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排序方式: 共有155条查询结果,搜索用时 125 毫秒
41.
Tailan Moretti Mattos Dandhara Rossi Carvalho Augusto de Salles Guerra-Júnior Francisco Gerson Araújo 《河流研究与利用》2023,39(2):151-162
The dynamics of fish assemblages in reservoirs depend on factors such as the morphometry of the catchment, habitat structure, and the uses of the reservoir. In the Paraíba do Sul (PSR) basin in southeastern Brazil, there are several types of reservoirs, some on the main channel, some are cascade reservoirs originated from a diversion of the waters of the PSR, and others are isolated reservoirs from tributaries. This study aimed to evaluate the influences of these three types of reservoirs on the taxonomic and functional distinctness of the fish assemblages. It was hypothesized that reservoirs on the main channel (more inflowing waters and habitat availability) have higher taxonomic and functional distinctness compared to cascade reservoirs, which in turn, have greater distinctness than isolated reservoirs. In addition, we expect assemblage structure to differ among these types of reservoirs because of the close relationship with local environmental conditions and habitat structure. Thirty measurements (26 quantitative and 4 categorical) from 34 fish species representing functional traits associated with locomotion, feeding, life strategy, and habitat use were taken. Fish assemblages differed among the three types of reservoirs, which was probably associated with different environmental and local habitat conditions. Higher taxonomic and functional distinctness were found for the isolated reservoirs, and lower for reservoirs on the main channel. This suggests that the fish fauna in this latter type of reservoir were probably composed of phylogenetically close and morphologically similar species. It is likely that limitation of the available resources induces fish to partition the available niches to coexist, favoring assemblages with species adapted to different functions. Our results demonstrate that assessing fish functional and taxonomic distinctness can be used to advance understanding of fish communities from reservoirs in Neotropical regions. 相似文献
42.
A number of unusual fatty acids were identified after isolation fromRhizobium. They include 11-methyl-octadec-11-enoic, 12-methoxy-11-methyl- and 11-methoxy-12-methyloctadecanoic, and 11-methoxy- and 13-methoxynonadecanoic acids. 相似文献
43.
Galvanic corrosion of laser weldments of AA6061 aluminium alloy 总被引:2,自引:1,他引:1
Galvanic corrosion of laser welded AA6061 aluminium alloy, arising from the varying rest potentials of the various weldment regions, was examined. The weld fusion zone is found to be the most cathodic region of the weldment while the base material is the most anodic region. The rate of galvanic corrosion, controlled by the cathodic process at the weld fusion zone, increases with time until a steady state maximum is reached. On galvanic corrosion the corrosion potential of the weld fusion zone shifts in the positive direction and the free corrosion current increases. It is proposed that the cathodic process at the weld fusion zone causes a local increase in pH that in turn causes dissolution of the surface film resulting in the loss of Al to solution and the increase of intermetallic phases. The increase in galvanic corrosion may result from either the build up of the intermetallic phases in the surface layer and/or significant increase in surface area of the weld fusion zone due to the porous nature of the surface layer. 相似文献
44.
Theory revision systems are designed to improve the accuracy of an initial theory, producing more accurate and comprehensible
theories than purely inductive methods. Such systems search for points where examples are misclassified and modify them using
revision operators. This includes trying to add antecedents to clauses usually following a top-down approach, considering
all the literals of the knowledge base. Such an approach leads to a huge search space which dominates the cost of the revision
process. ILP Mode Directed Inverse Entailment systems restrict the search for antecedents to the literals of the bottom clause.
In this work the bottom clause and mode declarations are introduced in a first-order logic theory revision system aiming to
improve the efficiency of the antecedent addition operation and, consequently, also of the whole revision process. Experimental
results compared to revision system FORTE show that the revision process is on average 55 times faster, generating more comprehensible
theories and still not significantly decreasing the accuracies obtained by the original revision process. Moreover, the results
show that when the initial theory is approximately correct, it is more efficient to revise it than learn from scratch, obtaining
significantly better accuracies. They also show that using the proposed theory revision system to induce theories from scratch
is faster and generates more compact theories than when the theory is induced using a traditional ILP system, obtaining competitive
accuracies.
This is an extended and revised version of the ILP 2008 paper (Duboc et al. 2008). 相似文献
45.
Ana Luiza Ferreira SantosKátia Yuri Fausta Kawase Gerson Luiz Vieira Coelho 《The Journal of Supercritical Fluids》2011,56(3):277-282
Lignocellulosic materials, such as agricultural residues, are abundant renewable resources for bioconversion to sugars. The sugar cane bagasse was studied here to obtain simple sugars for the production of alcohols and other chemicals. The crystalline structure of cellulose and the lignin that physically seals the surrounding cellulose fibers makes enzymatic hydrolysis difficult by preventing the contact between the cellulose and the enzyme. Two different samples of sugar cane (bagasse pulp and skin) were used and compared with microcrystalline cellulose (Avicel). The investigated samples were pretreated with SC-CO2 explosion before hydrolysis. The experiments were conducted at 12, 14 and 16 MPa at a temperature of 60 °C. In this process, particles of celluloses within the size range from 0.25 to 0.42 mm were placed in defined amounts inside the experimental vessel, CO2 was injected and let stand for 5 and 60 min. The explosion pretreatment of cellulosic materials by SC-CO2 was performed in an apparatus of a static type with 300 ml of volume. The hydrolysis reaction using cellulose enzyme was carried at 55 °C for 8 h. After the pretreatment, the glucose yield increased in 72% to the bagasse sample. The SC-CO2 pretreatment together with alkali increased the glucose yield in 20% as compared with alkali only. X-ray, microscopy and thermal analysis were used to investigate the effect of the pretreatment. 相似文献
46.
47.
OBJECTIVE: To describe the clinical and radiologic features of superficial siderosis of the CNS after treatment of a cerebellar tumor. METHODS: Clinical assessment and MRI in four patients with superficial siderosis were performed. RESULTS: Four patients with superficial siderosis had been treated for a primary cerebellar tumor (astrocytoma in three patients, medulloblastoma in one patient) during childhood. All patients were treated with surgery and three received radiotherapy. Slowly progressive bilateral sensorineural hearing loss, gait ataxia, and limb ataxia appeared 8 to 22 years after diagnosis of the cerebellar tumor. Other clinical features were mild cognitive impairment, dysarthria, nystagmus, optic neuropathy, anosmia, and upper motor neuron signs. The CSF contained erythrocytes and increased protein. MRI with fast spin-echo T2-weighted and gradient-echo T2* sequences showed a hypointense rim of iron coating the surface of the cerebellum and brainstem. Twenty-one other patients who had survived more than 5 years after treatment of a primary cerebellar tumor did not have symptoms or signs suggestive of superficial siderosis. CONCLUSIONS: Superficial siderosis is an uncommon late complication of the treatment of a childhood cerebellar tumor, but it is probably underrecognized. The diagnosis should be suspected in patients who present with slowly progressive sensorineural hearing loss and ataxia many years after eradication of a childhood cerebellar tumor. 相似文献
48.
Using unbalanced radio-frequency (RF) magnetron sputtering crystalline rutile films were synthesised on glass substrates at (combined Ar and O2) pressures of 0.4 Pa or less, at RF powers of 500 and 600 W with substrate to magnetron distances of 40 mm or longer. Anatase films were deposited at the greater pressure of 1.2 Pa (substrate to magnetron distance of 40 mm) or shorter substrate to magnetron distance of 20 mm (at 0.4 Pa). A mixture of anatase and rutile was formed at 0.5 Pa with all other conditions being as for those required for rutile or the power was reduced along with the substrate to magnetron distance (500 W and 20 mm). The crystallite sizes of rutile obtained were 1 - 3 nm. It is proposed that the greater the energy imparted to the substrate surface by the impinging positive species the greater the activation energy to crystalline phase formation that can be overcome. Hence the formation of rutile over anatase is favoured at greater power, longer magnetron to substrate distances and decreased pressure. Moreover, not only is it possible to control the phase of TiO2 formed it appears to be possible to control the degree of oxygen non-stoichiometry in the rutile films formed. Smaller O2 partial pressures, shorter substrate to magnetron distances and greater RF power are believed to produce an environment of reduced reaction of sputtered Ti species with O2 and to result in the formation of non-stoichiometric rutile structures resulting in increased band gap energies and decreased refractive indices. 相似文献
49.
Diego Alvarenga Botrel Soraia Vilela Borges Regiane Victória de Barros Fernandes Arianne Dantas Viana Joyce Maria Gomes da Costa Gerson Reginaldo Marques 《International Journal of Food Science & Technology》2012,47(11):2289-2296
Response surface methodology (RSM) was employed to investigate variations in powder characteristics with respect to spray drying operating parameters including both feed rates (L min?1) and inlet temperatures (°C). Inlet temperatures around 180 °C provided the lowest values for moisture. Powder recovery was significantly affected (P < 0.10) by inlet air temperature and feed rate, where a raise in inlet temperature and feed rate resulted in higher powder recovery. No significant difference (P > 0.05) was observed for water activity, solubility and hygroscopicity between treatments. Regarding oil retention, the results showed a significant (P < 0.05) interaction between the two studied factors. A tendency for higher values of oil retention was observed when using combinations of high inlet temperatures/low feed rates and low inlet temperatures/high feed rates. Particle size distribution averaged 2.0, 8.1 and 18.3 μm for D10, D50 and D90, respectively. The morphology of particles showed no cracks in most capsules. The results indicate that high temperature (185 °C) and moderated feed rate (0.63 L min?1) are the best spray drying conditions. 相似文献
50.