Local Moufang sets and PSL_2 over a local ring

We introduce local Moufang sets as a generalization of Moufang sets. We present a method to construct local Moufang sets from only one root group and one permutation. We use this to describe $\mathsf{PSL}_2$ over a local ring as a local Moufang set, and give necessary and sufficient conditions for a local Moufang set to be of this form.Comment: 23 pages, fixed a problem in Lemma 5.8, where we need an extra assumption. Other results remain unchange

Local Moufang sets

All known Moufang sets arise, in some way or another, from an algebraic structure which can be called `division' in some way. In this PhD dissertation, I made an attempt to develop a theory of local Moufang sets, which generalize Moufang sets in a way to allow constructing using the corresponding local algebraic structures. In the first of the two major parts of the dissertation, I develop the theory of local Moufang sets, while in the second part, some examples are constructed. The most general example constructed arises from a local Jordan pair (which corresponds to a local Jordan algebra), and one of the main theorems characterizes these local Moufang sets.Comment: PhD dissertation of 221 page

A critical approach to some new ideas about the Dutch flood risk system

Decisions on measures to improve a flood risk system are in part supported by general ideas about how the system works and should work. After the completion of the Dutch Delta Works around 1990, such new ideas regarding flood risk emerged. Some of these may be appealing at first, but appear debatable after a closer look. In this paper, fourteen such debatable ideas, familiar to most Dutch water professionals, are formulated and criticised, in order to find out what can be learned from them. The most important Dutch national flood risk policy documents since 1990 are reviewed for quotes that illustrate these ideas, complemented by scientific papers and other documents. These quotes present different expressions of these ideas, and their number can suggest whether they are broadly shared or marginal. In twelve of the twenty most important government documents, 47 quotes were found; in 26 documents of other types, another 39. Eleven quotes describe the idea that ‘water should not be our enemy, but our friend’. Fifteen quotes were based on the idea that flood protection entraps us in a dangerous ‘spiral of risk’, which can be stopped, 44 quotes are related to the idea that flood risk reducing measures should be ‘natural’ or ‘move with nature’. The remaining quotes illustrate other debatable ideas, such as ‘water should lead spatial planning’ and ‘rivers should not be squeezed into a corset’. The frequency of such quotes suggests that ideas about ‘water as a friend’, the ‘spiral of risk’ and ‘moving with nature’ have not been marginal. It is however difficult to determine how influential they have been in decision-making, since general ideas are not the only factors leading to decisions. The general critique to the three ideas is that they present preferred measures as generally logical conclusions without a systematic comparison of alternatives for particular situations. Behind the new ideas lies increasing societal interest for objectives like an attractive water landscape (water as a friend), reducing our dependence on technology (spiral of risk) and nature conservation and development (moving with nature). This analysis further suggests a couple of final remarks, which are hard to prove and are open for discussion

Acute acalculous cholecystitis in children

Acute acalculous cholecystitis (AAC)is a rare disease in African children and usually occurs as a complication of some other diseases, such as systemic infections. AAC can, however, be the primary pathology but, because of its low incidence, it is difficult to establish definite mechanisms and causes.The case histories of six children (mean age seven years) with AAC are presented. They were treated in Queen Elizabeth Central Hospital, Blantyre, Malawi and in Gweru Provincial Hospital in Zimbabwe between 1985 and 1996. In four children, pre-operative ultrasonography showed the typical signs of AAC.Cholecystectomy was performed on all seven children. One child died postoperatively from generalised sepsis and in two children a wound infection occurred.In the tropics, where many children are seen with gastro-enteritis and other infectious diseases, the possibiLity of AAC must be borne in mind when a child is admitted with right upper abdominal tenderness and fever. The role of ultrasonography is emphasised. It is a reliable, non-invasive and quick investigation, which helps to establish the diagnosis before surgery.Cholecystectomy is the treatment of choice,because of the high incidence of necrosis of the gallbladder wall.Keywords: acalculous cholecystitis, childre

Single-Port Laparoscopic Surgery for Inflammatory Bowel Disease

Background. Single Port Laparoscopic Surgery (SPLS) is being increasingly employed in colorectal surgery for benign and malignant diseases. The particular role for SPLS in inflammatory bowel disease (IBD) has not been determined yet. In this review article we summarize technical aspects and short term results of SPLS resections in patients with Crohn's disease or ulcerative colitis. Methods. A systematic review of the literature until January 2012 was performed. Publications were assessed for operative techniques, equipment, surgical results, hospital stay, and readmissions. Results. 34 articles, published between 2010 and 2012, were identified reporting on 301 patients with IBD that underwent surgical treatment in SPLS technique. Surgical procedures included ileocolic resections, sigmoid resections, colectomies with end ileostomy or ileorectal anastomosis, and restorative proctocolectomies with ileum-pouch reconstruction. There was a wide variety in the surgical technique and the employed equipment. The overall complication profile was similar to reports on standard laparoscopic surgery in IBD. Conclusions. In experienced hands, single port laparoscopic surgery appears to be feasible and safe for the surgical treatment of selected patients with IBD. However, evidence from prospective randomized trials is required in order to clarify whether there is a further benefit apart from the avoidance of additional trocar incisions