Results 1 - 10 of 11
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[en] Detection of cosmic ray fluxes makes it possible to study dynamics of the interplanetary magnetic field and gain information about processes that occur both on the solar surface and in the entire Solar system. The main variations in the cosmic ray intensity are 27-day variations and Forbush effects. These variations are caused by complex spatial solar-plasma formations resulting from various processes on the solar surface and propagating in space with widely varying velocities. The data recorded by the PAMELA magnetic spectrometer on board the Resurs-DK1 satellite in 2006–2016 are used.
[en] We study the motion of particles in the background of a scalar–tensor theory of gravity in which the scalar field is kinetically coupled to the Einstein tensor. We constrain the value of the derivative parameter z through solar system tests. By considering the perihelion precession we obtain the constraint /m>2.6×10 m, the gravitational redshift m>2.7×10 m, the deflection of light /m>1.6×10 m, and the gravitational time delay /m>7.9×10 m; thereby, our results show that it is possible to constrain the value of the z parameter in agreement with the observational tests that have been considered.
[en] Young Kepler’s daring ideas on the structure of the Solar system are applied to the analysis of planetary distances in the exoplanetary system HD 10180. Using Zhukovsky’s transformation, the essence of the spinor regularization of Kepler’s problem is explained as extracting the square root of an ellipse and using a Kepler eccentric anomaly instead of the usual time. The achievements of Kharkiv radio astronomers in the search for radio recombination lines of Rydberg carbon atoms at the UTR-2 radio telescope are considered. A generalized spinor regularization of the Kepler problem is used to analyze the energy spectra of Rydberg hydrogen atoms in a magnetic field. (author)
[en] We study the propagation of electromagnetic (EM) waves in the solar system and develop a Mie theory that accounts for the refractive properties of the free electron plasma in the extended solar corona. We use a generic model for the electron number density distribution and apply the eikonal approximation to find a solution in terms of Debye potentials, which is then used to determine the EM field both within the inner solar system and at large heliocentric distances. As expected, the solution for the EM wave propagating through the solar system is characterized by a plasma-induced phase shift and related change in the light ray’s direction of propagation. Our approach quantitatively accounts for these effects, providing a wave-optical treatment for diffraction in the solar plasma. As such, it may be used in practical applications involving big apertures, large interferometric baselines or otherwise widely distributed high-precision astronomical instruments. (paper)
[en] The effects of a quadratic gravity on astronomical observations and solar system experiments were recently considered in previous works. Its deviation from Einstein’s general relativity is characterized by a model parameter α and the cosmological constant Λ whose constraints were respectively found as m2 and m−2 in the solar system. In this paper, a new test of the gravity by measuring the gravitational time advancement is presented and studied. The gravitational time advancement arises in a two-way light propagation between an observer and a distant spacecraft, where the light traveling time is recorded by the observer’s proper time. It is found that (1) relying on their signs, α and Λ can make the gravitational time advancement smaller or larger than the one of general relativity; (2) the configuration of the inferior conjunction between the observer and the spacecraft is more suitable for detecting the advancement, because its effect is almost 3.5 times larger than the one in the superior conjunction; (3) the time advancement could be effectively complementary to Shapiro time delay for gravitational experiments in practice; and (4) the implement of planetary laser ranging and optical clocks in the future will provide much more insight into the gravity. (paper)
[en] Two different ways of generalizing Einstein’s general theory of relativity with a cosmological constant to Brans–Dicke type scalar–tensor theories are investigated in the linearized field approximation. In the first case a cosmological constant term is coupled to a scalar field linearly whereas in the second case an arbitrary potential plays the role of a variable cosmological term. We see that the former configuration leads to a massless scalar field whereas the latter leads to a massive scalar field. General solutions of these linearized field equations for both cases are obtained corresponding to a static point mass. Geodesics of these solutions are also presented and solar system effects such as the advance of the perihelion, deflection of light rays and gravitational redshift were discussed. In general relativity a cosmological constant has no role in these phenomena. We see that for the Brans–Dicke theory, the cosmological constant also has no effect on these phenomena. This is because solar system observations require very large values of the Brans–Dicke parameter and the correction terms to these phenomena becomes identical to GR for these large values of this parameter. This result is also observed for the theory with arbitrary potential if the mass of the scalar field is very light. For a very heavy scalar field, however, there is no such limit on the value of this parameter and there are ranges of this parameter where these contributions may become relevant in these scales. Galactic and intergalactic dynamics is also discussed for these theories at the latter part of the paper with similar conclusions. (paper)
[en] We investigate neutrino oscillation in the field of an axially symmetric space-time, employing the so-called q-metric, in the context of general relativity. Following the standard approach, we compute the phase shift invoking the weak and strong field limits and small deformation. To do so, we consider neutron stars, white dwarfs and supernovae as strong gravitational regimes whereas the solar system as weak field regime. We argue that the inclusion of the quadrupole parameter leads to the modification of the well-known results coming from the spherical solution due to the Schwarschild space-time. Hence, we show that in the solar system regime, considering the Earth and Sun, there is a weak probability to detect deviations from the flat case, differently from the case of neutron stars and white dwarfs in which this probability is larger. Thus, we heuristically discuss some implications on constraining the free parameters of the phase shift by means of astrophysical neutrinos. A few consequences in cosmology and possible applications for future space experiments are also discussed throughout the text.
[en] The cosmic-ray particles of TeV-regime, outside the solar system are blocked in their way to the Earth, a deficit of particles is observed corresponding to the location of the Sun known as the Sun shadow. The center of the Sun shadow is shifted from its nominal position due to the presence of magnetic fields in interplanetary space, and this shift is used indirectly as a probe to study the solar magnetic field that is difficult to measure otherwise. A detailed Monte Carlo simulation of galactic cosmic-ray propagation in the Earth–Sun system is carried out to disentangle the cumulative effects of solar, interplanetary and geomagnetic fields. The shadowing effects and the displacements results of the Sun shadow in different solar activities are reproduced and discussed. (paper)
[en] The detection of gravitational waves from merging binary black holes has led to a bound on the mass of a hypothetical massive carrier of the gravitational interaction predicted by some modified gravity theories (a massive graviton, for short), corresponding to a bound on the Compton wavelength km. This bound is six times more stringent than a 1988 bound inferred from solar-system dynamics. Using 30 years of improvements in solar system data, chiefly from missions involving orbiters and probes of planets from Mercury to Saturn, we revisit this bound. We show that data on the perihelion advance of Mars obtained from the Mars Reconnaissance Orbiter leads to a credible lower bound on between 1.2 and km, surpassing the gravitational-wave bound by an order of magnitude. We discuss ways in which each of these competing bounds may improve in the future. (letter)
[en] Solar dryers have become important components for the delivery of dried agricultural products of high quality. They generally are designed to maximize the production of a heating system based on solar radiation. This study involved the design, building and testing of a control system to allow the monitoring of temperature, solar radiations and control of humidity in a Photovoltaic (PV)- Greenhouse Solar Dryer (PVGSD). This was accomplished by assembling a solar charge controller, three solar panels, a power inverter, and a battery system. An Arduino UNO Rev3, DHT22-sensor, solderless breadboard, Liquid Crystal Display (LCD) screen, jumper cables, LightEmitting Diode (LED) red, Global System for Mobile (GSM) communication module, 10k Ω, 220 Ω and 1k Ω resistors and two 5V one channel relays formed the control system. These were assembled in a multi-functional workstation linked to the solar dryer. The GSM communication module was an innovation to allow connection to the internet over General Packet Radio Service (GPRS) network and send/receive SMS. It was used to control the fans remotely and further allowed logging of periodic sensor data (temperature, humidity, voltage and solar radiation values) by sending SMS to a phone number and server. Dryer and product characteristics were measured including temperature, humidity, solar radiation and moisture content. The temperature and humidity profile were monitored for 11 days in the empty PVGSD without the workstation and Open Sun Drying (OSD) showed that the PVGSD recorded the highest temperature of 69oC occurring between 12:00 and 14:00 hours GMT while the OSD recorded at 41.5oC. The highest relative humidity recorded in the PVGSD was 75.5% and 83% for OSD observed at night from 20:00 hours to 5:00 hours GMT. Two commodities, cassava (slices and chunks) and red pepper were dried to evaluate the dryer efficiency, and this was compared with OSD and existing greenhouse type solar dryer (GSD). The cassava slices dried faster than the cassava chunks in all the drying methods indicating that sample size influenced drying rate. PVGSD had a faster drying rate for cassava slices of 0.0732g/g.h compared to 0.04908g/g.h for GSD and 0.02074g/g.h for OSD, while drying rate of PVGSD, GSD and OSD for cassava chunks were 0.0457g/g.h, 0.0355g/g.h and 0.01667g/g.h respectively. Similarly, PVGSD was observed to obtain the highest rate of drying for red pepper of 0.097g/g.h compared to GSD of 0.094g/g.h and OSD of 0.047g/g.h. The drying method, time and sample size were found to have statistical significance (p<0.05) on temperature, moisture content, humidity and drying rate. The PVGSD dryer with the workstation was able to keep the humidity conditions in the dryer low to prevent moisture uptake during the night. The samples in this dryer showed consistent drop in moisture content throughout the drying period. To further evaluate the drying effect on the samples, laboratory analyses such as water activity, color profile and particle size determination were performed on the resultant dried cassava flour samples and red pepper (whole). cassava slices dried faster than the cassava chunks in all the drying methods indicating that sample size influenced drying rate. PVGSD had a faster drying rate for cassava slices of 0.0732g/g.h compared to 0.04908g/g.h for GSD and 0.02074g/g.h for OSD, while drying rate of PVGSD, GSD and OSD for cassava chunks were 0.0457g/g.h, 0.0355g/g.h and 0.01667g/g.h respectively. Similarly, PVGSD was observed to obtain the highest rate of drying for red pepper of 0.097g/g.h compared to GSD of 0.094g/g.h and OSD of 0.047g/g.h. The drying method, time and sample size were found to have statistical significance (p<0.05) on temperature, moisture content, humidity and drying rate. The PVGSD dryer with the workstation was able to keep the humidity conditions in the dryer low to prevent moisture uptake during the night. The samples in this dryer showed consistent drop in moisture content throughout the drying period. To further evaluate the drying effect on the samples, laboratory analyses such as water activity, color profile and particle size determination were performed on the resultant dried cassava flour samples and red pepper (whole). The color profile of red pepper flour and cassava flour from the PVGSD was observed to be better in terms of the redness (a * ) for red pepper, lightness (L * ) for cassava, browning index (BI) and color change (∆E). The color change of red pepper for PVGSD, GSD and OSD were 11.94, 16.43 and 25.25 respectively. The color change of cassava slices for PVGSD, GSD and OSD were 10.49, 10.84 and 11.59 respectively, while that for cassava chunks recorded at 10.60, 12.09 and 12.11 respectively for PVGSD, GSD and OSD. The SD50 values for flours from the slices were finer than those from the chunks. The SD50 values for cassava slices under PVGSD, GSD and OSD were 62 µm, 76 µm and 78 µm respectively, while SD50 values for cassava chunks under PVGSD, GSD and OSD recorded at 80 µm, 92 µm and 106 µm respectively. In general, cassava slices under the three drying methods demonstrated a better quality than the chunks in terms of color and particle size. All samples were dried to a water activity below 0.500 to prevent microbial spoilage. Final water activity for red pepper was 0.384, 0.388 and 0.414 respectively for PVGSD, GSD and OSD, while that for cassava slices and chunk for PVGSD was 0.361 and 0.415 respectively, GSD was 0.384 and 0.446 respectively and OSD recorded at 0.421 and 0.490 respectively. To further understand and describe the drying curves for the samples under the three drying methods, 12 Thin Layer Mathematical models were evaluated. The best model under this study for red pepper is the Midilli and Kucuk model under both PVGSD and GSD while Logarithmic model describes best under OSD. Approximation of diffusion model can be used for cassava slices under PVGSD and GSD, while Midilli and Kucuk model for OSD. These models were selected according to the lowest Root Mean Square Error (RMSE) and chi square (χ 2 ) and highest correlation coefficient (R2). (Author)