Origin and Longevity of Estuaries
Michael J. Kennish in Ecology of Estuaries Physical and Chemical Aspects, 2019
Weather conditions influence sedimentation rates. In temperate latitudes for example, the melting of ice and increased precipitation during the late winter and spring produce large river discharges and concomitant sediment influxes into estuaries. A case in point is the Susquehanna River discharging directly into the main body of Chesapeake Bay and delivering a substantial amount of clay and silt to the upper 30 km of the estuary.70 During the spring freshet, which persists for only several weeks along the Susquehanna River, approximately 70% of the annual suspended sediment load of the river is transported to Chesapeake Bay, with about 75% of this sediment being deposited in the upper reaches.71-73 The Susquehanna River discharges about 0.9 ± 0.3 × 106 MT (metric tons) of sediment to Chesapeake Bay during years when no major floods occur.74
Urban water supply and water treatment
Sandy Cairncross, Richard Feachem in Environmental Health Engineering in the Tropics, 2018
Sedimentation is usually assisted by adding chemicals called coagulants, often alum (aluminium sulfate), to the water. This causes the small solid particles to come together in larger clusters known as ‘flocs’, which can settle faster through the water. Lime is often added also to adjust the pH of the water to the level where the coagulant is most effective. The correct doses of coagulant and lime depend on the water being treated and may vary from day to day. The equipment for adding the chemicals should have as few moving parts as possible and preferably not require electricity. Some turbulence is required to mix the chemicals thoroughly with the water. This can be achieved by passing the water over a weir, through a constriction or around baffles, and no motor driven equipment is necessary. Subsequently slower agitation is required to cause small flocs to join together to form larger ones that will settle out faster.
Microbiological Diagnosis of Parasitic Diseases
Nancy Khardori in Bench to Bedside, 2018
Concentration techniques. These methods allow for the detection of parasites even when the parasites are present in low numbers in the clinical specimens (Levine and Estevez 1983, Truant et al. 1981). The basic principle of these procedures is the use of centrifugation and differences in the specific gravity to separate parasites from the fecal debris (Clinical and Laboratory Standards Institute, 2005, Garcia et al. 1979). The concentration techniques can be broadly classified into sedimentation techniques and floatation techniques. In general, sedimentation methods are more popular as they are simpler to perform and give good results. Formalin-ethyl acetate sedimentation concentration method is the most widely used concentration technique. Floatation techniques on the other hand, give a cleaner preparation; however, they may fail to concentrate some of the helminth eggs such as unfertilized eggs of Ascaris lumbricoides and eggs of trematodes.
Quantification methods for viruses and virus-like particles applied in biopharmaceutical production processes
Published in Expert Review of Vaccines, 2022
Keven Lothert, Friederike Eilts, Michael W. Wolff
The differential centrifugal sedimentation is mainly used for the determination of the size distribution of particles in solutions, based on their settling velocity. For this purpose, particles are injected into a rotation disc, filled with a density gradient of a fluid, through which the particles settle until they are detected at the endpoint of the disc radius by light attenuation. In the area of vaccine production, differential centrifugal sedimentation is generally used for the size characterization of vaccine formulations and for the monitoring of virus aggregations [131–133]. However, the peak area of the particle sedimentation curve can be used to determine the amount of particles, although this is not trivial [147]. To obtain particle concentrations, the measured size-distribution must be converted into a mass-weighted size distribution, which can then be used for the quantity calculation, based on the integrated peak and the knowledge about individual particle weights. A limitation is the difficult discrimination between virus- and other particles, such as extracellular vesicles.
Overcoming hydrolytic degradation challenges in topical delivery: non-aqueous nano-emulsions
Published in Expert Opinion on Drug Delivery, 2022
Arya Kadukkattil Ramanunny, Sachin Kumar Singh, Sheetu Wadhwa, Monica Gulati, Bhupinder Kapoor, Rubiya Khursheed, Gowthamarajan Kuppusamy, Kamal Dua, Harish Dureja, Dinesh Kumar Chellappan, Niraj Kumar Jha, Piyush Kumar Gupta, Sukriti Vishwas
The differential density of droplets and the dispersion medium determines the stability issues. If the dispersed droplets possess lower density in comparison to the dispersion medium, they tend to move upward. This phenomenon is known as creaming. The droplets with higher density experience higher gravitational pull and move downward. This is termed as sedimentation. The difference in chemical potential that exists between droplets and the Laplace pressure generated at the curved interface explains the frequency of Ostwald ripening [111]. When the potential is higher in smaller droplets, the mass transfer occurs resulting in the larger droplet. The smaller droplets merge with larger once gradually with time, resulting in giant droplets. Ostwald ripening is a major issue faced in the formulation development [112]. The instability problems associated with nano-emulsions are briefly represented in Figure 2.
Estimates of carbon nanotube deposition in the lung: improving quality and robustness
Published in Inhalation Toxicology, 2020
Matthew D. Wright, Alison J. Buckley, Rachel Smith
Impaction occurs when particles with sufficient inertia deviate from the gas streamline as the latter curves e.g. at a bend or bifurcation in the lung, and deposit on airway walls. Impaction is most important for large particles and higher air flow rates and is of primary concern in the upper airways. Sedimentation is the result of gravitational settling of particles and is more important in smaller airways, where flow velocity is lower and particle residence time is longer. Both these mechanisms are governed by the aerodynamic equivalent diameter of the particle (see Supplementary Information). A very large range of aerodynamic diameters, from 10 nm to over 100 μm, is obtained for ‘broadly-spherical’ CNT particles using typically observed dimensions and densities (Table 2). Because the density of ‘broadly-spherical’ CNT particles is usually expected to be below unit density, their aerodynamic diameter is likely to be smaller than their physical diameter.
Related Knowledge Centers
- Diffusion
- Macromolecule
- Molecule
- Peptide
- Protein
- Particle
- Suspension
- Settling
- Cell
- Solution