Simple Morphology Research Articles

A varying-radius cable equation for the modelling of impulse propagation in excitable fibres.

In this study, we present a varying-radius cable equation for nerve fibres taking into account the varying diameter along the neuronal segments. Finite element neuronal models utilising the classical (fixed-radius) and varying-radius cable formulations were compared using simple and realistic morphologies under intra- and extracellular electrical stimulation protocols. We found that the use of the classical cable equation to model intracellular neural electrical stimulation exhibited an error of 17% in a passive resistive cable model with abrupt change in radius from 1 to 2 μm, when compared to the known analytical solution and varying-radius cable formulation. This error was observed to increase substantially using more realistic neuron morphologies and branching structures. In the case of extracellular stimulation however, the difference between the classical and varying-radius formulations was less pronounced, but we expect this difference will increase under more complex stimulation paradigms such as high-frequency stimulation. We conclude that for computational neuroscience applications, it is essential to use the varying-radius cable equation for accurate prediction of neuronal responses under electrical stimulation.

Phylogeny, character evolution, and systematics of the fern family Ophioglossaceae based on Sanger sequence data, plastomes, and morphology

Adder's tongue ferns or Ophioglossaceae are best known among evolutionary biologists and botanists for their highest chromosome count of any known organisms, the presence of sporophores, and simple morphology. Previous studies recovered and strongly supported the monophyly of the family and the two multi-generic subfamilies, Botrychioideae and Ophioglossoideae, but the relationships among these and two other subfamilies (Helminthostachyoideae and Mankyuoideae) are not well resolved preventing us from understanding the character evolution. The monophyly of and the relationships in the species-rich genus, Ophioglossum, have not well been understood. In this study, new phylogenetic trees are reconstructed based on four datasets: Sanger sequences of eight plastid markers of 184 accessions, 22 plastomes (12 are new), 29 morphological characters, and combined Sanger and morphological data. Our major results include: (1) the relationships among the four subfamilies are well resolved and strongly supported in Bayesian and parsimony analyses based on plastomes: Mankyua is sister to the rest, followed by Ophioglossoideae which are sister to Helminthostachys + Botrychioideae; (2) Sanger data, plastomes, and combined Sanger and morphological data recovered and strongly supported the monophyly of Ophioglossum in its current circumscription (sensu lato; s.l.) in Bayesian and/or parsimony analyses; (3) within Ophioglossum s.l., four deeply diverged clades are identified and the relationships among the four clades are well resolved; (4) evolution of 34 morphological characters is analyzed in the context of the new phylogeny, among which shape of rhizomes, germination time of spores, shape of early gametophytes, and a number of other characters are found to contain interesting phylogenetic signal; and (5) based on the new phylogeny and character evolution, we propose a new classification of Ophioglossaceae in which the currently circumscribed Ophioglossum is divided into four genera including three new ones: Goswamia, Haukia, and Whittieria considering their molecular, morphological, ecological, and biogeographical distinctiveness.

Phylogenetic position of Newhousia (Dictyotales, Phaeophyceae) and the description of N. sumayensis sp. nov. from Guam

ABSTRACT The calcified encrusting brown algal genus Newhousia is reported from three new archipelagos in the Pacific: (1) Society Islands, French Polynesia; (2) Guam, Mariana Islands; and (3) Vanuatu. Newhousia presents a simple morphology consisting of small, rounded, two-layered calcified blades with limited interspecific variability in morphological features. Consequently, resolving cryptic diversity in Newhousia requires molecular phylogenetics. Bayesian and maximum likelihood phylogenetic trees, based on the concatenated cox1, cox3, psbA, rbcL and 18S rDNA sequences, supported a sister relationship of Newhousia with Lobophora/Zonaria clade. Analyses revealed five distinct evolutionary lineages within Newhousia. Genetic variation between the lineage from Guam and the two hitherto known Newhousia species, N. imbricata from Hawaii and N. yagha from Papua New Guinea, warrant the description of one new species, N. sumayensis sp. nov. The other two lineages, from the Society Islands and Vanuatu, were identified as geographically distinct populations of N. imbricata with limited genetic variation, rather than independent species. In the Society Islands, N. imbricata is common between depths of 10 m and 20 m as unattached spherical structures, or attached to hard substrate. In Guam, N. sumayensis sp. nov. grows abundantly in sciophilous habitats at depths of 10–21 m. We provide the first documentation of spores for this genus and of structures resembling plurilocular antheridia. Increased sampling throughout the Indo-Pacific region is required to further elucidate the distribution range and patterns of species richness in Newhousia.

Factors Controlling the Distribution of Agglutinated Foraminiferal Morphogroups as Palaeoenvironmental Tracers in the Kharga Oasis, Egypt

Abstract The present authors used the scanning electron microscopy and energy dispersive spectroscopy methodology as a standard approach for micropaleontological studies to detect test internal morphological and compositional features of agglutinated foraminifera grains collected from Maastrichtian-Paleogene of the Dakhla Oasis of Egypt. Five main morphogroups dominate Lower Kharga Member,the mixture of infaunal and epifaunal morphogroups indicating mesotrophic conditions during that time.All evolving new species found in the Early Paleocene are small and species richness remains low with small simple test morphologies resembling the under zone CF3 with a new appearance of morphogroup epifaunal flattened planispiral. Zone CF3 of Lower Kharga Member is characterized by the appearances of small-sized Trochammina which are associated with stressful environmental conditions. Zone P1c of the Upper Kharga Member is characterized by high percentages of calcareous agglutinated foraminifera and abundance of granular calcite and hyaline tests, which explained a sufficient quantity of calcium carbonate dissolved in the water and warm water basin. The strong decrease in diversity and heterogeneity of the assemblages, as well as the drastic drop in the number of infaunal elongated morphogroup coincident with the hiatus between CF3 and P1c (Maastrichtian/Danian boundary), indicate a dramatic decrease in the food supply to the sea-bottom floor.

Simple and complex burrow morphology in two Macrophthalmus species on the intertidal mudflats of Barr Al Hikman, Sultanate of Oman

ABSTRACT Burrowing Ocypodoidea crabs are an abundant component of many tropical and temperate coastal areas and central to the ecosystem functioning, for instance because they recycle nutrients, are important food for many shorebirds and alter the sediment through their burrowing behaviour. The burrow morphology of these crabs may differ between and within species, often correlated with differences in habitat preferences, crab morphology and life-history traits. Here we studied the burrow morphology and complexity of Macrophthalmus sulcatus and Macrophthalmus depressus, by means of casts (n = 7 and 10, respectively) and burrow excavations (n = 17 and 16, respectively) at the pristine intertidal mudflats of Barr Al Hikman in the Sultanate of Oman. We found that M. sulcatus construct simple burrows that were in all but one case inhabited by a single crab. By contrast, all burrows of M. depressus were complex, with multiple entrances and many (deep-reaching) branches. There was a strong relationship between M. sulcatus carapace width and burrow entrance size, indicating that the simple burrows are adapted to and made by the occupant. There was no relation between M. depressus carapace width and burrow entrance size, and in six burrows more than one crab was encountered, suggesting that the complex burrows are not made by and adapted to a single occupant. The complex burrows were found close to the shore whereas the simple burrows were found at the intermediate tidal zone. We speculate that the striking differences in burrow morphology may be explained by difference in habitat selection of the studied crabs, which most importantly relates to differences in sediment structure and tidal height. Crab morphology and life-history traits of the studied crabs could also account for the observed difference in burrow morphology.

Gene age shapes the transcriptional landscape of sexual morphogenesis in mushroom-forming fungi (Agaricomycetes).

Multicellularity has been one of the most important innovations in the history of life. The role of gene regulatory changes in driving transitions to multicellularity is being increasingly recognized; however, factors influencing gene expression patterns are poorly known in many clades. Here, we compared the developmental transcriptomes of complex multicellular fruiting bodies of eight Agaricomycetes and Cryptococcus neoformans, a closely related human pathogen with a simple morphology. In-depth analysis in Pleurotus ostreatus revealed that allele-specific expression, natural antisense transcripts, and developmental gene expression, but not RNA editing or a 'developmental hourglass,' act in concert to shape its transcriptome during fruiting body development. We found that transcriptional patterns of genes strongly depend on their evolutionary ages. Young genes showed more developmental and allele-specific expression variation, possibly because of weaker evolutionary constraint, suggestive of nonadaptive expression variance in fruiting bodies. These results prompted us to define a set of conserved genes specifically regulated only during complex morphogenesis by excluding young genes and accounting for deeply conserved ones shared with species showing simple sexual development. Analysis of the resulting gene set revealed evolutionary and functional associations with complex multicellularity, which allowed us to speculate they are involved in complex multicellular morphogenesis of mushroom fruiting bodies.

Accuracy and reliability of left atrial appendage morphology assessment by new 3D transesophageal echocardiographic rendering modalities: a comparative study with computed tomography

Abstract Funding Acknowledgements Type of funding sources: None. Background/Introduction. Left atrial appendage (LAA) morphology assessed by contrast-enhanced computed tomography (CT) has been associated to the risk of cardioembolic stroke in non-valvular atrial fibrillation. Subsequent studies with the traditional LAA classification system (CS) into 4 morphologies (Chicken wing, Cauliflower, Cactus and Windsock) yielded mixed results in terms of reliability and stroke risk association. Recently, a simple LAA morphology CS (new-LAAcs) based on the LAA bend angle measurement has been suggested. Three-dimensional transesophageal echocardiography (3D TOE) quality imaging has been improved and new volume rendering modalities developed. Purpose. Aim of this study was to evaluate the accuracy and reliability of 2D and new 3D TOE rendering modalities compared to CT in assessing LAA morphology. We used and validated a new simple LAA morphology classification system (new-LAAcs) based on the LAA bend angle in contrast to the traditional CS. Methods. 50 consecutive patients who underwent both cardiac CT and TOE were enrolled. LAA morphology was assessed by three different TEE modalities: (1) 2D TOE inspective evaluation (2D TOE), (2) 3D TOE multiplanar reconstruction (3D TOE MPR) and (3) 3D TOE Philips TrueVue Glass rendering (3D TOE GLASS). We assessed TOE accuracy compared to CT by sensitivity, specificity, accuracy, and Cohen’s kappa. Two trained readers independently adjudicated LAA morphologies in the new-LAAcs and the inter-rater reliability was obtained by percentage agreement and Cohen’s kappa. The reliability of the new- vs. traditional-LAAcs was assessed by CT in terms of reliability rates and influence on LAA morphology prevalence. Results. CT and TOE imaging analyses were feasible in all patients. 2D TOE was fairly accurate in identifying LAA morphology (κ 0.38, p = 0.022) and had only moderate inter-rater (κ 0.46, p = 0.027) and substantial intra-rater (κ 0.62, p = 0.003) reliability rates. 3D TOE showed high validity: 3D TOE MPR had an almost perfect accuracy (κ 0.84, p < 0.001) and substantial (κ 0.77, p < 0.001) inter-rater reliability; 3D TOE GLASS substantial accuracy (κ 0.67, p < 0.001) and almost perfect (κ 0.82, p < 0.001) inter-rater reliability. Intra-rater agreement was almost perfect for both 3D TOE modalities (κ 0.84, p < 0.001). In the comparison among CS the traditional-LAAcs inter-rater reliability was moderate (κ 0.47, p < 0.001) and the intra-rater reliability substantial (κ 0.68, p < 0.001) while the new-LAAcs yielded an almost perfect reliability level (inter-rater κ 0.84, p < 0.001 and intra-rater κ 0.93, p < 0.001). With the traditional-LAAcs, the prevalence of CW LAA was 30 (60%), while with the new-LAAcs the prevalence of low-risk-LAA was 13 (26%), leading to classify 17 (57%) CW morphologies as high-risk-LAA. Conclusions. 3D TOE is an accurate, reliable, and feasible alternative to CT in assessing LAA morphology with the new-LAAcs. The new-LAAcs shows higher reliability rates than the traditional one. Abstract Figure. Abstract Figure.

Fracture variation in high-rank coal induced by hydraulic fracturing using X-ray computer tomography and digital volume correlation

Hydraulic fracturing is a key technology for improving the permeability of coal reservoirs. Understanding the variation of hydraulically induced fractures is crucial for improving coalbed methane production. In this study, we conducted a laboratory-simulation of hydraulic fracturing in coal and applied X-ray computer tomography (CT) and digital volume correlation (DVC) to quantify the spatial distribution, structural variation, and propagation of fractures with an aperture greater than 28.4 μm. Hydraulic fracturing increased the aperture, volume (by 5.3, 32.2, 2.2 and 2.8 times) and surface area (by 1.1, 9.9, 1.8 and 0.8 times), and simplified fracture morphology in the four tested samples. Moreover, the significant influence range in the axial direction of hydraulic fracturing on fracture is 4.2 cm, 4.4 cm, 1.9 cm and 2.9 cm, respectively, with fracture connectivity reaching 61.8%, 99.3%, 77.7%, and 91.1%. A low in-situ stress differential resulted in the formation of a complex network of many fractures with a small volume. A high in-situ stress differential resulted in the formation of large fractures with a simple morphology. The X-ray CT images also showed that new fractures originated in and propagated along the mineral–maceral interface. DVC shows that high volume displacement and strain occur in the fracture area induced by hydraulic fracturing, and it has a good application prospect in the investigation of the microevolution and microdamage of fractures in coal.

First Molecular Phylogeny of Lumbrineridae (Annelida)

Lumbrineridae is a family of marine annelids with simple external morphology but complex and diverse jaw apparatuses consisting of paired maxillae and mandibles. Here we present the first phylogeny of lumbrinerids based on combination of nuclear (18S rDNA) and mitochondrial (COI, 16S rDNA) markers utilizing Bayesian inference and Maximum Likelihood approaches. Despite limited taxon sampling, our results support monophyly of the genera Abyssoninoe, Augeneria, Gallardoneris, Lumbrineriopsis, and Ninoe and indicate polyphyly of the genera Lumbrineris (the type genus of the family) and Scoletoma. None of the morphological characters traditionally used in lumbrinerid systematics, such as the presence of connecting plates, four pairs of maxillae, bidentate simple hooded hooks, colorless maxillae IV, and multidentate maxillae IV were found to be exclusive homologies for a well-supported clade and have probably evolved several times independently within Lumbrineridae.

Pterocladiella xiae sp. nov. (Gelidiales, Rhodophyta), a new species from southern China

ABSTRACT Turf-forming Gelidiales frequently occur in tropical coral reef regions. It is challenging to identify species correctly due to their small size and simple morphology. In the present study, we combined morphological and molecular phylogenetics methods to study turf-forming species of the genus Pterocladiella from tropical coral reef areas in southern China. Both COI-5P and rbcL gene analyses revealed a novel species described here, Pterocladiella xiae sp. nov. The species was less than 1 cm in height, with a distinctive slender thallus, compressed percurrent axis with up to two orders of ribbon-like branches, and short warty-like branchlets which usually occurred irregularly on the upper thallus. Pterocladiella bartlettii was also recorded in China for the first time. Additional descriptions of reproductive structure in P. musciformis and P. beachiae were also documented. This study enriches our understanding of the biodiversity of Pterocladiella in China and reveals the potential diversity of small turf-forming species in tropical coral reefs.

A new genus of soil green microalgae Edaphochloris gen. nov. (Chlorellaceae, Trebouxiophyceae)

The problem of studying the species diversity of small single-celled green coccoid microalgae (Chlorophyta) is still relevant, since their simple and uniform cellular morphology makes it extremely difficult to correctly identify them. It is now generally accepted that the best approach for creating a new, more natural classification of “little green balls” is an approach that combines morphological, ecological, physiological and molecular phylogenetic methods. Strains ACSSI 104 and ACSSI 144 were isolated from solonetz and chestnut soil (Volgograd region, Russia). Their cells have a typical Nannochloris-like morphology: single spherical or subspherical cells, chloroplast single, parietal, cup-shaped, without pyrenoid, but with starch grains in it. Old cells accumulate numerous oil droplets in cytoplasm. Reproduction by 2−4 autospores. Autospores of both strains are equal size and exhibit liberation by rupture of sporangium cell wall. Zoospores and sexual reproduction not observed. Both strains are part of independent cluster closely related to genera Marvania, Pumiliosphaera, Nannochloris and Gloeotila. A comparative analysis of morphological (cell size, chloroplast type) and ultrastructural characteristics (structure of cell wall and lamellar system), features of reproduction (asexual reproduction by autospores only) and habitat (soil) with other members of the Nannochloris-clade, as well as results of analysis of 18S rRNA gene and ITS2 secondary structure of the studied strains, allowed us to propose a new genus – Edaphochloris with the type species – E. andreyevae. The report was prepared based on the materials of the V All-Russian Scientific Conference with international participation "Algae: problems of systematics, ecology and use in monitoring", 2021.

The DYF-5 RCK and CDKL-1 CDKL5 kinases contribute differentially to shape distinct sensory neuron cilia morphologies in C. elegans.

The conserved CCRK, RCK, and CDKL5 kinases regulate cilia length in diverse organisms. In C. elegans , DYF-18 CCRK regulates DYF-5 RCK to shape both simple and complex cilia morphologies. The CDKL5 ortholog CDKL-1 has also been suggested to act downstream of DYF-18 but independently of DYF-5 to regulate lengths of simple rod-like cilia. Here we show that CDKL-1 is largely dispensable for regulation of complex cilia structures. Using genetic epistasis experiments, we confirm that CDKL-1 and DYF-5 act independently to control cilia architecture. Our results indicate that multiple kinases act via distinct pathways to regulate unique cilia ultrastructures.

Synthesis of Three‐Dimensional Reduced‐Graphene Oxide from Graphene Oxide

Carbon materials and their allotropes have been involved significantly in our daily lives. Zero‐dimensional (0D) fullerenes, one‐dimensional (1D) carbon materials, and two‐dimensional (2D) graphene materials have distinctive properties and thus received immense attention from the early 2000s. To meet the growing demand for these materials in applications like energy storage, electrochemical catalysis, and environmental remediation, the special category, i.e., three‐dimensional (3D) structures assembled from graphene sheets, has been developed. Graphene oxide is a chemically altered graphene, the desired building block for 3D graphene matter (i.e., 3D graphene macrostructures). A simple synthesis route and pore morphologies make 3D reduced‐graphene oxide (rGO) a major candidate for the 3D graphene group. To obtain target‐specific 3D rGO, its synthesis mechanism plays an important role. Hence, in this article, we will discuss the general mechanism for 3D rGO synthesis, vital procedures for fabricating advanced 3D rGO, and important aspects controlling the growth of 3D rGO.

Qualitative-Quantitative Assessment of Geodiversity of Western Samoa (SW Pacific) to Identify Places of Interest for Further Geoconservation, Geoeducation, and Geotourism Development

The assessment of geodiversity is a relatively new field of research connecting abiotic aspects of nature to the wider environment. The study of geodiversity is still in development, so a uniform and complete paradigm remains to be defined. Therefore, an assessment of geodiversity may be highly dependent on the nature of the territory subject to study, available databases, and the researchers’ field of specialization. The main quantitative method for the assessment of geodiversity was proposed to the scientific world only few years ago and may only be relevant to some places in the world, rather than all, which would be desirable. However, while similarities in research methods may be apparent, the directions, scales, and data utilized are clearly different. This article demonstrates a quantitative-qualitative method for an assessment of geodiversity, based on a five-point evaluation system and the utilization of widely available standard databases such as geological maps, SRTM models, and satellite images. Western Samoa Islands (Savai’i and Upolu Islands) were selected for assessment, as a typical example of basaltic ocean island volcanism generating relatively homogenous rock formations and subject to gradual geomorphology (e.g., shield volcano). While initially appearing as a region of simple geology and morphology, complexity is added by considering rock ages, the position and type of eruptive centres, and the coastal geoenvironment. By considering these factors, the assessment becomes specifically tailoring for geodiversity assessment of the islands of Samoa. In conclusion, it has been demonstrated a simple methodology of general assessment of geodiversity with additional improvements to take account of variability in other abiotic factors.

Construction of MOF-derived plum-like NiCo@C composite with enhanced multi-polarization for high-efficiency microwave absorption

Nowadays, facing the inevitable electromagnetic (EM) pollution caused by many electronic products, it is urgent to develop high-performance microwave absorbing materials. In particular, the bimetallic carbon-based composites derived from MOFs exhibit excellent microwave absorption potential due to their simple preparation, low cost, adjustable morphology and magnetoelectric synergy mechanism. In this work, we successfully prepared plum-like NiCo@C composite by simple solvothermal method and carbonization treatment, which displays strong absorption (-55.4 dB) and wide effective absorption band (EAB, 7.2 GHz) when the loading is 20 wt%. The plum-like structure greatly enriches the non-uniform interface and the structural anisotropy contributes to the dissipation of electromagnetic waves. At the same time, the band hybridization and magnetic coupling of NiCo@C contribute to the coordination of EM characteristics. Overall, this work proves the feasibility of NiCo@C hierarchical composite in the field of microwave absorbing, and provides insight for the development of high-performance absorbers.

Stability of Erythrocyte-Derived Nanovesicles Assessed by Light Scattering and Electron Microscopy.

Extracellular vesicles (EVs) are gaining increasing amounts of attention due to their potential use in diagnostics and therapy, but the poor reproducibility of the studies that have been conducted on these structures hinders their breakthrough into routine practice. We believe that a better understanding of EVs stability and methods to control their integrity are the key to resolving this issue. In this work, erythrocyte EVs (hbEVs) were isolated by centrifugation from suspensions of human erythrocytes that had been aged in vitro. The isolate was characterised by scanning (SEM) and cryo-transmission electron microscopy (cryo-TEM), flow cytometry (FCM), dynamic/static light scattering (LS), protein electrophoresis, and UV-V spectrometry. The hbEVs were exposed to various conditions (pH (4–10), osmolarity (50–1000 mOsm/L), temperature (15–60 °C), and surfactant Triton X-100 (10–500 μM)). Their stability was evaluated by LS by considering the hydrodynamic radius (Rh), intensity of scattered light (I), and the shape parameter (ρ). The morphology of the hbEVs that had been stored in phosphate-buffered saline with citrate (PBS–citrate) at 4 °C remained consistent for more than 6 months. A change in the media properties (50–1000 mOsm/L, pH 4–10) had no significant effect on the Rh (=100–130 nm). At pH values below 6 and above 8, at temperatures above 45 °C, and in the presence of Triton X-100, hbEVs degradation was indicated by a decrease in I of more than 20%. Due to the simple preparation, homogeneous morphology, and stability of hbEVs under a wide range of conditions, they are considered to be a suitable option for EV reference material.

New Species of Chloroidium (Trebouxiophyceae, Chlorophyta) from East Asia.

Chlorella-like green algae that reproduce only asexually by immotile autospores or motile zoospores are the most typical inhabitants of non-aquatic environments. They have a simple morphology that hampers their differentiation, but algae of such habit represent a diverse array of lineages, which are mostly in the classes Chlorophyceae and Trebouxiophyceae. One of these lineages is the order Watanabeales (Watanabea clade; Trebouxiophyceae), which comprises 10 genera that share a distinct mode of reproduction through unequally sized autospores. Most of these genera account for a few species that are rarely recorded in nature. In contrast, the genus Chloroidium is one of the most species-rich and widely distributed members of the order. Three strains of coccoid green alga were isolated during a study of soil algae in the temperate monsoon climate zone of Asia. These strains are described here as a new species, Chloroidium orientalis. SSU and ITS rDNA sequence data, morphological characteristics, and life cycle features differentiate these strains from known members of the genus.

Mixed approach on Chroodactylon ornatum (Stylonematophyceae, Rhodophyta) tolerance to hyposalinity: growth, photosynthetic performance and carbohydrate analysis

ABSTRACT Chroodactylon ornatum is a cosmopolitan non-Florideophycean red alga with a simple morphology, generally described as a euryhaline species. Herein, we compared the response of a marine strain under exposure to different salinities (3, 7.5, 15 and 30 psu) through the analyses of growth, morphology, chlorophyll a fluorescence, floridean starch properties, and mucilage composition. In 3 psu, the cultures consisted of solitary cells whereas the typical pseudofilamentous morphology of increasing length was found at higher salinities. The species grew in the whole range of salinities, although growth response together with photosynthetic efficiency were maximum in full seawater. The maximum relative electron transport rate (rETR) was significantly lower under hyposaline conditions, concomitant with the increase in photophysical decay but not in non-photochemical quenching of chlorophyll fluorescence (NPQ). Higher phycocyanin content at the highest salinity tested (30 psu) could be related to a more efficient energy transfer to the reaction centre. The amylopectin:amylose ratios were higher in 7.5 and 30 psu. Agarans extracted at different salinities showed similar sulphation degrees, but there was an increase in xylose content in the mucilage from lower salinities. This could be related to a change in physical properties of the sheath polysaccharide, yielding a polymer with lower gelling capacity which hampered the formation and/or elongation of pseudofilaments.

An arid-semiarid climate during the Noachian-Hesperian transition in the Huygens region, Mars: Evidence from morphological studies of valley networks

Fluvial activities play important roles in the geologic evolution of early Mars. As one of the most ancient fluvial features on Mars, the widely distributed valley networks (VNs) provide clues for understanding the early martian climate. Our study focuses on the morphological and hydrological features of VNs around the Huygens basin in the ancient southern highland. A total of 198 VNs are identified in the Huygens region with a total length of 23,991.6 km, among which 83 VNs are firstly identified. VNs possess drainage patterns of dendritic to parallel, and show average stream order of 2.45 with a maximum of 5, suggesting a simple branching morphology. Sinuosity indexes of mainstreams range from 1.02 to 1.98 with an average of 1.15, exhibiting a straight to winding form. Two types of VN channels are observed with distinct elevational distribution, headwater morphology, and longitudinal profile shape, and are considered to be sapping-related and surface runoff-related, respectively. Age estimations from crater size-frequency distribution measurements suggest that VN activities at the basin rim mainly started around the Noachian/Hesperian boundary at ~3.7 Ga, and decayed near the Early/Late Hesperian boundary. VNs at the basin floor show a younger age of ~3.5 Ga, which supports a potential short-lived lake inside the basin during the Noachian-Hesperian transition. A combined effect of rainfall and groundwater is considered as the dominant water sources of VNs in the Huygens region, with the climate condition characterized by transient warm and arid-semiarid periods under a possibly cold and arid environment.

Design and manufacturing of monolithic mechanical metastructures governing ultrawide low frequency three-dimensional bandgaps

The design and manufacturing of innovative monolithic mechanical metastructures capable of inducing ultrawide low-frequency subwavelength bandgaps, incorporating simple structure morphology and reliable performance, have received enormous attention amongst the scientific community due to the marvellous dynamic characteristics and their potential industrial application in vibration and noise control technology. Specifically, more emphasis is devoted to the mechanical and dynamical properties and innovative design of phononic structures, which leads to periodic systems with unprecedented mechanical and effective medium properties, including ultrawide bandgaps. The present study proposes two types of easily manufacturable 3-D monolithic mechanical metastructure designs, which possess the ability to induce ultrawide low frequency three-dimensional (3-D) complete bandgaps. Employing the principle of mode separation and numerical modal analysis through two different FEM codes, the generation mechanism of ultrawide bandgaps is examined and discussed. The finite supercell structure for both designs is created and numerical frequency response study is performed to validate the claimed properties. The 3-D prototypes are prepared by additive manufacturing technology and vibration tests are performed to confirm the wave attenuation over a broadband frequency range. Both numerical and experimental results are compared and possible discrepancies are discussed. The proposed monolithic metastructures can undoubtedly be manufactured by the conventional additive manufacturing technology, with potential applications in metadevices, where low frequency ultrawide multi-directional vibrations and noise control is desirable. Furthermore, the proposed designs can be employed for underwater acoustic wave manipulation and design of metasurfaces to be embedded at the water surface for ultrahigh transmission of acoustic waves at the water-air interface. • Additively manufactured metastructure designs, governing low-frequency ultrawide 3-D bandgaps, are studied. • Based on the principle of mode separation, the bandgap generation mechanism is examined and discussed. • Two finite element analysis codes are utilised for the numerical study to investigate the performance of ultrawide bandgaps. • Vibration test is performed on 3-D printed prototypes, which validates the efficacy of vibration attenuation. • Proposed metastructures can be deployed for elastic and acoustic waves manipulation over an ultrawide frequency range.