Certification of B-group vitamins (B1, B2, B6, and B12) in four food reference materials     

Ollilainen V  Finglas PM  van den Berg H  de Froidmont-Görtz I 《Journal of agricultural and food chemistry》2001,49(1):315-321

In 1989, the Community Bureau of Reference started a research program to improve the quality of vitamin analysis in food. To achieve this task, vitamin methodology was evaluated and tested by interlaboratory studies and the preparation of certified reference materials, which will be used for quality control of vitamin measurements. The main improvements in methodology were achieved by testing and standardizing the extraction condition and enzymatic hydrolysis procedures. Results for each individual material are derived from five replicate determinations using at least two independent methods: liquid chromatography (HPLC) and microbiological assay for vitamins B1, B2, and B6; and radioprotein binding and microbiological assays for vitamin B12. The certificate of analysis for four reference materials gives mass fraction values for water-soluble vitamins. These certified values were based on the acceptable statistical agreement of results from collaborating laboratories. Certified values with uncertainties (mg/kg dry matter) for each CRM are as follows: 4.63 (0.20) and 4.10 (0.51) for vitamins B1 and B6, respectively, in CRM 121 (wholemeal flour); 6.51 (0.24), 14.54 (0.3), 6.66 (0.43), and 0.034 (0.003) for vitamins B1, B2, B6, and B12, respectively, in CRM 421 (milk powder); 3.07 (0.17) and 4.80 (0.40) for vitamins B1 and B6, respectively, in CRM 485 (lyophilized mixed vegetables), and 8.58 (0.55), 106.8 (2.8), 19.3 1.5), and 1.12 (0.044) for vitamins B1. B2, B6, and B12, respectively, in CRM 487 (lyophilized pig liver).  相似文献   

Model for calculating regional energy use,industrial production and greenhouse gas emissions for evaluating global climate scenarios     

H. J. M. de Vries  J. G. J. Olivier  R. A. van den Wijngaart  G. J. J. Kreileman  A. M. C. Toet 《Water, air, and soil pollution》1994,76(1-2):79-131

In the integrated IMAGE 2.0 model the “Energy-Industry System” is implemented as a set of models to develop global scenarios for energy use and industrial processes and for the related emissions of greenhouse gases on a region specific basis. The Energy-Economy model computes total energy use, with a focus on final energy consumption in end-use sectors, based on economic activity levels and the energy conservation potential (“end-use approach”). The Industrial Production and Consumption model computes the future levels of activities other than energy use, which lead to greenhouse gas emissions, based on relations with activities defined in the Energy-Economy model. These two models are complemented by two emissions models, to compute the associated emissions by using emission factors per compound and per activity defined. For investigating energy conservation and emissions control strategy scenarios various techno-economic coefficients in the model can be modified. In this paper the methodology and implementation of the “Energy-Industry System” models is described as well as results from their testing against data for the period 1970–1990. In addition, the application of the models is presented for a specific scenario calculation. Future extensions of the models are in preparation.  相似文献   

Generation of unidirectionally propagated action potentials in a peripheral nerve by brief stimuli   总被引：1，自引：0，他引：1  

C van den Honert  J T Mortimer 《Science (New York, N.Y.)》1979,206(4424):1311-1312

Single, unidirectionally propagated action potentials can be elicited in peripheral nerves by electrical stimuli of short duration. Propagation in one direction is blocked anodically by means of a quasi-trapezoidal stimulus wave form and a modified tripolar electrode configuration. Propagation in the other direction proceeds unhindered. This technique may be applicable to collision blocking of motor nerves for neural prostheses.  相似文献   

Farming systems development: Synthesizing indigenous and scientific knowledge systems     

Christoffel den Biggelaar 《Agriculture and Human Values》1991,8(1-2):25-36

Agricultural development strategies to date were chiefly based on Western technological solutions, with mixed success rates. Farming Systems Research (FSR) was advanced as a way to increase the use of indigenous knowledge of farming to make new technologies more adaptable and appropriate to farming conditions. FSR has enabled researchers to focus attention on people and their knowledge by increasing people's participation in problem identification and new technology validation. In practice, though, FSR continues to be a top-down approach: technologies continue to be developed (in most cases) in the exogenous, Western knowledge system. Little has been done to develop indigenous technology generating and diffusing capacities already present in the rural areas. In this paper, a model adapted from Bell (1979) will be advanced that is based on cooperation and collaboration between the exogenous and indigenous knowledge systems leading to a synthesis of the two. The underlying principle of the model is that the ultimate solution for rural development is not the dumping of more scientists upon rural people (of whatever discipline) to make exogenously-generated technologies more adaptable and in-line with people's problems, but to strengthen, empower, and legitimize indigenous capacities for identifying problems and developing solutions for these problems. The “empowerment” of the indigenous knowledge/technology system (however difficult that may be politically) so that it has equal footing with Western knowledge may well be the most important step in a strategy of enabling the people in the developing countries themselves to alleviate their poverty.  相似文献   

Silver-intensified gold and peroxidase as dual ultrastructural immunolabels for pre- and postsynaptic neurotransmitters   总被引：3，自引：0，他引：3  

A N van den Pol 《Science (New York, N.Y.)》1985,228(4697):332-335

An ultrastructural immunostaining method that uses silver-intensified gold was combined with another procedure that uses biotin peroxidase conjugates to allow simultaneous identification of two neurotransmitter-related antigens in the central nervous system. Tyrosine hydroxylase-immunoreactive neurons labeled with silver-intensified gold could be differentiated at both light and electron microscopic levels from glutamate decarboxylase-immunoreactive neurons labeled with peroxidase. Cross reactivity of the second group of immunoreagents with the first group was reduced by the heavy metal silver shell formed around the colloidal gold immunoglobulin complex. With this dual pre-embedding method, peroxidase-stained axons containing the inhibitory neurotransmitter gamma-aminobutyric acid were found to synapse directly on silver-stained dopamine neurons in the rat dorsomedial hypothalamus. This approach can be used in combination with a post-embedding immunocytochemical colloidal gold procedure, allowing ultrastructural identification of three neurotransmitter-related antigens in the same tissue section.  相似文献   

Crystal structure of the long-chain fatty acid transporter FadL     

van den Berg B  Black PN  Clemons WM  Rapoport TA 《Science (New York, N.Y.)》2004,304(5676):1506-1509

The mechanisms by which hydrophobic molecules, such as long-chain fatty acids, enter cells are poorly understood. In Gram-negative bacteria, the lipopolysaccharide layer in the outer membrane is an efficient barrier for fatty acids and aromatic hydrocarbons destined for biodegradation. We report crystal structures of the long-chain fatty acid transporter FadL from Escherichia coli at 2.6 and 2.8 angstrom resolution. FadL forms a 14-stranded beta barrel that is occluded by a central hatch domain. The structures suggest that hydrophobic compounds bind to multiple sites in FadL and use a transport mechanism that involves spontaneous conformational changes in the hatch.  相似文献   

Implications for mantle dynamics from the high melting temperature of perovskite     

van Keken PE  Yuen DA  van den Berg AP 《Science (New York, N.Y.)》1994,264(5164):1437-1439

Recent studies have implied that (Mg, Fe)SiO(3)-perovskite, a likely dominant mineral phase in the lower mantle, may have a high melting temperature. The implications of these findings for the dynamics of the lower mantle were investigated with the use of numerical convection models. The results showed that low homologous temperatures (0.3 to 0.5) would prevail in the modeled lower mantle, regardless of the effective Rayleigh number and internal heating rates. High-temperature ductile creep is possible under relatively cold conditions. In models with low rates of internal heating, local maxima of viscosity developed in the mid-lower mantle that were similar to those obtained from inversion of geoid, topography, and plate velocities.  相似文献   

Galaxies, human eyes, and artificial neural networks     

Lahav O  Naim A  Buta RJ  Corwin HG  de Vaucouleurs G  Dressler A  Huchra JP  van den Bergh S  Raychaudhury S  Sodré L  Storrie-Lombardi MC 《Science (New York, N.Y.)》1995,267(5199):859-862

The quantitative morphological classification of galaxies is important for understanding the origin of type frequency and correlations with environment. However, galaxy morphological classification is still mainly done visually by dedicated individuals, in the spirit of Hubble's original scheme and its modifications. The rapid increase in data on galaxy images at low and high redshift calls for a re-examination of the classification schemes and for automatic methods. Here are shown results from a systematic comparison of the dispersion among human experts classifying a uniformly selected sample of more than 800 digitized galaxy images. These galaxy images were then classified by six of the authors independently. The human classifications are compared with each other and with an automatic classification by an artificial neural network, which replicates the classification by a human expert to the same degree of agreement as that between two human experts.  相似文献   

Directional dynamics in the photodissociation of oriented molecules     

Rakitzis TP  van den Brom AJ  Janssen MH 《Science (New York, N.Y.)》2004,303(5665):1852-1854

We observed directional dynamics in the photodissociation of an oriented molecule. When a laser dissociated hexapole-oriented carbonyl sulfide molecules, the three-dimensional recoil of carbon monoxide fragments, which we measured with ion imaging, was strongly asymmetric. We obtained a microscopic view of molecular bond breaking that revealed both the sign and the magnitude of the deflection angle of the fragment in the molecular frame. This experimental approach can be applied to study and control the three-dimensional dynamics of photoinitiated reactions of fixed molecules or molecules oriented by emerging techniques.  相似文献   

Size and age of the universe     

van den Bergh S 《Science (New York, N.Y.)》1981,213(4510):825-830

The age of the universe based on abundances of isotopes is in the range 10 billion to 15 billion years. This is consistent with the age range 12 billion to 20 billion years calculated from the evolution of the oldest galactic stars. A third estimate of the age of the universe is based on the Hubble relation between the velocities of galaxies and their distances from us, where the inverse of the Hubble parameter H is a measure of the age of a uniformly expanding universe. Evidence that has been accumulating over the past few years indicates that the expansion of the universe may exhibit a rather large local perturbation due to the gravitational attraction of the Virgo supercluster. Different types of observations still produce conflicting evidence about the velocity with which the Local Group of galaxies (of which our Milky Way system is a member) is falling into the Virgo cluster. The results to date indicate that this velocity lies somewhere in the range 0 to 500 kilometers per second. The resulting ambiguity in the flow pattern for relatively nearby galaxies makes values of H derived from galaxies with radial velocities less than 2000 kilometers per second particularly uncertain, and this restricts determinations of H to distant galaxies, for which distances are particularly uncertain. The best that can be said at present is that H(-1) yields a maximum time scale in the range 10 billion to 20 billion years.  相似文献