Terminal settling velocity and physical properties of pollen grains in still air

Numerical simulation of wind pollination requires knowledge of pollen grain physical parameters such as size, shape factor, bulk density, and terminal settling velocity. The pollen grain parameters for Japanese cedar, Japanese cypress, short ragweed, Japanese black pine, and Japanese red pine were assessed for dry condition. Terminal settling velocities of dry pollen grains in still air were measured using image analysis of scattered light tracks in a dark settling tube. The measurement system was validated by comparing results to those obtained for standard microspheres of known size and density. Dry pollen grain shape factors indicate the resemblance of particles to spheres, except for pine pollen. Circularity factors of dry pine pollen grains were 0.90–0.86, suggesting more irregular shape than those of other pollen species. Aerodynamic diameters of dry pollen grains were calculated based on the terminal settling velocity. Aerodynamic diameters of Japanese cedar, Japanese cypress, and short ragweed closely resembled the projected area equivalent diameters, suggesting that aerodynamic behaviors of these pollen grains can be managed simply in numerical simulations. However, aerodynamic diameters of dry pine pollen grains were nearly 30 % smaller than projected area equivalent diameters. Sacci on dry pine pollen can reduce the terminal settling velocity through low density and shape effects attributed to their non-sphericity, engendering aerodynamic diameter smaller by more than 10 µm from area equivalent diameters.     

A method for measuring the settling velocity distribution of large biotic particles

A simple method for measuring the settling velocity (V _s) distribution of pollen and spores 30–100 μm in diameter is detailed and evaluated. The method is called the ‘settling tower' and consists in taking sequential pictures of particles falling under gravity in calm air. The scene is illuminated by a cold light source, while a camera takes 15 pictures per second. Between 20,000 and 100,000 images are analysed to obtain the distribution of V _s for a given set of particles. The method was validated using two standard particles with mean diameters of 68 and 108 μm, respectively, as well as Lycopodium spores, with a mean diameter of 35 μm. For each set of particles, the theoretical V _s distribution was estimated from the particle diameter distribution and the volumetric mass using a non-Stokian law, as the Reynolds numbers of the particles were large. The mean V _s was measured with the ‘settling tower' with less than 12% error, while the standard deviation of the V _s distribution was estimated with less than 51% error. The maximum error on the mean V _s was 12% for the Lycopodium spores and less than 2% for the two larger particles. The mean V _s of Lycopodium spores was 4.2 cm s⁻¹, and its standard deviation was 0.7 cm s⁻¹. The reason for the small overestimation of V _s for Lycopodium spores by the ‘settling tower' method is discussed. Preliminary measurements shows that, the ‘settling tower' could be of great practical interest for measuring the distribution of V _s of maize pollen as well as other types of pollen or spores.     

The settling characteristics and mean settling velocity of granular sludge in upflow anaerobic sludge blanket (UASB)-like reactors

Mean settling velocity of granular sludge in full-scale UASB (upflow anaerobic sludge blanket) and EGSB (expanded granular sludge bed) reactors was evaluated by settling column tests, and a settling velocity model based on the experimental results and available literature data was developed. It is concluded that the settling velocity should be calculated by the Allen formula, because the settling process of the granules is in the category of intermediate flow regime rather than in the laminar flow one. The comparison between calculated and measured values of the settling velocity shows an excellent agreement, with an average relative error of 4.04%. A simple but reliable mathematical method to determine the settling velocity is therefore proposed.     

Estimation of the in-situ settling velocity of particles in lakes using a time series sediment trap

SUMMARY 1. We outline a simple method for estimating the in-situ settling velocity of particles in wind disturbed lakes. The total sedimentation rate (primary and secondary sedimentation) was measured during storm events in two lakes using a time series sediment trap.
2. The sediment trap had 12 sample bottles which were programmed to open for periods of 3–4 h, giving total deployment times ranging from 36 to 48 h.
3. Wave mixed layer theory was used to infer if and when sediment resuspension occurred and the first order rate equation was used to estimate the settling velocity of resuspended particles.
4. The settling velocity during three resuspension events in Lough Neagh and one in Lough Macnean were 34.3, 29.5, 24.1 and 77.3 m day⁻¹, respectively. These are similar to values obtained using recent in-situ video imaging in marine environments, but much larger than previous lake sediment trap studies.     

A simple apparatus for measuring cell settling velocity

Accurate cell settling velocity determination is critical for perfusion culture using a gravity settler for cell retention. We have developed a simple apparatus (a settling column) for measuring settling velocity and have validated the procedure with 15-μm polystyrene particles with known physical properties. The measured settling velocity of the polystyrene particles is within 4% of the value obtained using the traditional Stokes' law approach. The settling velocities of three hybridoma cell lines were measured, resulting in up to twofold variation among cell lines, and the values decreased as the cell culture aged. The settling velocities of the nonviable cells were 33-50% less than the corresponding viable cells. The significant variation of settling velocities among cell populations and growth phases confirms the necessity of routine measurement of this property during long-term perfusion culture.     

A generalized model for settling velocity of aerobic granular sludge

Aerobic granulation is a novel biotechnology recently receiving intensive research attention. Aerobic granules developed in SBR can be as big as several millimeters, thus the traditional models describing the settling velocity of activated sludge are no long valid in aerobic granules culture. In this study, a new type of model was developed for the settling velocity of aerobic granules. This model shows that the settling velocity of aerobic granules is the function of SVI, mean size of granules and biomass concentration of granules. When the size of bioparticle is small enough, the proposed model reduces to the well-known Vesilind equation. Results indicated that the proposed model could satisfactorily fit experimental results obtained in the course of aerobic granulation under different conditions, while the Vesilind equation failed to or very poorly fit the experimental data. In addition, the proposed model can also be extended to anaerobic granules. The settling velocity is one of the most important parameters in both aerobic and anaerobic granulation, and successful biogranulation is highly related to the manipulation of settling velocity. It was demonstrated that the proposed model can sever as a useful tool for design and operation engineers to properly select the settling velocity for enhanced aerobic and anaerobic granulation.     

The effect of Langmuir circulation on the distribution and settling of algae and suspended particles

The quantitative extent to which the large-scale organised water motion in the surface waters of lakes and reservoirs, known as Langmuir circulation, affects the distribution and settling of algae and other suspended particles is not known and has thus been ignored in conventionally used water quality models. Since the distribution and settling of these particles is important in determining water quality, this study set out to investigate these effects using a mathematical model based on the two-dimensional advection-diffusion mass transport equation describing the temporal and spatial distribution of suspended particles in a typical Langmuir cell. The Langmuir circulation flow field and turbulent diffusion coefficients are empirically modelled by relating them to environmental parameters (Buranathanitt et al., in press).The results show that Langmuir circulation does affect particle distribution and settling. For particles with small sinking speeds, such as the lighter algae, the circulation causes intense mixing, resulting in essentially uniform distribution of particles over the cell (as assumed in the well-mixed compartment model). For particles with high sinking velocities, however, aggregation can occur, giving rise to significant reduction in sinking loss. For diatoms, effective sinking speeds are as much as 6% less than when cells are not operating while for coarse silt particles in a cell of large width to depth ratio a reduction of more than 60% is possible.Two preliminary laboratory experiments have also been performed in order to obtain further information on both the physical characteristics of Langmuir cells and their effects on suspended particles. The results of a wind-wave tank experiment suggest that the Langmuir circulation scale of motion is related to the height of the surface waves, thus providing an empirical means of determining the size of Langmuir cells from environmental variables. A particle settling tank experiment confirmed, in a qualitative way, the results obtained in the analytical study, with both the uniformly mixed and aggregation phenomena being reproduced (Buranathanitti et al., submitted).Full details of the work described in this abstract will be published elsewhere (Buranathanitt et al., in press; Buranathanitt et al., submitted).)     

Size and settling velocity distributions of flocs in the Tamar estuary during a tidal cycle

Data extracted from video recordings of individual estuarine flocs near the estuary bed during the advance and retreat of the salt intrusion show changes in size and settling velocity distributions. The recordings were taken using INSSEV —IN Situ SEttling Velocity instrument. Size coupled with effective density variations due to both changes in floc structure and ambient salinity result in changes in the settling velocity during the tidal cycle. In particular, just after high water slack, the appearance of high settling velocity medium size flocs and individual particles suggest that the lower density flocs have been broken up by the intense vertical shear in the currents caused by the salt wedge intrusion. Current shear is shown to have a significant influence on floc effective density.     

Effect of carbohydrates to protein in EPS on sludge settling characteristics

Extracellular polymeric substances (EPS) are believed to play a role in the binding and formation of microbial flocs. However, the precise role is not well known Sludge settling characteristics and the carbohydrate to protein ratio in EPS were tested with various airflow rates in this study. Sludge, was collected from three modified sequencing batch reactors (SBRs), which were operated at 16°C with an airflow rate of 0.8 L/min, 3L/min and 6 L/min, respectively. During the operation, the reactor operated at an airflow rate of 0.8 L/min showed sludge volume index (SVI) of 80 to 90 mL/g and a constant ratio of carbohydrate to protein in the EPS, while a significant increase in the SVI was seen in the other reactors. Sludge bulking increased the amount of carbohydrate in the EPS, while kept protein almost constant in the airflow rate of 3 L/min and 6 L/min. Surface charge also increased with increases in the carbohydrate to protein ratio in the EPS, which weakens the attraction between the EPS and multivalent cations. The ratio of carbohydrate to protein in the EPS was inferred to be essential for bioflocculation.     

Morphology and reactivity characteristics of char biomass particles

In this work, 10 different biomasses were selected which included directly grown energy crops, industrial waste material and different wood types. Each biomass was sieved into six different size fractions and pyrolysed in a fixed bed furnace preheated to 1000 °C to produce a char residue. Intrinsic reactivity during burnout was measured using a non-isothermal thermogravimetric method. Scanning electron microscopy and oil immersion microscopy were used to characterise the morphology of the products. Char morphology was summarised in terms of degree of deformation, internal particle structure and wall thickness. Intrinsic reactivity corresponded directly with these morphology groupings showing a significant correlation between char morphotypes, char reactivity and the initial biomass material.     

Enzyme distribution and matrix characteristics in biocatalytic particles

In a study of Assemblase, an industrial immobilized penicillin-G acylase, various electron microscopic techniques were used to relate intra-particle enzyme heterogeneity with the morphological heterogeneity of the support material at various levels of detail. Transmission electron microscopy was used for the study of intra-particle penicillin-G acylase distribution in Assemblase particles of various sizes; it revealed an abrupt increase in enzyme loading at the particle surface (1.4-fold) and in the areas (designated halo's) surrounding internal macro-voids (7.7-fold). Cryogenic field-emission scanning electron microscopy related these abrupt local enzyme heterogeneities to local heterogeneity of the support material by revealing the presence of dense top layers surrounding both the particle exterior and the internal macro-voids. Furthermore, it showed a very distinct morphological appearance of the halo. Most probably, all these regions contained relatively more chitosan than gelatin (the polymers Assemblase was constructed of), which suggested local polymer demixing during particle production. A basic thermodynamic line of reasoning suggested that a difference in hydrophilicity between the two polymers induced local demixing. In the future, thermodynamic knowledge on such polymer interactions resulting in matrix heterogeneity may be used as a tool for biocatalyst design.     

Fluxes and composition of settling particles during summer in an Antarctic shallow bay of Livingston Island, South Shetlands

A moored experiment using a sediment trap was conducted at Johnson's Dock, Livingston Island from 11 December 1997 to 24 February 1998, as part of the EASIZ Programme activities carried out at the Juan Carlos I Spanish Antarctic base. Total mass vertical fluxes ranged from 23,235 mg m^-2 day^-1 to 89,073 mg m^-2 day^-1 during the experiment, with a mean value of 42,857 mg m^-2 day^-1. Lithogenic components were the major contributors to the settling particulate flux. Organic components accounted for a low fraction of the settling particulate matter, showing an inverse relation to total mass flux. Nevertheless, the fluxes of organic components at Johnson's Dock are as high as in the open sea. The increases in chlorophyll a in water were related to increases in the organic carbon content, which dominated over inorganic carbon during the whole experiment. Calcium carbonate particles settle without being significantly altered in the water column and are dissolved in the upper centimetres of the bottom sediments, once they are buried. The settling material consisted of fine particles, with coarse clasts transported by icebergs. Antarctic shallow environments receive important sediment fluxes from the erosion and transport action of ice.     

Surfactant-DNA gel particles: formation and release characteristics

Aqueous mixtures of oppositely charged polyelectrolytes undergo associative phase separation, resulting in coacervation, gelation, or precipitation. This phenomenon has been exploited here to form DNA gel particles by interfacial diffusion. We report on the formation of DNA gel particles by mixing solutions of DNA (either single-stranded (ssDNA) or double-stranded (dsDNA)) with solutions of cationic surfactant cetyltrimetrylammonium bromide (CTAB). By using CTAB, the formation of DNA reservoir gel particles, without adding any kind of cross-linker or organic solvent, has been demonstrated. Particles have been characterized with respect to the degree of DNA entrapment, surface morphology, and secondary structure of DNA in the particles. The swelling/deswelling behavior and the DNA release have been investigated in response to salt additions. Analysis of the data has suggested a higher degree of interaction between ssDNA and the cationic surfactant, confirming the stronger amphiphilic character of the denatured DNA. Fluorescence microscopy studies have suggested that the formation of these particles is associated with a conservation of the secondary structure of DNA.     

The velocity of conduction in nerve fiber and its electric characteristics

The theory developed in this paper shows that the propagation of spike potential along a nerve fiber and the conduction of an electric wave along an inert inorganic conductor follow a common quantitative relationship. This result gives further support to the belief that propagation of excitation is an electrical process. The basic idea of the theory is derived from the consideration that velocity has, by its mathematical definition, a local meaning; conduction in a nerve is completely determined by the local characteristics of the latter, as well as those of the wave. The final formula derived does not make use of any other field of science beyond the fundamental principles of electricity. It gives the conduction velocity in terms of the electric characteristics of the fiber and of the duration of the spike potential. The formula is in agreement with the known dependence of the conduction velocity on various parameters characterizing the axon. The computed velocity agrees with the measured ones on the squid giant axon, crab nerve axon, frog muscle fiber and Nitella cell. The membrane inductance appears as a velocity controling agent which prevents also a possible distortion of the spike potential during conduction. The structural meaning of the electric characteristics of the axon membrane is discussed from the viewpoint of the diffusion theory. A formula for the velocity of spread of the electrotonus is also derived.     

Dispersal, settling and layer formation

Motivated by examples in developmental biology and ecology, we develop a model for convection-dominated invasion of a spatial region by initially motile agents which are able to settle permanently. The motion of the motile agents and their rate of settling are affected by the local concentration of settled agents. The model can be formulated as a nonlinear partial differential equation for the time-integrated local concentration of the motile agents, from which the instantaneous density of settled agents and its long-time limit can be extracted. In the limit of zero diffusivity, the partial differential equation is of first order; for application-relevant initial and boundary-value problems, shocks arise in the time-integrated motile agent density, leading to delta-function components in the motile agent density. Furthermore, there are simple solutions for a model of successive layer formation. In addition some analytic results for a one-dimensional system with non-zero diffusivity can also be obtained. A case study, both with and without diffusion, is examined numerically. Some important predictions of the model are insensitive to the specific settling law used and the model offers insight into biological processes involving layered growth or overlapping generations of colonization.     

Mean velocity of optically detected intraaxonal particles measured by a cross-correlation method.

A method which uses by the cross correlation of optical signals is described for the determination of the mean velocity of somatopetally moving particles within nerve fibers. The method was validated by simulation experiments and by comparing the results with those obtained by averaging collections of velocities of individual particles. The significant contribution of the method is that it allows objective and rapid serial evaluation of mean particle velocity within individual nerve fibers with good accuracy and precision. A series of results from normal myelinated nerve fibers from Xenopus laevis is presented. Considerable variation (up to 50%) in mean velocity was found between individual nerve fibers. The mean of all determinations indicates that the mean velocity of somatopetally moving particles in axons with diameters greater than 10mum is in the region of 1.14 mum/s at a temperature of 22-24 degrees C. The findings are compared with small collection of such determinations which have been reported in the literature.     

Optimal pedalling velocity characteristics during maximal and submaximal cycling in humans

The aim of this study was to compare optimal pedalling velocities during maximal (OVM) and submaximal (OVSM) cycling in human, subjects with different training backgrounds. A group of 22 subjects [6 explosive (EX), 6 endurance (EN) and 10 non-specialised subjects] sprint cycled on a friction-loaded ergometer four maximal sprints lasting 6 s each followed by five 3-min periods of steady-state cycling at 150 W with pedalling frequencies varying from 40 to 120 rpm. The OVM and OVSM were defined as the velocities corresponding to the maximal power production and the lowest oxygen consumption, respectively. A significant linear relationship (r2 = 0.52, P < 0.001) was found between individual OVM [mean 123.1 (SD 11.2) rpm] and OVSM [mean 57.0 (SD 4.9) rpm, P < 0.001] values, suggesting that the same functional properties of leg extensor muscles influence both OVM and OVSM. Since EX was greater than EN in both OVM and OVSM (134.3 compared to 110.9 rpm and 60.8 compared to 54.0 rpm, P < 0.01 and P < 0.05, respectively) it could be hypothesised that the distribution of muscle fibre type plays an important role in optimising both maximal and submaximal cycling performance.