UV-B induced immunomodulation: a health risk     

Johan Garssen  Mary Norval  Henk Van Loveren 《Polar research》1999,18(2):339-343

The depletion in stratospheric ozone and changes in life-styles are likely to lead to an increased exposure to sunlight, including the UV-B waveband. Such irradiation may induce immunomodulation and therefore have adverse effects on human health. Alterations in immune responses could affect not only photocarcinogenesis but also resistance to infections, certain allergies and autoimmunity, and vaccination efficacy. In the present study, the risk of increased UV-B exposure has been estimated with respect to the resistance to a bacterial ( Listeria monocytogenes ) and a viral (herpes simplex virus) infection. The data indicate that suberythemal UV-B irradiation can have significant effects on immune responses to certain infectious diseases in human subjects.  相似文献   

Late Precambrian granitic and volcanic rocks and their relation to the cratonization of the Arabian Shield     

Henk J. Duyverman 《Precambrian Research》1982,16(4):A49

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A physical mechanism for the Atlantic–Pacific flow reversal in the early Miocene     

Anne Willem Omta  Henk A. Dijkstra   《Global and Planetary Change》2003,36(4):265

Barotropic wind-driven steady ocean circulation patterns have been calculated for several different continental geometries during the Tertiary. Using a shallow-water model, flows are computed at 5-Ma intervals within the 60–20 Ma period, while keeping a fixed pattern of the wind-stress forcing. The most interesting changes in ocean circulation occur between 35 and 20 Ma, in which (i) the Antarctic Circumpolar Current appears because of the widening of Drake Passage, (ii) the Tethys Current disappears because of the closure of the Tethys Seaway and (iii) the transport through Panama Straits (between North and South America) reverses. The results are qualitatively in agreement with interpretations of changes in ocean surface currents drawn on the basis of proxy studies. A physical mechanism of the flow reversal through the Panama Straits is proposed based on a detailed analysis of the changes in wind-driven transport of both the Tethys Current and the Antarctic Circumpolar Current.  相似文献   

Re-imagining spaces of (in)difference: Contextualising and reflecting on the intertwining of cities across borders     

Henk van Houtum  Huib Ernste 《GeoJournal》2001,54(1):101-105

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Analysis of modern and fossil plant cuticles by Curie point Py-GC and Curie point Py-GC-MS: Recognition of a new, highly aliphatic and resistant biopolymer     

M. Nip  E.W. Tegelaar  H. Brinkhuis  J.W. De Leeuw  P.A. Schenck  P.J. Holloway 《Organic Geochemistry》1986,10(4-6)

This paper investigates to what extent the chemical constituents of plant cuticles (waxes and cutin) can survive diagenesis. Recent and fossil plant cuticles were analyzed by means of Curie point pyrolysis-gas chromatography and Curie point pyrolysis-gas chromatography-mass spectrometry. Recent cuticles were analyzed without treatment, after solvent extraction and after cutin depolymerization. Extensive series of straight-chain alkanes, alk-1-enes and α,ω)-alkadienes dominate the pyrolysates, especially after removal of the wax and cutin. ¹³C-NMR spectroscopy of the residue after removal of the cutin confirmed the presence of a new, highly aliphatic biopolymer and a polysaccharide fraction.The abundance of straight-chain alkanes, alk-1-enes and α,ω-alkadienes in the fossil plant cuticles indicates the chemical resistence of the biopolymer to diagenesis and may explain the occurrence of straight-chain aliphatic moieties in organic-matter-rich sediments and coals as revealed by “C-NMR spectroscopy and flash pyrolysis methods. The highly aliphatic biopolymer may function as an important oil precursor.  相似文献   

Multivariate analysis of aquatic toxicity data with PLS   总被引：2，自引：0，他引：2  

Lennart Eriksson  Joop L. M. Hermens  Erik Johansson  Henk J. M. Verhaar  Svante Wold 《Aquatic Sciences - Research Across Boundaries》1995,57(3):217-241

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Intra- and interspecies comparison of energy flow in North Atlantic flatfish species by means of dynamic energy budgets   总被引：1，自引：0，他引：1  

Henk W. van der Veer  Sebastiaan A. L. M. Kooijman  Jaap van der Meer 《Journal of Sea Research》2001,45(3-4)

The quantitative aspects of growth and reproduction in four flatfish species (plaice, flounder, dab, sole) in terms of energy flow are described on the basis of a dynamic energy budget (DEB theory). This theory consists of general assumptions about energy uptake, storage and utilisation and describes an individual by two state variables: structure and reserve, whereby body size exerts its influence through the ratio between surface area and volume. Comparison between model estimates and field data shows that the DEB model successfully describes the energetics of growth and reproduction in a number of flatfish species. Differences between species could be captured in the same model using different parameter values. Intraspecific differences in growth between males and females are mainly caused by differences in maximum surface area-specific ingestion rates. Differences between species are reflected in the surface area-specific maximum ingestion rate, the energy partitioning over growth and reproduction, and in egg volume. According to these parameters at 283 K (10°C), the species could be ranked as follows: surface area-specific maximum ingestion rate (W m⁻²) plaice: 56.6; flounder: 54.5; sole: 45.1 and dab: 36.1 W m⁻². Fraction of energy allocated to reproduction (–): flounder: 0.35; plaice: 0.15; dab: 0.15 and sole 0.10. As a consequence of these differences in surface area-specific maximum ingestion rate and in the fraction of utilised energy allocated to reproduction, the gonad masses (g) of females of 0.5 kg wet mass differ considerably: flounder: 149 g; plaice: 86 g; sole: 70 g; and dab: 69 g. However, due to differences in egg size between species, the potential annual egg production shows a completely different pattern: dab: 2200 10³; flounder: 1560 10³; sole: 343 10³ and plaice: 130 10³ eggs.  相似文献   

Neural network modelling of wave overtopping at coastal structures     

Marcel R.A. van Gent  Henk F.P. van den Boogaard  Beatriz Pozueta  Josep R. Medina 《Coastal Engineering》2007

A method has been developed to estimate wave overtopping discharges for a wide range of coastal structures. The prediction method is based on Neural Network modelling. For this purpose use is made of a data set obtained from a large number of physical model tests (collected within the framework of the European project CLASH, see e.g. [Steendam, G.J., Van der Meer, J.W., Verhaeghe, H., Besley, P., Franco, L. and Van Gent, M.R.A. (2004). The international database on wave overtopping. World Scientific, Proc. 29th ICCE, vol. 4, pp. 4301–4313, Lisbon, Portugal.]). Moreover, a method was developed to obtain confidence intervals for the overtopping predictions of the neural network.  相似文献   

The timing and isotopic character of regional hydrothermal alteration and associated epigenetic mineralization in the western sector of the Kaapvaal Craton (South Africa)     

Michael J Duane  F.Johan Kruger  Audrey M Turner  Hannah T Whitelaw  Henk Coetzee  Balt T Verhagen 《Journal of African Earth Sciences》2004,38(5):69

The Kaapvaal Craton of South Africa comprises an Archaean core of ≈3.5 Ga lithospheric and crustal rocks surrounded by younger accreted terrains of ≈3.0–2.7 and ≈2.1–1.9 Ga. The craton is covered by relatively undeformed 3.0–2.4 Ga supracrustal rocks, which show the effects of thermal and hydrothermal interaction. Part of this activity is manifested by a large number of epigenetic Pb–Zn (±Ag, Au, Cu, F) deposits in the cover rocks of the Kaapvaal Craton. These include small volcanic and breccia hosted deposits in mafic and felsic volcanic rocks of the 2.7 Ga Ventersdorp Supergroup and the Mississippi Valley-type (MVT) deposits in the carbonates of the Transvaal Supergroup.MVT mineralization at the Pering (and other Zn–Pb deposits) is hosted in fracture-generated N–S breccia bodies in the Paleoproterozoic carbonate succession of the western Kaapvaal Craton. The fluids carrying the metals were focused in vertical bodies within the fracture zones (FZ), the metals and the sulphur being carried together and precipitated in organic-rich sectors of the basin. Two small Pb–Zn deposits within mafic rocks of the Ventersdorp Supergroup, stratigraphically below the basin-hosted MVTs on the southwestern part of the Kaapvaal Craton have secondary chlorite which is extremely Rb-rich, associated with the mineralization. This chlorite and the associated altered basaltic host rocks give a Rb–Sr date of ≈1.98 Ga, and the associated galena Pb isotope data plot on the same array as those of other Pb–Zn deposits, the radiogenic intercept giving a date of ≈2.0 Ga. We interpret these data to indicate a craton-wide epigenetic fluid-infiltration event, which exploited the Maquassie Quartz Porphyry (MQP) as the aquifer and metal source.Sr isotopic results for the ore-zone gangue minerals show highly radiogenic ⁸⁷Sr/⁸⁶Sr ratios (>0.710) which support earlier models that the origin of radiogenic Sr isotopic composition in the calcite cements is the felsic tuffs (MQP) of the Ventersdorp Supergroup occurring at deeper levels within the basin. Relationships between δ¹⁸O and δ¹³C performed on carbonate cements within the aquifers are complex: the range in δ¹³C for some of the cements represents a mixture from two sources and with a progression from heavy carbon in the host to somewhat lighter carbon in the cements. Similarly, the lighter δ¹⁸O values have a narrow range indicative of rapid exchanges between hydrous fluid and rock.  相似文献   

Determination of the cleat angle distribution of the RECOPOL coal seams, using CT-scans and image analysis on drilling cuttings and coal blocks   总被引：1，自引：1，他引：0  

Karl-Heinz A.A. Wolf  Frank van Bergen  Rudy Ephraim  Henk Pagnier 《International Journal of Coal Geology》2008,73(3-4):259-272

Cleat orientation, cleat frequency and cleat angle distribution of deep coal seams are only available by the use of drilling cores and from coal mine samples. Coal drilling cuttings are a cheap and fast alternative to measure cleat angle distributions with the use of image analysis techniques. In this study oriented coal samples and drilling cuttings of the RECOPOL field experiment are compared and used to explain and validate the proposed method. In other words, cleat angle distributions from drilling cuttings are measured by image analysis. The geological framework of the polish coals is described. The image analysis methodologies for the measurement of fracture faces of cuttings and from CT-scan images, derived from these coals, are explained. The results of the methods on the cuttings are compared with cleat orientation distributions from CT-scans and artificial fragments from coal blocks of the same seams. These evaluations show high agreements between the methods. The cleat angle distributions of drilling cuttings of four seams are compared with the cleat orientation distributions of a regional structural geological study. The high correlation in this study shows that cleat angle distributions of coal seams can be used as input parameters for reservoir modelling.  相似文献