This review covers several basic methodologies of surface treatment and their effects on titanium (Ti) implants. The importance of each treatment and its effects will be discussed in detail in order ...to compare their effectiveness in promoting osseointegration. Published literature for the last 18 years was selected with the use of keywords like titanium dental implant, surface roughness, coating, and osseointegration. Significant surface roughness played an important role in providing effective surface for bone implant contact, cell proliferation, and removal torque, despite having good mechanical properties. Overall, published studies indicated that an acid etched surface-modified and a coating application on commercial pure titanium implant was most preferable in producing the good surface roughness. Thus, a combination of a good surface roughness and mechanical properties of titanium could lead to successful dental implants.
The electrified medium‐scale traveling ionospheric disturbances (EMSTIDs) occurring as geomagnetically conjugate features in the middle latitude F region ionosphere are studied using multi‐instrument ...observations. Airglow imaging of OI 630 nm emission over Sata, Japan, and Darwin, Australia, are used to identify the occurrence of EMSTIDs. Thermospheric wind measurements made with the Fabry‐Perot interferometer observations of OI 630 nm from Shigaraki, Japan, and Darwin, Australia, are used along with ionosonde observations over Yamagawa, Japan, and Darwin, Australia, to study the thermospheric and ionospheric characteristics. These are the first results from such multi‐instrument observations simultaneously made from geomagnetic conjugate locations. Our results show that the amplitudes of the EMSTIDs are often different between the hemispheres. Thermospheric meridional winds appear to control the EMSTID amplitudes in the respective hemisphere. However, EMSTIDs are generated only when there is significant sporadic E activity with foEs often reaching greater than 6 MHz and (foEs − fbEs) reaching above 5 MHz at least for a short duration occurred. Existence of strong sporadic E activity on one of the hemispheres is found to be sufficient enough for generation of EMSTIDs in the conjugate F regions. These results conclusively indicate the importance of sporadic E layers in the generation of EMSTIDs. Further, it shows the significance of interhemispheric coupling between the E and F region ionospheres in the formation of EMSTIDs while their amplitudes in the respective hemispheres appear to have control of thermospheric neutral winds in the same hemisphere.
Key Points
Presence of significant sporadic E activity in at least one of the hemisphere is found to be necessary for formation of EMSTIDs
EMSTIDs form even when thermospheric winds are not favorable in one hemisphere as hemisphere coupled U × B electric fields are important
Amplitudes of EMSTIDs often differ between the hemispheres based on the thermospheric meridional winds
Auroral emission at 427.8‐nm from N2+ ions is caused by precipitation of energetic electrons, or by resonant scattering of sunlight by auroral N2+ ions. The latter often causes impressive purple ...aurora at high altitudes. However, statistical characteristics of auroral 427.8‐nm emission have not been well studied. In this paper we report occurrence characteristics of high 427.8‐nm emission intensities (more than 100 R) at subauroral latitudes, based on measurements by a filter‐tilting photometer over 14 years (2005–2018) at Athabasca, Canada (magnetic latitude: ~62°). We divided the data set into solar elevation angles (θs) more than and less than −24° (shadow height of sunlight: 600 km) to separate the 427.8‐nm emissions caused by resonant scattering of sunlight and those excited by auroral electrons, respectively. The occurrence rate of 427.8‐nm emissions of more than 100 R is 10.6% and 7.65% for θs more than and less than −24°, respectively, confirming that resonant scattering of sunlight by N2+ ions is a cause of the strong 427.8‐nm emissions of more than 100 R in the sunlit ionosphere. The occurrence rate is high in the postmidnight sector and increases with increasing geomagnetic activity, solar wind speed, and density. The occurrence rate is lowest in winter. A high occurrence rate was observed in 2015–2018, during the declining phase of the 11‐year solar activity. Superposed epoch analysis indicates that the 427.8‐nm emission exceeds 100 R when solar wind speed increases and solar wind density concurrently decreases, though the standard deviation of the data is rather large.
Plain Language Summary
Purple auroras can be caused either by energetic electrons at low altitudes (about 100 km), or by scattering of sunlight at much higher altitudes where the auroral curtains are in the Sun although the ground is in darkness. We have studied both types by sorting measurements of the purple emission from ionized nitrogen molecules depending on how far the Sun is below the horizon. We used 14 years' worth of data in order to study the effects over more than a solar cycle (11 years typically). The emission is stronger when general auroral activity increases, which is in turn related to solar wind speed and density. Same result was obtained by binning solar wind and geomagnetic activity data, timing them relative to strong purple aurora. It is also highest in the declining phase of the solar cycle. The emission intensity becomes low in winter. Recently, a type of purple aurora outside of the normal auroral oval has been reported, called “STEVE.” We note that we have studied the “traditional” type of purple aurora.
Key Points
We made a statistical study of auroral/resonant‐scattering 427.8‐nm emission observed at subauroral latitudes over 14 years
The resonant‐scattering 427.8‐nm emission indicates upflow of ionospheric nitrogen ions to higher altitudes
The emission increases during magnetic active periods and is associated with increases of solar wind speed and density
We report the first statistical study of stable auroral red (SAR) arcs detached from the main auroral oval during non‐storm time, using multi‐event conjugate measurements by the Defense ...Meteorological Satellite Program (DMSP) satellites (F13–F19) and a ground‐based all‐sky imager at Athabasca (Canada) (54.6°W, 246.36°Е, MLAT = 61.5°, MLON = 308.3°, L = 4.4). We found 63 events of detached SAR arc conjunctions with the DMSP satellites in the northern hemisphere and 18 events in the opposite southern hemisphere from 2006 to 2018. Measurements aboard DMSP satellites show that detached SAR arcs are in general associated with enhancements of electron temperature (60 cases) and electron density troughs (58 cases). Only 14 cases show strong horizontal flow associated with the detached SAR arcs, indicating that the strong plasma flow is not a necessary condition to cause the detached SAR arcs. The electron temperature measured by DMSP associated with detached SAR arcs positively correlates with F10.7 solar activity index. The measured emission intensities at 630.0 nm in the SAR arcs show a good correlation with the electron temperature. These results indicate that the detached SAR arcs during non‐storm time are caused by heat flux from the magnetosphere associated with substorms, and their intensity depends on the background plasma condition in the ionosphere.
Key Points
We show the first statistical study of stable auroral red (SAR) arcs detached from the auroral oval during non‐storm times using the Defense Meteorological Satellite Program satellites
Detached SAR arcs are mainly associated with electron temperature enhancement and electron density trough
In the pre‐midnight and midnight sectors, in some cases, detached SAR arcs are co‐located with horizontal flows
Two-dimensional structures of medium-scale traveling ionospheric disturbances (MSTIDs) over Europe have been revealed, for the first time, by using maps of the total electron content (TEC) obtained ...from more than 800 GPS receivers of the European GPS receiver networks. From statistical analysis of the TEC maps obtained 2008, we have found that the observed MSTIDs can be categorized into two groups: daytime MSTID and nighttime MSTID. The daytime MSTID frequently occurs in winter. Its maximum occurrence rate in monthly and hourly bin exceeds 70% at lower latitudes over Europe, whereas it is approximately 45% at higher latitudes. Since most of the daytime MSTIDs propagate southward, we speculate that they could be caused by atmospheric gravity waves in the thermosphere. The nighttime MSTIDs also frequently occur in winter but most of them propagate southwestward, in a direction consistent with the theory that polarization electric fields play an important role in generating the nighttime MSTIDs. The nighttime MSTID occurrence rate shows distinct latitudinal difference: The maximum of the occurrence rate in monthly and hourly bin is approximately 50% at lower latitudes in Europe, whereas the nighttime MSTID was rarely observed at higher latitudes. We have performed model calculations of the plasma density perturbations caused by a gravity wave and an oscillating electric field to reproduce the daytime and nighttime MSTIDs, respectively. We find that TEC perturbations caused by gravity waves do not show dip angle dependencies, while those caused by the oscillating electric field have a larger amplitude at lower latitudes. These dip angle dependencies of the TEC perturbation amplitude could contribute to the latitudinal variation of the MSTID occurrence rate. Comparing with previous studies, we discuss the longitudinal difference of the nighttime MSTID occurrence rate, along with the E- and F-region coupling processes. The seasonal variation, of the nighttime MSTID occurrence rate in Europe, is not consistent with the theory that the longitudinal and seasonal variations of the nighttime MSTID occurrence could be attributed to those of the Es layer occurrence.
We performed a superposed epoch analysis of solar wind, interplanetary magnetic field, geomagnetic index, and the rate of total electron content (TEC) index (ROTI) derived from global navigation ...satellite system‐TEC data during 652 geomagnetic storm events (minimum SYM‐H < −40 nT), to clarify the occurrence features and causes of storm‐time plasma bubbles in the equatorial to mid‐latitude ionosphere. In this analysis, we defined the time of the SYM‐H minimum as the zero epoch. As a result, the ROTI enhancement started at the duskside magnetic equator and expanded to higher latitudes during the main phase. Approximately 1 h after the onset of the recovery phase, the ROTI values at the magnetic equator in the dusk‐to‐midnight sectors decreased while those in the dawn sector increased. This situation persisted for at least 12 h. The ratio of the ROTI during the main phase to that during the quiet period in the dusk sector is the largest in May–July. The ratio of the ROTI during the recovery phase decreased during dusk with increasing solar activity. Considering the requirement of the Rayleigh‐Taylor instability, the difference in the magnetic local time of the ROTI signature, between the main and recovery phases, can be explained by a local time distribution of storm‐time electric fields associated with a prompt penetration electric field and disturbance dynamo. This implies that the occurrence feature of the plasma bubble is different from that during quiet times when the input of solar wind energy to the magnetosphere and ionosphere increases significantly.
Key Points
Superposed epoch analysis for characteristics of storm‐time plasma bubble is performed using global navigation satellite system‐rate of total electron content index data during 2000–2018
During the storm recovery phase, plasma bubbles can be generated in the post‐midnight sector and suppressed in the dusk sector
Seasonal variation of plasma bubble occurrence during the storm main phase is different from that during geomagnetically quiet periods
Synthetic FLAIR images are of lower quality than conventional FLAIR images. Here, we aimed to improve the synthetic FLAIR image quality using deep learning with pixel-by-pixel translation through ...conditional generative adversarial network training.
Forty patients with MS were prospectively included and scanned (3T) to acquire synthetic MR imaging and conventional FLAIR images. Synthetic FLAIR images were created with the SyMRI software. Acquired data were divided into 30 training and 10 test datasets. A conditional generative adversarial network was trained to generate improved FLAIR images from raw synthetic MR imaging data using conventional FLAIR images as targets. The peak signal-to-noise ratio, normalized root mean square error, and the Dice index of MS lesion maps were calculated for synthetic and deep learning FLAIR images against conventional FLAIR images, respectively. Lesion conspicuity and the existence of artifacts were visually assessed.
The peak signal-to-noise ratio and normalized root mean square error were significantly higher and lower, respectively, in generated-versus-synthetic FLAIR images in aggregate intracranial tissues and all tissue segments (all
< .001). The Dice index of lesion maps and visual lesion conspicuity were comparable between generated and synthetic FLAIR images (
= 1 and .59, respectively). Generated FLAIR images showed fewer granular artifacts (
= .003) and swelling artifacts (in all cases) than synthetic FLAIR images.
Using deep learning, we improved the synthetic FLAIR image quality by generating FLAIR images that have contrast closer to that of conventional FLAIR images and fewer granular and swelling artifacts, while preserving the lesion contrast.
The characteristics of nighttime medium‐scale traveling ionospheric disturbance (MSTID) features observed over Yonaguni (24.5°N, 123.0°E; 19.3°N dip latitude), Japan are studied using all‐sky imaging ...of OI 630.0 nm airglow emission. The uniqueness of these observations is that the area observed by the imager covers the transition region between low to middle latitudes in the ionosphere. Typical low‐latitude limit of midlatitude‐type nighttime MSTIDs possessing phase front alignments along the northwest to the southeast occurs in this region. These MSTID features are rarely sighted at dip latitudes below 15°. We selected 2 year period for analysis in which 1 year corresponded to the solar minimum conditions and another year to the solar maximum conditions. The MSTIDs were observed to extend to farther lower latitudes during the solar minimum conditions than during the solar maximum periods. Their observed range of wavelengths, phase velocities, phase front alignment, and propagation directions are similar to those observed at typical midlatitude sites. However, on many occasions the phase fronts of the observed MSTIDs did not extend over the whole field of view of the imager indicating that some process inhibits their extension to further lower latitudes. Detailed investigation suggests that the poleward propagating enhancement of airglow intensity, probably associated with the midnight pressure bulge, causes the MSTID features to disappear when they reach lower latitudes later in the night. When the MSTIDs reach lower latitudes well before midnight, they are found to be inhibited by the equatorial ionization anomaly crest region.
Key Points
Disappearance of MSTID phase fronts associated with airglow enhancementsDetailed statistical study of MSTIDs over YonaguniMSTID occurrences are high during solar minimum conditions
A ground‐based network of Global Navigation Satellite Systems receivers has been used to monitor medium‐scale traveling ionospheric disturbances (MSTIDs). MSTIDs were studied using total electron ...content perturbation maps and keograms over south‐southeast of Brazil during the period from December 2012 to February 2016. In total, 826 MSTIDs were observed mainly in daytime, thus presenting median values of horizontal wavelength, period, and horizontal phase velocity of 452 ± 107 km, 24 ± 4 min. and 323 ± 81 m/s, respectively. The direction of propagation varies on the season: during the winter (June–August), the waves preferentially propagated to north‐northeast, while in the other seasons the waves propagated to other directions. The anisotropy observed in the MSTID propagation direction could be associated with the region of the gravity wave generation that takes place in the troposphere. We also found that the MSTIDs were observed most frequently during the daytime, between 11 and 15 local time in winter and near to dusk solar terminator (17–19 local time) in the other seasons. Furthermore, the occurrence of MSTIDs was higher in winter. We suggest that atmospheric gravity waves in the thermosphere, mesosphere, and troposphere could play an important role in generating the MSTIDs and the propagation direction may depend on location of the wave sources.
Key Points
The paper presents the statistical study of MSTIDs in equatorial latitudes over south‐southeast of Brazil
The propagation direction of MSTIDs changes according to the seasons
The MSTIDs can be originated by gravity waves that propagate from the lower atmosphere
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