Power-law Fit Research Articles

Preferential acceleration of heavy ions in magnetic reconnection: Hybrid-kinetic simulations with electron inertia

Solar energetic particles (SEPs) in the energy range 10s KeV/nucleon - 100s MeV/nucleon originate from the Sun. Their high flux near Earth may damage the space-borne electronics and generate secondary radiation that is harmful for life on Earth. Thus, understanding their energization on the Sun is important for space weather prediction. Impulsive (or $ $He-rich) SEP events are associated with the acceleration of charge particles in solar flares by magnetic reconnection and related processes. The preferential acceleration of heavy ions and the extraordinary abundance enhancement of $ ^3$He in the impulsive SEP events are not understood yet. In this paper we study the acceleration of heavy ions and its consequences for their abundance enhancements by magnetic reconnection, an established acceleration source for impulsive SEP events in which heavy-ion enhancement is observed We employed a two-dimensional hybrid-kinetic plasma model (kinetic ions and inertial electron fluid) to simulate magnetic reconnection. All the ion species are treated self-consistently in our simulations. We find that heavy ions are preferentially accelerated to energies many times higher than their initial thermal energies by a variety of acceleration mechanisms operating in reconnection. The most efficient acceleration takes place in the flux pileup regions of magnetic reconnection. Heavy ions with sufficiently low values of charge-to-mass ratio ($Q/M$) can be accelerated by pickup mechanism in outflow regions even before any magnetic flux is piled up. The energy spectra of heavy ions develop a shoulder-like region, a nonthermal feature, as a result of the acceleration. The spectral index of the power-law fit to the shoulder region of the spectra varies approximately as $(Q/M)^ $. The abundance enhancement factor, defined as the number of particles above a threshold energy normalized to the total number of particles, scales as $(Q/M)^ alpha $, where alpha increases with the energy threshold. We discuss our simulation results in the light of the SEP observations.

Direct measurements of cosmic – Ray iron and nickel with CALET on the International Space Station

Iron and nickel cosmic ray nuclei play a key role in the understanding of the acceleration and propagation mechanisms of charged particles in our Galaxy. In fact, iron and nickel are the most abundant nuclei among the heavy elements and provide favorable conditions for a low background measurement thanks to the negligible contamination from spallation of higher mass elements. CALET, operating on the ISS since 2015, has excellent capabilities of charge discrimination up to nickel and can measure the energy of cosmic ray nuclei thanks to a lead tungstate calorimeter providing a direct and precise measurement of heavy charged nuclei spectra. In this contribution, a direct measurement of iron and nickel nuclei spectra in the energy range from 10 GeV/n to 2 TeV/n and from 8.8 GeV/n to 240 GeV/n, respectively is presented. More than five years of data collected by CALET were used. A detailed study of systematic uncertainties is also illustrated. The measured spectra are compared with the ones measured by other experiments and are compatible with a single power law fit in the energy region from 50 GeV/n to 2 TeV/n and from 20 GeV/n to 240 GeV/n for iron and nickel respectively. Also, the ratio between nickel and iron spectra is reported.

Radial Evolution of the Near-Sun Solar Wind: Parker Solar Probe Observations

Abstract A statistical study of the radial evolution of the solar wind within 0.3 au is shown in this Letter based on Parker Solar Probe observations. We show the radial distribution of the main solar wind parameters, including the solar wind speed V sw, magnetic field ∣B∣, the number density of electrons N e , protons N p , and α particles N α , and the temperature of protons T p and α particles T α . The power-law fitting results of these parameters in the near-Sun solar wind are compared with previous radial models. We also show the radial distribution of the angle between the magnetic field B , solar wind V sw, and radial vector R . In the solar wind within 0.3 au, θ BV sw , and θ BR mainly concentrate around 135°, and θ RV sw almost concentrates in the region less than 20°. Furthermore, we also present the radial distribution of the relative values between the solar wind parameters, including the electric neutrality estimation ((2 × N α + N p )/N e ≃ 1 within 0.2 au), relative number density ratio (N α /N p ≃ 0.02 in slow solar wind and N α /N p ≃ 0.04 in faster solar wind), relative temperature ratio (T α /T p decreases with the increase of heliocentric distance and its decay rate is larger in faster solar wind), and differential speed (both V α − V p and (V α − V p )/V A are larger in the faster solar wind and decrease as heliocentric distance increases).

Oxidation behavior of Zr-2.5Nb alloy exposed to steam in the temperature range of 600–1200 °C

Zr-2.5Nb pressure tube material was subjected to isothermal steam exposures in the range 600–1200 °C for different durations to predict its oxidation behavior during hypothetical accident scenarios. The oxidation exponent obtained from power law fitting of the thermogravimetry (TG) curves deviated from parabolic regime. Nevertheless, oxidation kinetics was described by determining the parabolic rate constants (Kp) in two temperature ranges: Kp = 0.029 exp(-111075/RT) (kg/m2)2/sec for 600–900 °C whereas Kp = 77652.6 exp(-254824/RT) (kg/m2)2/sec for 900–1200 °C. In the tested durations, only the 1000 °C sample has shown breakaway transition, after approximately 105 min and has absorbed the highest amount of hydrogen amongst all samples. The trend in hydrogen pickup fraction (HPUF) was verified by two complementary hydrogen determination methods. Clear differences were identified in the α-Zr(O) layer formed on the samples below and above 900 °C. In the α + β range of 600–900 °C, α-Zr(O) consisted of tiny β precipitates. At and above 900 °C in the fully β range, columnar α-Zr(O) grains were observed.

Root anatomy and biomechanical properties: improving predictions through root cortical and stele properties

PurposeQuantifying the stability of individual plants or their contribution to soil reinforcement against erosion or landslides requires an understanding of the tensile properties of their roots. This work developed a new analytical model to understand the tensile stress–strain behaviour of a single root axis, which is the first to incorporating root anatomical features, in order to reduce the existing uncertainty in predictions.MethodsThe root was modelled as a linear elastic stele connected to a surrounding linear elastic cortex by means of a linear elastic stele–cortex interface. By solving for force equilibrium, an analytical solution for the full tensile stress–strain behaviour — including any intermediate brittle failures of the stele, cortex and/or interface — was obtained. This model was compared to tensile tests and laser ablation tomography for maize roots.ResultsThe new modelling approach demonstrated that the root tensile strength is fully determined by the strength of the stele alone, which was an order of magnitude larger than that of the cortex while also 3–4 times stiffer. The reduction in root stiffness beyond the yield point was linked to continuing fracturing of the cortex and debonding along the stele–cortex interface. A larger proportion of the variation in experimentally measured biomechanical characteristics could be explained compared to root diameter power-law fitting methods typically applied in the literature.ConclusionStele and cortex biomechanical properties are substantially different, affecting the tensile behaviour of plant roots. Accounting for these anatomical traits increased the accuracy root biomechanical properties from tensile tests.

Covering factor in AGNs: Evolution versus selection

Aims. In every proposed unification scheme for active galactic nuclei (AGNs), an integral element is the presence of circumnuclear dust arranged in torus-like structures, partially obscuring the nuclear (accretion-associated) radiation. A crucial model parameter in this context is the covering factor (CF), which can be defined as the ratio of the infrared luminosity of the dusty torus, LIR, to the accretion disk bolometric luminosity, Lagn. Recent research has discussed the potential redshift evolution of the CF. Our study aims to determine whether this observed evolution is genuine or if selection effects significantly influence it. Methods. Based on cross-matched multiwavelength photometrical data from the five major surveys (SDSS, GALEX, UKIDSS, WISE, Spitzer), a sample of over 17 000 quasars was derived. The main parameters of quasars, such as black hole masses and the Eddington ratios, were calculated based on the spectroscopic data. The data were divided into two redshift bins: low-z quasars (redshift from 0.7 to 1.1) and high-z quasars (from 2.0 to 2.4). The associated smaller datasets with higher quality data were constructed from the WISE W3 and W4 detections with S/N > 5 and the Spitzer MIPS 24 μm photometry. The CF was determined by computing the ratio of integrated luminosities, LIR and Lagn, using two methods: power-law fitting and the area between all photometric points. We explored different selection effects and their influence on CF estimates. Finally, statistical tests were employed to assess the hypothesis of CF evolution within the higher-quality datasets. Results. We identified an issue with the accuracy of the WISE W4 filter. Whenever feasible, it is recommended to utilize Spitzer MIPS 24 μm data. Luminosities obtained through direct integration of all photometric data points exhibit higher accuracy compared to values derived from a power-law approximation. The Efron & Petrosian test confirmed the presence of luminosity evolution with redshift for both LIR and Lagn. The low-z and high-z samples both exhibit a similar correlation between Lagn and LIR. The calculated median CF values are comparable within the errors: log CFlow-z = −0.18 ± 0.11 and log CFhigh-z = −0.01 ± 0.13. Additionally, the Spitzer photometry dataset reinforces this consistency with log CFlow-z = −0.19 ± 0.11 and log CFhigh-z = −0.18 ± 0.11. Conclusions. No discernible evolution of the CF was observed in the subsample of quasars with high supermassive black hole (SMBH) mass bin or high luminosities, as the CF values for low-z and high-z quasars have the same distributions. The relationship between LIR and Lagn deviates slightly from the expected 1:1 scaling, suggesting a more intricate connection between CF and Lagn. However, no statistically significant dependence of CF on luminosities could be claimed across the entire dataset (merged redshifts). It is worth noting that the low-z/low-luminosity portion of the CF distribution is influenced by contamination, possibly due to polar dust, as suggested in the literature, while the high-z/high-luminosity segment is affected by observational biases.

Spectrum of gravitational waves from long-lasting primordial sources

We discuss long-lasting gravitational wave sources arising and operating during radiation-dominated stage. Under a set of assumptions, we establish the correspondence between cosmological evolution of a source and the resulting gravitational wave spectrum. Namely, for the source energy density ρs falling as a power law characterized by the exponent β, i.e., ρs ∝ 1/aβ , where a is the Universe scale factor, the spectrum takes the form Ωgw ∝ f 2β-8 in certain ranges of values of constant β and frequencies f. In particular, matching to the best fit power law shape of stochastic gravitational wave background discovered recently by Pulsar Timing Array collaborations, one identifies β ≈ 5. We demonstrate the correspondence with concrete examples of long-lasting sources: domain walls and cosmic strings.

Bifurcating paths: The relation between preferential pathways, channel splitting, under sampled regions, and tortuosity on the Darcy scale

Transport in porous media on the Darcy scale can be both Fickian and non-Fickian, an outcome dependent on the degree of homogeneity of the hydraulic conductivity pattern, as well as the boundary conditions and flow rate. The non-Fickian manifestation is generally associated with heterogeneous media, which promotes the formation of preferential pathways that funnel the transport. Yet this funneling occurs in both weakly and strongly heterogeneous domains, through a mechanism that is yet to be fully characterized. We model Darcy-scale transport using a particle tracking code (PT) that samples a 2D, lognormally distributed conductivity field with a variance representing a range of homogeneous to heterogeneous domains. We find that the resulting preferential pathways tend to split into more pathways (bifurcations), leaving regions into which particles do not invade, which we refer to as “under sampled regions” (USR), while forming a tortuous path. The fraction of bifurcations decreases downstream, reaching an asymptotic value, with a trend that can be fitted as a power-law of the variance. We show that the same power-law exponent relating the bifurcations to the variance holds true for the USR fraction, tortuosity, and fractal dimension with the same variance. An extension of our work is also presented for varying correlation length of the conductivity spatial distribution. We further expand our analysis to a case of impermeable fraction in a uniform conductivity field and show that the power-law fit still holds.Key PointsPreferential pathways at the Darcy scale can be characterized by their bifurcations, and USR formation formed by their tortuous path.The bifurcation fraction, USR, tortuosity, and fractal dimension scale with the conductivity heterogeneity.The same power law exponent captures the scaling of bifurcation fraction, USR, tortuosity, and fractal dimension.

Efficient single-run implementation of generalized Einstein relation to compute transport coefficients: A binary-based time sampling.

A robust and simple implementation of the generalized Einstein formulation using single equilibrium molecular dynamics simulation is introduced to compute diffusion and shear viscosity. The unique features underlying this framework are as follows: (1) The use of a simple binary-based method to sample time-dependent transport coefficients results in a uniform distribution of data on a logarithmic time scale. Although we sample "on-the-fly," the algorithm is readily applicable for post-processing analysis. Overlapping same-length segments are not sampled as they indicate strong correlations. (2) Transport coefficients are estimated using a power law fitting function, a generalization of the standard linear relation, that accurately describes the long-time plateau. (3) The use of a generalized least squares (GLS) fitting estimator to explicitly consider correlations between fitted data points results in a reliable estimate of the statistical uncertainties in a single run. (4) The covariance matrix for the GLS method is estimated analytically using the Wiener process statistics and computed variances. (5) We provide a Python script to perform the fits and automate the procedure to determine the optimal fitting domain. The framework is applied to two fluids, binary hard sphere and a Lennard-Jones near the triple point, and the validity of the single-run estimates is verified against multiple independent runs. The approach should be applicable to other transport coefficients since the diffusive limit is universal to all of them. Given its rigor and simplicity, this methodology can be readily incorporated into standard molecular dynamics packages using on-the-fly or post-processing analysis.

Magnetic studies of ultrafine CoFe2O4 nanoparticles with different molecular surface coatings.

Surface functionalized ultrafine CoFe2O4 nanoparticles (NPs), with mean diameter ∼5 nm, were investigated by means of DC magnetization and AC susceptibility over the temperature range of 4-400 K. All NPs present the same CoFe2O4 core, with different molecular surface coatings, increasing gradually the number of carbon atoms in the coating layer: glycine (C2H5NO2), alanine (C3H7NO2), aminobutanoic acid (C4H9NO2), aminohexanoic acid (C6H13NO2), and aminododecanoic acid (C12H25NO2). Samples were intentionally fabricated in order to modulate the core-core magnetic dipolar interaction, as the thickness of the coating layer increases with the number of carbon atoms in the coating molecule. The magnetic data of the uncoated CoFe2O4 NPs were also collected for comparison. All investigated CoFe2O4 NPs (coated and uncoated) are in a magnetically blocked state at room temperature as evidenced by ZFC/FC measurements and the presence of hysteresis with ∼700 Oe coercivity. Low temperature magnetization scans show slightly constricted hysteresis loops with coercivity decreasing systematically with a decreasing number of carbon atoms in the coating molecule, possibly resulting from differences in magnetic dipole coupling between NPs. Large thermomagnetic irreversibility, slow monotonic increase in the FC magnetization and non-saturation of the magnetization give evidence for the cluster glass (CG) nature in the CoFe2O4 NPs. The out of phase part (χ'') of AC susceptibility for all samples shows a clear frequency dependent hump which was analyzed to distinguish superparamagnetic (SPM), cluster glass (CG) and spin glass (SG) behavior by using Néel-Arrhenius, Vogel-Fulcher, and power law fittings. These analyses rule out the SPM state and suggest the presence of significant inter-cluster dipolar interaction, giving rise to CG cooperative freezing in the high-temperature region. In the low-temperature range, however, the disordered spins on the nanoparticle's surface play an important role in the formation of the SG-like state, as evidenced by Arrott plots and temperature dependency of dM/dH in the initial magnetization curves. In summary, the magnetic measurements showed that undercooling the system evolves from a SPM state of weakly interacting spin clusters, through the CG state induced by strong dipolar interaction, to the SG state resulting from the frustration of the disordered surface spins.

Evidence for five types of fixation during a random saccade eye tracking task and changes in fixation duration as a function of time-on-task.

Our interest was to evaluate changes in fixation duration as a function of time-on-task (TOT) during a random saccade task. We employed a large, publicly available dataset. The frequency histogram of fixation durations was multimodal and modelled as a Gaussian mixture. For this specific task, we found five fixation types. The "ideal" response would be a single accurate saccade after each target movement, with a typical saccade latency of 200-250 msec, followed by a long fixation (> 800 msec) until the next target jump. We found fixations like this, but they comprised only 10% of all fixations and were the first fixation after target movement only 23.4% of the time. More frequently (57.4% of the time), the first fixation after target movement was short (117.7 msec mean) and was commonly followed by a corrective saccade. Across the entire 100 sec of the task, median total fixation duration decreased. This decrease was approximated with a power law fit with R2 = 0.94. A detailed examination of the frequency of each of our five fixation types over time on task (TOT) revealed that the three shortest duration fixation types became more and more frequent with TOT whereas the two longest fixations became less and less frequent. In all cases, the changes over TOT followed power law relationships, with R2 values between 0.73 and 0.93. We concluded that, over the 100 second duration of our task, long fixations are common in the first 15 to 22 seconds but become less common after that. Short fixations are relatively uncommon in the first 15 to 22 seconds but become more and more common as the task progressed. Apparently. the ability to produce an ideal response, although somewhat likely in the first 22 seconds, rapidly declines. This might be related to a noted decline in saccade accuracy over time.

Determining Which Sine Wave Frequencies Correspond to Signal and Which Correspond to Noise in Eye-Tracking Time-Series.

The Fourier theorem states that any time-series can be decomposed into a set of sinusoidal frequencies, each with its own phase and amplitude. The literature suggests that some frequencies are important to reproduce key qualities of eye-movements ("signal") and some of frequencies are not important ("noise"). To investigate what is signal and what is noise, we analyzed our dataset in three ways: (1) visual inspection of plots of saccade, microsaccade and smooth pursuit exemplars; (2) analysis of the percentage of variance accounted for (PVAF) in 1,033 unfiltered saccade trajectories by each frequency band; (3) analyzing the main sequence relationship between saccade peak velocity and amplitude, based on a power law fit. Visual inspection suggested that frequencies up to 75 Hz are required to represent microsaccades. Our PVAF analysis indicated that signals in the 0-25 Hz band account for nearly 100% of the variance in saccade trajectories. Power law coefficients (a, b) return to unfiltered levels for signals low-pass filtered at 75 Hz or higher. We conclude that to maintain eyemovement signal and reduce noise, a cutoff frequency of 75 Hz is appropriate. We explain why, given this finding, a minimum sampling rate of 750 Hz is suggested.

Surveying the Whirlpool at Arcseconds with NOEMA (SWAN)

We present the first results from “Surveying the Whirlpool at Arcseconds with NOEMA” (SWAN), an IRAM Northern Extended Millimetre Array (NOEMA)+30 m large program that maps emission from several molecular lines at 90 and 110 GHz in the iconic nearby grand-design spiral galaxy M 51 at a cloud-scale resolution (∼3″ = 125 pc). As part of this work, we have obtained the first sensitive cloud-scale map of N2H+(1–0) of the inner ∼5 × 7 kpc of a normal star-forming galaxy, which we compared to HCN(1–0) and 12CO(1–0) emission to test their ability in tracing dense, star-forming gas. The average N2H+-to-HCN line ratio of our total FoV is 0.20 ± 0.09, with strong regional variations of a factor of ≳2 throughout the disk, including the south-western spiral arm and the center. The central ∼1 kpc exhibits elevated HCN emission compared to N2H+, probably caused by AGN-driven excitation effects. We find that HCN and N2H+ are strongly super-linearily correlated in intensity (ρSp ∼ 0.8), with an average scatter of ∼0.14 dex over a span of ≳1.5 dex in intensity. When excluding the central region, the data are best described by a power law of an exponent of 1.2, indicating that there is more N2H+ per unit HCN in brighter regions. Our observations demonstrate that the HCN-to-CO line ratio is a sensitive tracer of gas density in agreement with findings of recent galactic studies utilising N2H+. The peculiar line ratios present near the AGN and the scatter of the power-law fit in the disk suggest that in addition to a first-order correlation with gas density, second-order physics (such as optical depth, gas temperature) or chemistry (abundance variations) are encoded in the N2H+/12CO, HCN/12CO, and N2H+/HCN ratios.

Early Planet Formation in Embedded Disks (eDisk). VIII. A Small Protostellar Disk around the Extremely Low Mass and Young Class 0 Protostar IRAS 15398–3359

Protostellar disks are an ubiquitous part of the star formation process and the future sites of planet formation. As part of the Early Planet Formation in Embedded Disks large program, we present high angular resolution dust continuum (∼40 mas) and molecular line (∼150 mas) observations of the Class 0 protostar IRAS 15398–3359. The dust continuum is small, compact, and centrally peaked, while more extended dust structures are found in the outflow directions. We perform a 2D Gaussian fitting and find the deconvolved size and 2σ radius of the dust disk to be 4.5 × 2.8 au and 3.8 au, respectively. We estimate the gas+dust disk mass assuming optically thin continuum emission to be 0.6M J–1.8M J, indicating a very low mass disk. The CO isotopologues trace components of the outflows and inner envelope, while SO traces a compact, rotating disk-like component. Using several rotation curve fittings on the position–velocity diagram of the SO emission, the lower limits of the protostellar mass and gas disk radius are 0.022 M ⊙ and 31.2 au, respectively, from our Modified 2 single power-law fitting. A conservative upper limit of the protostellar mass is inferred to be 0.1 M ⊙. The protostellar mass accretion rate and the specific angular momentum at the protostellar disk edge are found to be in the range of (1.3–6.1) × 10−6 M ⊙ yr−1 and (1.2–3.8) × 10−4 km s−1 pc, respectively, with an age estimated between 0.4 × 104 yr and 7.5 × 104 yr. At this young age with no clear substructures in the disk, planet formation would likely not yet have started. This study highlights the importance of high-resolution observations and systematic fitting procedures when deriving dynamical properties of deeply embedded Class 0 protostars.

Survey of Bare Active Galactic Nuclei in the Local Universe (z < 0.2). I. On the Origin of Soft Excess

We analyze a sample of 21 “bare” Seyfert 1 active galactic nuclei, a subclass of Seyfert 1 galaxies, with intrinsic absorption N H ∼ 1020 cm−2, in the local Universe (z < 0.2) using XMM-Newton and Swift/XRT observations. The luminosities of the primary continuum, the X-ray emission in the 3–10 keV energy range, and the soft excess—the excess emission that appears above the low-energy extrapolation of the power-law fit of 3–10 keV X-ray spectra—are calculated. Our spectral analysis reveals that the long-term intrinsic luminosities of the soft excess and the primary continuum are tightly correlated . We also found that the luminosities are correlated for each source. This result suggests that both the primary continuum and soft excess emissions exhibit a dependency on the accretion rate in a similar way.

The MASSIVE survey – XVIII. Deep wide-field K-band photometry and local scaling relations for massive early-type galaxies

ABSTRACT We present wide-field, deep K-band photometry of 98 luminous early-type galaxies (ETGs) from the MASSIVE survey based on observations taken with the WIRCam instrument on the Canada–France–Hawaii Telescope. Using these images, we extract accurate total K-band luminosities (LK) and half-light radii (Re) for this sample of galaxies. We use these new values to explore the size–luminosity and Faber–Jackson relations for massive ETGs. Within this volume-limited sample, we find clear evidence for curvature in both relations, indicating that the most luminous galaxies tend to have larger sizes and smaller velocity dispersions than expected from a simple power-law fit to less luminous galaxies. Our measured relations are qualitatively consistent with the most massive elliptical galaxies forming largely through dissipationless mergers. When the sample is separated into fast and slow rotators, we find the slow rotators to exhibit similar changes in slope with increasing LK, suggesting that low-mass and high-mass slow rotators have different formation histories. The curvatures in the Re–LK and σ–LK relations cancel, leading to a relation between dynamical mass and luminosity that is well described by a single power law: Reσ2 ∝ LKb with b ≈ 1.2. This is consistent with the tilt of the fundamental plane observed in lower mass elliptical galaxies.

Open fracture clustering: Integrating subsurface and outcrop analogues, Asmari Formation, SW Iran

Fracture networks play a significant role in controlling fluid flow in carbonate reservoirs. Here we have utilized a modern and rigorous technique known as normalized correlation count (NCC) to investigate the 1D spatial arrangement and size distribution of conductive opening-mode fractures in the Asmari Formation, a naturally fractured carbonate reservoir in the Zagros Fold and Thrust Belt. To overcome subsurface sampling limitations, here we integrate data from a subsurface fault-related fold called the Gachsaran anticline, and from adjacent outcrops. The Oligo-Miocene Asmari Formation is composed of three units with different lithology, thickness, and stratal geometry. Subsurface and outcrop data from the Asmari Formation have different patterns of spatial arrangements. While the fractures from outcrop anticlines show indistinguishable from random arrangements, the subsurface scanlines from the Gachsaran anticline have various clustering patterns, from self-organized regularly-spaced fracture clustering in the backlimb to externally-imposed clustering in the forelimb. The NW-SE striking fracture set in outcrops and subsurface show clustering. Aperture-size data for all fracture sets are best-fit by log-normal distributions, but sampling biases against the smallest apertures may obscure a power-law aperture-size distribution. Forcing the power-law fit to aperture-size distribution indicates steeper slopes in the backlimb and gentler slopes in the forelimb, which reflect lower and higher strain, respectively. This is consistent with higher tendency of clustering in the forelimb of the anticline which correlates with higher productivity index. Our results demonstrate the ability of NCC to identify hierarchical fracture clusters as well as to distinguish between self-organized and extrinsic organization. The results of quantitative analysis of fracture clustering and patterns in the Asmari Formation provides valuable insights that can aid in the refinement of Discrete Fracture Network (DFN) models and help make informed decisions regarding fractured reservoir development and production.

Unveiling the magnetic structure and phase transition of Cr2CoAl using neutron diffraction

We report the detailed analysis of temperature dependent neutron diffraction pattern of the Cr2CoAl inverse Heusler alloy and unveil the magnetic structure up to the phase transition as well as its fully compensated ferrimagnetic nature. The Rietveld refinement of the diffraction pattern using the space group I4¯m2 confirms the inverse tetragonal structure over the large temperature range from 100 to 900 K. The refinement of the magnetic phase considering the wave vector k= (0, 0, 0) reveals the ferrimagnetic nature of the sample below 730±5 K. This transition temperature is obtained from empirical power law fitting of the variation in the ordered net magnetic moment variation in intensity of (110) peak as a function of temperature. The spin configuration of the microscopic magnetic structure suggests the nearly fully compensated ferrimagnetic behavior where the magnetic moments of Cr2 are antiparallel with respect to the Cr1 and Co moments. Moreover, the observed anomaly in the thermal expansion and lattice parameters at 730±5 K suggests that the distortion in the crystal structure may play an important role in the magnetic phase transition.

Improved Modelling of Vertical Velocity Profiles at a Tidal Energy Site

The Minas Passage, one of the Bay of Fundy’s tidal channels, located in Nova Scotia, Canada, presents significant potential for tidal energy development because of its highly energetic flows. As development in the region gains traction, the implementation of floating tidal energy platforms is a topic of growing interest. Tidal energy deployments in Minas Passage have historically been bottom-mounted and stationary, and the transition to arrays of floating turbines requires additional considerations. Particularly, this new application demands characterization of flow over the entire water column, including near the free surface. Complete vertical velocity profiles are essential for the successful deployment of floating tidal turbines, allowing for the estimation of key metrics such as tidal power and shear across turbine blades. Here we explore adaptations to the well-established logarithmic law of the wall with the goal of extending the vertical range over which a fitting regime based in classical turbulence theory can capture the observational records of flow in Minas Passage.&#x0D; Observational site characterization efforts in Minas Passage have primarily consisted of stationary, bottom mounted Acoustic Doppler Current Profiler (ADCP) deployments. Using historical ADCP records collected in Minas Passage between 2008 and 2021, we fit the vertical profiles of velocity using three methods: logarithmic law of the wall, power law, and an adapted logarithmic law of the wall which includes a “wake function” to improve fits in the upper water column. We find that although the law of the wall results in well-fitted estimations of the vertical velocity profiles near the seabed, observational profiles consistently deviate from the fitted curves in the middle and upper water column, recording significantly faster flow speeds than predicted by the law of the wall. The adapted model, which is rooted in turbulence theory and includes a wake term, is successful in capturing flow in the outer layer of the water column and allows for reverse shear to be captured in the profile. The resulting fits show a sizeable reduction in error throughout the entirety of the water column compared to the law of the wall profiles, and consistently reduce the error in the vertical profile fits when compared to power law fits. In addition to resulting in low error for both individual and averaged vertical profiles of flow, the physical quantities estimated from the adapted model, including drag coefficient, agree well with those computed from the law of the wall, demonstrating the physical usefulness of the adapted model.

Data‐Driven Empirical Conductance Relations During Auroral Precipitation Using Incoherent Scatter Radar and All Sky Imagers

AbstractWe present empirical conductance relations that are derived from incoherent scatter radar observations and correlated with all sky imager observations to identify the morphology of the aurora. We use 75,461 events collected using the Poker Flat Incoherent Scatter Radar (PFISR) with associated all sky imagers observations spanning the years 2012–2016. In addition to classifying these events based on auroral morphology, we estimated the Hall and Pedersen conductance and the differential number flux from which the energy flux and the average energy can be calculated. The differential number flux was estimated using the maximum entropy inversion method described in Semeter and Kamalabadi (2005, https://doi.org/10.1029/2004RS003042), but now incorporating the Fang et al. (2010, https://doi.org/10.1029/2010GL045406) ionization model. The main results of this investigation are the power law equations that describe the median, 90th, and 10th percentile Hall and Pedersen conductance as a function of energy flux and average energy. These power law fits are performed for different auroral morphology including all events, discrete, diffuse, and pulsating auroral events. The median Pedersen conductance is found to be in good agreement with past empirical conductance specifications by Robinson et al. (1987, https://doi.org/10.1029/JA092iA03p02565); however, the median Hall conductance from the PFISR observations is found to be larger than the empirical Hall conductance formulas by Robinson et al. (1987, https://doi.org/10.1029/JA092iA03p02565). Pulsating aurora is found to be the most frequently occurring auroral morphology. Furthermore, pulsating aurora has an important contribution to Hall conductance since it has higher average energies than discrete aurora. The results from this investigation are applicable to space weather models and may enable better agreement between model‐data comparisons.