Central Pit Research Articles

A Study of Central Peaks and Central Pits on the Moon and Vesta

Abstract Impact craters are present on all bodies in the solar system with many displaying complex interior morphologies such as central peaks and central pits. Central peaks form due to the uplift of material in the center of the crater during transient crater formation while central pit formation has been suggested to occur by a number of processes including impacts into a weaker target which may contain volatiles. Comparing central peaks and central pits on rocky bodies like the Moon and Vesta will provide information about the formation processes of these morphologies on volatile poor bodies. In this study, we surveyed 248 craters on the Moon and Vesta. Our study of these central pits and central peaks suggest that crustal strength may contribute to the formation of central pits on rocky bodies and supports the notion that volatiles may not contribute to the formation of central pits on rocky bodies.

Ripples, Transverse Aeolian Ridges, and Dark‐Toned Sand Dunes on Mars: A Case Study in Terra Sabaea

AbstractRipples, transverse aeolian ridges (TARs), and dark‐toned sand sheets and dunes are common aeolian bedforms on the Martian surface. They are important for understanding the nature of present‐day Martian sediments and regional aeolian processes. Here we present a case study investigation of ripples, TARs, a dark‐toned sand sheet, and dunes in an unnamed—but well‐covered by remote sensing datasets—crater in Terra Sabaea, Mars, to consider their nature and possible origin scenarios. Repeat high‐spatial resolution images show only minor albedo changes among the dark‐toned sand dunes but no obvious changes in the ripples and TARs. Visible and infrared spectra show that the megaripples and TARs are pyroxene‐bearing, while the dark‐toned sheet and dunes are olivine‐bearing. Thousands of TARs are superimposed on the crater walls, and they have a similar composition as the bedrock exposed around the central pit, suggesting that some percentage of the sediment composing the TARs may be locally derived. Megaripples have a similar composition as TARs, suggesting they may share a similar origin. Dark‐toned sand sheets and sand dunes show a different composition from the substrate of the crater, plus bedform orientations indicative of a dominant, north‐northwest wind, indicating that some of these dark sands might have been blown in from outside of the crater. Alternatively, the sand in the megaripples, TARs, sand sheets, and dunes could share a common source, and some or even all of them could be recycled from the weathering and erosion of the sand‐bearing clastic rocks exposed in the crater walls.

Airflow Analysis of the Haida Plank House, a Breathing Envelope

The Haida plank house is one of the most important models built by the native American Indians. Built on the southwest coast of Canada, it adapts the tradition of the ancient pit houses to the requirements of the humid and cold climate characteristic of the Haida Gwaii Islands. This construction is composed by two main pieces: the central pit covered by a wooden envelope. Both protect its dwellers and their hearths. The ventilation system is based on two solutions: the gaps between the wall planks and a smoke hole that can be opened or closed in the roof at will. The aim of the present research is to analyze the way these two elements arrange the indoor airflow in order to ensure the comfortability of the house. Four cases have been proposed, according to four different dimensions for the gaps: 1, 2, 3 and 4 cm. Each case has been doubled in order to determine how the state of the smoke hole affected the corresponding results. This way, it has been concluded that if the gaps’ width becomes higher than 4 cm, the airflow velocity comfort level would be exceeded. It is been possible to observe how the state of the smoke hole influences the way the air moves around the dwelling.

Laser ablation behavior and mechanism of Cf/SiC–ZrC ultra-high temperature ceramic matrix composite prepared by PIP method

Cf/SiC–ZrC ultra-high temperature ceramic matrix composites prepared by precursor impregnation and pyrolysis (PIP) method were exposed to laser with energy density of kW level and the ablation behavior and mechanism were investigated. The results show that under different ablation times, the composites exhibited similar ablation region divisions, namely, central ablation pit, ablation transition zone, oxidation zone and non-ablated zone. Sample subjected to laser ablation of 5 s has the largest linear ablation rate of 0.0946 mm/s, which decreased to 0.0748 mm/s for 10 s ablation sample, and after that increased to 0.0876 mm/s for 15 s ablation sample. Under high-energy laser ablation, ZrO2 was the main anti-ablative component among the oxides formed by the oxidation of the matrix, which underwent morphology changes from sheets, fragments to micro and nano particles. Dense structure and continuous anti-ablation layer with high melting point components are the key factors to improve the anti-laser ablation performance of materials.

The morphologic and morphometric characteristics of craters on Ceres and implications for the crust

The Dawn spacecraft revealed a heavily cratered surface of the dwarf planet Ceres. These impact craters can be used to uncover the target properties of Ceres by analyzing the morphologic and morphometric characteristics. A near-global crater database containing 44,594 craters with diameters (D) ≥ 1.0 km in the latitude range 84.66°S–89.62°N over all longitudes has been developed to further understand the target properties of Ceres. For this purpose, various interior morphologies were classified such as central peaks, central pits, and lobate flows. Central floor pit craters were only observed in the northern hemisphere on Ceres indicating a weaker crustal strength. Investigations into the peak-to-crater diameter ratio (Dpk/Dc) implies the crust of Ceres has strength more similar to rocky Mercury than to Mars which exhibits localized areas of the crust containing large amounts of ice, or the volatile-rich crust of Ganymede. The Dpk/Dc, however, does display regional variations, with the northern hemisphere having a larger Dpk/Dc consistent with a more volatile-rich crust. Analysis of the depth-diameter ratio for fresh impact craters suggesting the simple-to-complex transition diameter (Dsc) of ~10.0 km and the onset diameters for central peaks indicate a Dsc of ~17.0 km. This is higher than expected if Ceres is a purely icy body and lower than expected if Ceres is a completely rocky body. These results indicate that Ceres has a mixed rock/ice composition, as proposed by other studies.

Corrección de mordida cruzada posterior vestibular en dentición primaria. Reporte de dos casos clínico

La mordida cruzada posterior vestibular cruzada bucal o mordida en tijera ocurre cuando las cúspides linguales de los molares superiores ocluyen vestibularmente a las fosas centrales de los molares inferiores o cuando las caras palatinas de los dientes superiores están en contacto con las caras vestibulares de los dientes inferiores. Pueden ser funcionales, causadas por inclinación de los molares inferiores hacia lingual o por asimetrías mandibulares. El tratamiento temprano es recomendado para normalizar las relaciones transversales y promover un correcto desarrollo de la oclusión. Se presentan dos casos de mordida cruzada posterior vestibular unilateral en dentición primaria y mixta temprana. Caso 1: paciente masculino de 5 años de edad, presentó lesiones extensas de caries, normoclusión, mordida cruzada posterior vestibular unilateral derecha y fue tratado mediante aparato fijo tipo Bi-Helix con bandas cementadas a los segundos molares primarios. Caso 2: paciente masculino de 5 años de edad, presentó lesiones extensas de caries, normoclusión y mordida cruzada posterior vestibular unilateral Izquierda. Fueron colocadas pistas directas de resina. En ambos casos se logró una relación trasversal satisfactoria, corrigiendo la mordida cruzada vestibular. Conclusión: La mordida cruzada posterior vestibular puede presentarse debido a desviación mandibular por interferencias oclusales y a inclinaciones inapropiadas de los molares primarios. Cuando esta es la etiología, el tratamiento es exitoso al utilizar pistas directas de resina, eliminación de contactos prematuros y expansor inferior tipo Bi-Helix.

Gas flow in martian spider formation

Martian araneiform terrain, located in the Southern polar regions, consists of features with central pits and radial troughs which are thought to be associated with the solid state greenhouse effect under a CO2 ice sheet. Sublimation at the base of this ice leads to gas buildup, fracturing of the ice and the flow of gas and entrained regolith out of vents and onto the surface. There are two possible pathways for the gas: through the gap between the ice slab and the underlying regolith, as proposed by Kieffer (2007), or through the pores of a permeable regolith layer, which would imply that regolith properties can control the spacing between adjacent spiders, as suggested by Hao et al. (2019). We test this hypothesis quantitatively in order to place constraints on the regolith properties. Based on previously estimated flow rates and thermophysical arguments, we suggest that there is insufficient depth of porous regolith to support the full gas flow through the regolith. By contrast, free gas flow through a regolith–ice gap is capable of supplying the likely flow rates for gap sizes on the order of a centimetre. This size of gap can be opened in the centre of a spider feature by gas pressure bending the overlying ice slab upwards, or by levitating it entirely as suggested in the original Kieffer (2007) model. Our calculations therefore support at least some of the gas flowing through a gap opened between the regolith and ice. Regolith properties most likely still play a role in the evolution of spider morphology, by regolith cohesion controlling the erosion of the central pit and troughs, for example.

Compositional control on impact crater formation on mid-sized planetary bodies: Dawn at Ceres and Vesta, Cassini at Saturn

High-resolution mapping of Ceres, Vesta and the icy satellites of Saturn, Uranus and Pluto reveals a rich variety of well-preserved impact crater morphologies on these low gravity bodies. These objects provide a natural laboratory to study effects of composition on crater formation processes under similar surface gravity conditions (though mean impact velocities vary by several factors). Simple craters occur on all these bodies but subtle differences in morphology on Ceres and Vesta are recognized. Immature complex craters (with large floor mounds but not terraces or conical central peaks) occur on Vesta and while smaller than predicted are consistent with its silicate composition. Asymmetric simple craters (with incomplete scarp development) on all bodies are likely related to differential overburden stresses in the rim, and their occurrence is consistent with lower crustal strength on icy bodies including Ceres. Immature and mature complex craters exhibit increasing degrees of complexity, including spiral floor deformation patterns (related to failure in converging floor material), central peaks, and impact melt. Cerean crater morphologic types and simple-complex transition diameters are smaller than on Vesta but similar to those on icy satellites, indicating a much weaker rheology for Ceres' outer layers under impact conditions. These are consistent with geophysical indications of a low-density water ice and probably clathrate rich outer shell. Fluidized floor deposits (impact melt or melt-solid mixtures) are significant in craters >25 km across on Ceres but absent on Saturn satellites. Central pit craters are common on Ceres (at diameters of ~75 to 150 km consistent with gravity scaling from the larger Galilean satellites) but are absent on Saturnian satellites and Charon. The contrasting impact melt and central pit behaviors on Ceres and Saturn's moons is contrary to expectation given the higher impact velocities at Saturn but might be related to lower internal temperatures, or the higher fraction of non-ice material on Ceres. The correlation or scaling of transition diameters to surface gravity is near −0.65 rather than −1, perhaps due to increased porosity on lower gravity bodies. The fundamental similarity of crater morphologies on Ceres and icy satellites, however, indicates that the weaker rheology of water ice results in similar craters even if the non-(ice+clathrate) components are as high as ~30 vol%.

Evaluation of Internal Fit and Marginal Adaptation of Provisional Crowns Fabricated with Three Different Techniques.

Different techniques have been used to construct provisional crowns to protect prepared teeth. The purpose of this in vitro study was to assess the internal fit and marginal discrepancy of provisional crowns made by different methods. A total of 48 provisional crowns were constructed and divided into three groups (n = 16) according to the fabrication methods: fabricated manually-group MAN; computer-aided design/computer aided manufacturing technology-group CAM; and 3-dimensional (3D)-printed technology-group 3DP. The same standard tessellation language (STL) file was used for both CAD/CAM and 3D-printed group. The silicone-checked method was used to measure the internal gap distance. The marginal discrepancy was measured by using the polyvinyl siloxane (PVS) replica method and swept-source optical coherence tomography (OCT) scanning technique. Data were analyzed with one-way analysis of variance (ANOVA) nonparametric Kruskal-Wallis and Tukey tests at α = 0.05. At the central pit and axial walls, the gap distance mean values of group CAM were higher than those from group MAN and 3DP. The group 3DP was statistically significantly higher in gap distance at the location of occlusion than group MAN and group CAM (p < 0.05). The total gap distances assessed by silicone-checked method revealed there were no statistically significant differences between the tested groups (p > 0.05). The total mean values of absolute and horizontal marginal discrepancy of the group 3DP obtained by using the PVS-replica method and OCT scanning technique were significantly higher than the group MAN and CAM (p < 0.05). Regression correlation results of marginal discrepancy indicated a positive correlation (r = 0.902) between PVS-replica method and OCT scanning technique. The manually fabricated provisional crowns presented better internal fit and a smaller marginal discrepancy. Between different assessment techniques for marginal adaptation, PVS-replica method and OCT scanning technique have a positive correlation.

Experimental study concerning the oblique impact of low- and high-density projectiles on sedimentary rocks

We conducted four sets of impact experiments using sedimentary rock targets and three different kinds of projectiles at a variety of impact angles in order to examine how the density of a projectile affects the dimensions of a crater as the angle of impact decreases, the threshold angle for the formation of elliptical craters, and the threshold angle for the formation of pits. The crater profiles, crater volume, equivalent diameter, length, width, depth, and ellipticity of each set were carefully measured to be used in comparison with small craters that formed on the weak rocky surfaces of planetary bodies. The results indicate that the crater volume, equivalent diameter, width, and depth decrease with the impact angle, while the length of the crater within a set does not decrease monotonically with impact angle. This trend in crater length is consistent with the results of previous studies. Although craters formed at higher impact angles have a central pit, the pit becomes unclear and eventually disappears as the impact angle decreases. A larger threshold angle is required for the formation of pits at slower impact velocity than at higher impact velocity. Our results suggest that the presence of a central pit is indicative of impacts at higher angles and/or higher velocity. The ratio of the volume of craters resulting from oblique impacts to that of craters formed by normal impacts was proportional to the power of the sine of the impact angle. The power index was found to range between 1.46 and 2.20, with an average of 1.57. Comparison of the averaged power index to the power index of the π-group crater scaling rules, it is experimentally suggested that the hypothesis indicating that the vertical velocity component controls crater formation is plausible on a brittle target. The threshold angles for the formation of elliptical craters for three different kind of projectiles were almost consistent with those obtained in previous studies. Our results strongly suggested that the threshold angle for the formation of elliptical craters for high-density impactor, such as iron meteorites, are higher than for rocky impactors. We then obtained a relationship between the threshold angle for the formation of pits and the cratering efficiency. It is revealed that the threshold angle for the formation of pits is greater than the threshold angle for the formation of elliptical craters, when the cratering efficiency is in the range 7–30. A well-developed pit-spall structure in the crater may be used to indicate both, the impact angle and the vertical component of the impact velocity.

On the asymmetry of Nathair Facula, Mercury

Nathair Facula is the largest and most spectrally distinct of nearly 200 ‘bright red’ spots (faculae) on Mercury's surface, most of which are accepted to be deposits from explosive volcanic eruptions. Like most of Mercury's faculae, it hosts a non-circular central pit (in this case nearly 40 km wide and 3 km deep). However, the center of this facula does not coincide with its central pit's midpoint. Quantitative analysis of two sets of spectral data shows that the facula's midpoint is offset by 10–30 km northwards or northeastwards, and probably lies outside the pit. The pit area is almost certainly a ‘compound vent’, within which the locus of eruption has migrated between eruptive episodes. The asymmetry of the facula and the texture of the vent floor are consistent with the most energetic and/or the most recent eruptions having occurred from the northeastern part of the compound vent, but evidence that the center point of the facula lies outside the vent indicates that it may be necessary to invoke an additional factor such as asymmetric eruption fountains.

Martian Ice Revealed by Modeling of Simple Terraced Crater Formation

AbstractArcadia Planitia, a region in the northern midlatitudes of Mars, displays an uncommonly high abundance of simple craters with a concentric morphology, which is indicative of layering beneath the surface. Radar measurements suggest that the near surface layers could be made of excess water ice. In this study, we select two of these impact structures of similar size (Dc ~ 500 m), model their formation through iSALE shock physics code, and investigate the dependence of the final crater morphology on the material model parameters (cohesion and friction coefficient). Our parameter study shows that the intact and damaged cohesions of the nonporous ice play a fundamental role to obtain a good fit between our models and the topographic profiles taken from the digital terrain models in terms of crater diameter, crater wall inclination, and depth and size of the upper terrace. The central pit shape is instead controlled by the damaged friction coefficient of the basaltic crust, but it is mainly affected by projectile density and speed. Our results confirm that two layers of relatively pure water ice, each with different rheology and porosity, can explain the unique double‐terraced morphology of impact craters in Arcadia Planitia. The low values of cohesion we find for the ice might point to snowfall as emplacement mechanism in the region. The different thicknesses of the ice layers in the two crater areas seem to suggest variations in ice deposition and/or evolution history across Arcadia Planitia.

The varied sources of faculae-forming brines in Ceres\u2019 Occator crater emplaced via hydrothermal brine effusion

Before acquiring highest-resolution data of Ceres, questions remained about the emplacement mechanism and source of Occator crater’s bright faculae. Here we report that brine effusion emplaced the faculae in a brine-limited, impact-induced hydrothermal system. Impact-derived fracturing enabled brines to reach the surface. The central faculae, Cerealia and Pasola Facula, postdate the central pit, and were primarily sourced from an impact-induced melt chamber, with some contribution from a deeper, pre-existing brine reservoir. Vinalia Faculae, in the crater floor, were sourced from the laterally extensive deep reservoir only. Vinalia Faculae are comparatively thinner and display greater ballistic emplacement than the central faculae because the deep reservoir brines took a longer path to the surface and contained more gas than the shallower impact-induced melt chamber brines. Impact-derived fractures providing conduits, and mixing of impact-induced melt with deeper endogenic brines, could also allow oceanic material to reach the surfaces of other large icy bodies.

Influence of thermomechanical aging on marginal gap of CAD-CAM and conventional interim restorations

Statement of problemComputer-aided design and computer-aided manufacturing (CAD-CAM) milling and 3-dimensional printing are readily available for the fabrication of interim restorations. However, studies comparing the marginal gap after a long period of function are lacking. PurposeThe purpose of this in vitro study was to evaluate the marginal gap of interim crowns fabricated from different materials and with different techniques before and after receiving simulated oral stress. Material and methodsTwo conventional resins, a polymethyl methacrylate resin (Unifast Trad) and a bis-acryl resin (Protemp 4), a milled polymethyl methacrylate resin (Brylic Solid), and a 3-dimensionally printed bis-acrylate resin (Freeprint Temp) were evaluated. Interim crowns (n=10/group) were fabricated by using the conventional direct technique for Unifast Trad and Protemp 4, with a maxillary molar Dentiform tooth as a template and by using CAD-CAM for Brylic Solid and Freeprint Temp. After finishing and cementation, the marginal gap was measured at the middle of all surfaces and line angles. The average value from all 8 sites was used to represent the marginal gap of each specimen. Subsequently, all interim crowns were thermocycled (5000 cycles of 5 °C and 55 °C), and cyclic occlusal load with a 5-mm steel ball at central pit (100 000 at 100 N) and the marginal gap were remeasured. The effects of different material types and aging on marginal gap were analyzed with 2-way ANOVA. The difference in marginal gap before and after aging was analyzed by using the paired t test, and the increased marginal gap was analyzed with 1-way ANOVA (α=.05). ResultsBoth the material types and the aging regimen had a significant effect on marginal gap (P<.001). The Unifast Trad group and the Protemp 4 group had a significantly larger marginal gap than the Brylic Solid group and the Freeprint Temp group, both before and after aging (P<.01). Each group had a significantly larger marginal gap after the aging regimen (P<.001). The increased marginal gap was greatest in the Unifast Trad group, which differed statistically from the Freeprint Temp group (P=.004) but not from the other groups (P>.05). ConclusionsThe interim crowns fabricated with the Brylic Solid and the Freeprint Temp had a smaller marginal gap than those fabricated with Unifast Trad and Protemp 4, both before and after aging. The Unifast Trad group showed a significantly larger increase in marginal gap after the aging regimen than the Freeprint Temp group.

Nasal dermoid cyst excision with a lateral rhinotomy approach through the nasal alar sulcus

<i>Introduction:</i> Nasal dermoid tumors are the most common congenital midline nasal mass and develop as a result of failed involution of the neuroectomderm in the prenasal space. MRI is the diagnostic imaging study of choice. Nasal dermoids are classically treated by surgical excision. Many surgical approaches have been described including an external rhinoplasty, a lateral rhinotomy, a U-shaped or a longitudinal dorsal rhinotomy, a gull wing incision, a medial canthal incision, a nasal endoscopic resection, and a bicoronal incision. We present here a novel approach utilizing a lateral rhinotomy incision involving the nasal-alar sulcus with infratip and contralateral extension. <i>Case description:</i>We present a case of a 15-year-old male with acute swelling/tenderness to his nasal dorsum that did not resolve with 2 weeks of antibiotic therapy. Physical exam demonstrated a soft, compressible 2.5 × 2.5 cm mass on a saddled dorsum. CT and MRI imaging confirmed the presence of a nasal dermoid tumor within the anterior nose without evidence of intracranial extension. Surgical excision was performed using a novel approach to the nasal dorsum. A curvilinear incision was planned along the right nasal sidewall and continuing along the alar sulcus to the infra-tip lobule and up to the nasal alar sulcus on the left. A 4 mm punch was placed through the central pit on the lower third of the nasal dorsum along the midline axis to serve as a subcutaneous landmark during the dissection. A dorsal skin flap was elevated along the planed incision from right to left in the subcutaneous plane until reaching the punched central nasal pit. The midline dorsal mass was identified as well as the connecting stalk through the punch to the dorsal cutaneous pit. This mass was resected en bloc and was removed from the nasal cavity. Autologous rib harvest was used for nasal dorsum reconstruction. <i>Discussion:</i> When planning the surgical approach to the midline nasal mass should, the surgeon must understand that the approach taken should provide the ability to perform medial and lateral osteotomies if required, should favor rapid repair of cribiform defects with associated cerebrospinal fluid leak if present, should facilitate reconstruction of the nasal dorsum, and should offer the likely outcome of an acceptable scar. The approach described meets these requirements and provides tremendous access and visualization for resection. This approach may be considered for other prenasal soft tissue mass resections as well.

Quantum dot molecule formation in Si-Ge heteroepitaxy on pit–patterned Si(001) substrate: A theoretical study

Abstract Quantum dot molecules refer to nanostructures consisting of four quantum dots around a central pit. These are observed to form in Si-Ge heteroepitaxy and are considered as an alternative to quantum dots for strain relaxation. Here we use numerical simulations of a continuum model of strained heteroepitaxy to show the spontaneous formation of quantum dot molecules in thick Si 0.5 Ge 0.5 films grown on pit–patterned Si substrates. The route to their formation first involves a quantum dot in the pit, followed by removal of material from the pit to form quantum dot molecules. These molecules are formed for smaller pit widths, whereas larger pit widths tend to create a ridged surface. A mature single–walled quantum dot molecule has a typical size of about 220 nm. On reducing the wavelength of the original pit–pattern, we notice that multiple–walled quantum dot molecules form, due to the interactions with other nearby molecules. Our results broadly agree with experiment and suggest that QDM formation on patterned substrates does not necessarily have a nucleation barrier and can take place following the usual evolution of the Asaro–Tiller–Grinfeld instability.

Gastric heterotopic pancreas in children: A prospective endoscopic study

PurposeTo document the prevalence and variable appearance of gastric heterotopic pancreas (HP) in children undergoing upper gastrointestinal (GI) endoscopy. MethodsA prospective 4-year study of children undergoing flexible upper GI endoscopy in a single institution. ResultsA total of 607 upper GI endoscopies were performed in 478 pediatric patients during the 4-year period. Eleven children (6 girls, 5 boys) aged 2.9 to 16.9 years had endoscopic features typical of gastric HP. All but one lesion was located in the gastric antrum and most appeared as an umbilicated submucosal nodule measuring 1–2 cm in diameter. Five of 13 children with repaired esophageal atresia (EA) and two of nine children with trisomy 21 had gastric HP. The prevalence of endoscopically visualized gastric HP in children without a history of EA or trisomy 21 was 1.1%. ConclusionsGastric HP is present in about 1% of pediatric upper GI endoscopies. It is significantly more common in patients with EA and may also be associated with trisomy 21. Gastric HP typically appears as a single 1–2 cm antral submucosal nodule, usually with a central pit. Recognition of this lesion is important to avoid misdiagnosis and inappropriate treatment. Level of EvidenceLevel II (diagnostic).

The new encrusting microproblematicum &amp;lt;i&amp;gt;Circumpodium enigmaticum&amp;lt;/i&amp;gt; and its attachment trace &amp;lt;i&amp;gt;Circumpodichnus serialis&amp;lt;/i&amp;gt; from the Middle Jurassic of Normandy (France)

Abstract. A single specimen of an enigmatic new attachment etching, together with an unknown calcareous encruster partly preserved in situ, has been identified on a belemnite rostrum from the Marnes de Dives Formation (Callovian, Middle Jurassic) of the Falaises des Vaches Noires in Normandy, France. The trace fossil, here established as the new ichnotaxon Circumpodichnus serialis igen. et isp. n., is a uniserial arrangement of very shallow depressions, oval to fusiform in outline, with peripheral pouches and central pits. The trace maker has a morphology unlike any other known calcareous epibiont, fossil or recent, and is consequently described as the new microproblematicum Circumpodium enigmaticum gen. et sp. n. Its calcitic skeleton is composed of a chain of segments with perforate basal and lateral walls, anchored to the attachment trace in the substratum by vertical protrusions in the centre and feet-like protrusions in the periphery. The hypothetical upper wall of the segments was either organic-walled and has decayed or it was calcitic and has been abraded. Based on morphological criteria and the capacity to bioerode, C. enigmaticum can best be compared to encrusting bryozoans and foraminiferans. Candidate bryozoans are aberrant arachnidiid ctenostomes, early cheilostomes, or stomatoporid cyclostomes. Among the foraminiferans, webbinellid or ramulinid polymorphinids are closest in their characters. In addition, tintinnid or folliculinid ciliophorans are considered as an alternative interpretation, and similarities to the Palaeozoic microproblematicum Allonema are discussed.

A Global Inventory of Ice‐Related Morphological Features on Dwarf Planet Ceres: Implications for the Evolution and Current State of the Cryosphere

AbstractWe present a comprehensive global catalog of the geomorphological features with clear or potential relevance to subsurface ice identified during the Dawn spacecraft's primary and first extended missions at Ceres. We define eight broad feature classes and describe analyses supporting their genetic links to subsurface ice. These classes include relaxed craters; central pit craters; large domes; small mounds; lobate landslides and ejecta; pitted materials; depressions and scarps; and fractures, grooves, and channels. Features in all classes are widely distributed on the dwarf planet, consistent with multiple lines of observational evidence that ice is a key component of Ceres' crust. Independent analyses of multiple feature types suggest rheological and compositional layering may be common in the upper ~10 km of the crust. Clustering of features indicates that ice concentration is heterogeneous on nearly all length scales, from ~1 km to hundreds of kilometers. Impacts are likely the key driver of heterogeneity, causing progressive devolatilization of the low latitude and midlatitude crust on billion‐year timescales but also producing localized enhancements in near surface ice content via excavation of deep ice‐rich material and possible facilitation of cryomagmatic and cryovolcanic activity. Impacts and landslides may be the dominant mechanism for ice loss on modern Ceres. Our analysis suggests specific locations where future high‐resolution imaging can be used to probe (1) current volatile loss rates and (2) the history of putative cryomagmatic and cryovolcanic features. The Cerean cryosphere and its unique morphology promise to be a rich subject of ongoing research for years to come.

Red blood cells state and calcium content of in the blood plasma during physical activity in marathon runners of various qualifications

The aim of the work is to investigate the morpho-functional state of peripheral blood erythrocytes and the content of Ca2+ in the blood plasma during physical exercise in marathoners of different qualifications.&#x0D; Material and methods. The studies were conducted in three groups of marathoners aged 20–25 years old with conditionally high, medium and low performance. Exercise was performed for 90 minutes on a bicycle ergometer with a given power. The study of peripheral blood erythrocytes was performed before and after exercise. The osmotic resistance of erythrocytes, the content of Ca2+ and free fatty acids in the blood were determined. Morphological study of erythrocytes was performed using a scanning electron microscope and stained by standard techniques. The red blood cell form index was determined by a special formula. Changing the content of Ca2+ enhances lipid melting, increases membrane fluidity and increases surface tension, with the result that the discocytes are stretched and thinned, the central pits deepen and the surface roughness increases, the volume and number of conical pores, and peripheral blood erythrocytes density.&#x0D; Results. Marathon runners of different groups after physical exercise differed in terms of the frequency of cardiac sweeps, the content of free fatty acids and the osmotic resistance of red blood cells. This is closely correlated with changes in the electrolyte and metric composition of erythrocytes and the presence of their reversible and irreversible forms in the general circulation after exercise.&#x0D; Conclutions. Physical activity causes structural and functional reorganization of erythrocytes, which is based on a change in their microelement composition, a decrease in osmotic resistance, mainly in poorly trained marathoners, and the appearance of various forms of erythrocytes against the background of the destruction of degenerative forms and an increase in the active release of young forms, which is a sign of high adaptive capacity in highly skilled athletes.