Cell Residence Time Research Articles

Cost analysis and minimization of movement-based location management schemes in wireless communication networks: a renewal process approach

The paper makes new contributions to cost analysis and minimization of movement-based location management schemes in wireless communication networks. The main contributions of the paper are three-fold. First, we consider two different call handling models, that is, the call plus location update (CPLU) model and the call without location update (CWLU) model. We point out that all existing analysis of location update cost of a movement-based location management scheme (MBLMS) do not accurately capture the essence of the two models. Second, we analyze the exact location update cost of an MBLMS under both CPLU and CWLU models using a renewal process approach which has rarely been used before. We find that the location update cost of an MBLMS under the CWLU model is much easier to analyze than that of an MBLMS under the CPLU model. Furthermore, an MBLMS operated under the CWLU model has lower location update cost than an MBLMS operated under the CPLU model. Third, we are able to derive a closed form solution to the movement threshold that minimizes the total cost of location management in an MBLMS for the CPLU model when the inter-call time has an arbitrary distribution and the cell residence time has an Erlang distribution, and for the CWLU model when both inter-call time and cell residence time have arbitrary distributions. Such closed form solutions have not been available in the existing literature.

A Relation Between Near-Wall Particle-Hemodynamics and Onset of Thrombus Formation in Abdominal Aortic Aneurysms

A novel computational particle-hemodynamics analysis of key criteria for the onset of an intraluminal thrombus (ILT) in a patient-specific abdominal aortic aneurysm (AAA) is presented. The focus is on enhanced platelet and white blood cell residence times as well as their elevated surface-shear loads in near-wall regions of the AAA sac. The generalized results support the hypothesis that a patient's AAA geometry and associated particle-hemodynamics have the potential to entrap activated blood particles, which will play a role in the onset of ILT. Although the ILT history of only a single patient was considered, the modeling and simulation methodology provided allow for the development of an efficient computational tool to predict the onset of ILT formation in complex patient-specific cases.

Factors Affecting Residence Time of Mesenchymal Stromal Cells (MSC) Injected into the Myocardium

The therapeutic mechanism of mesenchymal stromal/stem cells (MSC) for the treatment of acute myocardial infarction is not well understood. Our goal was to get insights into this mechanism by analyzing the survival kinetics of allogeneic and syngeneic cell transplants under different tissue conditions. Two MSC cell banks, stably and equally expressing the luciferase reporter construct, were developed for these studies and injected directly to the myocardium of Lewis rat recipients under syngeneic or allogeneic transplantation conditions. Cell survival was monitored by real-time fashion for up to 2 weeks, using optical imaging device (IVIS, Xenogen Corp.). We found that both syngeneic and allogeneic grafts reduced significantly in size during the first week of transplantation, either in the normal or in the late infarcted heart (5 days after MI) and allotransplants became always smaller than syngeneic grafts during this period. Low dose of cyclosporine A treatment had a benefit on both allo- and syngeneic graft sizes, suggesting that multiple mechanisms play a role in early graft reduction. The MSC characteristic factors IL-6, IL-8, MCP-1, and VEGF were well above the control level in the heart tissue at 4 days after cell injection, suggesting that the peak therapeutic effect of MSC can be expected during the first week of the administration. Although allogeneic cells induced immunoglobulin production, their biological effects (cell survival, factor productions) are very similar to the syngeneic transplants and therefore they could deliver the same therapeutic effect as the syngeneic cells. Finally, freshly infarcted tissue (30 min) supported better the survival of MSC than late postischemic tissue (5 days) but only "off the shelf" allogeneic cell transplants fits with this treatment strategy.

Investigating the Fundamental Basis for Selectors to Improve Activated Sludge Settling

Aerobic, anoxic, and anaerobic selectors have become popular for controlling filamentous bulking in activated sludge systems; however, selectors are not always successful. Regression analyses of data collected from 48 full-scale wastewater treatment plants, with operating selectors, provided a method for ranking the importance of selector operating and design parameters (with respect to their influence on activated sludge settleability) and suggests optimum numerical ranges for these parameters for best selector performance. Selectors do not appear to control filamentous bulking in long mean cell residence time (MCRT) plants. Further, the elimination of all selector zones may help to control bulking in these plants. However, other design/operating parameters were shown to influence activated sludge settleability in long-MCRT plants. Aerobic selectors in short-MCRT plants can control filamentous bulking, if they are small enough to produce a biochemical oxygen demand (BOD) concentration gradient. Anoxic and anaerobic selectors can control filamentous bulking in short-MCRT plants, if the selector volume is large enough and/or the selector mixed-liquor suspended solids concentration is high enough. These unaerated selector systems do not appear to benefit from a BOD concentration gradient as the aerobic selectors in short-MCRT plants do. Although anaerobic/anoxic selector compartmentalization in these plants appears to improve settleability, this presumably is because of reduced selector short-circuiting.

Development of granular sludge for textile wastewater treatment

Microbial granular sludge that is capable to treat textile wastewater in a single reactor under intermittent anaerobic and aerobic conditions was developed in this study. The granules were cultivated using mixed sewage and textile mill sludge in combination with anaerobic granules collected from an anaerobic sludge blanket reactor as seed. The granules were developed in a single sequential batch reactor (SBR) system under alternating anaerobic and aerobic condition fed with synthetic textile wastewater. The characteristics of the microbial granular sludge were monitored throughout the study period. During this period, the average size of the granules increased from 0.02 ± 0.01 mm to 2.3 ± 1.0 mm and the average settling velocity increased from 9.9 ± 0.7 m h −1 to 80 ± 8 m h −1. This resulted in an increased biomass concentration (from 2.9 ± 0.8 g L −1 to 7.3 ± 0.9 g L −1) and mean cell residence time (from 1.4 days to 8.3 days). The strength of the granules, expressed as the integrity coefficient also improved. The sequential batch reactor system demonstrated good removal of COD and ammonia of 94% and 95%, respectively, at the end of the study. However, only 62% of color removal was observed. The findings of this study show that granular sludge could be developed in a single reactor with an intermittent anaerobic–aerobic reaction phase and is capable in treating the textile wastewater.

State-dependent stochastic mobility model in mobile communication networks

We apply finite state-dependent queueing networks to model mobility in mobile communication systems. Although they have been successfully used in the past to model vehicular traffic, state-dependent models have not been applied to mobile communication systems, to the best of our knowledge. The novelty of state-dependent stochastic mobility models is that the congestion phenomenon is explicitly considered, that is, the user speeds fall when the number of users in the system increases. We present a detailed description of the simulation model used to estimate the performance measures of the queueing networks and show computational results for a comprehensive set of instances. As we show, finite state-dependent stochastic models bring interesting new insights, for instance, that in some cases mixed bimodal distributions will better describe the cell residence time of a call than the classical probability distributions used in the past.

Enhancement of aerobic degradation of benzoate and 2-chlorobenzoate by adapted activated sludge

Activated sludge from the Stickney Water Reclamation Plant of the Metropolitan Water Reclamation District of Greater Chicago was adapted in the laboratory to either benzoate or 2-chlorobenzoate as the sole carbon source in sequencing batch reactors with a 48-h feed-aerate-settle-draw cycle and a mean cell residence time (MCRT) of 10 days. Benzoate degradation increased by more than 80-fold after 7 MCRTs compared to unadapted activated sludge. A greater than 15-fold increase in 2-chlorobenzoate metabolism occurred after adaptation for about 5-7 MCRTs. For each substrate the maximum rate measured for adapted cultures was near or above the highest previously reported in the literature. For both adapted and unadapted sludges, benzoate metabolism was considerably faster than that of 2-chlorobenzoate, and for both substrates the rate of metabolism increased incrementally with time of adaptation. As expected, addition of the benzoate-adapted sludge to unadapted sludge enhanced the latter's ability to degrade benzoate.

Decrease in Microvascular Blood Flow in Sickle Cell Anemia Is Triggered by Autonomic Signals and Not Directly by Hypoxia: A New Hypothesis for Sickle Crisis.

Abstract 1523Poster Board I-546Sickle cell anemia (SCA) is a genetic disorder characterized by recurring episodes of vaso-occlusive crisis (VOC) that can lead to hospitalization or sudden death. Hypoxia is an accepted trigger of sickling and degrees of nighttime hypoxia correlate with strokes and frequency of VOC. To better understand the mechanism of events leading to VOC, we simulated the occurrence of nocturnal hypoxia in SCA patients by administration of five breaths of 100% nitrogen. Tidal volume (Vt), arterial oxygen saturation, electrocardiogram (ECG), and microvascular perfusion (PU) by Laser-Doppler were continuously recorded.We had anticipated a drop in PU after each controlled episode of hypoxia. However, we observed multiple prominent drops in PU in SCA subjects (n=8) that were not as clearly evident in controls (CTL; n=9), and found no direct relationship between hypoxia and change in PU (p = NS). As deep breaths or sighs can trigger reflex peripheral vasoconstriction, we examined Vt respiratory tracings obtained simultaneously and observed that PU drops frequently followed sighs (see Figure) in SCA subjects, but rarely in CTL. A statistical algorithm was used to find all sighs and vasoconstrictive events (PU drops) during each 40-minute experimental session. PU drops were associated with sighs in 7 of 8 SCA patients and in 4 of 9 CTL subjects (P < 0.001, Poisson regression analysis). Five CTL and 1 SCA subjects had infrequent sighs and no association between sighs and PU drops. The likelihood ratio of sigh-associated PU drops was significantly higher in SCA than CTL subjects (median = 59.9 % vs. < 1 % for SCA vs. CTL, P = 0.008, rank-sum test) whereas the frequency of sighs was not significantly different between the two groups (median = 2.2 % vs. 1.3 % for SCA vs. CTL, P = 0.16, rank-sum test), indicating that SCA patients are much more likely to have sigh-associated peripheral vasoconstriction. Since the sigh-vasoconstrictor response is controlled by the autonomic nervous system (ANS), we measured heart rate variability (HRV) which is an accepted index of sympathetic/parasympathetic balance. These studies showed substantial reduction of parasympathetic modulation of HRV during hypoxia in SCA but not in CTL subjects (p < 0.01), indicating a marked abnormality of the ANS in SCA. [Display omitted] In overview, the likelihood of coupling between spontaneous sighs and subsequent vasoconstrictive events (PU drops) is much higher in SCA patients than in CTL. Thus, we speculate that a drop in perfusion secondary to increased neural coupling between the lung and vasculature may be an initiating event in VOC. Hypoxia may secondarily promote VOC by altering ANS sensitivity and increasing the probability that a sigh will in turn lead to reflex peripheral vasoconstriction. In a background of HbS, transient decreases in perfusion may prolong red cell residence time in the microvasculature, leading to HbS polymerization, sickling and vascular occlusion. DisclosuresNo relevant conflicts of interest to declare.

A new framework for characterising the number of handovers in cellular networks

AbstractThe handover process was widely studied in the literature in the past decade. While significant efforts addressed the mean handover rate, few attempted to characterise the distribution of the number of handovers under the assumption that the call and the cell residence times (CRTs) are generally distributed. Motivated by the increasing impact of handovers on the design and performance of the control and data planes in the emerging cellular networks, in this paper, we propose a new analytical framework to obtain the probability generating function (PGF) of the number of handovers. Our work covers three generic session behaviours, including new, roaming and location triggered calls, and thus facilitates the calculation of the mean number of handovers for such session types. When the distributions have rational Laplace transforms, we obtain closed form solutions that are simple‐to‐compute and hence provide cellular network designers and researchers with deeper insights into the performance of mobility aware wireless protocols for different application scenarios. Our results show that handover models for new sessions can reasonably approximate location triggered sessions while separate treatment for roaming sessions is generally required. The numerical examples based on the generic hyper‐Erlang session durations show the practicability of our framework. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Cell motion and recovery in a two-stream microfluidic device

The motion of cells in a two-stream microfluidic device designed to extract cryoprotective agents from cell suspensions was tested under a range of conditions. Jurkat cells (lymphoblasts) in a 10% dimethylsulfoxide solution were driven in parallel with phosphate-buffered saline solution wash streams through single rectangular channel sections and multiple sections in series. The influence of cell-stream flow rate and cell volume fraction (CVF) on cell viability and recovery were examined. The channel depth was 500 lm, and average cell stream velocity within the channels was varied from 3.6 to8.5 mm/s corresponding with cell stream Reynolds numbers of 2.6-6.0. Cell viability measured at device outlets was high for all cases examined indicating no significant cell damage within the device. Downstream of a single stage, cell recoveries measured 90-100% for average cell stream velocities ≥6 mm/s and for CVFs up to 20%. Cell recovery downstream of multistage devices also measured 90-100% after a critical device population time. This time was found to be five times the average cell residence time within the device. The measured recovery values were significantly larger than those typically obtained using conventional cell washing methods.

Optimization of an operating domestic wastewater treatment plant using elitist non-dominated sorting genetic algorithm

Multi-objective optimization of an operating domestic wastewater treatment plant is carried out using binary coded elitist non-dominated sorting genetic algorithm. Activated sludge model with extended aeration is used for optimization. For optimal plant operation, two different optimization problems are formulated and solved. The first optimization problem involves single-objective function to estimate kinetic parameters in activated sludge model using available plant data by minimizing the weighted sum-of-square errors between computed and plant values. The second optimization problem involves single-, two- and three-objective functions for efficient plant monitoring. In second category problem, objective functions are based on plant performance criteria (i.e., maximizing the influent flow rate of wastewater and minimizing the exit effluent concentration) and economic criteria (i.e., minimizing the plant operating cost). The important decision variables are: mean cell-residence time, mixed liquor suspended solid concentration in the reactor and underflow sludge concentration. Unique solution is obtained for the single-objective function optimization problem whereas a set of non-dominated solutions are obtained for the multi-objective optimization problems. A set of optimal operating conditions are proposed based on the present optimization study, which enhances the plant performance without affecting the discharge effluent quality. Finally, sensitivity analyses of the model results to the kinetic parameters and the kinetic parameters to the GA parameters are carried out to know the sensitivity of the obtained results with changes in the input parameter space.

Computationally efficient method for analyzing guard channel schemes

Call admission control (CAC) is important for cellular wireless networks in order to provide quality of service (QoS) requirements to users. Guard channel scheme is one of the CAC schemes. There are different computational models for analyzing the guard channel scheme which make unrealistic assumption of exponential distribution for both call holding duration and cell residence time for computational tractability. On the other hand, there are some more realistic models for guard channel schemes which capture general distributions of call holding duration and cell residence time by phase type distributions but are computationally cumbersome to implement. The state-spaces of the Markov chains for those models make the computation intractable. In this paper, we develop a tractable computational model to analyze guard channel scheme with general cell residence time and call holding duration captured by phase type distributions. We make our mathematical model computationally tractable by keeping track of the number of calls in different phases of the channel holding time instead of the phase of the channel holding time of individual calls.

Numerical Simulation of Blood Flow Through Microvascular Capillary Networks

A numerical method is implemented for computing blood flow through a branching microvascular capillary network. The simulations follow the motion of individual red blood cells as they enter the network from an arterial entrance point with a specified tube hematocrit, while simultaneously updating the nodal capillary pressures. Poiseuille's law is used to describe flow in the capillary segments with an effective viscosity that depends on the number of cells residing inside each segment. The relative apparent viscosity is available from previous computational studies of individual red blood cell motion. Simulations are performed for a tree-like capillary network consisting of bifurcating segments. The results reveal that the probability of directional cell motion at a bifurcation (phase separation) may have an important effect on the statistical measures of the cell residence time and scattering of the tube hematocrit across the network. Blood cells act as regulators of the flow rate through the network branches by increasing the effective viscosity when the flow rate is high and decreasing the effective viscosity when the flow rate is low. Comparison with simulations based on conventional models of blood flow regarded as a continuum indicates that the latter underestimates the variance of the hematocrit across the vascular tree.

Hybrid Location-Update Scheme for Mobile Networks

In this paper, we propose a hybrid location-update scheme, which combines the time- and movement-based location-update approaches. In the proposed scheme, a mobile user updates its location after the following two events have occurred: First, the mobile crossed <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> cell boundaries, and then, a time interval <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> elapsed. We also examine the inverse scheme, where an update is performed after the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> boundary crossings occur subsequent to the time interval <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> . We evaluate our scheme by applying it to various mobility models, such as <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">exponential</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cell-residence</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">times</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">with</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">constant</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mobility</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pattern</i> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">exponential</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cell-residence</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">times</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">with</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gamma-distributed</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mobility</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pattern</i> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">hyperexponential</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cell-residence</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">times</i> , and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cell-residence</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">times</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">with</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">small</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">coefficient</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">of</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">variation</i> . From our numerical analysis and simulation results, we learn that the movement-based-only method (i.e., <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> = 0) performs well when the coefficient of variation of the cell-residence time is relatively small. However, when the coefficient of variation is large, the proposed hybrid scheme (i.e., T> 0,n > 0) outperforms each of the two approaches, namely, the time- and movement-based location-update schemes, when these schemes are individually applied.

Anaerobic Digester Optimization using Factorial Design Approach

Anaerobic Digester Optimization using Factorial Design ApproachThe object of this study was to optimize operating conditions of anaerobic digesters using factorial design approach. Three operating parameters were of concern; (1) mixing, (2) mean cell residence time (MCRT) and (3) solids loadings. Mixing intensity was applied in two modes; low mixing and high mixing. MCRTs tested in the study were 15 and 25 days. The feed to the bench-scale digesters,...Author(s)Cheol ParkAlbana BegaJoseph FarrellJonathan KeaneyWilliam E. ToffeyJason A. HuntPaul M. KohlWilliam R. McKeonJohn WillisMetin DuranSourceProceedings of the Water Environment FederationSubjectSession 5 - Anaerobic Digestion 2Document typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2009ISSN1938-6478SICI1938-6478(20090101)2009:3L.350;1-DOI10.2175/193864709793846015Volume / Issue2009 / 3Content sourceResiduals and Biosolids ConferenceFirst / last page(s)350 - 361Copyright2009Word count279Subject keywordsAnaerobic digestionfactorial designmixingsolids loadingMCRT

Method for the Accurate Preparation of Cell-Spiking Standards

Preparation of calibration standards for cell enumeration is critical in characterizing the performance of any method or apparatus intended for recovering rare cells. Diluting a cell suspension serially is prone to statistical sampling errors as the cell suspension becomes more dilute, whereas transferring and injecting cells individually into a diluent with a micromanipulator is time-consuming. We developed a simple and robust method using a surface-modified glass capillary to siphon and eject cells. One-dimensional confinement of cells offered by the capillary made cell enumeration by visual counting simple and rapid, and cell ejection from the capillary was near 100% when the appropriate surface coating and cell solution was used. The residence time of cells in the capillary, however, could affect the percentage of cells that was ejected from the capillary. To characterize the performance of this method, we enumerated the ejected cell using both visual counting under a microscope and automated detection using a chip-based flow cytometer.

Kinetic analysis of enhanced biological phosphorus removal in a hybrid integrated fixed film activated sludge process

Hybrid integrated fixed film activated sludge is a promising process for the enhancement of nitrification, denitrification and phosphorus removal in conventional activated sludge systems that can be used for upgrading biological nutrient removal, particularly when they have space limitations or need modifications that will require large monetary expenses. In this research, successful implementation of hybrid integrated fixed film activated sludge process at temperate zone wastewater treatment facilities has been studied by the placement of fixed film media into aerobic, anaerobic and anoxic zones. The primary objective of this study was to investigate the incorporation of enhanced biological phosphorus removal into hybrid integrated fixed film activated sludge systems and study the interactions between the fixed biomass and the mixed liquor suspended solids with respect to substrate competition and nutrient removal efficiencies. A pilot-scale anaerobic-anoxic-oxic configuration system was used. The system was operated at different mean cell residence times and influent chemical oxygen demand/total phosphorus ratios and with split influent flows. The experimental results confirmed that enhanced biological phosphorus removal could be incorporated successfully into hybrid integrated fixed film activated sludge system, but the redistribution of biomass resulting from the integration of fixed film media and the competition of organic substrate between enhanced biological phosphorus removal and denitrification would affect performances. Also, kinetic analysis of the reactor with regarding to phosphorus removal has been studied with different kinetic models and consequently the modified Stover-Kincannon kinetic model has been chosen for modeling studies and experimental data analysis of the hybrid integrated fixed film activated sludge reactor.

Numerical simulation of distribution of neutrophils in a lattice alveolar capillary network

Neutrophils are known to be retained in narrow pulmonary capillaries, even in normal lungs, due to their low deformability, resulting in a higher concentration than that in systemic circulation. In this study, to obtain a fundamental understanding of the behavior of neutrophils, we simplified an alveolar capillary network to a rectangular grid of short capillary segments and numerically investigated the flow of a suspension of neutrophils and plasma through the capillary network for various concentrations of the suspension, Csus, injected into the network. The cells traveled limited preferential paths in the network while Csus was low. Retention of a cell or cells induced plugging of the segment with a cessation of blood flow, and as the result of the changed plasma flow field caused by such plugging, the cells took various routes differing from the preferential paths. A low incidence of plugging helped to accelerate the cells flowing in the network with tight segments, resulting in a decrease in their mean transit time through the network as compared with the case of a single-cell transit. On the contrary, however, an increasing incidence of plugging induced backward motion of the cells and a resultant increase in the mean transit time. The time-averaged number of cells in the network increased with the increase in Csus, and the fractional residence time of cells in individual segments approached a constant. This means that a high concentration of neutrophils facilitates their uniform distribution in the network. However, the ratio between the time-averaged concentration of the cells in the network and Csus decreased and our numerical simulation did not reach the experimentally obtained value. This implies that, in a real alveolar capillary bed, plasma leaks through the plugged segments or that the capillary network has bypasses through which the plasma can flow.

Modeling and Cost Analysis of Movement-Based Location Management for PCS Networks With HLR/VLR Architecture, General Location Area and Cell Residence Time Distributions

Location management plays a central role in guaranteeing the effective operation of personal communication service (PCS) networks. In current PCS networks, a two-tier system of home location register (HLR) and visitor location register (VLR) databases is commonly used for location management. To improve the performance of PCS networks, several dynamic location management schemes have been proposed. Among the existing dynamic schemes, the movement-based location management may be the most practical due to its effectiveness and easy implementation under the framework of current PCS networks. To implement location management in PCS networks, cost analysis is a crucial aspect. However, most of the existing cost analyses for the movement-based scheme are too simple and not available for PCS networks with the HLR/VLR architecture. One reason for this is the complexity and the difficulty associated with the problem. Li et al. and Rodriguez-Dagnino et al. challenged this task by considering the HLR/VLR architecture. However, the cost analysis developed by Li et al. was carried out under the assumption that the cell and location area (LA) residence times are exponentially distributed. Rodriguez-Dagnino et al. furthered Li et al.'s work by assuming that the LA residence time follows a hyperexponential distribution and that the cell residence time is generally distributed. However, Li et al. and Rodriguez-Dagnino et al. failed to consider VLR location updates that are caused by terminal movements between LAs. In this paper, we relax the restrictions imposed on the distributions of the cell and LA residence times and propose an analytical model to study the movement-based scheme with HLR/VLR architecture. The issue of VLR location updates that are caused by movements between LAs is addressed carefully and successfully. Analytical formulas for the costs of HLR and VLR location updates are derived using a unified approach. Numerical study suggests that the total cost is a convex function of the movement threshold and is sensitive to the variances of the cell and LA residence times. The result presented in this paper can serve as a guideline for the system design and the implementation of the movement-based scheme for PCS networks.

Optimization of Distance-Based Location Management for PCS Networks

Location management (LM) is an important function in a personal communication network to track movements of mobile terminals (MTs) for call delivery. It is well-known that the total signaling cost of a distance-based LM scheme is the lowest among dynamic location management schemes for PCS networks. In this paper, we derive the joint probability distribution of two random variables: the moving distance of an MT and the number of location updates resulting from the moving distances exceeding the distance threshold. As special cases, the probability distributions of an MT's moving distances and the number of location updates during an LM interval are obtained. These statistics are generally applicable to irregular cell topologies and general cell residence time distributions. Based on the derived statistics, the optimal distance thresholds for distance based LM schemes with blanket paging and sequential paging are solved analytically. Numeric results show that our optimized distance-based LM scheme outperforms some well-known LM schemes in total LM cost.