Atom collision-induced resistivity of carbon nanotubes     

Romero HE  Bolton K  Rosén A  Eklund PC 《Science (New York, N.Y.)》2005,307(5706):89-93

We report the observation of unusually strong and systematic changes in the electron transport in metallic single-walled carbon nanotubes that are undergoing collisions with inert gas atoms or small molecules. At fixed gas temperature and pressure, changes in the resistance and thermopower of thin films are observed that scale as roughly M(1/3), where M is the mass of the colliding gas species (He, Ar, Ne, Kr, Xe, CH4, and N2). Results of molecular dynamics simulations are also presented that show that the maximum deformation of the tube wall upon collision and the total energy transfer between the colliding atom and the nanotube also exhibit a roughly M(1/3) dependence. It appears that the transient deformation (or dent) in the tube wall may provide a previously unknown scattering mechanism needed to explain the atom collision-induced changes in the electrical transport.  相似文献   

Predatory Dinosaurs from the Sahara and Late Cretaceous Faunal Differentiation     

PC Sereno  DB Dutheil  M Iarochene  HCE Larsson  GH Lyon  PM Magwene  CA Sidor  DJ Varricchio  JA Wilson 《Science (New York, N.Y.)》1996,272(5264):986-991

Late Cretaceous (Cenomanian) fossils discovered in the Kem Kem region of Morocco include large predatory dinosaurs that inhabited Africa as it drifted into geographic isolation. One, represented by a skull approximately 1.6 meters in length, is an advanced allosauroid referable to the African genus Carcharodontosaurus. Another, represented by a partial skeleton with slender proportions, is a new basal coelurosaur closely resembling the Egyptian genus Bahariasaurus. Comparisons with Cretaceous theropods from other continents reveal a previously unrecognized global radiation of carcharodontosaurid predators. Substantial geographic differentiation of dinosaurian faunas in response to continental drift appears to have arisen abruptly at the beginning of the Late Cretaceous.  相似文献   

Performance of peach and plum based rootstocks of different vigour on a late peach cultivar in replant and calcareous conditions     

Sergio Jiménez  Jorge Pinochet  Jesús Romero  Yolanda Gogorcena  María Ángeles Moreno  José Luís Espada 《Scientia Horticulturae》2011

The field performance of fifteen peach and plum based rootstocks of different vigour (Adesoto, Evrica, Garnem, GF 677, HM-2, Krymsk^® 1, PAC 9801-02, PAC 960, PAC 9907-02, PAC 9917-26, PAC-MUT, PADAC 9907-23, ROOTPAC^® 40, ROOTPAC^® 70 and Tetra) grafted with ‘Calrico’ cultivar was compared after 7 years of establishment on an Armillaria infested replant site. ‘Calrico’ is a selected clone of “Calanda” late peach cultivar. Differences in parameters such as tree survival, leaf chlorophyll content, vigour, yield, cumulative yield, yield efficiency and fruit size were analyzed among rootstocks. All PAC 9801-02 and Tetra trees survived and the mortality rate was low in Evrica, PADAC 9907-23 and ROOTPAC^® 40. The rest of genotypes showed higher mortality rates. Leaf chlorophyll concentration was higher when grafted on Adesoto and Evrica and lower when grafted on PAC 9907-02 and PAC 9917-26. Garnem and PADAC 9907-23 were the most vigorous rootstocks. The highest yield efficiency was induced by Krymsk^® 1 and PAC 9801-02 due to their lower vigour. The highest fruit weight was also induced by Krymsk^® 1 but its cumulative yield was low. Other rootstocks that showed high fruit weight and cumulative yields were ROOTPAC^® 70 and Tetra. Overall, Evrica, PAC 9801-02, ROOTPAC^® 40 and Tetra were among the best adapted to soil sickness and calcareous soil showing a good agronomic performance. The first three rootstocks (Evrica, PAC 9801-02, ROOTPAC^® 40) also exhibited a high capacity to control tree vigour associated with high yield efficiency.  相似文献   

Hydroxytyrosol 4-beta-D-glucoside,an important phenolic compound in olive fruits and derived products     

Romero C  Brenes M  García P  Garrido A 《Journal of agricultural and food chemistry》2002,50(13):3835-3839

There is increasing interest in olive polyphenols because of their biological properties as well as their contribution to the color, taste, and shelf life of olive products. However, some of these compounds remain unidentified. It has been shown that hydroxytyrosol 4-beta-D-glucoside (4-beta-D-glucosyl-3-hydroxyphenylethanol) coeluted with hydroxytyrosol [(3,4-dihydroxyphenyl)ethanol] under reversed phase conditions in the phenolic chromatograms of olive pulp, vegetation water, and pomace of olive oil processing. A method to separate this compound from hydroxytyrosol by HPLC has been developed. The concentration of this glucoside increased in olive pulp with maturation and could be the main phenolic compound in mature olives. In contrast, the presence of this compound was not detected in olive oil by using HPLC-MS. The compound must be considered both in table olives and olive oil processing because of its glucose and hydroxytyrosol contribution to these products.  相似文献   

Polyphenol changes during fermentation of naturally black olives     

Romero C  Brenes M  García P  García A  Garrido A 《Journal of agricultural and food chemistry》2004,52(7):1973-1979

The individual evolution of phenolic compounds has been studied during the natural fermentation of black olives for the first time. Cyanidin 3-rutinoside and cyanidin 3-glucoside were the main anthocyanins identified in fresh olives, and they were not detected after 1 month of storage either in brine or in olive. The fruit colors were different when aerobic or anaerobic conditions were used and as a consequence of the different anthocyanin polymerizations that took place. At time zero, the polyphenols observed in the olive juice were hydroxytyrosol-4-beta-glucoside, oleuropein, hydroxytyrosol, tyrosol, salidroside, and verbascoside and, after 12 months, the main phenol was hydroxytyrosol. The polyphenol content in the oil phase of olives was also analyzed. The dialdehydic form of elenolic acid linked to hydroxytyrosol and tyrosol, oleuropein aglycon, and ligstroside aglycon were the main compounds found at the beginning of fermentation but were not detected after 3 months. In contrast, hydroxytyrosol, hydroxytyrosol acetate, tyrosol, and tyrosol acetate were the main polyphenols detected in the oil phase of the final product. The acid hydrolysis of the initial glucosides (in olive juice) and the aglycons (in oil phase) was, therefore, the main reaction that took place during fermentation.  相似文献   

The causes of piping in a set of abandoned agricultural terraces in southeast Spain   总被引：1，自引：0，他引：1  

A. Romero Díaz  P. Marín Sanleandro  A. Snchez Soriano  F. Belmonte Serrato  H. Faulkner 《CATENA》2007,69(3):282-293

This study aims to identify some of the factors contributing to the piping process in abandoned terraces in seven sites located in the Murcia Region (southeast Spain). The local landscape has the appearance of badland geomorphology, possessing deep valleys which until the 1970s were terraced and cultivated. The terraces have now been abandoned to the piping process. The research focuses on the relationship between the size and position of pipes and the physical and geochemistry properties of the local highly dispersive marl lithology; and the extent to which the reworking of the materials for terrace cultivation has exacerbated piping erosion.Morphologically, the terracing in the stream beds has resulted in a series of gentle benches separated by steeper risers with variable ‘drop’, (riser height). A series of flat infiltration surfaces result, and because the resculpting produces a reduced bulk density infill with enhanced throughflow, infiltrating water is forced along steep hydraulic gradients to a low outfall at the base of the riser.Paralleling studies of land levelling and terrace abandonment in similar materials elsewhere, piping in the study area is shown to be closely related to the physical and chemical characteristics of the materials its sodicity and dispersive character. Considerable differences in structure, texture, mineralogical composition and material's surface crust and subsoil geochemical properties emerged from ‘site signature’ plots, and these results suggest that agricultural processes affect the dispersive character of the crust materials, presumably because agricultural activity increases the buffering effect of organic acids on the dispersed clay. This is supported by the observation that on the one site that was levelled but not used for agriculture, a stable organically-distinct crust like the abandoned agricultural sites has not formed. The changes to the material's aggregate stability and bulk density properties when terracing occurs is examined, but insufficient evidence is available from the data collected to unpick the causes of aggregate stability changes in the study plots. The way in which differences between crust and subsoil enhance infiltration is discussed, and the role of the terrace ‘drop’ in influencing hydraulic gradients and pipe development is illustrated. A possible index to describe the relationship between evacuated material volumes and the controlling parameters discussed above is tested.It is concluded that terracing which is intended as a conservation practice has, in dispersive materials, actually enhanced piping, leading to the abandonment of farming.  相似文献   

Changes in the phenolic composition of virgin olive oil from young trees (Olea europaea L. cv. Arbequina) grown under linear irrigation strategies.     

M J Tovar  M J Motilva  M P Romero 《Journal of agricultural and food chemistry》2001,49(11):5502-5508

This study reports the HPLC profiles of phenolic compounds of virgin olive oils obtained from young olive trees (Olea europaea L. cv. Arbequina) and how the application of a linear irrigation strategy affected these. Hydroxytyrosol, tyrosol, vanillic acid, vanillin, 4-(acetoxyethyl)-1,2-dihydroxybenzene, p-coumaric acid, the dialdehydic form of elenolic acid linked to hydroxytyrosol and to tyrosol, lignans, and the oleuropein aglycon were found in all the oils. Hydroxytyrosol, tyrosol, vanillic acid, and p-coumaric acid contents in the oils were unaffected by linear irrigation. The concentration of lignans was lower in the oils from the least irrigated treatment and the concentration of vanillin increased as the amount of irrigation water applied to olive trees increased. However, 4-(acetoxyethyl)-1,2-dihydroxybenzene, the dialdehydic form of elenolic acid linked to hydroxytyrosol and to tyrosol, and the oleuropein aglycon, all of them hydroxyphenyl derivatives, decreased as the level of irrigation water increased. The latter three compounds represented the most considerable part of the phenolic fraction of the oils and they were shown to be correlated to the oxidative stability, the bitter index (K(225)), and the bitter, pungent, and sweet sensory attributes. Linear irrigation strategy changed the profile of the oil phenolic compounds and, therefore, changed both the organoleptic properties and the antioxidant capacity of the product.  相似文献   

Interrill and rill erodibility in the northern Andean Highlands   总被引：2，自引：0，他引：2  

Consuelo C. Romero  Leo Stroosnijder  Guillermo A. Baigorria 《CATENA》2007

There is a lack of quantitative information describing the physical processes causing soil erosion in the Andean Highlands, especially those related to interrill and rill erodibility factors. To assess how susceptible are soils to erosion in this region, field measurements of interrill (Ki) and rill (Kr) erodibility factors were evaluated. These values were compared against two equations used by the Water Erosion Prediction Project (WEPP), and also compared against the Universal Soil Loss Equation (USLE) erodibility factor. Ki observed in situ ranged from 1.9 to 56 × 10⁵ kg s m^− 4 whereas Kr ranged from 0.3 to 14 × 10^− 3 s m^− 1. Sand, clay, silt, very fine sand and organic matter fractions were determined in order to apply WEPP and USLE procedures. Most of the evaluated soils had low erodibility values. However, the estimated USLE K values were in the low range of erodibility values. Stepwise multiple regression analyses were applied to ascertain the influence of the independent soil parameters on the Ki and Kr values. After this, we yield two empirical equations to estimate Ki and Kr under this Andean Highlands conditions. Ki was estimated using as predictors silt and very fine sand, while Kr used as predictors clay, very fine sand and organic matter content. Relationship among Ki, Kr and K are described for the Highland Andean soils.  相似文献   

Correlations between soil parameters and radionuclide contents in samples from Biscay (Spain)     

C. Elejalde  M. Herranz  F. Romero  F. Legarda 《Water, air, and soil pollution》1996,89(1-2):23-31

The distribution of gamma emitting radioactive constituents in Biscay soils have been measured in 15 cm cores, at three depth levels, in fourteen sampling positions. Analyses were performed in Marinelli beakers with a gamma multichannel analyser provided with a Ge-HP detector. Additionally, each soil was characterized by a number of parameters (position, bulk density, pH, size distribution, total contents of carbon, nitrogen and hydrogen, thermogravimetric data and major cations soluble in ammonium acetate at pH 7). Seven natural radioisotopes (⁴⁰K, ²²⁸Ac, ²¹²Bi, ²⁰⁸TI, ²²⁶Ra, ²¹⁴Pb and ²¹⁴Bi) and ¹³⁷Cs were detected and measured. Relations between natural radionuclides (located before and after radon isotopes in both radioactive series) and soil parameters are mainly explained by two statistical multivariate methods (factor analysis and numerical taxonomy). The more complex dependence of radiocaesium contents on soil characteristics was elucidated by linear multiple regression.  相似文献   

Phytoextraction of Cd and Pb and physiological effects in potato plants (Solanum tuberosum var. Spunta): importance of root temperature.   总被引：1，自引：0，他引：1  

M Baghour  D A Moreno  G Víllora  J Hernández  N Castilla  L Romero 《Journal of agricultural and food chemistry》2001,49(11):5356-5363

Three consecutive years of field experiments were carried out to investigate the effect of different root-zone temperatures, induced by the application of mulches, on the concentration and accumulation of Cd and Pb and on bioindicators (chlorophylls, catalase, peroxidase and cell wall fractions) in different organs of potato plants (roots, tubers, stems, and leaflets). Four different plastic covers were employed (T1, transparent polyethylene; T2, white polyethylene; T3, white and black coextruded polyethylene, and T4, black polyethylene), using uncovered plants as the control (T0). The different treatments had a significant effect on the mean root-zone temperatures (T0 = 16 degrees C, T1 = 20 degrees C, T2 = 23 degrees C, T3 = 27 degrees C, and T4 = 30 degrees C) and induced significantly different responses in the Cd and Pb concentrations and phytoaccumulation, with T2 (23 degrees C) and T3 (27 degrees C) giving high concentrations of Cd in the roots and low concentrations in other organs. In relation to Pb, T2 and T3 reached higher levels in the tubers and lower levels in the roots, stems, and leaves. In terms of phytoaccumulation, the roots and tubers were the most effective organs for Cd and Pb. On the other hand, the highest values of peroxidase and catalase activities were obtained for T3. In addition, most of the carbohydrate fractions in both the roots and the tubers were highest for T3. Meanwhile, the lowest pigment values were registered for T1 (20 degrees C). For phytoremediation, it is necessary to ascertain the relevance and control of the thermal regime of the soil to optimize the phytoextraction of pollutant elements (Cd and Pb).  相似文献