System for measuring transients in fluid flow

When test valve is actuated, piston is moved by pressurized fluid, and displacement is monitored by electro-optical tracking system and recorded by oscilloscope camera. Electro-optical monitor produces output voltage proportional to displacement of piston

Is the Short Rate Drift Actually Nonlinear?

Virtually all existing continuous-time, single-factor term structure models are based on a short rate process that has a linear drift function. However, there is no strong a priori argument in favor of linearity, and Stanton (1997) and Ait-Sahalia (1996) employ nonparametric estimation techniques to conclude that the drift function of the short rate contains important nonlinearities. Comparatively little is known about the finite-sample properties of these estimators, particularly when they are applied to frequent sampling of a very persistent process, like short term interest rates. In this paper, we apply these estimators to simulated sample paths of a square-root diffusion. Although the drift function is linear, both estimators suggest nonlinearities of the type and magnitude reported in by Stanton (1997) and Ait-Sahalia (1996). These results, along with the results of a simple GMM estimation procedure applied to the Stanton and Ait-Sahalia data sets, imply that nonlinearity of the short rate drift is not a robust stylized fact.term structure, continuous-time

Risk measurement: an introduction to value at risk

This paper is a self-contained introduction to the concept and methodology of "value at risk," which is a new tool for measuring an entity's exposure to market risk. We explain the concept of value at risk, and then describe in detail the three methods for computing it: historical simulation; the variance-covariance method; and Monte Carlo or stochastic simulation. We then discuss the advantages and disadvantages of the three methods for computing value at risk. Finally, we briefly describe some alternative measures of market risk.Risk and Uncertainty,

Erratum: A yellow ‘Hippolais’ warbler trapped at Ngulia re-identified as Eastern Olivaceous Warbler Iduna pallida

No Abstract

Fishes of the Ohio River

Author Institution: Water Resources Laboratory, University of Louisville and Biology Department, Spalding UniversityTo date, 159 species of fishes (14 of them introduced by humans) have been reported from the Ohio River. Three native fishes {Acipenser fulvescens, Alosa alabamae, and Ammocrypta asprella) have apparently been eliminated from the river. The Ohio River fish community was severely affected by the siltation of clean gravel substrates, and the inundation of those substrates by the canalization of the river before 1927. In the past 20-30 years, populations of many species have increased, particularly in the upper third of the river. Some pollution-intolerant species which had disappeared from the upper reaches of the river between 1900 and 1950 have been returning since 1970 (e.g. Polyodon spathula, Hiodon tergisus, and Carpiodes velifer). A few pollution-tolerant species have declined in abundance since 1970 (e.g. bullheads and Ictalurus catus). The most abundant fishes in the lock chamber samples of 1957-87 were Notropis atherinoides, Dorosoma cepedianum, Aplodinotus grunniens, Notropis volucellus, and Ictalurus punctatus. The ongoing recovery of the Ohio River fish community should encourage us to take additional steps to protect the river from catastrophic spills of toxic materials and to reintroduce eliminated native fishes

Motile Aeromonas septicaemia of farmed Rana spp

The bacteria associated with septicaemic disease of farmed frogs in Thailand were investigated. A group of motile aeromonads, designated Au {Aeromonas unspeciated), was unusually homogeneous in their biochemical reactions for a geographically diverse collection, notably none of the Au isolates utilised sucrose. Bacteria conforming to the phenotypic reactions of Aeromonas hydrophila and Aeromonas sobria were isolated from the skin and intestine of disea.sed and clinically normal frogs but only Au isolates were found internally in septicaemic frogs. The DNA relatedness of the collection of aeromonads was examined using randomly amplified polymorphic DNA (RAPD) and 16s rDNA sequencing. RAPD analysis produced very consistent banding patterns for the Au isolates whilst producing scattered profiles for type strains and other aeromonads from Thailand. The RAPD profiles showed that the Au isolates were all closely related tOi4. hydrophila (HGl) but were more closely related to each other. 16s rDNA sequence analysis revealed that in the hypervariable region V3 of the 16s rDNA gene all the Au isolates were identical and differed from all previously published Aeromonas sequences. The phenotypic and genotypic findings strongly suggest that Au is a previously unspeciated motile aeromonad. Histological examination of tissues from frogs affected by acute Au septicaemia revealed widespread vascular congestion, severe cardiac myopathy and pulmonary, renal, hepatic and splenic necrosis. In pathogenicity studies, clinically normal animals challenged with Au, by both injection and bath challenge, developed acute septicaemic disease and yielded pure cultures of Au on bacteriological examination. Haemolysin activities against frog RBC were significantly different within the collection of aeromonads. Groups of high haemolytic activity (unspeciated Aeromonas, Au), moderate haemolytic activity (A. hydrophila) and low haemolytic activity (A. veronii biovar sobria, A. veronii biovar veronii, A. caviae, A. schubertii) were noted. DNA colony hybridisation studies revealed that Au isolates possessed a haemolysin gene (ASH1) which was not present in any other Thai aeromonads or type strains tested. Cells from rainbow trout were extremely sensitive to Au toxins but less so to toxins produced by other species. In contrast mammalian cells showed very little sensitivity to Au toxins but were more sensitive to toxins produced by A. hydrophilia. The selection of suitable assay substrates is therefore very important; cells from homeotherms may be insensitive to cytotoxins associated with pathogenic processes in poikilotherms