bluuebunny/crossref_metadata_2025 huggingface dataset:
Arthroscopic Primary Repair of the Posterior Cruciate Ligament
Authors: Vermeijden Harmen D. , van der List Jelle P. , DiFelice Gregory S.
Published: January 2021

The posterior cruciate ligament (PCL) is one of the four major stabilizers of the knee joint and functions as the primary restraint to posterior tibial translation. PCL tears rarely occur in isolation and most commonly presents in the setting of multiligamentous knee injuries. Several treatment strategies for these injuries have been proposed over the last decades, including ligament reconstruction and primary repair. Arthroscopic primary PCL repair has the potential to preserve native tissue using a more minimally invasive approach, thereby avoiding donor-site morbidity and allowing early mobilization. While arthroscopic PCL repair is certainly not an effective surgical approach for all patients, this procedure may be a reasonable and less morbid alternative to PCL reconstruction in selected patients treated for proximal or distal avulsion tears, with low failure rates, good knee stability, and good to excellent subjective outcomes. The surgical indications, surgical techniques, postoperative management, and outcomes for arthroscopic primary repair of proximal and distal PCL tears will be discussed in this review.
Blood Pressure Management Before, During, and After Endovascular Thrombectomy for Acute Ischemic Stroke
Authors: de Havenon Adam , Petersen Nils , Sultan-Qurraie Ali , Alexander Matthew , Yaghi Shadi , Park Min , Grandhi Ramesh , Mistry Eva
Published: January 2021

There is an absence of specific evidence or guideline recommendations on blood pressure management for large vessel occlusion stroke patients. Until randomized data are available, the periprocedural blood pressure management of patients undergoing endovascular thrombectomy can be viewed in two phases relative to the achievement of recanalization. In the hyperacute phase, prior to recanalization, hypotension should be avoided to maintain adequate penumbral perfusion. The American Heart Association guidelines should be followed for the upper end of prethrombectomy blood pressure: ≤185/110 mm Hg, unless post–tissue plasminogen activator administration when the goal is <180/105 mm Hg. After successful recanalization (thrombolysis in cerebral infarction [TICI]: 2b–3), we recommend a target of a maximum systolic blood pressure of < 160 mm Hg, while the persistently occluded patients (TICI < 2b) may require more permissive goals up to <180/105 mm Hg. Future research should focus on generating randomized data on optimal blood pressure management both before and after endovascular thrombectomy, to optimize patient outcomes for these divergent clinical scenarios.
Temporal and spatial variation in the soil seed bank of Nassella trichotoma (serrated tussock) in its native range
Authors: García Andrés , Loydi Alejandro , Distel Roberto A.
Published: January 2021

Serrated tussock (Nassella trichotoma (Nees) Hack. ex Arechav) is an unpalatable grass species that has been expanding in its native range and invading non-native ranges. In this study in its natural environment, we aimed to describe the spatial relationship between seed density, the cover and density of standing individuals of serrated tussock, the seasonal variation in the seed density in the soil seed bank, and to compare these results with those reported in non-native ranges. We took soil samples seasonally and recorded the cover and density of standing individuals of serrated tussock at two sites in the native Pampas grasslands in central-east Argentina. Seed density was evaluated by seedling emergence and seed extraction. Seed density showed a seasonality trend, with maximum values in the end of summer and minimum values in winter and spring. Seed density was independent of the cover and density of standing individuals of serrated tussock. The values of seed density were lower than those reported in the invaded ranges. Since seeds of serrated tussock are present in the seed bank regardless of the cover and density of its standing individuals, the maintenance of a high cover of desirable species may play a key role in preventing the establishment of serrated tussock in both its natural and invaded ranges.
Evolution in the weak-mutation limit: Stasis periods punctuated by fast transitions between saddle points on the fitness landscape
Authors: Bakhtin Yuri , Katsnelson Mikhail I. , Wolf Yuri I. , Koonin Eugene V.
Published: January 2021

Significance

The gradual character of evolution is a key feature of the Darwinian worldview. However, macroevolutionary events are often thought to occur in a nongradualist manner, in a regime known as punctuated equilibrium, whereby extended periods of evolutionary stasis are punctuated by rapid transitions between states. Here we analyze a simple mathematical model of population evolution on fitness landscapes and show that, for a large population in the weak-mutation limit, the process of adaptive evolution consists of extended periods of stasis, which the population spends around saddle points on the landscape, interrupted by rapid transitions to new saddle points when a beneficial mutation is fixed. Thus, phenomenologically, the default regime of biological evolution seems to closely resemble punctuated equilibrium.
Interpretations of ground-state symmetry breaking and strong correlation in wavefunction and density functional theories
Authors: Perdew John P. , Ruzsinszky Adrienn , Sun Jianwei , Nepal Niraj K. , Kaplan Aaron D.
Published: January 2021

Significance

The ground state of a quantum mechanical system is the lowest-energy eigenstate of the Hamiltonian. In isolation, it persists unchanged forever, with symmetries dictated by those of the Hamiltonian. But near-eigenstates of broken symmetry can persist for long times, even on the scale of human measurement. The appearance of broken symmetries of the electron density or spin density in a density functional calculation can reveal strong correlations among the electrons that are present in a symmetry-unbroken wavefunction. Symmetry breaking can arise when a wave-like fluctuation drops to zero frequency. The presented examples are the stretched hydrogen molecule, antiferromagnetism in solids, and the static charge-density wave in a low-density jellium, which is shown quantitatively to be a zero-frequency plasma wave.
Coronavirus replication–transcription complex: Vital and selective NMPylation of a conserved site in nsp9 by the NiRAN-RdRp subunit
Authors: Slanina Heiko , Madhugiri Ramakanth , Bylapudi Ganesh , Schultheiß Karin , Karl Nadja , Gulyaeva Anastasia , Gorbalenya Alexander E. , Linne Uwe , Ziebuhr John
Published: January 2021

Significance

We report an intersubunit interaction within the coronavirus replication–transcription complex that is critical for replication and evolutionarily conserved. We provide evidence that the nsp12-associated NiRAN domain has nucleoside monophosphate (NMP) transferase activity in trans and identified nsp9, an RNA-binding protein, as its target. NiRAN catalyzes the covalent attachment of an NMP moiety to the conserved nsp9 amino terminus in a reaction dependent on Mn
2+
ions and an adjacent conserved Asn residue. NiRAN activity and nsp9 NMPylation were found to be essential for coronavirus replication. The data lead us to connect this activity of a nidovirus enzymatic marker with previous observations within a functionally and evolutionarily coherent hypothesis on the initiation of RNA synthesis in a class of RNA viruses.
Photon ring structure of rotating regular black holes and no-horizon spacetimes
Authors: Kumar Rahul , Ghosh Sushant G
Published: January 2021

The Kerr black holes possess a photon region with prograde and retrograde orbits radii, respectively,

M
⩽

r

p

−

⩽
3
M

and

3
M
⩽

r

p

+

⩽
4
M

, and thereby always cast a closed photon ring or a shadow silhouette for a ⩽ M. For a > M, it is a no-horizon spacetime (naked singularity) wherein prograde orbits spiral into the central singularity, and retrograde orbits produce an arc-like shadow with a dark spot at the center. We compare Kerr black holes’ photon ring structure with those produced by three rotating regular spacetimes, viz Bardeen, Hayward, and nonsingular. These are non-Kerr black hole metrics with an additional deviation parameter of g related to the nonlinear electrodynamics charge. It turns out that for a given a, there exists a critical value of g, g
E such that Δ = 0 has no zeros for g > g
E, one double zero at r = r
E for g = g
E, respectively, corresponding to a no-horizon regular spacetime and extremal black hole with degenerate horizon. We demonstrate that, unlike the Kerr naked singularity, no-horizon regular spacetimes can possess closed photon ring when g
E < g ⩽ g
c, e.g. for a = 0.10M, Bardeen (g
E = 0.763 332M < g ⩽ g
c = 0.816 792M), Hayward (g
E = 1.052 97M < g ⩽ g
c = 1.164 846M) and nonsingular (g
E = 1.2020M < g ⩽ g
c = 1.222 461M) no-horizon spacetimes have closed photon ring. These results confirm that the mere existence of a closed photon ring does not prove that the compact object is necessarily a black hole. The ring circularity deviation observable ΔC for the three no-horizon rotating spacetimes satisfy ΔC ⩽ 0.10 as per the M87* black hole shadow observations. We have also appended the case of Kerr–Newman no-horizon spacetimes (naked singularities) with similar features.
Parity violating metric-affine gravity theories
Authors: Iosifidis Damianos , Ravera Lucrezia
Published: January 2021

We study a metric-affine gravitational theory given by the Einstein–Hilbert (EH) action plus a parity violating contribution (which we will refer to as the Hojman term, also known as Holst term) in vacuum. We find out that for a certain value of the Barbero–Immirzi (BI) parameter the total action possesses a remarkable invariance under particular transformations of the affine connection. We prove that in all cases, with appropriate gauge choices, the connection reduces to the Levi-Civita one and that the theory turns out to be equivalent to general relativity (GR) in vacuum. Subsequently, we generalize our discussion and analyze the case of metric-affine f(R) gravity plus the Hojman term. In particular, we show that for f′(R) ≠ constant the theory results to be on-shell equivalent to a metric-compatible torsionless scalar–tensor model with a propagating pseudo-scalar. Matter coupling of the aforementioned models is also discussed, together with explicit examples and applications.
New sum rules for Wigner 3jm symbols: application to expectation values of hydrogenic ions
Authors: Pain Jean-Christophe , Gilleron Franck
Published: January 2021

We present new sum rules for 3jm coefficients, which involve, in addition to the usual weighting factor (2j + 1) where j is an angular momentum, the quantity [j(j + 1)]
k
with k ⩾ 1. The sum rules appear for instance in the statistical modeling of rotational spectra within the theory of moments, and enable one to deduce the expectation values of r

k
(used in the theory of Stark effect for hydrogenic ions) in parabolic coordinates from the expectation values of r

k
in spherical coordinates.
CH3NH3PbI3 as a radio frequency decoupling capacitor: interplay between Maxwell–Wagner polarization and a pseudo inductive response
Authors: Besra Nripen , Sardar Kausik , Mazumder Nilesh , Bhattacharjee Souvik , Das Anjan , Das Bikram , Sarkar Saikat , Chattopadhyay Kalyan Kumar
Published: January 2021

Frequency-dispersive impedance analysis of CH3NH3PbI3 perovskite is carried out under the external Direct current (DC) field to investigate the interplay of dielectric polarization and delocalized carrier transport. Switching of capacitance from positive to negative values is observed in the radio frequency range (42.1–42.5 MHz) for the external bias ranging from 0–4 V. The switching frequency outlined a decreasing trend with an increase in bias. Upon fitting the experimentally obtained dispersions, a bi-relaxation mechanism is unveiled. One of its constituents arises due to the typical Maxwell–Wagner interfacial polarization between the grain cores and boundaries and acts at the lower frequencies. The other one is manifested via hopping of delocalized carriers, resulting in a high frequency degenerative pseudo inductive response. The interference of these two mechanisms is manifested into an asymmetric Breit–Wigner–Fano profile of the dielectric susceptance spectra. The results are further elaborated from a theoretical point of view involving the energy band structure, electron localization function, and Mulliken charge distribution.
Tunable polarization-independent MoS2-based coherent perfect absorber within visible region
Authors: Zamharir Sara Ghayeb , Karimzadeh Rouhollah , Luo Xin
Published: January 2021

The paper suggests a new perfect absorber design based on the coherent perfect absorption (CPA) phenomenon of two-dimensional MoS2 monolayer in the visible region. Our proposed structure consists of a single MoS2 layer that is sandwiched between a SiO2 layer and a silver film with the nanocube dielectric array. According to the finite difference time domain simulations, CPA occurs at 722.2 nm in the certain structural configuration. Our computational results confirm the tunability of CPA resonant wavelength as a function of geometric and optical parameters of the nanocube dielectric array. Therefore, our CPA design may offer a solution to the light absorption enhancement of MoS2 monolayer in the visible region for optoelectronics applications.
In situ and operando electron microscopy in heterogeneous catalysis—insights into multi-scale chemical dynamics
Authors: Chee See Wee , Lunkenbein Thomas , Schlögl Robert , Cuenya Beatriz Roldan
Published: January 2021

This review features state-of-the-art in situ and operando electron microscopy (EM) studies of heterogeneous catalysts in gas and liquid environments during reaction. Heterogeneous catalysts are important materials for the efficient production of chemicals/fuels on an industrial scale and for energy conversion applications. They also play a central role in various emerging technologies that are needed to ensure a sustainable future for our society. Currently, the rational design of catalysts has largely been hampered by our lack of insight into the working structures that exist during reaction and their associated properties. However, elucidating the working state of catalysts is not trivial, because catalysts are metastable functional materials that adapt dynamically to a specific reaction condition. The structural or morphological alterations induced by chemical reactions can also vary locally. A complete description of their morphologies requires that the microscopic studies undertaken span several length scales. EMs, especially transmission electron microscopes, are powerful tools for studying the structure of catalysts at the nanoscale because of their high spatial resolution, relatively high temporal resolution, and complementary capabilities for chemical analysis. Furthermore, recent advances have enabled the direct observation of catalysts under realistic environmental conditions using specialized reaction cells. Here, we will critically discuss the importance of spatially-resolved operando measurements and the available experimental setups that enable (1) correlated studies where EM observations are complemented by separate measurements of reaction kinetics or spectroscopic analysis of chemical species during reaction or (2) real-time studies where the dynamics of catalysts are followed with EM and the catalytic performance is extracted directly from the reaction cell that is within the EM column or chamber. Examples of current research in this field will be presented. Challenges in the experimental application of these techniques and our perspectives on the field’s future directions will also be discussed.
Tailoring the electronic structure and magnetic properties of pyrochlore Co2Ti1−x
Ge
x
O4: a GGA + U
ab initio study
Authors: Ghosh Sayandeep , Singh Sobhit , Das Debashish , Ghosh Subhradip , Mishra Pankaj Kumar , Thota Subhash
Published: January 2021

We report the electronic structure and magnetic properties of Co2Ti1−x
Ge
x
O4 (0 ⩽ x ⩽ 1) spinel by means of the first-principle methods of density functional theory involving generalized gradient approximation along with the on-site Coulomb interaction (U
eff) in the exchange-correlation energy functional. Special emphasis has been given to explore the site occupancy of Ge atoms in the spinel lattice by introducing the cationic disorder parameter (y) which is done in such a way that one can tailor the pyrochlore geometry and determine the electronic/magnetic structure quantitatively. For all the compositions (x), the system exhibits weak tetragonal distortion (c/a ≠ 1) due to the non-degenerate

d

z

2

and

d

x

2

−

y

2

states (e

g
orbitals) of the B-site Co. We observe large exchange splitting (ΔEX ∼ 9 eV) between the up and down spin bands of t
2g
and e

g
states, respectively, of tetrahedral and octahedral Co2+ (4A2(g)(F)) and moderate crystal-field splitting (ΔCF ∼ 4 eV) and the Jahn–Teller distortion (ΔJT ∼ 0.9 eV). These features indicate the strong intra-atomic interaction which is also responsible for the alteration of energy band-gap (1.7 eV ⩽ E

g
⩽ 3.3 eV). The exchange interaction (J
BB ∼ −4.8 meV, for (x, y) = (0.25, 0)) between the Co2+ dominates the overall antiferromagnetic behaviour of the system for all ‘x’ as compared to J
AA (∼−2.2 meV, for (x, y) = (0.25, 0)) and J
AB (∼−1.8 meV, for (x, y) = (0.25, 0)). For all the compositions without any disorderness in the system, the net ferrimagnetic moment (Δμ) remains constant, however, increases progressively with increasing x due to the imbalance of Co spins between the A- and B-sites.
Laser ray bundle: a thermometry method for HIFU heating
Authors: Daoud Hussein , Oweis Ghanem F
Published: January 2021

High-intensity focused ultrasound (HIFU) is a therapeutic modality that heats tissue by focusing a sound beam into a narrow, localized region. This paper is concerned with the thermo-optic lensing effect observed by Al-Qraini et al (Ultrasound Med. Biol.
39 647–59) when visible light was shone at a transparent tissue-mimicking phantom heated by HIFU. Thermal lensing was caused by light refraction as it passed through the thermal gradient region. HIFU thermal lensing was reproduced experimentally and studied analytically using the geometric (eikonal) ray equation to devise a method for temperature measurement. Under the Gaussian thermal field assumption, explicit closed form solutions were found for the forward thermo-optic ray deflection problem, and for the inverse opto-thermal conversion problem that yielded the underlying temperature field from measured ray deflections. Neither temperature calibration nor iterative computations were needed. In the experimental setup, a bundle of thin laser rays illuminated the HIFU-heated spot in a clear tissue-mimicking phantom. The ray deflections were recorded and directly converted into temperature with very good temporal and spatial resolution. These compared reasonably well against the output of an embedded thermocouple (TC)—considering the absorptive and viscous heating artifacts which were also investigated. The TC metallic tip junction was carefully positioned to coincide with the axis of peak heating. It was found that the TC stem (wire) transferred heat by conduction from the tip into the tissue located off the HIFU heating axis. The proposed thermometry method can be useful in elucidating heating from focused ultrasound sources, or from other sources of localized heating such as lasers.
Accurate and dynamic 3D shape measurement with digital image correlation-assisted phase shifting
Authors: Hu Pengyu , Yang Shuming , Zheng Fenghe , Yuan Ye , Wang Teng , Li Shusheng , Liu Haibao , Dear John P
Published: January 2021

Phase-shifting profilometry (PSP) has been widely used in structured-light (SL) systems for three-dimensional (3D) shape measurements, but the speed of the PSP technique is limited by increased phase-shifting patterns. This paper proposes an accurate and dynamic 3D shape measurement method by projecting only four patterns, including three-step phase-shifting patterns and one speckle pattern. Three-step phase-shifting images are used to obtain the initial unwrapped phase map with phase ambiguity. Based on the principle of digital image correlation and multi-view geometry, the absolute phase can be recovered reliably without requiring any embedded features or pre-defined information of the object. To improve the measurement accuracy, the projector coordinate is used as the measuring coordinate to establish a novel stereo SL system model. By solving a least square solution using the triple-view information, accurate 3D surface data can be reconstructed. The experimental results indicate that the proposed method can perform high-speed and accurate 3D shape measurements with an accuracy of 10.64 μm, which is superior to conventional methods and has certain instructive significance for 3D profilometry and measurement engineering.
Improved sodium storage properties of nickel sulfide nanoparticles decorated on reduced graphene oxide nanosheets as an advanced anode material
Authors: Li Kai , Yu Jianhua , Wang Qianyu , Li Lizhi , Zhang Wendi , Ma Jianru , Zhang Jianmin , Liu Pu , Li Dan
Published: January 2021

For sodium ion batteries, the fabrication of nanocrystal anode materials has been identified as a satisfactory strategy to improve electrochemical performance and maintain the structural integrity of electrodes. However, the issues of agglomeration and serious volume variation have always existed within the process of charging/discharging in anode materials. In this work, a series of composites of nickel sulfide nanoparticles decorated on reduced graphene oxide nanosheets (denoted as NiS2@rGO) were successfully synthesized via a simple one-step hydrothermal method under different temperatures. The strategy of confining nickel sulfide nanoparticles within the interlayer of graphene nanosheets can not only avoid the agglomeration, but also alleviate the volume change to some extent in electrode materials. For sodium ion storage, the NiS2@rGO synthesized at 160 °C exhibited a higher reversible capacity and better rate capability.
A novel hybrid 3D dose reconstruction approach for pre-treatment verification of intensity modulated proton therapy plans
Authors: Arjunan Manikandan , Sharma Dayananda Shamurailatpam , Kaushik Suryakant , Krishnan Ganapathy , Patro Kartikeshwar C , Padanthaiyil Noufal Mandala , Rajesh T , Jalali R
Published: January 2021

Aim. A novel hybrid three-dimensional (3D) dose reconstruction method, based on planar dose measured at a single shallower depth, was developed for use as patient-specific quality assurance (PSQA) of intensity modulated proton therapy (IMPT) plans. The accuracy, robustness and sensitivity of the presented method were validated for multiple IMPT plans of varying complexities. Methods and Materials. An in-house MATLAB program was developed to reconstruct 3D dose distribution from the planar dose (GyRBE) measured at 3 g cm−2 depth in water or solid phantom using a MatriXX PT ion chamber array. The presented method was validated extensively for 11 single-field optimization (SFO) and multi-field optimization (MFO) plans on Proteus Plus. A total of 47 reconstructed planar doses at different depths were compared against the corresponding RayStation treatment planning system (TPS) and MatriXX PT measurement using a gamma passing rate (γ%) evaluated for 3%/3 mm. The robustness of the reconstruction method with respect to depth, energy layers, field dimensions and complexities in the spot intensity map (SIM) were analysed and compared against the standard PSQA. The sensitivity of the reconstruction method was tested for plans with intentional errors. Results. The presented reconstruction method showed excellent agreement (mean γ% > 98%) and robustness with both TPS-calculated and measured dose planes at all depths (2.97–30 g cm−2), energy layers (82.1–225.5 MeV), field dimensions, target volume (17.7–1000 cm3) and SIMs from both SFO and MFO plans. In comparison to the overall mean ± SD γ% from standard PSQA, the reconstruction method showed reductions in mean γ% within 1% for both standard cubes and clinical plans. The reconstruction method was sensitive enough to detect intentional spot positional errors in a selected energy layer of a plan. Conclusion. The presented hybrid reconstruction method is sufficiently accurate, robust and sensitive to estimate planar dose at any user-defined depth. It simplifies the measurement setup and eliminates multiple depth measurements.
Low-frequency conductivity tensor imaging with a single current injection using DT-MREIT
Authors: Sadighi Mehdi , Şişman Mert , Açıkgöz Berk C , Eroğlu Hasan H , Eyüboğlu B Murat
Published: January 2021

Diffusion tensor-magnetic resonance electrical impedance tomography (DT-MREIT) is an imaging modality to obtain low-frequency anisotropic conductivity distribution employing diffusion tensor imaging and MREIT techniques. DT-MREIT is based on the linear relationship between the conductivity and water self-diffusion tensors in a porous medium, like the brain white matter. Several DT-MREIT studies in the literature provide cross-sectional anisotropic conductivity images of tissue phantoms, canine brain, and the human brain. In these studies, the conductivity tensor images are reconstructed using the diffusion tensor and current density data acquired by injecting two linearly independent current patterns. In this study, a novel reconstruction algorithm is devised for DT-MREIT to reconstruct the conductivity tensor images using a single current injection. Therefore, the clinical applicability of DT-MREIT can be improved by reducing the total acquisition time, the number of current injection cables, and contact electrodes to half by decreasing the number of current injection patterns to one. The proposed method is evaluated utilizing simulated measurements and physical experiments. The results obtained show the successful reconstruction of the anisotropic conductivity distribution using the proposed single current DT-MREIT.
An analytical model of full-field displacement and strain induced by amplitude-modulated focused ultrasound in harmonic motion imaging
Authors: McGarry Matthew D J , Campo Adriaan , Payen Thomas , Han Yang , Konofagou Elisa E
Published: January 2021

The majority of disease processes involves changes in the micro-structure of the affected tissue, which can translate to changes in the mechanical properties of the corresponding tissue. Harmonic motion imaging (HMI) is an elasticity imaging technique that allows the study of the mechanical parameters of tissue by detecting the tissue response by a harmonic motion field, which is generated by oscillatory acoustic radiation force. HMI has been demonstrated in tumor detection and characterization as well as monitoring of ablation procedures. In this study, an analytical HMI model is demonstrated and compared with a finite element model (FEM), allowing rapid and accurate computation of the displacement, strain, and shear wave velocity (SWV) at any location in a homogenous linear elastic material. Average absolute differences between the analytical model and the FEM were respectively 1.2% for the displacements and 0.5% for the strains for 41 940 force voxels at 0.22 s per displacement evaluation. A convergence study showed that the average difference could be further decreased to 1.0% and 0.15% for the displacements and strains, respectively, if force resolution is increased. SWV fields, as calculated with the FEM and the analytical model, have regional differences in velocities up to 0.57 m s−1 with an average absolute difference of 0.11 ± 0.07 m s−1, primarily due to imperfections in the non-reflecting FEM boundary conditions. The apparent SWV differed from the commonly used plane-wave approximation by up to 1.2 m s−1 due to near and intermediate field effects. Maximum displacement amplitudes for a model with an inclusion stabilize within 10% of the homogenous model at an inclusion radius of 10 mm while the maximum strain reacts faster, stabilizing at an inclusion radius of 3 mm. In conclusion, an analytical model for HMI stiffness estimation is presented in this paper. The analytical model has advantages over FEM as the full-field displacements do not need to be calculated to evaluate the model at a single measurement point. This advantage, together with the computational speed, makes the analytical model useful for real-time imaging applications. However, the analytical model was found to have restrictive assumptions on tissue homogeneity and infinite dimensions, while the FEM approaches were shown adaptable to variable geometry and non-homogenous properties.
First measurements of line-integrated electron density in an ITER-like configuration using the JET far infrared polarimeter diagnostic
Authors: Rossi Riccardo , Boboc Alexandru , Orsitto Francesco Paolo , Gelfusa Michela , Gaudio Pasquale
Published: January 2021

Polarimetry exploits the optical activity and birefringent properties of thermonuclear plasmas to calculate some important quantities for their control like the line-integrated electron density and magnetic field distribution. The Joint European Torus (JET) far infrared polarimeter shares the same probing laser beams of the interferometer, with eight channels, four vertical and four lateral. While the vertical channels were already optimised to provide accurate measurements of the Faraday rotation angle, Cotton–Mouton (CM) phase shift and ellipticity, the lateral channels had been only optimised for Faraday rotation angle alone. By setting the initial polarisation angle of the lateral channel at zero degrees the CM effect is minimised, the ellipticity is almost zero, and the CM phase shift angle is impossible to measure. During the recent JET experimental campaign (C38 in 2019–2020), the input polarisation for the lateral channels was altered for a class of pulses to analyse the possibility to measure the CM phase shift angle and the ellipticity, and, more important, to assess if it is possible to provide information of line-integrated electron density using the lateral channels of JET polarimetry in an ITER-like configuration. As a note, ITER will have only tangential channels with reflectors buried deep inside the first wall, so this setup was truly an ITER-like configuration. The results clearly show huge improvements, which can be achieved by just changing the input polarisation. Moreover, the analysis of the measurements shows that the polarimetric measurements have a systematic error, which is probably due to the effect of refraction and to the in-vessel mirrors, which was only partially taken into account during the calibration phase before the plasma. Thus, a new calibration method was developed and the results presented on a statistical basis. It has been demonstrated that, varying the input polarisation of the polarimeter and using the new calibration method, it is possible to measure the line-integrated electron density, using the CM phase shift (or the ellipticity) of the lateral channels, with good accuracy with respect to the electron density measured by the interferometer that was considered the reference.
Three-dimensional first principles simulation of a hydrogen discharge
Authors: Chew Junxian , Gibbon Paul , Brömmel Dirk , Wauters Tom , Gribov Yuri , de Vries Peter
Published: January 2021

Townsend discharge theory is commonly used to describe and approximate the ionisation fraction growth rate in the very early phase of plasma initiation in tokamak devices via ohmic breakdown. The prediction of the ionisation fraction growth rate is done most commonly with continuum or kinetic models, which in turn boil down to the relation between the first Townsend’s coefficient α, pressure p and electric field strength E (namely, α/p and E/p). To date there are few computational models that attempt to simulate the ionisation fraction growth rate via explicit modelling of each ionisation event through electron-neutral collisions. This is largely due to the challenge of addressing the exponential growth of charged particles from ionisation processes, combined with the high computational cost of N-body simulation. In this work, a new fully three-dimensional, first-principles model of a Townsend hydrogen discharge is demonstrated and benchmarked against prior experimental findings. These tests also include comparisons of three separate models for the scattering angle and their impact on the obtained α/p and mean electron drift velocity. It is found that isotropic scattering combined with restricting the freed electron’s scattering angle along the incident electron’s velocity vector during ionisation events gives the closest agreement of α/p compared to experimental measurements.
Jet quenching and medium response in high-energy heavy-ion collisions: a review
Authors: Cao Shanshan , Wang Xin-Nian
Published: January 2021

Jet quenching has been used successfully as a hard probe to study properties of the quark–gluon plasma (QGP) in high-energy heavy-ion collisions at both the relativistic heavy-ion collider and the large hadron collider. We will review recent progresses in theoretical and phenomenological studies of jet quenching with jet transport models. Special emphasis is given to effects of jet-induced medium response on a wide variety of experimental observables and their implications on extracting transport properties of the QGP in heavy-ion collisions.
Majorana bound state manipulation by current pulses
Authors: Lankhorst Martijn , Jansen Thies , Brinkman Alexander , Golubov Alexander
Published: January 2021

Majorana bound states (MBSs) can occur in Josephson junctions of conventional s-wave superconductors coupled via a strong topological insulator. In configurations of multiple line junctions meeting at a point, the criterion for the MBS to exist coincides with the presence of a fractional Josephson vortex with 2π phase winding. We investigate the dynamic stability of such vortices in arrays of tri- and quad-junctions. The existence of fractional vortices in arrays is demonstrated, but the dynamic stability is found to depend critically on the current-phase relation and the inductance. We propose the idea, and study the feasibility, of manipulating the location of the vortices in arrays by using current pulses, compatible with rapid single flux quantum technology. It is shown theoretically, using a modified resistively shunted junction model, that braiding operations can be achieved using current pulses injected from the edge of the array. It is necessary to use vortex sites with elevated critical current as traps.
Canted standing spin-wave modes of permalloy thin films observed by ferromagnetic resonance
Authors: Dąbrowski Maciej , Hicken Robert J , Frisk Andreas , Newman David G , Klewe Christoph , N’Diaye Alpha T , Shafer Padraic , van der Laan Gerrit , Hesjedal Thorsten , Bowden Graham J
Published: January 2021

Non-collinear spin structures in materials that combine perpendicular and in-plane magnetic anisotropies are of great technological interest for microwave and spin wave-assisted magnetization switching. [Co/Pt] multilayers are well-known perpendicular anisotropy materials that have the potential to pin the magnetization of a soft magnetic layer, such as permalloy (Py), that has in-plane anisotropy, thereby forming a magnetic exchange spring. Here we report on multilayered [Co/Pt]/Pt/Py films, where an additional ultrathin Pt spacer has been included to control the coupling between the sub-units with in-plane and perpendicular magnetic anisotropy. Vector network analyser (VNA)-ferromagnetic resonance (FMR) measurements were made to obtain a complete picture of the resonant conditions, while the dynamical response of the sub-units was probed by synchrotron-based element- and phase selective x-ray detected FMR (XFMR). For all samples, only slight pinning of the dynamic magnetization of the Py by the [Co/Pt] was noted, and the FMR results were dominated by the 50 nm thick Py layer. Out-of-plane VNA-FMR maps reveal the presence of additional modes, e.g. a perpendicular standing spin-wave (PSSW) state. However, as the magnetic field is reduced below the saturation field, the PSSW state morphs continuously through a series of canted standing spin-wave (CSSW) states into a horizontal standing spin-wave (HSSW) state. The PSSW, CSSW and HSSW states are well described using a multilayer model of the Py film. The observation of CSSW modes is of particular relevance to microwave assisted magnetic recording, where microwave excitation stimulates precession of a soft layer canted out of plane by a pulsed magnetic field.
Influence of local fields on the dynamics of four-wave mixing signals from 2D semiconductor systems
Authors: Hahn Thilo , Kasprzak Jacek , Machnikowski Paweł , Kuhn Tilmann , Wigger Daniel
Published: January 2021

In recent years the physics of two-dimensional semiconductors was revived by the discovery of the class of transition metal dichalcogenides. In these systems excitons dominate the optical response in the visible range and open many perspectives for nonlinear spectroscopy. To describe the coherence and polarization dynamics of excitons after ultrafast excitation in these systems, we employ the Bloch equation model of a two-level system extended by a local field describing the exciton–exciton interaction. We calculate four-wave mixing (FWM) signals and analyze the dependence of the temporal and spectral signals as a function of the delay between the exciting pulses. Exact analytical results obtained for the case of ultrafast (δ-shaped) pulses are compared to numerical solutions obtained for finite pulse durations. If two pulses are used to generate the nonlinear signal, characteristic spectral line splittings are restricted to short delays. When considering a three-pulse excitation the line splittings, induced by the local field effect, persist for long delays. All of the found features are instructively explained within the Bloch vector picture and we show how the exciton occupation dynamics govern the different FWM signals.
Thermodynamics of magnetic emergent crystals under coupled magnetoelastic fields
Authors: Hu Yangfan , Wan Xuejin , Wang Biao
Published: January 2021

Magnetic fields and mechanical forces can change the deformation and stability of magnetic emergent crystals (MECs) such as Bloch skyrmion crystal (SkX), Néel SkX and Anti-SkX. Due to the tensor nature of strains, mechanical loads provide more fruitful ways to manipulate the MECs, while their effect on MECs other than the Bloch SkX is hitherto unclear. We construct a thermodynamic model for noncentrosymmetric ferromagnets in all possible point groups when subjected to coupled magnetoelastic fields. Compared with classic theories, we include terms coupling the elastic strains, the magnetization, and its derivatives in the free energy, which lead to strain-induced Dzyaloshinskii–Moriya interaction anisotropy. For epitaxial thin films in three types of point groups (T, C
3v
, D
2d
) hosting Bloch SkX, Néel SkX and Anti-SkX, we find the newly added terms always deform the MECs and eventually lead to their instability as the misfit strains increase. Specifically, for Bloch SkX in group T materials and Néel SkX in group C
3v
materials, a novel magnetic phase called paired-skyrmion crystal (pSkX) appears. Our theory lays the path to study deformation and phase transitions of different MECs, and to explore novel states of MECs in chiral magnets when subjected to magnetoelastic fields.
A sparse multiscale nonlinear autoregressive model for seizure prediction
Authors: Yu Pen-Ning , Liu Charles Y , Heck Christianne N , Berger Theodore W , Song Dong
Published: January 2021

Objectives. Accurate seizure prediction is highly desirable for medical interventions such as responsive electrical stimulation. We aim to develop a classification model that can predict seizures by identifying preictal states, i.e. the precursor of a seizure, based on multi-channel intracranial electroencephalography (iEEG) signals. Approach. A two-level sparse multiscale classification model was developed to classify interictal and preictal states from iEEG data. In the first level, short time-scale linear dynamical features were extracted as autoregressive (AR) model coefficients; arbitrary (usually long) time-scale linear and nonlinear dynamical features were extracted as Laguerre–Volterra AR model coefficients; root-mean-square error of model prediction was used as a feature representing model unpredictability. In the second level, all features were fed into a sparse classifier to discriminate the iEEG data between interictal and preictal states. Main results. The two-level model can accurately classify seizure states using iEEG data recorded from ten canine and human subjects. Adding arbitrary (usually long) time-scale and nonlinear features significantly improves model performance compared with the conventional AR modeling approach. There is a high degree of variability in the types of features contributing to seizure prediction across different subjects. Significance. This study suggests that seizure generation may involve distinct linear/nonlinear dynamical processes caused by different underlying neurobiological mechanisms. It is necessary to build patient-specific classification models with a wide range of dynamical features.
Kinetic ballooning mode unstable in the 2nd stability regime as a possible source of the low-k broadband fluctuation observed in the wide-pedestal QH-mode
Authors: Kim J.Y. , Han H.S.
Published: January 2021

The kinetic ballooning mode destabilized by the ion magnetic curvature drift resonance in the 2nd ballooning stability regime is shown to be a plausible candidate for the low-k broadband fluctuation recently observed in the wide-pedestal quiescent-H (QH) mode of DIII-D. With its intrinsic real frequency approaching very closely to the ion pressure diamagnetic frequency in the pedestal-like condition with a steep gradient, this mode can be nearly free from the first-order ExB flow shear effect driven by the ion pressure gradient. As a result, it can be sensitive to the next-order one by toroidal rotation, with the possible strong excitation in the low toroidal rotation limit. The frequency in the lab frame and the peak wavenumber spectrum of the mode appear to be in the range similar to those of the observed low-k fluctuation.
Scaling of impurity fractions for divertor detachment in high-density high-power operation scenarios
Authors: Huber A. , Chankin A.V.
Published: January 2021

For future reactor designs and for planning of operational scenarios in the present and future machines, impurity fractions in the tokamak divertor plasma, c

Z
, is an essential input for predictive scalings of divertor detachment. A new quantitative scaling law for c

Z
, averaged over the scrape-off layer (SOL), required to attain detachment is developed for high power H-mode plasmas operated at high densities close to the density limit. It is based on a simple SOL radiation model which uses the combination of the empirical scaling laws for the H-mode power threshold and the separatrix density limit imposed by MHD instabilities. Additionally, it assumes, in agreement with experimental observations that the width of the power conducting layer outside of the separatrix scales approximately with the ion poloidal gyro-radius. The derived expression for c

Z
scales strongly with toroidal magnetic field, B, major radius R, the factor of access of the power flow through the separatrix over that required for the L–H transition, f
LH, and isotope mass A:

c

Z

∝

B

1.47

R

1.59

f

L
H

1.38

/

A

1.38

. Estimates of required impurity fractions for divertor detachment for an number of impurity species (N2, Ne and Ar) in future tokamak reactors ITER and DEMO are made in the paper.
Comparative Characteristics of Big Data Storage Formats
Authors: Belov Vladimir , Tatarintsev Andrey , Nikulchev Evgeny
Published: January 2021

One of the most important tasks of any platform for big data processing is the task of the storing data received. Different systems have different requirements for the storage formats of big data, which raises the problem of choosing the optimal data storage format to solve the current problem. This paper describes the five most popular formats for storing big data, presents an experimental evaluation of these formats and a methodology for choosing the format.
The two-stage classification based on 1-SVM and RF classifiers
Authors: Demidova Liliya , Klyueva Irina
Published: January 2021

The approach to the two-stage classification based on the 1-SVM classifier used as the main classifier and the RF classifier used as the auxiliary classifier has been considered. The proposed approach improves the quality of classification when using imbalanced datasets. The results of the comparative analysis of the proposed approach and the alternative approach to the two-stage classification, in which the binary SVM classifier is used as the main classifier, and the RF classifier as the auxiliary classifier, are presented.
Laboratory complex for studying the quality of materials using spectral analysis of signals
Authors: Khamitov R M , Kolchurina M A , Kolchurina I Y , Ponomareva K V , Silvestrov Y G
Published: January 2021

The article describes the process of development and testing of a laboratory complex for spectral analysis of measured data, which is based on a signal processing method based on measuring the frequency and amplitude of the signal (spectral method) with further evaluation using fast Fourier transform. The described laboratory complex consists of a spectrum analyzer connected to a personal computer with special software installed on it, a loudspeaker and a laser sensor. The paper substantiates the relevance of the development, due to the fairly wide use of spectral analysis methods in science, technology and production, the advantages of using a laboratory complex in comparison with analogues were shown. There is a description of the experiments to measure the speed of objects, control their location, vibration measurement. The procedure of verification and calibration is performed with the use of this complex, as well as the use of the system of automatic regulation and stabilization of production processes and the training of laboratory works for students of different directions of training in technical and economic specialties.
Ultrasonic testing of concrete hardening in pile foundations
Authors: Loseva E S , Potapov A I , Osokin A I
Published: January 2021

This article discusses the ultrasonic method for monitoring the strength of concrete in piles. Geotechnical conditions of the city territory are indicated. The conditions of hardening of the concrete mixture in the pile shaft and the normal conditions of hardening of concrete samples are described. A detailed description of the control technique is given. The dependence of the ultrasonic wave propagation velocity on the age of concrete in piles and concrete samples is established. Based on the results of the work, it was concluded that it is possible to control the strength of concrete in-situ.