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Objective: Arteriovenous fistula (AVF) operations are the most common method to facilitate hemodialysis in patients with chronic renal failure. The longevity of AVF is vital in patients undergoing hemodialysis. We investigated the effect of Transit Time Flow Meter (TTFM) use on AVF patency. Methods: 108 patients (42 in the study group, 66 in the control group) who underwent AVF formation for the first time in the last five years were included in the study. In the measurements made with TTFM, if the pulsatility index (PI) was >5 and the mean flow value was <30 mL/min, AVFs were considered insufficient. Results: Age, gender, lowdensity lipoprotein values (LDL), non-dominant extremity, and accompanying peripheral artery disease in the study group of patients were similar, and smoking in the study group and hypertension in the control group were the most common risk factors. PI and mean flow rates with TFTM in the study group were within the normal range. No statistically significant difference was found in the AVF patency rates when we compared the different periods between groups. However, when evaluating the AVF patency of the groups in the whole period, it was determined that the patency of the patients in the study group was better than the control, and this finding was statistically significant. Conclusion: Intraoperative use of TTFM helps detect AVF dysfunction. This method provides a longer vascular patency time. Increases patient comfort by prolonging the function and life of the AVF. [ABSTRACT FROM AUTHOR]

The purpose of this research is to address the multi-objective problem of minimising overall cost, transit time, and CO2e emissions in Pakistan's railway system. A multi-objective problem is designed using integer linear programming and reinforcement learning. This study is generally applied to transportation network design and planning challenges that need balancing various objectives. Integer linear programming is used to design a multi-objective problem, and reinforcement learning is used to identify the shortest path for a railway network. Pareto front solutions are also generated using the genetic algorithm. Using the Q-learning method, we estimated and analysed the cost, time, and greenhouse gas emissions of current and future railway networks. According to our findings, the shortest railway track connecting Pakistan's provinces of Punjab and Sindh outperforms the current railways (Fareed Express) in terms of cost, time and emissions. A cost, transit time, and CO2e emission reduction of 13% is possible when compared to the existing railway line. [ABSTRACT FROM AUTHOR]

The transit time on roads is essential to the intelligent traffic system in urban areas. If the transit time is predicted accurately, the traffic management system can work more effectively, and the public will enjoy rational travel strategies. However, the traditional prediction algorithms for transit time cannot adapt well to the complex road network and the sparsely deployed sensors in cities. By contrast, the particle filtering (PF) algorithm has strong adaptability to such a stochastic nonlinear problem. Therefore, this paper measures the spatiotemporal similarity between historical data on different roads at different moments with speed matrices, aiming to prevent the data degradation in transit time prediction. Besides, the PF algorithm was innovatively applied to build a transit time prediction model on urban roads. The traffic trend in historical data was modelled with weighted particles. Finally, the effectiveness of our algorithm was demonstrated through an empirical analysis. The results show that our algorithm outperforms the other transit time prediction algorithms in prediction accuracy and computing performance. [ABSTRACT FROM AUTHOR]

Vessel speed optimisation has, in recent years, been recognised as a practical and important cost reduction strategy in the maritime shipping industry. This paper takes a new look at the trade-off between sailing speed and the number of vessels required to maintain a given service frequency. Fundamental insights will be revealed, shedding light on how much (or limited) choice there really is when deciding on the number of vessels to deploy. To demonstrate the significance of our revelations in an optimisation setting, a new vessel speed optimisation model is proposed. A case study shows that by incorporating our findings, computation times can be reduced dramatically, up to over 4400 times faster. This computational benefit is especially timely in the current era of alliances and consolidation in the container shipping industry, when instances of the vessel speed optimisation problem can only be expected to grow in size. [ABSTRACT FROM AUTHOR]

The mean transit time (MTT) is an important descriptor of water storage and release dynamics in watersheds. Although MTT studies are numerous for many regions around the world, they are rare for prairie watersheds where seasonally cold or dry conditions require adequate methodological choices towards MTT estimation, especially regarding the handling of sparse data records and tracer selection. To examine the impact of such choices, we used timeseries of δ18O and δ2H from two contrasted years (2014 and 2015) and relied on two metrics and two modelling methods to infer MTTs in prairie watersheds. Our focus was on nested outlets with different drainage areas, geologies, and known run‐off generation mechanisms. The damping ratio and young water fraction (i.e., the fraction of streamflow with transit times lesser than 3 months) metrics, as well as the sine‐wave modelling and time‐based convolution modelling methods, were applied to year‐specific data. Results show that young water fractions and modelled MTT values were, respectively, larger and smaller in 2014, which was a wet year, compared with that in 2015. In 2014, most outlets had young water fractions larger than 0.5 and MTT values lesser than 6 months. The damping ratio, young water fraction, and sine‐wave modelling methods led to convergent conclusions about watershed water storage and release dynamics for some of the monitored sites. Contrasting results were, however, obtained when the same method was applied using δ2H instead of δ18O, due to differing evaporation fractionation, or when the time‐based convolution modelling method was used. Some methods also failed to provide any robust results during the dry year (i.e., 2015), highlighting the difficulty in inferring MTTs when data are sparse due to intermittent streamflow. This study therefore allowed the formulation of empirical recommendations for MTT estimation in prairie environments as a function of data availability and antecedent wetness conditions. [ABSTRACT FROM AUTHOR]

Abstract The ability of pulse-echo ultrasound transit time spectroscopy (PE-UTTS) to improve the axial and lateral spatial resolution of an ultrasound B-scan image was investigated in this study. An acrylic step-wedge sample was used, consisting of 6 axial steps of both 0.2 and 0.1 mm height, at lateral separations ranging from 0.75 mm to 24 mm. The sample was immersed in water and conventional B-scan images obtained using an industrial Olympus Omniscan system with 2.25, 5 and 10 MHz transducers along with a clinical GE Voluson scanner with a 12 MHz transducer. PE-UTTS B-scan images were also created utilising the Omniscan RF data. From a qualitative perspective, the PE-UTTS B-scan images, at all three frequencies, demonstrated significantly greater axial and lateral spatial resolution than the corresponding conventional B-scan images. Quantitative analysis was performed by comparing the actual depth and length of the acrylic step surfaces with those measured from the conventional and PE-UTTS B-scan images. Of particular note, the depth accuracy for PE-UTTS at 10 MHz was greater than the conventional clinical B-scan at 12 MHz, being 99.90–99.94% compared to 95.95–97.77%. Lateral accuracy was also higher for PE-UTTS at 10 MHz, ranging from 86.67% to 96.67%, compared to 40.00% to 84.58% for the conventional scanner at a frequency of 12 MHz. This scientific study suggests that PE-UTTS has potential to improve clinical ultrasound B-scan image fidelity. [ABSTRACT FROM AUTHOR]

Surface-emitted tracers with different dependencies on transit time (e.g., due to chemical loss or time-dependent boundary conditions) carry independent pieces of information on the age of air spectrum (the distribution of transit times from the surface). This paper investigates how and to what extent knowledge of tracer concentrations can be used to retrieve the age spectrum. Since the mixing ratios of the tracers considered depend linearly on the transit time distribution, the question posed can be formulated as a linear inverse problem of small dimension. An inversion methodology is introduced, which does not assume a prescribed shape for the spectrum. The performance of the approach is first evaluated on a constructed set of artificial radioactive tracers derived from idealized spectra. Hereafter, the inversion method is applied to outputs of a chemistry–transport model. The latter experiment highlights the limits of inversions using only parent radioactive tracers: they are unable to retrieve fine-scale structures such as the annual cycle. Improvements can be achieved by including daughter decaying tracers and tracers with an annual cycle at the surface. This study demonstrates the feasibility of retrieving the age spectrum from tracers and has implications for transport diagnosis in models and observations. [ABSTRACT FROM AUTHOR]

Watershed mean transit times (MTTs) are used to characterize the hydrology of watersheds. Watershed MTTs could have important implications for water quality, as relatively long MTTs imply lengthier water retention, thereby allowing more time for pollutant transformation and more moderate release of pollutants into streams. Although estimates of MTTs are common for undisturbed watersheds, only a few studies to date have applied MTT models to urbanized watersheds. In the present study, we use δ18O to compare estimates of MTTs for paired suburban‐industrial and agricultural watersheds in Toronto, Canada. Although differences in precipitation δ18O between the two watersheds were negligible, there were significant differences in stream δ18O, suggesting differences in water transport pathways. Less damping between input precipitation δ18O and output stream δ18O in the suburban‐industrial watershed indicated a larger streamflow contribution from quick‐flow transport pathways. We applied three transit time models to quantify MTTs. Considering overall model fit, root mean square error, and uncertainty in model parameters, the exponential model performed the best of the three models. Optimized MTTs using this distribution across the suburban‐industrial subwatersheds ranged from 2.1 to 2.9 months, whereas those in the agricultural subwatersheds ranged from 2.7 to 7.5 months. The relatively small difference between urban and agricultural MTTs coincides with observations elsewhere. Model efficiencies could potentially be improved, and MTTs estimated more reliably, with a higher sampling frequency that captures a greater volume of overall discharge. Overall, this work provides a distinct first glimpse into the separation of MTTs between paired watersheds with such a large contrast in their land use. [ABSTRACT FROM AUTHOR]

Clamp-on transit-time ultrasonic flowmeters (UFMs) suffer from poor accuracy compared with spool-piece UFMs due to uncertainties that result from the in-field installation process. One of the important sources of uncertainties is internal pipe wall roughness which affects the flow profile and also causes significant scattering of ultrasound. This paper purely focuses on the parametric study to quantify the uncertainties (related to internal pipe wall roughness) induced by scattering of ultrasound and it shows that these effects are large even without taking into account the associated flow disturbances. The flowmeter signals for a reference clamp-on flowmeter setup were simulated using 2-D finite element analysis including simplifying assumptions (to simulate the effect of flow) that were deemed appropriate. The validity of the simulations was indirectly verified by carrying out experiments with different separation distances between ultrasonic probes. The error predicted by the simulations and the experimentally observed errors were in good agreement. Then, this simulation method was applied on pipe walls with rough internal surfaces. For ultrasonic waves at 1 MHz, it was found that compared with smooth pipes, pipes with only a moderately rough internal surface (with 0.2-mm rms and 5-mm correlation length) can exhibit systematic errors of 2% in the flow velocity measurement. This demonstrates that pipe internal surface roughness is a very important factor that limits the accuracy of clamp on UFMs. [ABSTRACT FROM AUTHOR]

High power coherent electromagnetic radiation of a millimeter waveband is a tough research topic of plasma physics. In axial millimeter wave electromagnetic radiation devices, low power capacity and mode competition limited the output power. The radial structure is a promising candidate to realize high power millimeter wave radiation. Structural characteristics of a radial Ka-band high power millimeter wave transit time oscillator (TTO) are studied in this paper. Analysis without an electron beam indicates that if the average radius of radial cavities is increased, the mode of the stimulated field will not change, the power capacity will be improved, and the quality factor due to ohmic loss will remain unchanged. Particle-in-cell simulation proves that, for radial millimeter wave TTO, increasing the radius of the cathode and keeping sizes of the other parts unchanged, the output power will be increased, the efficiency will remain the same, and electric field growth will be slower than that in axial devices. Besides, taking ohmic loss into consideration, the efficiency will increase to a stable value. Therefore, by this method, high power coherent electromagnetic radiation in a millimeter wave can be realized. [ABSTRACT FROM AUTHOR]

Abstract Understanding the sources and transit times of water that generates streamflow in headwater streams is important for understanding catchment functioning. This study determines the water sources and transit times in first-order streams from a temperate rainforest in the Otway Ranges, southeast Australia. Comparison of the major ion geochemistry of soil water, water flowing through soil pipes (macropores), and groundwater from the riparian zone adjacent to the stream suggests that water from soil pipes is the major contributor to streamflow. The tritium (3H) activities of the stream water are between 1.80 and 2.06 TU, the water from the soil pipes has 3H activities between 1.80 and 2.25 TU, the riparian zone groundwater has 3H activities of 1.35–2.39 TU, and one sample of soil water has a 3H activity of 2.22 TU. These 3H activities are significantly lower than those of local modern rainfall (2.6–3.0 TU), and mean transit times calculated using a range of lumped parameter models are between 3 and 57 years. These estimates are consistent with the major ion and stable isotope data, which imply that mean transit times were sufficiently long to allow weathering of minerals and/or organic matter and evapotranspiration to occur. The long mean transit times imply that water flows in this upper catchment are buffered against year-on-year variations in rainfall, but may change due to longer-term variations in rainfall or landuse. Graphical abstract Image 1 Highlights • Upper catchment stream water provided largely by macropores. • Riparian groundwater and some soil water isolated from the stream. • Mean transit times of all waters are between 3 and 57 years. • Long mean transit times imply resilience to short-term climate fluctuations. [ABSTRACT FROM AUTHOR]

The South China Sea (SCS) is the largest semienclosed marginal sea in the western Pacific (WP) and connects to the west Pacific through the Luzon Strait (LU). In this study, we use the observation of transient tracer chlorofluorocarbon‐12 (CFC‐12) to calculate the ventilation time scales of the SCS, LU, and WP. The CFC‐12 and oxygen data are used together to identify the sandwiched structure vertically of the flows across the LU. The CFC‐12 and oxygen distributions reveal a pronounced decrease westward across the LU and a slight decrease southward in the transport of the SCS. The mean age gradient of the salinity minimum (Smin) water between the WP and the northern SCS could be a consequence of intensive mixing and entrainment of the inflow water from the WP. An expected difference in age between the LU and SSCS is verified to reflect the transit time for the given water layers in the SCS. Thus, a mean transit time of 77 ± 20 years is estimated for the intermediate water in the SCS interior. Plain Language Summary: In this study, we present CFC‐12 data of seawater, which were collected in the South China Sea and western Pacific during September and October 2016. The CFC‐12, together with the oxygen and hydrographic data, are used to provide general picture of tracer distributions and ventilation time scales of the South China Sea, Luzon Strait, and western Pacific. The CFC‐12 and oxygen data are used together as complementary tracers and identify the sandwiched structure vertically of the flows across the Luzon Strait. We calculate the mean ages using the transit time distributions method to quantify the time scale of waters. An expected difference in age between the Luzon Strait and southern South China Sea is verified to reflect the transit time for the given water layers in the South China Sea. Thus, a mean transit time of ~77 years is estimated for the intermediate water in the South China Sea interior. Key Points: The CFC‐12 and oxygen data are used together to identify the sandwiched structure vertically of the flows across the Luzon StraitThe ventilation times are estimated for subsurface and intermediate layers in the South China Sea, Luzon Strait, and western PacificThe mean transit time of approximately 77 years is estimated for the core of the intermediate water in the SCS interior [ABSTRACT FROM AUTHOR]

The question of why some types of organic matter are more persistent while others decompose quickly in soils has motivated a large amount of research in recent years. Persistence is commonly characterized as turnover or mean residence time of soil organic matter (SOM). However, turnover and residence times are ambiguous measures of persistence, because they could represent the concept of either age or transit time. To disambiguate these concepts and propose a metric to assess SOM persistence, we calculated age and transit time distributions for a wide range of soil organic carbon models. Furthermore, we show how age and transit time distributions can be obtained from a stochastic approach that takes a deterministic model of mass transfers among different pools and creates an equivalent stochastic model at the level of atoms. Using this approach we show the following: (1) Age distributions have relatively old mean values and long tails in relation to transit time distributions, suggesting that carbon stored in soils is on average much older than carbon in the release flux. (2) The difference between mean ages and mean transit times is large, with estimates of soil organic carbon persistence on the order of centuries or millennia when assessed using ages and on the order of decades when using transit or turnover times. (3) The age distribution is an appropriate metric to characterize persistence of SOM. An important implication of our analysis is that random chance is a factor that helps to explain why some organic matter persists for millennia in soil. Key Points: Persistence of organic matter in soils can be characterized by age distributions of carbonStochastic processes can help to explain the persistence of soil organic matterCarbon persists from centuries to millennia in soils when assessed with age distributions while for decades when assessed with transit time [ABSTRACT FROM AUTHOR]

A new method is proposed for obtaining cerebral perfusion measurements whereby blood oxygen level dependent (BOLD) MRI is used to dynamically monitor hyperoxia-induced changes in the concentration of deoxygenated hemoglobin in the cerebral vasculature. The data is processed using kinetic modeling to yield perfusion metrics, namely: cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). Ten healthy human subjects were continuously imaged with BOLD sequence while a hyperoxic (70% O 2 ) state was interspersed with baseline periods of normoxia. The BOLD time courses were fit with exponential uptake and decay curves and a biophysical model of the BOLD signal was used to estimate oxygen concentration functions. The arterial input function was derived from end-tidal oxygen measurements, and a deconvolution operation between the tissue and arterial concentration functions was used to yield CBF. The venous component of the CBV was calculated from the ratio of the integrals of the estimated tissue and arterial concentration functions. Mean gray and white matter measurements were found to be: 61.6 ± 13.7 and 24.9 ± 4.0 ml 100 g −1  min −1 for CBF; 1.83 ± 0.32 and 1.10 ± 0.19 ml 100 g −1 for venous CBV; and 2.94 ± 0.52 and 3.73 ± 0.60 s for MTT, respectively. We conclude that it is possible to derive CBF, CBV and MTT metrics within expected physiological ranges via analysis of dynamic BOLD fMRI acquired during a period of hyperoxia. [ABSTRACT FROM AUTHOR]

Abstract: Transit time distributions (TTDs) are crucial descriptors of flow and transport processes in catchments, which can be determined from stable water isotope data. Recently, the young water fraction (Fyw) has been introduced as an additional metric derivable from seasonal isotope cycles. In this study, we calculated Fyw and TTDs using monthly isotope data from 24 contrasting subcatchments in a mesoscale catchment (3,300 km2) in Germany. Fyw ranged from 0.01 to 0.27 (mean = 0.11) and was smallest in mountainous catchments. Assuming gamma‐shaped TTDs, we determined stationary TTDs with the convolution integral method for each subcatchment. The convolution integral was first calibrated against the isotope data only (i.e., traditional calibration) and, second, using a multiobjective calibration with the Fyw estimates as an additional constraint. This yielded largely differing TTD parameters even for neighboring catchments, with Fyw values below 0.1 generally involving a delayed peak in TTDs (i.e., gamma‐distribution shape parameter > 1). While the traditional calibration resulted in large uncertainties in TTD parameters, these uncertainties were reduced with the multiobjective calibration, thereby improving the assessment of mean transit times (2 years on average, ranging between 9.6 months and 5.6 years). This highlights the need for uncertainty assessment when using simple isotope models and shows that the traditional calibration might not yield an optimum solution in that it may give a TTD nonconsistent with Fyw. Given the robustness of Fyw estimates, isotope models should thus aim at accurately describing both Fyw and measured isotope data in order to improve the description of flow and transport in catchments. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the links between groundwater age, runoff generation processes, and their effects on stream water transit time (TT) is a major research challenge. Here we present new tritium age dating and hydrogeological characterization from 40 bedrock wells drilled at the intensively studied Maimai Experimental Watershed in New Zealand. We investigated the extent, dynamics, and age of the groundwater in a 4.5 ha headwater catchment over a 400 day period. In particular, we explored the controls of bedrock structure on aquifer dynamics, the aquifer flow domain and its influence on time‐varying stream water TT. We show that low permeability hillslope bedrock minimizes deep recharge, thereby regulating groundwater age, stream water MTT, and surface water‐groundwater interaction. Two distinct hydrologic units can represent catchment storage: shallow young soil storage and deep much older bedrock groundwater. Groundwater ages near discharge zones were up to 23 years compared to soil water ages that ranged between 0.1 and 0.5 years. This difference in age for the two main storages resulted in contrasting seasonal stream water TT response. During the 8 month wet season, stream water TT was young and stable while stream water TT in the slightly drier summer season was highly dynamic. These qualitative field observations are a process exemplar that support the Berghuijs and Kirchner (2017) quantitative descriptions of preferential release of young streamflow; and for the Maimai catchment, support the notion that most groundwater is exchanged only slowly with the surface and is therefore relatively old. [ABSTRACT FROM AUTHOR]

In a queueing system involving multiple service windows, choice behavior is a significant concern. This paper incorporates the choice of service windows into a queueing model with a floor represented by discrete cells. We contrived a logit-based choice algorithm for agents considering the numbers of agents and the distances to all service windows. Simulations were conducted with various parameters of agent choice preference for these two elements and for different floor configurations, including the floor length and the number of service windows. We investigated the model from the viewpoint of transit times and entrance block rates. The influences of the parameters on these factors were surveyed in detail and we determined that there are optimum floor lengths that minimize the transit times. In addition, we observed that the transit times were determined almost entirely by the entrance block rates. The results of the presented model are relevant to understanding queueing systems including the choice of service windows and can be employed to optimize facility design and floor management. [ABSTRACT FROM AUTHOR]

OBJECTIVE To evaluate gastrointestinal transit times in red-tailed hawks (Buteo jamaicensis) by use of contrast fluoroscopic imaging and investigate the effect of falconry hooding in these hawks on gastrointestinal transit time. DESIGN Prospective, randomized, blinded, complete crossover study. ANIMALS 9 healthy red-tailed hawks. PROCEDURES Hawks were gavage-fed a 30% weight-by-volume barium suspension (25 mL/kg [11.3 mL/lb]) into the crop. Fluoroscopic images were obtained at multiple time points after barium administration. Time to filling and emptying of various gastrointestinal tract organs and overall transit time were measured. The effect of hooding (hooded vs nonhooded) on these variables was assessed in a randomized complete crossover design. RESULTS In nonhooded birds, overall gastrointestinal transit time ranged from 30 to 180 minutes (mean ± SD, 100 ± 52 min). Time to complete crop emptying ranged from 30 to 180 minutes (83 ± 49 min). Contrast medium was present in the ventriculus in all birds within 5 minutes of administration and in the small intestines within 5 to 15 minutes (median, 5 min). Hooding of redtailed hawks resulted in a significant delay of complete crop emptying (no hood, 83 ± 49 minutes; hood, 133 ± 4 8 minutes), but no significant effects of hooding were found on other measured variables. CONCLUSIONS AND CLINICAL RELEVANCE These results indicated that overall gastrointestinal transit times are faster in red-tailed hawks than has been reported for psittacines and that the use of a falconry hood in red-tailed hawks may result in delayed crop emptying. Hooding did not exert significant effects on overall gastrointestinal transit time in this raptorial species. [ABSTRACT FROM AUTHOR]

In certain types of heterojunction bipolar transistors (HBTs), the carrier transit time associated with the base-collector (BC) space-charge region constitutes a significant contribution to the total transit time. In many compact models, the low-current BC transit time is lumped in with the total low-current transit time and often assumed to be constant—dependent only on the collector width and material saturation velocity. This assumption, however, is insufficient for modeling high-voltage Si-based HBTs as well as for III-V HBTs, where the negative differential mobility (NDM) effect can become relevant in high-speed low-power circuits. This paper presents a closed-form solution for the low-current collector transit time based on a novel accurate analytical velocity-field formulation, covering both group IV and group III-V semiconductor materials. The new solution includes the NDM effect and is suitable for implementation in compact models, and its relevance and accuracy are demonstrated for both TCAD simulated and measured data. [ABSTRACT FROM PUBLISHER]

Background Gastrointestinal symptoms are common in the general population and may originate from disturbances in gut motility. However, fundamental mechanistic understanding of motility remains inadequate, especially of the less accessible regions of the small bowel and colon. Hence, refinement and validation of objective methods to evaluate motility of the whole gut is important. Such techniques may be applied in clinical settings as diagnostic tools, in research to elucidate underlying mechanisms of diseases, and to evaluate how the gut responds to various drugs. A wide array of such methods exists; however, a limited number are used universally due to drawbacks like radiation exposure, lack of standardization, and difficulties interpreting data. In recent years, several new methods such as the 3D-Transit system and magnetic resonance imaging assessments on small bowel and colonic motility have emerged, with the advantages that they are less invasive, use no radiation, and provide much more detailed information. Purpose This review outlines well-established and emerging methods to evaluate small bowel and colonic motility in clinical settings and in research. The latter include the 3D-Transit system, magnetic resonance imaging assessments, and high-resolution manometry. Procedures, indications, and the relative strengths and weaknesses of each method are summarized. [ABSTRACT FROM AUTHOR]

Modeling commuters' choice behavior in response to transportation demand management (TDM) helps in predicting the consequences of TDM policies. Although research looking at choice behavior has evolved to investigate preference heterogeneity in response to factors influencing mode choice, as far as we know, no study has considered taste variation across commuters in response to multiple TDM policies. This paper investigates the presence of systematic preference heterogeneity across commuters, in response to the TDM policies that can be explained by their socio-economic or commuting-related characteristics. Analysis is based on results of a stated preference survey developed using a Design of Experiments approach. Five policies were assessed in order to study the impact they had on how commuters chose their mode of transportation. These include increasing parking cost, increasing fuel cost, implementing cordon pricing, reducing transit time and improving access to transit facilities. For the sake of assessing both systematic and random preference heterogeneity across car commuters, a form of the Mixed Multinomial Logit (MMNL) model that identifies sources of heterogeneity and consequently makes the choice models less restrictive in considering both systematic and random preference variation across individuals was developed. The sample includes 366 individuals who regularly commute to their workplace in the city center of Tehran, Iran. The likelihood function value of this model shows a significant improvement compared to the base MNL model, using the same variables. The MMNL model shows that taste variation across the studied commuters results in differences in influences estimated for three policies: increasing parking cost, reducing transit time and improving access to transit. The analysis examines several distributions for random parameters to test the impacts of restricting distributions to allow for only normality. The results confirm the potential to improve model fit with alternative distributions. [ABSTRACT FROM AUTHOR]

It is postulated that hemodynamic changes occur in the distal vascular bed post-deployment of Pipeline Embolization Devices (PEDs). In this paper, we evaluate changes in the contrast transit times (TTs) on digital subtraction angiography (DSA) post-PED interventions. DSA films were analyzed using custom-made software for the time-density relationship at baseline and compared to post-PED deployment. All analyses were performed within the middle cerebral artery (MCA) M1 segment. Analyses included TT10%-100% (time needed for the contrast to change from 10% image intensity to 100%), TT100%- 10%, and TT25%-25%. Forty-four patients were included. We found a significant decrease in TT10%-100% (2.79 to 2.24 seconds, p<0.001) post-PED. There was a significant correlation between the percentage change in TT10%-100% and aneurysm size (p=0.02). There was also a significant decrease in TT25%-25% (7.07 to 6.41 seconds, p=0.02) post-PED. Moreover, there was a significant correlation between the absolute or percentage changes in TT25%-25% and aneurysm size (rho=0.54, p=0.05 and rho=0.29, p=0.05, respectively). Statistically significant distal intracranial hemodynamic changes occur post-PED deployment. These hemodynamic changes appear to be more pronounced with large and giant aneurysms. [ABSTRACT FROM AUTHOR]

This study presents ultrasound transit time technique (UTTT) measurements of single Ar bubbles rising in GaInSn under an applied magnetic field. Two setups were used to analyze the bubble rise, which led to differently oriented zig-zag trajectories. UTTT is able to visualize the bubble trajectory and to measure the variations of the apparent bubble diameters associated with the zig-zag trajectory. Due to the straightening of the bubble trajectories with increasing magnetic field, an increase of the apparent bubble diameter was detected. [ABSTRACT FROM AUTHOR]

Let T be an infinite rooted tree with weights $$w_e$$ assigned to its edges. Denote by $$m_n(T)$$ the minimum weight of a path from the root to a node of the nth generation. We consider the possible behaviour of $$m_n(T)$$ with focus on the two following cases: we say T is explosive if and say that T exhibits linear growth if We consider a class of infinite randomly weighted trees related to the Poisson-weighted infinite tree, and determine precisely which trees in this class have linear growth almost surely. We then apply this characterization to obtain new results concerning the event of explosion in infinite randomly weighted spherically-symmetric trees, answering a question of Pemantle and Peres (Ann Probab 22(1), 180-194, 1994). As a further application, we consider the random real tree generated by attaching sticks of deterministic decreasing lengths, and determine for which sequences of lengths the tree has finite height almost surely. [ABSTRACT FROM AUTHOR]

We report on a simulation for an aluminum gallium nitride (AlGaN)/gallium nitride (GaN) resonant tunneling diode (RTD) with a step heterojunction emitter spacer (SHES) at room temperature. An SHES and low Al component barriers were introduced in to AlGaN/GaN RTDs to improve the electronic injection efficiency in to the emitter, reduce the transit time in the collector depletion region, and achieve lattice matching. The substitution of the emitter spacer for the SHES alters the dominant transport mechanism, increases the tunneling current, and restrains the thermionic current. As a result, the peak current was 1.683 A at 0.39 V and the peak-to-valley current difference was 0.93 A. [ABSTRACT FROM PUBLISHER]

Summary Understanding how water moves through catchments – from the time it enters as precipitation to when it exits via streamflow – is of fundamental importance to understanding hydrological and biogeochemical processes. A basic descriptor of this routing is the Transit Time Distribution (TTD) which is derived from the input–output behavior of conservative tracers, the mean of which represents the average time elapsed between water molecules entering and exiting a flow system. In recent decades, many transit time studies have been conducted, but few of these have focused on snow-dominated catchments. We assembled a 10-year time series of isotopic data (δ 18 O and δ 2 H) for precipitation and stream water to estimate the characteristics of the transit time distribution in a boreal catchment in northern Sweden. We applied lumped parameter models using a gamma distribution to calculate the Mean Transit Time (MTT) of water over the entire period of record and to evaluate how inter-annual differences in transit times relate to hydroclimatic variability. The best fit MTT for the complete 10-year period was 650 days (Nash–Sutcliff Efficiency = 0.65), while the best fit inter-annual MTT ranged from 300 days up to 1200 days. Whilst there was a weak negative correlation between mean annual total precipitation and the annual MTT, this relationship was stronger ( r 2 = 0.53, p = 0.02) for the annual rain water input. This strong connection between the MTT and annual rainfall, rather than snowmelt, has strong implications for understanding future hydrological and biogeochemical processes in boreal regions, given that predicted warmer winters would translate into a greater proportion of precipitation falling as rain and thus shorter MTT in catchments. Such a change could have direct implications for the export of solutes and pollutants. [ABSTRACT FROM AUTHOR]

We develop a theory for transit times and mean ages for nonautonomous compartmental systems. Using the McKendrick-von Förster equation, we show that the mean ages of mass in a compartmental system satisfy a linear nonautonomous ordinary differential equation that is exponentially stable. We then define a nonautonomous version of transit time as the mean age of mass leaving the compartmental system at a particular time and show that our nonautonomous theory generalises the autonomous case. We apply these results to study a nine-dimensional nonautonomous compartmental system modeling the terrestrial carbon cycle, which is a modification of the Carnegie-Ames-Stanford approach model, and we demonstrate that the nonautonomous versions of transit time and mean age differ significantly from the autonomous quantities when calculated for that model. [ABSTRACT FROM AUTHOR]

A novel pulse transit time proxy measurement, slope transit time (STT), is proposed in this letter. STT is based on geometrical considerations of the arriving photoplethysmographic cardiac waveform and its computation requires only the measurement of a single point on each cardiac beat arriving at the peripheral site. This novel transit time is explained conceptually and its implementation illustrated through its application to signals from respiratory effort, Müller maneuver, and obstructive sleep apnea trials. [ABSTRACT FROM PUBLISHER]

Proper determination of the effective electrode spacing (d eff ) of an ion chamber ensures proper determination of its collection efficiency either in continuous or in pulsed radiation in addition to the proper evaluation of the transit time. Boag's method for the determination of d eff assumes the spherical shape of the internal electrode of the spherical ion chambers which is not always true, except for some cases, its common shape is cylindrical. Current work provides a new approach for the evaluation of the effective electrode spacing in spherical ion chambers considering the cylindrical shape of the internal electrode. Results indicated that d eff values obtained through current work are less than those obtained using Boag's method by factors ranging from 12.1% to 26.9%. Current method also impacts the numerically evaluated collection efficiency ( f ) where values obtained differ by factors up to 3% at low potential ( V ) values while at high V values minor differences were noticed. Additionally, impacts on the evaluation of the transit time ( τ i ) were obtained. It is concluded that approximating the internal electrode as a sphere may result in false values of d eff , f , and τ i . [ABSTRACT FROM AUTHOR]

The distribution of transit times from the Northern Hemisphere (NH) midlatitude surface is a fundamental property of tropospheric transport. Here, the authors present an analysis of the transit-time distribution (TTD) since air last contacted the NH midlatitude surface, as simulated by the NASA Global Modeling Initiative Chemistry Transport Model. Throughout the troposphere, the TTD is characterized by young modes and long tails. This results in mean transit times or 'mean ages' Γ that are significantly larger than their corresponding modal transit times or 'modal ages' τmode, especially in the NH, where Γ ≈ 0.5 yr, while τmode < 20 days. In addition, the shape of the TTD changes throughout the troposphere as the ratio of the spectral width Δ-the second temporal moment of the TTD-to the mean age decreases sharply in the NH from ~2.5 at NH high latitudes to ~0.7 in the Southern Hemisphere (SH). Decreases in Δ/Γ in the SH reflect a narrowing of the TTD relative to its mean and physically correspond to changes in the contributions of fast transport paths relative to slow eddy-diffusive recirculations. It is shown that fast transport paths control the patterns and seasonal cycles of idealized 5- and 50-day loss tracers in the Arctic and the tropics, respectively. The relationship between different TTD time scales and the idealized loss tracers, therefore, is conditional on the shape of the TTD. [ABSTRACT FROM AUTHOR]

The South China Sea (SCS) is the largest semi-enclosed marginal sea in Southeast Asia, and is bounded by the Asian continent, Philippine Archipelago, and Great Sunda Islands. Due to the wide shelves on its northwestern and southern ends as well as the presence of numerous islets, atolls and reefs, the average depth of the SCS is only 1350 m. In this study we used measurements of the transient tracer CFC-11 from the SCS to calculate ventilation time-scales and the concentration of anthropogenic CO 2 (C ant ) based on the transit time distribution. The CFC-11 concentrations decreased consistently with depth and the deep and bottom water in the SCS had a CFC-11 value close to the detection limit (0.01 pmol kg −1 or 0.5 ppt). The ventilation times (mean ages) for the deep and bottom water column were ~500–600 years, and based on the mean age profiles the southern part of the intermediate SCS water was older than the northern part. The ventilation time distribution was in agreement with the existence of mean annual cyclonic circulation in the SCS. The mean column inventory of C ant in the northern SCS was 28.9 mol C m −2 (error range (ER): 22.8–35.6 mol C m −2 ), while in the southern SCS it was 28.4 mol m −2 (ER: 21.9–35.2 molCm −2 ). The total C ant inventory was estimated to be 1 Pg C (ER: 0.8–1.3 Pg C, referenced to the year 2011), suggesting that the SCS stores less C ant then the adjacent seas. The vertical diffusivity was estimated to be 2–4.6×10 −4 m 2 s −1 in the SCS based on the “transient steady state”. The upwelling was estimated as 13–34 myr −1 . The high diffusivity was probably due to the strong internal tide, while the strong upwelling was due to the persistent counterclockwise (cyclonic) circulation. [ABSTRACT FROM AUTHOR]

Reduction of passenger waiting time in a multiple elevator system is an important goal in the lift industry. Genetic algorithms (GAs) have been applied to the dispatching problem in vertical transportation. In this paper, we present an approach based on a GA with several relevant adjustments to adapt this type of algorithm to this problem. The algorithm serves calls currently registered in the system to create a dispatch plan, under the assumption that just one passenger has made each call (i.e. without passenger forecasting). We develop and investigate various versions of the GA incorporating one or more adjustments in this research area. The algorithms were implemented and evaluated using ELEVATE, for two different building configurations, in terms of incoming, outgoing and interfloor profiles. To compare results, one-factor analysis of variance tests were applied to passenger waiting times. The performance of the basic GA was significantly improved upon by making these adjustments. These adjustments turn out to be essential for a successful implementation of a GA in the dispatching problem. [ABSTRACT FROM AUTHOR]

Transit times through hydrologic systems vary in time, but the nature of that variability is not well understood. Transit times variability was investigated in a 1 m3 sloping lysimeter, representing a simplified model of a hillslope receiving periodic rainfall events for 28 days. Tracer tests were conducted using an experimental protocol that allows time-variable transit time distributions (TTDs) to be calculated from data. Observed TTDs varied with the storage state of the system, and the history of inflows and outflows. We propose that the observed time variability of the TTDs can be decomposed into two parts: 'internal' variability associated with changes in the arrangement of, and partitioning between, flow pathways; and 'external' variability driven by fluctuations in the flow rate along all flow pathways. These concepts can be defined quantitatively in terms of rank StorAge Selection (rSAS) functions, which is a theory describing lumped transport dynamics. Internal variability is associated with temporal variability in the rSAS function, while external is not. The rSAS function variability was characterized by an 'inverse storage effect,' whereby younger water is released in greater proportion under wetter conditions than drier. We hypothesize that this effect is caused by the rapid mobilization of water in the unsaturated zone by the rising water table. Common approximations used to model transport dynamics that neglect internal variability were unable to reproduce the observed breakthrough curves accurately. This suggests that internal variability can play an important role in hydrologic transport dynamics, with implications for field data interpretation and modeling. [ABSTRACT FROM AUTHOR]

We investigated the uniformity of electron transit times for two 5-in photomultiplier tubes: the Hamamatsu R1250 and the Adit B133D01S. We focused a highly attenuated short-pulse laser on the tubes while they were mounted on a programmable stage. The stage translated the tubes relative to the incident beam so that measurements could be made with light focused at points along a grid covering the entire photocathodes. A portion of the incident light was split from the incident beam and measured and recorded by a fast photodiode. Electron transit times were measured by computing the time delay between the recorded photodiode signal and photomultiplier signal using software constant-fraction discrimination. The Hamamatsu tube exhibited a uniform timing response that varied by no more than 1.7 ns. The Adit tube was much less uniform, with transit times that varied by as much as 57 ns. The Adit response also exhibited a spatially varying double-peak structure in its response. The technique described in this paper could be usefully employed by photomultiplier tube manufacturers to characterize the performance of their products. [ABSTRACT FROM AUTHOR]

Aims Food intake is known to have various effects on gastrointestinal luminal conditions in terms of transit times, hydrodynamic forces and/or luminal fluid composition and can therefore affect the dissolution behavior of solid oral dosage forms. The aim of this study was to investigate and detect the dosage form-dependent food effect that has been observed for two extended-release formulations of nifedipine using in vitro dissolution tests. Methods Two monolithic extended release formulations, the osmotic pump Adalat® XL 60 mg and matrix-type Adalat® Eins 30 mg formulation, were investigated with biorelevant dissolution methods using the USP apparatus III and IV under both simulated prandial states, and their corresponding quality control dissolution method. In vitro data were compared to published and unpublished in vivo data using deconvolution-based in vitro – in vivo correlation (IVIVC) approaches. Results Quality control dissolution methods tended to overestimate the dissolution rate due to the excessive solubilizing capabilities of the sodium dodecyl sulfate (SDS)-containing dissolution media. Using Level II biorelevant media the dosage form dependent food effect for nifedipine was described well when studied with the USP apparatus III, whereas the USP apparatus IV failed to detect the positive food effect for the matrix-type dosage form. Conclusions It was demonstrated that biorelevant methods can serve as a useful tool during formulation development as they were able to qualitatively reflect the in vivo data . [ABSTRACT FROM AUTHOR]

This paper proposes a practical tactical-level liner container assignment model for liner shipping companies, in which the container shipment demand is a non-increasing function of the transit time. Given the transit-time-sensitive demand, the model aims to determine which proportion of the demand to fulfill and how to transport these containers in a liner shipping network to maximize the total profit. Although the proposed model is similar to multi-commodity network-flow (MCNF) with side constraints, unlike the MCNF with time delay constraints or reliability constraints that is NP-hard, we show that the liner container assignment model is polynomially solvable due to its weekly schedule characteristics by developing two link-based linear programing formulations. A number of practical extensions and applications are analyzed and managerial insights are discussed. The polynomially solvable liner container assignment model is then applied to address several important decision problems proposed by a global liner shipping company. [ABSTRACT FROM AUTHOR]

Background and Purpose: Perfusion weighted imaging (PWI) is inherently unreliable in patients with severe perfusion abnormalities. We compared the diagnostic accuracy of a novel index of microvascular flow-patterns, so-called capillary transit time heterogeneity (CTH) to that of the commonly used delay parameter Tmax in patients with bilateral high grade internal carotid artery stenosis (ICAS). Methods: Consecutive patients with bilateral ICAS ≥ 70%NASCET who underwent PWI were retrospectively examined. Maps of CTH and Tmax were analyzed with a volumetric approach using several thresholds. Predictors of favorable outcome (modified Rankin scale at discharge 0–2) were identified using univariate and receiver operating characteristic (ROC) curve analysis. Results: Eighteen patients were included. CTH ≥ 30s differentiated best between patients with favorable and unfavorable outcome when both hemispheres were taken into account (sensitivity 83%, specificity 73%, area under the curve [AUC] 0.833 [confidence interval (CI) 0.635; 1.000]; p = 0.027). The best discrimination using Tmax was achieved with a threshold of ≥ 4s (sensitivity 83%, specificity 64%, AUC 0.803 [CI 0.585;1.000]; p = 0.044). The highest AUC was found for left sided volume with CTH ≥ 15s (sensitivity 83%, specificity 91%, AUC 0.924 [CI 0.791;1.000]; p = 0.005). Conclusion: The study suggests that CTH is superior to Tmax in discriminating ICAS patients with favorable from non-favorable outcome. This finding may reflect the simultaneous involvement of large vessels and microvessels in ICAS and underscore the need to diagnose and manage both aspects of the disease. [ABSTRACT FROM AUTHOR]

The acceptance of broadband ultrasound attenuation (BUA) for the assessment of osteoporosis suffers from a limited understanding of both ultrasound wave propagation through cancellous bone and its exact dependence upon the material and structural properties. It has recently been proposed that ultrasound wave propagation in cancellous bone may be described by a concept of parallel sonic rays; the transit time of each ray defined by the proportion of bone and marrow propagated. A Transit Time Spectrum (TTS) describes the proportion of sonic rays having a particular transit time, effectively describing the lateral inhomogeneity of transit times over the surface aperture of the receive ultrasound transducer. The aim of this study was to test the hypothesis that the solid volume fraction (SVF) of simplified bone:marrow replica models may be reliably estimated from the corresponding ultrasound transit time spectrum. Transit time spectra were derived via digital deconvolution of the experimentally measured input and output ultrasonic signals, and compared to predicted TTS based on the parallel sonic ray concept, demonstrating agreement in both position and amplitude of spectral peaks. Solid volume fraction was calculated from the TTS; agreement between true (geometric calculation) with predicted (computer simulation) and experimentally-derived values were R 2 = 99.9% and R 2 = 97.3% respectively. It is therefore envisaged that ultrasound transit time spectroscopy (UTTS) offers the potential to reliably estimate bone mineral density and hence the established T -score parameter for clinical osteoporosis assessment. [ABSTRACT FROM AUTHOR]

OBJECTIVES: Transit-time flow measurement (TTFM) parameters such as mean graft flow (MGF, ml/min), pulsatility index (PI) and diastolic filling (DF, %) have been extensively researched for internal mammary arterial or saphenous vein grafts. In our experience of using the right gastroepiploic arterial (GEA) graft for right coronary artery (RCA) grafting, we observed unique GEA graft flow waveforms.We analysed the GEA graft flow waveforms for their effectiveness in determining GEA graft patency by power spectral analysis. METHODS: Forty-five patients underwent off-pump coronary artery bypass using the GEA graft for RCA grafting individually. The means of intraoperative MGF, PI and DF were compared between patent and non-patent grafts, postoperatively. Furthermore, the GEA flow data were output and analysed using power spectral analysis. RESULTS: Forty grafts were 'patent' and five were 'non-patent'. There were no significant differences in the mean TTFM parameters between the patent and non-patent grafts (MGF: 22 vs 8 ml/min, respectively, P = 0.068; PI: 3.5 vs 6.5, respectively, P = 0.155; DF: 63 vs 53%, respectively, P = 0.237). Results of the power spectral analysis presented clear differences; the power spectral density (PSD) of patent grafts presented high peaks at frequency levels of 1, 2 and 3 Hz, and the non-patent graft PSD presented high peaks that were not limited to these frequencies. The PSD had a sensitivity and specificity of 80 and 87.5%, respectively. CONCLUSIONS: Power spectral analysis of the GEA graft flow is useful to distinguish between non-patent and patent grafts intraoperatively. This should be used as a fourth parameter along with MGF, PI and DF. [ABSTRACT FROM AUTHOR]

Background Intraoperative portal venous flow measurement provides surgeons with instant guidance for portal flow modulation during living-donor liver transplantation (LDLT). In this study, we compared the agreement of portal flow measurement obtained by 2 devices: transit time ultrasound (TTU) and conventional Doppler ultrasound (CDU). Methods Fifty-four recipients of LDLT underwent intraoperative measurement of portal flow after completion of vascular anastomosis of the implanted partial liver graft. Both TTU and CDU were used concurrently. Agreement of TTU and CDU was assessed by intraclass correlation coefficient using a model of 2-way random effects, absolute agreement, and single measurement. A Bland-Altman plot was applied to assess the variability between the 2 devices. Results The mean, median, and range of portal venous flow was 1456, 1418, and 117 to 2776 mL/min according to TTU; and 1564, 1566, and 119 to 3216 mL/min according to CDU. The intraclass correlation coefficient of portal venous flow between TTU and CDU was 0.68 (95% confidence interval, 0.51–0.80). The Bland-Altman plots revealed an average variation of 4.8% between TTU and CDU but with a rather wide 95% confidence interval of variation ranging from −57.7% to 67.4%. Conclusions Intraoperative TTU and CDU showed moderate agreement in portal flow measurement. However, a relatively wide range of variation exists between TTU and CDU, indicating that data obtained from the 2 devices may not be interchangeable. [ABSTRACT FROM AUTHOR]

Pulse transit time (PTT) is an important physiological parameter that directly correlates with the elasticity and compliance of vascular walls and variations in blood pressure. This paper presents a PTT estimation method based on photoplethysmographic imaging (PPGi). The method utilizes two opposing cameras for simultaneous acquisition of PPGi waveform signals from the index fingertip and the forehead temple. An algorithm for the detection of maxima and minima in PPGi signals was developed, which includes technology for interpolation of the real positions of these points. We compared our PTT measurements with those obtained from the current methodological standards. Statistical results indicate that the PTT measured by our proposed method exhibits a good correlation with the established method. The proposed method is especially suitable for implementation in dual-camera-smartphones, which could facilitate PTT measurement among populations affected by cardiac complications. [ABSTRACT FROM AUTHOR]

This study presents ultrasound transit time technique (UTTT) measurements of the diameter variations of single argon bubbles rising in a zig-zag trajectory in water. Simultaneous size measurements with a high-speed camera show that UTTT resolves both the apparent diameter and the tilt of the bubble axis with an accuracy of better than 7%. This qualifies UTTT for the measurement of bubble sizes in opaque liquids, such as liquid metals, or vessels. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method for estimating the perceived value of transit time of containers by shipping lines. The key idea is that a shipping line’s published schedule is the optimal decision that minimizes the sum of fuel cost and time-associated costs of the containers adopted by the shipping line. Using the proposed method, we find that the adopted values of transit time for nine trans-Pacific services operated by Orient Overseas Container Line and five trans-Pacific services operated by Maersk Line are between US$5/TEU/day and US$30/TEU/day. We further demonstrate how the adopted value can be used for designing the optimal transit times between ports, analyzing the viability of slow-steaming, checking whether ships should speed up to catch up to connecting ships on other services, and helping to predict the market share of less polluting fuels in view of rules on air emission. [ABSTRACT FROM AUTHOR]

Objective: Indicator-dilution curves (IDCs) for the estimation of pulmonary transit times (PTTs) can be generated noninvasively using contrast echocardiography. Currently, these IDCs are analyzed by manual inspection, which is not feasible in a clinical setting, or fit to a statistical model to derive parameters of interest. However, IDCs generated from patients are frequently subject to significant low-frequency noise and recirculation artifacts that obscure the first-pass signal and render model fitting impractical or inaccurate. Thus, the objective of this paper was to develop alternative computational methods to determine PTT using noisy clinical data in which the signal decay is not adequately visible. Methods: We report on a method that uses a model fit to the rise portion of the IDCs to determine the signal inflection point. Additionally, a signal truncation algorithm was developed that enables automated analysis of the IDCs. Results: We compare PTTs derived from our inflection point method to those obtained by manual inspection in 25 patients ( R^2 = 0.86) and to those obtained by mean transit time calculation following fitting to a local density random walk model (R^2 = 0.80) in a subset of this cohort. Conclusion: Combined with a signal truncation algorithm, the inflection point method provides robust, automated determination of PTT from noisy IDCs containing recirculation artifacts. Significance: The inflection point method addresses the need for computational analysis of IDCs obtained from contrast echocardiograms that are not amenable to first-pass model fitting. [ABSTRACT FROM PUBLISHER]

Summary While central in groundwater resources and contaminant fate, Transit Time Distributions (TTDs) are never directly accessible from field measurements but always deduced from a combination of tracer data and more or less involved models. We evaluate the predictive capabilities of approximate distributions (Lumped Parameter Models abbreviated as LPMs) instead of fully developed aquifer models. We develop a generic assessment methodology based on synthetic aquifer models to establish references for observable quantities as tracer concentrations and prediction targets as groundwater renewal times. Candidate LPMs are calibrated on the observable tracer concentrations and used to infer renewal time predictions, which are compared with the reference ones. This methodology is applied to the produced crystalline aquifer of Plœmeur (Brittany, France) where flows leak through a micaschists aquitard to reach a sloping aquifer where they radially converge to the producing well, issuing broad rather than multi-modal TTDs. One, two and three parameters LPMs were calibrated to a corresponding number of simulated reference anthropogenic tracer concentrations (CFC-11, 85 Kr and SF 6 ). Extensive statistical analysis over the aquifer shows that a good fit of the anthropogenic tracer concentrations is neither a necessary nor a sufficient condition to reach acceptable predictive capability. Prediction accuracy is however strongly conditioned by the use of a priori relevant LPMs. Only adequate LPM shapes yield unbiased estimations. In the case of Plœmeur, relevant LPMs should have two parameters to capture the mean and the standard deviation of the residence times and cover the first few decades [0; 50 years]. Inverse Gaussian and shifted exponential performed equally well for the wide variety of the reference TTDs from strongly peaked in recharge zones where flows are diverging to broadly distributed in more converging zones. When using two sufficiently different atmospheric tracers like CFC-11 and 85 Kr, groundwater renewal time predictions are accurate at 1–5 years for estimating mean transit times of some decades (10–50 years). 1-parameter LPMs calibrated on a single atmospheric tracer lead to substantially larger errors of the order of 10 years, while 3-parameter LPMs calibrated with a third atmospheric tracers (SF 6 ) do not improve the prediction capabilities. Based on a specific site, this study highlights the high predictive capacities of two atmospheric tracers on the same time range with sufficiently different atmospheric concentration chronicles. [ABSTRACT FROM AUTHOR]

Background: We determined reliability of cardiac output (CO) measured by pulse wave transit time cardiac output system (esCCO system; COesCCO) vs transthoracic echocardiography (COTTE) in mechanically ventilated patients in the early phase of septic shock. A secondary objective was to assess ability of esCCO to detect change in CO after fluid infusion. Methods: Mechanically ventilated patients admitted to the ICU, aged >18 years, in sinus rhythm, in the early phase of septic shock were prospectively included. We performed fluid infusion of 500ml of crystalloid solution over 20 minutes and recorded CO by EsCCO and TTE immediately before (T0) and 5 minutes after (T1) fluid administration. Patients were divided into 2 groups (responders and non-responders) according to a threshold of 15% increase in COTTE in response to volume expansion. Results: In total, 25 patients were included, average 64±15 years, 15 (60%) were men. Average SAPSII and SOFA scores were 55±21.3 and 13±2, respectively. ICU mortality was 36%. Mean cardiac output at T0 was 5.8±1.35 L/min by esCCO and 5.27±1.17 L/min by COTTE. At T1, respective values were 6.63 ± 1.57 L/min for esCCO and 6.10±1.29 L/min for COTTE. Overall, 12 patients were classified as responders, 13 as non-responders by the reference method. A threshold of 11% increase in COesCCO was found to discriminate responders from non-responders with a sensitivity of 83% (95% CI, 0.52-0.98) and a specificity of 77% (95% CI, 0.46-0.95). Conclusion: We show strong correlation esCCO and echocardiography for measuring CO, and change in CO after fluid infusion in ICU patients. [ABSTRACT FROM AUTHOR]

We recently extended the classic flow-diffusion equation, which relates blood flow to tissue oxygenation, to take capillary transit time heterogeneity (CTH) into account. Realizing that cerebral oxygen availability depends on both cerebral blood flow (CBF) and capillary flow patterns, we have speculated that CTH may be actively regulated and that changes in the capillary morphology and function, as well as in blood rheology, may be involved in the pathogenesis of conditions such as dementia and ischemia-reperfusion injury. The first extended flow-diffusion equation involved simplifying assumptions which may not hold in tissue. Here, we explicitly incorporate the effects of oxygen metabolism on tissue oxygen tension and extraction efficacy, and assess the extent to which the type of capillary transit time distribution affects the overall effects of CTH on flow-metabolism coupling reported earlier. After incorporating tissue oxygen metabolism, our model predicts changes in oxygen consumption and tissue oxygen tension during functional activation in accordance with literature reports. We find that, for large CTH values, a blood flow increase fails to cause significant improvements in oxygen delivery, and can even decrease it; a condition of malignant CTH. These results are found to be largely insensitive to the choice of the transit time distribution. [ABSTRACT FROM AUTHOR]

A novel Ka-band coaxial transit-time oscillator (TTO) with a four-gap buncher is proposed and investigated. Simulation results show that an output power of 1.27GW and a frequency of 26.18 GHz can be achieved with a diode voltage of 447 kV and a beam current of 7.4 kA. The corresponding power efficiency is 38.5%, and the guiding magnetic field is 0.6 T. Studies and analysis indicate that a buncher with four gaps can modulate the electron beam better than the three-gap buncher in such a Ka-band TTO. Moreover, power efficiency increases with the coupling coefficient between the buncher and the extractor. Further simulation demonstrates that power efficiency can reach higher than 30% with a guiding magnetic field of above 0.5 T. Besides, the power efficiency exceeds 30% in a relatively large range of diode voltage from 375 kV to 495 kV. [ABSTRACT FROM AUTHOR]