Rotationssinn nach dem Bogengangsprinzip bei Crustaceen

Summary Blinded crabs (Carcinus maenas andMaja verrucosa) show compensatory eye stalk movements on rotation about a vertical axis, in water and in air. On a sudden arrest of the turntable typical after-effects are observed, which show a striking resemblance to those known from vertebrates. All these reactions are abolished after bilateral elimination of the so-called thread hairs within the statocysts (experiments onMaja). In fresh preparations these hairs can be seen to follow the slightest movements of the surrounding fluid, swaying around their point of attachment.Elimination of the thread hairs does not diminish, but does markedly delay the compensatory eye stalk movements of a blinded crab on rotation about horizontal axes. The latter reactions are abolished if in addition the hook hairs (i.e. the sense hairs of the statolith-bearing type) are destroyed.It is concluded that the statocyst of crabs is a staticdynamic sense organ: the hook hairs are position receptors, the thread hairs react to angular displacements about all three main body axes; the group hairs may have no sensory function at all.Rotation sense may be expected to occur in other Crustacea possessing thread hairs or similar receptors in their statocysts as well.     

Recognizing Treelike k-Dissimilarities

A k-dissimilarity D on a finite set X, |X|????k, is a map from the set of size k subsets of X to the real numbers. Such maps naturally arise from edgeweighted trees T with leaf-set X: Given a subset Y of X of size k, D(Y ) is defined to be the total length of the smallest subtree of T with leaf-set Y . In case k?=?2, it is well-known that 2-dissimilarities arising in this way can be characterized by the so-called ??4-point condition??. However, in case k?>?2 Pachter and Speyer (2004) recently posed the following question: Given an arbitrary k-dissimilarity, how do we test whether this map comes from a tree? In this paper, we provide an answer to this question, showing that for k????3 a k-dissimilarity on a set X arises from a tree if and only if its restriction to every 2?k-element subset of X arises from some tree, and that 2?k is the least possible subset size to ensure that this is the case. As a corollary, we show that there exists a polynomial-time algorithm to determine when a k-dissimilarity arises from a tree. We also give a 6-point condition for determining when a 3-dissimilarity arises from a tree, that is similar to the aforementioned 4-point condition.     

The Limits of Precaution

The maximin rule can be used as a formal version of the precautionary principle. This paper evaluates the feasibility and the intuitive plausibility of this decision rule. The major conclusions are: (1) Precaution has to be applied symmetrically. (2) Precaution is only possible when outcomes are comparable in terms of value, so that it can be determined which outcome is worst. (3) Precaution is sensitive to standards of possibility. Far-away scenarios have to be excluded, and it is difficult to find a principled way to draw the line. (4) Precaution is sensitive to the framing of decision problems. Local cautiousness may add up to global incautiousness. This revised version was published online in July 2006 with corrections to the Cover Date.     

Über die Reizung des Ferntastsinns bei Fischen und Amphibien

Summary Fishes and aquatic amphibians are able to detect and locate moving bodies and even obstacles at some distance by means of their lateral-line sense organs (Ferntastsinn). As was shown experimentally, the main physical process involved in these reactions are certain local damming phenomena in front of the moving object (rise of pressure, displacement of water particles). Obstacles cause an alteration of the damming phenomena produced by the moving animal's body itself (increase of water resistance).Kramer's different view is rejected; he overlooked the existence of damming phenomena and was not aware of the fact thatXenopus laevis reacts to surface waves even when the animal is totally submerged.     

Sulindac sulfide suppresses 5-lipoxygenase at clinically relevant concentrations

Sulindac is a non-selective inhibitor of cyclooxygenases (COX) used to treat inflammation and pain. Additionally, non-COX targets may account for the drug’s chemo-preventive efficacy against colorectal cancer and reduced gastrointestinal toxicity. Here, we demonstrate that the pharmacologically active metabolite of sulindac, sulindac sulfide (SSi), targets 5-lipoxygenase (5-LO), the key enzyme in the biosynthesis of proinflammatory leukotrienes (LTs). SSi inhibited 5-LO in ionophore A23187- and LPS/fMLP-stimulated human polymorphonuclear leukocytes (IC₅₀ ≈ 8–10 μM). Importantly, SSi efficiently suppressed 5-LO in human whole blood at clinically relevant plasma levels (IC₅₀ = 18.7 μM). SSi was 5-LO-selective as no inhibition of related lipoxygenases (12-LO, 15-LO) was observed. The sulindac prodrug and the other metabolite, sulindac sulfone (SSo), failed to inhibit 5-LO. Mechanistic analysis demonstrated that SSi directly suppresses 5-LO with an IC₅₀ of 20 μM. Together, these findings may provide a novel molecular basis to explain the COX-independent pharmacological effects of sulindac under therapy.     

Stratified prokaryote network in the oxic-anoxic transition of a deep-sea halocline

The chemical composition of the Bannock basin has been studied in some detail. We recently showed that unusual microbial populations, including a new division of Archaea (MSBL1), inhabit the NaCl-rich hypersaline brine. High salinities tend to reduce biodiversity, but when brines come into contact with fresher water the natural haloclines formed frequently contain gradients of other chemicals, including permutations of electron donors and acceptors, that may enhance microbial diversity, activity and biogeochemical cycling. Here we report a 2.5-m-thick chemocline with a steep NaCl gradient at 3.3 km within the water column betweeen Bannock anoxic hypersaline brine and overlying sea water. The chemocline supports some of the most biomass-rich and active microbial communities in the deep sea, dominated by Bacteria rather than Archaea, and including four major new divisions of Bacteria. Significantly higher metabolic activities were measured in the chemocline than in the overlying sea water and underlying brine; functional analyses indicate that a range of biological processes is likely to occur in the chemocline. Many prokaryotic taxa, including the phylogenetically new groups, were confined to defined salinities, and collectively formed a diverse, sharply stratified, deep-sea ecosystem with sufficient biomass to potentially contribute to organic geological deposits.     

基于后缀树思想构造Web生物数据搜索的数据模型

针对Web上的公共生物学数据资源,提出一种适合于在线搜索生物学数据的数据模型.该模型基于后缀树思想,通过建立生物体的DNA、RNA、蛋白质序列数据的后缀树结构,并将之转化为更加空间有效的后缀数组,然后搜索数组以找到查询序列的近似匹配.结果表明,这种数据模型比常规的线性搜索模型在时间和空间开销上更加高效.     

Asymmetric pores in a silicon membrane acting as massively parallel brownian ratchets

The brownian motion of mesoscopic particles is ubiquitous and usually random. But in systems with periodic asymmetric barriers to movement, directed or 'rectified' motion can arise and may even modulate some biological processes. In man-made devices, brownian ratchets and variants based on optical or quantum effects have been exploited to induce directed motion, and the dependence of the amplitude of motion on particle size has led to the size-dependent separation of biomolecules. Here we demonstrate that the one-dimensional pores of a macroporous silicon membrane, etched to exhibit a periodic asymmetric variation in pore diameter, can act as massively parallel and multiply stacked brownian ratchets that are potentially suitable for large-scale particle separations. We show that applying a periodic pressure profile with a mean value of zero to a basin separated by such a membrane induces a periodic flow of water and suspended particles through the pores, resulting in a net motion of the particles from one side of the membrane to the other without moving the liquid itself. We find that the experimentally observed pressure dependence of the particle transport, including an inversion of the transport direction, agrees with calculations of the transport properties in the type of ratchet devices used here.     

Falsificationism Falsified

A conceptual analysis of falsificationism is performed, in which the central falsificationist thesis is divided into several components. Furthermore, an empirical study of falsification in science is reported, based on the 70 scientific contributions that were published as articles in Nature in 2000. Only one of these articles conformed to the falsificationist recipe for successful science, namely the falsification of a hypothesis that is more accessible to falsification than to verification. It is argued that falsificationism relies on an incorrect view of the nature of scientific inquiry and that it is, therefore, not a tenable research methodology.