The strongly regular (45,12,3,3) graphs

Using two backtrack algorithms based on dierent techniques, designed and implemented independently, we were able to determine up to isomorphism all strongly regular graphs with parameters v = 45, k = 12, λ = μ = 3. It turns out that there are 78 such graphs, having automorphism groups with sizes ranging from 1 to 51840

Are periodic solar wind number density structures formed in the solar corona?

[1] We present an analysis of the alpha to proton solar wind abundance ratio (AHe) during a period characterized by significant large size scale density fluctuations, focusing on an event in which the proton and alpha enhancements are anti-correlated. In a recent study using 11 years (1995–2005) of solar wind observations from the Wind spacecraft, N. M. Viall et al. [2008] showed that periodic proton density structures occurred at particular radial length-scales more often than others. The source of these periodic density structures is a significant and outstanding question. Are they generated in the interplanetary medium, or are they a relic of coronal activity as the solar wind was formed? We use AHe to answer this question, as solar wind elemental abundance ratios are not expected to change during transit. For this event, the anti-phase nature of the AHe variations strongly suggests that periodic solar wind density structures originate in the solar corona

ULF waves in the solar wind as direct drivers of magnetospheric pulsations

[1] Global magnetospheric ULF pulsations with frequencies in the Pc 5 range (f = 1.7–6.7 mHz) and below have been observed for decades in space and on the Earth. Recent work has shown that in some cases these pulsations appear at discrete frequencies. Global cavity and waveguide modes have been offered as possible sources of such waves. In these models the magnetosphere is presumed to resonate globally at frequencies determined solely by its internal properties such as size, shape, field topology, mass density distribution, etc. We show in this work that upstream solar wind number density and dynamic pressure variations precede and drive compressional magnetic field variations at geosynchronous orbit. Furthermore, spectral analysis shows that wave power spectra in both the solar wind and magnetosphere contain peaks at the same discrete frequencies. Therefore, in contrast to the cavity mode hypothesis, we suggest that discrete ULF pulsations observed within the magnetosphere are at least sometimes directly driven by density oscillations present in the ambient solar wind. Finally, we comment on possible sources for such pulsations observed in the solar wind

Static magnetic field models consistent with nearly isotropic plasma pressure

Using the empirical magnetospheric magnetic field models of Tsyganenko and Usmanov (TU), we have determined the self-consistent plasma pressure gradients and anisotropies along the midnight meridian in the near-Earth magnetosphere. By “inverting” the magnetic field, we determine what distributions of an anisotropic plasma, confined within the specified magnetic field configuration, are consistent with the magnetohydrostatic equilibrium condition, J × B = ∇ · P. The TU model, parameterized for different levels of geomagnetic activity by the Kp index, provided the magnetic field values from which J × B was numerically evaluated. A best fit solution was found that minimized the average difference between J × B and ∇ · P along an entire flux tube. Unlike previous semi-empirical models, the TU models contain magnetic stresses that can be balanced by a nearly isotropic plasma pressure with a reasonable radial gradient at the equator

Magnetospheric plasma pressures in the midnight meridian: Observations from 2.5 to 35 RE

Plasma pressure data from the ISEE 2 fast plasma experiment (FPE) were statistically analyzed to determine the plasma sheet pressure versus distance in the midnight local time sector of the near-earth (12–35 RE) magnetotail plasma sheet. The observed plasma pressure, assumed isotropic, was mapped along model magnetic field flux tubes (obtained from the Tsyganenko and Usmanov [1982] model) to the magnetic equator, sorted according to magnetic activity, and binned according to the mapped equatorial location. In regions (L ≳ 12 RE) where the bulk of the plasma pressure was contributed by particles in the energy range of the FPE (70 eV to 40 keV for ions), the statistically determined peak plasma pressures vary with distance similarly to previously determined lobe magnetic pressures (i.e., in a time-averaged sense, pressure balance normal to the magnetotail magnetic equator in the midnight meridian is maintained between lobe magnetic and plasma sheet plasma pressures). Additional plasma pressure data obtained in the inner magnetosphere (2.5 \u3c L \u3c 7) by the Explorer 45, ATS 5, and AMPTE CCE spacecraft supplement the ISEE 2 data. Estimates of plasma pressures in the “transition” region (7–12 RE), where the magnetic field topology changes rapidly from a dipolar to a tail-like configuration, are compared with the observed pressure profiles. The quiet time “transition” region pressure estimates, obtained previously from inversions of empirical magnetic field models, bridge observations both interior to and exterior to the “transition” region in a reasonable manner. Quiet time observations and estimates are combined to provide profiles of the equatorial plasma pressure along the midnight meridian between 2.5 and 35 RE

A statistical study of the global structure of the ring current

[1] In this paper we derive the average configuration of the ring current as a function of the state of the magnetosphere as indicated by the Dst index. We sort magnetic field data from the Combined Release and Radiation Effects Satellite (CRRES) by spatial location and by the Dst index in order to produce magnetic field maps. From these maps we calculate local current systems by taking the curl of the magnetic field. We find both the westward (outer) and the eastward (inner) components of the ring current. We find that the ring current intensity varies linearly with Dst as expected and that the ring current is asymmetric for all Dst values. The azimuthal peak of the ring current is located in the afternoon sector for quiet conditions and near midnight for disturbed conditions. The ring current also moves closer to the Earth during disturbed conditions. We attempt to recreate the Dst index by integrating the magnetic perturbations caused by the ring current. We find that we need to multiply our computed disturbance by a factor of 1.88 ± 0.27 and add an offset of 3.84 ± 4.33 nT in order to get optimal agreement with Dst. When taking into account a tail current contribution of roughly 25%, this agrees well with our expectation of a factor of 1.3 to 1.5 based on a partially conducting Earth. The offset that we have to add does not agree well with an expected offset of approximately 20 nT based on solar wind pressure

Content moderator coping strategies: associations with psychological distress, secondary trauma and wellbeing

Content moderators (CMs) apply policy set by platforms to protect users from harmful content. It is a stressful job, associated with reduced mental health and wellbeing. In this study, an anonymous survey was used to demonstrate most CMs cope by seeking support from colleagues and this is associated with lower psychological distress and secondary trauma and higher wellbeing whereas increased smoking and alcohol consumption is associated with increased symptomology. Wellbeing services were not related to a reduction in psychological distress or trauma. We argue these results fit within a framework of trauma-informed working and provide evidence for its utility in the trust and safety sector. They also highlight the need for continued research into ‘what works’ to support the resilience of frontline staff

The average magnetic field draping and consistent plasma properties of the Venus magnetotail

A new technique has been developed to determine the average structure of the Venus magnetotail (in the range from −8 Rv to −12 Rv) from the Pioneer Venus magnetometer observations. The spacecraft position with respect to the cross-tail current sheet is determined from an observed relationship between the field-draping angle and the magnitude of the field referenced to its value in the nearby magnetosheath. This allows us statistically to remove the effects of tail flapping and variability of draping for the first time and thus to map the average field configuration in the Venus tail. From this average configuration we calculate the cross-tail current density distribution and J × B forces. Continuity of the tangential electric field is utilized to determine the average variations of the X-directed velocity which is shown to vary from −250 km/s at −8 Rv to −470 km/s at −12 Rv. From the calculated J × B forces, plasma velocity, and MHD momentum equation the approximate plasma acceleration, density, and temperature in the Venus tail are determined. The derived ion density is approximately ∼0.07 p+/cm³ (0.005 O+/cm³) in the lobes and ∼0.9 p+/cm³ (0.06 O+/cm³) in the current sheet, while the derived approximate average plasma temperature for the tail is ∼6×106 K for a hydrogen plasma or ∼9×107 K for an oxygen plasma