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Academic literature on the topic 'Transit and Residence Times'

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Published: 11 March 2023

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Journal articles on the topic "Transit and Residence Times"

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Poulain, P. M., and S. Hariri. "Transit and residence times in the Adriatic Sea surface as derived from drifter data and Lagrangian numerical simulations." Ocean Science 9, no. 4 (August 6, 2013): 713–20. http://dx.doi.org/10.5194/os-9-713-2013.

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Abstract. Statistics of transit and residence times in the Adriatic Sea surface, a semi-enclosed basin of the Mediterranean, are estimated from drifter data and Lagrangian numerical simulations. The results obtained from the drifters are generally underestimated given their short operating lifetimes (half life of ∼40 days) compared to the transit and residence times. This bias can be removed by considering a large amount of numerical particles whose trajectories are integrated over a long time (750 days) with a statistical advection–dispersion model of the Adriatic surface circulation. Numerical particles indicate that the maximum transit time to exit the basin is about 216–260 days for particles released near the northern tip of the Adriatic, and that a particle entering on the eastern Otranto Channel will typically exit on the other side of the channel after 170–185 days. A duration of 150–168 days is estimated as the residence time in the Adriatic Basin.
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Poulain, P. M., and S. Hariri. "Transit and residence times in the surface Adriatic Sea as derived from drifter data and Lagrangian numerical simulations." Ocean Science Discussions 10, no. 1 (January 24, 2013): 197–217. http://dx.doi.org/10.5194/osd-10-197-2013.

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Abstract. Statistics of transit and residence times in the surface Adriatic Sea, a semi-enclosed basin of the Mediterranean, are estimated from drifter data and Lagrangian numerical simulations. The results obtained from the drifters are generally underestimated given their short operating lifetimes (half life of ~ 40 days) compared to the transit and residence times. This bias can be removed by considering a large amount of numerical particles whose trajectories are integrated over a long time (750 days) with a statistical advection-diffusion model of the Adriatic surface circulation. Numerical particles indicate that the maximum transit time to exit the basin is about 216–260 days for objects released near the northern tip of the Adriatic, and that a particle entering on the eastern Otranto Channel will typically exit on the other side of the Channel after 170–185 days. A value of 150–168 days is estimated for the residence time in the Adriatic basin.
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Waniewski, Jacek. "Mean Transit Time and Mean Residence Time for Linear Diffusion–Convection–Reaction Transport System." Computational and Mathematical Methods in Medicine 8, no. 1 (2007): 37–49. http://dx.doi.org/10.1080/17486700701298293.

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Characteristic times for transport processes in biological systems may be evaluated as mean transit times (MTTs) (for transit states) or mean residence times (MRT) (for steady states). It is shown in a general framework of a (linear) reaction–diffusion–convection equation that these two times are related. Analytical formulas are also derived to calculate moments of exit time distribution using solutions for a stationary state of the system.
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Sierra, Carlos A., Markus Müller, Holger Metzler, Stefano Manzoni, and Susan E. Trumbore. "The muddle of ages, turnover, transit, and residence times in the carbon cycle." Global Change Biology 23, no. 5 (November 25, 2016): 1763–73. http://dx.doi.org/10.1111/gcb.13556.

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White, Jessica F., Andrew S. Cowburn, Charlotte Summers, Karen A. Cadwallader, Iain Mackenzie, Raaj K. Praseedom, Edwin R. Chilvers, and A. Mike Peters. "The Influence of the Spleen on Neutrophil Apoptosis in Vivo." Journal of Cell Death 4 (January 2011): JCD.S6444. http://dx.doi.org/10.4137/jcd.s6444.

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In contrast to radiolabelled erythrocytes and platelets, radiolabelled neutrophils leave the circulating blood in an exponential manner, indicating random rather than age-dependent removal. Neutrophils transit the spleen with a range of residence times that are log normally distributed. We hypothesized that neutrophils are conditioned to undergo apoptosis to an extent that depends on their intrasplenic residence time and that this provides an explanation for the random removal of these cells from blood. Splenic venous and peripheral arterial blood was sampled simultaneously during abdominal surgery in four patients and age-dependent apoptosis assessed in whole blood using annexin V/PI staining. Apoptosis increased after 4 and 20 h ex-vivo incubation and was invariably higher in splenic venous vs arterial neutrophils. Transit through the spleen appears to promote neutrophil apoptosis, with subsequent high efficiency clearance by the liver. This may explain the mechanism underlying the random removal of neutrophils from the blood.
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Hoffmann, T., S. M. Mudd, K. van Oost, G. Verstraeten, G. Erkens, A. Lang, H. Middelkoop, et al. "Short Communication: Humans and the missing C-sink: erosion and burial of soil carbon through time." Earth Surface Dynamics Discussions 1, no. 1 (June 24, 2013): 93–112. http://dx.doi.org/10.5194/esurfd-1-93-2013.

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Abstract. Is anthropogenic soil erosion a sink or source of atmospheric carbon? The answer depends on factors beyond hillslope erosion alone because the probable fate of mobilised soil carbon evolves as it traverses the fluvial system. The transit path, residence times, and the resulting mechanisms of C loss or gain change significantly down-basin and are currently difficult to predict as soils erode and floodplains evolve – this should be a key focus of future research.
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Hoffmann, T., S. M. Mudd, K. van Oost, G. Verstraeten, G. Erkens, A. Lang, H. Middelkoop, et al. "Short Communication: Humans and the missing C-sink: erosion and burial of soil carbon through time." Earth Surface Dynamics 1, no. 1 (November 26, 2013): 45–52. http://dx.doi.org/10.5194/esurf-1-45-2013.

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Abstract. Is anthropogenic soil erosion a sink or source of atmospheric carbon? The answer depends on factors beyond hillslope erosion alone because the probable fate of mobilized soil carbon evolves as it traverses the fluvial system. The transit path, residence times, and the resulting mechanisms of C-loss or gain change significantly down-basin and are currently difficult to predict as soils erode and floodplains evolve – this should be a key focus of future research.
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Hasanloo, Davood, and Amir Etemad-Shahidi. "On the estimation of transport timescales – case study: the Dez reservoir." Journal of Hydroinformatics 13, no. 2 (April 29, 2010): 217–28. http://dx.doi.org/10.2166/hydro.2010.161.

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The purpose of this study is to demonstrate an application of a hydroinformatics methodology for analysis of transport timescales in a large reservoir. Therefore, a laterally averaged two-dimensional numerical model was used to estimate the transit time, flushing times and combination of these two timescales by modeling about 230 scenarios in the Dez reservoir. The model was calibrated using temperature profiles and then executed for a period of two years (2002–2004). A possible characterization of the flushing time as e-folding time was investigated and the results revealed that the e-folding time, which is simpler to estimate, can be used in place of the flushing time in the Dez reservoir. The effects of the location of the outlet on each of these timescales were also investigated. Results indicated that the mean residence and flushing times have their smallest value when the outlet is set in the middle of the Dez dam. The mean flushing times were also less sensitive to thermal structures of the Dez reservoir than the transit times. Finally, the temporal patterns of these timescales were elucidated. It was found that no single transport timescale can be used for all conditions.
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Audi, S. H., J. H. Linehan, G. S. Krenz, C. A. Dawson, S. B. Ahlf, and D. L. Roerig. "Estimation of the pulmonary capillary transport function in isolated rabbit lungs." Journal of Applied Physiology 78, no. 3 (March 1, 1995): 1004–14. http://dx.doi.org/10.1152/jappl.1995.78.3.1004.

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Recently, we presented a method for estimating the pulmonary capillary volume and transport function based on the use of a reference indicator and two or more indicators that rapidly equilibrate (radially) with the tissue (i.e., the concentrations in the vascular and extravascular spaces at a given axial location are in equilibrium) during transit through the capillaries in a bolus-injection indicator dilution method (S. H. Audi, G. S. Krenz, J. H. Linehan, D. A. Rickaby, and C. A. Dawson. J. Appl. Physiol. 77:332–351, 1994). The objectives of the present study were 1) to determine whether [14C]diazepam and [3H]alfentanil equilibrate sufficiently rapidly between the vascular space and tissue and with sufficiently different pulmonary extra-vascular mean residence times to be used in a single bolus to estimate the pulmonary capillary volume and transport function using this method and 2) to estimate the pulmonary capillary volume and transit time distribution in isolated perfused rabbit lungs. Both [14C]diazepam and [3H]alfentanil were found to be rapidly equilibrating indicators by the criteria that, over a wide range of flow rates, their respective venous effluent concentration curves were nearly congruent on a time scale normalized to the lung mean transit time for the reference indicator (fluorescein isothiocyanate dextran). In addition, at a given plasma albumin concentration, [14C]diazepam had a significantly longer extravascular mean residence time than [3H]alfentanil, e.g., at 6% plasma albumin concentration, the extravascular mean residence time of [14C]diazepam was more than twice that of [3H]alfentanil. On average, the estimated pulmonary capillary volume for a 2.7-kg was approximately 4.2 ml or approximately 44% of the total pulmonary vascular volume (9.5 ml). The relative dispersion of the pulmonary capillary transport function of the rabbit was approximately 90%.
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Kumar, Abhishek, and Meenakshi Bharkatiya. "A Review on Updates to Increase the Residence Time of Drug in the Stomach for Gastro Retentive Drug Delivery System." Indo Global Journal of Pharmaceutical Sciences 11, no. 02 (2021): 130–42. http://dx.doi.org/10.35652/igjps.2021.112008.

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Orally-administered controlled-release drug delivery systems are associated with the shortcomings of relatively short residence times in the human stomach as well as highly variable gastrointestinal (GI) transit times. Thus, considerable intra-individual and inter-individual differences in the bioavailability of drugs are observable. There are numerous drug substances which may benefit from prolonged and controlled GI passage times. As a solution to the problem, gastroretentive drug delivery systems (GRDDS), which feature an enhanced gastric residence time (GRT), were developed. Several approaches are currently used including Floating Drug Delivery System (FDDS), swelling and expanding system, polymeric bioadhesive systems, modified-shape systems, high density system and other delayed gastric emptying devices. The drugs having absorption window in the upper part of Gastro Intestinal Tract (GIT) have enhanced bioavailability when formulated through these techniques. The recent technological development for enhancing GRT including the physiological and formulation variables affecting gastric retention, patented delivery systems, approaches to design single-unit and multiple-unit floating systems, and their classification and formulation aspects are covered in detail. Despite the extensive research performed in the field of GRDDS, the development, the production, and the evaluation of floating devices are still challenging. The purpose of writing this review was to compile recent literature on pharmaceutical approaches used in enhancing the Gastric Residence Time (GRT). Enhancing the GRT may explore new potentials of stomach as drug-absorbing organ. © 2020 iGlobal Research and Publishing Foundation. All rights reserved.
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Dissertations / Theses on the topic "Transit and Residence Times"

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Grebenkov, Denis S. "Residence times of reflected brownian motion." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193387.

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Grebenkov, Denis S. "Residence times of reflected brownian motion." Diffusion fundamentals 6 (2007) 21, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A14195.

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McTait, Graeme Edgar. "Residence times and solid flows in rotary kilns." Thesis, University of Cambridge, 1999. https://www.repository.cam.ac.uk/handle/1810/251697.

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Müller, Thomas. "Recharge and residence times in an arid area aquifer." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-119348.

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Deteriorating water quality in the face of a rising demand for agricultural products triggered interest in the groundwater resources of the Najd dessert, an arid region of southern Oman. Groundwater in this area usually is abstracted from one of the largest aquifers on the Arabian Peninsula, the Umm Er Radhuma aquifer. Increased discharge stands in contrast to limited precipitation: the monsoon is an annual event but it is regionally limited; cyclones infrequently occur within the range of three to seven years. Both are possible sources for groundwater recharge in the Najd. With these preconditions in mind, the present study investigates recharge to the Najd groundwaters as part of an active flow system and evaluates the mean residence time in the deep groundwaters. The tools of choice are a groundwater flow model combined with environmental isotope tracer data. The two-dimensional flow model replicates the characteristics of the aquifer system from the potential recharge area in the south (Dhofar Mountains) to the discharge area in the north (Sabkha Umm as Sammim). The south-to-north gradients and the observed artesian heads in the confined aquifer are reproduced. Simulation results indicate that changes between wet and dry periods caused transient responses in heads and head gradients lasting for several thousand years. Based on the used parameters the model calibration indicated, that a recharge rate of around 4 mm a−1 is sufficient to reproduce current groundwater levels. Since rising groundwater levels were documented after cyclone Keila in November 2011, modern recharge evidently occurs. 36-Cl concentrations and dissolved-helium concentrations indicate that the deep groundwaters in the central Najd are up to 550,000 years old. Thus, radiocarbon values indicating groundwater residence times for the central Najd up to 20,000 years and the northern Najd up to 35,000 years underestimate the groundwater residence times and seem to have been strongly affected by mixing during sampling. Decreasing 36-Cl and increasing 4-He concentrations confirm the expected trend in the direction of groundwater flow and prove to be more robust tracers for age dating of Najd groundwaters. Backward pathline tracking was used to simulate the groundwater ages. The tracking results show that a total porosity value between 15 and 20 % is consistent with the range of the observed chlorine-36 and heliumbased ages. The results and parameters obtained in the present study provide the basis for future 3D-groundwater models designed to evaluate the water resources available to the Najd’s agricultural complex. In addition, the developed 2D-model allows for studies of paleoclimate scenarios and their influence on the groundwater regime
Ein steigender Bedarf nach landwirtschaftlichen Produkten - und damit Wasser - bei gleichzeitiger Abnahme des verfügbaren Wassers in Qualität und Menge in den bisherigen Anbaugebieten, führt zu einer intensiven Nutzung der Grundwasserressourcen der ariden Najd-Region in der Provinz Dhofar, im Süden des Sultanats Oman. Als Quelle dienen die Grundwasservorräte des Umm Er Radhuma-Aquifers, einer der Hauptaquifere auf der arabischen Halbinsel. Der steigenden Nutzung stehen mit dem jährlichen Monsoon, der regional limitiert ist, und unrgelmässigen, zwischen 3 und 7 Jahren auftretenden Unwettern (Zyklonniederschlag) nur begrenzte Niederschlagsmengen als Quellen für eine mögliche Zufuhr von Wasser (Grundwasserneubildung) zum Aquifersystem gegenüber. Der Ansatz der vorliegenden Arbeit besteht darin, mit Hilfe eines Grundwassermodells und der Einbeziehung von Umweltisotopen das tiefe und zur Nutzung geförderte Grundwasser in der Najd-Region als Teil eines aktiven Fließsystemes zu untersuchen und mittlere Verweilzeiten des Grundwassers abzuleiten. Ein 2D-Grundwassermodell entlang einer Fließlinie vom Dhofar Gebirge im Süden zur Sabkha Umm as Sammim im Nordosten wurde entwickelt. Das Modell reproduziert den Süd-Nord-Gradienten als auch den aufwärts gerichteten Gradienten mit höheren Grundwasserständen in den tiefen Grundwasserleitern. Die Simulationen zeigen, dass der Wechsel von ariden und humiden Phasen (wenig bzw. viel Grundwasserneubildung) zu Veränderungen der Grundwasseroberfläche führt die mehrere tausend Jahre anhalten können. Das kalibrierte Grundwassermodel zeigt, dass mit einer Neubildungsrate von 4 mm a−1 die natürlichen Grundwasserverhältnisse im Najd abgebildet werden können. Dass eine moderne Grundwasserneubildung stattfindet, konnte mittels Loggermessungen anhand steigender Grundwasserstände im tiefen Aquifersystem nach dem Extremunwetter im November 2011 (Zyklon Keila) eindeutig nachgewiesen werden. Die Analyse der 36Cl- und 4He-Konzentrationen zeigt, dass die tiefen Grundwasser im zentralen Najdgebiet bis 550 000 Jahren alt sein können. Das bedeutet allerdings, dass die über 14C Daten berechneten Grundwasseralter mit ca. 20 000 Jahren für das zentrale Najdgebiet und bis zu 35 000 Jahren für den nördlichen Najd, die Grundwasseralter deutlich unterschätzen. Die abnehmenden 36Cl und ansteigenden 4He Konzentrationen zeigen den erwarteten Trend in Grundwasserfließrichtung und können als aussagefähige Tracer für die Bewertung der Verweilzeiten und Alter des fossilen Grundwassers der Najd-Region angesehen werden. Mit Hilfe des Partickeltrackings wurden die Grundwasseralter, basierend auf den Isotopentracern, im Grundwassermodel simuliert. Die Porosität wurde dabei für das Aquifesystem mit Werten zwischen 15 und 20 % bestimmt. Die generierten Parameter und das gewonnene Systemverständnis sind eine wichtige Basis für zukünftige 3D-Modellstudien welche die Verfügbarkeit der Wasserresourcen im Najd untersuchen werden. Weitere Anwendungen für das in dieser Studie aufgebaute 2D-Modell sind Untersuchungen zum Paläoklima und dessen Einfluss auf das Grundwassersystem
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Sheikh, M. S. "Prediction of particle residence times in cascading rotary dryers." Thesis, Teesside University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378933.

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The objectives of this research were to provide a better understanding of particle motion in cascading rotary dryers. This would lead to more soundly based design procedures. Experiments were performed, to check the validity of a proposed design method for dryers operating in the under-loaded and design loaded conditions developed by Matchett and Baker, on a pilot plant rig at Teesside Polytechnic using wheat and sand in the absence of airflow. The model considers the particles to move in two parallel phases, the airborne phase contains the material in flight and the dense phase contains the remaining material which is caught on the flights and on the bottom of the drum. There is continuous Interchange of material between the two phases. A dimensionless number, dense phase velocity number 'a', has been defined which is a measure of the axial velocity of the material in the dense phase of the drum. The 'a' values were found to be in agreement with existing data and were found to be dependent on material and not on dryer speed or slope. Photographic studies of the dryer internals suggested that the assumption of a constant 0 value (measure of flight loading) In the original model was not valid and that 4) varied with number of flights. A model was developed to predict 0 which worked extremely well for large number of flights. The existing design model was therefore modified to take account of the variation In 4). However, the paired t-test Indicated that at 5% level of significance there was no difference between the original and the modified model, even though the modified model is physically more realistic. It is, however, recommended that the models be tested on a large number of flights and also large equipment, because It is expected that with a large number of flights there will be differences between the two models and the 0 model will be superior. The 'a' and am (the am value is a modified form of the 'a' value which takes into account the variation in flight loading) values were found to be Independent of operating conditions, flight angle and also dryer size but were dependent on material. The 'a' and am values were proportional to 1/number of flights. Particle motion in the dense is by bouncing, rolling and sliding, but the high dense phase velocity numbers obtained with zero flights (ar) suggested ii that rolling and sliding are the important mechanisms of the dense phase motion and may be far more important than bouncing. A model has also been developed to study the over-loaded regime. In the over-loaded regime It was found that dryer speed, slope, material and number of flights affected the dense phase motion and a simple relationship between the over-loaded dense phase velocity number (ao) and number of flights could not be developed with the limited data. Particle motion In the over-loaded regime was found to be very complex. The ao values could be predicted to within ± 35%. Estimates have been made of the transition holdup, marking the change from under-loaded to over-loaded behaviour, but It was found that the prediction of the transition holdup is also complex and could be predicted to within ± 45%. The am values could be predicted to an accuracy of ± 10%. Thus suggesting that the ao and the transition holdup numbers are not so reliable. Future work has been recommended particularly in the over-loaded regime and also on the transition region since it was found that the particle motion in these regions was complex. It has also been suggested that the models be tested in large Industrial units with and without air flow.
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Langkau, Katharina. "Flows over time with flow dependent transit times." [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968912656.

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Stolp, Bernard Jan. "Determining mean transit times of groundwater flow systems." Thesis, The University of Utah, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3614458.

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Water is the elementary component of life on Earth, and quantifying this resource is critical to understanding ecosystem viability on planetary, continental, and local scales. In a simplified partition of the Earthfs freshwater resources, 75% is ice at the north and south poles, 25% is groundwater, and 0.01% exists in lakes and streams. Mean transit time is a robust description of groundwater volume within the discrete aquifers that together make up the 25% of Earthfs freshwater. Mean transit time can be estimated using environmental tracer concentrations in springs and gaining streams. That is because springs and streams are locations where groundwater flow paths naturally converge. Converging flowpaths create discharge that is a flow]weighted mixture of water from the contributing aquifer. The age of that flow-weighted mixture is a good measure of the mean transit time of water as it discharges from the contributing aquifer. Mean transit time can be directly used to estimate the volume of groundwater storage in the aquifer.

Although simple in principle, there are several important topics that need to be considered when collecting and dating a broad mixture of flow paths. They include 1) the necessity for a basic conceptual perception of the investigated aquifer, 2) the non-conservative aspect of most age-dating environmental tracers once exposed to the atmosphere, and 3) the importance of estimating a transit-time distribution. These specific topics are discussed in this dissertation.

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Cevallos, Fabian. "Optimization of transit transfer times : a system-wide approach." FIU Digital Commons, 2006. http://digitalcommons.fiu.edu/etd/2099.

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This dissertation presents a system-wide approach, based on genetic algorithms, for the optimization of transfer times for an entire bus transit system. Optimization of transfer times in a transit system is a complicated problem because of the large set of binary and discrete values involved. The combinatorial nature of the problem imposes a computational burden and makes it difficult to solve by classical mathematical programming methods. The genetic algorithm proposed in this research attempts to find an optimal solution for the transfer time optimization problem by searching for a combination of adjustments to the timetable for all the routes in the system. It makes use of existing scheduled timetables, ridership demand at all transfer locations, and takes into consideration the randomness of bus arrivals. Data from Broward County Transit are used to compute total transfer times. The proposed genetic algorithm-based approach proves to be capable of producing substantial time savings compared to the existing transfer times in a reasonable amount of time. The dissertation also addresses the issues related to spatial and temporal modeling, variability in bus arrival and departure times, walking time, as well as the integration of scheduling and ridership data.
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Oliveira, Anabela Pacheco de. "Eulerian-Lagrangian analysis of transport and residence times in estuaries and coasts /." Full text open access at:, 1997. http://content.ohsu.edu/u?/etd,209.

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Hodal, Michal. "Net physical transports, residence times, and new production for Rivers Inlet, British Columbia." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/30635.

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A hydrographic dataset from the 2008-2009 Rivers Inlet Ecosystem Study (RIES) field program was used (a) to provide a more complete oceanographic description of Rivers Inlet, British Columbia and (b) to develop the first quantitative estimates of estuarine circulation and new production for this system. Water column observations show a highly stratified two-layer estuarine structure, particularly in the spring and summer months when river discharge and atmospheric heat inputs were high. The net air-sea heat flux had a seasonal range of approximately 220 Wm⁻² and peaked almost a month earlier in 2008 than in 2009. The main source of river input comes from the Wannock River. As temperatures begin to rise in the spring, the river discharge can suddenly increase by an order of magnitude (from about 100 m³ s⁻¹ to almost 1000 m³ s⁻¹) in less than two weeks. Residence times (ie. first-order estimates of estuarine circulation) were estimated for every cruise using salinity and temperature budgets in a two-layer box model parameterization of the flow structure. The results show that upper box residence times vary seasonally with river discharge; dropping from about 14 days in the winter to as low as 4 days in the spring at the freshet onset. An earlier flushing event in 2009 caused residence times to drop earlier and could have caused higher advection losses for phytoplankton in the early spring. Overall, residence times averaged to about 7 days for the upper layer and about 165 days for the lower layer during periods of high river discharge, and about twice that during periods of low river discharge. Deep water in the lower layer below the sill was renewed almost once a year in summer and was affected only by vertical diffusion during the rest of the year. Finally, a spring/summer new production estimate of 0.6-1.7 gCm⁻²d⁻¹ (which implies about 110-300 gCm⁻²y⁻¹ assuming no production during the other months) was obtained by combining transport estimates with observations of nutrients to infer a surface nitrate sink. This range compares well with independent estimates made in nearby regions.
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Books on the topic "Transit and Residence Times"

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Gallant, Mavis. In transit. London: Faber and Faber, 1990.

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Gallant, Mavis. In transit. Markham, Ont: Viking, 1988.

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Gallant, Mavis. In transit. Toronto: Penguin Books Canada, 1997.

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Gallant, Mavis. In transit. Markham, Ont: Penguin Books, 1989.

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Transit talks: Living through difficult times. New Delhi, India: AlterNotes Press, 2013.

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Gallant, Mavis. In transit: Twenty stories. New York, N.Y., U.S.A: Penguin Books, 1990.

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Gallant, Mavis. In transit: Twenty stories. New York: Random House, 1988.

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Kraft, Robert Brian. Estimation of link travel times from transit route data. Ottawa: National Library of Canada = Bibliothèque nationale du Canada, 1995.

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Vitvar, Tomás̆. Water residence times and runoff generation in a small prealpine catchment. Zürich: Geographisches Institut ETH, 1998.

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New York (State). Metropolitan Transportation Authority. Office of the Inspector General. Review of TA residency policy and practices. [New York, N.Y: The Office, 1994.

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Book chapters on the topic "Transit and Residence Times"

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Reed, G. "Measurement of residence times and residence-time distributions." In Radioisotope Techniques for Problem-Solving in Industrial Process Plants, 112–37. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-009-4073-4_9.

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Grandell, Jan. "Residence Times and Mean Concentrations." In Stochastic Models of Air Pollutant Concentration, 17–22. New York, NY: Springer New York, 1985. http://dx.doi.org/10.1007/978-1-4612-1094-8_4.

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Watt, Ted. "The naturalist-in-residence." In Education in Times of Environmental Crises, 55–64. First published 2016. | New York : Routledge, 2016.: Routledge, 2016. http://dx.doi.org/10.4324/9781315671970-8.

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Klingensmith, William C. "Regional Transit Times: Convolution Analysis." In The Mathematics and Biology of the Biodistribution of Radiopharmaceuticals - A Clinical Perspective, 75–88. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-26704-3_7.

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Dassargues, Alain. "Contaminant transport, residence times, prevention, and remediation." In Hydrogeology, 203–90. First Edition. | Boca Raton, Florida : Taylor & Francis, A CRC title, part of the Taylor & Francis imprint, a member of the Taylor & Francis Group, the academic division of T&F Informa plc, [2019]: CRC Press, 2018. http://dx.doi.org/10.1201/9780429470660-8.

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Ando, B., S. Baglio, S. La Malfa, C. Trigona, and A. R. Bulsara. "Perming Effect in Residence Times Difference Fluxgate Magnetometers." In Lecture Notes in Electrical Engineering, 257–60. Dordrecht: Springer Netherlands, 2009. http://dx.doi.org/10.1007/978-90-481-3606-3_50.

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Keudel, Walter. "Computer-Aided Line Network Design (DIANA) and Minimization of Transfer Times in Networks (FABIAN)." In Computer-Aided Transit Scheduling, 315–26. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-85966-3_27.

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Köhler, Ekkehard, Katharina Langkau, and Martin Skutella. "Time-Expanded Graphs for Flow-Dependent Transit Times." In Algorithms — ESA 2002, 599–611. Berlin, Heidelberg: Springer Berlin Heidelberg, 2002. http://dx.doi.org/10.1007/3-540-45749-6_53.

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Wagner, W. W. "Pulmonary Capillary Transit Times in Fully Recruited Networks." In New Aspects on Respiratory Failure, 115–21. Berlin, Heidelberg: Springer Berlin Heidelberg, 1992. http://dx.doi.org/10.1007/978-3-642-74943-8_12.

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Mangini, A., U. Christian, M. Barth, W. Schmitz, and H. H. Stabel. "Pathways and Residence Times of Radiotracers in Lake Constance." In Large Lakes, 245–64. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-84077-7_13.

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Conference papers on the topic "Transit and Residence Times"

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Dubey, Satish Kumar, Neelesh Agarwal, and P. Srinivasan. "Three Dimensional Transient Heat Transfer Model for Steel Billet Heating in Reheat Furnace." In ASME 2012 Heat Transfer Summer Conference collocated with the ASME 2012 Fluids Engineering Division Summer Meeting and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ht2012-58151.

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In steel rolling mills reheat furnaces are used to heat the billets prior to rolling processes. Reheating is one of the most energy intensive processes in the steel industries. Inadequate temperature measuring techniques and extremely complex analytical solution for temperature filed calculations demands suitable numerical model. In the present work a three dimensional transient heat transfer model is developed for billet heating in reheat furnaces. Conduction heat transfer within the billets is modeled using Finite Difference Method (FDM). Fully implicit spatial discretization approximation was used for three dimensional heat diffusion equation of billet. The three dimensional model takes into account the temperature dependent thermo physical properties, reaction heat effect and growing oxide layer. Algorithm is implemented in MATLAB® to solve three dimensional discretization equations. Model is capable of predicting the temperature field for billet and oxide scale thickness for any residence time. The predicted results are in reasonable concurrence with available data. The main objective of this work is to predict billet temperature field and oxide scale thickness for the various residence times, which may be vital for development of energy efficient optimization strategy for reheating process.
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Heberlein, J., N. P. Rao, A. Neuman, J. Blum, N. Tymiak, P. H. McMurry, and S. L. Girshick. "Thermal Spraying of Nanostructured Coatings by Hypersonic Plasma Particle Deposition." In ITSC 1997, edited by C. C. Berndt. ASM International, 1997. http://dx.doi.org/10.31399/asm.cp.itsc1997p0329.

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Abstract A novel plasma spray process for producing nanostructured coatings, hypersonic plasma particle deposition (HPPD), has been experimentally investigated. In HPPD, vapor phase precursors are injected into a plasma stream generated by a DC arc. The plasma is quenched by supersonic expansion through a nozzle into a vacuum (~ 2 torr) deposition chamber. Ultrafine particles nucleated in the nozzle are accelerated in the hypersonic free jet downstream of the nozzle and inertially deposited onto a substrate. The short transit times between the nozzle and the substrate (< 50 μs) prevent inflight agglomeration, while the high particle deposition velocities result in the formation of a consolidated coating. We have investigated the production of silicon and silicon carbide coatings using SiCl4 and CH4 precursors. Silicon deposits analyzed by transmission electron microscopy were found to have nanostructured regions with grain sizes varying from 5-20 nm. Corresponding particle size distributions measured before deposition using an extractive aerosol probe peaked around 15 nm, suggesting negligible grain growth occurred in the samples studied. Silicon carbide particle size distributions measured at various deposition chamber pressures verify that the low residence time characteristic of the HPPD process minimizes in-flight agglomeration.
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Cevasco, Riccardo, J. Parente, A. Traverso, and A. F. Massardo. "Off-Design and Transient Analysis of Saturators for Humid Air Turbine Cycles." In ASME Turbo Expo 2004: Power for Land, Sea, and Air. ASMEDC, 2004. http://dx.doi.org/10.1115/gt2004-53315.

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Considering the growing interest in the possible applications of HAT technology, characterized by the introduction of the humidification tower (saturator), this work proposes a novel model to analyze the saturator under both off-design and transient conditions. On the basis of this model, the TRANSAT code was developed and tested with experimental results from the pilot plant installed at the University of Lund in Sweden. Both off-design and transient analysis were performed. Saturator off-design analysis showed that the water inlet temperature and air/water mass flow ratio are the main parameters that control saturator operating behavior, especially saturator water and gas outlet conditions. On the assumptions made for the transient analysis, relevant results were achieved. The saturator showed a fast response to all the input variations. In particular, its characteristic times were essentially determined by the fluid residence time in the humidification tower. With regard to plant control, the main conclusion is that the integration of the saturator and the power plant is not expected to be critical for the control of the whole system.
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Kay, E. D., H. Power, and S. Hibberd. "Film Flow Characteristics of Droplet Cooling in a Simplified Bearing Chamber." In ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-94362.

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Droplet-cooled oil films develop on the internal surfaces of an aero-engine bearing chamber and are a primary mechanism in removing heat from the chamber as oil is continuously collected and externally cooled and recycled. Predicting the internal oil temperature and oil temperature history is an important thermal problem which becomes more apparent with potential increases in operating temperatures of gas turbines. Studying interacting oil flow and thermal processes within a simplified bearing chamber geometry provides useful information on the trends and characteristics which can arise under different applied flow conditions (e.g. mass flow rate of oil through the system) and insight to the effect chamber design parameters may have on oil degradation and cooling of chamber walls. Thin oil films develop on the walls of a bearing chamber as oil is injected or shed from bearings and impinges on the walls under a strong airflow set in motion by rotating components. Typically the film is also subject to a heat flux from the hot chamber walls and the droplets provide an important cooling effect through “heat-to-oil” mechanisms. We present a mathematical model for the depth-averaged flow and associated heat transfer by thin oil films on the walls of a simplified aero-engine bearing chamber. Cases corresponding to generic flow conditions relevant to an aero-engine bearing chamber are presented. Characteristics of the film and the efficacy of the flow regime to transfer heat from the chamber is explored through calculating residence times and time histories of oil particles as they make a transit of the internal system.
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Huang, Xiyong, Michael D. Protheroe, Ahmed M. Al-Jumaily, and Sharad P. Paul. "The Significance of Hair Thermal Diffusivity on Melanoma Incidence." In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-71693.

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There is an increased risk of melanoma in adulthood when a child (pre-puberty) has been exposed to high levels of ultraviolet radiation (UVR). It has also been hypothesized that the childhood body air (vellus hair) plays a role in the increased incidence of melanoma later in life. This is attributed to the fact that the vellus hair has properties and physiology which encourage the transmission of harmful energy into the follicle of the hair and ultimately cause damage to the stem cells in residence there. Later in life these damaged stem cells become involved in the generation of melanomas in the epidermis. It has been debated whether the UVR or the heat generated by it is the main contributor to melanoma occurrence. This research is the first step in investigating this phenomenon by focusing on the contribution of changes in thermal characteristics on the incidence of melanoma. To test the hypothesis that child hair can transmit energy more easily than adult hair the transient electro-thermal technique is used to determine the thermal diffusivity of the hair. This involved subjecting platinum coated hair samples to a current pulse and measuring the subsequent voltage response in the sample. Results show that the child hair has a thermal diffusivity around two times higher than adult hair, thus supporting the hypothesis. Further research will be needed, in particular, quantifying the optical transmission characteristics of child hair compared to adult hair.
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Struk, P. M., D. L. Dietrich, F. J. Miller, and J. S. T’ien. "Transient Numerical Modeling of Catalytic Channels." In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-41680.

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This paper presents a transient model of catalytic combustion suitable for isolated channels and monolith reactors. The model is a “lumped” two-phase (gas and solid) model where the gas phase is quasi-steady relative to the transient solid. Axial diffusion is neglected in the gas phase; lateral diffusion, however, is accounted for using transfer coefficients. The solid phase includes axial heat conduction and external heat loss due to convection and radiation. The combustion process utilizes detailed gas and surface reaction models. The gas-phase model becomes a system of stiff ordinary differential equations while the solid phase reduces, after discretization, into a system of stiff ordinary differential-algebraic equations. The time evolution of the system came from alternating integrations of the quasi-steady gas and transient solid. This work outlines the numerical model and presents some sensitivity studies on important parameters including internal transfer coefficients, catalytic surface site density, and external heat-loss (if applicable). The model is compared to two experiments using CO fuel: (1) steady-state conversion through an isothermal platinum (Pt) tube and (2) transient propagation of a catalytic reaction inside a small Pt tube. The model requires internal mass-transfer resistance to match the experiments at lower residence times. Under mass-transport limited conditions, the model reasonably predicted exit conversion using global mass-transfer coefficients. Near light-off, the model results did not match the experiment precisely even after adjustment of mass-transfer coefficients. Agreement improved for the first case after adjusting the surface kinetics such that the net rate of CO adsorption increased compared to O2. The CO / O2 surface mechanism came from a sub-set of reactions in a popular CH4 / O2 mechanism. For the second case, predictions improved for lean conditions with increased external heat loss or adjustment of the kinetics as in the first case. Finally, the results show that different initial surface-species distribution leads to different steady-states under certain conditions. These results demonstrate the utility of a lumped two-phase model of a transient catalytic combustor with detailed chemistry.
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Andò, B., A. Ascia, S. Baglio, A. R. Bulsara, V. In, N. Pitrone, C. Trigona, Adrian Ionescu, James Anthony, and Charles Bland. "Residence Times Difference Fluxgate Magnetometer for Magnetic Biosensing." In BIOMAGNETISM AND MAGNETIC BIOSYSTEMS BASED ON MOLECULAR RECOGNITION PROCESSES. AIP, 2008. http://dx.doi.org/10.1063/1.2956810.

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Hohloch, Martina, Andreas Huber, and Manfred Aigner. "Experimental Investigation of a SOFC/MGT Hybrid Power Plant Test Rig: Impact and Characterization of a Fuel Cell Emulator." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-57747.

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The main topic of the paper is the experimental investigation of a solid oxide fuel cell (SOFC) / micro gas turbine (MGT) hybrid power plant test rig. This comprises the proof of concept, the characterization of the operational range and the influence of the coupling on the MGT. The operational concept of the hybrid power plant is designed to reach a maximum flexibility in electrical power output. Therefore the power plant is operated at different MGT shaft speeds and electrical power outputs of the SOFC, thus leading to different SOFC temperatures. Instead of a real fuel cell an emulator was developed and built to emulate the fluid dynamic and thermodynamic behavior of a real SOFC. The test rig is based on a Turbec T100PH micro gas turbine. A specially designed interface connects the facility to the tubing system and the SOFC emulator. For the present investigation the SOFC emulator has been equipped with a gas preheater. It emulates the varying heat output of the fuel cell. The gas preheater is composed of a natural gas combustor based on the FLOX® technology, with a swirl-stabilized pilot stage and allows a wide range of emulating different SOFC outlet temperatures. In addition installations have been integrated into a pressure vessel, representing the SOFC cathode volume, to analyze the increase in residence time and pressure loss. Initially three different configurations of the test rig, no SOFC emulator – tube only, SOFC emulator with pressure vessels and fully equipped SOFC emulator (pressure vessels, installations and gas preheater) are compared regarding the influence of the different volumes, residence times and pressure losses. The operating range of the test rig equipped with gas preheater in cold (no fuel) as well as in hot conditions is investigated. As the velocity at the entrance of the gas turbine combustor increases with increased fuel cell outlet temperature the surge margin is strongly influenced. The operating range was determined for different shaft speeds and preheating (SOFC outlet) temperatures. Finally the transient behavior of the gas preheater and its impact on the MGT is analyzed. The results provide the required basis to implement a cyber physical system, in which the SOFC emulator is controlled by a SOFC model, as well as the basis for the real coupling of MGT and SOFC.
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Hu, Xiaoqing. "Development of Residence Buildings of Shanghai in Contemporary Times." In 2015 International Forum on Energy, Environment Science and Materials. Paris, France: Atlantis Press, 2015. http://dx.doi.org/10.2991/ifeesm-15.2015.248.

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Paxson, Vern. "On calibrating measurements of packet transit times." In the 1998 ACM SIGMETRICS joint international conference. New York, New York, USA: ACM Press, 1998. http://dx.doi.org/10.1145/277851.277865.

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Reports on the topic "Transit and Residence Times"

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Aflaki, R., and L. Handy. Chemical composition profiles during alkaline flooding at different temperatures and extended residence times. Office of Scientific and Technical Information (OSTI), December 1992. http://dx.doi.org/10.2172/6757634.

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Aflaki, R., and L. L. Handy. Chemical composition profiles during alkaline flooding at different temperatures and extended residence times. Office of Scientific and Technical Information (OSTI), December 1992. http://dx.doi.org/10.2172/10131802.

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Arhin, Stephen. Predicting Acceptable Wait Times for Patrons at Transit Bus Stops by Time of Day. Mineta Transportation Institute, October 2019. http://dx.doi.org/10.31979/mti.2019.1801.

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Arhin, Stephen, Babin Manandhar, Hamdiat Baba Adam, and Adam Gatiba. Predicting Bus Travel Times in Washington, DC Using Artificial Neural Networks (ANNs). Mineta Transportation Institute, April 2021. http://dx.doi.org/10.31979/mti.2021.1943.

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Washington, DC is ranked second among cities in terms of highest public transit commuters in the United States, with approximately 9% of the working population using the Washington Metropolitan Area Transit Authority (WMATA) Metrobuses to commute. Deducing accurate travel times of these metrobuses is an important task for transit authorities to provide reliable service to its patrons. This study, using Artificial Neural Networks (ANN), developed prediction models for transit buses to assist decision-makers to improve service quality and patronage. For this study, we used six months of Automatic Vehicle Location (AVL) and Automatic Passenger Counting (APC) data for six Washington Metropolitan Area Transit Authority (WMATA) bus routes operating in Washington, DC. We developed regression models and Artificial Neural Network (ANN) models for predicting travel times of buses for different peak periods (AM, Mid-Day and PM). Our analysis included variables such as number of served bus stops, length of route between bus stops, average number of passengers in the bus, average dwell time of buses, and number of intersections between bus stops. We obtained ANN models for travel times by using approximation technique incorporating two separate algorithms: Quasi-Newton and Levenberg-Marquardt. The training strategy for neural network models involved feed forward and errorback processes that minimized the generated errors. We also evaluated the models with a Comparison of the Normalized Squared Errors (NSE). From the results, we observed that the travel times of buses and the dwell times at bus stops generally increased over time of the day. We gathered travel time equations for buses for the AM, Mid-Day and PM Peaks. The lowest NSE for the AM, Mid-Day and PM Peak periods corresponded to training processes using Quasi-Newton algorithm, which had 3, 2 and 5 perceptron layers, respectively. These prediction models could be adapted by transit agencies to provide the patrons with accurate travel time information at bus stops or online.
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Arhin, Stephen, Babin Manandhar, Kevin Obike, and Melissa Anderson. Impact of Dedicated Bus Lanes on Intersection Operations and Travel Time Model Development. Mineta Transportation Institute, June 2022. http://dx.doi.org/10.31979/mti.2022.2040.

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Over the years, public transit agencies have been trying to improve their operations by continuously evaluating best practices to better serve patrons. Washington Metropolitan Area Transit Authority (WMATA) oversees the transit bus operations in the Washington Metropolitan Area (District of Columbia, some parts of Maryland and Virginia). One practice attempted by WMATA to improve bus travel time and transit reliability has been the implementation of designated bus lanes (DBLs). The District Department of Transportation (DDOT) implemented a bus priority program on selected corridors in the District of Columbia leading to the installation of red-painted DBLs on corridors of H Street, NW, and I Street, NW. This study evaluates the impacts on the performance of transit buses along with the general traffic performance at intersections on corridors with DBLs installed in Washington, DC by using a “before” and “after” approach. The team utilized non-intrusive video data to perform vehicular turning movement counts to assess the traffic flow and delays (measures of effectiveness) with a traffic simulation software. Furthermore, the team analyzed the Automatic Vehicle Locator (AVL) data provided by WMATA for buses operating on the study segments to evaluate bus travel time. The statistical analysis showed that the vehicles traveling on H Street and I Street (NW) experienced significantly lower delays during both AM (7:00–9:30 AM) and PM (4:00–6:30 PM) peak hours after the installation of bus lanes. The approximation error metrics (normalized squared errors) for the testing dataset was 0.97, indicating that the model was predicting bus travel times based on unknown data with great accuracy. WMATA can apply this research to other segments with busy bus schedules and multiple routes to evaluate the need for DBLs. Neural network models can also be used to approximate bus travel times on segments by simulating scenarios with DBLs to obtain accurate bus travel times. Such implementation could not only improve WMATA’s bus service and reliability but also alleviate general traffic delays.
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Schutt, Timothy, and Manoj Shukla. Predicting the impact of aqueous ions on fate and transport of munition compounds. Engineer Research and Development Center (U.S.), August 2021. http://dx.doi.org/10.21079/11681/41481.

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A model framework for natural water has been developed using computational chemistry techniques to elucidate the interactions between solvated munition compounds and eight common ions in naturally occurring water sources. The interaction energies, residence times, coordination statistics, and surface preferences of nine munition related compounds with each ion were evaluated. The propensity of these interactions to increase degradation of the munition compound was predicted using accelerated replica QM/MM simulations. The degradation prediction data qualitatively align with previous quantum mechanical studies. The results suggest that primary ions of interest for fate and transport modeling of munition compounds in natural waters may follow the relative importance of SO₄²⁻, Cl⁻ ≫ HCO₃⁻, Na⁺, Mg²⁺ > Ca²⁺, K⁺, and NH₄⁺.
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Perry, Russell W., and John R. Skalski. Design and Analysis of Salmonid Tagging Studies in the Columbia Basin : Evaluating Wetland Restoration Projects in the Columbia River Estuary using Hydroacoustic Telemetry Arrays to Estimate Movement, Survival, and Residence Times of Juvenile Salmonids, Volume XXII (22). Office of Scientific and Technical Information (OSTI), August 2008. http://dx.doi.org/10.2172/941576.

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Scholl, Lynn, Daniel Oviedo, and Orlando Sabogal-Cardona. Disrupting Personal (In)Security? The Role of Ride-Hailing Service Features, Commute Strategies, and Gender in Mexico City. Inter-American Development Bank, December 2021. http://dx.doi.org/10.18235/0003812.

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This paper sheds light on the personal security dimension of ride-hailing from a gender perspective. We explore how features of Transportation Network Companies (TNCs) services affect riders perceptions of security when commuting in ride-hailing services, and how general perceptions of fear of crime shape the way people value such features. Moreover, we analyze the strategies women and men are using to enhance their own security in ride-hailing and factors influencing these strategies. We conducted a survey of users of the TNC DiDi in Mexico City. The statistical methods used are structural equation models SEM and ordered logit models OLOGIT. Results show that women are more likely to value the information made available by ride-hailing applications (e.g., knowing your location or knowing driver information) and the presence of a panic button. The value given to information also increases if a person feels insecure in the streets, in a public transit station or in public transit. People who perceive higher insecurity in the streets have increased positive perceptions of the possibility of travelling without transfers. We also find that women are 64.4% less likely to share ride-hailing trips (pooling) and 2.14 times more likely to share details of their trips through their cellphones.
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Lewis, Sherman, Emilio Grande, and Ralph Robinson. The Mismeasurement of Mobility for Walkable Neighborhoods. Mineta Transportation Institute, November 2020. http://dx.doi.org/10.31979/mti.2020.2060.

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The major US household travel surveys do not ask the right questions to understand mobility in Walkable Neighborhoods. Yet few subjects can be more important for sustainability and real economic growth based on all things of value, including sustainability, affordability, and quality of life. Walkable Neighborhoods are a system of land use, transportation, and transportation pricing. They are areas with attractive walking distances of residential and local business land uses of sufficient density to support enough business and transit, with mobility comparable to suburbia and without owning an auto. Mobility is defined as the travel time typically spent to reach destinations outside the home, not trips among other destinations that are not related to the home base. A home round trip returns home the same day, a way of defining routine trips based on the home location. Trip times and purposes, taken together, constitute travel time budgets and add up to total travel time in the course of a day. Furthermore, for Walkable Neighborhoods, the analysis focuses on the trips most important for daily mobility. Mismeasurement consists of including trips that are not real trips to destinations outside the home, totaling 48 percent of trips. It includes purposes that are not short trips functional for walk times and mixing of different trips into single purposes, resulting in even less useful data. The surveys do not separate home round trips from other major trip types such as work round trips and overnight trips. The major household surveys collect vast amounts of information without insight into the data needed for neighborhood sustainability. The methodology of statistics gets in the way of using statistics for the deeper insights we need. Household travel surveys need to be reframed to provide the information needed to understand and improve Walkable Neighborhoods. This research makes progress on the issue, but mismeasurement prevents a better understanding of the issue.
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Meidan, Rina, and Joy Pate. Roles of Endothelin 1 and Tumor Necrosis Factor-A in Determining Responsiveness of the Bovine Corpus Luteum to Prostaglandin F2a. United States Department of Agriculture, January 2004. http://dx.doi.org/10.32747/2004.7695854.bard.

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The corpus luteum (CL) is a transient endocrine gland that has a vital role in the regulation of the estrous cycle, fertility and the maintenance of pregnancy. In the absence of appropriate support, such as occurs during maternal recognition of pregnancy, the CL will regress. Prostaglandin F2a (PGF) was first suggested as the physiological luteolysin in ruminants several decades ago. Yet, the cellular mechanisms by which PGF causes luteal regression remain poorly defined. In recent years it became evident that the process of luteal regression requires a close cooperation between steroidogenic, endothelial and immune cells, all resident cells of this gland. Changes in the population of these cells within the CL closely consort with the functional changes occurring during various stages of CL life span. The proposal aimed to gain a better understanding of the intra-ovarian regulation of luteolysis and focuses especially on the possible reasons causing the early CL (before day 5) to be refractory to the luteolytic actions of PGF. The specific aims of this proposal were to: determine if the refractoriness of the early CL to PGF is due to its inability to synthesize or respond to endothelin–1 (ET-1), determine the cellular localization of ET, PGF and tumor necrosis factor a (TNF a) receptors in early and mid luteal phases, determine the functional relationships among ET-1 and cytokines, and characterize the effects of PGF and ET-1 on prostaglandin production by luteal cell types. We found that in contrast to the mature CL, administration of PGF2a before day 5 of the bovine cycle failed to elevate ET-1, ETA receptors or to induce luteolysis. In fact, PGF₂ₐ prevented the upregulation of the ET-1 gene by ET-1 or TNFa in cultured luteal cells from day 4 CL. In addition, we reported that ECE-1 expression was elevated during the transitionof the CL from early to mid luteal phase and was accompanied by a significant rise in ET-1 peptide. This coincides with the time point at which the CL gains its responsiveness to PGF2a, suggesting that ability to synthesize ET-1 may be a prerequisite for luteolysis. We have shown that while ET-1 mRNA was exclusively localized to endothelial cells both in young and mature CL, ECE-1 was present in the endothelial cells and steroidogenic cells alike. We also found that the gene for TNF receptor I is only moderately affected by the cytokines tested, but that the gene for TNF receptor II is upregulated by ET-1 and PGF₂ₐ. However, these cytokines both increase expression of MCP-1, although TNFa is even more effective in this regard. In addition, we found that proteins involved in the transport and metabolism of PGF (PGT, PGDH, COX-2) change as the estrous cycle progresses, and could contribute to the refractoriness of young CL. The data obtained in this work illustrate ET-1 synthesis throughout the bovine cycle and provide a better understanding of the mechanisms regulating luteal regression and unravel reasons causing the CL to be refractory to PGF2a.
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