bluuebunny/crossref_metadata_2025 huggingface dataset:
Electoral College bias and the 2020 presidential election
Authors: Erikson Robert S. , Sigman Karl , Yao Linan
Published: October 2020

Significance

Donald Trump's 2016 victory in the Electoral College without leading in the popular vote has led to speculation of a repeat in 2020. If the Democrats were to win the popular vote but by less than a landslide, could they be thwarted from stopping Trump once again? We examine how Electoral College outcomes are conditioned by how states had voted in previous elections. Our simulations suggest that in 2020, the Electoral College bias is likely to again favor the Republicans. However, the expectation is less distortion of the popular will than in 2016. There is even the possibility that if Trump was to win the 2020 popular vote by a slim margin, it could be he who loses the Electoral College.
A mosaic analysis system with Cre or Tomato expression in the mouse
Authors: Wang Qun , Lin Yen-Yu , Zhang Baojun , Wu Jianxuan , Roy Sumedha , Ratiu Jeremy J. , Xu Yanping , Dai Meifang , Hale Laura P. , Xiong Yue , Li Qi-Jing , Zhuang Yuan
Published: October 2020

Significance

Somatic mutations are the driving force of many age-related diseases such as cancer and hematopoietic failure. A challenge in the field is to evaluate health impact of somatic mutations prior to the appearance of disease symptoms. We describe a genetic tool named MASCOT (mosaic analysis system with Cre or Tomato) for mosaic analysis of somatic mutations that drive clonal hematopoiesis and lymphomagenesis. MASCOT can be applied to mosaic analysis of broad tissue types, and thus provides a valuable tool to aid functional dissection of somatic mutations in studies of development and disease.
Sputtered Au–Ta films with tunable electrical resistivity
Authors: Bayu Aji L B , Engwall A M , Bae J H , Baker A A , Beckham J L , Shin S J , Lepro Chavez X , McCall S K , Moody J D , Kucheyev S O
Published: October 2020

Gold–tantalum alloy films are attractive for hohlraums used in indirect drive magnetized inertial confinement fusion. A high electrical resistivity of over ∼100 µΩ cm at cryogenic temperatures is an essential requirement for allowing an externally imposed pulsed magnetic field to soak through a hohlraum and magnetize the fusion fuel. Here, we systematically study properties of Au–Ta alloy films in the entire compositional range from pure Au to pure Ta with thicknesses up to 30 µm. These films are made by direct current magnetron co-sputtering on planar substrates. Films are characterized by a combination of high-energy ion scattering, x-ray diffraction, electron microscopy, nanoindentation, and electrical transport measurements. Results show that an alloy with ∼80 at.% of Ta forms a metallic glass exhibiting a maximum electrical resistivity of ∼300 µΩ cm with a weak temperature dependence in the range of 5–400 K. The deposition of a film with ∼80 at.% of Ta onto a sphero-cylindrical substrate for hohlraum fabrication is also demonstrated.
Spatio-temporal characterization of a pulsed DC atmospheric pressure plasma jet interacting with substrates
Authors: Johnson Michael J , Boris David R , Petrova Tzvetelina B , Walton Scott G
Published: October 2020

Atmospheric pressure plasmas generate a variety of chemically active species in open air, thus providing the unique ability to treat a variety of materials that do not require or are not compatible with vacuum systems. Producing the plasma-surface interaction that leads to a desired change in the substrate is complicated by the codependency between the plasma and the substrate: while the plasma will modify the surface, the surface will also influence the plasma properties. In this work, a pulsed-DC plasma jet produced in helium and impinging upon glass and metal substrates is studied over a range of applied voltage pulse widths extending from 1 to 10 µs. Current–voltage measurements, high speed images, and time-resolved optical emission from three important He and nitrogen excited species are used to examine the evolution of the plasma and its interaction with the surface. At ignition, a streamer is ejected into the open air from the jet exit and eventually collides with the substrate. For a glass substrate, the streamer will hit the surface and form a short-lived plasma across it. This surface plasma is almost completely unaffected by changes in the voltage pulse width. In contrast, when the streamer hits a metal substrate, a surface discharge will form that will last the entirety of the voltage pulse. If the pulse is long enough, a ‘reflected discharge’ will slowly develop that extends from the substrate back towards the outlet of the plasma jet. The emission intensity of the surface discharge closely matches that of the initial streamer, but not the reflected discharge, which suggests different electron kinetics between the two features. The addition of capacitors or resistors between the metal substrate and ground show how differences in substrate electrical properties can account for some of these behaviors. Emission line ratios are used to examine the evolution of electron temperature and the relative importance of Penning processes during the different plasma phases.
The effect of isovalent doping on the electronic band structure of group IV semiconductors
Authors: Polak Maciej P , Scharoch Paweł , Kudrawiec Robert
Published: October 2020

The band gap engineering of group IV semiconductors has not been well explored theoretically and experimentally, except for SiGe. Recently, GeSn has attracted much attention due to the possibility of obtaining a direct band gap in this alloy, thereby making it suitable for light emitters. Other group IV alloys may also potentially exhibit material properties useful for device applications, expanding the space for band gap engineering in group IV. In this work the electronic band structure of all group IV semiconductor alloys is investigated. Twelve possible A:B alloys, where A is a semiconducting host (A = C, Si, and Ge) and B is an isovalent dopant (B = C, Si, Ge, Sn, and Pb), were studied in the dilute regime (0.8%) of the isovalent dopant in the entire Brillouin zone (BZ), and the chemical trends in the evolution of their electronic band structure were carefully analyzed. Density functional theory with state-of-the-art methods such as meta-GGA functionals and a spectral weight approach to band unfolding from large supercells was used to obtain dopant-related changes in the band structure, in particular the direct band gap at the Γ point and indirect band gaps at the L(X) points of the BZ. Analysis of contributions from geometry distortion and electronic interaction was also performed. Moreover, the obtained results are discussed in the context of obtaining a direct fundamental gap in Ge:B (B = C, Sn, and Pb) alloys, and intermediate band formation in C:B (B = Sn and Pb) and Ge:C. An increase in localization effects is also observed: a strong hole localization for alloys diluted with a dopant of a larger covalent radius and a strong electron localization for alloys with a dopant of smaller radius. Finally, it is shown that alloying Si and Ge with other elements from group IV is a promising way to enhance the functionality of group IV semiconductors.
An analytical model on the gate control capability in p-GaN Gate AlGaN/GaN high-electron-mobility transistors considering buffer acceptor traps
Authors: Wang Fangzhou , Chen Wanjun , Sun Ruize , Wang Zeheng , Zhou Qi , Zhang Bo
Published: October 2020

An analytical model considering the buffer acceptor traps is presented in this paper to study the gate control capability in p-GaN gate AlGaN/GaN high-electron-mobility transistors (HEMTs). Through applying Gauss’ law from the buffer layer to the two-dimensional-electron-gas (2DEG) channel in the GaN channel layer, the contributions of buffer acceptor trap concentration (N
A) and energy level (E
T) are obtained for calculating the gate voltage (V
G) dependent 2DEG density (n
S) and threshold voltage (V
TH) performance. It is suggested that the deep E
T acceptor traps in the buffer layer are of great importance to the gate control capability. Plenty of the deep E
T acceptor traps could be ionized at the top region of the buffer layer. These ionized acceptor traps are negatively charged and electrostatically influence the 2DEG density, which is the role of deep E
T on gate control. Then, the n
S-V
G and V
TH characteristics of the devices could be significantly modulated by the N
A. Furthermore, the influence of the shallow E
T acceptor traps is not strong and could be ignored in the prediction of the n
S-V
G and V
TH distributions. This is due to the fact that few shallow E
T acceptor traps are ionized in the buffer layer. The analytical results are well supported by the calibrated TCAD simulation, revealing the impact mechanism of buffer acceptor traps on the device gate control capability and serving as more accurate guidance for designing the n
S-V
G and V
TH in p-GaN gate AlGaN/GaN HEMTs.
Spin transport through metal-dichalcogenides layers: a study from first-principles calculations
Authors: Devaraj Nayana , Tarafder Kartick
Published: October 2020

Spin transport through monolayer and trilayers of molybdenum dichalcogenides were studied considering Co as leads. Detailed investigations of the electronic structure of the Co/MoS2 interface and magnetic tri-junctions are carried out by using density functional theory calculations to understand transport behavior. The study revealed that new spin-polarized hybridized states appeared at the Fermi level due to the formation of Co/MoS2 interface that effectively acted as a spin filter and enhanced the spin injection efficiency of the systems. Spin-polarized current through the system as well as the magnetoresistance (MR) was estimated at different applied bias voltages. Large MR up to 78% was calculated for the trilayer MoS2 system at a relatively high applied bias voltage. The MR values are further improved by tuning the structure of the scattering region. A very large MR of 123% for MoS2/MoSe2/MoS2 trilayer at an applied bias 0.8 V was observed, which is much higher than the previously reported bias dependent MR values in similar systems.
Electric-field-induced spin spiral state in bilayer zigzag graphene nanoribbons
Authors: Prayitno Teguh Budi
Published: October 2020

We investigated the emergence of spin spiral ground state induced by the electric field in the bilayer zigzag graphene nanoribbons for the ferromagnetic edge states. To do that, we employed the generalized Bloch theorem to create flat spiral alignments for all the magnetic moments of carbon atoms at the edges within a constraint scheme approach. While the small ribbon width can preserve the ferromagnetic ground state, the large one shows the spiral ground state starting from a certain value of the electric field. We also pointed out that the spiral ground state is caused by the reduction of spin stiffness. In this case, the energy scale exhibits a subtle nature that can only be considered at the low temperature. For the last discussion, we also revealed that the spin spiral ground state appears more rapidly when the thickness increases. Therefore, we justify that the large ribbon width and large thickness can generate many spiral states induced by the electric field.
On the detection of surface spin freezing in iron oxide nanoparticles and its long-term evolution under ambient oxidation
Authors: Ghoshani M , Sánchez E H , Lee S S , Singh G , Yaacoub N , Peddis D , Mozaffari M , Binns C , De Toro J A , Normile P S
Published: October 2020

Exchange bias (EB) effects linked to surface spin freezing (SSF) are commonly found in iron oxide nanoparticles, while signatures of SSF in low-field temperature-dependent magnetization curves have been much less frequently reported. Here, we present magnetic properties of dense assemblies of similar-sized (∼8 nm diameter) particles synthesized by a magnetite (sample S1) and a maghemite (sample S2) method, and the influence of long-term (4 year) sample aging under ambient conditions on these properties. The size of the EB field of the different sample (fresh or aged) states is found to correlate with (a) whether a low-temperature hump feature signaling the SSF transition is detected in out-of-phase ac susceptibility or zero-field-cooled (ZFC) dc magnetization recorded at low field and with (b) the prominence of irreversibility between FC and ZFC curves recorded at high field. Sample S1 displays a lower magnetization than S2, and it is in S1 where the largest SSF effects are found. These effects are significantly weakened by aging but remain larger than the SSF effects in S2, where the influence of aging is considerably smaller. A non-saturating component due to spin disorder in S1 also weakens with aging, accompanied by, we infer, an increase in the superspin and the radius of the ordered nanoparticle cores. X-ray diffraction and Mössbauer spectroscopy provide indication of maghemite-like stoichiometry in both aged samples as well as thicker disordered particle shells in aged-S1 relative to aged-S2 (crystallographically-disordered and spin-disordered according to diffraction and Mössbauer, respectively). The pronounced diminution in SSF effects with aging in S1 is attributed to a (long-term) transition, caused by ambient oxidation, from magnetite-like to maghemite-like stoichiometry, and a concomitant softening of the spin-disordered shell anisotropy. We assess the impact of this anisotropy on the nature of the blocking of the nanoparticle superspins.
Template-assisted fabrication of Ag-nanoparticles@ZnO-nanorods array as recyclable 3D surface enhanced Raman scattering substrate for rapid detection of trace pesticides
Authors: Huo Dexian , Chen Bin , Li Mingtao , Meng Guowen , Lei Yong , Zhu Chuhong
Published: October 2020

We present a template-assisted fabrication method for a large-scale ordered arrays of ZnO nanorods (ZnO-NRs) modified with Ag nanoparticles (Ag-NPs), which possess high-density three-dimensional (3D) hot spots uniformly dispersed all over the substrate, being beneficial to ultrahigh sensitivity of surface enhanced Raman scattering (SERS) detection. These achieved Ag-NPs@ZnO-NRs arrays show high sensitivity, good spectral uniformity and reproducibility as substrates for SERS detection. Using the arrays, both dye molecules (rhodamine 6G, R6G) and organic pollutants like toxic pesticides (thiram and methyl parathion) are detected, with the detection limits of thiram and methyl parathion being 0.79 × 10−9 M and 1.51 × 10−8 M, respectively. In addition, the Ag-NPs@ZnO-NRs arrays have a self-cleaning function because the analyte molecules can be photocatalytic degraded using ultraviolet irradiation, showing that the 3D recyclable arrays have promising opportunities to be applied in rapid SERS-based detection of toxic organic pesticides.
Linac-integrated kV-cone beam CT polymer gel dosimetry
Authors: Jirasek A , Marshall J , Mantella N , Diaco N , Maynard E , Teke T , Hilts M
Published: October 2020

X-ray CT polymer gel dosimetry (PGD) remains a promising tool for three dimensional verification of high-dose treatment deliveries such as non-coplanar stereotactic irradiations. Recent demonstrations have shown a proof-of-principle application of linac-integrated cone beam CT-imaged (LI-CBCT) PGDs for 3D dose verification. LI-CBCT offers advantages over previous CT based PGD, including close to real-time imaging of the irradiated dosimeter, as well as the ability to maintain the dosimeter in the same physical location for irradiation and imaging, thereby eliminating spatial errors due to dosimeter re-positioning for read-out that may occur for other systems. However the dosimetric characteristics of a LI-CBCT PGD system remain to be established. The work herein determines the dosimetric properties and critical parameters needed to perform cone beam PGD. In particular, we show that imaging the dosimeter 20–30 min post irradiation offers excellent recovery of maximum polymerization yield (

>

90%), averaging with as few as 10 image averages can provide ∼90% gamma pass rates (3%, 3 mm) as compared to treatment planning, and that eliminating outlier averaging points can improve the precision and signal to noise ratio of resultant images. In summary, with appropriate methodology LI-CBCT PGD can provide dosimetric data capable of verification of complex high dose radiation deliveries in three dimensions and may find use in commissioning and validation of novel complex treatments.
Differentiation of pain levels by deploying various electroencephalogram synchronization features and a dynamic ensemble selection mechanism
Authors: Afrasiabi Somayeh , Boostani Reza , Masnadi-Shirazi Mohammad-Ali
Published: October 2020

Objective: The aim of this study was to measure pain intensity in an objective manner by analyzing electroencephalogram (EEG) signals. Although this problem has attracted the attention of researchers, increasing the resolution of this measurement by increasing the number of pain states significantly decreases the accuracy of pain level classification. Approach: To overcome this drawback, we adopt state-of-the-art synchronization schemes to measure the linear, nonlinear and generalized synchronization between different EEG channels. Thirty-two subjects executed the cold pressor task and experienced five defined levels of pain while their EEGs were recorded. Due to the large number of synchronization features from 34 channels, the most discriminative features were selected using the greedy overall relevancy method. The selected features were applied to a dynamic ensemble selection system. Main results: Our experiment provides 85.6% accuracy over the five classes, which significantly improves upon the results of past research. Moreover, we observed that the selected features belong to the channels placed over the ridge of the cortex, the area responsible for processing somatic sensation arising from nociceptive temperature. As expected, we noted that continuation of the painful stimulus for minutes engaged regions beyond the sensorimotor cortex (e.g. the prefrontal cortex). Significance: We conclude that the amount of synchronization between scalp EEG channels is an informative tool in revealing the pain sensation.
MOCVD growth of thick V-pit-free InGaN films on semi-relaxed InGaN substrates
Authors: White Ryan C , Khoury Michel , Wu Feng , Keller Stacia , Rozhavskaia Mariia , Sotta David , Nakamura Shuji , DenBaars Steven P
Published: October 2020

The MOCVD growth of InGaN:Si base layers on a semi-relaxed InGaN substrate, where growth is generally difficult due to the presence of V-pits, is examined. These V-pits can propagate through the crystal, causing severe morphological degradation and significantly reducing material quality for device use. Such V-pits may also be a source of leakage current if they extend from the substrate through p-n junction. A wide range of InGaN growth conditions and their impact on V-pit formation and density are investigated. The use of thin GaN interlayers, carrier gas selection, and V/III ratio are found play a critical role in managing V-pit quantity and size. Finally, high temperature GaN interlayers are implemented, fully eliminating V-pit formation in 1200 nm thick InGaN base layers grown coherently on semi-relaxed InGaN substrates.
Predicting task performance from biomarkers of mental fatigue in global brain activity
Authors: Yao Lin , Baker Jonathan L , Schiff Nicholas D , Purpura Keith P , Shoaran Mahsa
Published: October 2020

Objective. Detection and early prediction of mental fatigue (i.e. shifts in vigilance), could be used to adapt neuromodulation strategies to effectively treat patients suffering from brain injury and other indications with prominent chronic mental fatigue. Approach. In this study, we analyzed electrocorticography (ECoG) signals chronically recorded from two healthy non-human primates (NHP) as they performed a sustained attention task over extended periods of time. We employed a set of spectrotemporal and connectivity biomarkers of the ECoG signals to identify periods of mental fatigue and a gradient boosting classifier to predict performance, up to several seconds prior to the behavioral response. Main results. Wavelet entropy and the instantaneous amplitude and frequency were among the best single features across sessions in both NHPs. The classification performance using higher order spectral-temporal (HOST) features was significantly higher than that of conventional spectral power features in both NHPs. Across the 99 sessions analyzed, average F1 scores of 77.5% ± 8.2% and 91.2% ± 3.6%, and accuracy of 79.5% ± 8.9% and 87.6% ± 3.9% for the classifier were obtained for each animal, respectively. Significance. Our results here demonstrate the feasibility of predicting performance and detecting periods of mental fatigue by analyzing ECoG signals, and that this general approach, in principle, could be used for closed-loop control of neuromodulation strategies.
Q-PINE: A quick to implant peripheral intraneural electrode
Authors: Strauss Ivo , Niederhoffer Thomas , Giannotti Alice , Panarese Adele M , Bernini Fabio , Gabisonia Khatia , Ottaviani Matteo M , Petrini Francesco M , Recchia Fabio A , Raspopovic Stanisa , Micera Silvestro
Published: October 2020

Objective. The implantation of intraneural electrodes in amputees has been observed to be effective in providing subjects with sensory feedback. However, this implantation is challenging and time consuming. Surgeons must be especially trained to execute the implantation. Therefore, we aimed at developing a novel peripheral intraneural electrode and insertion mechanism, which could drastically reduce the overall implantation time while achieving a high neural selectivity. Approach. A new insertion method based on hollow microneedles was developed to realize the prompt and effective simultaneous implantation of up to 14 active sites in a transversal manner. Each needle guided two Pt/Ir microwires through the nervous tissue. After the insertion, the microneedles were released, leaving behind the microwires. Each microwire had one active site, which was coated with poly-3,4-ethylenedioxythiophene (PEDOT) to enhance the electrochemical properties. The active sites were characterized by evaluating the impedance, charge storage capacity, and maximum injectable charge. Twelve quick to implant peripheral intraneural electrodes (Q-PINEs) were implanted in four pig sciatic nerves to evaluate the implantation time and neural selectivity. We compared the stimulation of the sciatic nerve with that of its branches. Main results. The average surgical access time was 23 min. The insertion time for 12 electrodes was 6.7 min (std. ±1.6 min). The overall implantation time was reduced by 40.3 min compared to the previously reported values. The Q-PINE system demonstrated a satisfactory performance during in vitro and in vivo characterization. The electrochemical results showed that the PEDOT coating successfully increased the electrochemical parameters of the active sites. Significance. With an average impedance of 1.7 kΩ, a maximum charge level of 76.2 nC could be achieved per active site. EMG recruitment curves showed that 46% of the active sites exhibited selective stimulation of four out of six muscles. The histological analysis indicated that the microwires successfully penetrated the nerve and single fascicles.
Decoding network-mediated retinal response to electrical stimulation: implications for fidelity of prosthetic vision
Authors: Ho Elton , Shmakov Alex , Palanker Daniel
Published: October 2020

Objective. Patients with photovoltaic subretinal implant PRIMA demonstrated letter acuity ∼0.1 logMAR worse than sampling limit for 100 μm pixels (1.3 logMAR) and performed slower than healthy subjects tested with equivalently pixelated images. To explore the underlying differences between natural and prosthetic vision, we compare the fidelity of retinal response to visual and subretinal electrical stimulation through single-cell modeling and ensemble decoding. Approach. Responses of retinal ganglion cells (RGCs) to optical or electrical white noise stimulation in healthy and degenerate rat retinas were recorded via multi-electrode array. Each RGC was fit with linear–nonlinear and convolutional neural network models. To characterize RGC noise, we compared statistics of spike-triggered averages (STAs) in RGCs responding to electrical or visual stimulation of healthy and degenerate retinas. At the population level, we constructed a linear decoder to determine the accuracy of the ensemble of RGCs on N-way discrimination tasks. Main results. Although computational models can match natural visual responses well (correlation ∼0.6), they fit significantly worse to spike timings elicited by electrical stimulation of the healthy retina (correlation ∼0.15). In the degenerate retina, response to electrical stimulation is equally bad. The signal-to-noise ratio of electrical STAs in degenerate retinas matched that of the natural responses when 78 ± 6.5% of the spikes were replaced with random timing. However, the noise in RGC responses contributed minimally to errors in ensemble decoding. The determining factor in accuracy of decoding was the number of responding cells. To compensate for fewer responding cells under electrical stimulation than in natural vision, more presentations of the same stimulus are required to deliver sufficient information for image decoding. Significance. Slower-than-natural pattern identification by patients with the PRIMA implant may be explained by the lower number of electrically activated cells than in natural vision, which is compensated by a larger number of the stimulus presentations.
A semiclassical resonator model for terahertz generation
Authors: Basharov A M
Published: October 2020

The paper states a simple and analytically solvable model for the terahertz generation via a localized excited ensemble of identical three-level quantum particles within the resonator.
Quantum interference via nonradiative transitions between energy levels of atoms in one-dimensional photonic crystals
Authors: Kh Gainutdinov R , Garifullin A I , Khamadeev M A , Kh Salakhov M
Published: October 2020

The self-energy correction to the mass of an atomic electron placed into a void of the photonic crystal medium is investigated. In this study the one-dimensional photonic crystal made from gallium arsenide and vacuum layers is considered. We show that the electron mass change gives rise not only to the shifts of the atomic energies but also to the nonradiative transitions between atomic levels. These transitions add new channels to a decay of an atomic state that leads to a quantum interference between these channels.
FTIR spectroscopic study of enthalpy differences of conformers of substituted ethanes in PVB plasticized by PEGs
Authors: Kamalova D I , Abdrazakova L R
Published: October 2020

In present investigation, the enthalpy differences of conformers for substituted ethanes in PVB/PEG 200, PVB/PEG 400 and PVB/PEG600 blended systems with the compositions of 80:20, 70:30, 60:40 and 50:50 have been determined by FTIR spectroscopy. The influence of the plasticizer content and molecular weight of poly(ethylene glycol) on the enthalpy difference of the conformers has been studied.
Partially coherent photon echo in the presence of pulsed and static magnetic fields
Authors: Lisin Valery , Shegeda Anatoly , Samartsev Vitaly
Published: October 2020

The theory of a partially coherent photon echo in a static magnetic field at the presence of a pulsed magnetic field, causing oscillations of the echo intensity, is constructed. It is shown that the coherence time can be found by the dependence of the echo intensity on the laser frequency. The theory is compared with the experiment in LuLiF4:Er3+ (transition 4I15/2 -4F9/2) and in YLiF4:Er3+ at the same transition.
Localized waves in the nonlinear rhombic waveguide array
Authors: Maimistov A I , Lyashko E I , Elyutin E O
Published: October 2020

Solitary electromagnetic waves propagating along the waveguides forming a rhombic one-dimensional lattice are considered. Two waveguides that are part of the unit cell are assumed to be made of an optical linear material, while the third waveguide from the same array is composed of material with the cubic nonlinearity. The equations of the coupled waves spreading in each waveguide are solved under some approximation. These solutions represent the breather like solitary waves, which are akin to three component soliton.
Two-color vortex solitons in the quadratic nonlinear waveguide
Authors: Sazonov S V
Published: October 2020

Based on the averaged Lagrangian method, the possibility of forming a spatiotemporal soliton of the type of a two-frequency optical vortex in a waveguide with quadratic nonlinearity is investigated. In the approximation of the diffraction limit the corresponding analytical solutions are obtained.
Digital Assistance in the Maintenance of Offshore Wind Parks
Authors: Eggert Martin , Stepputat Marten , Fluegge Wilko
Published: October 2020

Harsh environmental conditions, time pressure due to tightly calculated maintenance windows, complex technical systems and high quality standards determine the working environment for the maintenance and repair of offshore wind farms. Despite good qualifications and diverse training courses, maintenance technicians are reliant on information from manuals and checklists when performing their tasks and must document their work results in protocols. Both the supply of information and the data acquisition show a multitude of media disruptions. Hence, the processes on site and in the postprocessing are carried out slowly and uncertainly. The assistance system presented is intended to contribute to a consistently digital information flow and to support the technicians in a task-specific manner. Augmented Reality (AR) offers a way of presenting information and interacting with the assistance system during work execution. Using the example of the maintenance of crane systems used in a variety of ways in offshore wind farms, this article shows which potential can be tapped through digital assistance systems and AR applications.
Friction coefficients for steel to steel contact surfaces in air and seawater
Authors: Pijpers R.J.M. , Slot H.M.
Published: October 2020

Through a series of laboratory friction tests on small scale specimens an understanding of the physical behaviour is gained. The test program of the friction tests contained 12 test specimen variants, with a combination of dry air and seawater environment and various surface conditions and contact pressures.
Comparison of Weather Window Statistics and Time Series Based Methods Considering Risk Measures
Authors: Lübsen J , Wolken-Möhlmann G
Published: October 2020

Offshore projects, like the installation of offshore wind farms, consist of a number of different and often weather dependent activities. These tasks and their relations are defined in project schedules, which have to be assessed for weather effects before the project realization. Here, often Weather Window Statistics are used to calculate probable weather delay times using relative frequencies of weather windows. Another possible approach is the Weather Time Series Scheduling (WaTSS) method which combines the given project schedule, weather restrictions and historical weather time series data for several decades. The aim of this paper is a comparison of the two approaches especially when it comes to risk analysis for project schedules using percentile values or related risk measures. The same ERA5 model data is used both as basis for the Weather Window Statistics and the WaTSS method. We calculate weather downtimes for each task, as well as for the total project, and apply the risk measures Value at Risk (VaR), Conditional Value at Risk (cVaR) and Upper Partial Moments (UPM). This is followed by an analysis of the results from Weather Window Statistics and the WaTSS method considering their applicability and consistence. We obtain that risk measurement for project schedules under use of Weather Window Statistics is not always practicable because certain risk values tend to overestimation. WaTSS method provides project adjusted modeling and leads to more realistic risk measurement for complex project schedules.
Design Optimization of Spar Floating Wind Turbines Considering Different Control Strategies
Authors: Hegseth John Marius , Bachynski Erin E. , Martins Joaquim R. R. A.
Published: October 2020

One of the challenges related to the design of floating wind turbines (FWTs) is the strong interactions between the controller and the support structure, which may result in an unstable system. Several control strategies have been proposed to improve the dynamic behaviour, all of which result in trade-offs between structural loads, rotor speed variation, and blade pitch actuator use, which makes controller design a challenging task. Due to the interactions, simultaneous design of the controller and support structure should be performed to properly identify and compare different solutions. In the present work, integrated design optimization of the blade-pitch controller and support structure is performed for a 10 MW spar FWT, considering four different control strategies, to evaluate the effect of the controller on the structural design and associated costs. The introduction of velocity feedback control reduces the platform pitch response and consequently the fatigue loads in the tower, which leads to a decrease in the tower costs compared to a simple PI controller. Low-pass filtering of the nacelle velocity signal to remove the wave-frequency components results in reduced rotor speed variation, but offers only small improvements in costs, likely due to the limited wave-frequency response for the considered designs. Comparisons with nonlinear time-domain simulations show that the linearized model is able to capture trends with acceptable accuracy, but that significant overpredictions may occur for the platform pitch response.
Structural Design of a Prestressed-Concrete Spar-type floater for 10 MW wind turbines
Authors: Oh Sho , Inoue Hiroto , Takahashi Yuya
Published: October 2020

Prestressed concrete is gaining growing interests as an alternative to steels for the construction material for floating platforms of wind turbines due to its low material costs. Investigation of the characteristics of the concrete structure under the fluctuating loadings are necessary to ensure the structural integrity, where a reference model of both the floating concrete platform and accompanying structural design are highly useful. In this study, a reference model for prestressed-concrete spar-type floater for 10 MW wind turbines is designed together with its concrete structure. Frequency-domain analysis showed that an optimum floater diameter that gives minimum pitch angle could be found. Although the maximum pitch angles were similar for floaters with diameters of 15 m to 17 m, structural design showed that the case with the wall thickness of 0.35 m will subject to prestressed-concrete steel yielding, concrete bending cracks, and shell buckling due to water pressure. Finally the reference model is designed for a floater diameter of 16 m and wall thickness of 0.45 m.
Feasibility of machine learning algorithms for classifying damaged offshore jacket structures using SCADA data
Authors: Cevasco D , Tautz-Weinert J , Smolka U , Kolios A
Published: October 2020

The best practise for structural damage detection currently relies on the installation of structural health monitoring systems for the collection of dedicated high frequency measurements. Switching to the employment of the wind turbine’s SCADA (Supervisory Control and Data Acquisition) signals and their commonly recorded low frequency statistics can lead to a reduction in the number of ad-hoc monitoring sensors and quantity of data required. In this paper, aero-hydro-servo-elastic simulations for a model of a turbine are used to assess its loads and any changes in the dynamics under healthy state and a damaged configuration case study. To prove the feasibility of the damage detection through low-resolution data, the statistics of the typically recorded signals from the SCADA and the structural monitoring systems are fed into a database for training and testing of classification algorithms. The ability of the machine learning models to generalise the classification for both stochasticity and uncertainties in the environmental conditions are tested. Decision tree-based classifiers showed the capability to capture the damage for the majority of the operating conditions considered. Though the setup of the traditional SCADA sensors had to be supplemented with an additional structural health monitoring sensor, the detection of the damage has been shown feasible by referring to low-frequency statistics only.
Sequential heuristic optimisation of a real offshore wind farm site considering turbine placement and cable layout
Authors: Taylor Peter , Campos-Gaona D , Yue H , Anaya-Lara O , Jia C , Ng C
Published: October 2020

Competition within the energy generation industry provides an incentive for developers to build offshore wind farms with a low levelised cost of energy. Therefore, there is a need for design optimisation to reduce costs and increase energy capture. A sequential approach to optimise turbine placement and cable layout is presented, using a heuristic k-opt algorithm and mixed-integer linear programming respectively. Energy storage is considered as a means to further improve the cable selection process. A case study is carried out on the Lillgrund offshore wind farm and the resulting layout improves energy capture by 6%. Cable costs are increased but the electrical losses are reduced such that there is an overall saving over the project lifetime of 20%. Energy storage as a means to peak shave the power seen by a cable in order to reduce electrical losses or de-rate a cable section was found to be impractically large and not profitable. Future work will consider secondary revenue streams to remedy this.
Vortex interaction in the wake of a two- and three-bladed wind turbine
Authors: Bartl Jan , Hansen Thomas H. , Ludwig Kuhn W. , Mühle Franz , Sætran Lars
Published: October 2020

The vortex interaction in the wake behind a two- and three-bladed model scale wind turbine is investigated. The two rotors have equal solidity, and produce similar power and thrust at the design tip speed ratio. Phase-averaged quantities of the wake flow from one to four rotor diameters behind the turbines are measured in a wind tunnel. It is found that the two-bladed turbine has slower wake recovery than the three-bladed turbine, and a larger velocity deficit is produced in the far wake. The tip vortices behind the two-bladed turbine is more stable than behind the three-bladed turbine, and the vortex structures exist further downwind. In a wind farm, this could reduce the power production and increase fatigue loads for the turbines operating in the wake flow, especially during stable atmospheric conditions.
GANs enabled super-resolution reconstruction of wind field
Authors: Tran Duy Tan , Robinson Haakon , Rasheed Adil , San Omer , Tabib Mandar , Kvamsdal Trond
Published: October 2020

Atmospheric flows are governed by a broad variety of spatio-temporal scales, thus making real-time numerical modeling of such turbulent flows in complex terrain at high resolution computationally unmanageable. In this paper, we demonstrate a novel approach to address this issue through a combination of fast coarse scale physics based simulator and a family of advanced machine learning algorithm called the Generative Adversarial Networks. The physics-based simulator generates a coarse wind field in a real wind farm and then ESRGANs enhance the result to a much finer resolution. The method outperforms state of the art bicubic interpolation methods commonly utilized for this purpose.
Identification and prioritization of low performing wind turbines using a power curve health value approach
Authors: Martin M , Pfaffel S , te Heesen H , Rohrig K
Published: October 2020

Since operational managers often monitor large numbers of wind turbines (WTs), they depend on a toolset to provide them with highly condensed information to identify and prioritize low performing WTs or schedule preventive maintenance measures. Power curves are a frequently used tool to assess the performance of WTs. The power curve health value (HV) used in this work is supposed to detect power curve anomalies since small deviations in the power curve are not easy to identify. It evaluates deviations in the linear region of power curves by performing a principal component analysis. To calculate the HV, the standard deviation in direction of the second principal component of a reference data set is compared to the standard deviation of a combined data set consisting of the reference data and data of the evaluated period. This article examines the applicability of this HV for different purposes as well as its sensitivities and provides a modified HV approach to make it more robust and suitable for heterogeneous data sets. The modified HV was tested based on ENGIE’s open data wind farm and data of on- and offshore WTs from the WInD-Pool. It proved to detect anomalies in the linear region of the power curve in a reliable and sensitive manner and was also eligible to detect long term power curve degradation. Also, about 7 % of all corrective maintenance measures were preceded by high HVs with a median alarm horizon of three days. Overall, the HV proved to be a promising tool for various applications.
City-planning transformation of the functional and planning structure of districts near a railway station in the largest megalopolises (international experience)
Authors: Akhmedova E A , Kuznetsov I V
Published: October 2020

The article deals with the peculiarities of functioning, renovation and redevelopment of city districts proximately adjacent to the territories of railway stations and roads. Both decaying, degenerating districts and successfully developing ones are of interest. The functional, compositional and planning principles of these districts’ development with their consecutive inclusion into the full-fledged city life are revealed by analysing foreign and Russian experience. The issue of city districts near a railway station’s transformation becomes actual not only in Russia, but in many cities around the world as well. It is conditional upon the fact that to a greater extent railway infrastructure objects formerly situated outside a city begin to contact closely with the urban area in the process of urban sprawl. It is impossible not to consider their influence on planning, functional as well as architectural and stylistic solution of the infrastructure. The aim of the research is to detect the main compositional, planning and functional peculiarities and principles of the site development situated in city districts near a railway station. The following tasks were to be solved to achieve the abovementioned aim: to distinguish the examples of various countries’ cities, the structure of which includes railway infrastructure objects actively; to study briefly the district history that can influence the further urban development of the site; to analyse the chosen cities’ city-planning situations; to find out the main functions of buildings and housing as well as the urban realm elements present in districts near a railway station; to study the functionality of buildings, constructions and urban spaces that appeared in urban realm in different historic periods; to define planning and functional interconnections between the different elements of city tissue in districts near a railway station.
Analysis of profitability of production in the construction industry of the Irkutsk region
Authors: Filatov E A
Published: October 2020

In economic practice, many specific indicators of profitability are used. They may differ in the complexity of the calculation, the availability of necessary information, and the usefulness of the analytical conclusions process. To measure the size of profit and the amount of funds used to achieve it in the industry economy, the indicator profitability of production is used. Profitability of production is an important parameter for determining the efficiency of the economy. Profitability of production is the most general, qualitative indicator of economic efficiency of production, efficiency of functioning of companies in the industry. This indicator is very important for making current and strategic decisions. The article presents the author’s model for analyzing the profitability of production. The article reveals the influence of factors affecting the change in profitability and are more methodical approaches to its calculation (methods of factor analysis developed by Filatov E. A.). The article presents the author’s analytic, systematic statistical material for the analysis of key indicators revealing the impact on the change of profitability of the construction industry in Irkutsk region of the Russian Federation.
Compounding features of composite gypsum binders for porous composites in construction printing technologies
Authors: Chernysheva N V , Shatalova S V
Published: October 2020

At this stage of development of construction technologies and widespread digitalization, one of the most promising and interesting areas of the Russian and international scientific community is construction printing. The main idea of construction printing is to create a finished product or structure with a single installation. The most important task now is to master printing with porous concrete to give structures the required thermal characteristics, without which additive construction cannot fully compete with conventional technologies in the construction of wall structures. One of the promising materials in this case is foam concrete, in which the rapid fixation of the porous structure and the given shape is provided by the use of a composite gypsum binder. The paper considers the possibility of moving away from traditional composition that include active mineral additives by using Portland cements with various mineral additives. The influence of the used foaming agent on the hardening process of the gyp-sum-Portland cement system with various mineral additives was studied. This solution is designed to simplify the technology, make it more attractive for small and medium-sized businesses, increase the compatibility of the binder with foaming agents, as well as its activity to ensure high mechanical performance of foam concrete.
Accounting policy of construction companies in accordance with International Financial Reporting Standards
Authors: Derzayeva G G
Published: October 2020

This paper examines the practical experience of construction companies in terms of their disclosure of information about significant elements of accounting policy in the notes to their financial statements prepared in accordance with International Financial Reporting Standards. The aim of the study is to identify the main problematic issues that arise in construction companies when preparing accounting policies in accordance with International Financial Reporting Standards and find ways to solve them. Using such methods as analysis and synthesis, comparison, logical and systematic approaches, the author identifies the main problems that occur in construction companies when drafting accounting policy, as well as offers solutions to them. As a result of the research, the paper compares the practice of forming accounting policy by leading construction companies, identifies the main problematic aspects and suggests ways to solve them. The article concludes on the uniformity of approaches to disclosure of information about significant elements of accounting policy, proves the identity of most of the problematic aspects that arise in the formation of accounting policy in accordance with International Financial Reporting Standards by construction companies, and substantiates the analogy of ways to solve them.