Eccentric Configuration Research Articles

Orbital and Atmospheric Characterization of the 1RXS J034231.8+121622 System using High-resolution Spectroscopy Confirms that the Companion is a Low-mass Star

The 1RXS J034231.8+121622 system consists of an M dwarf primary and a directly imaged low-mass stellar companion. We use high-resolution spectroscopic data from Keck/KPIC to estimate the objects' atmospheric parameters and radial velocities (RVs). Using PHOENIX stellar models, we find that the primary has a temperature of 3460 ± 50 K and a metallicity of 0.16 ± 0.04, while the secondary has a temperature of 2510 ± 50 K and a metallicity of 0.13−0.11+0.12 . Recent work suggests this system is associated with the Hyades, giving it an older age than previous estimates. Both metallicities agree with current Hyades [Fe/H] measurements (0.11–0.21). Using stellar evolutionary models, we obtain significantly higher masses for the objects, 0.30 ± 0.15 M ⊙ and 0.08 ± 0.01 M ⊙ (84 ± 11 M Jup), respectively. Using the RVs and a new astrometry point from Keck/NIRC2, we find that the system is likely an edge-on, moderately eccentric ( 0.41−0.08+0.27 ) configuration. We also estimate the C/O ratio of both objects using custom grid models, obtaining 0.42 ± 0.10 (primary) and 0.55 ± 0.10 (companion). From these results, we confirm that this system most likely went through a binary star formation process in the Hyades. The significant changes in this system's parameters since its discovery highlight the importance of high-resolution spectroscopy for both orbital and atmospheric characterization of directly imaged companions.

Numerical investigation of the combustion regime in pilot-ignited high-pressure direct-injection low reactivity fuel combustion with the injection system of eccentric configuration

The pilot-ignited high-pressure direct-injection (HPDI) combustion with the eccentric configuration is a practical approach to achieve high thermal efficiency and clean combustion. However, the combustion process and combustion regime still remain unclear. In this study, the effects of two key parameters “offset” (distance between concentric and eccentric injectors) and “dwell” (interval between concentric and eccentric injection timing) on the combustion process, combustion regime, and the corresponding performance are numerically investigated systematically. Results show that the interaction between the flame kernels of pilot fuel and the plumes of main fuel determines the combustion mode of each main fuel plume, and thereby different combustion regimes in the pilot-ignited HPDI engine can be generated by controlling the offset and dwell. Specifically, under the concentric configuration or the eccentric configuration with very small offset and dwell, all the main fuel plumes are in the non-premixed mode, exhibiting a diffusion combustion (DC) regime. Under the eccentric configuration with medium offset and dwell, some of the main fuel plumes are in the non-premixed and the others in the partially premixed mode, exhibiting a special combustion regime, which is named the multi-mode co-existing combustion (MMCC) in this study. Under the eccentric configuration with large offset and dwell, all the main fuel plumes are in the partially premixed mode, exhibiting a partially premixed combustion (PPC) regime. Among the three combustion regimes, the diffusion combustion regime exhibits the lowest ISFC and unburned HC emission but high NOx and soot emissions. The ISFC of the partially premixed combustion regime is almost double that of the other two regimes which is far from being acceptable. The MMCC regime shows a better comprehensive performance: achieving much lower ringing intensity and soot emission with almost the same ISFC compared to the diffusion combustion regime. In summary, the pilot-ignited HPDI combustion with the eccentric configuration can potentially achieve high fuel economy with low emissions, under the premise of the ratio of non-premixed and partially premixed combustion modes in the MMCC regime is well controlled.

Seismic performance and damage evolution of RC frames retrofitted by the novel GESB system: A numerical study

A novel gapped eccentric steel brace (GESB) system was developed to enhance the seismic performance of existing reinforced concrete (RC) frame structures. To thoroughly investigate the mechanism and damage mode of the novel retrofitting system, numerical analysis was conducted on retrofitted frames with various brace eccentricity configurations, using a comprehensive multi-scale finite element model. Six suitable damage indices were defined to carry out the structural damage evolution study during the whole loading process. On this basis, a simplified damage model was developed. The results demonstrated that GESB effectively modified the mechanical mechanism and failure modes of the frames. The brace eccentricity configuration exerted a significant influence on the structural strength, stiffness, and ductility. With regards to both of strength and ductility requirements, an eccentricity range of 0.3 to 0.4 was recommended. The proposed simplified damage model was used to indicate the allowable drift ratios associated to performance levels, which were found to be very variable with various eccentricity configurations. The outcomes are essential and timely for design decision of RC frames retrofitted by GESB.

Eccentricity-induced dielectrophoretic migration of a compound drop in a uniform external electric field

Eccentric compound drops, which are ubiquitous in many naturally inspired and engineering systems, can migrate under the sole presence of a uniform electric field, unlike the case of isolated single drops. Here, we report the migration of eccentric compound drops under a uniform electric field, imposed parallel to the line of centres of the constituting drops, by developing an approximate analytical model that applies to low Reynolds number limits under negligible droplet deformation, following axisymmetric considerations. In contrast to the sole influence of the electrohydrodynamic forces that has thus far been established to be emphatic for the eccentric configuration, here we report the additional effects induced by the dielectrophoretic forces to result in decisive manipulation in the drop migration. We show that the relative velocity between the inner and outer drops, which is a function of the eccentricity itself, dictates the dynamical evolution of the eccentricity variation under the competing electrohydrodynamic and dielectrophoretic interactions. This brings out four distinct regimes of the migration characteristics of the two drops based on their relative electro-physical properties. Our results reveal that an increase in eccentricity and the size ratio of the inner and outer droplets may induce monotonic or non-monotonic variation in the drop velocities, depending on the operating regime. We show how the interplay of various properties holds the control of selectively increasing or suppressing the eccentricity with time. These findings open up various avenues of electrically manipulative motion of encapsulated fluidic phases in various applications encompassing engineering and biology.

Numerical modeling of laminar and turbulent annular flows of power-law fluids in partially blocked geometries

The presence of cuttings bed in deviated wellbores has an undesirable effect on wellbore hydraulics by reducing the open flow area. In addition, pipe eccentricity affects the annular frictional pressure gradient under such configurations. The lack of practical correlations to account for the combined effects of cuttings bed and eccentricity on frictional pressure gradient of power-law fluids is the major motivation of this study. Thus, the effect of partially blocked eccentric annuli on frictional pressure gradient of power-law fluids is investigated. A numerical model is first developed to realize the laminar and turbulent annular flow of power-law fluids in eccentric configurations. The numerical solution of the governing equations is pursued using the finite difference method. The results of our numerical model are verified through comparisons with the published results of frictional pressure gradients in the literature. The numerical results indicate that with an increase in cuttings bed height the frictional pressure gradient can increase exponentially. Numerous simulation scenarios are considered for the flow of power-law fluids in partially blocked eccentric annuli. Then, the simulation results are fitted using regression analysis to obtain explicit correlations for the prediction of laminar and turbulent frictional pressure losses. The proposed correlations are essential for an accurate estimation of the annular frictional pressure gradient and equivalent circulating density, which ensures safe and optimized drilling operations.

Influence of eccentricity on the thermomechanical performance of a bayonet tube of a central solar receiver

This work numerically evaluates the thermal and mechanical behaviors of eccentric bayonet tubes to be used in external central receivers of solar power tower plants. A bayonet tube is composed of two tubes, one inside the other, creating circular and annular sections, through which the molten salt of the receiver sequentially flows. Eccentricity in the annular section is achieved by displacing the axis of the interior tube with regard to the exterior one. For comparative purposes, two examples of conventional tubes (single tubes with circular cross-sections with diameters of 25mm and 50mm) are also investigated in this work to compare their performances with those of bayonet tubes. The results obtained with the eccentric configurations show an enhancement of the heat transfer to the molten salt and a reduction of the tube wall overheating compared with the concentric bayonet tubes and the largest simple tube. For conditions representative of the normal operation of a solar power tower, eccentric bayonet tubes could reduce the pressure drop by 30.8% and increase the convective heat transfer achieved in a concentric configuration of the bayonet tube by 26.1%. Nevertheless, this pressure drop was considerably higher than those obtained in the smallest and largest simple tubes, which were 1.28 bar and 0.13 bar, respectively. To investigate whether the enhancement of the convection heat transfer experienced by bayonet tubes compensates for their higher pressure drop or not, a Performance Evaluation Criterion (PEC) was proposed and used to compare the global performance of bayonet tubes with that of conventional tubes. The bayonet tubes with eccentricity 0.45 obtained the largest PEC, which was up to 13% higher than reference conventional tubes. Enhancement of the tube wall refrigeration produced when increasing the eccentricity is reflected in the maximum tube temperature and thermal stresses, which are found to diminish by approximately 8.8% with the highest eccentricity. In addition, the largest eccentric bayonet tube layout obtains the smallest peak temperatures compared to conventional tubes. The lower inertial moment of the smallest conventional tube indicates that its thermal stress is 2.1% lower than the stress obtained in the most eccentric layout analyzed in this work. Nevertheless, the time to rupture associated with creep damage of the eccentric bayonet tube is 1.04 times higher than that obtained in the smallest simple tube, demonstrating that bayonet tubes could be a potential alternative to the current tubes of external tubular receivers.

Optimization of thermal energy storage: Evaluation of natural convection and melting-solidification time of eccentricity for a rotational shell-and-tube unit

Changing the eccentricity between outer and inner tubes in horizontal shell-and-tube unit during phase change of the heat storage medium is an economical procedure to improve overall heat transfer. However, because of the reverse effect of a fixed eccentric structure (downward or upward) on melting and solidification processes, investigators in previous studies have only examined the potential of performance improvement separately. Finding a technical approach to ensure lower times for melting and solidification in the fixed eccentric structure can yield significant benefits. This study numerically evaluates the processes of melting and solidification in the eccentric design for a shell-and-tube unit concurrently based on the second law of thermodynamics and natural convection. Based on the second law of thermodynamics analysis confirms that natural convection can be analyzed using the fractional entropy generation. The results show that downward eccentric designs enhance natural convection during the process of melting in stationary units. Solidification results show the significance of natural convection in the primary stage of the process. Melting time decreases by 71 % in the case with the eccentric number of 0.4 whereas solidification time decreases in upper eccentric cases (eccentric number of <0.1 in the stationary units). Reduction in solidification time by 13 % is demonstrated with the eccentric number of 0.05 and the diameter ratio of 2.52. This study presents a novel and applicable method (180-degree rotation) to achieve a shorter melting-solidification time in eccentric configurations. Additionally, a rotational mechanism is investigated to reduce the total melting-solidification time.

Electrohydrodynamic tuning of the migration characteristics of a sedimenting compound drop

Electrohydrodynamic sedimentation of simple drops has been a topic well-studied by researchers. However, electrohydrodynamic sedimentation of a compound drop would be critically influenced by the density of the involved phases and this has hitherto remained unaddressed. Herein, we develop a semi-analytical model for an eccentric compound drop settling under the action of gravity and an electric field using bispherical coordinates. The sedimentation velocity of the two drops (shell and core) is determined, and the same is applied to capture the influence of concomitant physical, hydrodynamic and electric properties on compound droplet sedimentation. The findings indicate that the compound drop may either sediment or de-sediment depending on the amount of eccentricity and its interplay with electrohydrodynamic parameters. Thereafter, the critical limit of eccentricity and time within which similar results are furnished by concentric and eccentric configurations is determined. It is found that, based on the property ratios, the eccentricity remains lower than 0.1 up to a non-dimensional time range of the order of 102–103, within which both the configurations can furnish a similar solution.

An Investigation of the Hysteretic Behavior of a Buckling-Restrained Brace Subsystem Frame with Out-of-Plane Eccentricity

This paper examines the differences in hysteretic behavior of buckling-restrained brace subsystem frames (BRBFs) with concentric and out-of-plane eccentric configurations. First, a quasi-static experiment was carried out on steel plate BRBF specimens to study the differences in mechanical properties, stability, and energy dissipation capacity between BRBFs with concentric and out-of-plane eccentric configurations. Second, a numerical simulation was carried out using the same steel plate BRBF specimens to study the difference in the stress distribution and high-order deformation patterns between the BRBFs with concentric and out-of-plane eccentric configurations. The test and numerical results showed that the out-of-plane eccentric BRBFs under in-plane quasi-static loads have different mechanical properties, larger compression strength adjustment factors ([Formula: see text]) under larger loading amplitudes, higher [Formula: see text] value increasing rates, lower equivalent viscous damping ratios ([Formula: see text]), different yield processes, and different generation processes of high-order core deformation compared with the concentric BRBFs.

Fluid-structure interaction analysis of eccentricity and leaflet rigidity on thrombosis biomarkers in bioprosthetic aortic valve replacements.

This work intends to study the effect of aortic annulus eccentricity and leaflet rigidity on the performance, thrombogenic risk and calcification risk in bioprosthetic aortic valve replacements (BAVRs). To address these questions, a two-way immersed fluid-structure interaction (FSI) computational model was implemented in a high-performance computing (HPC) multi-physics simulation software, and validated against a well-known FSI benchmark. The aortic valve bioprosthesis model is qualitatively contrasted against experimental data, showing good agreement in closed and open states. Regarding the performance of BAVRs, the model predicts that increasing eccentricities yield lower geometric orifice areas (GOAs) and higher normalized transvalvular pressure gradients (TPGs) for healthy cardiac outputs during systole, agreeing with in vitro experiments. Regions with peak values of residence time are observed to grow with eccentricity in the sinus of Valsalva, indicating an elevated risk of thrombus formation for eccentric configurations. In addition, the computational model is used to analyze the effect of varying leaflet rigidity on both performance, thrombogenic and calcification risks with applications to tissue-engineered prostheses. For more rigid leaflets it predicts an increase in systolic and diastolic TPGs, and decrease in systolic GOA, which translates to decreased valve performance. The peak shear rate and residence time regions increase with leaflet rigidity, but their volume-averaged values were not significantly affected. Peak solid stresses are also analyzed, and observed to increase with rigidity, elevating risk of valve calcification and structural failure. To the authors' knowledge this is the first computational FSI model to study the effect of eccentricity or leaflet rigidity on thrombogenic biomarkers, providing a novel tool to aid device manufacturers and clinical practitioners.

Explaining mercury via a single giant impact is highly unlikely

ABSTRACTThe classical scenario of terrestrial planet formation is characterized by a phase of giant impacts among Moon-to-Mars mass planetary embryos. While the classic model and its adaptations have produced adequate analogues of the outer three terrestrial planets, Mercury’s origin remains elusive. Mercury’s high-core mass fraction compared to the Earth’s is particularly outstanding. Among collisional hypotheses, this feature has been long interpreted as the outcome of an energetic giant impact among two massive protoplanets. Here, we revisit the classical scenario of terrestrial planet formation with focus on the outcome of giant impacts. We have performed a large number of N-body simulations considering different initial distributions of planetary embryos and planetesimals. Our simulations tested the effects of different giant planet configurations, from virtually circular to very eccentric configurations. We compare the giant impacts produced in our simulations with those that are more likely to account for the formation of Mercury and the Moon according to smoothed hydrodynamic simulations. Impact events that could lead to Moon’s formation are observed in all our simulations with up to ∼20 per cent of all giant impacts, consistent with the range of the expected Moon-forming event conditions. On the other hand, Mercury-forming events via a single giant impact are extremely rare, accounting for less than ∼1 per cent of all giant impacts. Our results suggest that producing Mercury as a remnant of a single giant impact that strips out the mantle of a differentiated planetary object with Earth-like iron-silicate ratio is challenging and alternative scenarios may be required (e.g. multiple collisions).

Seismic fragility investigation of hybrid structures BRBF with eccentric-configuration and self-centering frame

In this study, the incremental nonlinear dynamic analysis (IDA) is used to assess the seismic fragility investigation of hybrid structures with buckling-restrained braced frames with eccentric configuration (BRBFE) and self-centering frames. For this purpose, three systems BRBFE, BRBFE with the moment-resistant frame, and BRBFE with the self-centering frame, are designed and developed by numerical method for static pushover and IDAs. To prove the accuracy of the results of numerical studies, performed validation with experimental results. In this numerical study, 24 ground motions to perform IDAs are used, and IDA curves and fractile IDA curves are used to compare the seismic capacity of structures. Eventually, seismic fragility curves are plotted for structures in three performance levels of immediate occupancy (IO), repairability (RP), and collapse prevention (CP). The results showed that the BRBFE with moment-resistant frame was the most effective way to reduce the failure probability at IO performance level among the three systems. In contrast, the BRBFE with the self-centering frame was the most effective way to reduce the failure probability at two performance levels of RP and CP.

The effect of varying degrees of stenosis on transition to turbulence in oscillatory flows

Many complications in physiology are associated with a deviation in flow in arteries due to a stenosis. The presence of stenosis may transition the flow to weak turbulence. The degree of stenosis as well as its configuration whether symmetric or non-symmetric to the parent artery influences whether the flow would stay laminar or transition to turbulence. Plenty of research efforts focus on investigating the role of varying degrees of stenosis in the onset of turbulence under steady and pulsatile flow conditions. None of the studies, however, have focused on investigating this under oscillatory flow conditions as flow reversal is a major occurrence in a number of physiologic flows, and is of particular relevance in cerebrospinal fluid flow research. Following up on the previous work in which a 75% stenosis was studied, this contribution is a detailed investigation of the role of degrees of stenosis on transition in an oscillatory flow. A cylindrical pipe with 25%, 50% and 60% reductions in area in axisymmetric and eccentric configurations is studied for transition with 3 different pulsation frequencies of a purely oscillatory flow. Cycle averaged Reynolds numbers between 1800 and 2100 in steps of 100 are studied for each configuration resulting in 72 simulations each conducted on 76,800 CPU cores of a modern supercomputer. It is found that a higher degree of stenosis and eccentricity causes earlier transition to turbulence in oscillatory flow. The results further demonstrate that a higher frequency of oscillation results in larger hydrodynamic instability in the flow, which is more prominent in smaller degrees of stenosis.

Localization of travelling and standing waves in a circular membrane coupled to a continuous viscoelastic support

We present an analytical approach for realizing the localization of travelling and standing waves in a circular membrane by means of an interior, continuous, ring-type viscoelastic support when the membrane is subjected to harmonic boundary excitation. This work is a continuation of the wave separation dynamics induced by nonclassical damping in one-dimensional elastic continua. For a two-dimensional azimuthally symmetric configuration, a necessary and sufficient condition is established to realize wave localization, leading to uniformly distributed spring stiffness and damping coefficients for the interior support. A rotating wave localization pattern can also be realized by applying a circumferentially moving boundary excitation. The desired results are shown to depend strongly on the excitation frequency, the circumferential wavenumber, and the radius of the continuous support. For a weakly eccentric configuration with uniformly distributed boundary excitation, non-uniform required distributions of the support properties can be obtained analytically. However, waveform distortion will occur for either non-uniformly distributed boundary excitation with weak support eccentricity or highly eccentric coupling, such that the parameter values of the support have zero crossings on the nodal diameters of the membrane and thus lose physical meaning. The results presented in this work are expected to be useful in the design of mechanical and acoustic systems to localize energy to a sonic bullet by means of the continuous distribution of damping.

Experimental determination of the convection heat transfer coefficient in an eccentric annular duct

The use of bayonet tube heat exchangers and heaters is widespread in many industrial applications and an improvement in the heat transfer coefficient may provide benefits over other technologies. This work presents novel experimental results about the turbulent convection heat transfer coefficient of air in the annular section of a bayonet tube for two different configurations: concentric and eccentric tubes. For both configurations, the convection heat transfer coefficient was obtained at different air flow rates, therefore, at different Reynolds numbers. In the case of the eccentric configuration, the angular position of the inner tube was varied to determine the circumferential distribution of the local convective heat transfer coefficient. An increase of the convection coefficient was observed for both configurations at higher Reynolds numbers. Concerning the angular position with regard the inner tube, the largest local convective heat transfer coefficient was obtained at the angular position where the distance between the inner and outer tubes was maximum, yielding a value 22.3% higher than in the case of a concentric annular section. All these experimental results were used to propose a new correlation for the local convective heat transfer coefficient as a function of the Prandtl and Reynolds numbers, the eccentricity, and the angular position of the inner tube, with a maximum discrepancy between correlation and experimental data below 10%.

Multi relaxation time Lattice Boltzmann analysis of lid-driven rectangular cavity subject to various obstacle configurations

We have simulated two-dimensional laminar heat transfer in a lid-driven rectangular enclosure encapsulating heated obstacle filled with a regular viscous fluid. A square and rectangular-shaped heated blockage with different eccentric configurations is used in the physical domain to study mass and heat transfer in flow and temperature fields. We have applied D2Q9 and D2Q5 models of the Multi-Relaxation Time Lattice Boltzmann method to compute and simulate our results. The effect of dimensionless parameters like Grashof number (Gr=103, 104, 105, 106), Richardson number (Ri=0.01, 0.1, 1, 5, 10, 50, 100), Prandtl number (Pr=0.71, 1, 7) and of different eccentric placements of heated obstacle is studied on mixed convection heat transfer. The assigned value of the Reynolds number is 1000. We have also studied the impact of different aspect ratios (AR=2, 0.5, 5, 0.2) of the enclosure and the sizes of heated obstacles on fluid flow. We have also computed the local Nusselt number (Nulocal) average Nusselt number (Nu¯) along the cold wall of the enclosure.

Seismic behavior of dual buckling-restrained steel braced frame with eccentric configuration and post-tensioned frame system

The buckling-restrained steel braced frames with eccentric configurations (BRBFEs) have high energy dissipation capacities and an architectural advantage to create openings. However, recent investigations have shown that after the earthquake at the MCE hazard level, the residual drift in buildings with buckling-restrained steel braced frames (BRBF) is remarkable. In the present study, to reduce the residual drift in a BRBFE system, it has been suggested to add a post-tensioned frame (PTF) in parallel and create a BRBFE-PTF combined system. Moreover, a method has been proposed to design this combined system. In this method, the values of the two parameters of the self-centering ratio and cable cross-section area are selected arbitrarily. Then, after verifying the modeling, the pushover, cyclic, and time-history analyses of the prepared numerical models were performed. The results showed that if appropriate values were selected for the self-centering ratio and cable cross-section area, the proposed system had the desirable seismic performance in maximum drift demand and residual drift.

Dominant roles of eccentricity, fin design, and nanoparticles in performance enhancement of latent thermal energy storage unit

In this paper, numerical and experimental investigations of thermal performance enhancement of horizontal longitudinal shell and tube latent heat thermal energy storage unit (LHTESU) via eccentricity (e), fin design optimization, and nanoparticles in the phase change material (PCM) of stearic acid are presented. An enthalpy-porosity-based two-dimensional, transient numerical methodology is used after validating against the experimental results and the literature. Five different eccentric positions, e = 0.14, 0.28, 0.42, 0.56, and 0.63 are investigated by modifying the design of Y-finned tube. The eccentricity and fin design modifications improved natural convection effects as compared to concentric Y-finned tube. Thermal performances of LHTESU are analyzed on the basis of melting time, heat storage capacity, heat storage rate, and performance enhancement ratio. Based on the performance analysis, an optimum eccentric configuration of LHTESU is proposed. For optimized eccentric unit (e=0.42), a reduction of 34.14% in melting time along with 30.7% improvement in thermal energy storage rate is achieved as compared to concentric (e=0) LHTESU. The effect of temperature of the tube on PCM's melting time and heat transfer is also analyzed and two important correlations are proposed. The thermal performance of the optimized eccentric unit is further enhanced by adding nanoparticles of Al2O3 and CuO ranging from 0.5% to 10% by volume in the pure PCM. The nano-enhanced PCM with 1% of Al2O3 further improves melting and energy storage rates of optimum LHTESU by 10%.

Diagnostic Value of Sonographic Features in Distinguishing Malignant Partially Cystic Thyroid Nodules: A Systematic Review and Meta-Analysis.

Ultrasonography (US) is one of the most important methods for the management of thyroid nodules, which can be classified as solid, partially cystic, or cystic by composition. The various Thyroid Imaging Reporting and Data System classifications pay more attention to solid nodules and have reported pertinent US features associated with malignancy. However, the likelihood of malignancy of partially cystic thyroid nodules (PCTNs) is 3.3–17.6%, and few studies have systematically discussed the value of US in differentiating such entities. Therefore, we deemed it necessary to perform a systematic evaluation of US features in recognizing malignant PCTNs. Our systematic review and meta-analysis aimed to assess the value of US features in predicting malignant PCTNs. We searched the PubMed/MEDLINE, Web of Science, and Cochrane Library databases to find studies that researched US features of PCTNs and that were published before June 2020. Review Manager 5.3 was used to summarize suspicious US features and calculate the sensitivity, specificity, and likelihood ratios. MetaDiSc 1.4 was used to estimate receiver operating characteristic curves and calculate areas under the curves (AUCs). Our review included eight studies with a total of 2,004 PCTNs. Seven features were considered to be associated with malignancy. High specificity (>0.9) was found in nodules with a taller-than-wide shape, those that were spiculated/microlobulated or with an ill-defined margin, those with microcalcification, and a non-smooth rim. Among US features, eccentric configuration, microcalcification, and marked or mild hypoechogenicity were more reliable in predicting malignancy (AUC: 0.9592, 0.8504, and 0.8092, respectively). After meta-analysis, we recommend combining PCTN US features including an eccentric internal solid portion, marked or mild hypoechogenicity, and presence of microcalcification to better identify malignant nodules. More studies are needed to explore and improve the diagnostic value of US in PCTNs.

Predictions of the geomagnetic secular variation based on the ensemble sequential assimilation of geomagnetic field models by dynamo simulations

The IGRF offers an important incentive for testing algorithms predicting the Earth’s magnetic field changes, known as secular variation (SV), in a 5-year range. Here, we present a SV candidate model for the 13th IGRF that stems from a sequential ensemble data assimilation approach (EnKF). The ensemble consists of a number of parallel-running 3D-dynamo simulations. The assimilated data are geomagnetic field snapshots covering the years 1840 to 2000 from the COV-OBS.x1 model and for 2001 to 2020 from the Kalmag model. A spectral covariance localization method, considering the couplings between spherical harmonics of the same equatorial symmetry and same azimuthal wave number, allows decreasing the ensemble size to about a 100 while maintaining the stability of the assimilation. The quality of 5-year predictions is tested for the past two decades. These tests show that the assimilation scheme is able to reconstruct the overall SV evolution. They also suggest that a better 5-year forecast is obtained keeping the SV constant compared to the dynamically evolving SV. However, the quality of the dynamical forecast steadily improves over the full assimilation window (180 years). We therefore propose the instantaneous SV estimate for 2020 from our assimilation as a candidate model for the IGRF-13. The ensemble approach provides uncertainty estimates, which closely match the residual differences with respect to the IGRF-13. Longer term predictions for the evolution of the main magnetic field features over a 50-year range are also presented. We observe the further decrease of the axial dipole at a mean rate of 8 nT/year as well as a deepening and broadening of the South Atlantic Anomaly. The magnetic dip poles are seen to approach an eccentric dipole configuration.