Search

The study was carried out to quantitate the transfer of toxaphene and chlordane compounds from commercial fish feed into the edible part of rainbow trout, Oncorhynchus mykiss (Walbaum) under normal rearing conditions. Trout were fed with unspiked high energy feed for salmon (fat content 26-30%) over a period of 19 months. The average weight of trout increased from 10 g to more than 2092 g, reaching sizes of 51 cm length. Considerable amounts of toxaphene and chlordane residues were transferred from fish feed into trout muscle. Toxaphene concentrations increased up to 8.6 µg (Σ toxaphene indicator compounds 1-3)kg[sup -1] wet weight (w.w.) and chlordane reached 5.3 µg Σoxy-, trans-, cis-chlordane + t-nonachlor kg[sup -1] w.w. Results are also discussed on the contaminant levels based on the fat content and the effect of sexual maturation is considered in this study. The data allow the establishment of transfer rates for toxaphene and chlordane congeners from high energy diet into the edible part of farmed rainbow trout. [ABSTRACT FROM AUTHOR]

It was observed that farmed eels could be rendered unconscious and insensible instantaneously by passing an electrical current through fresh water. The general epileptiform insult on the EEG was characterized by a tonic/clonic and an exhaustion phase. After stunning, the ECG (electro-cardiogram) revealed fibrillation. The electrical stunning parameters were on average 194 ± 4 V and 0.636 ± 0.040 A/dm² for 1.6 ± 0.4 s. Within a confidence level of 95%%, taking into account the number of animals with a reliable EEG (n = 29), at least 93% of all eels are effectively stunned in fresh water by an average current of 0.636 ± 0.040 A/dm². The behaviour of groups of five eels, which were able to move freely in the water was observed before and after stunning with 50 V and 0.17A/dm². After 3-s stunning, two eels were turned upside down. They changed to a normal position after 10 and 13 s respectively. Subsequently, all eels were very active in swimming behaviour and stopped swimming after 75 s. When stunned for a longer duration, all eels were turned upside down and stopped breathing for a limited period of time. In the last experiment the eels were stunned in fresh water (500 µS) with a voltage of 200 V for approximately 1 s, which was followed by 50 V for 5 min. As soon as the stunning started the water was de-oxygenated by flushing nitrogen to kill the eels by suffocation during the period of unconsciousness and insensitivity. The oxygen saturation decreased from 74 ± 10 to 23 ± 11% at 22 °C. After stunning no brain activity and no responses to pain stimuli were observed on the EEG. The heart rate increased (P < 0.05) after stunning, which was followed by a significant decrease. Only 1 out of 18 eels returned partially from upside down to a normal position 2 h after stunning; however, the eel did not respond to pain stimuli in behaviour. The developed stunning procedure can be recommended for humane... [ABSTRACT FROM AUTHOR]

Recovery of fertilizer nitrogen (N) applied to winter wheat crops at tillering in spring is lower than that of N applied at later growth stages because of higher losses and immobilization of N. Two strategies to reduce early N losses and N immobilization and to increase N availability for winter wheat, which should result in an improved N use efficiency (= higher N uptake and/or increased yield per unit fertilizer N), were evaluated. First, 16 winter wheat trials (eight sites in each of 1996 and 1997) were conducted to investigate the effects of reduced and increased N application rates at tillering and stem elongation, respectively, on yield and N uptake of grain. In treatment 90-70-60 (90 kg N ha-1 at tillering, 70 kg N ha-1 at stem elongation and 60 kg N ha-1 at ear emergence), the average values for grain yield and grain N removal were up to 3.1 and 5.0 % higher than in treatment 120-40-60, reflecting conventional fertilizer practice. Higher grain N removal for the treatment with reduced N rates at tillering, 90-70-60, was attributed to lower N immobilization (and N losses), which increased fertilizer N availability. Secondly, as microorganisms prefer NH4 + to NO3 - for N immobilization, higher net N immobilization would be expected after application of the ammonium-N form. In a pot experiment, net N immobilization was higher and dry matter yields and crop N contents at harvest were lower with ammonium (ammonium sulphate + nitrification inhibitor Dicyandiamide) than with nitrate (calcium nitrate) nutrition. Five field trials were then conducted to compare calcium nitrate (CN) and calcium ammonium nitrate (CAN) nutrition at tillering, followed by two CAN applications for both treatments. At harvest, crop N and grain yield were higher in the CN than in the CAN treatment at each N supply level. In conclusion, fertilizer N use efficiency in winter wheat can be improved if N availability... [ABSTRACT FROM AUTHOR]

The float-zone crystal-growth process is investigated in the framework of the half-zone model. The influence of a temperature-dependent viscosity on the axisymmetric steady thermocapillary flow and its stability with respect to nonaxisymmetric perturbations is examined by means of a linear-stability analysis. The onset of oscillatory convection is studied numerically by a mixed Chebyshev-collocation finite-difference method. Detailed calculations have been carried out for PR = 4 and unit aspect ratio. It is found that the temperature-dependent viscosity decreases the critical Reynolds number for the onset of three-dimensional flow. Since the threshold shift is a function of the azimuthal wavenumber of the neutral mode, the critical mode may depend on the magnitude of the viscosity variation. [ABSTRACT FROM AUTHOR]

Now-a-days, increased efforts have been made to build up both data banks and data-bank-related information systems. There is a corresponding rise in the volume of machine-readable stored information including information about individuals at various data gathering points of society. However, more and more thought is being given to ways in which integrated use might be made of information which is available within society, but which lies dispersed in individual legal documents, archives or even data banks, firstly, in order to avoid double storage and duplication, and secondly, in order to achieve fuller use of data in relation to the data base employed. These two aims could be achieved by integrated data-bank-related information systems. The integration of data files within a data bank can be achieved by use of the computer-oriented data bank, which may be distinguished from other data banks such as card indexes, filing systems and archives by the fact that, owing to the computers storage and access capacity, once data elements have been put in an adequate format, they can be used as ordering criteria. Storing information in integrated data-bank-related information systems, of which data transfer is an integral part, enables one to overcome not only the poor data-access, and limited possibilities for the integration of data elements, resulting from the nature of conventional storage carriers and the physical separation of data files, but also the difficulty of integrating data files in different specialized data banks.

The half-zone model is investigated for unit aspect ratio, zero gravity, and Prandtl numbers Pr = 1.5 ... 7 by numerical simulations. For thermocapillary Reynolds numbers Re > Rec, the 2D stationary flow is unstable to 3D travelling waves. In the simulations, standing waves can be generated slightly above Rec. It is found, that these states are unstable and decay into either a clock-or a counter-clockwise propagating wave. Amplitude equations are used to quantitatively describe the instability of the standing wave states and to estimate the range of Pr within which only travelling waves are stable. [ABSTRACT FROM AUTHOR]

The thermocapillary flow in a differentially heated cylindrical liquid bridge under steady rotation of the hot disk is considered in the limit of zero capillary number. Steady flow states and their three-dimensional stability are calculated numerically. It is shown that the vortex breakdown caused by the rotation is strongly affected by the thermocapillary flow. A linear stability analysis reveals that the most dangerous perturbations are oscillatory with azimuthal wavenumber m = 1 or m = 2 depending on the parameters. [ABSTRACT FROM AUTHOR]

At very low velocities (v ≤ 0.1 m/s), hot-wire measurements are significantly influenced by free convection. To assess the contribution of free-convection heat transfer to the heat balance of hot-wire probes, measurements under gravitational and under microgravity conditions are compared in a velocity range 0 ≤ v ≤ 0.3 m/s corresponding to a Reynolds number range Re ≤ 0.1. The measurements were made with horizontal hot-wire probes in cross flow in air at 21.8°C. For creeping flow three distinct regions can be observed in which different factors dominate the heat transport. While free convection prevails at Re = 0, forced convection dominates for Re > Gr1/3. At intermediate Reynolds numbers both transport mechanisms must be considered. [ABSTRACT FROM AUTHOR]

The flow driven by buoyancy and thermocapillarity in a liquid bridge between coaxial differentially heated disks held by surface tension forces is investigated. We numerically determine the stability of axisymmetric flows by a linear stability analysis. In the present approach, the influence of buoyancy forces on the flow stability is taken into account through static meniscus deformations as well as through internal buoyancy. To elucidate the physical instability mechanisms the energy balance given by Reynolds-Orr-like equations is considered term by term. [ABSTRACT FROM AUTHOR]

The lid-driven cavity has been studied quite extensively both experimentally and numerically. Today it is the most wide-spread benchmark problem in CFD. Despite this fact, the linear stability of the steady two-dimensional flow has hardly been considered, not even for the square cavity. In the present study we revisit this classical problem and calculate the linear stability of the two-dimensional flow with respect to three-dimensional perturbations for various aspect ratios. The structure of the critical modes as well as the instability mechanism are addressed. [ABSTRACT FROM AUTHOR]

The transition from two-dimensional (2D) steady to three-dimensional (3D) flow is investigated experimentally in a two-sided lid-driven cavity for anti-parallel motion of two facing walls. Both wall speeds (Reynolds numbers) have the same absolute value. We present critical Reynolds numbers at the onset of steady three-dimensional flow as a function of the cross-sectional aspect ratio. The critical curve is composed of different neutral branches belonging to different instability modes. Comparison with numerical results enables insight into the corresponding mechanisms. [ABSTRACT FROM AUTHOR]