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排序方式: 共有270条查询结果,搜索用时 15 毫秒
51.
Schiros T Nordlund D Pálová L Prezzi D Zhao L Kim KS Wurstbauer U Gutiérrez C Delongchamp D Jaye C Fischer D Ogasawara H Pettersson LG Reichman DR Kim P Hybertsen MS Pasupathy AN 《Nano letters》2012,12(8):4025-4031
Robust methods to tune the unique electronic properties of graphene by chemical modification are in great demand due to the potential of the two dimensional material to impact a range of device applications. Here we show that carbon and nitrogen core-level resonant X-ray spectroscopy is a sensitive probe of chemical bonding and electronic structure of chemical dopants introduced in single-sheet graphene films. In conjunction with density functional theory based calculations, we are able to obtain a detailed picture of bond types and electronic structure in graphene doped with nitrogen at the sub-percent level. We show that different N-bond types, including graphitic, pyridinic, and nitrilic, can exist in a single, dilutely N-doped graphene sheet. We show that these various bond types have profoundly different effects on the carrier concentration, indicating that control over the dopant bond type is a crucial requirement in advancing graphene electronics. 相似文献
52.
Harish K. Patney Christina Nordlund Adam Moy Harry Rose Brent Young Michael A. Wilson 《Fullerenes, Nanotubes and Carbon Nanostructures》2013,21(6):941-971
Abstract Graphite has normally been used to synthesise fullerenes and nanotubes. However, coal is a cheaper and more suitable industrial material. Because coal is a molecular solid, unlike graphite, the mechanism by which fullerene and nanotubes are formed is different. Moreover, other products such as polyaromatic hydrocarbons (PAHs) and microfibres are also formed. In this review, the mechanism of formation of fullerene and nanotubes from coal is discussed. It is shown that the pathway involved is other than through the C1 intermediate route. The influence of other elements in coal such as hydrogen, oxygen, sulfur and iron is also discussed. It appears that, hydrogen, oxygen, iron and sulfur affect the yield and type of fullerenes and nanotubes formed. 相似文献
53.
Taxt T Jirík R Rygh CB Grüner R Bartos M Andersen E Curry FR Reed RK 《IEEE transactions on bio-medical engineering》2012,59(4):1012-1021
Multipass dynamic MRI and pharmacokinetic modeling are used to estimate perfusion parameters of leaky capillaries. Curve fitting and nonblind deconvolution are the established methods to derive the perfusion estimates from the observed arterial input function (AIF) and tissue tracer concentration function. These nonblind methods are sensitive to errors in the AIF, measured in some nearby artery or estimated by multichannel blind deconvolution. Here, a single-channel blind deconvolution algorithm is presented, which only uses a single tissue tracer concentration function to estimate the corresponding AIF and tissue impulse response function. That way, many errors affecting these functions are reduced. The validity of the algorithm is supported by simulations and tests on real data from mouse. The corresponding nonblind and multichannel methods are also presented. 相似文献
54.
Monitoring nonlactating cow intramammary infection dynamics using DHI somatic cell count data 总被引:2,自引:0,他引:2
Although the nonlactating period presents a risk for intramammary infection, efficient systems to monitor infection status of recently calved cows have not been developed, and benchmarks for interpretation have not been established. Individual cow somatic cell count (SCC) data for the current and previous six monthly Dairy Herd Improvement milk tests and the last SCC of the previous lactation and first SCC of the current lactation were summarized for all milking cows in a selection of Wisconsin dairy herds. Prevalence of infection, herd new infection rate, fresh cow contribution to herd new infection rate, dry cow new infection rate, heifer new infection rate, and dry cow cure rate were estimated using a threshold of 200,000/ml. In 145 herds, mean (range) heifer new infection rate was 21.3% (0 to 58%). The cut-point for the 10th percentile of herds was 8%. Mean (range) dry cow new infection rate in cows that were uninfected at the last test before dry off was 22.4% (0 to 71%), and the cut-point for the 10th percentile of herds was 9%. Although nonlactating cow and heifer new infection rates increased with weighted 6-mo mean herd SCC, the between-herd variation was large, suggesting that on-farm factors are important in determining the rates of infection. In a subset of 51 Wisconsin dairy herds, significant monthly variation in weighted SCC, prevalence, herd new infection rate, and fresh cow contribution to herd new infection rate were detected. Elevations in SCC and prevalence of infection during the summer (July through September) were associated with significant increases in fresh cow and herd new infection rates. 相似文献
55.
Karin Petersson Emilia Nordlund Eva Tornberg Ann‐Charlotte Eliasson Johanna Buchert 《Journal of the science of food and agriculture》2013,93(4):882-889
BACKGROUND: Rye and wheat bran were treated with several xylanases and endoglucanases, and the effects on physicochemical properties such as solubility, viscosity, water‐holding capacity and particle size as well as the chemical composition of the soluble and insoluble fractions of the bran were studied. A large number of enzymes with well‐defined activities were used. This enabled a comparison between enzymes of different origins and with different activities as well as a comparison between the effects of the enzymes on rye and wheat bran. RESULTS: The xylanases derived from Bacillus subtilis were the most effective in solubilising dietary fibre from wheat and rye bran. There was a tendency for a higher degree of degradation of the soluble or solubilised dietary fibre in rye bran than in wheat bran when treated with most of the enzymes. CONCLUSION: None of the enzymes increased the water‐holding capacity of the bran or the viscosity of the aqueous phase. The content of insoluble material decreased as the dietary fibre was solubilised by the enzymes. The amount of material that may form a network to retain water in the system was thereby decreased. © 2012 Society of Chemical Industry 相似文献
56.
Outi K. Santala Emilia A. Nordlund Kaisa S. Poutanen 《Food and Bioprocess Technology》2013,6(11):3102-3112
The aim of the work was to elucidate the impacts of treatment with xylanase at high (90 %) and low (40 %) water contents on the structural and physicochemical properties of wheat bran. The bran treatments at 40 % water content, both with and without added xylanase, resulted in a smaller average bran particle size, more changes in bran microstructure, and higher solubilization of polysaccharides than the corresponding treatments at 90 %. Also, the water holding capacity of bran (3.6?±?0.1 g water/g bran dm), determined by Baumann method, decreased more already after 4-h xylanase treatments at 40 % (2.4?±?0.1) than at 90 % (2.9?±?0.2). The solubility of salt-extractable bran proteins decreased during the treatments, especially at 40 %, also without added xylanase. Protein aggregation was detected in the SDS?+?DTT-extractable bran fraction, which also contained small proteins of 10–20 kDa not detectable in the untreated bran. The use of xylanase had only minor effect on bran proteins as compared to the treatments without added xylanase. The results indicate the large role of mechanical shear on the bran properties at 40 % water content. The low arabinose/xylose ratio (0.32) in the bran water extract after 24-h xylanase treatment at 40 %, however, suggests that the solubilization of arabinoxylan was caused by enzymatic action, and not by mechanical degradation. Arabinose/xylose ratio of the bran water extract decreased similarly during all the treatments, suggesting similar solubilization pattern of arabinoxylan at both water contents. The study showed that bran properties can be significantly modified by adjusting the water content and mechanical energy used in processing. 相似文献
57.
Abstract We present an experimental realization of discrimination between non-orthogonal polarization states at the Helstrom bound for minimum probability of error. The experiment was performed with highly attenuated laser light with a mean number of about 0·1 photons per pulse. 相似文献
58.
Mikael Solymar Eberhard Lehmann Peter Vontobel Anders Nordlund 《Bulletin of Engineering Geology and the Environment》2003,62(1):85-88
Neutron tomography experiments were undertaken on a quartz arenite sample in order to determine saturation variations in
the sample after the initially water-saturated sample was subjected to air flushing. The experiments were carried out in order
to study the applicability of the neutron tomography facility at the Paul Scherrer Institute, Switzerland, for imaging fluid
distribution in porous rocks. The variation in water saturation was related to the pore geometry of the sample as investigated
by petrographic image analysis of thin sections. A variation in fluid saturation was successfully imaged. The spatial saturation
distribution noted from the neutron tomography corresponds well with variations in pore geometry, indicating that the water
was preferentially flushed from the coarse-grained laminae.
Résumé. Des mesures tomographiques neutroniques ont été réalisées sur un échantillon de grès quartzeux dans le but d'y déterminer
des variations de degré de saturation après que l'échantillon initialement saturé en eau ait été soumis à un drainage forcé.
Les expériences ont été conduites afin d'étudier la capacité d'un dispositif de tomographie neutronique de l'Institut Paul
Scheerer (Suisse) à donner une image de la répartition des fluides dans les roches poreuses. Des variations de degré de saturation
ont été identifiées avec succès, variations en relation avec la géométrie des pores de l'échantillon comme cela a pu être
identifié par des techniques d'analyse d'image de lames minces. La répartition spatiale du degré de saturation observée à
partir de la tomographie neutronique correspond bien à des variations dans la géométrie des pores, indiquant que l'eau avait
été préférentiellement chassée des lamines constituées de gros grains.
Electronic Publication 相似文献
59.
Erling Havn 《AI & Society》1991,5(4):308-320
In Scandinavia theories and methods for cooperative design tools for the computer supported craftsman have been the topics for intensive research for several years. This paper widens the discussion by taking in the question of CIM and the reshaping of the division of labour, work organisation and manufacturing processes. The paper argues for an evaluation of methods and tools developed for very different aspects of integrated manufacturing. 相似文献
60.
EE Medrano JZ Farooqui RE Boissy YL Boissy B Akadiri JJ Nordlund 《Canadian Metallurgical Quarterly》1993,90(5):1790-1794
In the human epidermis, melanocytes are distributed at a distance from each other. In contrast, melanocytes in nevi, which are considered benign neoplasms of melanocytes, are grouped in nests. Although still not well defined, environmental factors are thought to play an important role in the development of nevi. We found that chronic growth stimulation by leukotriene C4, a compound found in increased amounts in inflamed skin, induced pleiotropic modifications in the normal melanocyte phenotype. These changes include loss of contact inhibition and formation of structures resembling tumor spheroids. In parallel with these changes, there was a constitutive expression of Fos protein. Switching these cultures to medium supplemented with phorbol ester sustained growth with reversion of the altered phenotype. In contrast, a cAMP stimulator, cholera toxin, induced features of terminal differentiation. Our findings suggest a role for inflammatory mediators in human epidermal melanocytes. This observation provides insight into melanocyte growth alterations which may have relevance in early stages of melanocyte oncogenesis. 相似文献