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排序方式: 共有753条查询结果,搜索用时 15 毫秒
741.
Nieto P Pijper E Barredo D Laurent G Olsen RA Baerends EJ Kroes GJ Farías D 《Science (New York, N.Y.)》2006,312(5770):86-89
The Born-Oppenheimer approximation of uncoupled electronic and nuclear motion is a standard tool of the computational chemist. However, its validity for molecule-metal surface reactions, which are important to heterogeneous catalysis, has been questioned because of the possibility of electron-hole pair excitations. We have performed experiments and calculations on the scattering of molecular hydrogen from a catalytically relevant metal surface, obtaining absolute probabilities for changes in the molecule's velocity parallel to the representative Pt(111) surface. The comparison for in-plane and out-of-plane scattering and results for dissociative chemisorption in the same system show that for hydrogen-metal systems, reaction and diffractive scattering can be accurately described using the Born-Oppenheimer approximation. 相似文献
742.
743.
Potato is the third most important food crop in the world and is crucial to ensure food security. However, increasing biotic and abiotic stresses jeopardize its stable production. Fortunately, breeders count on a rich pool of wild relatives that provide sources for disease resistance and tolerance to environmental stresses. To use such traits effectively, breeders require tools that facilitate exploration and exploitation of the genetic diversity of potato wild relatives. Introgression programs to incorporate such alien chromatin into the crop have so far relied on cytogenetic and genetic studies to tap desired traits from these wild resources. The available genetic and cytogenetic tools, supplemented with more recent genomic technologies, can assist in the use of potato relatives in pre-breeding. This information can also facilitate cisgenesis and genome editing to improve potato cultivars. Despite the abundant and rapidly growing genomic information of potato, that of its wild relatives is still limited. 相似文献
744.
745.
Diego A. Portela Luis Campoy Pablo E. Otero Manuel Martin-Flores Robin D. Gleed 《Veterinary anaesthesia and analgesia》2017,44(3):636-645
Objective
To describe ultrasound-visualized anatomy and the spread characteristics of a dye injected in the thoracic paravertebral (TPV) space under ultrasound guidance.Study design
Anatomic cadaver study.Animals
Seven dog cadavers.Methods
One cadaver was used to observe, identify, and describe the relevant TPV anatomy. In the remaining six, the left fifth TPV space was randomly assigned to be injected with either a low volume (LV; 0.05 mL kg?1) or high volume (HV; 0.15 mL kg?1) of dye. Subsequently, the contralateral side was injected with the alternative volume. Anatomic dissections were conducted to determine the incidence of complete spinal nerve staining (>1 cm circumferential coverage), number of contiguous spinal nerves dyed and the absence or presence of solution in particular locations.Results
The ultrasound-visualized anatomy of the TPV space was defined as the intercostal space abaxial to the vertebral body, delimited by the parietal pleura ventrally and the internal intercostal membrane dorsally. The endothoracic fascia divides the paravertebral space into dorsal and ventral compartments. The target nerve was completely dyed in five of six and six of six injections in the LV and HV conditions, respectively. In one LV injection, the nerve was partially dyed. No multisegmental spread affecting contiguous spinal nerves was found in either treatment. Multisegmental spread was found in the ventral compartment of the TPV space, affecting the sympathetic trunk on 3 (0–3) and 3.5 (1–6) vertebral spinal levels in the LV and HV conditions, respectively, but differences between volumes were not significant. No intrapleural, ventral mediastinal or epidural migration was observed.Conclusions and clinical relevance
Ultrasound-guided TPV block is a potentially reliable technique. The LV appeared sufficient to dye a single spinal nerve and multiple sympathetic trunk vertebral levels. Multiple TPV injections may be needed to provide adequate thoracic analgesia in dogs undergoing thoracic surgery. 相似文献746.
A multi-criteria approach to identify favorable areas for goat production systems in Veracruz,México
Emmanuel de Jesús Ramírez-Rivera Jose Lopez-Collado Pablo Díaz-Rivera Eusebio Ortega-Jiménez Glafiro Torres-Hernández Jazmín Jacinto-Padilla Erasmo Herman-Lara 《Tropical animal health and production》2017,49(4):725-731
This research identifies favorable areas for goat production systems in the state of Veracruz, Mexico. Through the use of the analytic hierarchy process, layers of biophysical and soil information were combined to generate a model of favorability. Model validation was performed by calculating the area under the curve, the true skill statistic, and a qualitative comparison with census records. The results showed the existence of regions with high (4494.3 km2) and moderate (2985.8 km2) favorability, and these areas correspond to 6.25 and 4.15%, respectively, of the state territory and are located in the regions of Sierra de Huayacocotla, Perote, and Orizaba. These regions are characterized as mountainous and having predominantly temperate-wet or cold climates, and having montane mesophilic forests, containing pine, fir, and desert scrub. The reliability of the distribution model was supported by the area under the curve value (0.96), the true skill statistic (0.86), and consistency with census records. 相似文献
747.
Alessio Vovlas Simona Santoro Vincenzo Radicci Paola Leonetti Pablo Castillo Juan E. Palomares-Rius 《European journal of plant pathology / European Foundation for Plant Pathology》2017,149(1):193-199
A survey was conducted in 16 fields cultivated with broad bean (Vicia faba L.) and garden pea (Pisum sativum L.) in nine localities of Apulia, southern Italy, to determine whether annual weeds were susceptible to the pea cyst nematode (PEACN), Heterodera goettingiana, and could therefore serve as alternate host for the nematode. The results of this study showed that black medick (Medicago lupulina L.) is a good host for the nematode increasing its population levels in the soil in the absence of the primary hosts. The identity of the PEACN was confirmed by integrative taxonomic approaches (classical, and molecular), resulting identical in all cases (broad bean and garden pea, as well as the spontaneous black medick infections). The phylogenetic analyses using ITS and coxI gene regions strongly support the identification of the populations of H. goettingiana from Italy. Also, ITS and coxI gene sequences were obtained from the same cyst, confirming the species identity in comparison to other nematodes and populations in the Goettingiana group, demonstrating that ITS and coxI gene regions of the PEACN are suitable molecular markers for accurate and unequivocal identification of the PEACN. Reproduction and histopathological analyses demonstrated a good host-suitability of black medick to the PEACN. This record enlarges the relatively narrow host-range of the pea cyst nematode and indicates the need to control M. lupulina to avoid the increase of the nematode population in the absence of the main host crop. 相似文献
748.
Carlos Esse Pablo J Donoso Victor Gerding Francisco Encina-Montoya Celso Navarro 《Southern Forests》2018,80(3):233-240
Nothofagus dombeyi is distributed on very diverse sites in the temperate forests of Chile and Argentina. In Chile, studies on its dynamics and productivity in forests, where it is the dominant species, have been carried out mainly in the foothills of the Andes, but the productivity and growth of these forests in the Coastal Range are almost unknown. The objective of this study was to evaluate the construction of a single dominant height/age growth model for two homogeneous edaphoclimatic zones (ZEH 2 and 5) previously defined for this species in the Coastal Range of southcentral Chile. The results showed that the Chapman-Richards model was the best candidate function, in terms of goodness of fit and predictive capabilities. Using this function, specific parameters (a, b and c) were obtained for each zone, from which site models were constructed by the Algebraic Difference Approach method for a base age of 35 years. This model is intended to contribute to better estimations of site productivity for N. dombeyi forests in the Coastal Range of south-central Chile, and thus facilitate private and public decisions regarding their management. 相似文献
749.
Héctor A. Bahamonde Guillermo Martínez Pastur María V. Lencinas Rosina Soler Yamina M. Rosas Brenton Ladd Sandra Duarte Guardia Pablo L. Peri 《Annals of Forest Science》2018,75(2):45
Key message
Soil texture and temperature-related variables were the variables that most contributed to Nothofagus antarctica forest height in southern Patagonia. This information may be useful for improving forest management, for instance related to the establishment of silvopastoral systems or selection of suitable sites for forest reforestation in southern Patagonia.Context
Changes in forest productivity result from a combination of climate, topography, and soil properties.Aims
The relative importance of edaphic and climatic variables as drivers of productivity in Nothofagus antarctica forests of southern Patagonia, Argentina, was evaluated.Methods
A total of 48 mature stands of N. antarctica were selected. For each study site, we measured the height of three mature dominant trees, as an indicator of productivity. Seven soil, five spatial, and 19 climatic features were determined and related to forest productivity. Through partial least squares regression analyses, we obtained a model that was an effective predictor of height of mature dominant trees in the regional data set presented here.Results
The four variables that most contributed to the predictive power of the model were altitude, temperature annual range, soil texture, and temperature seasonality.Conclusion
The information gathered in this study suggested that the incidence of the soil and temperature-related variables on the height of dominant trees, at the regionally evaluated scale, was higher than the effect of water-related variables.750.
Alejandro Alcudia-Aguilar Hans van der Wal Juan Suárez-Sánchez Pablo Martínez-Zurimendi María Mercedes Castillo-Uzcanga 《Agroforestry Systems》2018,92(5):1329-1339
We studied whether agrobiodiversity in home gardens reflects the cultural landscapes that embed them. We compared floristic composition, biomass and cover of trees in home gardens between the cultural landscapes on mountain slopes (MSL), small hills (SHL), and floodplains (FPL) in a segment of the Grijalva–Usumacinta watershed in the tropical lowlands of Tabasco, Mexico. We characterized the cultural landscapes based on information obtained through questionnaires, identified species and measured tree height and diameter at breast height in random samples of home gardens from two localities in each case. The cultural landscapes showed distinct land use combinations: MSL comprised subsistence agriculture, pasturelands and forests; SHL pasturelands, some secondary vegetation and industrial agriculture fields; and FPL mainly industrial agriculture fields and pasturelands. Total species richness was greater in MSL than in SHL and FPL. Mean species richness was greater in MSL and SHL (22.4 and 15.8 respectively) than in FPL (7.2), as was the mean number of individuals per home garden (98.2, 94.1 and 20.4. Dominant species in home gardens in FPL and SHL included particular secondary species for each landscape, whereas single or double occurrences of mature forest species were distinctive of home gardens in MSL. Mean biomass was greater in MSL than in SHL and FPL (37.1, 28.2 and 23.7 Mg C ha?1), as was tree cover (1.06, 0.95 and 0.76 m2/m2). We conclude that agrobiodiversity varies considerably among cultural landscapes and recommend the design of specific policies to enhance its conservation in each of them. 相似文献