Experimental model of the interfacial instability in aluminium reduction cells

A solution has been found to the long-standing problem of experimental modelling of the interfacial instability in aluminium reduction cells. The idea is to replace the electrolyte overlaying molten aluminium with a mesh of thin rods supplying current down directly into the liquid metal layer. This eliminates electrolysis altogether and all the problems associated with it, such as high temperature, chemical aggressiveness of media, products of electrolysis, the necessity for electrolyte renewal, high power demands, etc. The result is a room temperature, versatile laboratory model which simulates Sele-type, rolling pad interfacial instability. Our new, safe laboratory model enables detailed experimental investigations to test the existing theoretical models for the first time

Use of remotely-derived bathymetry for modelling biomass in marine environments

The paper presents results on the influence of geometric attributes of satellite-derived raster bathymetric data, namely the General Bathymetric Charts of the Oceans, on spatial statistical modelling of marine biomass. In the initial experiment, both the resolution and projection of the raster dataset are taken into account. It was found that, independently of the equal-area projection chosen for the analysis, the calculated areas are very similar, and the differences between them are insignificant. Likewise, any variation in the raster resolution did not change the computed area. Although the differences were shown to be insignificant, for the subsequent analysis we selected the cylindrical equal area projection, as it implies rectangular spatial extent, along with the automatically derived resolution. Then, in the second experiment, we focused on demersal fish biomass data acquired from trawl samples taken from the western parts of ICES Sub-area VII, near the sea floor. The aforementioned investigation into processing bathymetric data allowed us to build various statistical models that account for a relationship between biomass, sea floor topography and geographic location. We fitted a set of generalised additive models and generalised additive mixed models to combinations of trawl data of the roundnose grenadier (Coryphaenoides rupestris) and bathymetry. Using standard statistical techniques—such as analysis of variance, Akaike information criterion, root mean squared error, mean absolute error and cross-validation—we compared the performance of the models and found that depth and latitude may serve as statistically significant explanatory variables for biomass of roundnose grenadier in the study area. However, the results should be interpreted with caution as sampling locations may have an impact on the biomass–depth relationship

Realisation of Bullard's disc dynamo

We report experimental results from three successful runs of a Bullard-type homopolar disc dynamo. The set-up consisted of a copper disc with a radius of 30 cm and thickness of 3 cm which was placed co-axially beneath a flat, multi-arm spiral coil of the same size and connected to it electrically at the centre and along the circumference by sliding liquid-metal contacts. The magnetic field was measured using Hall probes which were fixed on the top face of the coil. We measured also the radial voltage drop across the coil. When the disc rotation rate reached $\Omega\approx 7$ Hz, the magnetic field increased steeply approaching $B_{0}\approx 40$ mT in the central part of the coil. This field was more than two orders of magnitude stronger than the background magnetic field. In the first two runs, the electromagnetic torque braking the disc in the dynamo regime exceeded the breakdown torque of the electric motor driving the disc. As a result, the motor stalled and the dynamo was interrupted. Stalling did not occur in the third run when the driving frequency was set higher and increased faster. We also propose an extended disc dynamo model which qualitatively reproduces the experimental results.Comment: 21 page, 11 figure

Single-magnet rotary flowmeter for liquid metals

We present a theory of single-magnet flowmeter for liquid metals and compare it with experimental results. The flowmeter consists of a freely rotating permanent magnet, which is magnetized perpendicularly to the axle it is mounted on. When such a magnet is placed close to a tube carrying liquid metal flow, it rotates so that the driving torque due to the eddy currents induced by the flow is balanced by the braking torque induced by the rotation itself. The equilibrium rotation rate, which varies directly with the flow velocity and inversely with the distance between the magnet and the layer, is affected neither by the electrical conductivity of the metal nor by the magnet strength. We obtain simple analytical solutions for the force and torque on slowly moving and rotating magnets due to eddy currents in a layer of infinite horizontal extent. The predicted equilibrium rotation rates qualitatively agree with the magnet rotation rate measured on a liquid sodium flow in stainless steel duct.Comment: 15 pages, 6 figures, revised version, to appear in J. Appl. Phy

Putative fishery-induced changes in biomass and population size structures of demersal deep-sea fishes in ICES Sub-area VII, Northeast Atlantic Ocean

This work was supported by a series of NERC grants to the principal investigators including NE/C512961/1. The results of the early joint SAMS and IOS surveys were digitized with support from EU MAST Contract MAS2-CT920033 1993–1995, and data analyses was supported by EU FP7 Projects HERMES and HERMIONE. We thank Alain Zuur from Highland Statistics Ltd. for advice with the statistical analyses and Odd Aksel Bergstad for valuable comments that helped to improve the manuscript. We thank the ships’ companies of the RRS Challenger and RRS Discovery.Peer reviewedPublisher PD

Which probes are most useful when undertaking cognitive interviews?

This paper reports the use of verbal probes in cognitive interviews (CIs) undertaken to test the usefulness, validity and reliability of survey questions. Through examining the use of probes by three interviewers undertaking interviews as part the piloting of a cross-national crime survey, we examine which of the various types of probes used in CIs produce the most useful information. Other influences on interview quality are examined, including differences between interviewers and respondents themselves. The analyses rely on multi-level modelling and suggest that anticipated, emergent and conditional probes provide the most useful data. Furthermore, age, gender and educational levels appear to have no bearing on the quality of the data generated

Procjena uzgoja Aspergillus niger u geometrijski različitim bioreaktorima na osnovi morfoloških analiza

The growth of Aspergillus niger, citric acid production and mycelia morphology changes were compared under different mixing conditions in bioreactors with two types of stirrers: Rushton turbine stirrers (RTS1 or RTS2) and axial counterflow stirrers (ACS1 or ACS2). The characteristics of growth, productivity and morphology varied with the mixing system and the applied agitation regime. In the first series of experiments, the flow characteristics of Aspergillus niger broth under different mixing conditions were analysed in a model bioreactor using RTS1 and ACS1. The kinetic energy E of flow fluctuations was measured in gassed and ungassed water and fermentation broth systems using a stirring intensity measuring device (SIMD-f1). The difference of energy E values at different points was more pronounced in the bioreactor with RTS1 than in the case of ACS1. High viscous A. niger broths provided higher energy E values in comparison with water. It was observed that the Aspergillus niger growth rate and citric acid synthesis rate decreased at very high energy E values, the behaviour obviously being connected with the influence of the irreversible shear stress on the mycelial morphology. In the second series of experiments, a higher citric acid yield was achieved in the case of ACS2 at a power input approximately twice lower than in the case of RTS2. Morphological characterization of A. niger pellets was carried out by the image analysis method. ACS2 provided the development of morphology, where pellets and cores had larger area, perimeter and diameter, and the annular region of pellets was looser and more »hairy« in comparison with the case of RTS2. The pellets from the fermentation with RTS2 were smaller, denser, with shorter hyphae in the annular region of pellets, and the broth was characterized by a higher percentage of diffuse mycelia. Power input studies of RTS2 and ACS2 were made at different agitator rotation speeds and gas flow rates using water and Aspergillus niger broths. RTS2 was a high power number mixing system (PO = 6.8), whose PO was practically invariable in different media under study. For ACS2, PO increased approximately 3 times from 0.68 in water to 2.11 in high viscous Aspergillus niger broth. The effect of the agitation and aeration rates on the power input of RTS2 and ACS2 was analysed. ACS2 proved to be more effective, since it lost much less power due to aeration.Ispitivani su rast Aspergillus niger, proizvodnja limunske kiseline i promjene u morfologiji micelija pod različitim uvjetima miješanja u bioreaktorima s dva tipa miješalica: Rushton turbinske miješalice (RTS1 ili RTS2) i aksijalno protustrujne miješalice (ACS1 i ACS2). Značajke rasta, proizvodnosti i morfologija mijenjali su se s vrstom miješalica i načinom miješanja. U prvoj seriji pokusa analizirane su značajke protoka komine s A. niger pod različitim uvjetima miješanja u modelnom bioreaktoru s miješalicama RTS1 i ACS1. Kinetička energija E fluktuacije protoka mjerena je u vodi s aeracijom i bez nje, te u fermentacijskim kominama koristeći uređaj za mjerenje intenziteta miješanja (SIMD-f1). Razlika u količini energije E na različitim mjestima u bioreaktoru bila je izrazitija u bioreaktoru s RTS1 nego s ACS1. Jako viskozna A. niger komina zahtijevala je veće vrijednosti E u usporedbi s vodom. Opaženo je da brzina rasta A. niger i sinteza limunske kiseline opadaju pri visokim vrijednostima energije E, što je očito povezano s utjecajem ireverzibilnog naprezanja na posmik na morfologiju micelija. U drugoj seriji pokusa postignuti su veliki prinosi limunske kiseline primjenom ACS2, pri približno dvostruko manjem utrošku energije u usporedbi s primjenom RTS2. Morfološka karakterizacija peleta A. niger provedena je postupkom analize fotografija. Primjenom ACS2 peleti i jezgre bili su veći po opsegu i promjeru, a anularno područje peleta bilo je labavije i »dlakavije« u usporedbi s pokusima s RTS2. Peleti od fermentacije s RTS2 bili su manji, gušći, s kraćim hifama u anularnom području peleta, a komina je sadržavala veći postotak difuznih micelija. Studije utroška snage primjenom RTS2 i ACS2 provedene su pri različitim brzinama okretaja miješalica i protoka zraka u vodi i u komini s A. niger. RTS2 ima sustav miješanja s velikim utroškom snage (P0 = 6,8) koji se praktički ne mijenja ako se promijeni medij. Za ACS2 se P0 povećava približno tri puta, od 0,68 u vodi do 2,11 u viskoznoj komini s A. niger. Analiziran je utjecaj miješanja i jačine aeracije na utrošak energije primjenom RTS2 i ACS2. ACS2 bio je djelotvorniji jer se aeracijom gubilo puno manje energije

Diesel engine fuel injection monitoring using acoustic measurements and independent component analysis

Air-borne acoustic based condition monitoring is a promising technique because of its intrusive nature and the rich information contained within the acoustic signals including all sources. However, the back ground noise contamination, interferences and the number of Internal Combustion Engine ICE vibro-acoustic sources preclude the extraction of condition information using this technique. Therefore, lower energy events; such as fuel injection, are buried within higher energy events and/or corrupted by background noise. This work firstly investigates diesel engine air-borne acoustic signals characteristics and the benefits of joint time-frequency domain analysis. Secondly, the air-borne acoustic signals in the vicinity of injector head were recorded using three microphones around the fuel injector (120° apart from each other) and an Independent Component Analysis (ICA) based scheme was developed to decompose these acoustic signals. The fuel injection process characteristics were thus revealed in the time-frequency domain using Wigner-Ville distribution (WVD) technique. Consequently the energy levels around the injection process period between 11 and 5 degrees before the top dead center and of frequency band 9 to 15 kHz are calculated. The developed technique was validated by simulated signals and empirical measurements at different injection pressure levels from 250 to 210 bars in steps of 10 bars. The recovered energy levels in the tested conditions were found to be affected by the injector pressure settings

A homopolar disc dynamo experiment with liquid metal contacts

We present experimental results of a homopolar disc dynamo constructed at CICATA-Quer\'etaro in Mexico. The device consists of a flat, multi-arm spiral coil which is placed above a fast-spinning metal disc and connected to the latter by sliding liquid-metal electrical contacts. Theoretically, self-excitation of the magnetic field is expected at the critical magnetic Reynolds number Rm~45, which corresponds to a critical rotation rate of about 10 Hz. We measured the magnetic field above the disc and the voltage drop on the coil for the rotation rate up to 14 Hz, at which the liquid metal started to leak from the outer sliding contact. Instead of the steady magnetic field predicted by the theory we detected a strongly fluctuating magnetic field with a strength comparable to that of Earth's magnetic field which was accompanied by similar voltage fluctuations in the coil. These fluctuations seem to be caused by the intermittent electrical contact through the liquid metal. The experimental results suggest that the dynamo with the actual electrical resistance of liquid metal contacts could be excited at the rotation rate of around 21 Hz provided that the leakage of liquid metal is prevented.Comment: 6 pages, 5 figures (to appear in Magnetohydrodynamics

Bathyal demersal fishes of Charlie Gibbs Fracture Zone region (49–54°N) of the Mid-Atlantic Ridge, I : Results from trawl surveys

Peer reviewedPublisher PD