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Hybrid simulations of Venus have produced nightside structure. It is believed these are the first simulations to produce the structure reported by spacecraft such as the Pioneer Venus Orbiter (PVO). The simulations reveal that the structure is created by the ∇ Pe ambipolar electric field when it aligns with local IMF (interplanetary magnetic field) direction. Thus, the orientation of the IMF in and near the ionosphere controls where on the nightside the tail structure will occur. The structure size and density is found to agree well with that measured by the PVO spacecraft. Further, comparisons with ion energy and velocity distributions also agree well with the summary conclusions from a variety of PVO papers and with some nightside observations by Venus Express. The agreement between the data and simulations lends confidence that the simulation results have merit. [ABSTRACT FROM AUTHOR]

Type Ia supernovae (SNe Ia) are thought to be thermonuclear explosion of white dwarfs (WDs). Their progenitors are not well understood. One popular scenario is the double-degenerate (DD) scenario, which attributes SNe Ia to WD–WD binary mergers. The fates of the WD mergers depend on the rate of 12C + 12C reaction. Recently, the 12C + 12C cross-sections have been measured and the analysis of the data using the Trojan Horse Method suggested that the astrophysical reaction rate is larger than conventional rates at astrophysical temperatures due to possible resonances. The resonance contribution results in a decrease of the carbon burning ignition temperature. Therefore, accretion-induced collapse occurs more easily and increases the birth rate of Galactic neutron stars with the contribution of the DD scenario to the SNe Ia rate becoming even smaller. [ABSTRACT FROM AUTHOR]

Within the framework of the modified potential cluster model, the possibility of describing the available experimental data on the astrophysical S-factor for the p14N capture reaction to the first excited state of the 15O nucleus at 5.18 MeV for proton energies up to 1 MeV is considered. Under the assumption that this excited state is a D wave, we have successfully described the experimental data for the astrophysical S-factor. [ABSTRACT FROM AUTHOR]

Since the first discovery of Jovian Synchrotron Radiation (JSR) from Jovian radiation belt in late 1950s, origin of its time variations has been one of the main subjects of the Jovian radiation belt study. JSR is reported to be strongly correlated with solar wind ram pressure with a possible time lag, which remains an unsolved issue. In our study, the influence of dawn‐to‐dusk electric field modulated with solar wind ram pressure on JSR variations is investigated. Alongside the original diffusion coefficient (DLL(UV)), a new diffusion coefficient (DLL(Elec)) which is dependent on solar wind conditions is applied to a one‐dimensional lossy radial diffusion model, and we reproduce long‐term variations of JSR between 1971 and early 2018. For the specific choice of DLL(UV) = 3.0 × 10−10L3[s−1], the correlation coefficient is found to be 0.6 between the simulated JSR and the ground observation data prior to 2005, and the intermittent observation after 2005 supports our simulation as well. We suggest that while DLL(UV) is the primary mode of diffusion that determines the steady profile of electron population and JSR, DLL(Elec) serves as a secondary mode, which controls long‐term variations of JSR. Key Points: Radial diffusion coefficient derived from dawn‐to‐dusk electric field fluctuations controlled by solar wind conditions is introducedThe coefficient is comparable to dynamo electric field influence on Jupiter's upper atmosphere at the outer part of the radiation beltOur radial diffusion model provides the best reproduction of Jovian synchrotron radiation observed in the past [ABSTRACT FROM AUTHOR]

Recent analysis of an event observed by the Van Allen Probes in the source region outside the plasmapause has shown that fast magnetosonic waves (also referred to as equatorial noise) propagate preferentially in the azimuthal direction, implying that wave amplification should occur during azimuthal propagation. To demonstrate this, we carry out 2‐D particle‐in‐cell simulations of the fast magnetosonic mode at the dipole magnetic equator with the simulation box size, the magnetic field inhomogeneity, and the plasma parameters chosen from the same event recently analyzed. The self‐consistently evolving electric and magnetic field fluctuations are characterized by spectral peaks at harmonics of the local proton cyclotron frequency. The azimuthal component of the electric field fluctuations is larger than the radial component, indicating wave propagation mainly along the azimuthal direction. Because the simulation box is within the source region, this also implies wave amplification mainly during azimuthal propagation. The excellent agreement between the wave polarization properties of the present simulations and the recently reported observations is clear evidence that the main wave amplification occurs during azimuthal propagation in the source region. Key Points: A first‐principles description of the fast magnetosonic mode propagating at the dipole magnetic equator is providedA direct comparison between the simulated and observed wave polarization properties is madeWave amplification occurs dominantly during azimuthal propagation in the source region [ABSTRACT FROM AUTHOR]

The coupling of equatorial and low‐latitude ionosphere has been an active area of research for many years. At low latitude, the occurrences of E and valley region irregularities during postsunset hours are obviously different from those around the magnetic equator. In this work, we statistically investigated the occurrences of postsunset ionospheric E, valley, and F region irregularities, the postsunset rise of F layer, and their correlations by using the Sanya (18.4°N, 109.6°E, dip latitude 12.8°N) very high frequency radar and ionosonde observations during equinoctial months of 2012–2016. A statistically significant correlation between the presence of valley region irregularities and that of equatorial spread F (ESF) was found over Sanya. For the days without ESF, valley region irregularity was rarely observed. The Doppler velocities of valley region irregularities were mainly upward which resemble those of simultaneous ESF irregularities. On the other hand, an occurrence peak of E region irregularities was detected around sunset. After sunset, E region irregularity echo was frequently disrupted. The disruption can appear on both ESF and non‐ESF days, when the amplitudes of F layer postsunset rise were significantly different. The effects of polarization electric field associated with ESF and of equatorial ionospheric background condition on the E and valley region irregularities over Sanya are discussed. Key Points: Occurrences of low‐latitude E, valley, and F region irregularities are statistically investigated with a large data setClose link between low‐latitude E, valley region irregularities, and ESF after sunsetMappings of electric fields from equatorial to low‐latitude ionosphere modify the evolution of E and valley region irregularities over Sanya [ABSTRACT FROM AUTHOR]

Without an upstream monitor at Mars to provide a contemporaneous measurement of solar wind conditions, it is useful to have techniques of inferring the upstream solar wind conditions using downstream data. We develop a method to estimate the upstream interplanetary magnetic field (IMF) clock angle, defined as the orientation of the IMF vector in the plane perpendicular to the solar wind velocity, at Mars using magnetometer data from the Mars Atmosphere and Volatile Evolution (MAVEN) mission. The technique fits MAVEN magnetometer data from within the Martian magnetosheath to a model of the draped magnetic field direction in a coordinate system aligned with the motional electric field. The results provide a proxy for the clock angle that agrees with upstream measurements and reproduces the observed distribution of clock angles. Even if upstream observations are available for a given orbit, the proxy provides an estimate of the clock angle at the time when the spacecraft is in the magnetosheath, which may correct for inherent temporal variability, because the solar wind varies on timescales shorter than the 4.5‐hr MAVEN orbit. The clock angle proxy can be applied for any orientation of the MAVEN orbit, even when MAVEN does not traverse into the upstream solar wind. Key Points: A proxy for the upstream IMF clock angle is derived from Martian magnetosheath magnetic fieldsThe distribution of inferred clock angles reproduces the measured distributionThe uncertainty of the proxy reflects IMF fluctuations with time [ABSTRACT FROM AUTHOR]

Based on careful analysis of 16 years of hourly variations of the strength of equatorial electrojet (EEJ) derived using the ground‐based magnetometers over the Indian sector, the role played by disturbance dynamo electric field disturbances on equatorial ionosphere is identified. It is found that most prominent cases of the effects of disturbance dynamo occurred during equinoctial months in high solar activity period. In three extreme cases, the reduction in EEJ strength from quiet time average values of the respective month is more than twice the standard deviations for at least 3 hr. Based on the methodology described in Pandey et al. (2017, https://doi.org/10.1016/j.jastp.2017.03.012), it is found that the westward electric field perturbations are as large as 0.7 ± 0.2 to 1.2 ± 0.3 mV/m around noon hours for these three cases. In contrast to the expectation of disturbance dynamo electric field perturbations over equatorial latitudes from the earlier models, these values during daytime are significantly larger and even caused reversals of EEJ on two occasions. A possible additional source to augment the reduction in the electric field is indicated. Key Points: Large reduction in equatorial electrojet strength during daytime associated with disturbance dynamoCorresponding changes in electric field on some occasions are much larger than those reported earlierAdditional influence of semidiurnal tides is proposed to account for the large reduction [ABSTRACT FROM AUTHOR]

We simulate equatorial plasmaspheric electron densities using a physics‐based model (Cold PLasma, CPL; used in the ring current‐atmosphere interactions model) of the source and loss processes of refilling and erosion driven by empirical inputs. The performance of CPL is evaluated against in situ measurements by the Van Allen Probes (Radiation Belt Storm Probes) for two events: the 31 May to 5 June and 15 to 20 January 2013 geomagnetic storms observed in the premidnight and postmidnight magnetic local time (MLT) sectors, respectively. Overall, CPL reproduces the radial extent of the plasmasphere to within a mean absolute difference of |ΔLavg|=0.5±0.1 L. The model electric field responsible for E × B convection and the parameterization of geomagnetic conditions (under the Kp‐index and solar wind properties) implemented by CPL did not account for localized enhancements in the duskward electric field during increased activity. Rather, it was found to be largely dependent on the measure of the quiet time background. This property indicates that the agreement between these simulations and observations does not account for the complete set of physical processes during extreme (strong or weak) geomagnetic conditions impacting the plasmasphere. Nevertheless, at the presented resolution of the model CPL does provide good agreement in reproducing Radiation Belt Storm Probes observations of plasmaspheric density and plasmapause location. Key Points: Simulations of premidnight and postmidnight plasmapause encounters achieve agreement with RBSP observations to within 0.5 L absolute errorSolar wind parameterization of convection produces at least 0.5 L deeper erosion at onset of activity than the Kp‐index parameterizationSolar wind parameterization of convection produces at least 0.5 L larger plasmasphere during recovery than the Kp‐index parameterization [ABSTRACT FROM AUTHOR]

Abstract The nature of dark matter is one of the most pressing questions in physics. Yet all our present knowledge of the dark sector to date comes from its gravitational interactions with astrophysical systems. Moreover, astronomical results still have immense potential to constrain the particle properties of dark matter in the near future. We introduce a simple 2D parameter space which classifies models in terms of a particle physics interaction strength and a characteristic astrophysical scale on which new physics appears, in order to facilitate communication between the fields of particle physics and astronomy. We survey the known astrophysical anomalies that are suggestive of non-trivial dark matter particle physics, and present a theoretical and observational program for future astrophysical measurements that will shed light on the nature of dark matter. [ABSTRACT FROM AUTHOR]

Abstract Recent results from the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) show an anomalous spectral feature at redshifts z ∼ 15 – 20 in its 21-cm absorption signal. This deviation from cosmological predictions can be understood as a consequence of physics that either lower the hydrogen spin temperature or increases the radiation temperature through the injection of soft photons in the bath. In the latter case, standard model neutrino decays ν i → ν j γ induced by effective magnetic and electric transition moments (μ eff) are precluded by the tight astrophysical constraints on μ eff. We show that if mirror neutrinos are present in the bath at early times, an analogous mechanism in the mirror sector can lead to a population of mirror photons that are then “processed” into visible photons through resonant conversion, thus accounting for the EDGES signal. We point out that the mechanism can work for mirror neutrinos which are either heavier than or degenerate with the standard model (SM) neutrinos, a scenario naturally realized in mirror twin Higgs models. [ABSTRACT FROM AUTHOR]

Plasma convection in the coupled inner magnetosphere‐ionosphere is influenced by different factors such as neutral winds, penetration electric fields, and polarization electric fields. Several crucial insights about the dynamics in the region have been derived by interpreting observations in conjunction with numerical simulations, and recent expansion in ground‐ and space‐based measurements in the region along with improvements in theoretical modeling has fueled renewed interest in the subject. In this paper we present a comprehensive review of the literature with an emphasis on studies since 2012 relevant to the National Science Foundation Geospace Environment Modeling program. We cover four specific areas: (1) the subauroral polarization stream, (2) penetration electric fields, (3) the disturbance dynamo, and (4) quiet time subauroral convection. We summarize new observations and resulting insights relevant to each of these topics and discuss various outstanding issues and unanswered questions. Key Points: Subauroral convection is driven by complex interactions involving neutral winds, penetration electric fields, and polarization electric fieldsKey results on subauroral convection are summarized, with an emphasis on studies related to the SIMIC focus group of the NSF GEM programModeling quiet geomagnetic conditions in conjunction with observations is necessary to understand the physics behind subauroral convection [ABSTRACT FROM AUTHOR]

We investigate THEMIS satellite measurements made in a tail‐aligned constellation during a time interval on 1–2 January 2009, which has previously been attributed to an interval of an interplanetary magnetic field By‐driven magnetotail twisting. We find evidence for that the orientation of the convection electric field in the tail is twist‐mode dependent. For earthward flow and a negative twist (induced tail By< 0), the electric field is found to have northward Ez and tailward Ex components. During a positive twist (induced tail By> 0), the directions of Ez and Ex are reversed. The Ey component shows the expected dawn‐to‐dusk direction for earthward flow. The electric field components preserve their orientation across the neutral sheet, and a quasi‐collinear field is observed irrespective to the tail distance. The electric field associated with the tailward flow has an opposite direction compared to the earthward flow for the negative twist. For the positive twist, the results are less clear. The corresponding plasma convection and thus the magnetic flux transport have an opposite dawn‐dusk direction above and below the neutral sheet. The directions depend on the tail twist mode. The hemispherically asymmetric earthward plasma flows are suggested to be a manifestation of an asymmetric Dungey cycle in a twisted magnetotail. The role of tailward flows deserve further investigation. Key Points: Orientation of the convection electric field depends on the tail twist modeThe electric field preserves its direction across the neutral sheetMagnetospheric convection exhibits dawn‐dusk asymmetry with respect to the neutral sheet [ABSTRACT FROM AUTHOR]

Regions of persistent westward directed flows are often observed equatorward of the auroral oval in the dusk‐midnight sector. In general, the midnight narrow flows are termed as subauroral ion drifts and the duskside broader flows are termed subauroral polarization streams (SAPS). SAPS/subauroral ion drift electric fields play an important role in controlling the dynamics of the midlatitude ionosphere. In this paper we analyze longitudinally extended observations of SAPS measured by midlatitude Super Dual Auroral Radar Network (SuperDARN) radars under varied geomagnetic conditions. We find that SAPS speeds exhibit a strong dependence on geomagnetic activity, with flows exceeding 1,500 m/s during geomagnetic storms and dropping to 100 m/s during periods of geomagnetic quiet. Moreover, SAPS flows turn increasingly poleward when moving from the midnight sector toward dusk and this effect is more pronounced during disturbed geomagnetic conditions. The variations in SAPS speeds with magnetic local time (MLT) are also found to be strongly dependent on geomagnetic conditions. Specifically, SAPS speeds increase quasilinearly with MLT during disturbed geomagnetic conditions, whereas during relatively quiet geomagnetic conditions there is no discernible trend. This behavior suggests the possibility of different mechanisms influencing SAPS during geomagnetically quiet conditions. Average cross‐SAPS potentials increase with geomagnetic activity and typically vary between 15 and 45 kV. Finally, a new empirical model of SAPS potentials has been developed parameterized by Asy‐H index, MLT, and magnetic latitude. Key Points: We present a new empirical model of SAPS potentials parameterized by Asy‐H, MLT, and magnetic latitudeSAPS speeds exhibit considerable differences during storm time and non‐storm time conditionsSAPS speeds increase quasilinearly with MLT during disturbed geomagnetic conditions; no trend is seen for quiet times [ABSTRACT FROM AUTHOR]

A certain type of impulsive signal in the Solar Terrestrial Relations Observatory (STEREO) electric field data has been identified as impacts of small dust, nanodust, entrained by the solar wind and accelerated to solar wind speeds, so that their speed compensates, in the emitted cloud, for their small size. It is argued here that these signals, called single hit signals, are not due to nanodust nor to dust impacts at all, as they have some characteristics which are not compatible with random hits by interplanetary and interstellar dust. The major observational data for the flux of nanodust are then in question. Another cause of these signals, however, is not given, and their cause is unknown. Key Points: STEREO single hits are not dust impactsObservational evidence for accelerated nanodust is inadequateSTEREO single hit cause is unknown [ABSTRACT FROM AUTHOR]

According to present-day ideas, nonlinear saturation of the astrophysical dynamo and, in particular, the solar dynamo, are based on the consideration of the magnetic helicity balance, to which the helicities of the large-scale magnetic field and small-scale field related to it contributed. We show that, in a mirrorasymmetric medium, the small-scale magnetic field generated by the small-scale dynamo also has a nonzero magnetic helicity, which also should be taken into account in the magnetic helicity balance. [ABSTRACT FROM AUTHOR]

We develop a theoretic model to study the linear stability behaviour of pulsational (gravito-electrostatic) mode in a self-gravitating, magnetized, collisional, turbulent and unbounded dust molecular cloud (DMC). The analytic model consists of lighter electrons and ions; and massive charged dust grains with partial ionization over the geometrically infinite extension. The semi-empirically obtained Larson logatropic equation of state, correlating all the thermo-turbo-magnetic pressures concurrently, is included afresh to model the constituent fluid turbulence pressures arising because of multiple randomized aperiodic flow scales of space and time. A linear normal mode analysis over the slightly perturbed composite cloud, relative to the defined homogeneous hydrostatic equilibrium, results in a unique mathematical construct of generalized polynomial (octic) dispersion relation with different coefficients sensitively dependent upon the diversified equilibrium cloud parameters. The main features of the modified pulsational mode dynamics are numerically explored over a commodious window of parametric values. It is shown and established that the grain mass introduces a dispersive stabilizing effect to the mode (with enhancement in phase speed), and vice-versa. A spatiotemporal illustrative tapestry is also portrayed for further confirmation of the dispersive mode with sporadic properties. The tentative application of our findings in different space and astrophysical circumstances is briefly outlined. [ABSTRACT FROM AUTHOR]

Upcoming observations of the 21-cm signal from the epoch of reionization will soon provide the first direct detection of this era. This signal is influenced by many astrophysical effects, including long-range X-ray heating of the intergalactic gas. During the preceding cosmic dawn era, the impact of this heating on the 21-cm signal is particularly prominent, especially before spin temperature saturation. We present the largest volume (349 Mpc comoving = 244 h−1Mpc) full numerical radiative transfer simulations to date of this epoch which include the effects of helium and multifrequency heating, both with and without X-ray sources. We show that X-ray sources contribute significantly to early heating of the neutral intergalactic medium and, hence, to the corresponding 21-cm signal. The inclusion of hard, energetic radiation yields an earlier, extended transition from absorption to emission compared to the stellar-only case. The presence of X-ray sources decreases the absolute value of the mean 21-cm differential brightness temperature. These hard sources also significantly increase the 21-cm fluctuations compared to the common assumption of temperature saturation. The 21-cm differential brightness temperature power spectrum is initially boosted on large scales, before decreasing on all scales. Compared to the case of the cold, unheated intergalactic medium, the signal has lower rms fluctuations and increased non-Gaussianity, as measured by the skewness and kurtosis of the 21-cm probability distribution functions. Images of the 21-cm signal with resolution around 11 arcmin still show fluctuations well above the expected noise for deep integrations with the SKA1-Low, indicating that direct imaging of the X-ray heating epoch could be feasible. [ABSTRACT FROM AUTHOR]

We use the observed properties of fast radio bursts (FRBs) and a number of general physical considerations to provide a broad-brush model for the physical properties of FRB sources and the radiation mechanism. We show that the magnetic field in the source region should be at least 1014 G. This strong field is required to ensure that the electrons have sufficiently high ground state Landau energy so that particle collisions, instabilities and strong electromagnetic fields associated with the FRB radiation do not perturb electrons' motion in the direction transverse to the magnetic field and destroy their coherent motion; coherence is required by the high observed brightness temperature of FRB radiation. The electric field in the source region required to sustain particle motion for a wave period is estimated to be of the order of 1011 esu. These requirements suggest that FRBs are produced near the surface of magnetars perhaps via forced reconnection of magnetic fields to produce episodic, repeated, outbursts. The beaming-corrected energy release in these bursts is estimated to be about 1036 erg, whereas the total energy in the magnetic field is at least ~1045 erg.We provide a number of predictions for this model which can be tested by future observations. One of which is that short duration FRB-like bursts should exist at much higher frequencies, possibly up to optical. [ABSTRACT FROM AUTHOR]

The era of interferometric observations leads to the need of a more and more precise description of physical structures and dynamics of star-forming regions, from pre-stellar cores to protoplanetary discs. The molecular emission can be traced in multiple physical components such as infalling envelopes, outflows and protoplanetary discs. To compare with the observations, a precise and complex radiative transfer modelling of these regions is needed. We present GASS (Generator of Astrophysical Sources Structure), a code that allows us to generate the three-dimensional (3D) physical structure model of astrophysical sources. From the GASS graphical interface, the user easily creates different components such as spherical envelopes, outflows and discs. The physical properties of these components are modelled thanks to dedicated graphical interfaces that display various figures in order to help the user and facilitate the modelling task. For each component, the code randomly generates points in a 3D grid with a sample probability weighted by the molecular density. The created models can be used as the physical structure input for 3D radiative transfer codes to predict the molecular line or continuum emission. An analysis of the output hyper-spectral cube given by such radiative transfer code can be made directly in GASS using the various post-treatment options implemented, such as calculation of moments or convolution with a beam. This makes GASS well suited to model and analyse both interferometric and single-dish data. This paper is focused on the results given by the association of GASS and LIME, a 3D radiative transfer code, and we show that the complex geometry observed in star-forming regions can be adequately handled by GASS+LIME. [ABSTRACT FROM AUTHOR]

The electrostatics of electrohydrodynamic atomization (EHDA) process in a shuttle-chamber for polymeric particle fabrication was investigated. The electrical potential field between the spray nozzle and the ground plate inside the chamber was measured three-dimensionally and demonstrated that the electrical field strength increased with decreasing nozzle-plate distance and made more effect on liquid spraying. Four liquids, two inorganic liquids (water, KCl) and two organic liquids (PLGA + DCM ( w / v = 7%), PLGA + acetonitrile ( w / v = 8%)) were tested and the organic liquids were sprayed to fabricate micro-particles. For spraying inorganic liquids the current scaling was I ~ Q 1/2 but for spraying organic liquids the current scaling was I ~ Q 1/4 . The accuracy of current scaling depended on the values of δ μ δ 1/3 , which was independent of the nozzle-plate distances (electric field strength). In addition, the spray current increased with decreasing nozzle-plate distance (or increasing liquid flow rate or liquid conductivity). As a result of spraying polymer solution with volatile organic solvent, particles with size of 0.61– 36.10 μm were fabricated. Particle size decreased with decreasing nozzle-plate distance as well as increasing conductivity of polymer solution or decreasing the liquid flow rate. For all cases of particle fabrication, Rayleigh limit was never reached and no coulomb fission occurred in the experiments. [ABSTRACT FROM AUTHOR]

Spectra of sunspots in the regions of the Li I 6708 Å line and certain Fe I and Ca I lines are presented. The observations wee carried out in August 2014 using a CCD array mounted at the BST-2 telescope of the Crimean Astrophysical Observatory. Sunspot models based on the observed Fe I and Ca I line profiles have been computed, and used together with the observed Li I 6708 Å profiles to determine the lithium abundances. The mean lithium abundance for the sunspots observed on August 26, 2014 is log A(Li) = 1.2 (on a scale for which log A(H) = 12.0). Sunspot spectra obtained on October 8, 2011 were also analyzed, yielding log A(Li) = 1.02. [ABSTRACT FROM AUTHOR]

This informal article discusses the central role of magnetic and kinetic helicity in relation to the evolution of magnetic fields in geophysical and astrophysical contexts. It is argued that the very existence of magnetic fields of the intensity and scale observed is attributable in large part to the chirality of the background turbulence or randomwave field of flow, the simplest measure of this chirality being non-vanishing helicity. Such flows are responsible for the generation of large-scale magnetic fields which themselves exhibit magnetic helicity. In the geophysical context, the turbulence has a 'magnetostrophic' character in which the force balance is primarily that between buoyancy forces, Coriolis forces and Lorentz forces associated with the dynamo-generated magnetic field; the dominant nonlinearity here arises from the convective transport of buoyant elements erupting from the 'mushy zone' at the inner core boundary. At the opposite extreme, in a highly conducting low-density plasma, the near-invariance of magnetic field topology (and of associated helicity) presents the challenging problem of 'magnetic relaxation under topological constraints', of central importance both in astrophysical contexts and in controlled-fusion plasma dynamics. These problems are reviewed and open issues, particularly concerning saturation mechanisms, are reconsidered. [ABSTRACT FROM AUTHOR]

We explore Noether symmetries of the Friedmann-Robertson-Walker universe model in modified Gauss-Bonnet gravity for both vacuum and nonvacuum (dust fluid) cases. We evaluate symmetry generators and the corresponding conserved quantities by using separation of variables and a power-law form. We construct exact f( G) models and study accelerating expansion of the universe in terms of a scale factor, deceleration, and the EoS parameters. We also check the validity of energy conditions through the weak energy conditions for our constructed model. The state finder parameters indicate the resemblance of our constructed models to the ΛCDM model. We conclude that our results are consistent with the recent astrophysical observations. [ABSTRACT FROM AUTHOR]

A turbulent, laser-generated plasma can amplify magnetic fields to cosmic scales. [ABSTRACT FROM AUTHOR]

The study of the 2H(d,p)3H reaction is very important for the nucleosynthesis in both the standard Big Bang and stellar evolution, as well as for the future fusion reactor's planning of energy production. The 2H(d,p)3H bare nucleus astrophysicai S(E) factor has been measured indirectly at energies from about 400 keV down to several keV by means of the Trojan-horse method applied to the quasifree process 2H(Li,pt)4He induced at a lithium beam energy of 9.5 MeV, which is closer to the zero-quasifree-energy point. An accurate analysis leads to the determination of the Sbare(0) = 56.7 ± 2.0 keV b and of the corresponding electron screening potential Ue = 13.2 ± 4 .3 eV. In addition, this work gives an updated test for the Trojan-horse nucleus invariance by comparing with previous indirect investigations using the 3He = (d + p) breakup. [ABSTRACT FROM AUTHOR]

In situ spacecraft data on the solar wind show events identified as magnetic reconnection with wide outflows and extended "X lines," 10³-104 times ion scales. To understand the role of turbulence at these scales, we make a case study of an inertial-range reconnection event in a magnetohydrodynamic simulation. We observe stochastic wandering of field lines in space, breakdown of standard magnetic flux freezing due to Richardson dispersion, and a broadened reconnection zone containing many current sheets. The coarse-grain magnetic geometry is like large-scale reconnection in the solar wind, however, with a hyperbolic flux tube or apparent X line extending over integral length scales. [ABSTRACT FROM AUTHOR]

The Galactic 1.809-MeV γ-ray signature from the β decay of 26gAl is a dominant target of γ-ray astronomy, of which a significant component is understood to originate from massive stars. The 26gAl(p,γ)27Si reaction is a major destruction pathway for 26gAl at stellar temperatures, but the reaction rate is poorly constrained due to uncertainties in the strengths of low-lying resonances in 27Si. The 26gAl(d,p)27Al reaction has been employed in inverse kinematics to determine the spectroscopic factors, and hence resonance strengths, of proton resonances in 27Si via mirror symmetry. The strength of the 127-keV resonance is found to be a factor of 4 higher than the previously adopted upper limit, and the upper limit for the 68-keV resonance has been reduced by an order of magnitude, considerably constraining the 26gAl destruction rate at stellar temperatures. [ABSTRACT FROM AUTHOR]

The β-decay half-lives of 110 neutron-rich isotopes of the elements from Rb37 to Sn50 were measured at the Radioactive Isotope Beam Factory. The 40 new half-lives follow robust systematics and highlight the persistence of shell effects. The new data have direct implications for r-process calculations and reinforce the notion that the second (A≈130) and the rare-earth-element (A≈160) abundance peaks may result from the freeze-out of an (n,γ)⇄(γ,n) equilibrium. In such an equilibrium, the new half-lives are important factors determining the abundance of rare-earth elements, and allow for a more reliable discussion of the r process universality. It is anticipated that universality may not extend to the elements Sn, Sb, I, and Cs, making the detection of these elements in metal-poor stars of the utmost importance to determine the exact conditions of individual r-process events. [ABSTRACT FROM AUTHOR]

A laboratory simulation experiment to study the spontaneous breakup of distilled and polluted water drops suspended in horizontal electric field of 0, 100, 300, 500 kV m −1 has been performed in a small vertical wind tunnel. Water drops are formed from distilled water and from 100 ppm solution of ammonium sulfate and potassium nitrate. Results show that the life time of the both distilled and polluted water drops decreases with the increase in electric field. The water drops formed from both distilled and polluted water become more oblate as the electric field is increased. The results have been interpreted in terms of enhanced instability of water drops due to the changes in surface tension, viscosity, conductivity and hydro-dynamics of the water drop. Significance of the results is discussed in view of the possible modification of the drop size distribution and consequent growth of raindrops and lightning activity due to the combined effect of pollutants and electrical forces in clouds formed over big cities. [ABSTRACT FROM AUTHOR]

The hydromagnetic α²-dynamo process for a localized uniform field in a three-dimensional space is discussed. The phenomena of the field growth along the initial field and in the ortogonal plane with a super exponential growth rate is demonstrated. The cell-structure of the magnetic field is shown and the size of these cells is estimated. For small and large time, the expansion of the initial field is studied. [ABSTRACT FROM AUTHOR]

The article discusses the study conducted which analyses the Gamma-Teller transition strengths from 56Fe extracted from the 56Fe(t, ³He) reaction for estimating weak reaction rates of importance for a wide variety of astrophysical applications. Topics discussed include Differential cross sections and excitation-energy spectra, calculations using quasi-particle random-phase approximation (QRPA), and nuclear excitations in which spin and isospin are transferred.

The oblique collision of nonlinear quantum dust-acoustic (NQDA) solitary waves in a three-dimensional (3D) magnetized dense dusty plasma is investigated. Furthermore, two coupled Kortwege-de Vries equations for describing our model and the analytical phase shifts after the oblique collision of two NQDA solitary waves are derived using the extended Poincaré-Lighthill-Kuo (PLK) method. The modification in the phase shift and the trajectory of the NQDA solitary waves structures due to the inclusion of oblique collision and external magnetic field are discussed numerically. The numerical results are applied to high density astrophysical situations such as in superdense white dwarfs. [ABSTRACT FROM AUTHOR]

We study substorms from two perspectives, i.e., magnetosphere-ionosphere coupling across the auroral oval at dusk and at midnight magnetic local times. By this approach we monitor the activations/expansions of basic elements of the substorm current system (Bostrøm type I centered at midnight and Bostrøm type II maximizing at dawn and dusk) during the evolution of the substorm activity. Emphasis is placed on the R1 and R2 types of field-aligned current (FAC) coupling across the Harang reversal at dusk. We distinguish between two distinct activity levels in the substorm expansion phase, i.e., an initial transient phase and a persistent phase. These activities/phases are discussed in relation to polar cap convection which is continuously monitored by the polar cap north (PCN) index. The substorm activity we selected occurred during a long interval of continuously strong solar wind forcing at the interplanetary coronal mass ejection passage on 18 August 2003. The advantage of our scientific approach lies in the combination of (i) continuous ground observations of the ionospheric signatures within wide latitude ranges across the auroral oval at dusk and midnight by meridian chain magnetometer data, (ii) "snapshot" satellite (DMSP F13) observations of FAC/precipitation/ion drift profiles, and (iii) observations of current disruption/near-Earth magnetic field dipolarizations at geostationary altitude. Under the prevailing fortunate circumstances we are able to discriminate between the roles of the dayside and nightside sources of polar cap convection. For the nightside source we distinguish between the roles of inductive and potential electric fields in the two substages of the substorm expansion phase. According to our estimates the observed dipolarization rate (δBz/δt) and the inferred large spatial scales (in radial and azimuthal dimensions) of the dipolarization process in these strong substorm expansions may lead to 50-100 kV enhancements of the cross-polar-cap potential due to inductive electric field coupling. [ABSTRACT FROM AUTHOR]

Jet collimation in astrophysical plasmas and in the laboratory has recently received much attention. When the magnetohydrodynamics (MHD) model is used to represent both systems, scale invariance allows for the simple extension of the parameters encountered in laboratory experiments to much larger systems, like astrophysical outflows. However, the validation of such a model requires a precise comparison of numerical simulations with experimental data. Using radial foils as an experimental setup to generate strongly collimated plasma jets, we show that the Hall MHD model included in the PERSEUS code does well to capture the plasma dynamics of collimated jets, even with restrictive conditions such as a constant ionization number and the neglect of normally important transport processes. Very importantly, we show that jet collimation is not only the result of magnetic forces, but also converging radial flows. [ABSTRACT FROM AUTHOR]

The ground electronic, vibrational and rotational state of the OH molecule is currently of interest as it can be manipulated by electric and magnetic fields for experimental studies in ultracold chemistry and quantum degeneracy. Based on our recent exact solution of the corresponding effective Stark-Zeeman Hamiltonian, we present an analytical study of the crossings and avoided crossings in the spectrum. These features are relevant to non-adiabatic transitions, conical intersections and Berry phases. Specifically, for an avoided crossing employed in the evaporative cooling of OH, we compare our exact results to those derived earlier from perturbation theory. [ABSTRACT FROM AUTHOR]

We have carried out experimental and theoretical studies of three body electron attachment (TBEA) to O 2 in N 2/O 2 mixtures. We have applied three different experimental methods to determine the apparent rate constant k for TBEA to O 2 for reduced electric fields E/ n from 0.5 Td up to 4.5 Td and O 2 concentrations from 0.02% up to 3%. From the apparent rate constant k we have evaluated three body rate constant for electron attachment to O 2 in pure O 2$$\left( {k_{O_2 } } \right)$$ and in pure N 2$$\left( {k_{N_2 } } \right)$$ . The comparison of present data with former studies shows that the former values of $$k_{N_2 }$$ overestimated the efficiency of this reaction, while in case of $$k_{O_2 }$$ we have found agreement with earlier studies. We have solved numerically the Boltzmann equation of the electrons and calculated the values of k, $$k_{N_2 }$$ and $$k_{O_2 }$$ using well established cross sections. Using the known collision cross section set for TBEA to O 2, very good agreement between calculated and measured results for $$k_{O_2 }$$ was found, while in the case of k and $$k_{N_2 }$$ we had to introduce a scaling function, which describes the decrease of the efficiency of TBEA to O 2 in presence of N 2 and the dependence of the scaling function on E/ n was determined. [ABSTRACT FROM AUTHOR]