Transverse Ridges Research Articles

Transverse Aeolian Ridge Growth Mechanisms and Pattern Evolution in Scandia Cavi, Mars

In Scandia Cavi on Mars, barchans migrating over a field of transverse aeolian ridges (TARs) leave behind distinctive trails (“wakes”) comprising both TARs undergoing exhumation and coarse-grained ripples being shed from the barchans. With distance upwind from the barchans, the combined pattern of these bedforms coarsens and defect density decreases, thus appearing to mature with exposure time. We present results of morphological analyses of the wake bedform crestlines using HiRISE images, seeking to determine how the wake pattern reflects TAR growth and pattern development. TARs interact with each other, exhibiting defect repulsions and possible lobe extensions, indicating that these bedforms have migrated in the past, despite the lack of identifiable change in overlapping images spanning 9.5 years. Mapping one wake in detail, we found that the TAR pattern is not affected by superposing ripples. However, the ripples undergo many interactions, first with one another, and later (with distance upwind) with the underlying TARs. Near the dune, many ripples laterally link, growing in length, and they preferentially form along TAR crests, resulting in small bedform repulsions and longer superposing ripples. Most of these ripples will be consumed by the TARs, an as-yet unreported growth dynamic for TARs that is consistent with the work of others, who have found a continuum between TARs and the meter-scale ripples that form on dunes. Constructing a DTM, orthorectifying HiRISE images, and measuring dune migration rates places the timescale of ripple absorption by TARs in a wake at several thousand years, with the first ∼1,000 years dominated by lateral linking of ripples. Assuming that TAR growth is accomplished entirely through dune burial and subsequent ripple consumption, we estimate a lower limit age of the TARs, and by extension, the dune field, to be ∼270 kyr.

Dingo Gap: Curiosity Went Up a Small Transverse Aeolian Ridge and Came Down a Megaripple

AbstractRover data can provide important constraints on the possible origin of wind‐related martian features that have been termed “Transverse Aeolian Ridges” (TARs). The large aeolian bedform traversed by Curiosity at Dingo Gap has a planform and albedo similar to members of nearby TAR fields, so that the crossing at Dingo Gap revealed the surface characteristics of a small TAR. Mars Hand Lens Imager images documented 1–2 mm diameter, well‐rounded particles on the Dingo Gap bedform, along with numerous images obtained from the Mastcam, Hazcam, and Navcam science and engineering cameras on the rover. These images confirm that this feature (and, by extension, all small TARs) can be considered a megaripple whose surface is coated by rounded particles that are too large to be set into motion through saltation, but they may be induced to roll (creep) along the surface by the impact of saltating sand grains (a characteristic of megaripples on Earth). The images also confirm that a bimodal wind was present here, a condition that could have contributed to the symmetrical profile of the bedform. The bearing strength at Dingo Gap was better than that of the Purgatory megaripple that trapped Opportunity for several weeks, so that all megaripples should not be automatically presumed to represent a trafficability hazard for a rover.

PlaNet: A Neural Network for Detecting Transverse Aeolian Ridges on Mars

Transverse aeolian ridges (TARs) are unusual bedforms on the surface of Mars. TARs are common but sparse on Mars; TAR fields are small, rarely continuous, and scattered, making manual mapping impractical. There have been many efforts to automatically classify the Martian surface, but they have never explicitly located TARs successfully. Here, we present a simple adaptation of the off-the-shelf neural network RetinaNet that is designed to identify the presence of TARs at a 50-m scale. Once trained, the network was able to identify TARs with high precision (92.9%). Our model also shows promising results for applications to other surficial features like ripples and polygonal terrain. In the future, we hope to apply this model more broadly and generate a large database of TAR distributions on Mars.

Formation of the Wahiba Sand Sea in the Sultanate of Oman: implications of change in wind energy

The Wahiba Sand Sea is a north-south aeolian field that occupies the northeast corner of the Sultanate of Oman. Two main phases of sand dunes are conspicuous in this dune field as revealed by satellite data, namely High Sands in the north and Low Sands in the south. They are completely different in grain color and dune morphology. Granulometric and mineralogical analyses of sediments reveal more than a single source of sand supply for the two regions. Linear dune belts cover the northern dune field and complex transverse ridges predominate at the southern area. Hourly wind data from two meteorological stations at Ibra and Masirah in the north and south of the sand sea, respectively, were collected for 11 years (Jan. 2000 to Dec. 2010) in order to calculate the seasonal and annual sand drift potential along the sides of the sand sea. Results showed that wind energy is extremely high at Masirah due to the SW summer and fall monsoons, whereas at Ibra, wind energy is very low. The drop of sand drift potential (DP) from south to north is clearly observed from analyzing sand moving winds by empirical equations. The morphology of dunes and the direction of sand drift potential suggest two dune fields in the sand sea. The current pattern of wind regime in the north is presumably different from the prevailing wind during dune formation, whereas the dunes in the south were significantly formed by the recent wind regimes. This observation implies that two connected dune fields constitute the Wahiba Sand Sea.

Dynamic processes of the Dora Kamiyama rockslide in the Tibetan Plateau, China: geomorphic implication

The mechanisms of high-speed and long-runout landslides are reflected in the geomorphology of their deposits. Comprehensive field investigation using unmanned aerial vehicles photography was undertaken to observe special landforms of the Dora Kamiyama rockslide in the Tibetan Plateau. The dynamic processes of the rockslide were analysed based on the complex topography that remained. The age of sediments sampled from the landslide lake was tested through optically stimulated luminescence (OSL). In translation zone II, the landslide material near both edges underwent sinistral or dextral shearing motions, forming levees. In accumulation subzones III-1 and III-2, a rapid extensional sliding process contributed to toreva block formation. Transverse and longitudinal ridges developed due to compression-dominated processes in subzone III-2. Meanwhile, high-speed material was overturned in subzone III-3 due to the original topographical resistance, and carapace facies featuring abundant megablocks were clearly visible on the surface. Ridges confined by troughs were well-developed across the area experiencing rapid radial spreading motion in subzone III-4. Finally, dynamic parameters of the rockslide were calculated. The equivalent friction coefficient and the angle of reach were 0.40 and 21.80°, respectively. The maximum sliding velocity was estimated between 37.42 and 54.73 m/s. The OSL ages showed that the occurrence time of the rockslide can be estimated to be 4.24 ± 0.35 ka, defining it as an ancient landslide in the Holocene.

Laminar drag reduction in microchannels with liquid infused textured surfaces

Liquid infused surfaces (LIS) achieve non-wetting properties through asperity structures containing pockets of a lubricating liquid rather than air. Although studies have demonstrated several potential applications of LIS, the effect of liquid infused texture on the flow of liquid in microchannels has not been systematically addressed. The present work focuses on the effect of liquid-infused texture geometry and the infused liquid properties on the flow characteristics of a bulk fluid in rectangular and round microchannel geometries. Considering four different textured geometries of transverse ridges, longitudinal ridges, in-lined square posts and staggered squares, a detailed parametric study is presented to assess the resulting drag reduction and friction factor, expressed in terms of the Poiseuille number, on the flow in microchannels. The effect of geometrical parameters is investigated for different asperity solid fraction (ϕs), asperity height (hs) and channel thickness (H) or tube diameter (D), while the effect of the infused fluid is studied in terms of a ratio of its viscosity relative to the viscosity of the flowing bulk fluid. Based on the results of the parametric study an extension of the conventional Moody diagram for non-wetting surfaces is developed. Further, a design of experiments study is conducted to relate the drag reduction and Poiseuille number to the various governing parameters, using which conditions that maximize drag reduction are identified.

An Epidemiological Study on Orodental Disorders in 3,791 Working Donkeys in Egypt: Prevalence and Risk Factors

Orodental disorders are common in equidae and can lead to serious clinical complications. This study determines the prevalence rate (PR) of orodental disorders in working donkeys in Egypt and their potential risk factors. During 4 years, 3,791 donkeys were examined in six Egyptian governorates. Full case history and thorough clinical and oral examinations were performed. Radiography and oroendoscopy were undertaken whenever possible. All data were statistically analyzed using Poisson generalized linear models to compare PR among governorates, sex, years, body condition score, and age groups and to determine the potential risk factors. Of 3,791 examined donkeys, 954 donkeys (25.17%) had orodental disorders. The PRs of acquired disorders were 9.81% sharp enamel points, 5.86% buccal ulcers, 4.88% hook, 4.70% overgrown teeth, 4.19% periodontal disease, 3.11% ramp, 2.60% dental caries, 2.37% dental calculus, 2.30% diastema, 2.06% step mouth, 2.00% soft tissue injuries other than buccal ulcers, 1.77% worn tooth, 1.37% loose tooth, 1.29% exaggerated transverse ridge, 1.24% fractured teeth, 0.82% missing teeth, 0.69% wave mouth, 0.50% molar table angle change, and 0.45% wolf tooth overgrowth. The PRs of the congenital disorders were 1.90% displaced teeth, 1.37% deviated teeth, 0.58% retained teeth, 0.16% overbite, 0.16% underbite, 0.11% supernumerary teeth, and 0.11% premolar cap. The risk factors significantly associated (P < .05) with the orodental disorders were age and sex of the animal, geographic location, and year of examination. This study provides a database for future studies on orodental disorders and for designing effective preventive and therapeutic strategies for these disorders in donkeys.

A Broad Continuum of Aeolian Impact Ripple Morphologies on Mars is Enabled by Low Wind Dynamic Pressures

AbstractAeolian ripples are common in sandy environments on Earth and Mars. On Earth, ripples in sorted dune sands typically are &lt;1 cm high and are erased in high winds. On Mars in similar sands, ripple wavelengths commonly exceed 2 m, with much smaller ripples superimposed. Large Martian ripple sizes and juxtaposition of multiple wavelengths have raised questions about origins and the applicability of terrestrial aeolian physics to different planetary environments. Here, two hypotheses are evaluated for large Martian ripples: (1) fluid/wind drag, analogous to ripples formed under water on Earth, as proposed previously for Martian large ripples; and (2) saltation impact splash, the mechanism creating aeolian ripples of much smaller size on Earth. This study evaluates these hypotheses with numerical experiments and Mars rover observations, and concludes that large Martian ripples develop through the saltation impact splash mechanism. The low‐density Martian atmosphere enables aeolian impact ripples to grow much higher into the boundary layer before reaching maximum heights constrained by wind dynamic pressure effects at crests. In this concept, boundary layer conditions influence mature ripple heights more directly than wavelengths. On Mars, low wind dynamic pressures, combined with the impact splash mechanism, also help to explain other distinctively Martian aeolian bedforms, including large longitudinal ripples observed by rovers and orbiters, and transverse aeolian ridges (TARs) distributed widely across the Martian surface. Compared with Earth, low wind dynamic pressures on Mars permit a wider range of ripple sizes, relative ages, morphologies, and orientations in close proximity, as displayed in rover observations.

Paleoecologic and paleoenvironmental implications of a new trace fossil recording infaunal molting in Devonian marginal-marine settings

Luancaia igen. nov. and its two new ichnospecies, L. candasensis and L. elongata, from the Middle Devonian Naranco Formation of Asturias, northern Spain, record infaunal molting. The new ichnogenus has an elongate to oblong outline, and displays a distinctly trilobate appearance that includes an axial longitudinal lobe characterized by a distinctive ridge flanked by lateral lobes at each side. Well-defined transverse ridges convey a metameric-like appearance consisting of up to nine distinct segments. The anterior-most part is more variable, but consistently features a pair of oval strongly convex, or a subtriangular fan-like ridge in well-preserved specimens.Luancaia is similar to Rusophycus in its general segmented appearance, suggesting a euarthropod producer, but differs in the presence of a distinctive axial ridge and in the absence of scratch imprints. Luancaia closely resembles the dorsal side of the enigmatic Carboniferous oniscid-like euarthropod Camptophyllia. We propose that Luancaia records supine (i.e. upside-down) infaunal molting of a euarthropod with a dorsal exoskeletal morphology similar to Camptophyllia, in which exuviation was facilitated by dorsal anchoring on a firm muddy substrate.The Naranco Formation records sedimentation in a shallow- and marginal-marine setting that at times was affected by fluvial discharge most likely during storm floods. In particular, Luancaia is preserved in storm-flood beds that accumulated in relative proximity to a river mouth. These latter deposits consist of sparsely bioturbated sandstone and mudstone that reflect deposition under stressful conditions, such as salinity stress, erosion and by pass high sedimentation rate, and turbidity. By burrowing into the sediment, the producer avoided the stressed physical conditions of the sediment surface. Marginal-marine settings, where competition and predation pressures were significantly lower than in adjacent fully marine environments, may have served as safe molting sites during the mid-Paleozoic marine radiation.

Seismic Crustal Structure and Morphotectonic Features Associated With the Chain Fracture Zone and Their Role in the Evolution of the Equatorial Atlantic Region.

Oceanic transform faults and fracture zones (FZs) represent major bathymetric features that keep the records of past and present strike‐slip motion along conservative plate boundaries. Although they play an important role in ridge segmentation and evolution of the lithosphere, their structural characteristics, and their variation in space and time, are poorly understood. To address some of the unknowns, we conducted interdisciplinary geophysical studies in the equatorial Atlantic Ocean, the region where some of the most prominent transform discontinuities have been developing. Here we present the results of the data analysis in the vicinity of the Chain FZ, on the South American Plate. The crustal structure across the Chain FZ, at the contact between ∼10 and 24 Ma oceanic lithosphere, is sampled along seismic reflection and refraction profiles. We observe that the crustal thickness within and across the Chain FZ ranges from ∼4.6–5.9 km, which compares with the observations reported for slow‐slipping transform discontinuities globally. We attribute this presence of close to normal oceanic crustal thickness within FZs to the mechanism of lateral dike propagation, previously considered to be valid only in fast‐slipping environments. Furthermore, the combination of our results with other data sets enabled us to extend the observations to morphotectonic characteristics on a regional scale. Our broader view suggests that the formation of the transverse ridge is closely associated with a global plate reorientation that was also responsible for the propagation and for shaping lower‐order Mid‐Atlantic Ridge segmentation around the equator.

Residual Sediments of the Vema Fracture Zone, Central Atlantic

The Vema Fracture Zone orthogonally intersecting the Mid-Atlantic Ridge along 11° N is a complex tectono-sedimentary system, through which bottom water is transferred from the western to the eastern Atlantic. The southern surrounding of the fault valley is an extended (about 320 km) transverse ridge. At the early stages of the Vema System evolution, the ridge was located at shallow depths in the photosynthesis zone, which led to the formation of extensive biogenic carbonate buildups on its surface. Spreading, general sinking of the system, and associated movements along faults caused disintegration of ultramafic basement and bioherms with subsequent fractionation of colluvial–pelagic sediments and their eastward transport by bottom currents. The formation of coarse-grained residual sands completely devoid of pelitic material is associated with the high flow rates of Antarctic bottom waters. The presence of rounded pebbles of organogenic limestones and ultramafic rocks with traces of bioproductivity indicates that clastic material was transferred over a few hundred kilometers.

A new genus of Pharaxonothinae from Australia (Coleoptera: Erotylidae).

Australonotha gen. nov. (type species: A. monteithi sp. nov.) is described for two specimens collected from Mount Bellender Ker, Queensland, Australia. Apart from having a monocondylic meso-metaventrital articulation, Australonotha shows similarities with other erotylid subfamilies including Dacninae, Cryptophilinae and some smaller bodied glabrous Languriinae. Australonotha is placed in Pharaxonothinae based on the presence of a transverse occipital ridge and absence of abdominal calli. It can be distinguished from members of all other erotylid taxa by the pronotum lacking a basal transverse groove and having a pair of submedial longitudinal pronotal grooves that are deep and widened posteriorly, have sharp edges laterad, and form part of a distinct rectilinear impression in the basal third.

From surface morphologies to inner structures: insights into hypermobility of the Nixu rock avalanche, southern Tibet, China

Large rock avalanches often result in many deaths and catastrophic damage to infrastructure far from source. No consensus has yet been reached on mechanisms causing their extraordinarily long runout since the first study at the Elm Slide, Switzerland. Much current understanding of rock avalanche kinematics and dynamics has been gained from observations of their surface morphologies and inner structures. Based on field surveys, high-resolution satellite image interpretation, and laboratory sieving, we analyzed the ancient, earthquake-induced Nixu rock avalanche in southern Tibet, China, which has unique exposures of both morphological features and inner structures of the deposits. The study revealed that (1) the Nixu rock avalanche probably could be disintegrated into three emplacement stages, transforming from an initial deep-seated rockslide into a large secondary debris avalanche, plus a relatively small third debris avalanche. The spreading of the secondary debris avalanche contributed to the subsequent long-runout propagation. (2) The morphological features observed in successive proximal to distal exposures (such as scarps, flowbands, transverse ridges, grid grooves, hummocks, and splash zones) reflect the change in stress-strain state of debris in motion from tension, to compression, to shear and tension. (3) The complicated inner structures exposed along river banks (such as jigsaw structures, fragmented clasts, inner shear zones, conjunction faults, convoluted lamination, decollements, sand injections, and intrusions) indicate the existence of a thin basal shear zone and a pressurized entrained substrate between the substrate and rock avalanche debris. (4) This suggests turbulent flow with bulldozing in the front, but a laminar flow under a simple shear model for the main body. (5) The analysis suggests that the rock avalanche’s extraordinary mobility involves a combination of momentum transfer, substrate entrainment, liquefied basal shearing, internal shearing, and rock fragmentation.

A comparison of measured film thicknesses with quantitative predictions from an elastohydrodynamic, perturbation analysis at high slide-roll ratios

The behaviour of elastohydrodynamic contacts at high slide-roll ratios (SRR) differs markedly from that found in rolling conjunctions and at low SRRs. Behaviour is dominated by viscosity reduction due to shear-thinning and by temperature rises in the fluid and mating surfaces. These have a major influence on both the performance of smooth contacts and the behaviour of rough surfaces. This paper presents a set of experimental results for these conditions where artificial roughness in the form of transverse ridges is present. These are then compared to the results of a perturbation analysis to see whether this rapid analysis technique can adequately predict the behaviour. It is shown that very powerful feedback mechanisms exist in both the thermal and shear thinning and that these make the behaviour of surface roughness relatively insensitive to changes in fluid properties. In contrast to most previous work, real temperature, pressure and shear dependences of viscosity as measured in viscometers have been employed.

Ultra-depleted melt refertilization of mantle peridotites in a large intra-transform domain (Doldrums Fracture Zone; 7–8°N, Mid Atlantic Ridge)

The Doldrums transform system offsets the Equatorial Mid Atlantic Ridge by ~630 km at 7–8° N. This transform system consists of four intra-transform spreading centers (ITRs) bounded by five transform faults. The northernmost ITR is linked to the MAR axis by a ~ 180 km-long transform. Here, during two R/V A. N. Strakhov expeditions (S06 and S09), mantle peridotites were dredged along the transverse and median ridge of the transform, across the western flank of the ITR valley. Residual harzburgites were mainly sampled along the northern Doldrums transform valley, whereas plagioclase-bearing peridotites showing evidence for melt-rock interaction characterize the ITR domain. Petrological and geochemical observations reinforced by geochemical modelling are used to define the behaviour of trace elements during melt extraction and melt-rock reaction in our rocks. Results suggest that residual peridotites derive from mantle rocks that have undergone a degree of partial melting up to 12%, with melting likely starting at the transition of garnet-spinel stability fields, whereas peridotites which suffered melt-rock reactions have been divided into two types: (i) pl-impregnated peridotites, formed by migration of melts at high porosity and high melt-rock ratio; and (ii) refertilized peridotites, generated at reduced porosity, when small fractions of the same percolating melt crystallized clinopyroxene and minor plagioclase. We suggest that the refertilizing agent was a melt highly depleted in incompatible trace elements, in turn produced by an ultra-depleted mantle source. This mantle experienced previous degrees of melt extraction at the ridge axis, before being transposed laterally along the transform where it melted a second time during the opening of the intra-transform spreading segment.

Interpretation, age and significance of a relict paraglacial and periglacial boulder-dominated landform assemblage in Alnesdalen, Romsdalsalpane, southern Norway

A boulder-dominated landform assemblage in an alpine setting in Norway is described, interpreted and dated using a combination of Schmidt-hammer exposure-age dating (SHD) and cosmogenic 10Be surface-exposure dating. The origin and formation of these features is determined from their morphology, topographic setting and age. Three main components of the assemblage are recognized. First a ~300 m long and ~160 m wide, tongue-shaped rock-slope failure with a SHD age of 11.49 ± 0.82–12.96 ± 0.86 ka is identified on the basis of its planform, thickness, ‘runout distance’ and association with a fractured backing scarp. This is interpreted as a relict paraglacial landform triggered by deglaciation. Second, a 400-m long unequivocal pronival (protalus) rampart with an SHD age of 6.95 ± 0.97–8.35 ± 1.21 ka is identified on the basis of its narrow ridge form aligned close to the foot of an extensive talus slope. Although formation of the rampart probably commenced with deglaciation, the younger SHD ages indicate formation at a diminishing rate through the Holocene. Third, a ~550 m by ~150 m lobate component with transverse ridges, longitudinal and transverse depressions and enclosed pits, previously identified as a rock glacier, is dated to 11.33 ± 0.83–13.33 ± 0.90 ka with the Schmidt hammer and between 13.3 ± 2.0–14.7 ± 2.0 ka with 10Be. This third component may also be a product of rock-slope failure but attribution to rock-glacier creep associated with either interstitial ice (permafrost) or buried glacier ice during the Allerød Interstadial – Younger Dryas Stadial, and to which one or more rock-slope failures contributed debris, cannot be rejected. The advantages and limitations of compiling such evidence for identifying, differentiating and classifying apparently similar boulder-dominated colluvial landforms are exemplified.

The Morphology of the Mandibles of the Larval and Adult Lobster Shrimp Boasaxius princeps and Leonardsaxius amurensis (Decapoda: Axiidea: Axiidae)

The morphology of the mandibles in the lobster shrimps Boasaxius princeps and Leonardsaxius amurensis is described at different stages of ontogenesis. The incisor process of the mandibles in axiid zoeae is flattened antero-posteriorly, with three stout terminal teeth; the molar process is broad, the grinding surface is formed by transverse cuticular ridges and bears a fringe of brush-like projections on the anterior edge of the left mandible and on the posterior edge of the right mandible; between the terminal teeth of the incisor process and the molar process is a spine row formed by groups of spines. The general plan of the structure of the mandibles is retained in all zoeal stages; the number of transverse ridges on the molar process and the number of spine groups in the spine row increase as the larvae develop. In the megalopa stage, the mandible shape changes: the incisor process becomes broad and concave, the molar process is perpendicular to it; spines and ridges on the grinding surface of the molar process become reduced, small spines on the incisor process are retained on the cutting edge. Adult lobster shrimp lack cuticular structures on the molar and incisor processes of the mandibles. Despite the marked differences in the adult mandible morphology, the mandibles of the zoeae of Axiidea show similarity to the mandibles of the larvae of some caridean shrimps (e.g., the family Lysmatidae).

Unique Fine Morphology of Mouthparts in Haematoloecha nigrorufa (Stål) (Hemiptera: Reduviidae) Adapted to Millipede Feeding.

Millipede assassin bugs are a diverse group of specialized millipede predators. However, the feeding behavior of Ectrichodiinae remains poorly known, especially how the mouthpart structures relate to various functions in feeding. In this study, fine morphology of the mouthparts and feeding performance of Haematoloecha nigrorufa (Stål, 1867) was observed and described in detail for the first time. The triangular labrum is divided by a conspicuous transverse membrane into a strongly sclerotized basilabrum and a less sclerotized distilabrum. Fifteen types of sensilla are distributed on the mouthparts. Each mandibular stylet has an expanded spatulate apex and about 150 approximately transverse ridges on the external middle side; these help in penetrating the ventral trunk area and the intersegmental membranes of millipede prey. The right maxilla is tapered. On the internal surface are a row dorsal short bristles near the apex and a row of ventral bristles preapically. A longitudinal row of long lamellate structures extend proximate for a considerable distance, lie entirely within the food canal, and bear several short spines and short bristles. There is no obvious difference between males and females in the distribution, number, and types of sensilla on mouthparts. The adult feeding process involves several steps, including searching and capturing prey, paralyzing prey, a resting phase, and a feeding phase. The evolution of the mouthpart morphology and the putative functional significance of their sensilla are discussed, providing insight into the structure and function of the mouthparts adapted for millipede feeding.

Reversing transverse dunes: Modelling of airflow switching using 3D computational fluid dynamics

Airflow dynamics across dune surfaces are the primary agent of sediment transport and resulting dune migration movements. Using 3D computational fluid dynamic modelling, this study examined the behaviour of near surface airflow travelling over transverse (reversing) dunes on a beach system. Wind direction was modelled in two opposing directions (both perpendicular to dune crestline) to investigate surface alteration of flow on the dune topography. Surface shear stress, velocity streamlines and potential sediment flux were extracted from the modelling. The work shows that under SW winds the surface (under the configuration measured) underwent almost 10% more aeolian flux than with opposing NE winds of the same magnitude. Differences were also noted in the airflow behaviour with SW winds staying attached to the surface with less turbulence while NE winds had detached flow at dune crests with more localised turbulence. The work provides detailed insights into how 3D airflow behaviour is modified according to incident flow direction of reversing dune ridges and the resulting implications for their topographic modification. These dune types also provide interesting analogues for similarly scaled Transverse Aeolian Ridges found on Mars and the findings here provide important understanding of flow behaviour of such landforms and their potential movement.

&lt;strong&gt;Contribution to the knowledge of oribatid mites (Acari, Oribatida) of Uganda, with description of a new species of the genus &lt;em&gt;Machadobelba&lt;/em&gt; (Machadobelbidae)&lt;/strong&gt;

A list of identified oribatid mite taxa from Uganda, including 21 species/subspecies from 17 genera and 14 families, is presented. A new species of the family Machadobelbidae is described from leaf litter. Machadobelba ugandaensis sp. nov. differs from Machadobelba barbata Sanyal, Saha &amp; Chakraborty, 2005 and Machadobelba dispar Balogh, 1958 by the presence of one pair of lateral teeth of the rostrum, prodorsal transverse ridge between costulae and foveolate body surface. Revised generic diagnosis and an identification key to the known species of Machadobelba are presented.