Use Of Larger Particles Research Articles

Activity patterns in the terebellid polychaete Eupolymnia nebulosa assessed using a new image analysis system

The activity and surface sediment displacement by the terebellid polychaete Eupolymnia nebulosa were monitored, using new image acquisition and image analysis procedures. We used a video sensor mounted on a motorized table, to acquire adjacent images of the whole studied aquarium within about 2 s. These images were then grouped within a composite image acquired every 15 s. Consecutive composite images were compared to infer activity and surface sediment displacement. This procedure proved efficient for E. nebulosa as indicated by (1) the continuity of the tentacles within composite images, and (2) the direct comparison of images and detected activities. There were important temporal changes in the relative importance of the three main types of activity: feeding, tube-building and (both partial and total) emergence from the tube, accounting, respectively, for 75, 15 and 10% of the entire experiment duration. Activity intensity (cm2 min-1) was assessed through the surface of pixels with grey levels differing by more than 20 (on a 0–255 scale) between two consecutive images. Feeding was associated with low activity intensity, whereas tube-building and emergence from the tubes were associated with high activity intensities. Surface sediment displacement mostly resulted from tentacle activity both during feeding and tube-building and was almost zero when worms emerged from their tube. We used our experimental set up to assess spatial changes in activity intensity and particle displacements along the tentacles. Most of the activity occurred within the first 4–6 cm from the tube aperture. Particle loss during their transfer along the tentacles preferentially affected larger particles as postulated by the model of particle selection and transport in tentaculate deposit-feeders. Moreover, the speed of the particles along the tentacles correlated negatively with their size. This contributed to increase in the residence time of larger particles on the tentacles and thus, to further enhance their probability of being lost. The size distributions of particles during feeding and tube-building did not differ significantly although visual observations confirmed the preferential use of larger particles for tube-building. This suggests the existence of a sorting step occurring elsewhere than on the tentacles as already demonstrated for spionid polychaetes.

Use of non-crystallising particles to mitigate crystallisation fouling

Fouling in heat exchangers is of paramount importance considering its impact on the overall performance of a process plant. Fouling can be controlled by using different methods that affect the deposition rate and/or the removal rate. The use of larger particles (of the order of several millimetres) in fluid bed heat exchangers has been quite successful for heat transfer with severely fouling fluids. In this study, we will investigate the role of much smaller (micron size), non-crystallising particles on crystallisation fouling in a heat exchanger. This will be done by measuring global fouling resistance and pressure drop across the heat exchanger. The smaller particles have been found to be effective in mitigating the crystallisation fouling substantially by lowering the deposition rate and by increasing the removal rate.

Bronchial challenge tests in patients with asthma sensitized to cats: the importance of large particles in the immediate response.

Our aim was to compare bronchial responses to major cat allergen (Fel d 1) in individuals with intermittent asthma sensitized to cats (19 subjects) according to the droplet particle size. We used three nebulizers, which delivered particles with mass median aerodynamic diameters of 1.4, 4.8, and 10.3 microm. A dosimeter nebulizer was used. The cat allergen was diluted to obtain the same amount of Fel d 1 per puff with each nebulizer. Each patient underwent three methacholine bronchial challenge tests (BCT), each followed 24 hours later by a cat allergen BCT, each performed with a different nebulizer (randomly selected each time, with patient and tester always blinded). Subjects did not differ for methacholine responsiveness, FEV1, mean forced expiratory flow during the middle half of the FVC (FEF25-75), PEF, or dyspnea (Borg scale) before any of the three cat BCTs. Cat allergen PD20 was 271 ng of Fel d 1 with the 1.4 microm nebulizer, 46 ng with the 4.8 microm nebulizer, and 13.5 ng with the 10.3 microm nebulizer (p = 0.00001). Inhalation of small particles (1.4 microm) resulted in significantly lower FEF25-75 24 hours after provocation than large particles did. In conclusion, immediate bronchial response appears to be localized in large airways, and the use of large particles is more appropriate for cat allergen BCTs.

Use of large particles support for fast analysis of methadone and its primary metabolite in human plasma by liquid chromatography–mass spectrometry

A bioanalytical method was developed for the quantitation of methadone (MTD) and its primary metabolite, (EDDP) in plasma. The extraction step was performed within a capillary column packed with large particles (35×0.3 mm I.D.; d p 30 μm) at high flow-rate conditions (450 μl/min). The separation was performed on a microbore analytical column (55×2 mm I.D.; d p 3 μm) coupled to a mass spectrometer (MS). This procedure was based on a column-switching unit. Analytes of interest were retained on the precolumn by hydrophobic interactions and backflushed from the precolumn to the analytical column. The detection was carried out with a MS single quadrupole equipped with an electrospray interface. The total analysis time was 6 min. The limits of quantification were evaluated at 10 and 25 ng/ml for MTD and EDDP, respectively. At this level, good accuracies were obtained for both analytes with repeatability values less than 18%.

Modelling the global efficiency of dissolved air flotation

The purpose of this paper is to examine how the efficiency of dissolved air flotation is affected by the size of bubbles and particles. The rise speed of bubble/particle agglomerates is modelled as a function of bubble and particle size, while the kinematics of the bubble attachment process is modelled using the population balance approach adopted by Matsui, Fukushi and Tambo. It is found that flotation, in general, is enhanced by the use of larger particles and larger bubbles. In particular, it is concluded that for the ultra-high surface loading rates of 25 m/hr or more planned for future flotation tanks, bubble size will have to be increased by a factor of two over the size currently employed in many facilities during dissolved air flotation.

Liquid Phase Hydrogenation of Maleic Anhydride to 1,4-Butanediol in a Packed Bubble Column Reactor

The liquid phase hydrogenation of maleic anhydride was investigated in a packed bubble column reactor using different copper-based catalysts. A copper-zinc catalyst was found to be active in the formation of 1,4-butanediol, whereas on zinc-free copper catalysts, mainly succinic anhydride and γ-butyrolactone were formed. At suitable reaction conditions, maleic anhydride hydrogenation over a copper-zinc catalyst gave valuable products with high yield and selectivity whereas succinic anhydride was absent in the reactor outlet. Based on a three-phase reactor model and a kinetic model of the reaction mechanism, the influence of reaction conditions on reactor performance was determined. It was observed that the use of large particles and a high axial dispersion of liquid phase is a necessary condition for the feasibility of a “one-step-hydrogenation” of highly concentrated maleic anhydride feed solutions because of a significant decrease of succinic anhydride formation rate.

Effect of temperature and density on the performance of micropacked columns in supercritical fluid chromatography

The effects on the efficiency of micropacked columns in supercritical fluid chromatography (SFC) of density at fixed temperature and of temperature at fixed density were investigated. The variation of the retention and resolution achievable for a given pair of solutes with the mobile phase density under different isothermal conditions was also studied. The linear velocity was varied using several flow restrictors of different lengths and inner diameters. The column type investigated was characterized by an inside diameter of <1 mm and the use of large particles (by HPLC standards), resulting in a particle-to-column diameter ratio of 0.1–0.3. Owing to the better permeability derived from both the large particle diameters and the high value of the interparticle porosity, the use of these columns may be an interesting approach in SFC.

The formation and role of a phase with glassy appearance in the Tl-Ca-Ba-Cu system

A phase with a glassy appearance has been detected in samples of the Tl–Ca–Ba–Cu system. The presence of such a phase is expected to have a negative effect on the critical current density in a bulk superconductor. Samples of 2-2–2-3 starting composition were prepared from Tl2O3, BaO2, and relatively large particles of CaO and CuO. These samples were then heat-treated at 867°C for various periods of time. The use of large particles of CaO and CuO facilitates the examination of the morphological changes associated with the formation of the superconducting phases. Using scanning electron microscopy, a layer of the 2122 phase was found to form on the surface of the large CaO particles whereas near the surface of the large CuO particles, large voids were observed. By varying some of the experimental conditions, a liquid phase with a composition close to 2-0–2-3 was inferred to form. The voids observed in the surroundings of the CuO particles may be due to the formation of such a melt. This liquid phase, after cooling, apparently leads to the “glassy” phase detected in the reacted samples. This glassy phase may play a role as an intermediate in the formation of the 2122 phase, which could result by a direct reaction between the liquid phase and CaO, A part may remain, however, among the superconducting grains, thus having a negative effect on the critical current density.

Theoretical optimization of operating parameters in non-ideal displacement chromatography

A mathematical model was developed for the simulation of non-ideal displacement chromatography. The model incorporates finite mass transport to the solid adsorbent by using a linear driving force approximation with a coupled external film and internal pore mass transfer coefficient. Equilibrium adsorption at the fluid—solid interface is described using competitive langmuirian adsorption isotherms. A finite difference numerical technique was employed to approximate the system of coupled, non-linear partial differential equations. The model was used to simulate the effluent concentration profiles under various displacement chromatographic conditions. The effects of axial dispersion and finite mass transport were examined by varying the Peclet and Stanton numbers, respectively. Slow mass transfer rates were shown to have a dispersive effect on the shock waves generated in displacement chromatography, resulting in greater zone overlap. Constant pattern formation was observed under non-ideal conditions. The throughput obtained in displacement chromatography was examined as a function of feed load, flow velocity, and displacer concentration. For non-ideal systems, the throughput was shown to exhibit a maximum at unique values of these operating parameters. The effects of particle diameter and solute diffusivity on the throughput were also examined. Model predictions indicate that the use of large particles could be detrimental to the performance of displacement systems when high velocities are employed. For macromolecular separations by displacement chromatography, small particles are required regardless of the linear velocity. The model presented here is a useful tool for the optimization and scale-up of displacement chromatographic processes.

Effect of Biphase Lubricants on Dynamics of Rigid Rotors

The dynamic behavior of rigid rotors as affected by the use of liquid-solid biphase lubricants in the supporting hydrodynamic bearings is studied theoretically. Two categories of dynamic behavior viz (a) unbalance response at low rotor speeds, and (b) half frequency whirl at high speeds, are studied. It is shown that the use of liquid-solid biphase lubricants causes considerable reduction in the size of journal orbit of an unbalanced rotor. The influence of particle size and dispersion concentration is studied. It is observed that an early reversal of journal surface velocity in the trailing half of crushing zone reduces the efficacy of the crushing action of the solid phase to some extent and results in periodic pulses applied by the solid phase on the journal. At higher journal speeds at which the operating point of the journal becomes unstable and the phenomenon of half-frequency whirl sets in, the use of biphase lubricants with small and medium-size particles causes a reduction in the size of whirl orbits. The journal, however, keeps whirling in a manner such that the whirl ratio crosses the value of + 1/2 twice in an orbit and thus the bearing loses its rotational load bearing capacity twice in an orbit. The use of large particles with heavy or medium weight rotors results in a significant qualitative change in the nature of whirl orbit. The journal center in such cases does not encircle the bearing center and the whirl ratio of + 1/2 is never reached. The liquid phase retains rotational load bearing capacity and shares the major part of rotor weight throughout.

Mechanism of differential staining of nucleic acids.

WORK in this Department, to be published elsewhere, has shown that several histological methods for the demonstration of mucin depend for their selectivity on the use of cations of large size. Thus alcian blue, with a molecular weight of about 1,341 (ref. 1), is almost specific for acid mucins, being apparently unable to enter other, more dense, basophilic structures. The dialysed iron method2 similarly depends on the use of large particles (colloidal ferric hydroxide), while in Southgate's mucicarmine the small carmine molecule is probably adsorbed on to colloidal aluminium hydroxide.