Introduction to spherical elementary current systems

Abstract This is a review of the Spherical Elementary Current System or SECS method, and its various applications to studying ionospheric current systems. In this chapter, the discussion is more general, and applications where both ground-based and/or satellite observations are used as the input data are discussed. Application of the SECS method to analyzing electric and magnetic field data provided by the Swarm satellites will be discussed in more detail in the next chapter

Induced currents due to 3D ground conductivity play a major role in the interpretation of geomagnetic variations

Abstract Geomagnetically induced currents (GICs) are directly described by ground electric fields, but estimating them is time-consuming and requires knowledge of the ionospheric currents and the three-dimensional (3D) distribution of the electrical conductivity of the Earth. The time derivative of the horizontal component of the ground magnetic field (dH∕dt) is closely related to the electric field via Faraday‘s law and provides a convenient proxy for the GIC risk. However, forecasting dH∕dt still remains a challenge. We use 25 years of 10 s data from the northern European International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer network to show that part of this problem stems from the fact that, instead of the primary ionospheric currents, the measured dH∕dt is dominated by the signature from the secondary induced telluric currents at nearly all IMAGE stations. The largest effects due to telluric currents occur at coastal sites close to high-conducting ocean water and close to near-surface conductivity anomalies. The secondary magnetic field contribution to the total field is a few tens of percent, in accordance with earlier studies. Our results have been derived using IMAGE data and are thus only valid for the stations involved. However, it is likely that the main principle also applies to other areas. Consequently, it is recommended that the field separation into internal (telluric) and external (ionospheric and magnetospheric) parts is performed whenever feasible (i.e., a dense observation network is available)

Distribution and Occurrence Frequency of dB/dt Spikes During Magnetic Storms 1980–2020

The physical magnetospheric cause for geomagnetically induced currents (GICs) are rapid time-varying magnetic fields (dB/dt), which occur mainly during magnetic substorms and storms. When, where and why exactly such rapid dB/dt may occur is insufficiently understood. We investigated all storms since 1980 and analyzed the negative and positive dB/dt spikes (>|500| nT/min) in the north and east component using a worldwide coverage (SuperMAG). Our analysis confirmed the existence of two dB/dt spikes “hotspots” located in the pre-midnight and in the morning magnetic local time sector, independently of the geographic location of the stations. The associated physical phenomena are probably substorm current wedge onsets and westward traveling surges (WTS) in the evening sector, and wave- or vortex-like current flows in the morning sector known as Omega bands. We observed a spatiotemporal evolution of the negative northern dB/dt spikes. The spikes initially occur in the pre-midnight sector, and then develop in time toward the morning sector. This spatiotemporal sequence is correlated with bursts in the AE index, and can be repeated several times throughout a storm. Finally, we investigated the peak value of Dst and AE during the storm period in comparison with the dB/dt spike occurrence frequency, we did not find any correlation. This result implies that a moderate storm with many spikes can be as (or more) dangerous for ground-based infrastructures than a major storm with fewer dB/dt spikes. Our findings regarding the physical causes and characteristics of dB/dt spikes may help to improve the GIC forecast for the affected regions

Spherical elementary current systems applied to swarm data

Abstract This chapter describes how the Spherical Elementary Current Systems (SECS) are applied to analyze the magnetic and electric field measurements provided by the Swarm spacecraft. The Swarm/SECS method produces two-dimensional (latitude–longitude) maps of the ionospheric horizontal and field-aligned currents around the satellite paths. If also electric field data are available, similar maps of the electric field and conductances can be obtained

Outcomes of endodontic treatments performed by dental students:a follow-up study

Abstract Aim: We aimed to evaluate the quality of the root canal treatments performed by undergraduate dental students. Material and Methods: Data comprised 105 teeth of which digital radiographs were analyzed. Radiographic periapical findings at baseline were compared with those after the follow-up period. Properties of the root fillings i.e. length and density, as well as types of teeth were considered in analyses. Patients with missing information i.e. no diagnosis or poor quality radiographs, were excluded. Results: Second premolar was the most common tooth for endodontic treatment. Teeth with preoperative periapical lesions had healing rate of 84.0%, when the respective figure for teeth without preoperative periapical lesions was 96.7%. The best healing rate was detected in mandibular premolars and poorest in mandibular incisors and canines. Maxillary molars had biggest proportion of negative changes. Outcome was significantly better for root fillings of optimal length compared to those which were not (p=0.019). Teeth with filling material outside the apex were noticed to have the lowest healing rate (69.2%). No effect on periapical healing due to the use of posts was observed. Isolating the root canal filling was associated with better outcome compared to the situation without any isolation. Conclusion: In our study, the outcome of endodontic treatments by dental students was better than reported in earlier studies. Good outcome was associated with good quality of root fillings. There still are unnecessary short-comings in recording diagnosis and the course of treatment

Usefulness of an endodontic case difficulty assessment form of root canal treatments in dental education in Finland

Abstract According to current care guidelines, it would be beneficial to evaluate the difficulty of a root canal treatment (RCT) after the decision of an indicated RCT. For this matter, several difficulty assessment forms have been developed. In this pilot study, fifth-year dental students evaluated the usefulness of the Endodontic Case Difficulty Assessment Form (ECAF) presented in the Finnish Current Care Guidelines for Endodontic Treatment (2014). Another aim was to postoperatively investigate how well the evaluation by dental students using the ECAF associated with the outcome of RCT evaluated by a specialist in endodontics. The dental students’ (n = 33) and the supervisor’s assessments of the RCTs were compared postoperatively at the Dental Educational Unit, Oulu, Finland. After completing the ECAF, the students’ experiences of its use were explored with a structured form. In ECAF, patient-derived factors, such as gagging, deviant crown morphology, and complications in previous endodontic treatment, were all significantly associated with complications in RCTs by the dental students (p < 0.05). The assessments by students and the supervisor differed in 55% of cases, especially in moderately difficult cases. In the majority of these cases (71%), the students evaluated the case to be easier than the teacher. Students found the ECAF user-friendly, even if it did not demonstrate their competence in accomplishing RCTs. The ECAF appears useful for junior dentists, specifically in terms of distinguishing the least and most difficult cases. A simpler form could be useful for students and clinicians