Journal articles on the topic 'Transit and Residence Times'
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1
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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Popkin, Cathy. "Chekhov as Ethnographer: Epistemological Crisis on Sakhalin Island." Slavic Review 51, no. 1 (1992): 36–51. http://dx.doi.org/10.2307/2500260.
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In 1890, Anton Chekhov traveled all the way across Siberia, spending five months in transit and three more in residence, to visit the penal colony on Sakhalin Island. The trip was enormously eccentric—it was dangerous, arduous, ill-advised for someone of Chekhov's delicate constitution and uncharacteristically adventuresome for someone so sedentary. Its eccentricity is heightened by the battery of cavalier explanations advanced by the writer, who justified his trip first as an attempt to erase a portion of his life, then as an effort to produce the only halfyear worth remembering, now as a mere change of pace, then as a pressing need to flee a romantic entanglement, at times as a scientific enterprise, at other times as a symptom of "Sakhalin mania."
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Kong, Ah-Ng, and William J. Jusko. "Definitions and Applications of Mean Transit and Residence Times in Reference to the Two-Compartment Mammillary Plasma Clearance Model." Journal of Pharmaceutical Sciences 77, no. 2 (February 1988): 157–65. http://dx.doi.org/10.1002/jps.2600770213.
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Fine, D. R., D. Glasser, D. Hildebrandt, J. Esser, R. E. Lurie, and N. Chetty. "An anatomic and physiological model of hepatic vascular system." Journal of Applied Physiology 79, no. 3 (September 1, 1995): 1008–26. http://dx.doi.org/10.1152/jappl.1995.79.3.1008.
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Hepatic function can be characterized by the activity/time curves obtained by imaging the aorta, spleen, and liver. Nonparametric deconvolution of the activity/time curves is clinically useful as a diagnostic tool in determining organ transit times and flow fractions. The use of this technique is limited, however, because of numerical and noise problems in performing deconvolution. Furthermore, the interaction of part of the tracer with the spleen and gastrointestinal tract, before it enters the liver, further obscures physiological information in the deconvolved liver curve. In this paper, a mathematical relationship is derived relating the liver activity/time curve to portal and hepatic behavior. The mathematical relationship is derived by using transit time spectrum/residence time density theory. Based on this theory, it is shown that the deconvolution of liver activity/time curves gives rise to a complex combination of splenic, gastrointestinal, and liver dependencies. An anatomically and physiologically plausible parametric model of the hepatic vascular system has been developed. This model is used in conjunction with experimental data to estimate portal, splenic, and hepatic physiological blood flow parameters for eight normal volunteers. These calculated parameters, which include the portal flow fraction, the splenic blood flow fraction, and blood transit times are shown to adequately correspond to published values. In particular, the model of the hepatic vascular system identifies the portal flow fraction as 0.752 +/- 0.022, the splenic blood flow fraction as 0.180 +/- 0.023, and the liver mean transit time as 13.4 +/- 1.71 s. The model has also been applied to two portal hypertensive patients. The variation in some of the model parameters is beyond normal limits and is consistent with the observed pathology.
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Harter, Till S., Alexandra G. May, William J. Federspiel, Claudiu T. Supuran, and Colin J. Brauner. "Time course of red blood cell intracellular pH recovery following short-circuiting in relation to venous transit times in rainbow trout, Oncorhynchus mykiss." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 315, no. 2 (August 1, 2018): R397—R407. http://dx.doi.org/10.1152/ajpregu.00062.2018.
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Accumulating evidence is highlighting the importance of a system of enhanced hemoglobin-oxygen (Hb-O2) unloading for cardiovascular O2 transport in teleosts. Adrenergically stimulated sodium-proton exchangers (β-NHE) create H+ gradients across the red blood cell (RBC) membrane that are short-circuited in the presence of plasma-accessible carbonic anhydrase (paCA) at the tissues; the result is a large arterial-venous pH shift that greatly enhances O2 unloading from pH-sensitive Hb. However, RBC intracellular pH (pHi) must recover during venous transit (31–90 s) to enable O2 loading at the gills. The halftimes ( t1/2) and magnitudes of RBC β-adrenergic stimulation, short-circuiting with paCA and recovery of RBC pHi, were assessed in vitro, on rainbow trout whole blood, and using changes in closed-system partial pressure of O2 as a sensitive indicator for changes in RBC pHi. In addition, the recovery rate of RBC pHi was assessed in a continuous-flow apparatus that more closely mimics RBC transit through the circulation. Results indicate that: 1) the t1/2 of β-NHE short-circuiting is likely within the residence time of blood in the capillaries, 2) the t1/2 of RBC pHi recovery is 17 s and within the time of RBC venous transit, and 3) after short-circuiting, RBCs reestablish the initial H+ gradient across the membrane and can potentially undergo repeated cycles of short-circuiting and recovery. Thus, teleosts have evolved a system that greatly enhances O2 unloading from pH-sensitive Hb at the tissues, while protecting O2 loading at the gills; the resulting increase in O2 transport per unit of blood flow may enable the tremendous athletic ability of salmonids.
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Livingstone, Steve. "METHODS FOR EVALUATING THE ACCURACY OF FISSION PRODUCT CONCENTRATION MEASUREMENTS IN NUCLEAR REACTOR PRIMARY HEAT TRANSPORT SYSTEMS." AECL Nuclear Review 3, no. 01 (June 1, 2014): 29–36. http://dx.doi.org/10.12943/anr.2014.00029.
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Fission product concentration in reactor primary heat transport systems is a common diagnostic indicator for assessing reactor core condition and determining the presence, size, power, location, residence time, burnup, etc., of defected fuel. Typically, diagnostic assessment assumes a priori that measured data (activity concentration measurements and reactor parameters) are accurate; however, this is not always a valid assumption. A set of novel methods has been developed for detecting minor discrepancies in fission product concentration measurements and reactor parameters (such as issues with transit times, purification, and spectral analysis). A variety of techniques are discussed and applied to a variety of reactor types (mainly commercial power plant designs); these techniques and concepts can be modified and applied for research and (or) commercial applications.
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Najib, N., A. R. Mansour, and G. L. Amidon. "Gastrointestinal transit time: An in vitro study of parameters controlling the mean relative residence times of particles in a laminar fluid flowin." Chemical Engineering Journal 37, no. 3 (March 1988): B39—B46. http://dx.doi.org/10.1016/0300-9467(88)80017-0.
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Farlin, J., and P. Maloszewski. "On the use of spring baseflow recession for a more accurate parameterization of aquifer transit time distribution functions." Hydrology and Earth System Sciences Discussions 9, no. 12 (December 20, 2012): 14109–28. http://dx.doi.org/10.5194/hessd-9-14109-2012.
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Abstract. Baseflow recession analysis and groundwater dating have up to now developed as two distinct branches of hydrogeology and were used to solve entirely different problems. We show that by combining two classical models, namely Boussinesq's Equation describing spring baseflow recession and the exponential piston-flow model used in groundwater dating studies, the parameters describing the transit time distribution of an aquifer can be in some cases estimated to a far more accurate degree than with the latter alone. Under the assumption that the aquifer basis is sub-horizontal, the mean residence time of water in the saturated zone can be estimated from spring baseflow recession. This provides an independent estimate of groundwater residence time that can refine those obtained from tritium measurements. This approach is demonstrated in a case study predicting atrazine concentration trend in a series of springs draining the fractured-rock aquifer known as the Luxembourg Sandstone. A transport model calibrated on tritium measurements alone predicted different times to trend reversal following the nationwide ban on atrazine in 2005 with different rates of decrease. For some of the springs, the best agreement between observed and predicted time of trend reversal was reached for the model calibrated using both tritium measurements and the recession of spring discharge during the dry season. The agreement between predicted and observed values was however poorer for the springs displaying the most gentle recessions, possibly indicating the stronger influence of continuous groundwater recharge during the dry period.
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McLafferty, Sara, and Valerie Preston. "Geographies of Frontline Workers: Gender, Race, and Commuting in New York City." Sustainability 15, no. 4 (February 13, 2023): 3429. http://dx.doi.org/10.3390/su15043429.
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The COVID-19 pandemic amplified social, economic, and environmental inequalities in American cities, including inequities in commuting and access to employment. Frontline workers—those who had to work on site during the pandemic—experienced these inequalities in every aspect of their daily lives. We examine the labor force characteristics and commuting of frontline workers in New York City with a focus on gender and race/ethnic disparities in wages and commuting modes and times. Using Census PUMS microdata for a sample of New York City residents in the 2015–2019 period, we identify frontline workers from detailed industry and occupation codes and compare characteristics of frontline workers with those of essential workers who could work remotely. The data highlight wide disparities between frontline and remote workers. Minority men and women are concentrated in the frontline workforce. The residential geographies of frontline and remote workers differ greatly, with the former concentrated in low- and moderate- income areas distant from work sites and with long commute times. Compared to men, women frontline workers rely heavily on public transit to commute and transit dependence is highest among Black and Latina women. Low-wage employment, long commute times, and transit dependence intersected to increase minority women’s economic and social vulnerability during the pandemic.
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Cai, Zhaoyang, and Jianwei Yan. "Analysis of residents' travel characteristics along Beijing rail transit line based on binary choice model." Archives of Transport 47, no. 3 (September 30, 2018): 19–27. http://dx.doi.org/10.5604/01.3001.0012.6504.
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From ancient to modern times, in the historical process of urban development, urban transportation has been developing along with the development of the city's political, economic and cultural industries, and the relationship between each other has always been a topic constantly discussed by planning scholars. The development of urban transportation promotes the urban population gathering and industrial development, and promotes the development of urban geographical space. At the same time, it also brings endless convenience to urban residents, so that they can complete the displacement from the beginning to the destination with relatively low cost. However, with the rapid development of urban scale and the rapid growth of urban population, the problems of traffic congestion and land resource shortage in big cities of China seriously restrict the improvement of the quality of life of residents and the further development of the city. In this context, compact city is the inevitable choice for future urban development, while the transportation system supporting compact city form can only be public transportation. As a high-volume, efficient and rapid public transport mode, rail transit can not only solve the traffic congestion problem in high-density areas of cities, but also optimize the development and utilization of urban land and adjust the urban spatial layout, which is of great significance for the sustainable development of cities. The network of rail transit in Beijing becomes the backbone of public passenger transport system, and play an irreplaceable role in guiding the urban space layout adjustment, population migration and the transformation of traffic structure. The study of travel characteristics of the residents who live along the rail transit, in-depth analysis the relationship of the rail transit, the population migration and commuter travel, it is of great significance providing decision support for urban planning. Based on binary choice model, establishing the residents' travel choice model, rail transit impact model of different crowds. Study the relationship between rail transit and residents' travel characteristics, predict the rail transit to guide the trend of population migration.
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Huang, Jie, David Levinson, Jiaoe Wang, Jiangping Zhou, and Zi-jia Wang. "Tracking job and housing dynamics with smartcard data." Proceedings of the National Academy of Sciences 115, no. 50 (November 19, 2018): 12710–15. http://dx.doi.org/10.1073/pnas.1815928115.
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Residential locations, the jobs–housing relationship, and commuting patterns are key elements to understand urban spatial structure and how city dwellers live. Their successive interaction is important for various fields including urban planning, transport, intraurban migration studies, and social science. However, understanding of the long-term trajectories of workplace and home location, and the resulting commuting patterns, is still limited due to lack of year-to-year data tracking individual behavior. With a 7-y transit smartcard dataset, this paper traces individual trajectories of residences and workplaces. Based on in-metro travel times before and after job and/or home moves, we find that 45 min is an inflection point where the behavioral preference changes. Commuters whose travel time exceeds the point prefer to shorten commutes via moves, while others with shorter commutes tend to increase travel time for better jobs and/or residences. Moreover, we capture four mobility groups: home mover, job hopper, job-and-residence switcher, and stayer. This paper studies how these groups trade off travel time and housing expenditure with their job and housing patterns. Stayers with high job and housing stability tend to be home (apartment unit) owners subject to middle- to high-income groups. Home movers work at places similar to stayers, while they may upgrade from tenancy to ownership. Switchers increase commute time as well as housing expenditure via job and home moves, as they pay for better residences and work farther from home. Job hoppers mainly reside in the suburbs, suffer from long commutes, change jobs frequently, and are likely to be low-income migrants.
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Tiessler, Michaela, Roman Engelhardt, Klaus Bogenberger, Christoph Hessel, and Magdalena Serwa-Klamouri. "Integration of an Urban Ropeway into Munich’s Transit System Demand Modeling." Transportation Research Record: Journal of the Transportation Research Board 2673, no. 10 (May 12, 2019): 47–57. http://dx.doi.org/10.1177/0361198119844760.
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Whereas in some cities ropeways already belong to the transit system, in Germany they are better known from skiing in the alps or as tourist attractions that were implemented in relation to expositions as in Koblenz or Berlin. Nonetheless, a ropeway system has several advantages, which make it an interesting alternative in urban public transportation. In this paper, we investigate the varying attitude of residents and commuters towards a ropeway system and its potential on a route in the north of Munich. To get an impression of their opinion, we conducted an online survey focusing on route choice depending on transit mode and travel times. In general, the respondents had a positive attitude towards this novel option and rate it with similar attractiveness to subway. To investigate the demand for the ropeway, the results of the survey were used to add a new transportation mode in the VISUM model for transit in Munich.
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Rump, Adrian, Marie-Luise Kromrey, Eberhard Scheuch, Vincent Jannin, Lara Rehenbrock, Mladen Vassilev Tzvetkov, Werner Weitschies, and Michael Grimm. "In Vivo Evaluation of a Gastro-Resistant HPMC-Based “Next Generation Enteric” Capsule." Pharmaceutics 14, no. 10 (September 21, 2022): 1999. http://dx.doi.org/10.3390/pharmaceutics14101999.
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Many orally dosed APIs are bioavailable only when formulated as an enteric dosage form to protect them from the harsh environment of the stomach. However, an enteric formulation is often accompanied with a higher development effort in the first place and the potential degradation of fragile APIs during the coating process. Ready-to-use enteric hard capsules would be an easily available alternative to test and develop APIs in enteric formulations, while decreasing the time and cost of process development. In this regard, Lonza Capsugel® Next Generation Enteric capsules offer a promising approach as functional capsules. The in vivo performance of these capsules was observed with two independent techniques (MRI and caffeine in saliva) in eight human volunteers. No disintegration or content release in the stomach was observed, even after highly variable individual gastric residence times (range 7.5 to 82.5 min), indicating the reliable enteric properties of these capsules. Seven capsules disintegrated in the distal part of the small intestine; one capsule showed an uncommonly fast intestinal transit (15 min) and disintegrated in the colon. The results for this latter capsule by MRI and caffeine appearance differed dramatically, whereas for all other capsules disintegrating in the small intestine, the results were very comparable, which highlights the necessity for reliable and complementary measurement methods. No correlation could be found between the gastric residence time and disintegration after gastric emptying, which confirms the robust enteric formulation of those capsules.
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Morse, Lawrence B., and Julian M. Benjamin. "Analysis of Feeling of Security on Public Transit among Residents of Small Urban Area." Transportation Research Record: Journal of the Transportation Research Board 1557, no. 1 (January 1996): 28–31. http://dx.doi.org/10.1177/0361198196155700105.
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Magnitude estimation for assessing personal security is introduced. Magnitude estimates were obtained and used to compute security indexes. The advantage of magnitude estimate–based indexes over summated scales is that they are ratio rather than ordinal data. Residents of Greensboro, North Carolina, were surveyed regarding crime in the vicinity of bus stops. Responses were analyzed, and violent crime around bus areas was rated 2.5 times more serious than nonviolent crime (e.g., panhandling). In a model of the index, the gender of residents, an interaction term denoting crime victimization and taking precautionary measures, and the crime rate were significant predictors; race and age were not.
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Heer, Tej, Mathew G. Wells, P. Ryan Jackson, and Nicholas E. Mandrak. "Modelling grass carp egg transport using a 3-D hydrodynamic river model: the role of egg retention in dead zones on spawning success." Canadian Journal of Fisheries and Aquatic Sciences 77, no. 8 (August 2020): 1379–92. http://dx.doi.org/10.1139/cjfas-2019-0344.
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Invasive grass carp (Ctenopharyngodon idella) are known to spawn in the Sandusky River, Ohio, USA, within the Great Lakes Basin, and are threatening to expand throughout the Great Lakes. Successful spawning is thought to require that eggs remain in suspension until hatching, which depends on river hydrodynamics and temperature-dependent egg development. Previous modelling efforts used one-dimensional hydrodynamic models that simplify egg movement by not simulating low-velocity zones within the river. To examine the effect of low-velocity zones on egg transit times and hatching rates, we developed a novel coupling of a biophysical Lagrangian particle tracker and three-dimensional hydrodynamic model on the Sandusky River during a high-flow event. The model successfully predicted egg-capture data for a range of developmental stages and revealed a mechanism that resuspends eggs trapped in low-velocity zones. The resuspension mechanism increases the residence time of grass carp eggs in spawning tributaries and can lead to successful hatching occurring in shorter distances than previously estimated. Grass carp potentially spawning in shorter tributary lengths has widespread implications for efforts preventing establishment in the Great Lakes Basin.
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Marshall, Wesley E., and Alejandro Henao. "The Shock Heard round the Suburbs: Assessing the Vulnerability, Resilience, and Transportation Affordability of Higher Fuel Price Scenarios." Transportation Research Record: Journal of the Transportation Research Board 2531, no. 1 (January 2015): 63–75. http://dx.doi.org/10.3141/2531-08.
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With transportation the second highest household expenditure, understanding the disproportionate impact that a drastic increase in the gas price might have on a major city and region is vital. This study sought to increase the understanding of resiliency, vulnerability, and transportation affordability issues by asking the following questions: What would happen if the cost to drive suddenly doubled or tripled? Who would be better off and why? How much would residency near downtown or near one's job make a difference? What would matter in terms of transit infrastructure? How much of a role would current travel behavior play? This study derived resiliency scenarios in which the cost to drive increased one and one-half, two, and three times with the use of a multinomial logistic regression mode choice model developed with major travel surveys conducted in 1997 and 2008, a time period during which gas prices more than tripled. The focus of this study was on work trips, which were those trips most likely to be nondiscretionary. The annual cost to commute was estimated as a percentage of the median household income. Transit infrastructure, active transportation, built environment, land use, and socioeconomic status were assessed for their influences on resiliency, vulnerability, and transportation affordability. Although high income represented one path to resilience, the study results suggested that higher resilience could also be found in locations with proximity to high levels of employment, with more compact and connected street networks, and with better transit infrastructure. Beyond current travel behaviors, a significant option value to transit was also found in the resiliency scenarios. Transportation choice was found to create network redundancy and to facilitate adaptability under extreme conditions.
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Penninx, Rinus. "International migration and related policies in europe 1950 - 2015." Glasnik Srpskog geografskog drustva 96, no. 2 (2016): 18–41. http://dx.doi.org/10.2298/gsgd1602014p.
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Immigration in Europe has been shaped by: a) its particular development in time; b) the geographical patterns of migration within and towards European countries; and c) the shifting types of migration and characteristics of migrants involved. The first part of this contribution outlines changes in these three basic migration-related factors. Migration outcomes are not haphazard nor are these the result of unhindered economic push and pull factors in a free market. Immigration policies of receiving countries do greatly influence the volume and patterns of migration, the place of settlement and the characteristics of migrants. Regulations on conditions of residence and integration do furthermore influence significantly the position of immigrants in their new destination, among others by setting conditions for their stay (residence rights) and access to the labour market. The second part of this chapter outlines the migration and integration regimes that have been developed by states of different parts of Europe and by the European Union. In conclusion, immigration has become a relevant phenomenon in all EU countries. However, as a consequence of different timing of immigration, different socio-economic contexts and varying governmental migration and integration policies, European countries are confronted with different forms migration (immigration, emigration, transit migration) and with different types of migrants. European states have also developed different governmental policies of migration and integration. Historically, a common denominator in the framing of European policies is that countries do not see themselves as immigration countries; they are immigration countries against their will. In recent times, such framing is reinforced by populist and nationalist movements that see immigrants not only as economic competitors, but also as a threat to the national "culture and world views". The more Europe needs immigrants for economic and demographic reasons, the less they are welcomed for cultural and political reasons.
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Ramos, Andre, Michael J. Whelan, Ian Guymer, Raffaella Villa, and Bruce Jefferson. "On the potential of on-line free-surface constructed wetlands for attenuating pesticide losses from agricultural land to surface waters." Environmental Chemistry 16, no. 8 (2019): 563. http://dx.doi.org/10.1071/en19026.
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Environmental contextPesticide losses from land to surface waters have the potential to cause ecological damage. Furthermore, pesticides in surface waters present a major challenge for water companies accessing these waters for the domestic supply, in terms of complying with water quality regulations. Here, we evaluate the potential of field- and ditch-scale free-surface constructed wetland systems for reducing pesticide transfers from land to surface waters. AbstractPesticides make important contributions to agriculture but losses from land to water can present problems for environmental management, particularly in catchments where surface waters are abstracted for drinking water. ‘On-line’ constructed wetlands have been proposed as a potential means of reducing pesticide fluxes in drainage ditches and headwater streams. Here, we evaluate the potential of two free-surface constructed wetland systems to reduce pesticide concentrations in surface waters using a combination of field monitoring and dynamic fugacity modelling. We specifically focus on metaldehyde, a commonly used molluscicide that is moderately mobile and has been regularly detected at high concentrations in drinking water supply catchments in the UK over the past few years. We also present data for the herbicide metazachlor. Metaldehyde losses from the upstream catchment were significant, with peak concentrations occurring in the first storm events in early autumn, soon after application. Concentrations and loads appeared to be minimally affected by transit through the monitored wetlands over a range of flow conditions. This was probably due to short solute residence times (quantified via several tracing experiments employing rhodamine WT – a fluorescent dye) exacerbated by solute exclusion phenomena resulting from patchy vegetation. Model analyses of different scenarios suggested that, even for pesticides with short aquatic half-lives, wetland systems would need to exhibit much longer residence times (RTs) than those studied here in order to deliver any appreciable attenuation. If the ratio of wetland surface area to the area of the contributing catchment is assumed to be a surrogate for RT (i.e. not accounting for solute exclusion), then model predictions suggest that this needs to be greater than 1% to yield load reductions of 3 and 7% for metaldehyde and metazachlor respectively.
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Le, Hoang T. M. D., Kai K. Lie, Angela Etayo, Ivar Rønnestad, and Øystein Sæle. "Physical and nutrient stimuli differentially modulate gut motility patterns, gut transit rate, and transcriptome in an agastric fish, the ballan wrasse." PLOS ONE 16, no. 2 (February 11, 2021): e0247076. http://dx.doi.org/10.1371/journal.pone.0247076.
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The effects of nutrient and mechanical sensing on gut motility and intestinal metabolism in lower vertebrates remains largely unknown. Here we present the transcriptome response to luminal stimulation by nutrients and an inert bolus on nutrient response pathways and also the response on gut motility in a stomachless fish with a short digestive tract; the ballan wrasse (Labrus berggylta). Using an in vitro model, we differentiate how signals initiated by physical stretch (cellulose and plastic beads) and nutrients (lipid and protein) modulate the gut evacuation rate, motility patterns and the transcriptome. Intestinal stretch generated by inert cellulose initiated a faster evacuation of digesta out of the anterior intestine compared to digestible protein and lipid. Stretch on the intestine upregulated genes associated with increased muscle activity, whereas nutrients stimulated increased expression of several neuropeptides and receptors which are directly involved in gut motility regulation. Although administration of protein and lipid resulted in similar bulbous evacuation times, differences in intestinal motility, transit between the segments and gene expression between the two were observed. Lipid induced increased frequency of ripples and standing contraction in the middle section of the intestine compared to the protein group. We suggest that this difference in motility was modulated by factors [prepronociceptin (pnoca), prodynorphin (pdyn) and neuromedin U (nmu), opioid neurotransmitters and peptides] that are known to inhibit gastrointestinal motility and were upregulated by protein and not lipid. Our findings show that physical pressure in the intestine initiate contractions propelling the bolus distally, directly towards the exit, whereas the stimuli from nutrients modulates the motility to prolong the residence time of digesta in the digestive tract for optimal digestion.
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Nabi, I. R., and E. Rodriguez-Boulan. "Increased LAMP-2 polylactosamine glycosylation is associated with its slower Golgi transit during establishment of a polarized MDCK epithelial monolayer." Molecular Biology of the Cell 4, no. 6 (June 1993): 627–35. http://dx.doi.org/10.1091/mbc.4.6.627.
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An endogenous Madin-Darby canine kidney (MDCK) lysosomal membrane glycoprotein that exhibits a basolateral targeting pathway to the lysosome is shown here to exhibit significant N-terminal amino acid sequence identity to lysosomal associated membrane proteins (LAMP-2) of other species. During establishment of the MDCK monolayer after only 1 d of culture, this canine LAMP-2 has a larger molecular size (110 kDa) than following formation of a confluent monolayer after 3 d of culture (100 kDa) due to the increased presence of N-linked polylactosamine oligosaccharide chains. Neither polylactosamine glycosylation of LAMP-2 in MDCK cells nor truncation of N-linked oligosaccharide chains of LAMP-2 in a ricin-resistant MDCK-RCAR cell line influenced the basolateral polarity of its targeting. However, the rate of basolateral delivery of LAMP-2 in MDCK cells plated for 3 d was significantly faster (t1/2 = 28 min) than in 1-d cells (t1/2 = 40 min); in MDCK-RCAR cells the rate of basolateral delivery at both 1 and 3 d of plating was similar (t1/2 = 40 min). The rate differential in MDCK cells occurred after arrival of LAMP-2 to the Golgi apparatus because the rate of acquisition of endoglycosidase H resistance was the same (t1/2 = 25 min) at both days of plating. The rate of transit of LAMP-2 through the Golgi apparatus to the basolateral domain was therefore far more rapid (approximately 4-fold) in 3 d compared with 1-d MDCK cultures. The increased polylactosamine glycosylation of MDCK LAMP-2 at early times of plating during the establishment of a confluent epithelial monolayer may thus be related to its longer residence time in the Golgi apparatus.
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Welsh, Molly K., Sara K. McMillan, and Philippe G. Vidon. "Impact of Riparian and Stream Restoration on Denitrification in Geomorphic Features of Agricultural Streams." Transactions of the ASABE 63, no. 5 (2020): 1157–67. http://dx.doi.org/10.13031/trans.13777.
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HighlightsDenitrification enzyme activity (DEA) was measured in stream sediments of restored and unrestored agricultural streams.Nitrate, sediment characteristics, riparian vegetation, and geomorphology influenced DEA.Pools at restored sites had lower organic carbon, coarser sediment textures, and lower denitrification potential.Restoration strategies should increase organic carbon and residence times through complex flowpaths.Abstract. Agricultural land use, channel modifications, and riparian vegetation composition can affect instream denitrification by altering geomorphic features, such as sediment texture, organic matter, retention time, and hyporheic exchange. Stream and riparian restoration is widely implemented in agricultural watersheds to mitigate excess nutrient export to sensitive downstream waters; however, the cumulative impact of channel reconstruction and altered channel and near-stream morphology on nitrogen dynamics remains poorly understood. We measured denitrification enzyme activity (DEA) and environmental variables (e.g., water chemistry, sediment texture, and organic matter) in different geomorphic features in agriculturally influenced streams in North Carolina with varied channel and riparian zone characteristics. Our results indicate that denitrification is primarily influenced by increased transport of nitrate (NO3-) to the streams in wetter months. Secondarily, structural factors, including riparian vegetation and stream geomorphology, impact denitrification by controlling the distribution of sediment texture and organic carbon. In the newly restored stream, we observed coarser streambed sediments and low sediment organic carbon, especially in scour pools constructed downstream from cross-vanes. Lower DEA was observed in restored pools (39.1 ng N g-1 dry mass h-1) compared to naturally occurring pools (70.7 to 278.1 ng N g-1 dry mass h-1). These results highlight the need for restoration strategies to be directed at increasing organic carbon and residence times through complex flowpaths (e.g., meanders, root wads, artificial woody debris dams). Keywords: Denitrification, Freshwater, Nitrogen, Restoration, Riparian, Stream, Water quality.
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Chen, Bowen, Junwu Dai, and Zhipeng Shao. "Modeling of Hyper-Viscoelastic Properties of High-Damping Rubber Materials during the Cyclic Tension and Compression Process in the Vertical Direction." Polymers 14, no. 24 (December 9, 2022): 5395. http://dx.doi.org/10.3390/polym14245395.
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With the rapid development of the economy and urbanization, the construction of the urban rail transit system has had a great impact on the work, life, and health of residents in buildings along the rail transit line. Thus, it is particularly urgent and necessary to develop base isolation technologies to control and reduce the impact of vibrations of rail transit systems on building structures. High-damping rubber isolation bearings have shown significant effectiveness in the reduction of this impact, and their isolation performance mainly depends on the mechanical and damping energy dissipation characteristics of the high-damping rubber material. This paper aims to investigate the hyper-viscoelastic properties of the high-damping rubber material used for high-damping rubber isolation bearings during the cyclic tension and compression process in the vertical direction. These properties include hyperelastic parameters, viscoelastic coefficients, and the relaxation times of the material. For this purpose, uniaxial cyclic tension and compression tests were conducted. A three-element Maxwell rheological model combining a strain energy density function was proposed for modeling the hyper-viscoelastic behaviors of the materials during the cyclic tension and compression process. Based on the obtained results, an iterative identification procedure was used to determine the constitutive parameters of the material for each loading-unloading cycle. The aforementioned parameters were further expressed as a function of the number of cycles. New insights into hyper-viscoelastic property changes in this high-damping rubber material during the cyclic tension and compression process were gained in this work. These investigations could facilitate the development of computational tools, which would regulate fundamental guidelines for the better controlling and optimization of the isolation performance of the high-damping rubber material used for high-damping rubber isolation bearings, which have a wider perspective of applications in the urban rail transit system.
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Fried, Travis, Thet Hein Tun, Jacqueline M. Klopp, and Benjamin Welle. "Measuring the Sustainable Development Goal (SDG) Transport Target and Accessibility of Nairobi’s Matatus." Transportation Research Record: Journal of the Transportation Research Board 2674, no. 5 (April 16, 2020): 196–207. http://dx.doi.org/10.1177/0361198120914620.
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The urban Sustainable Development Goal (SDG) includes the target to provide “access to safe, affordable, accessible and sustainable transport systems for all” by 2030. However, debate exists around the best indicator to measure this target, and few actual measurements exist. This is in part because basic transit data are missing from many of the world’s cities, including in Africa where popular or “informal” systems dominate. This paper explores how to make progress in measuring indicators for the SDG transport target using Nairobi’s minibus system, matatus, as a case study. We partially measure the SDG indicator for the city as currently defined by the UN and then compare the SDG measurement to a location-based accessibility indicator that incorporates income data, travel times, and land-use considerations for Nairobi’s highly monocentric spatial urban form. We show that although the SDG analysis suggests generally favorable transit coverage, it also points to underlying transport inequalities for low-income residents. The more fine-grained location-based accessibility analysis reveals rapidly decreasing accessibility to opportunities as distance increases from the city’s central business district. This accessibility-based analysis further highlights income-based transport inequalities, identifying opportunities for improving integrated transport for residents living on the city’s near and far peripheries. Improving non-motorized transport access for those living in low-income areas with high access potential would also be important to improve access. We recommend that cities start using open-source software and open data to measure a variety of indicators needed for data-driven policy, to meet SDG 11.2 and go further to improve access to opportunities for all residents.
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Popp, Achim P., Johannes Hettich, and J. Christof M. Gebhardt. "Altering transcription factor binding reveals comprehensive transcriptional kinetics of a basic gene." Nucleic Acids Research 49, no. 11 (June 1, 2021): 6249–66. http://dx.doi.org/10.1093/nar/gkab443.
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Abstract Transcription is a vital process activated by transcription factor (TF) binding. The active gene releases a burst of transcripts before turning inactive again. While the basic course of transcription is well understood, it is unclear how binding of a TF affects the frequency, duration and size of a transcriptional burst. We systematically varied the residence time and concentration of a synthetic TF and characterized the transcription of a synthetic reporter gene by combining single molecule imaging, single molecule RNA-FISH, live transcript visualisation and analysis with a novel algorithm, Burst Inference from mRNA Distributions (BIRD). For this well-defined system, we found that TF binding solely affected burst frequency and variations in TF residence time had a stronger influence than variations in concentration. This enabled us to device a model of gene transcription, in which TF binding triggers multiple successive steps before the gene transits to the active state and actual mRNA synthesis is decoupled from TF presence. We quantified all transition times of the TF and the gene, including the TF search time and the delay between TF binding and the onset of transcription. Our quantitative measurements and analysis revealed detailed kinetic insight, which may serve as basis for a bottom-up understanding of gene regulation.
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Thakuriah, Piyushimita, and Paul Metaxatos. "Effect of Residential Location and Access to Transportation on Employment Opportunities." Transportation Research Record: Journal of the Transportation Research Board 1726, no. 1 (January 2000): 24–32. http://dx.doi.org/10.3141/1726-04.
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Women who have been on public assistance need to obtain and maintain steady employment because they stand to lose their public benefits and also because it is the only way out of poverty. Although the sociodemographic and general economic influences on job retention have been examined in the literature, the effects of transportation and of place of residence in a metropolitan area vis-à-vis entry-level job locations have not been studied systematically. Four sets of factors—transportation, location, sociodemographic, and family effects—are examined for their effect on job retention. In particular, it was found that employment security for female welfare clients or former clients does not come from job retention (i.e., tenure with the same employer) but from “employment retention” (i.e., jobs with different employers, possibly with a trend toward upward mobility). The effects of transportation and location on job and employment retention are complex. Although access to a vehicle is important for increasing employment retention, even more important is the number of job opportunities accessible by private vehicle or public transit within a tolerable travel time. Female welfare clients who retain a job longer and hold more jobs within a 2-year period are more likely to live in subareas of the metropolitan area with greater access to jobs within reasonable travel times; the competition for those jobs from other low-income individuals is low. Furthermore, female welfare clients with a high school diploma, when given the appropriate accessibility and location opportunities, enjoy increased job retention.
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Tambasco, Mauro, and David A. Steinman. "On Assessing the Quality of Particle Tracking Through Computational Fluid Dynamic Models." Journal of Biomechanical Engineering 124, no. 2 (March 29, 2002): 166–75. http://dx.doi.org/10.1115/1.1449489.
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Quantification of particle deposition patterns, transit times, and shear exposure is important for computational fluid dynamic (CFD) studies involving respiratory and arterial models. To numerically compute such path-dependent quantities, it is necessary to employ a Lagrangian approach where particles are tracked through a pre-computed velocity field. However, it is difficult to determine in advance whether a particular velocity field is sufficiently resolved for the purposes of tracking particles accurately. Towards this end, we propose the use of volumetric residence time (VRT)—previously defined for 2-D studies of platelet activation and here extended to more physiologically relevant 3-D models—as a means of quantifying whether a volume of Lagrangian fluid elements (LFE’s) seeded uniformly and contiguously at the model inlet remains uniform throughout the flow domain. Such “Lagrangian mass conservation” is shown to be satisfied when VRT=1 throughout the model domain. To demonstrate this novel concept, we computed maps of VRT and particle deposition in 3-D steady flow models of a stenosed carotid bifurcation constructed with one adaptively refined and three nominally uniform finite element meshes of increasing element density. A key finding was that uniform VRT could not be achieved for even the most resolved meshes and densest LFE seeding, suggesting that care should be taken when extracting quantitative information about path-dependent quantities. The VRT maps were found to be useful for identifying regions of a mesh that were under-resolved for such Lagrangian studies, and for guiding the construction of more adequately resolved meshes.
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WOOLFENDEN, H. C., and M. G. BLYTH. "Motion of a two-dimensional elastic capsule in a branching channel flow." Journal of Fluid Mechanics 669 (January 5, 2011): 3–31. http://dx.doi.org/10.1017/s0022112010004829.
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The transit of a two-dimensional elastic fluid-filled capsule through a channel with a side branch is investigated numerically. The mathematical formulation allows for a capsule carried in a pressure-driven flow of fluid of generally different viscosity to that inside the capsule. Far upstream and downstream in the main channel, and downstream in the side branch, the fluid velocity profiles are assumed to adopt those of unidirectional Poiseuille flow with prescribed flow rates. The capsule boundary is treated as a two-dimensional elastic membrane developing elastic tensions and bending moments according to simple constitutive laws. A boundary-integral formulation allows for the explicit computation of the fluid pressures upstream and downstream of the branching. The novelty of the approach is the inclusion of a notional boundary at the entrance to the side branch, which avoids the need to collocate the channel ends. The deformation experienced by the capsule in the region of the junction is found to depend strongly on the branch angle. The deformation is ameliorated by increasing the membrane stiffness or lowering the viscosity of the suspending fluid relative to the encapsulated fluid. When a capsule exits the branch region, a distance of many decades of capsule diameters is required before the capsule relaxes to an equilibrium shape. Capsule residence times in the vicinity of the branch region can be considerable, depending on the line of approach into the junction and the capsule deformability. The path selection of a cell at a branch junction can depend crucially on capsule deformability: capsules with different elastic properties may follow different routes out of the junction in otherwise identical flow conditions.
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Mpogole, Hosea, and Samira Msangi. "Traffic Congestion in Dar es Salaam: Implications for Workers’ Productivity." Journal of Sustainable Development 9, no. 6 (November 30, 2016): 103. http://dx.doi.org/10.5539/jsd.v9n6p103.
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Inadequately planned transport systems result to traffic congestion, a challenge that has for long been a thorn in Dar es Salaam, the city most affected in Tanzania. Although traffic congestion has been a major concern in Dar es Salaam, marked reluctance has been noticed in taking measures towards a lasting solution thus, it is of diminutive surprise that limited studies and documentations on the same are in existence. Therefore, this study assesses traffic congestion in Dar es Salaam and particularly its implications for workers’ productivity. Travel time and productivity indexes were established from a sample of 96 workers who used public transport along Morogoro and Mandela Roads. Travel time index (TTI) is the ratio of the average travel time during peak period to the travel time during off-peak period. Findings reveal that TTI was 2.19. Workers spent about 2 times of the average commuting time to work and 3 times of the same commuting from work to their various residences. About 2.5 hours were lost on traffic jam per day and that people worked 1.4 times less than the required time due to traffic congestion. It was further established that in 10 working days, almost 3 days were lost to traffic congestion. Since there are ongoing efforts to improve the transport system through the Bus Rapid Transit (BRT) project, it remains to be seen as to what extent traffic congestion will be reduced. In either case, this study provides a benchmark for comparisons.
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García-Gamero, Vanesa, Tom Vanwalleghem, Adolfo Peña, Andrea Román-Sánchez, and Peter A. Finke. "Modelling the effect of catena position and hydrology on soil chemical weathering." SOIL 8, no. 1 (April 12, 2022): 319–35. http://dx.doi.org/10.5194/soil-8-319-2022.
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Abstract. The sensitivity of chemical weathering to climatic and erosional forcing is well established at regional scales. However, soil formation is known to vary strongly along catenas where topography, hydrology, and vegetation cause differences in soil properties and, possibly, chemical weathering. This study applies the SoilGen model to evaluate the link between the topographic position and hydrology with the chemical weathering of soil profiles on a north–south catena in southern Spain. We simulated soil formation in seven selected locations over a 20 000-year period and compared it against field measurements. There was good agreement between simulated and measured chemical depletion fraction (CDF; R2=0.47). An important variation in CDF values along the catena was observed that is better explained by the hydrological variables than by the position along the catena alone or by the slope gradient. A positive trend between CDF data and soil moisture and infiltration and a negative trend with water residence time was found. This implies that these hydrological variables are good predictors of the variability in soil properties. The model sensitivity was evaluated with a large precipitation gradient (200–1200 mm yr−1). The model results show an increase in the chemical weathering of the profiles up to a mean annual precipitation value of 800 mm yr−1, after which it drops again. A marked depth gradient was obtained for CDF up to 800 mm yr−1, and a uniform depth distribution was obtained with precipitation above this threshold. This threshold reflects a change in behaviour, where the higher soil moisture and infiltration lead to shorter water transit times and decreased weathering. Interestingly, this corroborates similar findings on the relation of other soil properties to precipitation and should be explored in further research.
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Nowak, Martin E., Valérie F. Schwab, Cassandre S. Lazar, Thomas Behrendt, Bernd Kohlhepp, Kai Uwe Totsche, Kirsten Küsel, and Susan E. Trumbore. "Carbon isotopes of dissolved inorganic carbon reflect utilization of different carbon sources by microbial communities in two limestone aquifer assemblages." Hydrology and Earth System Sciences 21, no. 9 (August 31, 2017): 4283–300. http://dx.doi.org/10.5194/hess-21-4283-2017.
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Abstract. Isotopes of dissolved inorganic carbon (DIC) are used to indicate both transit times and biogeochemical evolution of groundwaters. These signals can be complicated in carbonate aquifers, as both abiotic (i.e., carbonate equilibria) and biotic factors influence the δ13C and 14C of DIC. We applied a novel graphical method for tracking changes in the δ13C and 14C of DIC in two distinct aquifer complexes identified in the Hainich Critical Zone Exploratory (CZE), a platform to study how water transport links surface and shallow groundwaters in limestone and marlstone rocks in central Germany. For more quantitative estimates of contributions of different biotic and abiotic carbon sources to the DIC pool, we used the NETPATH geochemical modeling program, which accounts for changes in dissolved ions in addition to C isotopes. Although water residence times in the Hainich CZE aquifers based on hydrogeology are relatively short (years or less), DIC isotopes in the shallow, mostly anoxic, aquifer assemblage (HTU) were depleted in 14C compared to a deeper, oxic, aquifer complex (HTL). Carbon isotopes and chemical changes in the deeper HTL wells could be explained by interaction of recharge waters equilibrated with post-bomb 14C sources with carbonates. However, oxygen depletion and δ13C and 14C values of DIC below those expected from the processes of carbonate equilibrium alone indicate considerably different biogeochemical evolution of waters in the upper aquifer assemblage (HTU wells). Changes in 14C and 13C in the upper aquifer complexes result from a number of biotic and abiotic processes, including oxidation of 14C-depleted OM derived from recycled microbial carbon and sedimentary organic matter as well as water–rock interactions. The microbial pathways inferred from DIC isotope shifts and changes in water chemistry in the HTU wells were supported by comparison with in situ microbial community structure based on 16S rRNA analyses. Our findings demonstrate the large variation in the importance of biotic as well as abiotic controls on 13C and 14C of DIC in closely related aquifer assemblages. Further, they support the importance of subsurface-derived carbon sources like DIC for chemolithoautotrophic microorganisms as well as rock-derived organic matter for supporting heterotrophic groundwater microbial communities and indicate that even shallow aquifers have microbial communities that use a variety of subsurface-derived carbon sources.
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Hammer, Tobin J., Daniel H. Janzen, Winnie Hallwachs, Samuel P. Jaffe, and Noah Fierer. "Caterpillars lack a resident gut microbiome." Proceedings of the National Academy of Sciences 114, no. 36 (August 22, 2017): 9641–46. http://dx.doi.org/10.1073/pnas.1707186114.
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Many animals are inhabited by microbial symbionts that influence their hosts’ development, physiology, ecological interactions, and evolutionary diversification. However, firm evidence for the existence and functional importance of resident microbiomes in larval Lepidoptera (caterpillars) is lacking, despite the fact that these insects are enormously diverse, major agricultural pests, and dominant herbivores in many ecosystems. Using 16S rRNA gene sequencing and quantitative PCR, we characterized the gut microbiomes of wild leaf-feeding caterpillars in the United States and Costa Rica, representing 124 species from 15 families. Compared with other insects and vertebrates assayed using the same methods, the microbes that we detected in caterpillar guts were unusually low-density and variable among individuals. Furthermore, the abundance and composition of leaf-associated microbes were reflected in the feces of caterpillars consuming the same plants. Thus, microbes ingested with food are present (although possibly dead or dormant) in the caterpillar gut, but host-specific, resident symbionts are largely absent. To test whether transient microbes might still contribute to feeding and development, we conducted an experiment on field-collected caterpillars of the model speciesManduca sexta. Antibiotic suppression of gut bacterial activity did not significantly affect caterpillar weight gain, development, or survival. The high pH, simple gut structure, and fast transit times that typify caterpillar digestive physiology may prevent microbial colonization. Moreover, host-encoded digestive and detoxification mechanisms likely render microbes unnecessary for caterpillar herbivory. Caterpillars illustrate the potential ecological and evolutionary benefits of independence from symbionts, a lifestyle that may be widespread among animals.
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Cervero, R., and K.-L. Wu. "Polycentrism, Commuting, and Residential Location in the San Francisco Bay Area." Environment and Planning A: Economy and Space 29, no. 5 (May 1997): 865–86. http://dx.doi.org/10.1068/a290865.
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The San Francisco Bay Area has taken on a distinct polycentric metropolitan form, with three tiers of hierarchical employment centers encircling downtown San Francisco, the region's primary center. In this paper it is found that polycentric development is associated with differentials in suburban and urban commute trip times: commute trips made by employees of suburban centers are shorter in duration than commute trips made by their counterparts in larger and denser urban centers. Differentials were even greater, however, with respect to commuting modal splits. Lower density, outlying employment centers averaged far higher rates of drive-alone automobile commuting and insignificant levels of transit commuting. Smaller, outlying centers were also the least self-contained, with a large number averaging twenty or more times as many external as internal commutes. The effects of housing availability and prices on the residential locational choices of those working both in urban and in suburban employment centers are also investigated in this paper. Locational choices are stratified by occupational class and type of center. High housing prices in and around employment centers were found to displace workers to residences in other subregions, except in the case of professional workers in fast-growing, outlying centers. These workers were attracted to higher-priced nearby housing. In the empirical analysis, significant segmentation in housing choices among workers in fast-growing suburban centers was found. This could be partly due to selective land-use policies implemented by local governments in these areas.
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Krüger, Fred, Alexandra Titz, Raphael Arndt, Franziska Groß, Franziska Mehrbach, Vanessa Pajung, Lorenz Suda, Martina Wadenstorfer, and Laura Wimmer. "The Bus Rapid Transit (BRT) in Dar es Salaam: A Pilot Study on Critical Infrastructure, Sustainable Urban Development and Livelihoods." Sustainability 13, no. 3 (January 20, 2021): 1058. http://dx.doi.org/10.3390/su13031058.
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Inner-city transportation looms large in big cities in the so-called Global South due to rapid population and urban growth. To tackle this challenge, a Bus Rapid Transit (BRT) system was implemented in Dar es Salaam (Tanzania) in 2016. This paper reports on the results of a pilot study on the impacts of the BRT on city development and livelihoods in Dar. Our pilot study, which is part of the collaborative research project LIPSINDAR (Linking Partners for a Sustainable and Inclusive Dar es Salaam), was not designed to provide a comprehensive insight into the problems of urban planning, infrastructure modification and their impact on urban livelihoods. Rather, using the example of Dar es Salaam, the study served as an entry point to highlight challenges and future research demands in the context of urban insecurities and risks in large cities of the Global South. In particular, our study investigated the BRT as an element of critical infrastructure in Dar es Salaam and probed into its impact on residents’ livelihoods, focusing on the influence of service disruptions on everyday routines, and on different stakeholders’ views on the functionality of the BRT. Elaborating on this topic, interviews, street vendor surveys and mappings were used as methods to describe the processes. To examine the results more closely, the outcome was divided into groups of different fields of activity, namely Traffic Management, Local Residents, City Administration, Basic Provision Services and Street Vendors. In summary, the pilot study confirms that the implementation of the BRT system has, in general, served to improve urban livelihoods. Reducing commuting times and enhancing access to basic services found positive results. There is, however, still potential for improvement: the bus network, in particular, needs to be expanded and the vulnerability to natural extreme events, especially flooding, needs to be addressed.
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Bugaev, V. F., and D. P. Pogorelova. "FORMATION OF «FALSE ANNUAL RINGS» ON SCALE OF JUVENILE COHO SALMON ONCORHYNCHUS KISUTCH IN LAKE KURSIN (LOWER KAMCHATKA RIVER)." Izvestiya TINRO 198 (October 2, 2019): 61–76. http://dx.doi.org/10.26428/1606-9919-2019-198-61-76.
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During spring-summer flood (in June-July). transit underyearling of coho salmon, having or having no scales, migrate to Lake Kursin at the lower Kamchatka River, where resident coho salmon never spawn. In this case, additional zones of closely-spaced sclerites (ZCS) can be formed on their scale because of feeding change (additional ZCS of the 1st type). Seasonal growth restarts and annual zones of close sclerites (annual ring) form in middle May — early June on scales of yearlings and elder coho salmon wintered in Lake Kursin. These results contradict to the earlier conclusion of G.V. Bazarkin (2003) that the coho yearlings have no additional ZCSs in Lake Kursin, though the same collection of scale was analyzed. In late July — August, other additional ZCS can be formed on the scale of coho yearlings in the lake (additional ZCS of the 2nd type) that is next after the well-differentiated first annual ring. Possibly, the additional ZCSs were omitted by G.V. Bazarkin because of the scale measuring with high magnification — 113 times, without preliminary evaluation with lower magnification — 35–50 times, when the boundaries of certain or uncertain ZCSs are visible better. Rate of the sclerites forming was examined for coho juveniles of age 1+ by repeated observations in Lake Kursin in 2001 and evaluated as 15.60 days/sclerite between June 9 — July 1, 7.52 days/sclerite between July 1–21, and 7.94 days/sclerite between July 21 — August 30; on average one sclerite was formed in 10.35 days. The results demonstrate longer time of sclerites forming than reported earlier by G.V. Bazarkin (2003).
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Ma, Siyong, Jiancheng Weng, Chang Wang, Dimitrios Alivanistos, and Pengfei Lin. "Bus passenger flow congestion risk evaluation model based on the Pressure-State-Response framework: A case study in Beijing." Science Progress 103, no. 1 (November 14, 2019): 003685041988356. http://dx.doi.org/10.1177/0036850419883567.
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Urban public transport is a very essential mode for urban residents’ commute travel; however, the unbalanced spatial and temporal distribution of travel demand usually leads to passenger flow congestion risk at certain section and time. Meanwhile, the risk is short of quantified description. Based on the Pressure-State-Response framework, the study puts forward three bus passenger flow congestion risk evaluation indexes including the alternative pressure, the congestion intensity, and the transport efficiency. Then, the evaluation model is proposed based on the entropy method, and the risk is divided into four levels by K-means clustering. The article considers the 3rd Ring Road corridor in Beijing as a case to identify the risk level. The results show that the risk in the peak hours of weekdays is generally about 1.5 times higher than the risk in the weekends. The congestion risk is stable in level 3 during the majority time of morning peak hours. The duration intensity of level 4 risk is less than 0.1 during weekdays, indicating that the highest flow congestion can be quickly evacuated in a short time. The integrated passenger risk identification and evaluation model was proposed to identify the passenger flow risk level and induce the network flow distribution more reasonable. The study also provides technical support for ensuring the public transit system safety.
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Zheng, Zhicheng, Haoming Xia, Shrinidhi Ambinakudige, Yaochen Qin, Yang Li, Zhixiang Xie, Lijun Zhang, and Haibin Gu. "Spatial Accessibility to Hospitals Based on Web Mapping API: An Empirical Study in Kaifeng, China." Sustainability 11, no. 4 (February 22, 2019): 1160. http://dx.doi.org/10.3390/su11041160.
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The accessibility of hospital facilities is of great importance not only for maintaining social stability, but also for protecting the basic human right to health care. Traditional accessibility research often lacks consideration of the dynamic changes in transport costs and does not reflect the actual travel time of urban residents, which is critical to time-sensitive hospital services. To avoid these defects, this study considered the city of Kaifeng, China, as an empirical case, and directly acquired travel time data for two travel modes to the hospital in different time periods through web mapping API (Application Program Interface). Further, based on travel time calculations, we compared five baseline indicators. For the last indicator, we used the optimal weighted accessibility model to measure hospital accessibility for each residential area. The study discovered significant differences in the frequency and spatial distribution of hospital accessibility using public transit and self-driving modes of transportation. In addition, there is an imbalance between accessibility travel times in the study area and the number of arrivals at hospitals. In particular, different modes of transportation and different travel periods also have a certain impact on accessibility of medical treatment. The research results shed new light on the accessibility of urban public facilities and provide a scientific basis with which local governments can optimize the spatial structure of hospital resources.
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Blanco, Natalia, J. Kristie Johnson, John D. Sorkin, Alison D. Lydecker, Lauren Levy, Lona Mody, and Mary-Claire Roghmann. "Transmission of resistant Gram-negative bacteria to healthcare personnel gowns and gloves during care of residents in community-based nursing facilities." Infection Control & Hospital Epidemiology 39, no. 12 (October 8, 2018): 1425–30. http://dx.doi.org/10.1017/ice.2018.247.
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AbstractObjectiveTo estimate the risk of transmission of antibiotic-resistant Gram-negative bacteria (RGNB) to gowns and gloves worn by healthcare personnel (HCP) when providing care to residents of community-based nursing facilities to identify the types of care and resident characteristics associated with transmission.DesignProspective observational study.Settings and participantsResidents and HCP from 13 community-based nursing facilities in Maryland and Michigan.MethodsPerianal swabs were collected from residents and cultured to detect RGNB. HCP wore gowns and gloves during usual care activities, and at the end of each interaction, these were swabbed in a standardized manner. Transmission of RGNB from a colonized resident to gowns and gloves was estimated. Odds ratios (ORs) of transmission associated with type of care or resident characteristic were calculated.ResultsWe enrolled 403 residents and their HCP in this study. Overall, 19% of enrolled residents with a perianal swab (n=399) were colonized with at least 1 RGNB. RGNB transmission to either gloves or gowns occurred during 11% of the 584 interactions. Showering the resident, hygiene or toilet assistance, and wound dressing changes were associated with a high risk of transmission. Glucose monitoring and assistance with feeding or medication were associated with a low risk of transmission. Residents with a pressure ulcer were 3 times more likely to transmit RGNB than residents without one (OR, 3.3; 95% confidence interval [CI], 1.0–11.1).ConclusionsGown and glove use in community nursing facilities should be prioritized for certain residents and care interactions that are deemed a high risk for transmission.
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Wallmann, K., B. Schneider, and M. Sarnthein. "Effects of eustatic sea-level change, ocean dynamics, and iron fertilization on atmospheric <i>p</i>CO<sub>2</sub> and seawater composition over the last 130 000 years." Climate of the Past Discussions 11, no. 3 (June 29, 2015): 2405–81. http://dx.doi.org/10.5194/cpd-11-2405-2015.
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Abstract. We developed and employed an earth system model to explore the forcings of atmospheric pCO2 change and the chemical and isotopic evolution of seawater over the last glacial cycle. Concentrations of dissolved phosphorus, reactive nitrogen, molecular oxygen, dissolved inorganic carbon (DIC), total alkalinity (TA), 13C-DIC and 14C-DIC were calculated for 24 ocean boxes. The bi-directional water fluxes between these model boxes were derived from a 3-D circulation field of the modern ocean (Opa 8.2, NEMO) and tuned such that tracer distributions calculated by the box model were consistent with observational data from the modern ocean. To model the last 130 kyr, we employed records of past changes in sea-level, ocean circulation, and dust deposition. According to the model, about half of the glacial pCO2 drawdown may be attributed to marine regressions. The glacial sea-level low-stands implied steepened ocean margins, a reduced burial of particulate organic carbon, phosphorus, and neritic carbonate at the margin seafloor, a decline in benthic denitrification, and enhanced weathering of emerged shelf sediments. In turn, they led to a distinct rise in the standing stocks of DIC, TA, and nutrients in the global ocean, promoted the glacial sequestration of atmospheric CO2 in the ocean, and added 13C- and 14C-depleted DIC to the ocean as recorded in benthic foraminifera signals. The other half of the glacial drop in pCO2 was linked to reduced deep ocean dynamics, a shoaling of Atlantic meridional overturning circulation, and a rise in iron fertilization. The increased transit time of deep waters in the glacial ocean led to significant 14C depletions with respect to the atmosphere. The deglacial rapid and stepwise rise in atmospheric pCO2 was induced by upwelling both in the Southern Ocean and subarctic North Pacific and promoted by a drop in dust-borne iron discharge to the Southern Ocean. The deglacial sea-level rise led to a gradual decline in nutrient, DIC, and TA stocks, a slow change due to the large size and extended residence times of dissolved chemical species in the ocean. Thus, the rapid deglacial rise in pCO2 was dominated by fast changes in ocean dynamics and reduced dust deposition whereas the gradual pCO2 rise over the Holocene may be linked to the slow drop in nutrient and TA stocks that continued to promote an ongoing CO2 transfer from the ocean into the atmosphere.
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Joesoef, Andrew, David L. Kirchman, Christopher K. Sommerfield, and Wei-Jun Cai. "Seasonal variability of the inorganic carbon system in a large coastal plain estuary." Biogeosciences 14, no. 21 (November 8, 2017): 4949–63. http://dx.doi.org/10.5194/bg-14-4949-2017.
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Abstract. Carbonate geochemistry research in large estuarine systems is limited. More work is needed to understand how changes in land-use activity influence watershed export of organic and inorganic carbon, acids, and nutrients to the coastal ocean. To investigate the seasonal variation of the inorganic carbon system in the Delaware Estuary, one of the largest estuaries along the US east coast, dissolved inorganic carbon (DIC), total alkalinity (TA), and pH were measured along the estuary from June 2013 to April 2015. In addition, DIC, TA, and pH were periodically measured from March to October 2015 in the nontidal freshwater Delaware, Schuylkill, and Christina rivers over a range of discharge conditions. There were strong negative relationships between river TA and discharge, suggesting that changes in HCO3− concentrations reflect dilution of weathering products in the drainage basin. The ratio of DIC to TA, an understudied but important property, was high (1.11) during high discharge and low (0.94) during low discharge, reflecting additional DIC input in the form of carbon dioxide (CO2), most likely from terrestrial organic matter decomposition, rather than bicarbonate (HCO3−) inputs due to drainage basin weathering processes. This is also a result of CO2 loss to the atmosphere due to rapid water transit during the wet season. Our data further show that elevated DIC in the Schuylkill River is substantially different than that in the Delaware River. Thus, tributary contributions must be considered when attributing estuarine DIC sources to the internal carbon cycle versus external processes such as drainage basin mineralogy, weathering intensity, and discharge patterns. Long-term records in the Delaware and Schuylkill rivers indicate shifts toward higher alkalinity in estuarine waters over time, as has been found in other estuaries worldwide. Annual DIC input flux to the estuary and export flux to the coastal ocean are estimated to be 15.7 ± 8.2 × 109 mol C yr−1 and 16.5 ± 10.6 × 109 mol C yr−1, respectively, while net DIC production within the estuary including inputs from intertidal marshes is estimated to be 5.1 × 109 mol C yr−1. The small difference between riverine input and export flux suggests that, in the case of the Delaware Estuary and perhaps other large coastal systems with long freshwater residence times, the majority of the DIC produced in the estuary by biological processes is exchanged with the atmosphere rather than exported to the sea.
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KLEIN, H. A. "Oesophageal transit times." Nuclear Medicine Communications 6, no. 11 (November 1985): 746. http://dx.doi.org/10.1097/00006231-198511000-00011.
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Jensen, Alexandria K., and William I. Ford. "Quantifying Nitrate Dynamics of a Confluence Floodplain Wetland in a Disturbed Appalachian Watershed: High-Resolution Sensing and Modeling." Transactions of the ASABE 62, no. 6 (2019): 1545–65. http://dx.doi.org/10.13031/trans.13278.
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Abstract. Floodplain wetlands often form at confluences of main river channels and small, low-order tributary streams, yet their impact on nutrient removal and downstream loading is poorly understood. We coupled high-resolution water quality data with deterministic numerical modeling of hydrologic, hydraulic, and biochemical processes impacting nitrate fate and transport in a confluence floodplain wetland along the Ohio River from June 2017 to May 2018. The modeling results were used to quantify loading from a disturbed forested watershed (Fourpole Creek watershed) and the nitrate removal capacity of the wetland. Loading from the Fourpole Creek watershed to the wetland was on the same order of magnitude of other disturbed forested systems on an annual basis (3.6 kg N ha-1 year-1); however, the timing of peak nitrate loading and concentration from the tributary was associated with high flow conditions, contrasting with the timing of loadings typical of disturbed forested landscapes. Our results show that coupling the model with high-resolution data allowed us to estimate removal rates in the wetland, suggesting that 2.6% to 58.5% (optimally 12.7%) of nitrate was removed on an annual basis, despite the wetland comprising only 0.42% of the overall drainage area. We found that increasing inundation of the wetland confluence promoted enhanced residence times of stormflows and was the most important driver of nitrate removal rate and loading, with peak wetland inundation periods representing 26% of the removal load but occurring only 9% of the time. The findings of this study highlight the importance of using high-resolution data-model integration to quantify nutrient dynamics in complex landscapes, identifies the significance of connectivity of watershed nitrate loadings to floodplain wetland soils, and highlights the importance that these features will have in the future, given the enhanced potential for harmful algal blooms in the Ohio River. Keywords: Confluence floodplain wetlands, High-resolution water quality data, Nitrate fate and transport modeling, Nitrate loading, Wetland nitrate removal.