Effect of Pulsing Mixing Interruptions on the Aspergillus niger Morphology and Citric Acid Production

The effect of short pulsing mixing interruptions on the Aspergillus niger R3 morphology and fermentation performance was studied in 5 l agitated fermenters with double Rushton turbine impellers. A stable increase in the mycelia concentration and higher biomass concentrations at the end of the process were achieved in two continuous mixing fermentations, while in two fermentations with mixing interruptions biomass accumulation level was significantly lower. The highest citric acid concentration, in comparison with continuous mixing fermentations, was obtained in the pulsed on/off mixing fermentation with gas blending, and the pulsed mixing fermentation without gas blending. Small pellets (with about 0.6 – 0.8 mm mean equivalent diameter) developed in continuous mixing fermentations. The largest mean equivalent pellet diameter (approximately 0.9 – 1.1 mm) and the longest hyphae in the outer zone of a pellet were observed in the most productive fermentation with mixing oscillations accompanied by gas blending

Effect of Pulsing Mixing Interruptions on the Aspergillus niger Morphology and Citric Acid Production

The effect of short pulsing mixing interruptions on the Aspergillus niger R3 morphology and fermentation performance was studied in 5 l agitated fermenters with double Rushton turbine impellers. A stable increase in the mycelia concentration and higher biomass concentrations at the end of the process were achieved in two continuous mixing fermentations, while in two fermentations with mixing interruptions biomass accumulation level was significantly lower. The highest citric acid concentration, in comparison with continuous mixing fermentations, was obtained in the pulsed on/off mixing fermentation with gas blending, and the pulsed mixing fermentation without gas blending. Small pellets (with about 0.6 – 0.8 mm mean equivalent diameter) developed in continuous mixing fermentations. The largest mean equivalent pellet diameter (approximately 0.9 – 1.1 mm) and the longest hyphae in the outer zone of a pellet were observed in the most productive fermentation with mixing oscillations accompanied by gas blending

Searching speeds and the energetic feasibility of an obligate whale-scavenging fish

Two recently published models reach opposite conclusions on the energetic feasibility of a scavenging fish that specialises oil whale carcasses. We argue that the key difference between these models lies in their estimate of the likely searching speed of such a hypothetical scavenger. Neither of the previous models considers that although faster searching will allow food sites to be found more quickly, it will also reduce the time between meals that the fish can survive on its reserves. Hence, we present a novel model that encapsulates this trade-off, and use this model to predict the optimal searching speed for Such a hypothetical scavenger. The model predicts that the optimal speed should increase with mass and be in the range 0.1-0.2 m s(-1) for fish of the range of sizes found for the ubiquitous grenadier Coryphaenoides armatus. These values accord with most estimates of the swimming speeds for this species. Hence, we conclude that rejection of a whale-carcass feeding specialist fish on energetic grounds is premature. Although, we see no reason to dismiss Such a specialist oil energetic grounds, we argue that such a fish will be unlikely oil ecological grounds, although a deep-sea fish that gathered much of its energy from scavenging at relatively large food packages oil the ocean floor should be feasible

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

Inviscid helical magnetorotational instability in cylindrical Taylor-Couette flow

This paper presents the analysis of axisymmetric helical magnetorotational instability (HMRI) in the inviscid limit, which is relevant for astrophysical conditions. The inductionless approximation defined by zero magnetic Prandtl number is adopted to distinguish the HMRI from the standard MRI in the cylindrical Taylor-Couette flow subject to a helical magnetic field. Using a Chebyshev collocation method convective and absolute instability thresholds are computed in terms of the Elsasser number for a fixed ratio of inner and outer radii \lambda=2 and various ratios of rotation rates and helicities of the magnetic field. It is found that the extension of self-sustained HMRI modes beyond the Rayleigh limit does not reach the astrophysically relevant Keplerian rotation profile not only in the narrow- but also in the finite-gap approximation. The Keppler limit can be attained only by the convective HMRI mode provided that the boundaries are perfectly conducting. However, this mode requires not only a permanent external excitation to be observable but also has a long axial wave length, which is not compatible with limited thickness of astrophysical accretion disks.Comment: 12 pages, 9 figures, published version with a few typos correcte

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

Human subjective response to steering wheel vibration caused by diesel engine idle

This study investigated the human subjective response to steering wheel vibration of the type caused by a four-cylinder diesel engine idle in passenger cars. Vibrotactile perception was assessed using sinusoidal amplitude-modulated vibratory stimuli of constant energy level (r.m.s. acceleration, 0.41 m/s(2)) having a carrier frequency of 26 Hz (i.e. engine firing frequency) and modulation frequency of 6.5 Hz (half-order engine harmonic). Evaluations of seven levels of modulation depth parameter m (0.0, 0.1, 0.2, 0.4, 0.6, 0.8, and 1.0) were performed in order to define the growth function of human perceived disturbance as a function of amplitude modulation depth. Two semantic descriptors were used (unpleasantness and roughness) and two test methods (the Thurstone paired-comparison method and the Borg CR-10 direct evaluation scale) for a total of four tests. Each test was performed using an independent group of 25 individuals. The results suggest that there is a critical value of modulation depth m = 0.2 below which human subjects do not perceive differences in amplitude modulation and above which the stimulus-response relationship increases monotonically with a power function. The Stevens power exponents suggest that the perceived unpleasantness is non-linearly dependent on modulation depth m with an exponent greater than 1 and that the perceived roughness is dependent with an exponent close to unity

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

A taste of the deep-sea: The roles of gustatory and tactile searching behaviour in the grenadier fish <i>Coryphaenoides armatus</i>

The deep-sea grenadier fishes (Coryphaenoides spp.) are among the dominant predators and scavengers in the ocean basins that cover much of Earth's surface. Baited camera experiments were used to study the behaviour of these fishes. Despite the apparent advantages of rapidly consuming food, grenadiers attracted to bait spend a large proportion of their time in prolonged periods of non-feeding activity. Video analysis revealed that fish often adopted a head-down swimming attitude (mean of 21.3 degrees between the fish and seafloor), with swimming velocity negatively related to attitude. The fish also swam around and along vertical and horizontal structures of the lander with their head immediately adjacent to the structure. We initially hypothesised that this behaviour was associated with the use of the short chin barbel in foraging. Barbel histology showed numerous taste buds in the skin, and a barbel nerve with about 20,000 axons in adult fish. A tracing experiment in one undamaged animal revealed the termination fields of the barbel neurons in the trigeminal and rhombencephalic regions, indicating both a mechanoreceptory and a gustatory role for the barbel. Our conclusion was that olfactory foraging becomes ineffective at close ranges and is followed by a search phase using tactile and gustatory sensing by the barbel. The development of this sensory method probably co-evolved alongside behavioural changes in swimming mechanics to allow postural stability at low swimming speeds