Continuous drying of alginate aerogel particles: Residence time measurement and process optimization under high pressure conditions

Ultrafast and complete drying of ecamsule solution using supercritical carbon dioxide with fluctuating pressure technique

An assessment of residence and influence times in Xiamen Bay, China

Fluidized Bed Dryers — Recent Advances

Residence time measurements in a coal hydrogenation process

Information on the mean residence time and the residence time distribution is of importance when optimizing a continuous dryer. In this study, an industrial method for determining the mean residence time is developed. The produced method is benchmarked on a laboratory scale against the stop-and-empty method. The method, which uses LiCl as the tracer does not cause any disturbances in the biofuel drying or pelleting processe.

an upland agricultural stream. We measured solute concentrations ( 15 NO3 , 15 N2 (g), as well as NO3 ,N H3, DOC, DO, Cl − ), and hydraulic transport parameters (head, flow rates, flow paths, and residence time distributions) of the reach and along HZ flow paths of an instrumented gravel bar. HZ exchange was observed across the entire gravel bar (i.e., in all wells) with flow path lengths up to 4.2 m and corresponding median residence times greater than 28.5 h. The HZ transitioned from a net nitrification environment at its head (short residence times) to a net denitrification environment at its tail (long residence times). NO3 increased at short residence times from 0.32 to 0.54 mg‐ NL −1 until a threshold of 6.9 h and then consistently decreased from 0.54 to 0.03 mg‐ NL −1 . Along these same flow paths, declines were seen in DO (from 8.31 to 0.59 mg‐O2 L −1 ) and DOC (from 3.0 to 1.7 mg‐ CL −1 ). The rates of the DO and DOC removal and net nitrification were greatest during short residence times, while the rate of denitrification was greatest at long residence times. 15 NO3 tracing confirmed that a fraction of the NO3 removal was via denitrification as 15 N2 was produced across the entire gravel bar HZ. Production of 15 N2 across all observed flow paths and residence times indicated that denitrification microsites are present even where nitrification was the net outcome. These findings demonstrate that the HZ is an active nitrogen sink in this system and that the distinction between net nitrification and denitrification in the HZ is a function of residence time and exhibits threshold behavior. Consequently, incorporation of HZ exchange and water residence time characterizations will improve mechanistic predictions of nitrogen cycling in streams.

Water circulation over coral reefs can determine the degree to which reef organisms are exposed to the overlying waters, so understanding circulation is necessary to interpret spatial patterns in coral health. Because coral reefs often have high geomorphic complexity, circulation patterns and the duration of exposure, or “local residence time” of a water parcel, can vary substantially over small distances. Different meteorologic and oceanographic forcings can further alter residence time patterns over reefs. Here, spatially dense Lagrangian surface current drifters and Eulerian current meters were used to characterize circulation patterns and resulting residence times over different regions of the reefs in Faga’alu Bay, American Samoa, during three distinct forcing periods: calm, strong winds, and large waves. Residence times varied among different geomorphic zones of the reef and were reflected in the spatially varying health of the corals across the embayment. The relatively healthy, seaward fringing reef consistently had the shortest residence times, as it was continually flushed by wave breaking at the reef crest, whereas the degraded, sheltered, leeward fringing reef consistently had the longest residence times, suggesting this area is more exposed to land-based sources of pollution. Strong wind forcing resulted in the longest residence times by pinning the water in the bay, whereas large wave forcing flushed the bay and resulted in the shortest residence times. The effect of these different forcings on residence times was fairly consistent across all reef geomorphic zones, with the shift from wind to wave forcing shortening mean residence times by approximately 50%. Although ecologically significant to the coral organisms in the nearshore reef zones, these shortened residence times were still 2–3 times longer than those associated with the seaward fringing reef across all forcing conditions, demonstrating how the geomorphology of a reef environment sets a first-order control on reef health.

Gene expression noise is not just ubiquitous but also variable, and we still do not understand some of the most elementary factors that affect it. Among them is the residence time of a transcription factor (TF) on DNA, the mean time that a DNA-bound TF remains bound. Here, we use a stochastic model of transcriptional regulation to study how residence time affects the gene expression noise that arises when a TF induces gene expression. We find that the effect of residence time on gene expression noise depends on the TF’s concentration and its affinity to DNA, which determine the level of induction of the gene. At high levels of induction, residence time has no effect on gene expression noise. However, as the level of induction decreases, short residence times reduce gene expression noise. The reason is that fast on-off TF binding dynamics prevent long periods where proteins are predominantly synthesized or degraded, which can cause excessive fluctuations in gene expression. As a consequence, short residence times can help a gene regulation system acquire information about the cellular environment it operates in. Our predictions are consistent with the observation that experimentally measured residence times are usually modest and lie between seconds to minutes.

Determination of axial dispersion coefficients in plate heat exchangers using residence time measurements

Residence times of multiple particles in non-newtonian holding tube flow: Effect of process parameters and development of dimensionless correlations

Inherent differences between naturally-formed lakes and human-made reservoirs may play an important role in shaping zooplankton community structure. For example, because many reservoirs are created by impounding and managing lotic systems for specific human purposes, zooplankton communities may be affected by factors that are unique to reservoirs, such as shorter water residence times and a reservoir’s management regime, compared to natural lakes. However, the environmental factors that structure zooplankton communities in natural lakes vs. reservoirs may vary at the continental scale and remain largely unknown. We analyzed data from the 2007 U.S. Environmental Protection Agency’s National Lakes Assessment and the U.S. Army Corps of Engineers’ National Inventory of Dams to compare large-bodied crustacean zooplankton communities (defined here as individuals retained by 0.243 mm mesh size) in natural lakes and reservoirs across the continental U.S. using multiple linear regressions and regression tree analyses. We found that large-bodied crustacean zooplankton density was overall higher in natural lakes compared to reservoirs when the effect of latitude was controlled. The difference between waterbody types was driven by calanoid copepods, which were also more likely to be dominant in the >0.243 mm zooplankton community in natural lakes than in reservoirs. Regression tree analyses revealed that water residence time was not a major driver of calanoid copepod density in natural lakes but was one of the most important drivers of calanoid copepod density in reservoirs, which had on average 0.5-year shorter water residence times than natural lakes. Reservoirs managed for purposes that resulted in shorter residence times (e.g., hydroelectric power) had lower zooplankton densities than reservoirs managed for purposes that resulted in longer residence times (e.g., irrigation). Consequently, our results indicate that water residence time may be an important characteristic driving differing large-bodied zooplankton dynamics between reservoirs and natural lakes.

Fibrinogen adsorbed to polymeric surfaces and then allowed to reside on the surface while it is kept in a buffer solution for a period of time (the 'residence time') undergoes postadsorptive changes that decrease its SDS elutability, displaceability by plasma, polyclonal antifibrinogen binding, and ability to support platelet adhesion (summarized in Chinn et al. J. Biomed. Mater. Res. 26, 757 (1992)). In order to better understand the nature of the changes in adsorbed fibrinogen, the binding of ten different monoclonal antifibrinogen molecules to fibrinogen adsorbed from plasma to Biomer and several other surfaces has been measured after increasing residence time in buffer. Three of the monoclonal antibodies used bind to sequences that have been implicated in platelet binding to fibrinogen. One of these (M1) binds to the C-terminal region of the gamma chain (402-411), another (R1) binds to the N-terminal region of the A alpha chain containing an RGDF sequence (95-98), and the third (R2) binds to the C-terminal region of the A alpha chain containing an RGDS sequence (572-575). Two other antibodies (P1 and K4) also bind to the C-terminal region of the gamma chain (373-385 and 392-406, respectively). Five other antibodies that bind to other regions in fibrinogen were also used. Two of the antibodies (K4 and P1) are also known to be sensitive to conformational changes in the fibrinogen molecule. The binding of the various antibodies changed with residence time in ways that were highly dependent on the particular antibody. The binding of some antibodies was very stable with respect to residence time, others rose with time, some declined with residence time and one appears to pass through a maximum. However, none of the changes in antibody binding were nearly as fast as has been observed for the changes in platelet binding reported previously. Binding to the platelet binding region near the gamma chain C-terminal region either did not change with residence time (M1), increased with residence time (K4), or else decreased more slowly than observed for platelets (P1). Binding of the antibodies to the RGD sequences near the N-terminus of the A alpha chain (95-98) was very low initially but increased with residence time, while the binding to the RGD sequence near the C-terminus of the A alpha chain (572-575) increased slightly at short residence times but then declined substantially after longer residence times. Thus, the changes in the expression of the putative platelet binding domains do not correlate with the declines in platelet binding to plasma preadsorbed Biomer.(ABSTRACT TRUNCATED AT 400 WORDS)

Manipulating dissolved oxygen concentration to control the partitioning between carbon oxidation and redirection in the A-stage high rate activated sludge process

The drying of carbohydrate suspensions on polypropylene particles in a pulsed fluidized bed was studied by means of a 25 experimental design, to determine the effect of the air flow and temperature, suspension flow rate, and free section and rotating speed of the rotary plate on the Nusselt number, the moisture content of the product, and the percentage of solids retained inside the bed (which were minimized to 4.9 and 14.4%, respectively) with an air flow of 600 m3/h at 90°C and 720 mmHg, a suspension flow rate of 6 L/h, and a plate with 6% free section, rotating at 50 rpm. Additionally, the effects of temperature, air flow, and suspension flow rate on the residence time distribution (RTD) were determined, using the stimulus-response methodology. The RTD was represented by 1.1 to 2 tanks in series, according to this model. The mean residence time of the dried carbohydrate particles was between 5.4 and 8.2 min. Finally, an egg suspension could be dried at 4 L/h, with air at 90°C, with a mean residence time about 50% longer that that found for drying carbohydrate suspensions.

Residence time analysis of RNA polymerase transcription dynamics: A Bayesian sticky HMM approach