Average Transit Time Research Articles

Hydrodynamic Simulation of Circulation and Residence Time in Clifton Court Forebay

Circulation in Clifton Court Forebay (CCF) was simulated using the three-dimensional (3–D) hydrodynamic model UnTRIM. These numerical simulations were performed to provide a better understanding of circulation patterns, flow pathways, and residence time in Clifton Court Forebay in support of ongoing studies of pre-screen loss and fish facility efficiency for delta smelt (Hypomesus transpacificus) at the California State Water Project (SWP) export facilities. The 3–D hydrodynamic model of CCF was validated through comparisons to observed water surface elevations inside CCF, and comparisons to observed drifter paths and velocity measurements collected by the U.S. Geological Survey as part of this study. Flow measurements collected near the radial gates for 2 days during relatively low inflows suggest that the Hills (1988) gate equations may over-estimate inflow by as much as 39% when the CCF radial gates are only partially opened. Several alternative approaches to improve the implementation of the radial gate flows in the UnTRIM model were evaluated. The resulting model accurately predicts water surface elevations and currents inside CCF over a range of wind and operating conditions. The validated model was used to predict residence time and other transport time scales for two 21-day simulation periods, one of very low daily SWP export pumping averaging 19.3 m3 s-1 and one for moderate daily SWP export pumping averaging 66.6 m3 s-1. The average transit time, indicating the time from entering CCF to reaching the fish facility, was estimated as 9.1 days for low export conditions and 4.3 days for moderate export conditions. These transport time scale estimates may be used to inform estimates of pre-screen losses inside CCF due to predation or other causes.

PTH-191 Case Series of 162 Video Capsule Endoscopies from a Single UK Tertiary Referral Centre

IntroductionVideo capsule endoscopy (VCE) is now a routine procedure for investigating the small bowel. It is not apparent whether the yield and utility of the procedure is the same when...

Pre and post-operative evaluation of gastroesophageal reflux and esophageal motility in neurologically impaired children using combined pH–multichannel intraluminal impedance measurements

BackgroundGastroesophageal reflux disease (GERD) in patients with neurological impairment (NI) has not been fully studied before and after fundoplication procedure because their characteristics such as generalized gastrointestinal dysmotility, non-acid reflux, and the proximal reflux due to feeding of enteral nutrition via a nasogastric tube prevent their GERD from being detected by 24 h pH monitoring. The aim of this study was to elucidate whether multichannel impedance–pH measurement (pH/MII) is able to detect the subtypes of GERD and the differences in the reflux episodes of the severity of GERD, the ingestion pathway, and before and after fundoplication. The second aim was to determine whether a trial evaluation of dry swallows was able to be used to assess the esophageal motility of NI patients as an alternative examination.Patients and methodsThe 24 h pH/MII was conducted on 20 NI children [15 were the patients before Nissen’s fundoplication (BN), of whom, six were fed orally (FO) and nine were fed via nasogastric tube (NGT), and five were the patients after Nissen’s fundoplication (AN)]. All reflux episodes were evaluated and compared between patients with pathological GERD (PG) and non-pathological GERD (NG) and between patients who had FO and NGT and patients between BN and AN. Dry swallows were conducted to evaluate the esophageal motility. The average bolus presence time (BPT) and total bolus transit time (TBTT) were compared between the PG and NG, FO and NGT, and the BN and AN subgroups.ResultsA total of 1,064 reflux episodes were detected by pH/MII. Of those, 303 (28.5 %) were non-acid-related and 477 episodes reached the proximal esophagus. Of the 12 patients (57.1 %) showing pathological GERD, two cases (16.7 %) demonstrated predominantly weakly acidic PG. More than half of the reflux episodes of PG patients reached to the proximal esophagus. The numbers of total reflux and proximal reflux episodes in the PG were significantly higher than those in NG patients. The number of proximal reflux episodes in the FO group was significantly higher than that in the NGT groups, whereas NGT patients showed more non-acidic reflux episodes than FO patients. A trial evaluation of dry swallows demonstrated no significant differences in this study.ConclusionThe pH/MII was useful to detect the subtype of GERD in NI patients which could not be detected by 24 h pH monitoring. It can, therefore, be considered to have first priority for testing NI patients who are suspected to be suffering from GERD.

Dynamics extracted from fixed cells reveal feedback linking cell growth to cell cycle

Biologists have long been concerned about what constrains variation in cell size, but progress in this field has been slow and stymied by experimental limitations. Here we describe a new method, ergodic rate analysis (ERA), that uses single-cell measurements of fixed steady-state populations to accurately infer the rates of molecular events, including rates of cell growth. ERA exploits the fact that the number of cells in a particular state is related to the average transit time through that state. With this method, it is possible to calculate full time trajectories of any feature that can be labelled in fixed cells, for example levels of phosphoproteins or total cellular mass. Using ERA we find evidence for a size-discriminatory process at the G1/S transition that acts to decrease cell-to-cell size variation.

TRANSIT TIME DISTRIBUTION AND MOBILITY IN MONTE CARLO SIMULATIONS OF THE GAUSSIAN DISORDER MODEL

We study the distribution of transit times in Monte Carlo simulations of the Gaussian disorder model (GDM). The GDM is one of the most successful models to describe the charge transport in random organic materials. The transit time is the time it takes for a charge carrier to travel across a sample. We find that the distribution of transit times over many charge carriers and over different realizations of Gaussian energies shows a heavy tail in the long time limit at low temperatures. This heavy tail can be described by a power law with an exponent that depends on temperature. This sets a limitation on the calculation of mobility of charge carriers using an average transit time at low temperatures. We discuss the implication of these results on dispersive transport.

The Bonobo–Dialium Positive Interactions: Seed Dispersal Mutualism

A positive interaction is any interaction between individuals of the same or different species (mutualism) that provides a benefit to both partners such as increased fitness. Here we focus on seed dispersal mutualism between an animal (bonobo, Pan paniscus) and a plant (velvet tamarind trees, Dialium spp.). In the LuiKotale rainforest southwest of Salonga National Park, Democratic Republic of Congo, seven species of the genus Dialium account for 29.3% of all trees. Dialium is thus the dominant genus in this forest. Dialium fruits make up a large proportion of the diet of a habituated bonobo community in this forest. During the 6 months of the fruiting season, more than half of the bonobos' feeding time is devoted to Dialium fruits. Furthermore, Dialium fruits contribute a considerable proportion of sugar and protein to bonobos' dietary intake, being among the richest fruits for these nutrients. Bonobos in turn ingest fruits with seeds that are disseminated in their feces (endozoochory) at considerable distances (average: 1.25 km after 24 hr of average transit time). Endozoochory through the gut causes loss of the cuticle protection and tegumentary dormancy, as well as an increase in size by water uptake. Thus, after gut passage, seeds are better able to germinate. We consider other primate species as a potential seed disperser and conclude that Dialium germination is dependent on passage through bonobo guts. This plant-animal interaction highlights positive effects between two major organisms of the Congo basin rainforest, and establishes the role of the bonobo as an efficient disperser of Dialium seeds. Periodicals, Inc.

Performance of photo-sensors for KM3NeT

The future deep-sea neutrino telescope of multi cubic-km size, KM3NeT, has been designed for an efficient search for high energy neutrinos originating from galactic and extragalactic sources. The detection principle relies on the measurement of Cherenkov light emitted from relativistic charged secondary particles caused by the interaction of neutrinos with matter inside or surrounding the active detection volume. In order to provide a homogeneous photon acceptance and to reduce the environmental background by local coincidences between neighbouring photo sensors, a digital optical module (DOM) containing an array of 31 3-in. diameter photomultiplier tubes (PMTs) has been designed. Optimum performance requires sensitivity to single-photo electrons, high collection efficiency at low dark noise, homogeneous photo-cathode response and excellent timing properties. We have studied the response to single photo electrons of a newly developed 3-in. diameter PMT from ET Enterprises Ltd. A 2D-scanning system with a picosecond laser illuminating various positions on the photo-cathode surface was employed to study the timing and homogeneity of the PMT. Results of these investigations indicate good photo-cathode homogeneity, low dark noise on the sub-kHz level, and an average transit-time spread below 2ns. Simulations indicate a significantly improved signal-to-background ratio in the multi-PMT DOM as compared to a triplet of optical modules each housing a single 10-in. PMT.

The time-of-flight experiment and the average transit-time

The time-of-flight experiment is a transient photo-current measurement commonly used to measure the mobility of organic semiconductors. The experiment has a well established procedure to extract the average transit-time of the photo-generated carriers across the sample from the current versus time signal. In this work, we compare, for a dispersive signal, the transit-time as inferred from the experimental procedure with the statistically defined average transit-time. We show that the two quantities are not only numerically different, the experimental transit-time being always smaller than the exact one, but they also have markedly different electric field and sample length dependencies. Our results are relevant for any attempt to model an experimental time-of-flight mobility.

Nonzero azimuthal magnetic fields at the solar source surface: Extraction, model, and implications

A recent two‐dimensional (radial distancer and solar longitude ϕ) model for the solar wind is driven using 1 h average data from the Wind spacecraft. We extend the treatment of the Sun's magnetic field in comparison with previous models to allow a nonzero intrinsic azimuthal component Bϕ at the solar source surface, in addition to the radial component Br. We find nonzero azimuthal magnetic fields at the source surface which dominate the variability in B(r, ϕ) at 1 AU and beyond. The averages 〈|Bϕ(Rs)|〉 and 〈|Br(Rs)|〉 inferred over solar cycle 23 were 0.44 ± 0.48 μT (4.4 ± 4.8 mG) and 120 ± 30 μT (1.2 ± 0.3 G) at the photosphere, respectively, where Rs equals one solar radius. While the surface magnetic field is closely radial on average as expected, it is sometimes over 20° from radial. Both Bϕ and Br vary smoothly on periods of order of a day, with evidence for relatively narrow current sheets, and vary differently with the solar cycle: Br(Rs) is correlated with the sunspot number while Bϕ(Rs) has a two‐level behavior. The typical fields |Br(Rs)| are consistent with previous estimates. This consistency, the finding of a linear relation between the data‐smoothing time period and the average transition time for each component and other arguments support the contention that theBϕ(Rs) fields found are intrinsic. Our results and model can account naturally for non‐Parker‐like magnetic field directions at 1 AU and allr above the source surface.

Characterizing sexual histories of women before formal sex-work in south India from a cross-sectional survey: implications for HIV/STI prevention

BackgroundInterventions designed to prevent HIV and STIs in female sex-workers (FSWs) reach women after they formally enter the sex-trade. We aimed to characterize the pattern of sexual behaviour among FSWs from first-sex to when they identify as sex-workers (transition period) in a region with traditional (historically characterized by dedication into sex-work at first-sex) and non-traditional forms of sex-work.MethodsWe conducted a cross-sectional survey of 246 traditional and 765 non-traditional FSWs across three districts in Karnataka, India. We performed univariate and multivariate logistic regression to profile FSWs most likely to engage in a commercial first-sex before identifying as a sex-worker. Sexual life-course patterns were distinguished using univariate and multivariate linear regression based on key events associated with length of transition period.ResultsOverall, 266 FSWs experienced a commercial first-sex, of whom 45.9% (95% CI: 38.2,53.7) continued a long-term relationship with the first partner. In adjusted analysis, traditional FSWs were more likely to experience a commercial first-sex (AOR 52.5, 95% CI: 27.4,100.7). The average transition time was 8.8 years (SD 3.9), but there was considerable variability between respondents. Among women who experienced a commercial first-sex, a slower transition was independently associated with non-traditional sex-work, the presence of long-term partnerships during the transition period, and ongoing partnerships at time of entry into sex-work. In the absence of a commercial first-sex, a faster transition was associated with traditional sex-work and the dissolution of long-term partnerships, while a slower transition was associated with the presence of long-term partnerships and widowhood. Only 18.5% (95% CI: 12.7,26.2) and 47.3% (95% CI: 32.7,62.3) of women reported ‘always’ condom use with their long-term and occasional partners during the transition period, respectively.ConclusionsFSWs identify as sex-workers several years after becoming sexually active, even when the first-sex is commercial in nature. Long-term partnerships are common after a commercial first-sex, and are associated with a delay in formally entering the sex-trade. The findings call for a better understanding of HIV/STI risk before FSWs identify as sex-workers, and an adaptive programme to reach this period of vulnerability.

Quantifying Dispersal and Connectivity of Surface Waters Using Observational Lagrangian Measurements

Abstract Probability distribution functions of displacement are central to Lagrangian statistics and the study of fluid dispersal. A method for computing marginal probability distributions of passive tracer dispersal from Lagrangian observations is developed. Using a pseudotrack approach, probability distributions for the domain of occupation and transit time are developed, complimenting more frequently used bulk statistics for average transit time and overall crossing probability. To demonstrate application of this technique to observations, likelihoods and time scales of dispersal from the Gulf Stream to the Azores are quantified using World Ocean Circulation Experiment (WOCE) Surface Velocity Program (SVP) near-surface drifter data for the years 1992–2008. Over observable time scales, the transit of a particle in the near-surface ocean from the Gulf Stream to the Azores occurs across a spectrum of time scales, from tens to hundreds of days, with an overall likelihood of 42% ± 4% and a mean time scale of 321 ± 41 days. The exclusion of measurements from drifters released after 1 January 2004 (which have been shown to potentially exhibit bias) slightly increases the overall likelihood of connection (49% ± 6%), consistent with recent surface current shifts in the northern North Atlantic, and increases the mean connection time scale (371 ± 52 days), potentially reflecting spurious acceleration of drifters in recent years. The method presented is general and applicable to a wide range of applications in physical and ecological oceanography.

Electric field dependence of charge carrier hopping transport within the random energy landscape in an organic field effect transistor

We extended our analytical effective medium theory [Phys. Rev. B 81, 045202 (2010)] to describe the temperature-dependent hopping charge carrier mobility at arbitrary electric fields in the large carrier density regime. Special emphasis was made to analyze the influence of the lateral electric field on the Meyer--Neldel (MN) phenomenon observed when studying the charge mobilities in thin-film organic field-effect transistors (OFET). Our calculations are based on the average hopping transition time approach, generalized for large carrier concentration limit finite fields, and taking into account also spatial energy correlations. The calculated electric field dependences of the hopping mobility at large carrier concentrations are in good agreement with previous computer simulations data. The shift of the MN temperature in an OFET upon applied electric field is shown to be a consequence of the spatial energy correlation in the organic semiconductor film. Our calculations show that the phenomenological Gill equation is clearly inappropriate for describing conventional charge carrier transport at low carrier concentrations. On the other hand a Gill-type behavior has been observed in a temperature range relevant for measurements of the charge carrier mobility in OFET structures. Since the present model is not limited to zero-field mobility, it allows a more accurate evaluation of important material parameters from experimental data measured at a given electric field. In particular, we showed that both the MN and Gill temperature can be used for estimating the width of the density of states distribution.

Describing the Highly Three Dimensional Right Ventricle Flow

Visualization of the three-dimensional flow within the Right Ventricle (RV) is a challenging issue due to the fully three-dimensional geometry of the ventricular cavity. To date proper characterization and quantification of the RV flow still remains incomplete, and techniques that can be easily applied to current medical imaging are scarce. A method for simulating the highly complex, multi directional flow within the RV is presented by coupling 4D echocardiography imaging with numerical simulations based on the Immersed Boundaries Method (IBM). A novel formulation for accurately computing the space-time distribution of the blood residence time inside the cavity is introduced. Results showed an initial compact vortex forming past the tricuspid orifice at early diastole that quickly breaks into a weakly turbulent flow pattern and rearranges, during systole, into a peculiar stream-wise vortex spinning out towards the pulmonary orifice. This arrangement is maintained when the Ejection Fraction (EF) is reduced from 58 to 32%. The average blood transit time is found to scale almost inversely proportional to the EF. A careful analysis of the residence time permitted to assess the relative significance of the different flow components (from the direct flow, with a residence time less than one heartbeat, to the residual volume, that stagnates in the ventricle) and their distribution in space.

Modeling on ion rejection using membranes comprising ultra-small radii carbon nanotubes

In this paper, we investigate the complete ion rejection using carbon nanotube membranes comprising ultra-small radii nanotubes. Three acceptance radii for a water molecule, a sodium ion and a chloride ion are determined assuming the continuous approximation. Given the acceptance radii, we may confine the scope of the nanotube radius so that only water molecules can pass through but the heavier sodium and chloride ions are repulsed from the nanotube ends. We assume that the collective motion of water molecules inside a sufficiently long nanotube is driven by atomic vibrations so that classical phonon theory might be used to deduce the average water transit time inside the nanotube for ion rejection. We predict that for carbon nanotube membranes comprising nanotubes of radii lying between 3.4 and 3.9 A, only water molecules will pass through, and sodium and chloride ions will not, which together using phonon theory, we deduce that the smaller the nanotube radius, the lower the average water transit time and the higher the efficiency of the membrane for ion rejection purposes. The present theoretical approach has the merit of rapid computational times and indicates those nanotube radii where future experimental work might be focussed.

The Relationship between Physical Activity Level and Completion Rate of Small Bowel Examination in Patients Undergoing Capsule Endoscopy

Capsule endoscopy (CE) allows direct examination of the small bowel in a safe, noninvasive and well-tolerated manner. Nonetheless, experience indicates failure to reach the cecum in 20-30% of patients within the 8 hour battery life. Attempts to improve the completion rate (CR) as defined by reaching the cecum have been unsuccessful. This study was to investigate the relationship between patients' physical activity and CR. Between January 2009 and January 2010, 76 patients (44 men, 32 women; median age 64.5 yr) underwent CE for the diagnosis of small intestinal disorders. Indications for CE were obscure gastrointestinal bleeding/anemia (62 cases), others (14 cases). Patients were divided into an outpatient group (n=23), mild bed rest group (n=35) and strict bed rest group (n=18). For all patients, the average gastric transit time was 65.5 minutes, small bowel transit time was 301.4 minutes and the CR was 86.8%. However, the CR was 100% (23/23) in the outpatient group, an 85.7% (30/35) in the mild bed rest group, and 72.2% (13/18) in the strict bed rest group. The CR increased with physical activity of patients by Cochran-Armitage Trend Test (p=0.009). In multivariate logistic regression analyses, low physical activity was a significant risk factor for failure to reach the cecum during CE examination; adjusted OR: 3.39, 95% CI: 1.01-11.42 (p=0.048). Our observations suggested that increasing physical activity would increase the likelihood of a complete bowel examination by CE. Further, for CE, inconvenient bowel preparations like the use of polyethylene glycol may be avoided.

A Method for the Control of Multigrasp Myoelectric Prosthetic Hands

This paper presents the design and preliminary experimental validation of a multigrasp myoelectric controller. The described method enables direct and proportional control of multigrasp prosthetic hand motion among nine characteristic postures using two surface electromyography electrodes. To assess the efficacy of the control method, five nonamputee subjects utilized the multigrasp myoelectric controller to command the motion of a virtual prosthesis between random sequences of target hand postures in a series of experimental trials. For comparison, the same subjects also utilized a data glove, worn on their native hand, to command the motion of the virtual prosthesis for similar sequences of target postures during each trial. The time required to transition from posture to posture and the percentage of correctly completed transitions were evaluated to characterize the ability to control the virtual prosthesis using each method. The average overall transition times across all subjects were found to be 1.49 and 0.81 s for the multigrasp myoelectric controller and the native hand, respectively. The average transition completion rates for both were found to be the same (99.2%). Supplemental videos demonstrate the virtual prosthesis experiments, as well as a preliminary hardware implementation.

Temporally resolved ion velocity distribution measurements in a radio-frequency plasma sheath

The ion velocity distribution function (IVDF) above and within a radio-frequency (RF) biased plasma sheath is studied experimentally with a pulsed laser-induced fluorescence diagnostic in an industrial plasma etch tool. Temporally resolved measurements taken at eight different phases of the 2.2 MHz bias waveform show that the ion dynamics vary dramatically throughout the RF cycle (the ratio of the average ion transit time through the sheath to the RF period is τion/τRF = 0.3). The position of the presheath/sheath edge is constant throughout the RF cycle and the time-averaged ion flux is conserved within the sheath region. The characteristic bimodal structure of the time-averaged ion distributions found in previous experiments is observed to arise from the time-dependent ion dynamics, in accord with existing theory. The large temporal variation of the IVDF has implications for the plasma chemistry and etching quality.

Distribution of pellets in the gastrointestinal tract. The influence on transit time exerted by the density or diameter of pellets.

The influence on transit time exerted by the density or diameter of pellets has been established in six ileostomy subjects. An increase in density from 1.0 to 1.6 significantly increased the average transit time of pellets in the small intestine. The average transit time for the light and heavy pellets being 7 and 25 h respectively. The diameter of pellets is of minor significance. The findings suggest the use of density as a means of modifying the period of absorption of controlled-release pellets.

Effects of epidural morphine on gastrointestinal transit in unmedicated horses

ObjectiveTo evaluate the effect of epidural morphine on gastrointestinal (GI) motility in horses. Study designRandomly ordered crossover design. AnimalsSix healthy adult horses weighing 585 ± 48 kg (mean ± SD). MethodsHorses were randomly assigned to receive either 0.2 mg kg−1 morphine or an equal volume (0.04 mL kg−1) of saline epidurally (the first inter coccygeal space) with 2 weeks between treatments. The horses were stabled, fed a standardized diet and allowed water ad libitum throughout the duration of the study. Radiopaque spheres were administered by stomach tube. Xylazine 0.2 mg kg−1 intravenously was administered prior to epidural injection. Heart rate, respiratory rate, GI sounds score and behavior score were recorded before drug administration and after epidural injection at 4, 8, 12, 18, 24 hours and every 12 hours thereafter for 6 days. Feces were weighed, radiographed and the number of spheres counted. Data were analyzed using a mixed effect model. ResultsAt no time did horses exhibit signs of colic or show significant differences between treatments regarding heart rate, respiratory rate, GI sounds score, behavior score, or cumulative number of spheres. The concentration of spheres per kg of feces was significantly lower (p < 0.05) for the morphine group at 18 and 24 hours. Using the centroid of the curves (spheres kg−1 plotted versus time) the average transit time after saline epidural was 38 hours and after morphine it was 43 hours. The weight of feces hour−1 was significantly lower (p < 0.05) at only 4 and 8 hours after morphine. Conclusions and clinical relevanceEpidural morphine, at a dose of 0.2 mg kg−1, temporarily reduced GI motility but did not cause ileus or colic in this small group of healthy unfasted horses. Care should be taken when extrapolating these data to situations in which other factors may also affect GI motility.

What is the fate of the river waters of Hudson Bay?

We examine the freshwater balance of Hudson and James bays, two shallow and fresh seas that annually receive 12% of the pan-Arctic river runoff. The analyses use the results from a 3-D sea ice-ocean coupled model with realistic forcing for tides, rivers, ocean boundaries, precipitation, and winds. The model simulations show that the annual freshwater balance is essentially between the river input and a large outflow toward the Labrador shelf. River waters are seasonally exchanged from the nearshore region to the interior of the basin, and the volumes exchanged are substantial (of the same order of magnitude as the annual river input). This lateral exchange is mostly caused by Ekman transport, and its magnitude and variability are controlled by the curl of the stress at the surface of the basin. The average transit time of the river waters is 3.0 years, meaning that the outflow is a complex mixture of the runoff from the three preceding years.