分类： 生物学 >> 植物学 提交时间： 2017-07-13
摘要： The pollen morphology of 48 species and two varieties, representing 18 genera of the family Annonaceae from Thailand, is described and illustrated based on observations with scanning electron microscopy (SEM). The results reaffirm the great diversity in Annonaceae at the pollen morphological level, with the size of pollen varying from small, medium-sized to large, the shape of monads being elliptic, spheroidal or triangular with monosulcate, disulculate or no visible aperture, and the shape of tetrads being tetragonal, rhomboidal, tetrahedral, T-shaped or decussate. Ornamentation is echinate, psilate, microreticulate, rugulate, scabrate or verrucate. Decussate tetrads in Goniothalamus, and tetragonal, rhomboidal, T-shaped and decussate tetrads and new tetrad type in Mitrephora are first reported. The pollen grains of Anaxagorea show slightly bilateral and no visible aperture as a result of intine extrusion. The palynological evidence confirms the close relationship of Dasymaschalon, Desmos and Asian Friesodielsia, and shows the high diversity of pollen morphology within genera in Annonaceae.
分类： 地球科学 >> 地质学 提交时间： 2017-08-24 合作期刊: 《古脊椎动物学报》
摘要： Regalerpeton weichangensis was established in 2009 on an incomplete skeleton preserved mainly as an impression from the Lower Cretaceous of Hebei, China. However, several anatomical characters were misinterpreted due to distortion of the holotype, and its taxonomic position has been in debate. In this paper, R. weichangensis is redescribed based on eight new specimens and its diagnosis and phylogenetic position are re-examined. This work shows that R. weichangensis was a neotenic form with ossified carpals and tarsals. It has a series of unique combination of characteristics including the vomer with a transverse vomerine tooth row, anterior end of the cultriform process of the parasphenoid indented, basibranchial II triradiate and scapulocoracoid with a rectangular coracoid end. Phylogenetic analysis suggests Regalerpeton, Jeholotriton and Pangerpeton should be placed in the suborder Salamandroidea with three synapomorphies. Moreover, they also share unicapitate ribs with Cryptobranchoidea, which indicates that they represent an important stage of evolution in the Cryptobranchoidea-Salamandroidea split. 围场皇家螈(Regalerpeton weichangensis)于2009年基于一件产自河北围场下白垩统不完整的骨骼印痕标本命名。然而由于标本变形导致皇家螈的部分解剖学特征被曲解，系统发育位置也存在争论。本文基于八件新标本对该蝾螈的鉴定特征和系统发育位置进行了修订。研究显示，皇家螈是一种腕骨和跗骨骨化的幼态持续型蝾螈，具有独特的特征组合，包括犁骨齿列横向排列、副蝶骨前端呈齿状、基鳃骨II呈三射型以及肩胛乌喙骨的乌喙端呈矩形。新的系统发育分析根据三个近裔共性将围场皇家螈、热河螈和胖螈归入蝾螈亚目。此外，它们还与隐鳃鲵亚目共有“肋骨单关节头”这一特征，显示这三种蝾螈可能代表了隐鳃鲵亚目与蝾螈亚目分离时期这一重要演化阶段。
分类： 生物学 >> 人类学 提交时间： 2024-03-06
摘要： The inference of Mesozoic avialan bird diets previously relied on traditional methods such as morphological comparisons among taxa and direct evidence such as identifiable stomach contents. However, the application of these approaches has been limited because of uncommon preservation of relevant fossil evidence. We searched for additional informative characteristics to help develop new methods to assess the diet of fossil birds. In particular, the morphology of the avialan neck is highly modularized and plays roles in multiple functions including food acquisition. The structure of and variation among the cervical vertebrae likely reflects the demands of feeding ecology in fossil and extant birds because the avialan neck evolved to, at least in part, replace the forelimbs by assisting with activities such as cranioinertial feeding and other ecological functions. Here, we utilize morphometric and statistical analyses to establish an initial quantitative relationship between cervical morphology and dietary modes in both extant and extinct birds. This morphometric framework derived from the cervical morphology of living birds is used as a basis to estimate the diet categories of five taxa of Mesozoic birds. The results indicate that there is a quantitative correlation between cervical morphology differentiation and their interrelated feeding modes. The enantiornithine taxa examined exhibit cervical morphologies similar to extant insectivorous or carnivorous birds. The ornithurine species show cervical morphologies that are more aligned with generalist or herbivorous birds, and exhibit preliminary morphological features tied to aquatic adaptions. These findings are consistent in part with other direct fossil evidence, as well as hypotheses developed from other skeletal comparisons. Therefore, the cervical vertebral series, as a skeletal system closely linked to food acquisition, can serve as one of the valuable metrics to provide information for inferring the diet of long extinct Mesozoic birds.
分类： 机械工程 >> 机械制造工艺与设备 提交时间： 2024-05-12
Munish Kumar Gupta
Hamza El Etri
Mehmet Erdi Korkmaz
Nimel Sworna Ross
Grzegorz M. Krolczyk
Józef Gawlik
Nafiz Yaşar
Danil Yu Pimenov
摘要： Being easily fabricated, welded, biocompatible, having a high strength-to-weight ratio, withstanding comparatively high temperatures up to 800 °C and low modulus of elasticity make grade titanium and its alloys an important choice for automotive, biomedical and aerospace industries. In contempt of the different pleasant assets of Ti–6Al–4V alloy, the operation of this alloy is restricted especially when it comes to tribological and surface morphological characteristics. Enhancing these properties is important, for this purpose, a diversity of attempts and studies have been conducted. This paper mounts a review of morphological and tribological behaviors of titanium alloys including Ti–6Al–4V against different materials counting with carbide tools and other types of materials under dry and lubricated sliding conditions. The surface morphological, wear, and other properties have been discussed in this review article.
分类： 地球科学 >> 地理学 提交时间： 2023-07-17 合作期刊: 《干旱区科学》
摘要：Alpine revegetated dunes have been barely researched in terms of morphological change and migration within its regional aeolian environments. To reveal the sand-fixing and land-reforming mechanisms of artificial vegetation, we observed the morphology and migration of four dunes with four revegetated types (Hippophae rhamnoides Linn., Salix cheilophila Schneid., Populus simonii Carr., and Artemisia desertorum Spreng.) using unpiloted aerial vehicle images and GPS (global positioning system) mapping in 2009 and 2018. Spatial analysis of GIS (geographic information system) revealed that the revegetated dunes exhibited a steady progression from barchan dune shapes to dome or ribbons shapes mainly through knap planation, wing amplification, and slope symmetrization. Generally, conditions of northern aspects, smaller slope degree, and larger altitude of unvegetated dunes would suffer more serious wind erosion. The southward movement of dune wings with a migration speed of 2.0–5.0 m/a and the alternating motion of sand ridges in eastwestern directions led greater stability in revegetated dunes. The moving distances of revegetated dunes remarkably changed in patterns of quadratic or linear function with depositional depth. Compared with unvegetated dunes, the near-surface wind velocity of revegetated dunes decreased by 20%–30%, which led to heavy accumulation in low-flat dunes and erosion in high-steep dunes, but all vegetation species produced obvious sand-fixing benefits (100%–450% and 3%–140% in the lower and higher dune scales of revegetated dunes, respectively) with decreasing sand transport rates and increasing coverages. In practice, the four vegetation species effectively anchored mobile dunes by adapting to regional aeolian environment. However, future revegetation efforts should consider optimizing dune morphology by utilizing H. rhamnoides as a pioneer plant, S. cheilophila and P. microphylla in windward and northward dune positions, and A. desertorum in a sand accumulative southward position. Also, we should adjust afforestation structure and replant some shrub or herbs in the higher revegetated dunes to prevent fixed dune activation and southward expansion.
分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： Poly (methyl methacrylate) (PMMA) pellets are irradiated using 60Co gamma-ray in air and successfully formed by hot pressing at constant conditions. The irradiated PMMA membranes are prepared by supercritical carbon dioxide (scCO2) as a physical blowing agent using the pressure quench method. Effects of foaming conditions such as adsorbed dose, saturation temperature, pressure on the morphology and cell size of the microcellular PMMA membranes are investigated in detail. The results showed that the irradiated PMMA membranes possess spherically closed-cell structure with uniform cell size. They have a high cell density compared with virgin PMMA. The cell size uniformity becomes poor at dose lower than 10 kGy, but increases with the dose at dose higher than 10 kGy. The mean cell diameter is less than 10 m and the cell density increases with increasing dose. The average cell size of irradiated PMMA membranes decreases and cell density increases with increased saturation temperature and pressure. The changes in morphology of membranes are attributed to the gamma-ray radiation and scCO2 synergistic effect.
分类： 生物学 >> 植物学 提交时间： 2022-12-12 合作期刊: 《干旱区科学》
摘要：Leaf traits can directly reflect the adaptation strategies of plants to the environment. However, there is limited knowledge on the adaptation strategies of heteromorphic leaves of male and female Populus euphratica Oliv. in response to individual developmental stages (i.e., diameter class) and canopy height changes. In this study, morphological and physiological properties of heteromorphic leaves of male and female P. euphratica were investigated. Results showed that both male and female P. euphratica exhibited increased leaf area (LA), leaf dry weight (LDW), leaf thickness (LT), net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (gs), proline (Pro), and malondialdehyde (MDA) concentration, decreased leaf shape index (LI) and specific leaf area (SLA) with increasing diameter and canopy height. Leaf water potential (LWP) increased with increasing diameter, LWP decreased significantly with increasing canopy height in both sexes, and carbon isotope fraction (δ13C) increased significantly with canopy height in both sexes, all of which showed obvious resistance characteristics. However, males showed greater LA, LT, Pn, Tr, and Pro than females at the same canopy height, and males showed significantly higher LA, SLA, LT, Pn, Tr, gs, and MDA, but lower LWP and δ13C than females at the same canopy height, suggesting that male P. euphratica have stronger photosynthetic and osmoregulatory abilities, and are sensitive to water deficiency. Moreover, difference between male and female P. euphratica is closely related to the increase in individual diameter class and canopy height. In summary, male plants showed higher stress tolerance than female plants, and differences in Pn, gs, Tr, Pro, MDA, δ13C, and LWP between females and males were related to changes in leaf morphology, diameter class, and canopy height. The results of this study provide a theory for the differences in growth adaptation strategies during individual development of P. euphratica.
分类： 生物学 >> 植物学 提交时间： 2017-07-13
摘要： Premise of research. Comparative development of staminate and pistillate flowers of Pseuduvaria trimera (Annonaceae) is firstly investigated to understand its sexual differentiation and developmental processes of flowers. Comparisons of morphological and anatomical features between mature stamens and staminodes are also described, in order to clarify the mode of anther dehiscence and understand the mechanism underlying the sterility of the staminodes. Methodology. Flowers at different developmental stages and mature stamens and staminodes were examined with SEM and light microscopy. Pivotal results. Flowers have complex whorled phyllotaxis as in other Annonaceae, with double positions in the outmost whorl of reproductive organs and variable stamen and carpel organ numbers per whorl. The stomium region of each theca is composed of the septum and stomium. The septum and stomium cells of stamens could be degenerated developmentally, facilitating anther opening, whereas those of staminodes maintain intact, forming indehiscent anthers. Conclusions. The developmental data suggest that staminate flower is unisexual from inception, while pistillate flower is morphologically hermaphroditic. The morphologically hermaphroditic flowers are nevertheless functionally pistillate as the anthers are indehiscent, and the structural andromonoecy of P. trimera actually functions as monoecy. The mechanism underlying the sterility of the indehiscent staminodes and delayed dehiscent outer stamens might be effective in promoting xenogamy. The occurrence of staminode is closely correlated with the acquisition and evolution of functional unisexual flowers in the genus Pseuduvaria.
分类： 地球科学 >> 地理学 提交时间： 2024-02-21 合作期刊: 《干旱区科学》
摘要： The development of bare patches typically signifies a process of ecosystem degradation. Within the protection system of Shapotou section of the Baotou-Lanzhou railway, the extensive emergence of bare sand patches poses a threat to both stability and sustainability. However, there is limited knowledge regarding the morphology, dynamic changes, and ecological responses associated with these sand patches. Therefore, we analyzed the formation and development process of sand patches within the protection system and its effects on herbaceous vegetation growth and soil nutrients through field observation, survey, and indoor analysis methods. The results showed that sand patch development can be divided into three stages, i.e., formation, expansion, and stabilization, which correspond to the initial, actively developing, and semi-fixed sand patches, respectively. The average dimensions of all sand patch erosional areas were found to be 7.72 m in length, 3.91 m in width, and 0.32 m in depth. The actively developing sand patches were the largest, and the initial sand patches were the smallest. Throughout the stage of formation and expansion, the herbaceous community composition changed, and the plant density decreased by more than 50.95%. Moreover, the coverage and height of herbaceous plants decreased in the erosional area and slightly increased in the depositional lobe; and the fine particles and nutrients of soils in the erosional area and depositional lobe showed a decreasing trend. In the stabilization phases of sand patches, the area from the inlet to the bottom of sand patches becomes initially covered with crusts. Vegetation and 0–2 cm surface soil condition improved in the erosional area, but this improvement was not yet evident in the depositional lobe. Factors such as disturbance, climate change, and surface resistance to erosion exert notable influences on the formation and dynamics of sand patches. The results can provide evidence for the future treatment of sand patches and the management of the protection system of Shapotou section of the Baotou-Lanzhou railway.
分类： 地球科学 >> 地球科学史 提交时间： 2020-06-22 合作期刊: 《干旱区科学》
摘要： Disturbance by rodents alters the morphologies and nutrients of plants as well as the physical-chemical properties of the soils. Changes in plants are considered to be mechanisms of defense against the disturbance by rodents. Rodents gnaw on the assimilating branches of Haloxylon ammodendron (CA Mey.) Bunge and burrow under the bushes in the desert ecosystems of Xinjiang, China. However, eco-physiological responses of different age groups of H. ammodendron to the disturbance by rodents are not well understood. In this study, soil physical-chemical properties under the shrubs and the above-ground morphological, physiological and biochemical features of assimilating branches of H. ammodendron of different age groups (i.e., young, 30−100 cm; middle-aged, 100−200 cm; and mature, >200 cm) in burrowed and non-burrowed (control) areas were studied in 2018. We found that disturbance by rodents significantly increased the crown width and total branching rates of young and middle-aged H. ammodendron. Photosynthetic pigment contents of assimilating branches of H. ammodendron were significantly reduced under the disturbance by rodents. In term of plant nutrients, the main differences among different age groups of H. ammodendron under the disturbance by rodents occurred in the total soluble sugar and reducing sugar contents that decreased in young plants, increased in middle-aged plants, and did not affect in mature plants. Crude protein and phosphorus contents significantly increased, while crude fiber and calcium contents significantly decreased in young plants. Crude fat and calcium contents significantly decreased in middle-aged plants. Soil organic matter (SOM), total nitrogen (TN), available nitrogen (AN) and available potassium (AK) contents in the topsoil (0–20 cm), which are conducive to forming ''fertile islands'', also increased under the disturbance by rodents. In particular, soil AN and AK were the major factors affecting the above-ground morphological characteristics of H. ammodendron in burrowed areas. Overall, the response and defense strategies of H. ammodendron to the disturbance by rodents differed among different age groups, and the effect of the disturbance by rodents on H. ammodendron gradually weakened with the increasing plant age.
分类： 生物学 >> 生物物理学 >> 神经科学 提交时间： 2016-05-11
Liu, Yi
Sun, Zhishan
Duan, Yunxia
Shi, Jingfei
Qi, Zhifeng
Meng, Ran
Sun, Yongxin
Ji, Xunming
Liu, Yi
Liu, Yi
Sun, Zhishan
Zeng, Xianwei
Sun, Shufeng
Chui, Dehua
Chui, Dehua
摘要： Hypoxic preconditioning (HPC) elicits resistance to more drastic subsequent insults, which potentially provide neuroprotective therapeutic strategy, but the underlying mechanisms remain to be fully elucidated. Here, we examined the effects of HPC on synaptic ultrastructure in olfactory bulb of mice. Mice underwent up to five cycles of repeated HPC treatments, and hypoxic tolerance was assessed with a standard gasp reflex assay. As expected, HPC induced an increase in tolerance time. To assess synaptic responses, Western blots were used to quantify protein levels of representative markers for glia, neuron, and synapse, and transmission electron microscopy was used to examine synaptic ultrastructure and mitochondrial density. HPC did not significantly alter the protein levels of astroglial marker (GFAP), neuron-specific markers (GAP43, Tuj-1, and OMP), synaptic number markers (synaptophysin and SNAP25) or the percentage of excitatory synapses versus inhibitory synapses. However, HPC significantly affected synaptic curvature and the percentage of synapses with presynaptic mitochondria, which showed concomitant change pattern. These findings demonstrate that HPC is associated with changes in synaptic ultrastructure. (C) 2014 Wiley Periodicals, Inc.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-12-08
摘要： This paper presents a morphological investigation of the early-type spiral galaxy M81 (NGC 3031) through decomposition by fitting radial profiles of surface brightness using the software GALFIT, aimed at exploring structural components of M81 and quantifying their morphology. In this work, we adopt 6 types of decompositions with different numbers of morphological components, among which the most complicated one contains 5 components such as a bulge, a disk, a pair of outer spiral arms, a pair of inner spiral arms, and a galactic nucleus. The results show that, M81 hosts a classical bulge with the Sersic index 5.0; the morphology and the luminosity for the bulge are almost constant in the different decomposition types. The disk of M81 has the Sersic index 1.2 but the morphology and the luminosity are found sensitive to the inclusion of the inner spiral arms in the decomposition or not. The results of this work indicate that the combination of individual substructures has a considerable impact on the morphology of the galaxy as a mixture. On the basis of the results, the usability of the different types of decomposition is suggested in this work. The three-component decomposition, i.e., bulge + disk + nucleus, is applicable to statistics of large samples of galaxies; more complicated decomposition with spiral arms taken into account is suitable for precise measurements of individual galaxies in small samples. This work is based on the single-band Spitzer-The Infrared Array Camera (IRAC) 4.5 m image. In the future, we will carry out multi-wavelength decomposition, for the purpose of investigating spectral energy distributions and stellar population properties for the galactic substructures, and thereby deduce their formation history and evolution processes.
分类： 地球科学 >> 地理学 提交时间： 2019-06-20 合作期刊: 《干旱区科学》
摘要： Aerial photographs and 3-D laser scans of a 90-m high star dune at the Crescent Moon Spring scenic spot in Dunhuang, China, are used to investigate the changes in dune morphology on timescales from months to decades. The result revealed that relative-equilibrium airflow strength in three wind directions of northeast, west and south was an important condition for the stability of star dunes with limited migration. Transverse and longitudinal airflows exerted a crucial impact on variation processes of star dune morphology. Controlled by transverse airflows, the easterly winds, the east side was dominated by wind erosion; and strong deposition occurred on the south-south-east arm with a maximum deposition rate of 0.44 m/a in the 46-a monitoring period, causing the east side becoming steep and high. Controlled by longitudinal airflows, the westerly winds, the west-north-west side was mainly eroded and the north arm migrated from west to east with a rate of 0.30 m/a, causing the dune slope becoming gentle and elongate. The local air circulation (southerly winds) exerted a significant impact on the development process of the star dune. Due to the influence of human activities, the south side present surface processes from a concave profile to a convex profile in 46 a, which is a potential threat to the Crescent Moon Spring. The results indicate that rehabilitating the airflow field at most is a crucial strategy to the protection of Crescent Moon Spring from burial. Opening up the passage of easterly, westerly and southerly winds through intermediately cutting the protection forest, demolishing the enclosed wall and changing the pavilion into a porous pattern have been suggested to protect the Crescent Moon Spring from burial.
分类： 生物学 >> 植物学 提交时间： 2018-03-29 合作期刊: 《广西植物》
摘要： Based on the reliable flowering specimens collected from some populations of Phyllostachys in eastern China, field investigations and anatomical observations, the morphological characteristics of the inflorescence, pseudospikelet and floret of four species within this genus, Ph. dulcis McClure, Ph. longiciliata G. H. Lai, Ph. purpureociliata G. H. Lai and Ph. yunhoensis S. Y. Chen et C. Y. Yao, were described and supplemented, and the photos of flowering branchlets and inflorescences showing main characters were provided. All the vouchers were deposited in Herbarium of Guangde Forestry Institute, Anhui Province (GDFI).
分类： 核科学技术 >> 核材料与工艺技术 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： In this study, strains of Aspergillus niger 4# for hyper citric acid were irradiated to different doses by 80 MeV/u 12C6+ ion beams. Seven mutant strains showed marked citric acid over-production records and faster productivity than initial Aspergillus niger 4# by shaking flash fermentation. The maximum product yield was 132.8 -g L-1( the H4002 strain) being a 8.8% increase to the initial strain. The scale-up experiment was carried out in a 100 L bioreactor. The mutant H4002 can accumulate 187 -g L-1 product yield of citric acid from starch liquefying supernatant. The productivity of citric acid was 2.75 g L-1 h-1. So, the mutant H4002 possesses rapid sugar katabolism for producing citric acid. Meanwhile, the pellet morphology kept compact and round during the whole submerged fermentation, which was suited to produce citric acid. The results indicate that mutant H4002 has potential ability to produce citric acid rapidly.
分类： 材料科学 >> 材料科学（综合） 提交时间： 2017-05-09
Pan, LL [Pan, Lulu][ 1 ]
Ban, JF [Ban, Jianfeng][ 3 ]
Lu, SR [Lu, Shaorong][ 1 ]
Chen, GX [Chen, Guoxin][ 2 ]
Yang, J [Yang, Jin][ 1 ]
Luo, QY [Luo, Qiyun][ 1 ]
Wu, LY [Wu, Linyan][ 1 ]
Yu, JH [Yu, Jinhong][ 1,2 ]
摘要： Perylene tetracarboxylic anhydride (PTCDA) was reacted with 6-aminocaproic acid to form the corresponding perylene bisimide (PBI). PBI was used as the foundation for oligomerisation of glycidol in a ring-opening reaction of glycidol leading to a hyper branched, water-soluble glycidol derivative of perylene (PBI-HPG). PBI-HPG was bound to the reduced graphene oxide via p–p stacking resulting in a compound termed PBI-HPG/RGO. The structure and morphology of PBI-HPG/RGO were investigated by infrared spectroscopy (FT-IR), wide angle X-ray diffractometry (WAXD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). PBI- HPG/RGO was blended at different loadings in order to improve the thermal and mechanical properties of epoxy composites. The maximum Tg of the epoxy composites was about 20 C and the decomposition temperature (Td) was 26 C higher than that of neat epoxy. The incorporation of PBI- HPG/RGO yields a material with an impact strength of 39.6 kJ m 2 and a tensile strength at 0.7 wt%. It increased by 50.8% and 62.3%, respectively, compared to the neat epoxy.
提交时间： 2017-05-02
Li, Y [Li, Ya][ 1,2 ]
Zhou, J [Zhou, Jian][ 1 ]
Zhang, JQ [Zhang, Jianqiang][ 1 ]
Gou, QT [Gou, Quting][ 1 ]
Gu, Q [Gu, Qun][ 1 ]
Wang, ZB [Wang, Zongbao][ 3 ]
摘要： Melt crystallization of PEO-b-PCL thin films was conducted under compressed CO2 and the morphology of the spherulites obtained at various pressures was investigated by polarizing optical microscopy [POM] and atomic force microscopy [AFM]. At 3 MPa CO2 cla
分类： 生物学 >> 动物学 提交时间： 2021-11-26 合作期刊: 《古脊椎动物学报》
摘要： The Qaidam Basin is a key area for understanding the paleoenvironmental and faunal history of the Tibetan Plateau. The fossil schizothoracine fish, Hsianwenia wui, evolved extraordinarily thickened bones to adapt to the aridification of the Qaidam Basin during the Pliocene. However, the nature of the bone thickening itself remains elusive. To promote the further investigation of the physiological mechanism of the pachyostosis and the phylogenetic interrelationships of Hsianwenia and all relevant cyprinids, here we present a comprehensive morphological study of Hsianwenia. We have new information on the anterior part of the cranial cavity, a large supraneural 3 in the Weberian apparatus, numerous procurrent caudal fin rays supported by the preural centrum (Pu) 5, and a neural arch on Pu2. We also find the differentiated pattern of the bone-thickening: the pachyostosis exists in the endoskeleton but not in the dermal skeleton; it is more obvious in ventral bones than in dorsal ones, when the thickening is present in the dorsally and ventrally grouped endoskeletal bones (e.g., the epineural and epipleural intermuscular bones). Considering the integrity of musculoskeletal system manipulating the chewing activities, we suspect that the thickened pharyngeal jaws and the hard food processing might be associated with the unique hind protrusion (cleithral “humeral” process) of the dermal pectoral girdle of Hsianwenia.
分类： 地球科学 >> 地质学 提交时间： 2024-06-21 合作期刊: 《干旱区科学》
摘要： Quantifying surface cracks in alpine meadows is a prerequisite and a key aspect in the study of grassland crack development. Crack characterization indices are crucial for the quantitative characterization of complex cracks, serving as vital factors in assessing the degree of cracking and the development morphology. So far, research on evaluating the degree of grassland degradation through crack characterization indices is rare, especially the quantitative analysis of the development of surface cracks in alpine meadows is relatively scarce. Therefore, based on the phenomenon of surface cracking during the degradation of alpine meadows in some regions of the Qinghai-Tibet Plateau, we selected the alpine meadow in the Huangcheng Mongolian Township, Menyuan Hui Autonomous County, Qinghai Province, China as the study area, used unmanned aerial vehicle (UAV) sensing technology to acquire low-altitude images of alpine meadow surface cracks at different degrees of degradation (light, medium, and heavy degradation), and analyzed the representative metrics characterizing the degree of crack development by interpreting the crack length, length density, branch angle, and burrow (rat hole) distribution density and combining them with in situ crack width and depth measurements. Finally, the correlations between the crack characterization indices and the soil and root parameters of sample plots at different degrees of degradation in the study area were analyzed using the grey relation analysis. The results revealed that with the increase of degradation, the physical and chemical properties of soil and the mechanical properties of root-soil composite changed significantly, the vegetation coverage reduced, and the root system aggregated in the surface layer of alpine meadow. As the degree of degradation increased, the fracture morphology developed from "linear" to "dendritic", and eventually to a complex and irregular "polygonal" pattern. The crack length, width, depth, and length density were identified as the crack characterization indices via analysis of variance. The results of grey relation analysis also revealed that the crack length, width, depth, and length density were all highly correlated with root length density, and as the degradation of alpine meadows intensified, the underground biomass increased dramatically, forming a dense layer of grass felt, which has a significant impact on the formation and expansion of cracks.
提交时间： 2017-03-30
摘要： The combinative effects of thermal annealing and additive processes on the performance of all-polymer bulk heterojunction (BHJ) solar cells with composites of different donor polymers (PTQ1, P3HT, PTB7-Th) and poly[1,8-bis(dicarboximide)-2,6-diyl)-alt-5,5
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