VHF transequatorial propagation via three dimensional waveguides

Tall RC chimneys form an important component of major industries and power plants. Since pollution control standards are getting stringent every passing day, the mandatory height requirements of chimneys are increasing. Such increased heights pose structural challenges for designing against dynamic loads such as wind gust and seismic forces. Arriving at an economic and efficient structural profile is one of the important aspects of the analysis and design of tall chimneys. Most of the chimneys constructed in industry are of circular cross section. With increase in heights, chimneys become more vulnerable to dynamic loads. In order to combat these loads and design an economical and efficient structural solution needs to be evolved. Elliptical cross-section provides one such possible alternate solution. Therefore evaluating the behavior of chimneys of varying heights with elliptical cross-section and comparing the same with that of circular cross-section assume significance. Chimneys with circular and elliptical cross sections of five different heights viz. 275m, 300m, 325m, 350m and 400m with two different profiles in elevation - one tapering from bottom to top and the other tapering from bottom to 2/3 H and straight afterwards - have been analyzed for seismic and vortex shedding effects caused by wind forces; further, analyses have been carried out for three R/t ratios - 15, 20 and 25. In total 120 models have been analyzed 60 for seismic forces and 60 for vortex shedding effects. Analytical results in terms of stresses induced on the structure, earthquake base shear, joint acceleration, joint displacements and vortex shedding base shear are evaluated. Maximum values of seismic forces induced base shear is only 1% of the self weight of the structure for all heights. It is interesting to note that chimneys with elliptical cross section experience less accelerations compared to that with circular cross section. Circular chimneys undergo higher displacement than the elliptical chimneys which is attributed to the higher accelerations they are subjected to by seismic forces. As the height of the chimneys is increased vortex shedding phenomenon induces increased forces compared to that due to earthquakes.

Lately, the drip irrigation systems find more and more application, which led to the production of a new type of drip laterals – with flat to elliptic cross section and comparatively small thickness of the wall – from 0.2 to 0.9 mm, compared to the conventional ones with circular cross section and wall thickness over 1 mm. The main advantage of the first type is that they are comparatively cheap and are offered in the form of small rolls, the length of the hose being from 500 to 3500 m which makes their transportation to warehouses, assembly and disassembly very convenient. With the smaller thickness of the walls, the laterals have almost clenched form and are intended to be used for one irrigation season, while those with higher thickness, with elliptic form, may be used for several seasons. The inside welded emitters are flat and have a very small water-stopping head area compared to the annular water-stopping cross section of the cylindrical drippers in the conventional circular type of laterals. This is connected with the smaller head losses in the movement of water in them, which is an important advantage. The paper presents and analyses the results of the hydraulic test of the two types of drip hoses – with circular and elliptic cross section, in order to find the head losses for different lengths - 40, 60 and 80 m and heads in the beginning of 6, 8, 10, 12, 14 and 16 m, as well as the coefficients of uniformity for both types. The following hoses of both types were tested: JUNIOR, with circular cross section and internal diameter of 13.8 mm, nominal diameter 16 mm, thickness of wall 1.1mm, cylindrical type of drippers with a flow rate of 2.1 l/h and interval between nozzles 0.30 m (Irritec, Italy); DP Line (D5), with elliptic cross section, with the same sizes and intervals but with a wall thickness 0.6 mm and flat type of drippers (Irritec, Italy). The results indicate that irrespectively of the elliptic form of the cross section which is with a very small hydraulic radius, the head losses are almost equal to those with the circular cross section with cylindrical drippers, which is due to the minor head losses because of the flat nozzles in them. The values of the absolute coefficient of uniformity and the calculated one according to the method of Christiansen for all options are presented. The test is performed for zero slope, while modelling is performed for slopes 1% and 2%. The analysis of the data indicates that for zero slope of the terrain the increase of head leads to increase of the coefficients of uniformity for the three tested lengths of laterals; for 1% are observed very small tendencies for reduction of those coefficients, while for 2% the coefficients have higher values compared to the other slopes, again with slightly expressed tendency for change. The higher values in the 2% slope are due to the additional head caused by the geodetic level difference of the terrain.

The article discusses a field geophysical complex that includes the Earth's gravity and magnetic fields parameters meters — an digital zenith camera (DZC), a relative gravimeter, onboard quantum magnetometer and ground magnetovariation station. This complex allows determining such parameters of the Earth's gravity field as acceleration and anomalies of gravity, plumb line deviations, horizontal components of the acceleration of gravity and gravitational gradients, and parameters of the Earth's magnetic field — absolute and anomalous values of induction. Maps of the Earth's gravity and magnetic fields can be used in various fields, in particular, in the creation and testing of integrated autonomous navigation systems using the parameters of these fields. The paper presents examples of parameter maps created using this complex. The measurement error of acceleration and gravity anomaly is 10 µGal, plumb line deviation is ≈ 0.2″, horizontal components of gravity acceleration are ≈ 1 mGal, gravitational gradients are 10 Eötvös at a distanc

A waveguide model is proposed for the evening type transequatorial propagation mode. Field aligned irregularities observed in equatorial ionosphere are assumed to form dielectric waveguides. A local Champan type layer electron density distribution is taken inside the guide. The transequatorial wave propagation is treated by using this model and the propagation theory of dielectric waveguides. The total attenuation is computed between two points located in opposite hemispheres. The analytic form of the results permits easy interpretation of the propagation characteristics. A good agreement is observed between the experimental results and the theoretical calculations for the total attenuation. Comparisons have also been done for the propagation delay and the incoming elevation angle at the reception point.

We study the influence of the shape of the plasma container on the dynamics of the reversed-field pinch (RFP). The geometries we consider are periodic cylinders with elliptical and circular-shaped cross-sections. Numerical simulations of fully nonlinear viscoresistive magnetohydrodynamics are carried out to illustrate how the plasma dynamics is affected by shaping. It is shown that independent of the plasma shape, the quantity $\beta$ , comparing the hydrodynamic pressure to the magnetic pressure, decreases for increasing values of the Lundquist number, but the pressure gradient fluctuations remain roughly constant, when compared to the Lorentz force. Different elliptical shapes of the cross-section of the domain lead to the excitation of different toroidal (or axial) magnetic and dynamic modes. Furthermore, it is found that in a geometry with circular cross-section, a significant local poloidal angular momentum is observed, absent in the geometries with elliptical cross-section. Because the confinement is dominantly determined by plasma movement, and the dynamics of the velocity and magnetic field are modified by the modification of the geometry, shaping can thus affect the performance of RFP devices.

Robust attitude and heading estimation with respect to a known reference is an essential component for indoor localization in robotic applications. Affordable Attitude and Heading Reference Systems (AHRS) are typically using 9-axis solid-state MEMS-based sensors. The accuracy of heading estimation on such a system depends on the Earth's magnetic field measurement accuracy. The measurement of the Earth's magnetic field using MEMS-based magnetometer sensors in an indoor environment, however, is strongly affected by external magnetic perturbations. This paper presents a novel approach for robust indoor heading estimation based on skewed-redundant magnetometer fusion. A tetrahedron platform based on Hall-effect magnetic sensors is designed to determine the Earth's magnetic field with the ability to compensate for external magnetic field anomalies. Additionally, a correlation-based fusion technique is introduced for perturbation mitigation using the proposed skewed-redundant configuration. The proposed fusion technique uses a correlation coefficient analysis for determining the distorted axis and extracts the perturbation-free Earth's magnetic field vector from the redundant magnetic measurement. Our experimental results show that the proposed scheme is able to successfully mitigate the anomalies in the magnetic field measurement and estimates the Earth's true magnetic field. Using the proposed platform, we achieve a Root Mean Square Error of 12.74° for indoor heading estimation without using an additional gyroscope.

To calculate the equilibrium and stability of finite aspect ratio tokamaks, even for circular and elliptical plasma cross-sections, intricate numerical methods must usually be employed, which require a fast and large computer. So far, these calculations have been carried out analytically only for infinite aspect ratio. In fact certain analytical equilibrium solutions at finite aspect ratio are known, but these do not include such important cases as elliptical cross-sections. In this paper, finite aspect ratio equilibrium solutions are derived for circular, prolate and oblate elliptical cross-sections and for a flat current profile. In addition, the problem of axisymmetric stability is studied for prolate elliptical cross-sections, the approach being almost entirely analytical.

Asymmetric magnetic field inside a cylindrical flux rope

Magnetoreception

A model of the ionospheric MHD waveguide is considered that enables one, using fairly clear and simple equations, to describe the main physical features of the waveguide propagation of geomagnetic pulsations. The proposed model makes it possible to identify a number of ionospheric parameters, in terms of which the mode cutoff frequencies and the phase and group velocities of modes may be expressed.

Alternative geometry for cylindrical natural draft cooling tower with higher cooling efficiency under crosswind condition

Exact solutions are constructed for the butt-end region of electron beams in the form of finite-length cylinders; truncated cones; cylindrical and conical rings; toroidal, spherical, and ellipsoidal Brillouin formations; a cylindrical magnetron in the subcritical mode; and a cylindrical diode. Problems for finite-length cylinders with elliptic and circular cross sections are investigated. The cylinders are considered in the presence of a uniform longitudinal magnetic field for the case when the longitudinal velocity in a flow exhibits a cycloidal variation and the Cauchy conditions are exactly fulfilled on the flow’s boundary. Relativistic and nonrelativistic flows are analyzed. In the latter case, both the electrostatic and magnetostatic problems are solved. Solution of the magnetostatic problem provides for the continuous transition from the eigenfield to the external magnetic field on a beam’s boundary.

The cross sections of solar coronal loops are suggested to be rarely circular. We examine linear kink oscillations in straight, density-enhanced, magnetic cylinders with elliptical cross sections by solving the three-dimensional magnetohydrodynamic equations from an initial-value-problem perspective. Motivated by relevant eigenmode analyses, we distinguish between two independent polarizations, one along the major axis (the M-modes) and the other along the minor one (the m-modes). We find that, as happens for coronal loops with circular cross sections, the apparent damping of the transverse displacement of the loop axis is accompanied by the accumulation of transverse Alfvénic motions and the consequent development of small scales therein, suggesting the robustness of the concepts of resonant absorption and phase mixing. In addition, two stages can in general be told apart in the temporal evolution of the loop displacement: a Gaussian time dependence precedes an exponential one. For the two examined density ratios between loops and their surroundings, the periods of the M-modes (m-modes) tend to increase (decrease) with the major-to-minor-half-axis ratio, and the damping times in the exponential stage for the M-modes tend to exceed their m-mode counterparts. This is true for the two transverse profiles we examine. However, the relative magnitudes of the damping times in the exponential stage for different polarizations depend on the specification of the transverse profile or the density contrast. The applications of our numerical findings are discussed in the context of coronal seismology.

The order of magnitude of increased growth, multiplication rate, and decreased sporulation of Bacillus subtilis after exposure to nanotesla magnetic fields (MFs) relative to control samples were observed experimentally. Earth's total magnetic field intensity was reduced from 47.9 ± 0.4 μT to cover the range from 97.5 ± 1.7 nT to 1115 ± 158 nT in eight subsequent experiments by using three pairs of Helmholtz coils combined with Mu-metal shielding. The growth, multiplication rate, sporulation, and potassium content were measured in the probe and control containing B. subtilis cultures after 24 h of exposure to nanotesla and Earth's magnetic fields, respectively. The observed effect is discussed with regard to its possible repercussions on Earth's living species during geomagnetic reversals that occurred when the magnetic field was much weaker than the field that exists today. In addition, effects on future manned voyages into deep space, an environment with reduced magnetic field intensity, are considered.

Migratory birds are known to use the Earth's magnetic field as an orientation cue on their tremendous journeys between their breeding and overwintering grounds. The magnetic compass of migratory birds relies on the magnetic field's inclination, i.e. the angle between the magnetic field lines and the Earth's surface. As a consequence, vertical or horizontal field lines corresponding to 0 or 90 deg inclination should offer no utilizable information on where to find North or South. So far, very little is known about how small the deviations from horizontal or vertical inclination are that migratory birds can detect and use as a reference for their magnetic compass. Here, we asked: what is the steepest inclination angle at which a migratory bird, the Eurasian blackcap (Sylvia atricapilla), can still perform magnetic compass orientation in Emlen funnels? Our results show that blackcaps are able to orient in an Earth's strength magnetic field with inclination angles of 67 and 85 deg, but fail to orient in a field with 88 deg inclination. This suggests that the steepest inclination angle enabling magnetic compass orientation in migratory blackcaps tested in Emlen funnels lies between 85 and 88 deg.