Phase transitions related to the pigeonhole principle

Since Paris introduced them in the late seventies (Paris1978), densities turned out to be useful for studying independence results. Motivated by their simplicity and surprising strength we investigate the combinatorial complexity of two such densities which are strongly related to the pigeonhole principle. The aim is to miniaturise Ramsey's Theorem for $1$-tuples. The first principle uses an unlimited amount of colours, whereas the second has a fixed number of two colours. We show that these principles give rise to Ackermannian growth. After parameterising these statements with respect to a function f:N->N, we investigate for which functions f Ackermannian growth is still preserved

WZW-like Action for Heterotic String Field Theory

We complete the construction of the Neveu-Schwarz sector of heterotic string field theory begun in hep-th/0406212 by giving a closed-form expression for the action and gauge transformations. Just as the Wess-Zumino-Witten (WZW) action for open superstring field theory can be constructed from pure-gauge fields in bosonic open string field theory, our heterotic string field theory action is constructed from pure-gauge fields in bosonic closed string field theory. The construction involves a simple alternative form of the WZW action which is consistent with the algebraic structures of closed string field theory.Comment: 22 pages, no figures, LaTeX2

Organic layers on silicon result in a unique hybrid fet

A Field-Effect Transistor (FET) is presented that combines the conventional lay-out of the silicon substrate (channel and source and drain connections) with a Si-C linked organic gate insulator contacted via an organic, conducting polymer. It is shown that this hybrid device combines the excellent electrical behavior of the silicon substrate and the ease of use and good properties of organic insulators and contacting materials.\ud Keywords: organic monolayer, FET, conducting polyme

Biodiversity of Antarctic nematodes: the ‘NEMASLAN’ project

Recent biodiversity research reveals that more than 50% of the free-living marine nematode species found in before unexplored environments, such as Antarctica, are new to science. Too few taxonomists remain to describe them all. Additionally, there are problems with the quality control of the identification of nematode samples since fewer labs possess all the literature (and manpower) required to verify the morphological characteristics of the animals.NEMASLAN, software for a tree-based classification system (Access) is a methodological approach for improving identification, classification and description of specimens in difficult taxonomic groups such as free-living marine nematodes. It seeks to serve as an easy research tool for central management of information of the taxon of the nematodes, and this for people with little training in database technologies.The program consists of four main modules: (see demonstration)1. Module for data- entering: provides possibilities to enter geographic, morphological, ecological, and literature data on species in a record database. An additional connection between these database records and the actual digital sources (e.g. scanned literature from original descriptions and good recent publications) enlarges the scientific value of the system.Personal metadatasets can be created, for example for the use of drawings and/or pictures of undescribed species or not yet published taxonomic papers. 2. Module for document consultation: data sources (PDF documents of original descriptions, text documents, photographs,…) and their references can be consulted. 3. Module for Quick Search: Morphological data from the species identification (e.g. shape and/or position of amphid, cuticle, buccal cavity, tail, oesophagus, caudal glands and spinneret; feeding type; numerical fields of de Man ratios, length, setae, nerve ring, excretory porus, spicule, gubernaculum, male supplements) and other information such as type of biotope and water depth distribution can be consulted; datasheets can be generated.4. Search Module: The output and search within the database can be user configured (i.e. questions like ‘give me all the nematode species so far described from the coastal sites with a spicule longer than 30µm and cuticular punctuations’ get an answer from this database). SQL (Structured Query Language) is the formal language used to query databases. An in-depth knowledge of the fairly complex SQL language is not required.The Windows application functions for multi-users in a local network environment (LAN). The program is distributed free of charge through a website (at present http://allserv.rug.ac.be/~tdeprez: later on through a more specified Antarctic database website) at which demonstration datasets are distributed.NEMASLAN was applied to Antarctic nematodes. The resulting ‘Biodiversity of Antarctic Nematodes’ CD-ROM version includes an archive of all numerical and nominal information for each species ever described in the Southern Ocean. About 350 species have thus been digitized. There is an urgent need to develop appropriate information tools on Antarctic marine biodiversity for scientific, environmental management and conservation purposes. Therefore, the collaboration of three laboratory pioneers in Antarctic biodiversity databases (e.g. Antarctic nematodes, amphipods and echinids, see other presentations) will seek for further developments such as the construction of a common portal, common mapping applications, or links to pertinent information sources of Antarctic benthic biodiversity. The resulting ‘biodiversity information system’ will be made available to the scientific community. This will be done within the framework of the OSTC project on Antarctica - BIANZO (BIodiversity of three representative groups of the ANtarctic ZOobenthos). It will contribute to the DIVERSITAS, SA 2000, CoML-OBIS and GBIF initiatives

γ-H2AX foci as in vivo effect biomarker in children emphasize the importance to minimize x-ray doses in paediatric CT imaging

Objectives: Investigation of DNA damage induced by CT x-rays in paediatric patients versus patient dose in a multicentre setting. Methods: From 51 paediatric patients (median age, 3.8 years) who underwent an abdomen or chest CT examination in one of the five participating radiology departments, blood samples were taken before and shortly after the examination. DNA damage was estimated by scoring gamma-H2AX foci in peripheral blood T lymphocytes. Patient-specific organ and tissue doses were calculated with a validated Monte Carlo program. Individual lifetime attributable risks (LAR) for cancer incidence and mortality were estimated according to the BEIR VII risk models. Results: Despite the low CT doses, a median increase of 0.13 gamma-H2AX foci/cell was observed. Plotting the induced gamma-H2AX foci versus blood dose indicated a low-dose hypersensitivity, supported also by an in vitro dose-response study. Differences in dose levels between radiology centres were reflected in differences in DNA damage. LAR of cancer mortality for the paediatric chest CT and abdomen CT cohort was 0.08 and 0.13% respectively. Conclusion: CT x-rays induce DNA damage in paediatric patients even at low doses and the level of DNA damage is reduced by application of more effective CT dose reduction techniques and paediatric protocols

Nematoda - free living

The list was compiled by Guy De Smet, a non-specialist, who was assisted by nematologists Magda Vincx, Ann Vanreusel, Sandra Vanhove, Jan Vanaverbeke and Maaike Steyaert. Dr. F. Riemann gave useful advice for the genus Daptonema. The classification in the list is based upon Lorenzen (1979, 1994). Information on the geographic distribution in the list is based upon Gerlach and Riemann (1973, 1974), Platt and Warwick (1983, 1988) and Warwick et al. (1998).ReferencesLorenzen, S. Entwürf eines Phylogenetischen Systems der Freilebenden Nematoden, Kiel, 1979.Lorenzen, S. The Phylogenetic Systematics of Freeliving Nematodes, The Ray Society, 1994.Gerlach, S. A. and Riemann, F. The Bremerhaven Checklist of Aquatic Nematodes. Veröffentlichungen des Instituts für Meeresforschung in Bremerhaven, Supplement 4, (Heft 1 1973, Heft 2 1974).Platt, H. M. and Warwick, R. M. Free-living Marine Nematodes (Part I British Enoplids) Synopses of the British Fauna (New series) No. 28, 1983.Platt, H. M. and Warwick, R. M. Free-living Marine Nematodes (Part II British Chromadorids) Synopses of the British Fauna (New series) No. 38, 1988.Warwick, R. M., Platt, H. M. and Somerfield, P. J. Free-living Marine Nematodes (Part III Monhysterids) Synopses of the British Fauna (New series) No. 53, 1998.</ul

Spinor classification of the Weyl tensor in five dimensions

We investigate the spinor classification of the Weyl tensor in five dimensions due to De Smet. We show that a previously overlooked reality condition reduces the number of possible types in the classification. We classify all vacuum solutions belonging to the most special algebraic type. The connection between this spinor and the tensor classification due to Coley, Milson, Pravda and Pravdov\'a is investigated and the relation between most of the types in each of the classifications is given. We show that the black ring is algebraically general in the spinor classification.Comment: 40 page

Rolling Closed String Tachyons and the Big Crunch

We study the low-energy effective field equations that couple gravity, the dilaton, and the bulk closed string tachyon of bosonic closed string theory. We establish that whenever the tachyon induces the rolling process, the string metric remains fixed while the dilaton rolls to strong coupling. For negative definite potentials we show that this results in an Einstein metric that crunches the universe in finite time. This behavior is shown to be rather generic even if the potentials are not negative definite. The solutions are reminiscent of those in the collapse stage of a cyclic universe cosmology where scalar field potentials with negative energies play a central role.Comment: 13 pages, 2 figures, LaTeX. Replaced version: one reference adde

Cosmological tachyon from cubic string field theory

The classical dynamics of the tachyon scalar field of cubic string field theory is considered on a cosmological background. Starting from a nonlocal action with arbitrary tachyon potential, which encodes the bosonic and several supersymmetric cases, we study the equations of motion in the Hamilton-Jacobi formalism and with a generalized Friedmann equation, appliable in braneworld or modified gravity models. The cases of cubic (bosonic) and quartic (supersymmetric) tachyon potential in general relativity are automatically included. We comment the validity of the slow-roll approximation, the stability of the cosmological perturbations, and the relation between this tachyon and the Dirac-Born-Infeld one.Comment: 20 pages JHEP style, 1 figure; v4: misprints corrected, matches the published versio