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1
Shi, Yun, e Mark von Itzstein. "How Size Matters: Diversity for Fragment Library Design". Molecules 24, n. 15 (5 agosto 2019): 2838. http://dx.doi.org/10.3390/molecules24152838.
Testo completoAbstract (sommario):
Fragment-based drug discovery (FBDD) has become a major strategy to derive novel lead candidates for various therapeutic targets, as it promises efficient exploration of chemical space by employing fragment-sized (MW < 300) compounds. One of the first challenges in implementing a FBDD approach is the design of a fragment library, and more specifically, the choice of its size and individual members. A diverse set of fragments is required to maximize the chances of discovering novel hit compounds. However, the exact diversity of a certain collection of fragments remains underdefined, which hinders direct comparisons among different selections of fragments. Based on structural fingerprints, we herein introduced quantitative metrics for the structural diversity of fragment libraries. Structures of commercially available fragments were retrieved from the ZINC database, from which libraries with sizes ranging from 100 to 100,000 compounds were selected. The selected libraries were evaluated and compared quantitatively, resulting in interesting size-diversity relationships. Our results demonstrated that while library size does matter for its diversity, there exists an optimal size for structural diversity. It is also suggested that such quantitative measures can guide the design of diverse fragment libraries under different circumstances.
2
Maldonado-Coelho, Marcos, e Miguel Â. Marini. "Effects of Forest Fragment Size and Successional Stage on Mixed-Species Bird Flocks in Southeastern Brazil". Condor 102, n. 3 (1 agosto 2000): 585–94. http://dx.doi.org/10.1093/condor/102.3.585.
Testo completoAbstract (sommario):
Abstract We analyzed patterns of species richness, size, structure, and composition of mixed-species flocks in relation to forest fragment size and forest successional stage during dry and rainy seasons, at the state of Minas Gerais, southeastern Brazil. Three forest fragments (1.7, 50, and 200 ha) were used for fragment size analysis, and two fragments (200 and 300 ha) were used for successional stage analysis. Fragment size and season affected flock richness, size, stability, and composition. In the 1.7-ha fragment, flock species richness, size, and stability were significantly different only during the rainy season. Fragment successional stage also influenced flock richness and size, although season did not. Flock composition also had changes related to fragment successional stage. Fragment geometry seems to be an important factor influencing flock structure and composition.
3
Calle-Rendón, Bayron R., Renato R. Hilário e José Julio de Toledo. "Effect of Site Attributes and Matrix Composition on Neotropical Primate Species Richness and Functional Traits: A Comparison Among Regions". Diversity 11, n. 5 (25 maggio 2019): 83. http://dx.doi.org/10.3390/d11050083.
Testo completoAbstract (sommario):
Fragmentation threatens biodiversity and forest-dwelling animals can be especially vulnerable. Neotropical primates inhabit forests and play ecological roles in maintaining forest biodiversity. Currently, many primate communities are restricted to forest fragments. We (1) evaluated the influence of environmental, matrix, and site attributes on species richness and functional traits of primates in the Neotropics; and (2) evaluated the effect of the sub-region on the relationships between primates and environmental, matrix, and site attributes. We conducted literature searches to find published data on primate communities in forest fragments throughout the Neotropics. Each fragment was assigned to 1 of 11 sub-regions: Mesoamerica, Tumbes-Chocó-Magdalena, Caribbean, Orinoco, Amazon, Atlantic Forest, Cerrado, Chaco, Andes, Caatinga, and Pampa. Based on actual and expected species occurrences, we calculated the proportion of primate species retained in the fragments, the mass retained, and dietary items retained considering reproductive and vegetative plant parts and prey. We used linear mixed models to correlate primate variables with environmental, matrix, and site attributes. Fragment area was more important for primate retention than environmental, matrix, and site attributes, with primate retention being higher in larger fragments. Fragment size was positively correlated with all primate variables, except for retention of prey consumption, whose retention decreased as water bodies and density of buildings in the matrix increased. Fragments within protected areas retained larger species than unprotected fragments. The proportion of extant mass retained and vegetative plant parts in the diet were highest in Mesoamerica and lowest in the Atlantic Forest. Conservation planning of Neotropical primates should consider both the differences among sub-regions, forest restoration to increase fragment size, and the creation of new protected areas, even in fragmented landscapes.
4
Shi, Yun, e Mark von Itzstein. "How Size Matters: Designing Diverse Fragment Libraries for Novel Drug Discovery". Proceedings 22, n. 1 (14 novembre 2019): 107. http://dx.doi.org/10.3390/proceedings2019022107.
Testo completoAbstract (sommario):
Fragment-based drug discovery (FBDD) has become a major strategy to derive novel lead candidates for both new and established therapeutic targets, as it promises efficient exploration of chemical space by employing fragment-sized (MW 300) compounds. One of the first challenges in implementing a FBDD approach is the design of a fragment library, and more specifically, the choice of its size and individual members. In order to construct a library that maximises the chances of discovering novel chemical matter, a large number of fragments with sufficient structural diversity are often sought. However, the exact diversity of a certain collection of fragments remains elusive, which hinders direct comparisons among different selections of fragments. Building upon structural fingerprints that are commonly utilised in cheminformatics, we herein introduced quantitative measures for the structural diversity of fragment libraries. Structures of commercially available fragments were retrieved from the ZINC database and filtered by physicochemical properties, after which they were subject to selections with library sizes ranging from 100 to 100,000 compounds. The selected libraries were evaluated and compared quantitatively, resulting in interesting size-diversity relationships. Our results suggested the existence of an optimal size for structural diversity and demonstrated that such quantitative measures can guide the design of diverse fragment libraries under various circumstances
5
Kostia, Silja, Jukka Palo e Sirkka-Liisa Varvio. "DNA sequences of RAPD fragments in artiodactyls". Genome 39, n. 2 (1 aprile 1996): 456–58. http://dx.doi.org/10.1139/g96-057.
Testo completoAbstract (sommario):
A bovine RAPD profile, generated by a 10-mer primer, was analysed by sequencing the major fragments. Three of four different fragments showed homologies to previously characterized mammalian sequences. One was 61–66% identical to LINE sequences and another was 78.5% identical to a human chromosome 2 sequence tagged site. The third fragment was 93.1% identical to the human type 2 inositol 1,4,5-trisphosphate receptor gene. This fragment had counterparts in white-tailed deer and reindeer; fragments of slightly different size in these species showed high sequence similarity and the size differences were due to varying numbers of dinucleotide microsatellite repeats inside the fragment. Key words : RAPD, artiodactyls, sequence similarity, microsatellites, type 2 inositol 1,4,5-trisphosphate receptor.
6
Fernández-Juricic, Esteban. "Local and Regional Effects of Pedestrians on Forest Birds in a Fragmented Landscape". Condor 102, n. 2 (1 maggio 2000): 247–55. http://dx.doi.org/10.1093/condor/102.2.247.
Testo completoAbstract (sommario):
Abstract I assessed the effects of pedestrians on the distribution of forest bird species in wooded parks in the city of Madrid within and between fragments. Within fragments, increasing levels of pedestrians reduced species richness and overall abundance of individuals within circular plots. The abundance of foraging individuals of four species (Magpies Pica pica, Blackbirds Turdus merula, Starlings Sturnus unicolor, and Woodpigeon Columba palumbus) diminished when pedestrians walked near sampling plots, as well as their breeding densities in relation to increasing disturbance levels. Between fragments, after controlling for fragment size effects, pedestrian rate was negatively related to species richness in two breeding seasons. Species turnover was positively associated to mean pedestrian rate and inter-annual variability in pedestrian rate. At the species level, pedestrian rate negatively affected the probabilities of fragment occupation of 16 species beyond the effects of fragment size and isolation. Locally, the short-term behavioral responses to visitors may reduce the suitability of highly disturbed parks in such a way as to decrease breeding densities and the probabilities of fragment occupation and persistence. The effects of human disturbance in fragmented landscapes should be incorporated into management decisions as another relevant factor that may reduce habitat quality.
7
Messick, Joanne B., Geoffrey Smith, Linda Berent e Sandra Cooper. "Genome size ofEperythrozoon suisand hybridization with 16S rRNA gene". Canadian Journal of Microbiology 46, n. 11 (1 novembre 2000): 1082–86. http://dx.doi.org/10.1139/w00-088.
Testo completoAbstract (sommario):
The genome size of Eperythrozoon suis, an unculturable haemotropic mycoplasma, was estimated using pulsed-field gel electrophoresis (PFGE). Gamma irradiation was used to introduce one (on the average) double-strand break in the E. suis Illinois chromosome. Restriction enzymes that cut infrequently were also used to analyze genome size. The size estimate for the full-length genome was 745 kilobases (kb), whereas the size estimates based on the summation of restriction fragments ranged from 730 to 770 kb. The 16S rRNA gene was located on the 120-kb MluI fragment, 128-kb NruI fragment, 25-kb SacII fragment, and 217-kb SalI fragment by Southern blotting.Key words: Eperythrozoon suis, 16S rRNA, Mycoplasma pneumoniae group, pulsed-field gel electrophoresis, genome size.
8
Vinnikov, Vladimir, Maria Gritsevich e Leonid Turchak. "Shape estimation for Košice, Almahata Sitta and Bassikounou meteoroids". Proceedings of the International Astronomical Union 10, S306 (maggio 2014): 394–96. http://dx.doi.org/10.1017/s1743921314013519.
Testo completoAbstract (sommario):
AbstractThis paper is concerned with a meteoroid shape estimation technique based on statistical laws of distribution for fragment masses. The idea is derived from the experiments that show that brittle fracturing produces multiple fragments of size lesser than or equal to the least dimension of the body. The number of fragments depends on fragment masses as a power law with exponential cutoff. The scaling exponent essentially indicates the initial form of the fragmented body. We apply the technique of scaling analysis to the empirical data on the mass distributions for Košice, Almahata Sitta and Bassikounou meteorites.
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Cho, Sang Ho, Masaaki Nishi, Masaaki Yamamoto e Katsuhiko Kaneko. "Fragment Size Distribution in Blasting". MATERIALS TRANSACTIONS 44, n. 5 (2003): 951–56. http://dx.doi.org/10.2320/matertrans.44.951.
Testo completo
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Mouliere, Florent, Dineika Chandrananda, Anna M. Piskorz, Elizabeth K. Moore, James Morris, Lise Barlebo Ahlborn, Richard Mair et al. "Enhanced detection of circulating tumor DNA by fragment size analysis". Science Translational Medicine 10, n. 466 (7 novembre 2018): eaat4921. http://dx.doi.org/10.1126/scitranslmed.aat4921.
Testo completoAbstract (sommario):
Existing methods to improve detection of circulating tumor DNA (ctDNA) have focused on genomic alterations but have rarely considered the biological properties of plasma cell-free DNA (cfDNA). We hypothesized that differences in fragment lengths of circulating DNA could be exploited to enhance sensitivity for detecting the presence of ctDNA and for noninvasive genomic analysis of cancer. We surveyed ctDNA fragment sizes in 344 plasma samples from 200 patients with cancer using low-pass whole-genome sequencing (0.4×). To establish the size distribution of mutant ctDNA, tumor-guided personalized deep sequencing was performed in 19 patients. We detected enrichment of ctDNA in fragment sizes between 90 and 150 bp and developed methods for in vitro and in silico size selection of these fragments. Selecting fragments between 90 and 150 bp improved detection of tumor DNA, with more than twofold median enrichment in >95% of cases and more than fourfold enrichment in >10% of cases. Analysis of size-selected cfDNA identified clinically actionable mutations and copy number alterations that were otherwise not detected. Identification of plasma samples from patients with advanced cancer was improved by predictive models integrating fragment length and copy number analysis of cfDNA, with area under the curve (AUC) >0.99 compared to AUC <0.80 without fragmentation features. Increased identification of cfDNA from patients with glioma, renal, and pancreatic cancer was achieved with AUC > 0.91 compared to AUC < 0.5 without fragmentation features. Fragment size analysis and selective sequencing of specific fragment sizes can boost ctDNA detection and could complement or provide an alternative to deeper sequencing of cfDNA.
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HARRINGTON, G. N., A. N. D. FREEMAN e F. H. J. CROME. "The effects of fragmentation of an Australian tropical rain forest on populations and assemblages of small mammals". Journal of Tropical Ecology 17, n. 2 (marzo 2001): 225–40. http://dx.doi.org/10.1017/s0266467401001158.
Testo completoAbstract (sommario):
Small mammals were trapped in four rain forest fragments (3, 8, 20 and 97 ha), in an agricultural landscape, and in comparable continuous tropical rain forest in north Queensland, Australia over 2 y. The most frequently captured species were four murid rodents. Melomys cervinipes were captured in similar numbers in both continuous and fragmented forest. This species achieves greatest abundance at forest edges and this study suggests that edges of fragments and edges of continuous forest will support similar densities. Abundance of Uromys caudimaculatus was positively correlated with size of fragment and peaked in continuous forest. This species had a home range larger than the smaller fragments and was thus disadvantaged but its ability to utilize the agricultural matrix between fragments mitigated the effect. Rattus leucopus and R. fuscipes were most abundant in fragments and continuous forest respectively but both species occurred in similar abundance in the 97-ha fragment. This suggests their population size is related to habitat rather than competitive exclusion as previously postulated. Ordination of the populations of the nine most commonly captured mammals, separated the fragment and continuous sites but placed the largest fragment closest to the continuous sites. The contrasting response of the two Rattus spp. was the primary influence on the ordination. Second in importance was Trichosurus vulpecula, a folivorous possum, which was absent from the continuous sites. The fragments may have had more nutrient-rich, pioneer tree foliage than continuous forest. Isoodon macrourus, Perameles nasuta, Antechinus godmani and Uromys hadrourus also showed positive or negative response to fragmentation. Species utilizing the matrix between forest fragments and species adapted to forest edge are advantaged by the fragmentation process whereas forest specialists tend to extinction in fragments, particularly where the home range of the animal is not many times smaller than the fragment.
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Röschard, Jacqueline, e Flavio Roces. "Fragment-size determination and size-matching in the grass-cutting ant Atta vollenweideri depend on the distance from the nest". Journal of Tropical Ecology 19, n. 6 (24 ottobre 2003): 647–53. http://dx.doi.org/10.1017/s0266467403006047.
Testo completoAbstract (sommario):
Fragment-size determination by workers of the grass-cutting ant Atta vollenweideri and the extent of size-matching between ant size and fragment size were investigated as a function of the distance from the nest. Foragers and their loads were sampled in four different sectors along a 30-m foraging trail in the field: directly on the harvested source, in the patch, on the trail and close to the nest. Ants sampled on the source immediately after cutting were significantly larger than carrying ants on any trail sector, whereas body mass did not differ among other samples. Thus, foraging was partitioned into at least two stages, with large ants cutting the source and smaller ants carrying the fragments to the nest. Fragments collected directly after cutting were significantly larger than those carried on the trail, indicating that the fragments were cut once again on their way to the nest. Size-matching depended on the trail sector considered. It was stronger in ants sampled closer to the nest, suggesting that carriers either collect dropped fragments according to their body mass, or cut fragments out of the dropped fragments in sizes corresponding to their body mass prior to transport.
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Röschard, Jacqueline, e Flavio Roces. "Sequential Load Transport in Grass-Cutting Ants (Atta vollenweideri): Maximization of Plant Delivery Rate or Improved Information Transfer?" Psyche: A Journal of Entomology 2011 (2011): 1–10. http://dx.doi.org/10.1155/2011/643127.
Testo completoAbstract (sommario):
Sequential transport of plant fragments was studied in the grass-cutting antAtta vollenweideri. Two competing hypotheses concerning its occurrence were tested. Based on the “economic-transport hypothesis," sequential transport occurs because of a mismatch between load size and ant body size, and it is therefore considered a way to improve size-matching and so the plant delivery rate. Alternatively, the “information-transfer hypothesis" states that sequential transport improves the information flow during foraging. By transferring its load, a worker may return earlier to the foraging site so as to intensify chemical recruitment. To distinguish between these two competing hypotheses, standardized paper fragments that differed either in size or in quality were presented to workers of a field colony, and sequential transport was quantified. Neither an increase in fragment mass nor in fragment length influenced the occurrence of transport chains. Sequential transport took longer than transport by a single carrier. However, the occurrence of sequential transport increased with increasing fragment quality. High-quality fragments were transferred more frequently and after shorter distances than less-attractive fragments. Taken together, these results strongly support the hypothesis that sequential load transport has been favoured during evolution because of an improvement in the information flow during foraging.
14
Xiao, Songqiang, Zhaolong Ge, Yiyu Lu, Zhe Zhou, Qian Li e Lei Wang. "Investigation on Coal Fragmentation by High-Velocity Water Jet in Drilling: Size Distributions and Fractal Characteristics". Applied Sciences 8, n. 10 (19 ottobre 2018): 1988. http://dx.doi.org/10.3390/app8101988.
Testo completoAbstract (sommario):
Water jet drilling (WJD) technology is a highly efficient method to extract coalbed methane from reservoirs with low permeability. It is crucial to efficiently remove the coal fragments while drilling. In this study, to disclose coal fragmentation features and size distributions under water jet impact in drilling, the image processing method was utilized to obtain the geometric dimensions of coal fragments. The size distributions, morphologies and fractal characteristics of coal fragmentation were studied based on generalized extreme value distribution and fractal theory. The effects of the jet impact velocity and coal strength on the fragmentation features were analyzed. The results show that fine particles dominate the coal fragments in WJD for coal seams with various strengths. In experiments conducted at the Fengchun coal mine, owing to the higher coal strength of the M7 coal seam, the fragmentation degree of coal subjected to water jets during WJD is lower in the M7 coal steam than in the M8 coal seam, which results in a large dominant fragment size and small fractal dimension under the same impact energy. It was found that the higher the jet impact velocity is, the higher the quantity of fragments generated from WJD and the smaller the particle size. The NUM-based cumulative probability distribution curves of coal fragments are more intensive in the range of relatively small particle sizes and then become sparser with the increase in particle size. When the impact velocity increases, (i) the size distribution curves move toward smaller particle sizes, and the dominant fragment size decreases; (ii) the shape (major axis/minor axis) of coal fragments move toward the upper left, and the curve shape for a high impact velocity attains unity more quickly; and (iii) the fractal dimension value increases linearly. In addition, the fractal dimensions are obviously affected by the dominant fragment size; they increase with the decrease in the dominant fragment size. This study can provide a basis for further research on coal fragment transportation in WJD and parameter selection for discharging coal fragments during drilling for CBM development.
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Klass, Keren, Sarie Van Belle, Alvaro Campos-Villanueva, Fernando Mercado Malabet e Alejandro Estrada. "Effects of variation in forest fragment habitat on black howler monkey demography in the unprotected landscape around Palenque National Park, Mexico". PeerJ 8 (10 agosto 2020): e9694. http://dx.doi.org/10.7717/peerj.9694.
Testo completoAbstract (sommario):
Habitat loss and fragmentation are leading threats to biodiversity today, and primates are particularly vulnerable to anthropogenic habitat disturbance. However, few studies have examined how differential effects of variation in forest fragment characteristics on males and females in a primate population may affect demography and population persistence. We quantified the effects of variation in forest fragment characteristics on the within-fragment demography of black howler monkeys (Alouatta pigra) in forest fragments around Palenque National Park, Mexico, and how these effects differed between adult males and females. We quantified forest loss in the landscape between 2000 and 2017, and used a redundancy analysis to examine the effects of 15 variables quantifying fragment dimensions, forest composition and physical structure, and isolation on fragment population size and density, the proportion of adult males and females in the fragment population, and the mean number of adult males and females per group in 34 fragments (N = 393 monkeys). We hypothesized that (i) population size is positively correlated with fragment area, while population density is negatively correlated, and (ii) the composition of fragment populations results from differential effects of fragment variables on adult males and females. Forest cover decreased by 23.3% from 2000 to 2017. Our results showed a significant effect of fragment variables on population demography in fragments, accounting for 0.69 of the variance in the demographic response variables. Population size increased with fragment area and connectivity, while density decreased. Larger, less isolated fragments with better connectivity, characteristics indicative of abundant secondary growth, and those with more diverse vegetation but lower Simpson’s evenness indices tended to have more adult females per group and a higher proportion of adult females in the population. In contrast, fragments that were largely similar in characteristics of forest composition and structure, but that were more isolated from nearby fragments, had more adult males per group and a higher proportion of adult males. These results may stem from black howler females preferentially remaining in natal groups and fragments when possible, and dispersing shorter distances when they disperse, while males may be more likely to disperse between fragments, traveling longer distances through the matrix to more isolated fragments. These differential effects on males and females have important conservation implications: if females are more abundant in larger, less isolated fragments, while males are more abundant in more isolated fragments, then to effectively conserve this population, both landscape connectivity and fragment areas should be maintained and increased.
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Chen, Danqi, Hongjun Yue, Michelle M. Spiering e Stephen J. Benkovic. "Insights into Okazaki Fragment Synthesis by the T4 Replisome". Journal of Biological Chemistry 288, n. 29 (31 maggio 2013): 20807–16. http://dx.doi.org/10.1074/jbc.m113.485961.
Testo completoAbstract (sommario):
In this study, we employed a circular replication substrate with a low priming site frequency (1 site/1.1 kb) to quantitatively examine the size distribution and formation pattern of Okazaki fragments. Replication reactions by the T4 replisome on this substrate yielded a patterned series of Okazaki fragments whose size distribution shifted through collision and signaling mechanisms as the gp44/62 clamp loader levels changed but was insensitive to changes in the gp43 polymerase concentration, as expected for a processive, recycled lagging-strand polymerase. In addition, we showed that only one gp45 clamp is continuously associated with the replisome and that no additional clamps accumulate on the DNA, providing further evidence that the clamp departs, whereas the polymerase is recycled upon completion of an Okazaki fragment synthesis cycle. We found no support for the participation of a third polymerase in Okazaki fragment synthesis.
17
Dantas, S. M., T. M. Sanaiotti e A. L. K. M. Albernaz. "Effects of fragmentation on Thamnophilus stictocephalus (aves, Thamnophilidae) in semideciduous forest of Alter-do-Chão, Pará". Brazilian Journal of Biology 65, n. 3 (agosto 2005): 423–30. http://dx.doi.org/10.1590/s1519-69842005000300007.
Testo completoAbstract (sommario):
Effects of fragmentation on biodiversity have received much attention in recent decades, as fragmentation can greatly reduce viable areas for living organisms. We studied its effect on Thamnophilus stictocephalus (Thamnophilidae), an understory bird, in semideciduous forest fragments in Alter-do-Chão, Santarém, Pará. We tested whether the density of Thamnophilus stictocephalus was a function of fragment size and shape, density of vegetation, or arthropod biomass. Density of Thamnophilus was positively related to fragment size, but not to the other factors analyzed. Arthropod biomass was positively related to fragment size. The density of T. stictocephalus in fragments was significantly higher than it was in continuous forest. Fragmentation processes had a pronounced effect on the relative density of T. stictocephalus.
18
Crawford, David A. "Models of fragment penetration and fireball evolution". International Astronomical Union Colloquium 156 (maggio 1996): 133–56. http://dx.doi.org/10.1017/s0252921100115490.
Testo completoAbstract (sommario):
A new analytical model that is calibrated against numerical simulations performed with the CTH shock physics code provides a useful description of the entry of Periodic Comet Shoemaker-Levy 9 into the Jovian atmosphere. Mass loss due to radiative heating of fragments larger than 100 m in diameter is insignificant because of energy conservation during the ablative process. Nevertheless, radiative ablation is a major contributor to atmospheric energy deposition at high altitude and plays an important role in early-time fireball evolution. The analytical model provides the initial conditions from which fireball and plume evolution can be calculated using CTH. The results from these simulations suggest that if the tops of the plumes originated from a specific level of the Jovian atmosphere then maximum plume heights are independent of fragment size provided the fragments penetrated at least 30 km below this level. If the tops of the plumes originated from the visible cloud tops, then fragment masses greater than 4 x 1012 g, corresponding to 200 m diameter fully dense water ice, are required to explain the observations. If the plumes originated from the NH4SH layer then masses greater than 3 x 1013 g (400 m water ice) are required. The lateral extent and mass of the observable plume are functions of fragment size and contribute to the lateral extent and albedo of the debris patterns after re-impact with the atmosphere. The apparent gap between the central disturbance of the impact site and the inner front of the crescent-shaped ejecta may reflect the fragment's depth of penetration below the source layer of the visible ejecta.
19
Yang, Rui, Xiaodi Wang, Hao Zha, Xiuzhang Yang, Yang Zhang, Gang Huang e Yongjie Yang. "Classification and Fractal Characteristics of Limestone Fragments Obtained in Conventional Compression and Cyclic Loading Tests under Uniaxial and Triaxial Conditions". Advances in Materials Science and Engineering 2020 (24 aprile 2020): 1–16. http://dx.doi.org/10.1155/2020/3802471.
Testo completoAbstract (sommario):
The mechanical response characteristics of rocks under cyclic loading conditions are crucial factors for evaluating and analyzing the stability of rock mass during underground excavation. In this study, based on fractal theory and a series of tests using the MTS815.02 rock mechanics test system, the classification and fractal characteristics of limestone specimen fragments are investigated. The results show that limestone specimens subjected to cyclic loading can generate more small-sized fragments than conventional compression, but the large-fragment-producing abilities of the two tests exhibit small difference. The mass fraction of the fragments in the cyclic loading test is obviously greater than that in the conventional test when the fragment size is less than 4.75 mm; however, only a small difference is observed between the cyclic loading tests with frequencies of 0.25 and 0.5 Hz. In the same type of test, a confining pressure is helpful in reducing the fragmentation of limestone specimen. As the size interval decreases, the shapes of limestone fragment transition from rectangular to long slice and then to square. The results also indicate that the confining pressure has a significant influence on the size-quantity and size-mass fractal dimensions of limestone fragments. The former has a positive correlation with the confining pressure, whereas the latter decreases with confining pressure. The conclusions obtained in this investigation can enrich the theoretical research on the failure response and mechanism of rock under cyclic loading conditions.
20
Åberg, Johan, Jon E. Swenson e Henrik Andrén. "The dynamics of hazel grouse (Bonasa bonasia L.) occurrence in habitat fragments". Canadian Journal of Zoology 78, n. 3 (1 aprile 2000): 352–58. http://dx.doi.org/10.1139/z99-210.
Testo completoAbstract (sommario):
The aim of this study was to evaluate the effects of habitat fragment size and isolation on the dynamics of hazel grouse (Bonasa bonasia L.) occurrence. Habitat fragments surrounded by nonhabitat coniferous forest, in an intensively managed forested landscape, were censused during seven seasons. None of the 33 habitat fragments were occupied in all seven seasons and 7 were never occupied. Turnover occurred in 79% of the habitat fragments. The most common occupation of a habitat fragment was by only one hazel grouse male (84%). Thus, the dynamics of hazel grouse occurrence in the habitat fragments was basically monitored on the scale of individuals. Large and less isolated habitat fragments with a high amount of cover were occupied significantly more often than small, isolated fragments. The effect of size appeared most clearly when analyzing the total number of hazel grouse occupying a habitat fragment. The appearance of hazel grouse in the habitat fragments was best explained by the amount of cover, distance to the nearest suitable habitat, and size of the habitat fragment. The effects of interfragment distance on the occurrence and appearance of hazel grouse implies that the habitat has become functionally disconnected for hazel grouse and suggests that the amount of suitable hazel grouse habitat left in this landscape has fallen below a critical level.
21
Chow, T. L., e H. W. Rees. "Effects of coarse-fragment content and size on soil erosion under simulated rainfall". Canadian Journal of Soil Science 75, n. 2 (1 maggio 1995): 227–32. http://dx.doi.org/10.4141/cjss95-031.
Testo completoAbstract (sommario):
Farmers have long considered coarse fragments a hindrance in potato production. Rock picking or crushing has become a routine operation. Using simulated rainfall events and runoff-erosion plots (1 m × 1 m), the effects of coarse-fragment content (0, 7, 15 and 25% by volume) and size (1.0–1.9, 1.9–5.1 and 5.1–7.6-cm diam) on runoff, infiltration and soil loss were evaluated on an Orthic Dystric Brunisol. Study objectives were to quantify the influence of coarse fragments on soil erosion and to convert these relationships into mathematical equations for use with existing models to predict soil loss. Although there were only marginal increases in infiltration and reductions in runoff attributable to increasing content and size of coarse fragments, the rate of soil loss from the control was higher than that from all other treatments. In general, the rate of soil loss decreased with increasing content and size of coarse fragments. The effects of content and size of coarse fragments on soil-loss reduction, either individually or in combination, were expressed mathematically with correlation coefficients greater than 0.82. The study also revealed that for a given volumetric coarse-fragment content, the percentage surface cover increased with increasing coarse-fragment size. This finding has important practical implications because most reporting of coarse fragments is done on the basis of volume rather than percentage surface cover. Key words: Rock content, rock size, rainfall simulator, infiltration, soil loss
22
Skakov, Мazhyn, Gulzhaz Uazyrkhanova e Natalya Popova. "Electron Microscopic Analysis of 30CrMnSi Steel Surface Layers after Hot Deformation". Applied Mechanics and Materials 395-396 (settembre 2013): 336–41. http://dx.doi.org/10.4028/www.scientific.net/amm.395-396.336.
Testo completoAbstract (sommario):
Using electron microscopy were investigated character of change microdiffraction pattern of fragmented substructure, the relationship between average size micrograins, which forming the diffraction pattern, and the point reflections number on the ring. Also the integrated degree of plastic deformation was assessed in the roll surface layers, made of steel 30CrMnSi during hot deformation. It was shown that the fragments generated during steel deformation considerably disoriented with respect to each other. Formed by heat treatment steel fragments practically is not disoriented. Found that average size of fragments to be achieved in layer at distance of 2 mm from roll surface, for anisotropic fragments amounts to 0.27×0.66 μm, for isotropic - 0.43 μm, average size of fragments - 0.44 μm. Here plastic deformation degree ε0.70. Found that in layer located at distance of 0.5 mm from roll surface, anisotropic fragments have size 0.25×0.56 μm value, for isotropic - 0.39 μm, average fragment size - 0.40 μm. Here plastic deformation degree achieved value ε0.75. It is shown that on roll surface are present only isotropic fragments with average size 0.22 μm. Corresponds to it plastic deformation degree ε0.85.
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Wang, W. X., e F. Bergholm. "Fragment size estimation without image segmentation". Imaging Science Journal 56, n. 2 (aprile 2008): 91–96. http://dx.doi.org/10.1179/174313108x268312.
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Roper, James J., André M. X. Lima e Angélica M. K. Uejima. "Experimental food supplementation increases reproductive effort in the Variable Antshrike in subtropical Brazil". PeerJ 6 (6 novembre 2018): e5898. http://dx.doi.org/10.7717/peerj.5898.
Testo completoAbstract (sommario):
Food limitation may interact with nest predation and influence nesting patterns, such as breeding season length and renesting intervals. If so, reproductive effort should change with food availability. Thus, when food is limited, birds should have fewer attempts and shorter seasons than when food is not limiting. Here we experimentally test that increased food availability results in increased reproductive effort in a fragmented landscape in the Variable Antshrike (Thamnophilus caerulescens) in southern Brazil. We followed nesting pairs in a naturally fragmented habitat and experimentally supplemented food for half of those pairs. Birds were seen, but evidence of nesting was never found in two small fragments, even though these fragments were larger than individual territories. Pairs with supplemented food were more likely to increase clutch size from two to three eggs and tended to renest sooner (20 d on average) than control pairs. Also, fragment size was associated with breeding patterns, although fragment replicates were unavailable. Nest duration, nest success and breeding season length were all greater, while renesting intervals were shorter, in the largest fragments. Simulations showed that only the largest fragments were able to have a net production of young. Food availability clearly influenced reproductive effort and as a consequence, because of the interaction with predation risk, forest fragments of varying sizes will have complex reproductive dynamics.
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Aguirre-Jaimes, Armando, Juan Carlos López-Acosta e Rodolfo Dirzo. "Tropical rainforest fragmentation affects plant species richness, composition and abundance depending on plant-size class and life history". Botanical Sciences 99, n. 1 (27 ottobre 2020): 92–103. http://dx.doi.org/10.17129/botsci.2679.
Testo completoAbstract (sommario):
Background: Tropical rain forests have been impacted by land use change, leading to major deforestation and fragmentation. Understanding how fragmentation impacts plant communities is central for tropical conservation.
Questions: i) How does species richness vary across a range of fragment sizes, and does it vary with plant size-structure? ii) how are species composition and floristic similarity affected by forest fragmentation? iii) does habitat fragmentation affect the representation of species with different life-history and regeneration patterns?
Studied species: We sampled overall plant communities and calculated diversity metrics of mature-forest and light-demanding species, considering plants of different size-categories (defined by diameter at breast height, DBH).
Study site: This study was carried out at Los Tuxtlas, Veracruz, Mexico. An area originally dominated extensive evergreen tropical forest, but currently highly fragmented
Methods: We sampled plants in five forest fragments representing (2 - 36 ha), and a large patch of continuous forest (700 ha). Within each site we established ten-50 × 2 m transects and registered all woody plants with DBH > 1 cm.
Results: Species richness declined as fragment size became smaller. Such decline was significant considering all plants (DBH > 1.0 cm) but became non-significant as plant size-category increased (DBH > 2.5, or > 10 cm.). Small fragments had distinguishable assemblages compared to continuous forest and also a reduction in the representation of mature-forest species compared to light-demanding species.
Conclusions: Our findings confirm that fragmentation affects tropical plant species diversity, but the effect is differential, depending on plant size-category and life history.
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Ouchterlony, Finn. "The Case for the Median Fragment Size as a Better Fragment Size Descriptor than the Mean". Rock Mechanics and Rock Engineering 49, n. 1 (15 marzo 2015): 143–64. http://dx.doi.org/10.1007/s00603-015-0722-1.
Testo completo
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Huang, Yanqin, Jiayi Mu, Lina Qi, Weiting Ge, Xuefeng Fang, Yongmao Song, Ying Yuan e Shu Zheng. "Diverse fragment lengths dismiss size selection for serum cell-free DNA: a comparative study of serum and plasma samples". Clinical Chemistry and Laboratory Medicine (CCLM) 58, n. 9 (27 agosto 2020): 1451–59. http://dx.doi.org/10.1515/cclm-2020-0078.
Testo completoAbstract (sommario):
AbstractBackgroundThe objective of this study was to determine the features of fragment length for circulating cell-free DNA (cfDNA) from plasma and serum samples.MethodsPlasma and serum samples from different sources were randomly collected. Circulating cfDNA was extracted and purified by a precipitation-enriched and spin-column-based kit. The concentration of the purified DNA was immediately measured by a highly sensitive dsDNA quantitative assay, and then the fragment length was analyzed by capillary electrophoresis. The abundance of a specific fragment was estimated by the area under curve (AUC) for the fragment peak in the capillary electrophoresis.ResultsA total of 199 plasma and 117 serum samples were extracted and analyzed. The average yield of cfDNA from the serum samples (131.67 ng/mL) was significantly higher than that from the plasma samples (32.78 ng/mL, p < 0.001). The average abundance of the 20–400 bp fragments in plasma cfDNA (84.4%) was significantly higher than that of serum cfDNA (51.9%, p < 0.001). Fragment peaks in serum cfDNA always presented in regions around 190 bp, 430 bp, and 630 bp, but plasma cfDNA generally showed a sharp peak in the 165–190 bp region and a much lower peak in the 300<uni-2013;400 bp region. Large fragments in plasma cfDNA were longer than 1000 bp and peaked around the 3000<uni-2013;4000 bp region while the large fragments in serum cfDNA were always shorter and peaked around the 1000 bp region.ConclusionsThe fragment lengths of serum cfDNA and plasma cfDNA have very different features. Fragment size selection is suitable for plasma cfDNA but may not apply to serum cfDNA.
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Hyun, Sangwon, e Hyoungshick Kim. "Secure and DoS-Resilient Fragment Authentication in CCN-Based Vehicular Networks". Wireless Communications and Mobile Computing 2018 (2018): 1–12. http://dx.doi.org/10.1155/2018/8071267.
Testo completoAbstract (sommario):
Content-Centric Networking (CCN) is considered as a promising alternative to traditional IP-based networking for vehicle-to-everything communication environments. In general, CCN packets must be fragmented and reassembled based on the Maximum Transmission Unit (MTU) size of the content delivery path. It is thus challenging to securely protect fragmented packets against attackers who intentionally inject malicious fragments to disrupt normal services on CCN-based vehicular networks. This paper presents a new secure content fragmentation method that is resistant to Denial-of-Service (DoS) attacks in CCN-based vehicular networks. Our approach guarantees the authenticity of each fragment through the immediate fragment verification at interim nodes on the routing path. Our experiment results demonstrate that the proposed approach provides much stronger security than the existing approach named FIGOA, without imposing a significant overhead in the process. The proposed method achieves a high immediate verification probability of 98.2% on average, which is 52% higher than that of FIGOA, while requiring only 14% more fragments than FIGOA.
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MARINI, MIGUEL Â. "Effects of forest fragmentation on birds of the cerrado region, Brazil". Bird Conservation International 11, n. 1 (marzo 2001): 13–25. http://dx.doi.org/10.1017/s0959270901001034.
Testo completoAbstract (sommario):
Bird surveys were conducted through observations and mist-netting in six forest fragments in the cerrado region of central Brazil, to evaluate the effects of fragmentation on bird species richness and community composition. Smaller forest fragments had fewer species than larger fragments. The proportion of species in most foraging guilds did not change with forest size, except for that of granivores, which decreased as fragment size increased. The proportion of forest-dependent species increased significantly with increasing fragment size while that of semi-dependent species significantly decreased. Forest-dependent endemic birds, however, were not area sensitive, but appeared to be partially dependent on the flooded forests of the region. Conservation policies for the region should conserve both large and small forest fragments urgently, and flooded forests especially.
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Bayne, Erin, e Keith Hobson. "Relative use of contiguous and fragmented boreal forest by red squirrels (Tamiasciurus hudsonicus)". Canadian Journal of Zoology 78, n. 3 (1 aprile 2000): 359–65. http://dx.doi.org/10.1139/z99-219.
Testo completoAbstract (sommario):
We examined whether forest fragmentation by agriculture influenced the abundance of North American red squirrels (Tamiasciurus hudsonicus) in the southern boreal mixedwood forest of Saskatchewan. During the summers of 1995 and 1997, we determined the relative abundance of red squirrels in 43 forest fragments ranging in size from 0.2 to 82 ha and in 15 sites in nearby contiguous forest. Relative abundance was determined using acoustic point count surveys, in which all squirrel vocalizations were recorded. Within the fragmented agricultural landscape, we found that red squirrel abundance increased slightly with forest-fragment size, whereas the abundance of red squirrels was negatively correlated with the amount of forest cover within 1 km of a site. We also compared squirrel abundance in forest fragments with that in contiguous forest and found that red squirrels were significantly more abundant in forest fragments than in contiguous forest. We speculate that changes in dispersal patterns in fragmented forest habitats, higher squirrel survival in forest fragments, and differences in diet between contiguous and fragmented forest habitats contributed to this pattern. Our results suggest that forest fragmentation may not be particularly detrimental to habitat generalists like the red squirrel. However, an increased abundance of red squirrels in forest fragments may result in negative effects on other species, such as forest songbirds.
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Haab, Brian B., e Richard A. Mathies. "Optimization of Single-Molecule Fluorescence Burst Detection of ds-DNA: Application to Capillary Electrophoresis Separations of 100–1000 Basepair Fragments". Applied Spectroscopy 51, n. 10 (ottobre 1997): 1579–84. http://dx.doi.org/10.1366/0003702971939136.
Testo completoAbstract (sommario):
Methods for optimizing the dye labeling, laser excitation, and data analysis for single-molecule fluorescence burst detection of ds-DNA have been developed and then validated through capillary electrophoresis (CE) separations of 100–1000 basepair (bp) DNA. Confocal microscopy is used to observe fluorescence bursts from individual DNA fragments labeled with the intercalation dye TO6 as they pass through the ∼ 2-μm-diameter focused laser beam. The dye concentration and laser power were optimized by studying fluorescence burst intensities from pBluescript DNA fragments. The optimal TO6 concentration was ≤100 nM, and the optimal laser power was ≤1 mW. Single-molecule counting was then used to detect CE separations of a 100–1000 bp DNA sizing ladder in 3% linear polyacrylamide. Discrete and baseline-resolved fluorescence bursts were observed in bands as small as 100 bp, and the average burst size within each band increased linearly with fragment size. By counting events using a single optimally chosen discriminator level, we achieve maximum signal-to-noise ratio (S/N) for each fragment size. If the discriminator level is ramped linearly with fragment size to achieve a constant detection efficiency, then the number of events properly reflects the relative fragment concentrations.
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Zanette, Liana, e Bert Jenkins. "Nesting Success and Nest Predators in Forest Fragments: A Study Using Real and Artificial Nests". Auk 117, n. 2 (1 aprile 2000): 445–54. http://dx.doi.org/10.1093/auk/117.2.445.
Testo completoAbstract (sommario):
Abstract Area sensitivity in songbirds is commonly attributed to increased nest predation in forest fragments. In 1995 and 1996, we tested whether the nest predators and nesting success of an area-sensitive forest bird, the Eastern Yellow Robin (Eopsaltria australis), varied with fragment size, and we also conducted an artificial nest experiment. The study occurred in two small (55 ha) and two large (>400 ha) forest fragments in a matrix of agricultural land in New South Wales, Australia. Predation accounted for 95% of all failures of 282 robin nests, and the survival of robin nests was negatively correlated with how frequently we observed avian nest predators near nests (i.e. nest-predator activity). Of 461 artificial nests, 84% were depredated, nearly all (99%) by birds. Thus, birds were important predators of nests. The abundance, species richness, and activity of avian nest predators were not related to fragment size. Survival of robin nests averaged 19%; nests in small fragments had a 22% chance of producing at least one fledgling compared with 15% in large fragments, but the difference was not significant. Survival of artificial nests averaged 12% in both small and large fragments. Nest-predator activity accounted for the most variation (68%) in the fate of robin nests, followed by the cumulative density of open-cup nesters (16%). The placement of robin nests had no influence on nest fate. We conclude that nest predation was not area dependent and propose food supply as an alternative hypothesis to explain area sensitivity. We suggest that, rather than being related to fragment size, nest predation increases with decreasing forest cover in a landscape. Increased nest predation in fragmented compared with contiguous landscapes may lower the population viability of songbirds in a region, and hence regional numbers. Therefore, the spatial scale at which fragmentation influences nest predation and songbird populations must be considered carefully.
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Jia, Senqing, Fusheng Wang, Lingjun Yu, Zheng Wei e Bin Xu. "Numerical study on the impact response of aircraft fuselage structures subjected to large-size tire fragment". Science Progress 103, n. 1 (27 settembre 2019): 003685041987774. http://dx.doi.org/10.1177/0036850419877744.
Testo completoAbstract (sommario):
By applying finite element software ANSYS/LS-DYNA, finite element models of front bulkhead and main cabin are established, which aims to assess the dynamic response of fuselage structures impacted by tire fragment under bursting mode. Besides, dynamic characteristics of the two fuselage structures impacted by tire fragment are simulated and critical damage velocities of each working condition are obtained. The results show that composite front bulkhead cannot bear the impact load of front tire fragment at the velocity of 100 m/s, but aluminum alloy front bulkhead can. Main cabin with two properties both can bear the impact loads of front and main tire fragments. When impacted by front tire fragment, critical damage velocity of front bulkhead is approximately half of that of main cabin, while critical damage velocity of aluminum alloy fuselage is larger than that of composite fuselage. However, when impacted by main tire fragment, critical damage velocity of aluminum alloy main cabin is less than that of composite main cabin. Furthermore, maximum contact pressure of composite fuselage is 3–3.3 times than that of aluminum alloy fuselage. The difference in concave deformation is not significant when impacted by front tire fragment, but the difference is great when impacted by main tire fragment.
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Rodrigues, Pablo José Francisco Pena, Rodolfo Cesar Real de Abreu, Eduardo M. B. Barcellos, Haroldo Cavalcante de Lima e Fabio Rubio Scarano. "Population structure and one-year dynamics of the endangered tropical tree species Caesalpinia echinata Lam. (Brazilian red-wood): the potential importance of small fragments for conservation". Rodriguésia 60, n. 1 (marzo 2009): 211–20. http://dx.doi.org/10.1590/2175-7860200960112.
Testo completoAbstract (sommario):
ABSTRACT Caesalpinia echinata Lam. an endangered species, occurs in forest fragments of the Cabo Frio region, in Rio de Janeiro, Brazil. Data from four sub-populations were used to describe local population patterns and one-year dynamics. In each subpopulation, 0.1 ha-plots were set up and all C. echinata trees were mapped, and diameter and height were measured. The fragments sampled had different sizes and were subjected to various degrees of man-made disturbance, representing a succession gradient from an earlier (small fragment) to a later stage (large fragment). We compared the sub-populations as regards density, size structure, spatial distribution, germination and mortality, to identify short-term responses to mechanical injuries (broken stems, sand burial and man-made cuts). Matrix analysis considering the four C. echinata sub-populations together showed a slight tendency for population expansion (λ = 1.0211) if injury patterns do not lead to habitat extinction. On the other hand, sub-populations showed aggregated distribution patterns, particularly at forest edges. Diameter size structure varied from a reversed-J pattern, i.e. seedling abundance in the small fragment (more impacted sub-population) to a uniform plant distribution of size classes in the large one (less impacted sub-population). The sub-population in the smallest fragment showed the highest birth and mortality, in contrast to reduced demographic variation in the largest fragment. Moreover, the smallest fragment also showed the largest seedling stand density and biomass. These data indicate the potential importance of small fragments for the conservation of the Brazilian red-wood.
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Hermanto, Bambang. "The Growht of Acropora Formosa Fragment in Different Sizes Using Transplantation Method in Lembeh Strait". JURNAL ILMIAH PLATAX 3, n. 2 (16 febbraio 2016): 90. http://dx.doi.org/10.35800/jip.3.2.2015.13224.
Testo completoAbstract (sommario):
Transplantation method is an effective way for rehabilitating the degraded coral reef. Acropora formosa is one of the coral species that is used for transplantation method which is a kind of branching corals that have a rapid growth up to 8 cm/year. This study aimed to determine the effect of coral fragment size to the coral growth, survival rate and the growth rate of Acropora formosa at several locations in the Lembeh Strait. The research was conducted in February - June 2015 using concrete block transplantation method. The results showed that Acropora formosa with the initial fragment length 8 cm have the highest of survival rates (84 %), absolute growth (0,8 cm) and growth rate (0,201 cm/month). The initial fragments length of Acropora formosa can affect the coral growth in transplantation method (p <0.05). Keywords: Coral transplantation, Acropora formosa, Fragment size, North Sulawesi ABSTRAK Metode transplantasi merupakan metode yang cukup efektif untuk merehabilitasi kondisi terumbu karang yang mengalami degradasi. Salah satu jenis yang sering digunakan untuk metode transplantasi yaitu jenis Acropora formosa yang merupakan jenis karang bercabang yang memiliki pertumbuhan yang cukup cepat hingga 8 cm/tahun. Penelitian ini bertujuan untuk mengetahui pengaruh ukuran fragmen terhadap pertumbuhan karang, tingkat kelangsungan hidup serta laju pertumbuhan fragmen karang Acropora formosa pada beberapa lokasi di perairan Selat Lembeh. Penelitian dilakukan pada bulan Februari - Juni 2015 dengan menggunakan metode transplantasi lepas dasar (substrat beton). Hasil penelitian menunjukkan bahwa fragmen karang Acropora formosa dengan panjang fragmen awal 8 cm memiliki tingkat kelangsungan hidup, pertumbuhan mutlak dan laju pertumbuhan tertinggi yaitu mencapai 84% (survival rate), 0,8 cm (pertumbuhan mutlak tinggi) dan 0,201 cm/bln (laju pertumbuhan). Ukuran panjang awal fragmen Acropora formosa cukup berpengaruh terhadap pertumbuhan karang (p<0,05). Kata kunci: Transplantasi karang, Acropora formosa, ukuran fragmen, Sulawesi Utara
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Kelman, W. M., G. M. Lodge e R. A. Culvenor. "Influence of panicle fragment size on ant seed-harvesting and seedling recruitment in Phalaris aquatica". Australian Journal of Experimental Agriculture 42, n. 5 (2002): 571. http://dx.doi.org/10.1071/ea01140.
Testo completoAbstract (sommario):
Successful seedling recruitment events in sparse stands of the grass Phalaris aquatica (phalaris) are rare. A major contributing factor to this situation is the seed-harvesting activity of ants. In recently developed cultivars of phalaris, the seed is retained within the glumes of the floret and is shed in a seed-retaining panicle fragment. We tested the hypothesis that seed contained in panicle fragments was less likely to be harvested by ants than naked seed and that this would be reflected in increased seedling recruitment. Observations of ant seed-harvesting activity and records of seedling recruitment following dispersal of seed and panicle fragments onto field plots were made at Canberra, Australian Capital Territory, and Tamworth, New South Wales, over 2 years. In the second year, the effects of 2 pasture renovation treatments (sheep-grazing and shallow-discing) on seedling recruitment from seed and panicle fragments were examined. Averaged over the 2 localities, 4% of large-sized (>10�florets), 13% of medium-sized (5-10 florets) and 27% of the small-sized (2 or 3 florets) panicle fragments were harvested in a 24 h period by ants (mainly Pheidole spp.), compared with 83% of the naked phalaris seed. The effects of panicle fragment size on recruitment were variable depending on site in the first year and the interaction of site and renovation treatments in the second year, but contrary to expectation, recruitment often was not higher in panicle fragment treatments than in seeded treatments. Seedling recruitment at Canberra (a hardsetting sandy loam) was lower (22 plants/m2 from naked seed and 15 plants/m2 from seed in panicle fragments) because of the competition from existing vegetation and germination of subterranean clover from the seedbank, than at Tamworth (a self-mulching red chromosol; 179 plants/m2 from naked seed and 118 plants/m2 from seed in panicle fragments), where seedling recruitment was also significantly increased by the sheep-grazing renovation treatment. At Tamworth, a larger seedbank was recovered from plots of oversown panicle fragments compared with plots oversown with naked phalaris seed. This suggested that protection of seeds in panicle fragments over the summer months on the Tablelands of New South Wales would increase the time over which phalaris seeds are available for recruitment. Further work is needed to test seedling recruitment in panicle shattering v. non-shattering phalaris populations and to define the conditions under which the seedbank contained in the panicle fragments can be exploited to improve stand persistence.
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Martens, A., D. Maes, B. Boussauw, R. Forsyth, K. J. Boening e J. Declercq. "Dorsoproximal proximal phalanx osteochondral fragmentation in 117 Warmblood horses". Veterinary and Comparative Orthopaedics and Traumatology 22, n. 01 (2009): 1–6. http://dx.doi.org/10.3415/vcot-08-02-0016.
Testo completoAbstract (sommario):
SummaryThe objective of the present study was to determine clinical and arthroscopic characteristics associated with dorso-proximal proximal phalanx (P1) fragments in Warmblood horses, as well as to examine their histopathological appearance. One hundred sixty-eight fragments were removed from 150 fetlocks of 117 Warmblood horses. Details of signalment and results of clinical examination were collected prior to surgery. After arthroscopic fragment removal and joint evaluation for synovial and/or cartilage abnormalities, the fragments were measured and evaluated histopathologically. The vast majority of the fragments (95.2%) were found medially, without predilection for front or hind limbs. In 10% of the joints, more than one fragment was present. The mean size of the fragments was 6.8 ± 2.6 mm. Only eight horses presented fetlock-related lameness. Horses of seven years of age and older (OR=13.32; p=0.033) and the presence of more than one fragment (OR=11.12; p=0.016) were significantly associated with lameness. Arthroscopic evaluation revealed one or more abnormalities in 50.7% of the joints. On histopathology, osteochondral fragments presented as a bony center covered with smooth hyaline cartilage on one side and some fibrous tissue on the other side. No clear histopathological signs were indicating precisely their origin. In Warmblood horses with dorsoproximal P1 fragments, the age (seven years and older) and the presence of more than one fragment in a fetlock significantly increased the risk of lameness. The osteochondral dorsoproximal P1 fragments could be defined as a developmental orthopaedic disease.
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Bogosian, David, e Bence Gerber. "Analytical Predictions of Fragment Penetration through Hollow Concrete Masonry Units". Shock and Vibration 15, n. 1 (2008): 61–70. http://dx.doi.org/10.1155/2008/586876.
Testo completoAbstract (sommario):
Modeling steel casing fragment impacts on hollow CMU poses some problems, since the fragments will typically penetrate through the front face and may also penetrate the back face. Techniques are needed for predicting (a) the size of the hole created by the penetration, (b) the size of the annular region of damaged concrete around the hole, and (c) the residual velocity of the fragment. A series of calculations using the AUTODYN code were performed to investigate the accuracy and reliability of the model. The model uses the smooth particle hydrodynamics (SPH) approach to represent the CMU. A variety of steel fragment sizes were projected at a layer of CMU, and the resulting hole size, damage, and fragment residual velocity were tabulated. Results were validated against existing empirical relationships to insure the model's applicability, while additional analyses demonstrated trends and parametric sensitivity.
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West, Amanda M., Dustin F. Lewis e Robert J. Richardson. "Fragment Size and Planting Depth Affect the Regenerative Capacity of Bushkiller (Cayratia japonica)". Invasive Plant Science and Management 5, n. 4 (dicembre 2012): 397–401. http://dx.doi.org/10.1614/ipsm-d-12-00007.1.
Testo completoAbstract (sommario):
AbstractBushkiller (Cayratia japonica) is a herbaceous, perennial vine that reproduces from seed and vegetative root structures within its native range. However, this species is considered invasive in the United States due to prolific shoot production, which can overtop surrounding vegetation. Cultural control practices, such as mulching, have been observed to further the spread of this species through regeneration of root fragments. Research was conducted to determine the regenerative capacity of bushkiller root fragments (1 to 7 cm; 2.5 to 18 inches) buried at various depths (0 to 40 cm). Root length and planting depth affected leaf number, shoot number, plant height, and shoot biomass. Bushkiller leaf density, shoot density, plant height, and dry weight increased as root fragment length increased from 1 to 7 cm; conversely, these variables decreased as planting depth increased from 0 to 40 cm. Results indicate bushkiller regeneration capacity from root fragments is extremely high and control practices that fragment roots should be avoided to reduce further spread.
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Chanyenga, Tembo F., Coert J. Geldenhuys e Gudeta W. Sileshi. "Effect of population size, tree diameter and crown position on viable seed output per cone of the tropical conifer Widdringtonia whytei in Malawi". Journal of Tropical Ecology 27, n. 5 (2 agosto 2011): 515–20. http://dx.doi.org/10.1017/s0266467411000204.
Testo completoAbstract (sommario):
Abstract:The tropical montane conifer tree Widdringtonia whytei is found in small fragments on Mulanje Mountain in Malawi. A study was conducted with the objectives of determining the effect of population size, tree stem diameter and crown position on the proportion of viable seeds per cone produced by W. whytei at three sites (Sombani, Chambe and Lichenya) on Mulanje Mountain. Three population sizes, namely small (fragments with ≤10 cone-bearing trees), medium (fragments with 11–20 cone-bearing trees) and large (fragments with >20 cone-bearing trees) and isolated trees were sampled at each study site. In each fragment, four cone-bearing trees were randomly located, 20 mature cones were collected from each tree and the viability of seeds was tested. Only 23% of the seeds per cone were viable but seed viability per cone was highly variable among fragments. Large fragment populations produced the highest proportion of viable seeds per cone (30%), followed by similar proportions in small fragments (28.3%) and isolated trees (26.1%), with the lowest proportions in medium-sized fragments (18.7%), indicating a non-linear relationship between viable seed output per cone and population size. Tree stem diameter and crown position had no effect on the proportion of viable seeds per cone. Further studies are needed to identify the factors that lead to the low viable seed output per cone, and how this influences whole-tree seed production in W. whytei.
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Wu, Xiao Ying, e Fan Li. "Study on Numerical Simulation of Shrapnel Fragments at the Components Damage Effect on Armored Vehicle Concept". Advanced Materials Research 998-999 (luglio 2014): 763–67. http://dx.doi.org/10.4028/www.scientific.net/amr.998-999.763.
Testo completoAbstract (sommario):
we studies the grenade fragment to view damage effect of aiming an armored vehicle parts (fragment size, shape, fragment velocity) with the finite element method,The damage processs of grenade fragments of armored vehicle concept aiming component is simulated by the AUTODYN software. Through the analysis of the results of numerical simulation,weobtained parameters values at the damage assessment components (attenuation penetration depth, diameter and velocity degree) and grenade fragment to the gunner aimed at the damage rule, mirrorand lay the foundation for the fragment of the armored equipment parts damage assessment.
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Franceschinelli, Edivani Villaron, Giuliana Mara Patrício Vasconcelos, Elena Charlotte Landau, Kátia Yukari Ono e Flávio Antonio Maes Santos. "The genetic diversity of Myrciaria floribunda (Myrtaceae) in Atlantic Forest fragments of different sizes". Journal of Tropical Ecology 23, n. 3 (24 aprile 2007): 361–67. http://dx.doi.org/10.1017/s0266467407004099.
Testo completoAbstract (sommario):
The genetic diversity of Myrciaria floribunda, a common Atlantic Forest tree, was investigated in six populations located in two small fragments (10 and 18 ha), two medium-sized fragments (36 and 44 ha) and one large fragment (3003 ha). Two populations occur in the large fragment. It is expected that smaller fragments should have lower genetic diversity and higher inbreeding. Distances between fragments varied from 0.66 to 10 km. On average 32 young trees smaller than 20 cm basal girth were sampled in each population. Allozyme electrophoresis was carried out, and six loci were scored. The effective number of alleles was lower for populations of the two small fragments (1.46 and 1.51) and higher for populations of the large (1.62 and 1.71) and medium ones (1.69 and 1.84). Small fragments showed lower values of expected and observed heterozygosities than large and medium fragments. Most of the genetic variability occurs within populations, and there was a moderate genetic variation among them ($\hat{\theta}_p$ = 0.097). Our findings show a tendency of lower genetic diversity within small and isolated fragments and higher genetic differentiation among them. But, few correlations between genetic diversity indices and fragment features (size and isolation) were significant.
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Javed, A. M., Ch H. Cannon e R. Wickneswari. "Microsatellite DNA markers in Shorea platyclados (Dipterocarpaceae): genetic diversity, size homoplasy and mother trees". Journal of Forest Science 60, No. 1 (30 gennaio 2014): 18–27. http://dx.doi.org/10.17221/71/2013-jfs.
Testo completoAbstract (sommario):
Cross-specific amplification of microsatellite loci greatly enhances the effectiveness of this marker system. This shortcut would greatly enhance our examination of the gene flow and population structure of trees in diverse tropical rainforests. To explore the effectiveness and limitations of this approach, we examined allelic diversity at six microsatellite loci, originally developed in a congeneric species, in three populations of Shorea platyclados from Peninsular Malaysia. Fragment sizing was performed by an efficient and sensitive (1 bp resolution) technique using capillary electrophoresis, ethidium bromide detection, and minimal clean-up. Fragment size ranges were conserved between species and null allele frequencies were low. Higher overall levels of genetic diversity were detected in our study. Variation among populations was directly related to geographic distance. Fragment size class distributions suggest that each locus should be studied using different evolutionary models. Direct sequencing of SSR fragments revealed that size differences were due to changes in both the flanking regions and repeat motifs. Several clear examples of size homoplasy were observed, along with the disruption of perfect repeats, suggesting that cross-specific amplification of microsatellite loci requires an additional level of confirmation at the DNA sequence level before the influence of size homoplasy and changes in repeat structure can be assessed. Simulation studies demonstrate that the increasing intensity of timber harvest leads to higher variability in levels of potential heterozygosity and decreasing total number of alleles in the remnant "mother trees" The careful selection of "mother" trees can greatly enhance the future genetic diversity of populations.
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Bellesso, Marcelo, Rodrigo D. Velasques, Luis F. Pracchia, Beatriz Beitler, Vera L. Aldred, Dalton Chamone, Jose M. Kutner e Juliana Pereira. "Bone Marrow Biopsy for the Staging of Diffuse Large B-Cell Lymphoma: Is It Necessary Bilateral Trephine Biopsy?." Blood 110, n. 11 (16 novembre 2007): 4427. http://dx.doi.org/10.1182/blood.v110.11.4427.4427.
Testo completoAbstract (sommario):
Abstract In this retrospective analysis we study the usefulness of bilateral rather than unilateral iliac trephine biopsies in demonstrating Diffuse Large B-Cell Lymphoma (DLBCL) in the bone marrow (BM). A total of 28 DLBCL cases with BM infiltration were investigated with bilateral iliac trephine biopsy during staging. Our propose was to evaluate the incidence of unilateral BM involvement, and we compare the BM biopsy size with negative and positive BM infiltration. In 28 cases studied it was analyzed 70 BM fragments. These fragments were reviewed separately by pathologist about size and infiltration. In this group, 6 cases (21.4%) were unilaterally positive. The median number of fragment per case was 2.5; the median size of BM fragment was 11.01 mm (± 5.12) and BM fragment per case was 27.53mm. It was not found difference between size BM fragment in negative or positive fragments 11,57mm (±5.2) versus 10.95mm (±5.1), p>0.05, respectively. In 24 cases it was possible to compare negative and positive BM infiltration with age, sex, LDH and computerized tomography (CT) staging. In addition, it was not found difference between unilateral and bilateral BM infiltration about LDH and age, and CT. (Table 1). Conclusion: Although in unilateral infiltration cases did not change risk factor in International Prognostic Index (stage III–IV) by CT, we conclude that bilateral trephine biopsy is superior to unilateral, because bilateral biopsy could increase by 21,4% the detection of BM involvement by DLBCL, without difference between the size in negative versus positive fragments. Table 1. Distribution of Unilateral and Bilateral Bone Marrow infiltration by categories Unilateral infiltration (%) Bilateral infiltration (%) Age < 60 21% 50% Age ≥ 60 4% 25% Sex Male 16% 29% Sex Female 8% 47% CT staging I–II - 35% CT staging III–IV 26% 39% LDH Normal 8% 34% LDH Elevated 16% 42%
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Delciellos, Ana C., Marcus V. Vieira, Carlos E. V. Grelle, Priscilla Cobra e Rui Cerqueira. "Habitat quality versus spatial variables as determinants of small mammal assemblages in Atlantic Forest fragments". Journal of Mammalogy 97, n. 1 (30 ottobre 2015): 253–65. http://dx.doi.org/10.1093/jmammal/gyv175.
Testo completoAbstract (sommario):
Abstract Fragment size, isolation, and matrix properties have received considerable attention as predictors of species richness, abundance, and composition in habitat patches. However, measurements of habitat attributes or habitat quality are more directly related to the proximate effects of habitat fragmentation and may be more determinant of assemblages than traditional explanatory variables at local scales. We determine how habitat structure in fragments—a measure of habitat quality—compares to fragment size, isolation, and matrix properties as determinants of richness, abundance, and composition of non-volant small mammals in a fragmented landscape of Atlantic Forest. Small mammals were surveyed once in 25 fragments in the Macacu River watershed, Rio de Janeiro, Brazil, from 1999 to 2001 and 2005 to 2009. A total of 83 candidate models were formulated and compared by Akaike Information Criteria. Habitat structure was one of the main determinants of small mammal assemblages in fragments, as important as fragment isolation for species composition and climatic season for species richness. Rodents were more abundant in fragments with increased overstory and understory vegetation density and more fallen logs. The contrary pattern was found for overall species richness and for species of terrestrial habit, which were more abundant in fragments with more open forest: decreased overstory and understory vegetation density and less fallen logs. Habitat quality in fragments may be a more important determinant of assemblages of small mammals and other vertebrates than previously considered in landscape and land use studies. O tamanho e isolamento dos fragmentos e as propriedades da matriz têm recebido considerável atenção como preditores da riqueza, abundância e composição de espécies em manchas de habitat. Entretanto, medidas dos atributos do habitat ou da qualidade do habitat são mais diretamente relacionadas aos efeitos imediatos da fragmentação de habitat, e seriam mais determinantes das comunidades do que as variáveis explicativas tradicionais. Determinamos como a estrutura do habitat nos fragmentos—uma medida da qualidade do habitat—se compara ao tamanho e isolamento dos fragmentos, e às propriedades da matriz como determinantes da riqueza, abundância e composição de espécies de pequenos mamíferos não-voadores em uma paisagem fragmentada de Mata Atlântica. Os pequenos mamíferos foram amostrados uma vez em 25 fragmentos na Bacia do Rio Macacu, Rio de Janeiro, Brasil, de 1999 a 2001 e de 2005 a 2009. Um total de 83 modelos foram formulados e comparados utilizando o Critério de Informação de Akaike. A estrutura do habitat foi um dos principais determinantes das comunidades de pequenos mamíferos nos fragmentos de mata, tão importante quanto o isolamento entre fragmentos para a composição de espécies e os efeitos das estações climáticas sobre a riqueza de espécies. Os roedores foram mais abundantes nos fragmentos com estratificação vertical e sub-bosque mais densos e com maior presença de troncos caídos. O padrão contrário foi encontrado para a riqueza total de espécies e para espécies de hábito terrestre, que foram mais abundantes em fragmentos com estratificação vertical e sub-bosque menos densos e menor presença de troncos caídos. A qualidade do habitat em fragmentos pode ser determinante das comunidades de pequenos mamíferos e outros vertebrados, mais importante do que considerado previamente em estudos de paisagens e uso da terra.
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Liu, Xiaohui, Songyong Liu e Ping Tang. "Coal fragment size model in cutting process". Powder Technology 272 (marzo 2015): 282–89. http://dx.doi.org/10.1016/j.powtec.2014.12.015.
Testo completo
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Zhou, Fenghua, Jean-François Molinari e K. T. Ramesh. "Characteristic fragment size distributions in dynamic fragmentation". Applied Physics Letters 88, n. 26 (26 giugno 2006): 261918. http://dx.doi.org/10.1063/1.2216892.
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Jug, Jasmin, Stjepan Strelec, Mario Gazdek e Boris Kavur. "Fragment Size Distribution of Blasted Rock Mass". IOP Conference Series: Earth and Environmental Science 95 (dicembre 2017): 042013. http://dx.doi.org/10.1088/1755-1315/95/4/042013.
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Campi, X., e H. Krivine. "Fluctuations and intermittency in fragment size distributions". Nuclear Physics A 589, n. 3 (luglio 1995): 505–20. http://dx.doi.org/10.1016/0375-9474(95)00190-c.
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Nagahama, H. "Fractal fragment size distribution for brittle rocks". International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 30, n. 4 (agosto 1993): 469–71. http://dx.doi.org/10.1016/0148-9062(93)91728-2.
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