Comparison of the magnetic field before the subsolar magnetopause with the magnetic field in the solar wind before the bow shock

Crossings of the magnetopause near the subsolar point are analyzed using data of THEMIS mission. Variations of the magnetic field near magnetopause measured by one of THEMIS satellites are studied and compared with simultaneous measurements in the solar wind by another THEMIS satellite. The time delay of the solar wind arrival at the subsolar point of the magnetopause is taken into account. 30 and 90 s averaging of the magnetic field in the magnetosheath is produced. The results of averaging are compared with the results of measurements in the solar wind before the bow shock and foreshock. It is shown, that _Bx$B_x$ component of the magnetic field near magnetopause is near to zero, which supports the possibility to consider the magnetopause as the tangential discontinuity. Comparatively good correlation of _By$B_y$ component in the solar wind and near the magnetopause is observed. The correlation of _Bz$B_z$ component near the magnetopause and IMF is practically absent, the sign of the _Bz$B_z$ near the subsolar point does not coincide with the sign of IMF _Bz$B_z$ in ∼$\sim$30% cases.     

A proposal on the test of general relativity by clock transportation experiments

We propose a test of the gravitational time dilation in general relativity by long term clock comparison between two stations separated in height. The geopotential difference between the two National time keeping centers in China, Lintong (A)$(A)$ and Beijing (B)$(B)$ is around 4000 geopotential unit, which corresponds to the height difference of 400 m. Two clocks _CA$C_A$ and _CB$C_B$ are fixed at stations A and B, respectively, which are synchronized at beginning by a portable clock C in a short time period with go-back synchronization approach. After one month, the clock C is again transported between A and B  , comparing the records of the keeping time by clocks _CA$C_A$ and _CB$C_B$, respectively. Calculations show that, after one month, the difference of the time durations between the clocks _CA$C_A$ and _CB$C_B$ is around 121 ns, if general relativity is correct.     

Zero,minimum and maximum relative radial acceleration for planar formation flight dynamics near triangular libration points in the Earth–Moon system

Assume a constellation of satellites is flying near a given nominal trajectory around _L4$L_4$ or _L5$L_5$ in the Earth–Moon system in such a way that there is some freedom in the selection of the geometry of the constellation. We are interested in avoiding large variations of the mutual distances between spacecraft. In this case, the existence of regions of zero and minimum relative radial acceleration with respect to the nominal trajectory will prevent from the expansion or contraction of the constellation. In the other case, the existence of regions of maximum relative radial acceleration with respect to the nominal trajectory will produce a larger expansion and contraction of the constellation. The goal of this paper is to study these regions in the scenario of the Circular Restricted Three Body Problem by means of a linearization of the equations of motion relative to the periodic orbits around _L4$L_4$ or _L5$L_5$. This study corresponds to a preliminar planar formation flight dynamics about triangular libration points in the Earth–Moon system. Additionally, the cost estimate to maintain the constellation in the regions of zero and minimum relative radial acceleration or keeping a rigid configuration is computed with the use of the residual acceleration concept. At the end, the results are compared with the dynamical behavior of the deviation of the constellation from a periodic orbit.     

Nonlinear electromagnetic perturbations in a degenerate electron–positron plasma

Nonlinear propagation of fast and slow magnetosonic perturbation modes in an ultra-cold, degenerate (extremely dense) electron–positron (EP) plasma (containing non-relativistic, ultra-cold, degenerate electron and positron fluids) has been investigated by the reductive perturbation method. It is shown that due to the property of being equal mass of the plasma species (_me=_mp$m_e=m_p$, where _me$m_e$ and _mp$m_p$ are electron and positron mass, respectively), the degenerate EP plasma system supports the K-dV solitons which are associated with either fast or slow magnetosonic perturbation modes. It is also found that the basic features of the electromagnetic solitary structures, which are found to exist in such a degenerate EP plasma, are significantly modified by the effects of degenerate electron and positron pressures. The applications of the results in an EP plasma medium, which occurs in compact astrophysical objects, particularly in white dwarfs, have been briefly discussed.     

Semi-empirical model of the maximum electron concentration in the ionosphere: Comparison with data from Toluca (México)

A simple semi-empirical model to determine the maximum electron concentration in the ionosphere (_NmF2$N_m{F}_2$) for South American locations is used to calculate _NmF2$N_m{F}_2$ for a northern hemisphere station in the same longitude sector. _NmF2$N_m{F}_2$ is determined as the sum of two terms, one related to photochemical and diffusive processes and the other one to transport mechanisms. The model gives diurnal variations of _NmF2$N_m{F}_2$ representative for winter, summer and equinox conditions, during intervals of high and low solar activity. Model _NmF2$N_m{F}_2$ results are compared with ionosonde observations made at Toluca-México (19.3°N; 260°E). Differences between model results and observations are similar to those corresponding to comparisons with South American observations. It seems that further improvement of the model could be made by refining the latitude dependencies of coefficients used for the transport term.     

Dynamics of the plasma sheet in the magnetotail: Interrelation of turbulent flows and thin current sheet structures

Dynamics of the magnetotail involves elementary processes of magnetic field merging (reconnection layer formation) occurring on medium spatial scales. Every such process features two different stages, a fast one and a subsequent slower one. The corresponding short time scale _T1$T_1$ is associated with disturbances propagating in the tail lobes. The longer time scale _T2$T_2$ is associated with plasma motions in the plasma sheet. A disturbance appearing in the magnetotail on the time scale _T1$T_1$ results in a loss of equilibrium in the plasma sheet. By means of theoretical argument and numerical simulation, it is shown that the relaxation process which follows on the time scale _T2$T_2$, produces extremely thin embedded current sheets, along with generation of fast plasma flows. The process provides an effective mechanism for transformation of magnetic energy accumulated in the magnetotail, into energy of plasma flows. The fast flows may drive turbulent motions on shorter spatial scales. In their turn, those motions can locally produce very thin current sheets; after that, nonlinear tearing process leads to generation of neutral lines, and reconnection. The latter produces new fast disturbances on the time scale _T1$T_1$ closing the feedback loop.     

Calculation of fast neutron removal cross sections for different lunar soils

The interaction of galactic cosmic rays (GCRs) and solar energetic particles (SEPs) with the lunar surface produces secondary radiations as neutrons. The study of the production and attenuation of these neutrons in the lunar soil is very important to estimate the annual ambient dose equivalent on the lunar surface and for lunar nuclear spectroscopy. Also, understanding the attenuation of fast neutrons in lunar soils can help in measuring of the lunar neutron density profile and to measure the neutron flux on the lunar surface. In this paper, the attenuation of fast neutrons in different lunar soils is investigated. The macroscopic effective removal cross section (_ΣR)$({\mathrm{\Sigma }}_R)$ of fast neutrons was theoretically calculated from the mass removal cross-section values (_ΣR/ρ)$({\mathrm{\Sigma }}_R/\rho )$ for various elements in soils. The obtained values of (_ΣR)$({\mathrm{\Sigma }}_R)$ were discussed according to the density. The results show that the attenuation of fast neutrons is more important in the landing sites of Apollo 12 and Luna 16 than the other landing sites of Apollo and Luna missions.     

A possible redshift evolution of the time-lag and variability luminosity relations for long gamma-ray bursts

Several luminosity relations currently exist for long gamma-ray bursts (GRBs). Some were derived from the light curves; others were obtained from the spectra. In this study, we consider two of these luminosity relations: the time-lag, _τlag${\tau }_{\mathit{lag}}$, relation and the variability, V, relation and investigate their possible dependence on (or “evolution” with) the redshift, z.     

Strong geomagnetic activity forecast by neural networks under dominant southern orientation of the interplanetary magnetic field

The paper deals with the relation of the southern orientation of the north–south component _Bz$B_z$ of the interplanetary magnetic field to geomagnetic activity (GA) and subsequently a method is suggested of using the found facts to forecast potentially dangerous high GA. We have found that on a day with very high GA hourly averages of _Bz$B_z$ with a negative sign occur at least 16 times in typical cases. Since it is very difficult to estimate the orientation of _Bz$B_z$ in the immediate vicinity of the Earth one day or even a few days in advance, we have suggested using a neural-network model, which assumes the worse of the possibilities to forecast the danger of high GA – the dominant southern orientation of the interplanetary magnetic field. The input quantities of the proposed model were information about X-ray flares, type II and IV radio bursts as well as information about coronal mass ejections (CME). In comparing the GA forecasts with observations, we obtain values of the Hanssen–Kuiper skill score ranging from 0.463 to 0.727, which are usual values for similar forecasts of space weather. The proposed model provides forecasts of potentially dangerous high geomagnetic activity should the interplanetary CME (ICME), the originator of geomagnetic storms, hit the Earth under the most unfavorable configuration of cosmic magnetic fields. We cannot know in advance whether the unfavorable configuration is going to occur or not; we just know that it will occur with the probability of 31%.     

The relation between the Black hole mass and the Bulge mass for low redshift AGNs. Part I: Ground-based observations

Using the bulge data from AGN image decomposition with ground-based observations, we calculate the ratios of the central supermassive black hole mass(SMBH) to the Bulge mass (_Mbh/_Mbulge$M_{\text{bh}}/M_{\text{bulge}}$) in a sample of X-ray selected AGNs, including 15 Narrow-line Seyfert 1 galaxies (NLS1s) and 18 broad-line Seyfert 1 galaxies (BLS1s). We found that the mean value of log(_Mbh/_Mbulge)$\log (M_{\text{bh}}/M_{\text{bulge}})$ is -3.81±0.11$-3.81\pm 0.11$ for 15 NLS1s, and -2.91±0.13$-2.91\pm 0.13$ for 18 BLS1s, showing the lower _Mbh/_Mbulge$M_{\text{bh}}/M_{\text{bulge}}$ in NLS1s relative to BLS1s. The calculation shows that the Bulge mass from the host image decomposition in NLS1s is statistically smaller than that from Hubble-type correction method, and a linear mass relation is suggested for NLS1s and a nonlinear mass relation for BLS1s. The studying of host galaxies with ground-based observations strongly limited by the atmospheric seeing. We need to do the decomposition of host images for NLS1s with Hubble Space Telescope observation in the future.