vibrating sample magnetometry, and Mössbauer spectroscopy. The refined XRD patterns confirmed that the crystalline structure of FeS2 was cubic (Pa-3 space group) with lattice constant a0 = 5.417 Å. The temperature dependence of the zero-field-cooled and field-cooled curves and the hysteresis loops were measured at various temperatures between 4.2 and 295 K. The Mössbauer spectra collected in the temperature range of 4.2–500 K were fitted with one doublet. The ΔEQ values increased slightly with decreasing temperature owing to changes in the Fe–S distance. The charge state was determined to be Fe2+ based on the isomer shift (δ).
US government acts to reduce dependence on China for rare-earth magnets
Authors: Kramer David
Published: January 2021

Although the US has sufficient raw materials, the domestic supply chain to alloy and manufacture rare-earth permanent magnets is almost nonexistent.
Spectroelectrochemistry: A Powerful Tool for Studying Fundamental Properties and Emerging Applications of Solid-State Materials Including Metal–Organic Frameworks
Authors: D'Alessandro Deanna M. , Usov Pavel M.
Published: January 2021

Spectroelectrochemistry (SEC) encompasses a broad suite of electroanalytical techniques where electrochemistry is coupled with various spectroscopic methods. This powerful and versatile array of methods is characterised as in situ, where a fundamental property is measured in real time as the redox state is varied through an applied voltage. SEC has a long and rich history and has proved highly valuable for discerning mechanistic aspects of redox reactions that underpin the function of biological, chemical, and physical systems in the solid and solution states, as well as in thin films and even in single molecules. This perspective article highlights the state of the art in solid-state SEC (ultraviolet–visible–near-infrared, infrared, Raman, photoluminescence, electron paramagnetic resonance, and X-ray absorption spectroscopy) relevant to interrogating solid state materials, particularly those in the burgeoning field of metal–organic frameworks (MOFs). Emphasis is on developments in the field over the past 10 years and prospects for application of SEC techniques to probing fundamental aspects of MOFs and MOF-derived materials, along with their emerging applications in next-generation technologies for energy storage and transformation. Along with informing the already expert practitioner of SEC, this article provides some guidance for researchers interested in entering the field.
Extent and effect of the 2019-20 Australian bushfires on upland peat swamps in the Blue Mountains, NSW
Authors: Fryirs Kirstie A. , Cowley Kirsten L. , Hejl Natalie , Chariton Anthony , Christiansen Nicole , Dudaniec Rachael Y. , Farebrother Will , Hardwick Lorraine , Ralph Timothy , Stow Adam , Hose Grant
Published: January 2021

The devastating bushfires of the 2019–20 summer are arguably the most costly natural disaster in Australian recorded history. What is little known is that these fires severely affected the temperate highland peat swamps on sandstone (THPSS), a form of upland wetland that occurs in the water supply catchments of Sydney in the Greater Blue Mountains World Heritage Area and National Park. During the fires, 59% of THPSS was burnt and 72% of those by a high severity burn. Upland swamps at Newnes were the most affected, with 96% of swamps burnt and 84% of these experiencing a very high burn severity. We present an analysis of the spatial extent and severity of the bushfire on the THPSS and discuss some of the likely consequences on their geomorphological, hydrological and ecological structure, function and recovery potential.
Direct field evidence of autocatalytic iodine release from atmospheric aerosol
Authors: Tham Yee Jun , He Xu-Cheng , Li Qinyi , Cuevas Carlos A. , Shen Jiali , Kalliokoski Joni , Yan Chao , Iyer Siddharth , Lehmusjärvi Tuuli , Jang Sehyun , Thakur Roseline C. , Beck Lisa , Kemppainen Deniz , Olin Miska , Sarnela Nina , Mikkilä Jyri , Hakala Jani , Marbouti Marjan , Yao Lei , Li Haiyan , Huang Wei , Wang Yonghong , Wimmer Daniela , Zha Qiaozhi , Virkanen Juhani , Spain T. Gerard , O'Doherty Simon , Jokinen Tuija , Bianchi Federico , Petäjä Tuukka , Worsnop Douglas R. , Mauldin Roy L. , Ovadnevaite Jurgita , Ceburnis Darius , Maier Norbert M. , Kulmala Markku , O’Dowd Colin , Dal Maso Miikka , Saiz-Lopez Alfonso , Sipilä Mikko
Published: January 2021

Significance

Recycling of reactive iodine from heterogeneous processes on sea-salt aerosol was hypothesized over two decades ago to play an important role in the atmospheric cleansing capacity. However, the understanding of this mechanism has been limited to laboratory studies and has not been confirmed in the atmosphere until now. We present atmospheric measurement of gas-phase iodine interhalogen species and show that their production via heterogeneous processing on marine aerosols is remarkably fast. These observations reveal that the atmospheric recycling of atomic iodine through photolysis of iodine interhalogen species is more efficient than previously thought, which is ultimately expected to lead to higher ozone loss and faster new particle formation in the marine environment.
Novel function ofN-acetyltransferase for microtubule stability and JNK signaling inDrosophilaorgan development
Authors: Mok Jung-Wan , Choi Kwang-Wook
Published: January 2021

Significance

Post-translational modification is crucial for regulating protein function. Acetylation of N-terminal residues is a major form of post-translational modification, but the functions of N-terminal acetyltransferases in vivo are not well understood. Here, we report aDrosophilaNAT, which we name Mnat9, that plays an essential role in development. Loss of Mnat9 leads to the abnormal activation of JNK signaling, causing cell death in developing organs. Additionally, Mnat9 directly binds and stabilizes microtubules. We show that these Mnat9 functions are independent of its acetylation activity. Furthermore, Mnat9 and human NAT9 are functionally conserved. This study shows the developmental function of a microtubule-associated NAT in JNK signaling, providing insight into the function of human NAT9.
Dynamic competition between SARS-CoV-2 NSP1 and mRNA on the human ribosome inhibits translation initiation
Authors: Lapointe Christopher P. , Grosely Rosslyn , Johnson Alex G. , Wang Jinfan , Fernández Israel S. , Puglisi Joseph D.
Published: January 2021

Significance

SARS-CoV-2 is the causative agent of the COVID-19 pandemic. A molecular framework for how the virus manipulates host cellular machinery to facilitate infection is needed. Here, we integrate biochemical and single-molecule strategies to reveal molecular insight into how NSP1 from SARS-CoV-2 inhibits translation initiation. NSP1 directly binds to the small (40S) subunit of the human ribosome, which is modulated by human initiation factors. Further, NSP1 and mRNA compete with each other to bind the ribosome. Our findings suggest that the presence of NSP1 on the small ribosomal subunit prevents proper accommodation of the mRNA. How this competition disrupts the many steps of translation initiation is an important target for future studies.
Humanitarian need drives multilateral disaster aid
Authors: Dellmuth Lisa M. , Bender Frida A.-M. , Jönsson Aiden R. , Rosvold Elisabeth L. , von Uexkull Nina
Published: January 2021

Significance

Threats to human livelihoods resulting from natural hazards are increasing due to climate change. Climate-related disasters such as floods, storms, and droughts have destroyed shelter, reduced crop yields, harmed livestock, and fueled conflict, especially in developing countries. The key finding is that UN aid in the aftermath of climate-related disasters is largely driven by humanitarian need. The UN seems able to fend off donor states’ strategic interest and allocate more aid after disasters where hazard severity is greater and need is more pressing. Based on this finding, we argue that the UN lives up to its stated principles of neutrality, impartiality, and independence in disaster aid, corroborating the legitimacy of the UN in allocating disaster aid.
Loss of sweet taste despite the conservation of sweet receptor genes in insectivorous bats
Authors: Jiao Hengwu , Xie Huan-Wang , Zhang Libiao , Zhuoma Nima , Jiang Peihua , Zhao Huabin
Published: January 2021

Significance

The sense of taste provides key information on diet, but evolution of taste receptor genes in vertebrates is sometimes unable to predict their feeding ecology. Here we use behavioral experiments and functional assays to demonstrate the loss of sweet taste despite the conservation of sweet receptor genes in insectivorous bats. Although sweet taste receptor genes were highly conserved between frugivorous and insectivorous bats at the sequence level, our behavioral experiments revealed dramatic divergence in two bat species with distinct diets: the insectivorous bat showed no preference for natural sugars, whereas the frugivorous bat showed strong preferences for sucrose and fructose. Our cell-based assays from multiple representative bat species across the phylogeny further supported the behavioral preference tests.