Het "Waarom" van de Intensive Care

Rede, in verkorte vorm, uitgesproken bij het aanvaarden van het ambt van bijzonder hoogleraar met als leeropdracht Intensive Care aan het Erasmus MC, faculteit van de Erasmus Universiteit Rotterdam, op 13 april 200

Essays in international trade and economic geography

This thesis studies how the spatial distribution of economic activity matters for the transmission of, and is in turn affected by different shocks. In Chapter 2, I show that the agglomeration-congestion cost trade-off studied by urban economists alters both the distributional effects of, and gains from trade. Correspondingly, I demonstrate that openness to trade affects the spatial distribution of economic activity across cities of different densities. First, I show that the export intensity of firms and sectors is higher in denser locations. I propose an open economy economic geography model that rationalizes these stylized facts. When testing the underlying mechanisms proposed by the model, I find that the higher export intensity in denser places is driven by differences in productivity across firms, differences in factor intensities across sectors and trade-specific gains from agglomeration that lead to lower variable export cost in denser places. In line with the model predictions, I further find that a decrease in trade cost, proxied by exogenous changes in export market access, leads to a reallocation of economic activity to denser places. In currently on-going work I am exploring whether ignoring the increase in aggregate congestion costs from the rise in spatial concentration leads to an overestimation of the gains from trade. In Chapter 3 I study how an exogenous population shock affects the spatial distribution of population. To this end I exploit the end of movement restrictions for black South Africans at the end of Apartheid to generate an exogenous population shock. Until 1991, black South Africans were severely restricted in their location choices and many were forced to live in homelands. Following the abolition of apartheid, they were free to migrate. Given the general gravity structure of migration, a town closer to the homelands is expected to receive a larger inflow of migrants than towns further away. Using this exogenous variation, I find that on average there is no endogenous reallocation of population following this exogenous immigration. When separately looking at rural and urban places, I find that there is a displacement of incumbents in the former while there are additional inflows in urban areas. Chapter 4 provides evidence for the importance of trading opportunities for settlement location during the Iron Age. It finds that regions in the Mediterranean that are better connected across the open sea have more economic activity proxied by the number of archaeological sites. This correlation becomes particularly strong around 750 BC when the Phoenicians started to regularly cross the open sea. Analysis at the global level corroborates the finding that more connected locations have a higher population density in 1 AD. Overall, I find that trade and migration shocks have important effects on the long-run distribution of population and economic activity in space

Gravitational binding in 4D dynamical triangulation

In the dynamical triangulation model of four dimensional euclidean quantum gravity we investigate gravitational binding. Two scalar test particles (quenched approximation) have a positive binding energy, thereby showing that the model can represent gravitational attraction.Comment: 19 pages, LaTeX2e, version as accepted by Nucl Phys

Cluster analysis of flow cytometric list mode data on a personal computer

A cluster analysis algorithm, dedicated to analysis of flow cytometric data is described. The algorithm is written in Pascal and implemented on an MS-DOS personal computer. It uses k-means, initialized with a large number of seed points, followed by a modified nearest neighbor technique to reduce the large number of subclusters. Thus we combine the advantage of the k-means (speed) with that of the nearest neighbor technique (accuracy). In order to achieve a rapid analysis, no complex data transformations such as principal components analysis were used. \ud Results of the cluster analysis on both real and artificial flow cytometric data are presented and discussed. The results show that it is possible to get very good cluster analysis partitions, which compare favorably with manually gated analysis in both time and in reliability, using a personal computer

A new principle of cell sorting by using selective electroporation in a modified flow cytometer

When a strong electric field pulse of a few microseconds is applied to biological cells, small pores are formed in the cell membranes; this process is called electroporation. At high field strengths and/or long pulse durations the membranes will be damaged permanently. This eventually leads to cell kill. \ud We have developed a modified flow cytometer in which one can electroporate individual cells selected by optical analysis. The first experiments with this flow cytometer were designed to use it as a damaging sorter; we used electric pulses of 10 s and resulting field strengths of 2.0 and 3.2 X 106 V/m to kill K562 cells and lymphocytes respectively. The hydrodynamically focused cells are first optically analyzed in the usual way in a square flow channel. At the end of this channel the cells are forced to flow through a small Coulter orifice, into a wider region. If optical analysis indicates that a cell is unwanted, the cell is killed by applying a strong electric field across the Coulter orifice. The wanted living cells can be subsequently separated from the dead cells and cell fragments by a method suitable for the particular application (e.g., centrifugation, cell growth, density gradient, etc.). \ud The results of these first experiments demonstrate that by using very simple equipment, sorting by selective killing with electric fields is possible at rates of 1,000 cells/s with a purity of the sorted fraction of 99.9%

Cardiac Complications after Non-cardiac Surgery: Perioperative Risk Prediction and Reduction Strategies

__Abstract__ Introduction | 9 I More than 200 million people worldwide undergo non-cardiac surgery annually. It is estimated that 2-5 percent of these patients suffer a cardiac complication (i.e. myocardial infarction, congestive heart failure, arrhythmia), resulting in death in approximately 0.5 percent of all patients. The frequent occurrence of devastating cardiac complications necessitates a thorough assessment of the risk of cardiac complications in every patient scheduled for non-cardiac surgery. This risk is influenced by the preoperative condition of the patient and the invasiveness of the planned procedure, and is modifiable by vari

Remarks on the quantum gravity interpretation of 4D dynamical triangulation

We review some of the phenomenology in 4D dynamical triangulation and explore its interpretation in terms of a euclidean effective action of the continuum form \intx \sqrt{g} [\mu -\frac{1}{16\pi G} R + \cdots].Comment: Talk presented at LATTICE96(gravity); 3 pages; LaTeX, espcrc2.st

The TRB West Group

In 1979 the by now classic work on the pottery of the TRB West group of Jan Albert Bakker was published. In his book Bakker deals with the research history and typochronology of the TRB pottery. Also he gives a detailed account of the other TRB finds such as flint and stone artefacts and of course the most important TRB sites. Over the years this book has become a standard-work for anyone who is interested in hunebeds and their makers. The author wrote a new introduction to this reprint in which he describes how the book of 1979 came together and the research that has been carried out since then

Practical Use of Lactate Levels in the Intensive Care

Hyperlactatemia is a strong predictor of mortality in diverse populations of critically ill patients. In this article, we will give an overview of how lactate is used in the intensive care unit. We describe the use of lactate as a predictor of outcome, as a marker to initiate therapy and to monitor adequacy of initiated treatments