Magnetic Resonance Velocimetry Measurement of Viscous Flows through Porous Media: Comparison with Simulation and Voxel Size Study

Studies that use magnetic resonance velocimetry (MRV) to assess flows through porous media require a sufficiently small voxel size to determine the velocity field at a sub-pore scale. The smaller the voxel size, the less information is lost through the discretization. However, the measurement uncertainty and the measurement time are increased. Knowing the relationship between voxel size and measurement accuracy would help researchers select a voxel size that is not too small in order to avoid unnecessary measurement effort. This study presents a systematic parameter study with a low-Reynolds-number flow of a glycerol–water mixture sent through a regularly periodic porous matrix with a pore size of 5 mm. The matrix was a 3-dimensional polymer print, and velocity-encoded MRV measurements were made at 15 different voxel sizes between 0.42 mm and 4.48 mm. The baseline accuracy of the MRV velocity data was examined through a comparison with a computational fluid dynamics (CFD) simulation. The experiment and simulation show very good agreement, indicating a low measurement error. Starting from the smallest examined voxel size, the influence of the voxel size on the accuracy of the velocity data was then examined. This experiment enables us to conclude that a voxel size of 0.96 mm, which corresponds to 20% of the pore size, is sufficient. The volume-averaged results do not change below a voxel size of 20% of the pore size, whereas systematic deviations occur with larger voxels. The same trend is observed with the local velocity data. The streamlines calculated from the MRV velocity data are not influenced by the voxel size for voxels of up to 20% of the pore size, and even slightly larger voxels still show good agreement. In summary, this study shows that even with a relatively low measurement resolution, quantitative 3-dimensional velocity fields can be obtained through porous flow systems with short measurement times and low measurement uncertainty.

An Algorithm Using DBSCAN to Solve the Velocity Dealiasing Problem

Velocity dealiasing is an essential task for correcting the radial velocity data collected by Doppler radar. To improve the accuracy of velocity dealiasing, traditional dealiasing algorithms usually set a series of empirical thresholds, combine three- or four-dimensional data, or introduce other observation data as a reference. In this study, we transform the velocity dealiasing problem into a clustering problem and solve this problem using the density-based spatial clustering of applications with noise (DBSCAN) method. This algorithm is verified with a case study involving radar data on the tropical cyclone Mangkhut in 2018. The results show that the accuracy of the proposed algorithm is close to that of the four-dimensional dealiasing (4DD) method proposed by James and Houze; yet, it only requires two-dimensional velocity data and eliminates the need for other reference data. The results of the case study also show that the 4DD algorithm filters out many observation gates close to the missing data or radar center, whereas the proposed algorithm tends to retain and correct these gates.

Another Superdense Sub-Neptune in K2-182 b and Refined Mass Measurements for K2-199 b and c*

We combine multiple campaigns of K2 photometry with precision radial velocity measurements from Keck-HIRES to measure the masses of three sub-Neptune-sized planets. We confirm the planetary nature of the massive sub-Neptune K2-182 b (P b = 4.7 days, R b = 2.69 R ⊕) and derive refined parameters for K2-199 b and c (P b = 3.2 days, R b = 1.73 R ⊕ and P c = 7.4 days, R c = 2.85 R ⊕). These planets provide valuable data points in the mass–radius plane, especially as TESS continues to reveal an increasingly diverse sample of sub-Neptunes. The moderately bright (V = 12.0 mag) early K dwarf K2-182 (EPIC 211359660) was observed during K2 campaigns 5 and 18. We find that K2-182 b is potentially one of the densest sub-Neptunes known to date (20 ± 5 M ⊕ and 5.6 ± 1.4 g cm−3). The K5V dwarf K2-199 (EPIC 212779596; V = 12.3 mag), observed in K2 campaigns 6 and 17, hosts two recently confirmed planets. We refine the orbital and planetary parameters for K2-199 b and c by modeling both campaigns of K2 photometry and adding 12 Keck-HIRES measurements to the existing radial velocity data set (N = 33). We find that K2-199 b is likely rocky, at 6.9 ± 1.8 M ⊕ and 7.2 − 2.0 + 2.1 g cm−3, and that K2-199 c has an intermediate density at 12.4 ± 2.3 M ⊕ and 2.9 − 0.6 + 0.7 g cm−3. We contextualize these planets on the mass–radius plane, discuss a small but intriguing population of “superdense” sub-Neptunes (R p < 3 R ⊕, M p >20 M ⊕), and consider our prospects for the planets’ atmospheric characterization.

Chemical abundances of three new Ba stars from the Keck/HIRES spectra

Based on high resolution, high signal-to-noise (S/N) ratio spectra from Keck/HIRES, we have determined abundances of 20 elements for 18 Ba candidates. The parameter space of these stars is in the range of 4880 ≤ T eff ≤ 6050 K, 2.56 ≤ log g ≤ 4.53 dex and − 0.27 ≤ [Fe/H] ≤ 0.09 dex. It is found that four of them can be identified as Ba stars with [s/Fe] > 0.25 dex (s: Sr, Y, Zr, Ba, La, Ce and Nd), and three of them are newly discovered, which include two Ba giants (HD 16178 and HD 22233) and one Ba subgiant (HD 2946). Our results show that the abundances of α, odd and iron-peak elements (O, Na, Mg, Al, Si, Ca, Sc, Ti, Mn, Ni and Cu) for our program stars are similar to those of the thin disk, while the distribution of [hs/ls] (hs: Ba, La, Ce and Nd, ls: Sr, Y and Zr) ratios of our Ba stars is similar to those of the known Ba objects. None of the four Ba stars show clear enhancement in carbon including the known CH subgiant HD 4395. It is found that three of the Ba stars present clear evidence of hosting stellar or sub-stellar companions from the radial velocity data.

An account of low level wind shear over Chennai airport - Part II : Turbulence and eddy dissipation

In-flight reports on Low Level Wind Shear (LLWS) received from aircrafts are used to issue wind shear alerts for all subsequent landing aircrafts as per standing guidelines of International Civil Aviation Organisation (ICAO). In this paper, winds reported by aircrafts at 1000 and 1800 ft. are used to validate the wind estimated from DWR measured radial wind data employing standard algorithms. Turbulence indices and parameters have been computed independently using conventional (RS/RW) upper air data, aircraft measured winds and DWR estimated winds and compared these with wind shear induced turbulence reported by aircrews. Mean power law (wind escalation law) profiles in the boundary layer have been arrived at for unstable and stable atmospheric conditions. Three dimensional shear (3DS) upto 600 m a.g.l. has been worked out from DWR measured radial velocity data and compared with wind shear computed from RS/RW and aircraft measured winds and DWR estimated winds. It is found that 3DS values of more than 16 * 10-3 s-1 predict well the occurrence of moderate turbulence. Contrary to the general belief that wind shear is a short lived phenomenon which may last for a few minutes only, it has been observed that incidences of LLWS and induced moderate turbulence lasting more than 10 hrs are not at all uncommon over Chennai aircraft.

SCExAO/CHARIS Direct Imaging of A Low-mass Companion At A Saturn-like Separation from an Accelerating Young A7 Star

We present the SCExAO direct imaging discovery and characterization of a low-mass companion to the nearby young A7IV star, HD 91312. SCExAO/CHARIS JHK (1.1–2.4 μm) spectra and SCExAO/HiCIAO H-band imaging identify the companion over a two year baseline in a highly inclined orbit with a maximum projected separation of 8 au. The companion, HD 91312 B, induces an 8.8σ astrometric acceleration on the star as seen with the Gaia & Hipparcos satellites and a long-term radial-velocity trend as previously identified by Borgniet et al. HD 91312 B’s spectrum is consistent with that of an early-to-mid M dwarf. Hipparcos and Gaia absolute astrometry, radial-velocity data, and SCExAO/CHARIS astrometry constrain its dynamical mass to be 0.337 − 0.044 + 0.042 M ⊙, consistent with - but far more precise than - masses derived from spectroscopy, and favors a nearly edge-on orbit with a semimajor axis of ∼9.7 au. This work is an example of precisely characterizing properties of low-mass companions at solar system-like scales from a combination of direct imaging, astrometry, and radial-velocity methods.

Placenta mediates the effect of maternal hypertension polygenic score on offspring birth weight: a study of birth cohort with fetal growth velocity data

Background Low birth weight (LBW) and fetal growth restriction are associated with the development of cardio-metabolic diseases later in life. A recent Mendelian randomization study concluded that the susceptibility of LBW infants to develop hypertension during adulthood is due to the inheritance of hypertension genes from the mother and not to an unfavorable intrauterine environment. Therein, a negative linear association has been assumed between genetically estimated maternal blood pressure (BP) and birth weight, while the observed relationship between maternal BP and birth weight is substantially different from that assumption. As many hypertension genes are likely involved in vasculature development and function, we hypothesized that BP-increasing genetic variants could affect birth weight by reducing the growth of the placenta, a highly vascular organ, without overtly elevating the maternal BP. Methods Using a birth cohort in the Japanese population possessing time-series fetal growth velocity data as a target and a GWAS summary statistics of BioBank Japan as a base data, we performed polygenic score (PGS) analyses for systolic BP (SBP), diastolic BP, mean arterial pressure, and pulse pressure. A causal mediation analysis was performed to assess the meditation effect of placental weight on birth weight reduced by maternal BP-increasing PGS. Maternal genetic risk score constituted of only “vasculature-related” BP single nucleotide polymorphisms (SNPs) was constructed to examine the involvement of vascular genes in the mediation effect of placental weight. We identified gestational week in which maternal SBP-increasing PGS significantly decreased fetal growth velocity. Results We observed that maternal SBP-increasing PGS was negatively associated with offspring birth weight. A causal mediation analysis revealed that a large proportion of the total maternal PGS effect on birth weight was mediated by placental weight. The placental mediation effect was remarkable when genetic risk score was constituted of “vasculature-related” BP SNPs. The inverse association between maternal SBP PGS and fetal growth velocity only became apparent in late gestation. Conclusions Our study suggests that maternal hypertension genes are strongly associated with placental growth and that fetal growth inhibition is induced through the intrauterine environment established by the placenta.

A Kiloparsec-scale Molecular Wave in the Inner Galaxy: Feather of the Milky Way?

We report the discovery of a velocity coherent, kiloparsec-scale molecular structure toward the Galactic center region with an angular extent of 30° and an aspect ratio of 60:1. The kinematic distance of the CO structure ranges between 4.4 and 6.5 kpc. Analysis of the velocity data and comparison with the existing spiral arm models support that a major portion of this structure is either a subbranch of the Norma arm or an interarm giant molecular filament, likely to be a kiloparsec-scale feather (or spur) of the Milky Way, similar to those observed in nearby spiral galaxies. The filamentary cloud is at least 2.0 kpc in extent, considering the uncertainties in the kinematic distances, and it could be as long as 4 kpc. The vertical distribution of this highly elongated structure reveals a pattern similar to that of a sinusoidal wave. The exact mechanisms responsible for the origin of such a kiloparsec-scale filament and its wavy morphology remains unclear. The distinct wave-like shape and its peculiar orientation makes this cloud, named as the Gangotri wave, one of the largest and most intriguing structures identified in the Milky Way.

Inversion of dry and saturated P- and S-wave velocities for the pore-aspect-ratio spectrum using a cracked porous medium elastic wave theory

Subsurface rocks contain pores and cracks of various sizes. The cracked porous medium elastic wave theory that describes wave propagation characteristics due to the pore-crack interaction is extended to include cracks of different aspect ratios. The extended theory is applied to model P- and S-wave velocity data of dry and fluid-saturated rock under pressure loading conditions, so as to determine the pore-aspect-ratio spectrum through an inversion procedure. The inversion result is consistent with that from the scanning electron microscope analysis, showing significant improvement versus previous inversion. The inverted pore-aspect-ratio spectrum is input into the wave theory to predict the velocity dispersion of the rock in the full frequency range. The predicted dispersion and its variation trend with pressure agree with the data measured in the (2–200, 106) Hz range at various differential pressures, whereas the modeling using a single-aspect-ratio theory has difficulty matching the data. This research work provides not only a method for analyzing the pore structure characteristics of rocks from the laboratory ultrasonic velocity data, but also a way to predict the seismic wave dispersion from the data.