Form Of Dipole Research Articles

Time characteristics of microsatellite attitude control at intervals between reac-tion wheels desaturations

The article is devoted to the processes study of changing the microsatellite reaction wheels angular velocities during its stabilization, turn and detumbling. Satellite control is considered under conditions of constant and harmonic external torques, as well as under gravitational, aerodynamic and magnetic disturbing torques. Expressions that describe the change in the reaction wheels angular velocities during satellite stabilization under the action of constant and harmonic torques at a frequency equal to the orbital angular velocity are given. The influence of the magnetic disturbing torque caused by the constant component of the satellite's dipole moment on the accumulation of the reaction wheels angular momentum has been studied. The formula for determining the magnitude of the reaction wheels angular velocities oscillations was obtained using a model of the Earth's magnetic field in the form of the straight dipole and taking into account a circular orbit. Moreover, its use for calculating the maximum values of angular velocities gives results that are very close to the results of modeling taking into account accurate models of the Earth’s magnetic field and the satellite’s center of mass trajectory. The maximum possible operating time intervals of the control system without forced desaturation of its controls are estimated.

Study of the Antenna System of the Marine Vessels Phase Radio Navigation System

Currently the antenna in the form of a half-wave dipole with a gain of about 2 dB is used in the ‘Krabik’ phase radio navigation system. To increase the range of the RNS of sea vessels, various options of more complex antenna systems are considered in the work, providing an increase in the gain compared to the existing antenna. It is shown that the most optimal solution is a collinear antenna with a gain of about 5 dB based on two wave vibrators.

Drivers of Last Millennium Antarctic Climate Evolution in an Ensemble of Community Earth System Model Simulations

Improved understanding of the drivers of climate variability, particularly over the last millennium, and its influence on Antarctic ice melt have important implications for projecting ice sheet resilience in a changing climate. Here, we investigated the variability in Antarctic climate and sea ice extent during the last millennium (850–1850 CE) by comparing paleoenvironmental reconstructions with simulations from the Community Earth System Model Last Millennium Ensemble (CESM-LME). Atmospheric and oceanic response to external forcing in CESM-LME simulations typically take the form of an Antarctic dipole: cooling over most of Antarctica and warming east of the Antarctic Peninsula. This configuration is also observed in ice core records. Unforced variability and a dipole response to large volcanic eruptions contribute to weaker cooling in the Antarctic than the Arctic, consistent with the absence of a strong volcanic signal in Antarctic ice core records. The ensemble does not support a clear link between the dipole pattern and baseline shifts in the Southern Annular Mode and El Niño-Southern Oscillation proposed by some paleoclimate reconstructions. Our analysis provides a point of comparison for paleoclimate reconstructions and highlights the role of internal climate variability in driving modeled last millennium climate evolution in the Antarctic.

Preliminary Assessment of the Soil Foundation Characteristics Utilizing the 2D Resistivity Imaging and Down-Hole Seismic Refraction Techniques: A Case Study in Tenth of Ramadan City, Egypt

Two-dimensional electrical resistivity imaging and seismic refraction, in the form of down-hole survey, were applied to delineate the subsurface section and elastic moduli and identify geotechnical characteristics of subsurface materials in the 10th of Ramadan industrial area, Cairo, Egypt. The results of four 2-D profiles of electrical resistivity, in the form of dipole–dipole and Wenner configurations, revealed that the subsurface section contains two main geo-electrical layers; the first is made of sand, some silt, and gravels, reflecting low resistivity values ranging from 25 to 65.5 ohm m. This layer is overlying a high resistivity layer (65.5 to135 ohm m), corresponding to medium to coarse sand, with gravel and calcareous materials. It is worth noting that that the down-hole technique was used to measure velocities of P and S waves in order to derive the low strain dynamic elastic properties, such as Poisson’s ratio, Shear modulus, stress ratio, concentration index, N-value, and the ultimate and allowable bearing capacities of the subsurface soil, down to an approximate depth of 30 m in the borehole at the site. In addition, the Vs30 value was calculated and revealed that the soil is categorized as a NEHRP class (D). Furthermore, the results of geotechnical parameters and elastic moduli were found to be realistic and sensible for the purposes of engineering constructions and imply that the soil in the study area is characterized by fairly to moderately competent quality. A new empirical correlation is proposed between the obtained Vs and resistivity values, where Vs = 1.0302 ρ + 172.74.

A Single-Layer Low-Profile Broadband Metasurface Antenna Array for Sub-6 GHz 5G Communication Systems

This article presents a planar, low-profile, and single-layer metasurface (MTS)-based wideband 4 × 4 array antenna operating in the 5G sub-6 GHz band. The proposed antenna consists of 4 × 4 unequal size MTS unit cells fed by a simple parallel microstrip feed network in the form of a thin strip cross dipole. The wide impedance bandwidth (IBW) and improved boresight gain characteristics are realized due, respectively, to the excitation of multiple TM resonance modes that are closely spaced and the relatively large lateral size that supports in-phase currents. With an overall size of 1.40λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×1.22λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.054λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at the center frequency of 5.64 GHz), the proposed antenna realizes an IBW of 41.13% (4.48-6.80 GHz), a peak boresight gain of 10.14 dBi, low cross-polarization in the E- and H-planes, and higher front-to-back ratio. Because of the advantages of low-profile, planar and single-layer structure, as well as equal E- and H-planes 3 dB beamwidth, the proposed antenna is a competitive candidate for several modern wireless communications systems, including 5G in the sub-6 GHz band.

Control of the RF magnetic field pattern by tunable metasurface in 1.5 T MRI

A metasurface with a unit cell in the form of a half-wave dipole can be used as a base for the creation of wireless coils for magnetic resonance imaging (MRI). In a real structure based on a metasurface concept, the number of elements is always limited. Therefore, some elements at the edges become weaker coupled and radiofrequency (RF) magnetic field pattern becomes distorted. In this paper, we investigate metasurface-based structure with added non-uniform electrical capacitance at the ends of the resonant unit cells. We show that such a structure can be easily adjusted to work within the frequency range of the clinical 1.5 T MRI machine. Also, we demonstrate that by adding of non-uniform edge capacitances at the resonant elements, it is possible to control the RF magnetic field pattern above the structure.

New functionality in microwave interferometry by application of metastructure as a tunable beam-splitter

A new functionality of microwave interferometry is demonstrated by application of metastructure, meta-surface or meta-atom as controlled original beam-splitter in modified interferometer on basis of h-plane waveguide tee. Specific selectively-tunable interference peaks are observed in transmission of microwaves due to influence of metastructure properties on shape, frequency and intensity of interference peak, when controlled structure resonance approaches interference peak. We investigated following structures as a beam-splitter: ferrite plate, individual conductive resonant element in the form of varactor-loaded butterfly dipole, and metastructure wire grating/varactor-loaded copper strip placed orthogonally. The obtained results open new possibilities to design microwave multifarious multiband spectral filtering and implement selective electric or magnetic tuning, required in multifunctional and multichannel wireless communication.

Reconfigurable graphene antenna for THz applications: a mode conversion approach

A reconfigurable graphene antenna is designed and numerically analyzed. The antenna structure contains a radiating graphene patch and non-radiating graphene ring. The operating frequency of the antenna can be tuned by applying the gate voltage on the graphene patch. This proximity coupled antenna structure operates with the mode. In this configuration, the field is distributed in the form of horizontal magnetic dipole. The application of gate voltage at the periphery of graphene ring converts the field configuration to the form of the vertical electric dipole. Thus, the mode of operation of the antenna is changed to Consequently, the radiation pattern of the antenna can be steered in different directions as per the location of the applied gate voltage at the periphery of the graphene ring.

Diffuse characteristics and piezoelectric properties of Tb-doped BCZT ceramics with CaCl2 as sintering aid

Lead-free ceramics 47(Ba0.7Ca0.3)TiO3–0.53Ba(Zr0.2Ti0.8)O3 (BCZT) + 0.2mol% Tb and xCaCl2 (x = 0.1,0.2 and 0.3wt%) were prepared at different temperatures (1300, 1350 and 1410℃) by solid-state reaction method. The experimental results reveal that dopants can effectively promote the growth of grain at relatively low sintering temperature and CaCl2 as the well sintering aid can produce a pronounced liquid phase to fill the gap between grains sintered at 1410℃ with 0.2wt%. Relative densities and piezoelectric properties of samples can be improved by the introduction of Tb and CaCl2. Comparing with pure BCZT, the residual polarization (Pr) and piezoelectric coefficient (d33*) of ceramics increase from 8.2 to 11.4μC/cm2 and 568–720pm/V with 0.2mol% Tb and 0.2wt% CaCl2 doped. The enhanced properties of samples may be related to the appearance of liquid phase which can increase relative densities of ceramics to 96% and the form of defect dipole in ceramics. Moreover, introduction of CaCl2 makes dielectric peaks (Tc) move to the high-temperature zone about 13℃ and become more and more diffuse (γ = 1.71–1.86), which may have the potential electro-caloric effect application in ferroelectrics.

Investigation of structured microwave discharge based on data from the scattered radiation

The development of a microwave discharge is accompanied by noticeable scattering of the incident electromagnetic field. The scattered radiation includes information about the time evolution of the discharge formation and its integral parameters. In this work a method of diagnostics using scattered radiation to study a single thin plasma channel (plasmoid, plasma dipole) and corresponding experimental results in air within the pressure range P = 70–150 Torr are presented. A simple analytical model for analysis of the experimental results of microwave scattering from a plasmoid is proposed. Information concerning the average elongation velocity of the plasma channel in the direction parallel to the incident electric field and the induced dipole moment of the plasmoid is obtained. Based on information about the dipole moment as well as the form and sizes of the plasma dipole the effective cross section, the total charge, the current averaged over the channel length, the plasma density and conductivity averaged over the channel volume, the electric field amplitude in the central region of the channel and the absorbed power are estimated. The estimated value of the plasma density is shown to agree with experimental results obtained using spectroscopic methods.

Core structure of a interfacial superdislocations in a nickel-base superalloy during high-temperature and low-stress creep

Dislocation substructures were investigated in a nickel-base single crystal superalloy subjected to 85h creep at 1100°C and 130MPa using conventional and high resolution transmission electron microscopy. Both hexagonal and square-like interfacial dislocation networks were observed. The square-like networks, which were caused by two perpendicular sets of a/2<110> dislocations forming a[100] superdislocations, were tested. It was concluded that the a[100] interfacial dislocation occurred in the form of a dislocation dipole. The creation and destruction of dislocation dipoles proceeded reversibly via a slip-and-climb mechanism.

Washable hydrophobic smart textiles and multi-material fibers for wireless communication

This paper reports on the performance and environmental endurance of the recently presented wirelessly communicating smart textiles with integrated multi-material fiber antennas. Metal–glass–polymer fiber composites were fabricated using sub-1 mm hollow-core silica fibers and liquid state silver deposition technique. These fibers were then integrated into textiles in the form of center-fed dipole and loop antennas during standard weaving procedure. Fiber antennas performance was found to be directly comparable to classic ‘rigid’ solutions in terms of return loss, gain and radiation patterns, which allowed transmitting data through Bluetooth protocol at 2.4 GHz frequency. Applied superhydrophobic coatings (water contact angle = 152°, sliding angle = 6°) allow uninterrupted wireless communication of the textiles under direct water application even after multiple washing cycles.

Estimating the macroanisotropy of a horizontally layered section from controlled-source radiomagnetotelluric soundings

The possibilities of estimating the macroanisotropic parameters of the earth by radiomagnetotelluric soundings with a controlled source in the form of a horizontal electric dipole (a cable with a finite length) are studied in the case of the measurements in the transition zone of the source, where the galvanic and induction modes of the excited electromagnetic field are both important. The forward problem for the considered high frequency band (up to 1000 kHz) is solved with allowance for the displacement currents in the ground and air. The algorithm of anisotropic 1D inversion of the sounding data is presented. The resolution parameters are estimated from the derivatives of the electromagnetic field components with respect to the model parameters. Based on the synthetic examples, it is shown that joint inversion of the impedance and tipper data in the transition zone of the source constrains the space of equivalent models and makes it possible to determine the macroanisotropy coefficient of the section.

Introduction to this special section: Borehole geophysics and sonic logging

Sonic logs are most frequently used to tie surface and borehole seismic amplitude measurements to P- and S-wave velocities encountered along wellbore trajectories. Other common uses of sonic logs include the estimation of dynamic elastic properties for geomechanical analysis, such as wellbore stability studies and the design and planning of hydrofracturing operations. Modern sonic logs are acquired with multiple transmitters and an array of closely spaced receivers (anywhere between eight and 13 receivers) in the form of time waveforms. Sonic transmitters can come in the form of monopole, dipole, and quadrupole actuators. By design, sonic transmitters are immersed in a fluid — the borehole mud — whereby formation shear waves can be detected and quantified only by the elastic coupling that exists between wave motion taking place in the borehole fluid and in the surrounding rock formations. Such an elastic coupling gives rise to markedly frequency-dispersive behavior of the detected waves that presents some technical challenges when one interprets their speeds.

Выявление источников искажения формы кривой напряжения в электроэнергетических системах

The installation of devices to normalize the nonsinusoidal electrical modes – harmonic filters - is one of the measures to improve the power quality and increase the reliability of power systems. The choice of nodes for the installation of filters is associated with the task of identification sources of distortion in the power networks. This paper presents a method of assessing the impact of power consumers on the voltage waveform distortion to identify the sources of the higher harmonics in the electric power system. The use of characteristics such as the autonomous voltage of n -th harmonic and the influence factor for the n -th harmonic is proposed as the criteria for distortion sources localization. The parameters for the equivalent circuit of power consumers in the form of active dipole are used to calculate the proposed characteristics. The results of testing the proposed method on a model of the electric power system are presented. To determine the parameters of the equivalent circuits the method of two measurements of the electrical mode parameters was used. The possibility of identifying distorting, non-distorting and mixed loads in the electrical network is proved without the use of a priori information about the composition of electrical equipment of power consumers. The features of the method in case of ring connections in the electrical network are marked; the prospects of applying the method in the power systems are outlined.

Mechanical separation of chiral dipoles by chiral light

We calculate optical forces and torques exerted on a chiral dipole by chiral light fields and reveal genuine chiral forces in combining the chiral contents of both light field and dipolar matter. Here, the optical chirality is characterized in a general way through the definition of optical chirality density and chirality flow. We show, in particular, that both terms have mechanical effects associated, respectively, with reactive and dissipative components of the chiral forces. Remarkably, these chiral force components are directly related to standard observables: optical rotation for the reactive component and circular dichroism for the dissipative one. As a consequence, the resulting forces and torques are dependent on the enantiomeric form of the chiral dipole. This suggests promising strategies for using chiral light forces to mechanically separate chiral objects according to their enantiomeric form.

Optical input impedance of nanostrip antennas

We conduct an investigation into optical nanoantennas in the form of a strip dipole made from aluminum. With the finite-difference time domain simulation both optical input impedance and radiation efficiency of nanostrip antennas are addressed. An equivalent circuit is presented as well for the nanostrip antennas at optical resonances. The optical input resistance can be adjusted by varying the geometric parameters of antenna strips. By changing both strip area and strip length simultaneously, optical input resistance can be adjusted for matching impedance with an external feeding or loading circuit. It is found that the optical radiation efficiency does not change significantly when the size of a nanostrip antenna varies moderately.

Observation of anisotropy in the arrival direction distribution of cosmic rays above TeV energies with IceCube

The IceCube neutrino telescope, completed in December 2010, is a cubic-kilometer scale detector buried under the South Pole ice. Between May 2009 and May 2010, IceCube recorded 32 billion of atmospheric muons generated in air showers produced by cosmic rays in the TeV energy range. This high statistics data sample can be used to look for anisotropy in the arrival directions of the cosmic ray particles at the per-mille level. IceCube observes, for the first time in the southern hemisphere, an energy dependence in the Galactic cosmic ray anisotropy up to a few hundred TeV. This study shows that the same large-scale anisotropy observed at median energies around 20TeV is not present at 400TeV; the anisotropy observed at 400TeV shows substantial differences with respect to that at lower energy. In addition to the large-scale features observed at 20TeV in the form of strong dipole and quadrupole moments, the data include several localized regions of excess and deficit on scales between 10° and 30°. The features observed at both large and small scales are statistically significant, but their origin is currently unknown.

OBSERVATION OF ANISOTROPY IN THE ARRIVAL DIRECTIONS OF GALACTIC COSMIC RAYS AT MULTIPLE ANGULAR SCALES WITH IceCube

Between 2009 May and 2010 May, the IceCube neutrino detector at the South Pole recorded 32 billion muons generated in air showers produced by cosmic rays with a median energy of 20 TeV. With a data set of this size, it is possible to probe the southern sky for per-mil anisotropy on all angular scales in the arrival direction distribution of cosmic rays. Applying a power spectrum analysis to the relative intensity map of the cosmic ray flux in the southern hemisphere, we show that the arrival direction distribution is not isotropic, but shows significant structure on several angular scales. In addition to previously reported large-scale structure in the form of a strong dipole and quadrupole, the data show small-scale structure on scales between 15° and 30°. The skymap exhibits several localized regions of significant excess and deficit in cosmic ray intensity. The relative intensity of the smaller-scale structures is about a factor of five weaker than that of the dipole and quadrupole structure. The most significant structure, an excess localized at (right ascension α = 1224 and declination δ = −474), extends over at least 20° in right ascension and has a post-trials significance of 5.3σ. The origin of this anisotropy is still unknown.

Nonlinear beam steering by fractional vortex dipoles

We study the ability of beams with complex phase dislocations to guide and steer signal beams in self-focusing nonlinear media. In particular, we report on the experimental demonstration of signal deflection by beams carrying step-screw phase dislocation in the form of a fractional vortex dipole. We show how the beam deflection can be ruled by the geometry and orientation of the dipole.