F. van der Meulen

Quantitative Aspects of the Destruction of Red Cells Sensitized with IgG1 Autoantibodies: An Application of Flow Cytofluorometry

Summary. The purpose of this study was to determine whether quantitative or qualitative factors are of major importance in the destruction of red cells sensitized with incomplete warm autoantibodies of subclass IgG1.

Erosion processes in a dune landscape along the Dutch coast

Abstract The landscape of the dunes along the Dutch coast is the result of the interaction of biological and geomorphological processes. Where the latter prevail, new landforms are created: blowouts by wind erosion, and rills and accumulation footslopes by overland flow. Spatial extent and rate of the erosion processes have been assessed by mapping and by measuring. It appears that dune sand is either sensitive to erosion by wind, or erosion by water, depending on the presence of organic material. Clean (yellow) sand is cohesionless and easily blown away, but has no surface runoff. Grey sand containing organic matter on the other hand will resist wind erosion, but it is waterrepellent and will be washed from slopes when rain follows a period of dry weather. Once the grey surface sand is removed from the surfaces by water erosion, wind erosion begins in the underlying yellow sand. Present-day geomorphological processes reshape the slopes of the original parabolic dunes.Wind is particularly active in summit areas where new blowouts are formed, whereasoverland flow creates concave south-exposed slopes. The stepped surface of the north-exposed slopes is due to mass movements following rabbit activity.

The development of dune blowouts, as measured with erosion pins and sequential air photos

Abstract The development of blowouts in dune terrains where no stabilization measures are taken requires constant watch to detect unwanted developments at an early stage. Two methods for investigating blowout development are in use. Since 1983, blowouts in a 40 ha section of Meijendel, a coastal dune area near The Hague have been twice yearly measured with erosion pins. Most of the 32 to 35 blowouts grew in length against the prevailing SW wind. The total blowout deflation area increased from 2.8 to 3.3% of the terrain in 4 years time. Air photos of 1958, 1967, 1977, 1984 and 1986 were used to study blowouts in a nearby area, De Blink north of Noordwijk, one of the most severely eroded dune terrains along the Dutch mainland coast. Total deflation area here increased from 0.8% in 1958 to 3.7% in 1986. There is a definite modal length class but the size is site-specific: 25 to 30 m in Meijendel, 15 to 20 m in De Blink. Many blowouts disappear shortly after they are formed. From the results it appears that the processes involved in the formation of blowouts can best be investigated with erosion pins whereas aerial photographs are preferable when changes in the spatial and temporal pattern of blowouts and the contributing factors are of interest.

Photodynamic destruction of Haemophilus parainfluenzae by endogenously produced porphyrins

Bacterial resistance against antibiotic treatment is becoming an increasing problem in medicine. Therefore methods to destroy microorganisms by other means are being investigated, one of which is photodynamic therapy (PDT). It has already been shown that a variety of Gram-positive and Gram-negative bacteria can be killed in vitro by PDT using exogenous sensitizers. An alternative method of photosensitizing cells is to stimulate the production of endogenous sensitizers. The purpose of this study was to investigate the bactericidal efficacy of PDT for Haemophilus parainfluenzae with endogenously produced porphyrins, synthesized in the presence of delta-aminolaevulinic acid (delta-ALA). H. parainfluenzae incubated with increasing amounts of delta-ALA showed decreased survival after illumination with 630 nm light. No photodynamic effect on the bacterial viability was found when H. parainfluenzae was grown without added delta-ALA. H. influenzae, grown in the presence of delta-ALA, but not capable of synthesizing porphyrins from delta-ALA, was not affected by PDT. Of the range of incident wavelengths, 617 nm appeared to be the most efficient in killing the bacteria. Spectrophotometry of the bacterial porphyrins demonstrated that the maximum fluorescence occurred at approximately 617 nm, with a much lower peak around 680 nm. We conclude that a substantial killing of H. parainfluenzae by PDT in vitro after endogenous sensitization with delta-ALA can be achieved.

Grazing as a control against ‘grass-encroachment’ in dry dune grasslands in the Netherlands

Abstract A study in dune grasslands in two Dutch coastal dune areas suggests that ‘grass-encroachment’, the dominance of a few tall grass species in formerly open, species-rich dune grasslands in the Netherlands, results in a loss of species, notably therophytes, bryophytes and lichens, as well as a strong reduction of the availability of daylight at the ground floor. Grazing with cattle and ponies as a control against ‘grass-encroachment’ has been studied in two coastal dune areas. Grazing with shetland ponies in ‘de Zepeduinen’ began in 1983. Aerial photographs of 1978, 1988 and 1993 were compared. After an initial increase in tall grass communities in both the valleys and the elevated dune ridges (8–20%) at the expense of more open vegetation, the photographs of 10 years of grazing revealed a decrease of tall grass cover (7–8%) and an increase of low grassland communities (4–5%). Grazing experiments in ‘het Zwanenwater’ started in parts of the area in 1984 and 1989. Comparison of vegetation maps of 1986 and 1992 revealed that tall grass cover increased over this period in the grazed areas (from 1–4% to 21–26%), but open communities were still prevalent (38–53%). In the non-grazed area, open communities declined dramatically (from 77% to 17%) and tall grass cover increased accordingly (from 3% to 53%). These preliminary results suggest that the present grazing regimes are perhaps not sufficient to stop grass-encroachment completely, but grazing seems a reasonably effective tool of management in terms of vegetation structure.

Nature conservation and integrated coastal zone management in Europe: present and future.

Abstract The present and future of integrated coastal zone management (ICZM) in Europe is discussed with an emphasis on nature conservation. The position of nature conservation in physical planning and in legislation is discussed within the historical perspective of the Netherlands. With regard to the present position of nature conservation in planning and legislation, differences in Europe between the northwest, the south and the east are discussed. The roles of various organisations (such as NGOs, GOs, Universities and the European Union) in ICZM is briefly mentioned. The paper advocates a strong position for nature conservation in integrated coastal zone management if it is to be developed on a sustainable basis.

Cryopreservation of human monocytes

Abstract Monocytes were isolated from human peripheral blood by Ficoll-Isopaque density-gradient centrifugation and adherence to glass. These cells were then frozen according to an automatically controlled cooling program and stored in liquid nitrogen. After the freezing, thawing and washing, 63% of the cells present before cryopreservation were recovered. Over 95% of the recovered cells excluded trypan blue. Storage at −196 °C did not alter the percentage of monocytes (70–80%) in the supensions. Although the percentage of cells that formed rosettes with erythrocytes sensitized with IgG antibodies (EAIgG) was unaltered after freezing, formation of EA rosettes was more readily inhibited by free IgG. The capacity of monocytes to lyse EAIgG was not influenced by cryopreservation, in contrast with their potency to phagocytize zymosan particles, which was decreased. The chemotactic response toward casein was also diminished after freezing. There was no significant difference in reactivity between monocytes frozen for a short time (2–15 hr) and those frozen for a longer period (more than 3 months). Electron microscopic examination showed alterations in the mitochondrial structure of the frozen cells.

Laserlithotripsy of salivary stones: A comparison between the pulsed dye laser and the Ho-YSGG laser

The feasibility of laser lithotripsy of salivary stones was investigated. Two types of laser systems were evaluated: a 504 nm flashlamp pumped dye laser and a Ho-YSGG laser. With the dye laser, plasma flashes and acoustic phenomena could be observed. The number of laser shots per unit mass necessary to fragment the stone decreased in proportion to the energy per laser pulse to the power −2.7. With the Ho-YSGG laser, a more ablative kind of stone decomposition was observed. Here the number of shots per unit mass necessary for fragmentation was inversely proportional to the energy per laser pulse. For both lasers the total time necessary to fragment the stones is much too long to compete with conventional stone removal.

The use of a GIS in assessing the impacts of sea level rise on nature conservation along the Dutch coast: 1990–2090

The Dutch coastline is expected to change considerably during the next 100 years. Erosion will prevail, although accretion will occur locally.To establish a new policy for coastal defence management an integrated policy analysis study was performed. Major dune functions (nature conservation, recreation, public drinking water supply, housing and industry) have been inventarized by using a Geographic Information System.This study reports on the part of the analysis which takes nature conservation interests into account. Evaluation of nature interests has been based on the criteria: rarity and diversity of plant species c.q. vegetation types, succession stage, and completeness. This results in a classification of nature into five classes, based on abiotic as well as biotic characteristics of the landscape. Losses of nature interests were studied due to: loss of land because of shoreline retreat, to remodelling of the foredune ridge, and to changes of the dune groundwater level.An evaluation is given of the methods used to assess ecological impacts.Ideas are presented for further research on the prediction of ecological impacts and on coastline management which combines traditional coastal defence with nature conservation.

Aeolian dynamics in relation to vegetation in a blowout complex in the Meijendel dunes, The Netherlands

Changes in surface elevation in a former blowout in the coastal dunes of Meijendel, The Netherlands, have been monitored almost weekly during one year at 48 erosion pin sites, distributed over 12 units. The units are characterized by specific geomorphological processes. The changes in elevation are caused by wind, slope wash and mass movements. At almost each pin, periods of erosion alternate with periods of accumulation in a random way. Erosion and accumulation sequences are relatively long in areas dominated by aeolian activity, but even here they are randomly distributed. It is the balance between the effects of periods of erosion and periods of accumulation which determines the formation of blowouts or dunes.Units with the highest degree of erosion or accumulation at the end of the year of monitoring also show the highest fluctuations in elevation during that year. In the accumulation units there is even a significant positive correlation between surface lowering by erosion and surface rise by accumulation.Plant species in the blowout are divided into four groups on the basis of responses to aeolian dynamics: (1)Sedum acre is the only species associated with deflation; it might be suitable for blowout stabilization; (2)Ammophila arenaria, Festuca rubra andOnonis repens are associated with aeolian accumulation and can be used for the stabilization of accumulation sites; (3)Erodium cicutarium, Koeleria macrantha andCorynephorus canescens, occurring at lower aeolian activity; (4)Tortula ruralis var.ruraliformis andGalium verum are found where slope wash and mass movements (Galium) are active.In the relationship between aeolian dynamics and vegetation, the former appears to be the independent variable: there is no consistent relationship between accumulation and vegetation cover. This means that the formation of blowouts and adjacent dunes is not controlled by vegetation with its present cover.