Eccentric Dipole Evolution during the Last Reversal, Last Excursions, and Holocene Anomalies. Interpretation Using a 360-Dipole Ring Model

The eccentric dipole (ED) is the next approach of the geomagnetic field after the generally used geocentric dipole. Here, we analyzed the evolution of the ED during extreme events, such as the Matuyama-Brunhes polarity transition (~780 ka), the Laschamp (~41 ka) and Mono Lake (~34 ka) excursions, and during the time of two anomalous features of the geomagnetic field observed during the Holocene: the Levantine Iron Age Anomaly (LIAA, ~1000 BC) and the South Atlantic Anomaly (SAA, analyzed from ~700 AD to present day). The analysis was carried out using the paleoreconstructions that cover the time of the mentioned events (IMMAB4, IMOLEe, LSMOD.2, SHAWQ-Iron Age, and SHAWQ2k). We found that the ED moves around the meridian plane of 0–180° during the reversal and the excursions; it moves towards the region of the LIAA; and it moves away from the SAA. To investigate what information can be extracted from its evolution, we designed a simple model based on 360-point dipoles evenly distributed in a ring close to the inner core boundary that can be reversed and their magnitude changed. We tried to reproduce with our simple model the observed evolution of the ED, and the total field energy at the Earth’s surface. We observed that the modeled ED moves away from the region where we set the dipoles to reverse. If we consider that the ring dipoles could be related to convective columns in the outer core of the Earth, our simple model would indicate the potential of the displacement of the ED to give information about the regions in the outer core where changes start for polarity transitions and for the generation of important anomalies of the geomagnetic field. According to our simple model, the regions in which the most important events of the Holocene occur, or in which the last polarity reversal or excursion begin, are related to the regions of the Core Mantle Boundary (CMB), where the heat flux is low.

Astrometric Calibration of the Clementine Meridian Line (1702) of S. Maria degli Angeli on the Zodiacal Signs, in the IGEA Observational Campaign (2018/21)

The meridian line is a basic instrument for positional astronomy, it was used to study the motion of Sun, Moon, planets and the position of stars by measuring position and time of their passage through the meridian plane. The accuracy of such positions was dependent on precise theories of the atmospheric refraction (Cassini, 1655 and Laplace, 1825) and by the use of reference marks present originally on the meridian line, and now cancelled by the centuries. From October 27, 2018 the new pinhole of the meridian line in the Basilica of S. Maria degli Angeli in Rome (1702) is a circle 25 mm wide and 6.11 mm thick and its position is fixed, in order to perform a series of observations of astrometric quality, the IGEA campaign. The comparison of the observed positions of the meridian passages of the Sun, Southern and Northern limbs, with the ephemerides of Calsky.org and Stellarium 0.20.2 for the Sun are examined for the dates of the ingresses into the zodiacal signs, when the ecliptic longitude is exactly 0°/180° (Aries and Libra, spring and fall equinox), 30°/150° (Taurus, Virgo), 60°/120° (Gemini, Leo), 90° (Cancer), 330°/210° (Pisces, Scorpio), 300°/240° (Aquarius/Sagittarius), 270° (Capricorn). The former geometrical calibration of the marks present on the line, with a total station, is compared with another calibration done with a metal and laser meter. The first star on the floor of the Basilica representing the position of the Sun on August 20, 1702 when the pope Clement XI visited the meridian line, financed by him, has been calibrated with the solar image. The present pinhole is 4.4±0.1 mm South with respect to the original one of 1702.

A modal boundary element method for axisymmetric acoustic problems in an arbitrary uniform mean flow

This paper presents a new numerical analysis approach based on an improved Modal Boundary Element Method (MBEM) formulation for axisymmetric acoustic radiation and propagation problems in a uniform mean flow of arbitrary direction. It is based on the homogeneous Modal Convected Helmholtz Equation (MCHE) and its convected Green’s kernel using a Fourier transform method. In order to simplify the flow terms, a general modal boundary integral solution is formulated explicitly according to two new operators such as the particular and convected kernels. Through the use of modified operators, the improved MBEM approach with flow takes a convective form of the general MBEM approach and has a similar form of the nonflow MBEM formulation. The reference and reduced Helmholtz Integral Equations (HIEs) are implicitly taken into account a new nonreflecting Sommerfeld condition to solve far field axisymmetric regions in a uniform mean flow. For isolating the singular integrations, the modal convected Green’s kernel and its modified normal derivative are performed partly analytically in terms of Laplace coefficients and partly numerically in terms of Fourier coefficients. These coefficients are computed by recursion schemes and Gauss-Legendre quadrature standard formulae. Specifically, standard forms of the free term and its convected angle resulting from the singular integrals can be expressed only in terms of real angles in meridian plane. To demonstrate the application of the improved MBEM formulation, three exterior acoustic case studies are considered. These verification cases are based on new analytic formulations for axisymmetric acoustic sources, such as axisymmetric monopole, axial and radial dipole sources in the presence of an arbitrary uniform mean flow. Directivity plots obtained using the proposed technique are compared with the analytical results.

THE PASSAGE OF THE SUN THROUGH THE MERIDIAN AS AN ASTRONOMICAL FACTOR OF CHANGES IN DEPENDENT VARIABLES IN PHYSICAL SENSORS AND BIOMARKERS

The results of measurements of the photocurrent of a photoresistor installed in the focal plane of a telescope-reflector at st. Novolazarevskaya (Antarctica) in order to register the “culmination” signal from the passage of the Sun through the meridian (culmination). As a result of photocurrent measurements conducted on 03.02.2013 and 04.02.2013 in the midday interval from 11h00m to 11h50m (UT), the “response” (effect) of the photocurrent to the Sun's influence in the position of the meridian plane (culmination) is established. The results of the study of the reaction of the main human biomarkers (in vivo) to the culmination of the Sun, obtained in the analysis of observational data for the period from 20.01.2017, are also presented for 18.04.2017 at the Arctic station “Ice Base Cape Baranova” (arch. Northern Land). Conclusions are made about the sensitivity of the arterial systolic (upper) to the moment of climax and its dependence on the near-surface atmospheric pressure at the frequency of "five-minute" fluctuations (r ~ 0,8). In conclusion, the role of the culmination of the Sun as an astronomical factor in the processes of living and inanimate nature is noted.

Aerodynamic optimization of a SCO2 radial-inflow turbine based on an improved simulated annealing algorithm

Supercritical carbon dioxide plays a vital role in the development of power generation applications. It owns the characteristics of high density and low viscosity, which can ensure a compact structure for turbomachinery. With the blossom of optimization algorithm, an interdisciplinary research which applies optimization method to a traditional design process of turbomachinery can accelerate the course and promote the validity by leaps and bounds. We improve the traditional simulated annealing algorithm and establish an optimization process containing the optimization of rotor meridian plane and nozzle profile. This process can effectively reduce the computation time by establishing a surrogate model of coarse mesh simulation. The effects of traditional simulated annealing algorithm (SAA), genetic algorithm (GA) and improve simulated annealing algorithm (ISAA) are compared. As a result, we realize a maximum of 4.94% promotion for isentropic efficiency in ISAA computation. Also, ISAA method saves the computation time by 59.6% compared to GA and by 41.5% compared to SAA. Applying ISAA optimization method to the turbine in a kW-scale solar-driven Brayton cycle power system, we realize a 1.17% increase for the system efficiency.

Influence of Inflow Distributions on Swirling Flow in Rotor-Stator Cavity With Centripetal and Centrifugal Superposed Flow

The disk cavity of the rotor-stator system is one of important parts of the aero-engine air system. The rotating speed of airflow determines the relative velocity between the airflow and the rotating assembly, so the maintaining characteristic for swirling flow of the rotor-stator cavity will affect the windage of the rotating assembly in the cavity, and the exporting characteristic for swirling flow of the rotor-stator cavity will affect the windage of the rotating assembly in the downstream chamber. Dual-inlet rotor-stator disk cavity is a typical structure of aero-engine. But there are few reports about the flow structure in the dual-inlet rotor-stator disk cavity in the open literature. In this paper, the influence of inflow distributions on maintaining and exporting characteristics for swirling flow was investigated by numerical simulation, aiming at the interaction between the two inflows. The SST turbulence model was well validated against published experimental results. The simulation results show that there are two flow regions in the rotor-stator cavity from the perspective of meridian plane, and there is a rotating vortex in each flow region. In order to quantify the rotational capacity of the airflow, the angular momentum coefficient was defined. Under different inflow distribution ratios, the sizes of the dominant regions of the two vortices in the cavity get varied, which results in the variation of maintaining and exporting characteristics for swirling flow. It was also found that inflow distributions have the same effect on maintaining and exporting characteristics for swirling flow under different rotational Reynolds numbers and different throughflow coefficients, but the capacity of maintaining and exporting swirling flow are different.

On the velocity at wind turbine and propeller actuator discs

The first version of the actuator disc momentum theory is more than 100 years old. The extension towards very low rotational speeds with high torque for discs with a constant circulation became available only recently. This theory gives the performance data like the power coefficient and average velocity at the disc. Potential flow calculations have added flow properties like the distribution of this velocity. The present paper addresses the comparison of actuator discs representing propellers and wind turbines, with emphasis on the velocity at the disc. At a low rotational speed, propeller discs have an expanding wake while still energy is put into the wake. The high angular momentum of the wake, due to the high torque, creates a pressure deficit which is supplemented by the pressure added by the disc thrust. This results in a positive energy balance while the wake axial velocity has lowered. In the propeller and wind turbine flow regime the velocity at the disc is 0 for a certain minimum but non-zero rotational speed. At the disc, the distribution of the axial velocity component is non-uniform in all actuator disc flows. However, the distribution of the velocity in the plane containing the axis, the meridian plane, is practically uniform (deviation <0.2 %) for wind turbine disc flows with tip speed ratio λ>5, almost uniform (deviation ≈2 %) for wind turbine disc flows with λ=1 and propeller flows with advance ratio J=π, and non-uniform (deviation 5 %) for the propeller disc flow with wake expansion at J=2π. These differences in uniformity are caused by the different strengths of the singularity in the wake boundary vorticity strength at its leading edge.

The increase in the curvature radius of geomagnetic field lines preceding a classical dipolarization

Based on assumptions that substorm field line dipolarization at geosynchronous altitudes is associated with the arrival of high-velocity magnetotail flow bursts referred to as bursty bulk flows, the following sequence of field line dipolarization is proposed: (1) slow magnetoacoustic wave excited through ballooning instability by enhanced inflows in pre-onset intervals towards the equatorial plane; (2) in the equatorial plane, slow magnetoacoustic wave stretching of the flux tube in dawn–dusk directions resulting in spreading plasmas in dawn–dusk directions and reduction in the radial pressure gradient in the flux tube. As a consequence of these processes, the flux tube assumes a new equilibrium geometry in which the curvature radius of new field lines increased in the meridian plane, suggesting an onset of field line dipolarization. The dipolarization processes associated with changing the curvature radius preceded classical dipolarization caused by a reduction of cross-tail currents and pileup of the magnetic fields. Increasing the curvature radius induced a convection surge in the equatorial plane as well as inductive westward electric fields of the order of millivolts per meter (mV m−1). Electric fields transmitted to the ionosphere produce an electromotive force in the E layer for generating a field-aligned current system of Bostrom type. This is also equivalent to the creation of an incomplete Cowling channel in the ionospheric E layer by the convection surge.