Cell Dwell Time Research Articles

Dynamic handover cost modeling in hybrid VLC/RF networks

In this paper, a dynamic handover cost model is proposed to solve the cost evaluation problem in hybrid visible light communication (VLC)/ radio frequency (RF) heterogeneous networks. According to this model, the cost of handover scenarios with different network deployment and user mobility characteristics can be evaluated, providing a unified standard for the performance evaluation of handover schemes. By utilizing the received signal strength (RSS)-based association policy, the probability of user-to-access point (AP) association is derived. By utilizing stochastic geometry and modeling the locations of APs using a Poisson point process (PPP), the impact of user mobility and network parameters on handover performance is quantified and the expressions for the user’s cell dwell time and handover rate are derived. By analyzing the detailed flow of handover and combining it with the handover rate, a comprehensive handover cost expression is derived. Finally, by simulation and analysis, the applicability and effectiveness of the proposed handover cost model are demonstrated. Compared with the original handover cost model, the proposed model has better dynamic adaptability as well as reliability.

State Aware-Based Prioritized Experience Replay for Handover Decision in 5G Ultradense Networks

The traditional handover decision methods depend on the handover threshold and measurement reports, which cannot efficiently resolve the frequent handover issue and ping-pong effect in 5G (5 generation) ultradense networks. To reduce the unnecessary handover and improve the QoS (quality of service), combine with the analysis of dwell time, we propose a state aware-based prioritized experience replay (SA-PER) handover decision method. First, the cell dwell time is computed by the geometrical analysis of real-time locations of mobile users in cellular networks. The constructed state aware sequence including SINR, load coefficient, and dwell time is normalized by max-min normalization method. Then, the handover decision problem in 5G ultradense networks is formalized as a discrete Markov decision process (MDP). The random sampling and small batch sampling affect the performance of deep reinforcement learning methods. We adopt the prioritized experience replay (PER) method to resolve the learning efficiency problems. The state space, action space, and reward functions are designed. The normalized state aware decision matrix inputs the DDQN (double deep Q-network) method. The competitive and collaborative relationships between vertical handover and horizontal handover in 5G ultradense networks are mainly discussed. And the high average network throughput and long average cell dwell time make sure of the communication quality for mobile users.

Movement Aware CoMP Handover in Heterogeneous Ultra-Dense Networks

The densification of base station (BS) deployments is driving the evolution of network structures towards heterogeneous ultra-dense networks (UDN), making coordinated multipoint (CoMP) a viable and promising transmission solution. However, the BS cooperation regions formed by applying CoMP in the UDN are small and irregular, which causes frequent handover for mobile users. Different from most existing work that focus on the trigger time of handover, we explore how to choose the appropriate BS cooperation set to reduce handover rate. In this paper, we consider movement aware CoMP handover (MACH). By estimating cell dwell time, a user would be intelligently assigned to macro cell or small cell according to its movement trend. To enhance reliability, we further proposed improved MACH (iMACH) to achieve a trade-off between BSs with long dwell time and the current best performed BS for multipoint cooperation while user moving. Using stochastic geometry method, expressions of coverage probability, handover probability and throughput that characterize performance of the proposed schemes are derived. The numerical results indicate that the theoretical analyses fit the simulation results well and the proposed schemes surpass the existing schemes in terms of the aforementioned metrics, and more intelligent and suitable for ultra-dense scenarios.

Performance Sensitivity to the High-Order Statistics of Time Interval Variables in Cellular Networks

Cell dwell time (DT) and unencumbered interruption time (IT) are fundamental time interval variables in the teletraffic analysis for the performance evaluation of mobile cellular networks. Although a diverse set of general distributions has been proposed to model these time interval variables, the effect of their moments higher than the expected value on system performance has not been reported in the literature. In this paper, sensitivity of teletraffic performance metrics of mobile cellular networks to the first three standardized moments of both DT and IT is investigated in a comprehensive manner. Mathematical analysis is developed considering that both DT and IT are phase-type distributed random variables. This work includes substantial numerical results for quantifying the dependence of system level performance metrics to the values of the first three standardized moments of both DT and IT. For instance, for a high mobility scenario where DT is modeled by a hyper-Erlang distribution, we found that call forced termination probability decreases around 60% as the coefficient of variation (CoV) and skewness of DT simultaneously change from 1 to 20 and from 60 to 2, respectively. Also, numerical results confirm that as link unreliability increases the forced termination probability increases while both new call blocking and handoff failure probabilities decrease. Numerical results also indicate that for low values of skewness, performance metrics are highly sensitive to changes in the CoV of either the IT or DT. In general, it is observed that system performance is more sensitive to the statistics of the IT than to those of the DT. Such understanding of teletraffic engineering issues is vital for planning, designing, dimensioning, and optimizing mobile cellular networks.

An orthotopic xenograft model for high-risk non-muscle invasive bladder cancer in mice: influence of mouse strain, tumor cell count, dwell time and bladder pretreatment

BackgroundNovel theranostic options for high-risk non-muscle invasive bladder cancer are urgently needed. This requires a thorough evaluation of experimental approaches in animal models best possibly reflecting human disease before entering clinical studies. Although several bladder cancer xenograft models were used in the literature, the establishment of an orthotopic bladder cancer model in mice remains challenging.MethodsLuciferase-transduced UM-UC-3LUCK1 bladder cancer cells were instilled transurethrally via 24G permanent venous catheters into athymic NMRI and BALB/c nude mice as well as into SCID-beige mice. Besides the mouse strain, the pretreatment of the bladder wall (trypsin or poly-L-lysine), tumor cell count (0.5 × 106–5.0 × 106) and tumor cell dwell time in the murine bladder (30 min – 2 h) were varied. Tumors were morphologically and functionally visualized using bioluminescence imaging (BLI), magnetic resonance imaging (MRI), and positron emission tomography (PET).ResultsImmunodeficiency of the mouse strains was the most important factor influencing cancer cell engraftment, whereas modifying cell count and instillation time allowed fine-tuning of the BLI signal start and duration – both representing the possible treatment period for the evaluation of new therapeutics. Best orthotopic tumor growth was achieved by transurethral instillation of 1.0 × 106 UM-UC-3LUCK1 bladder cancer cells into SCID-beige mice for 2 h after bladder pretreatment with poly-L-lysine. A pilot PET experiment using 68Ga-cetuximab as transurethrally administered radiotracer revealed functional expression of epidermal growth factor receptor as representative molecular characteristic of engrafted cancer cells in the bladder.ConclusionsWith the optimized protocol in SCID-beige mice an applicable and reliable model of high-risk non-muscle invasive bladder cancer for the development of novel theranostic approaches was established.

Intramuscular administration potentiates extended dwell time of mesenchymal stromal cells compared to other routes

BackgroundMesenchymal stromal cells (MSCs) offer great potential for diverse clinical applications. However, conventional systemic infusion of MSCs limits their therapeutic benefit, since intravenously (IV) infused cells become entrapped in the lungs where their dwell time is short. MethodsTo explore possible alternatives to IV infusion, we used in vivo optical imaging to track the bio-distribution and survival of 1 million bioluminescent MSCs administered IV, intraperitoneally (IP), subcutaneously (SC) and intramuscularly (IM) in healthy athymic mice. ResultsIV-infused MSCs were undetectable within days of administration, whereas MSCs implanted IP or SC were only detected for 3 to 4 weeks. In contrast, MSCs sourced from human umbilical cord matrix or bone marrow survived more than 5 months in situ when administered IM. Long-term survival was optimally achieved using low passage cells delivered IM. However, MSCs could undergo approximately 30 doublings before their dwell time was compromised. Cryo-preserved MSCs administered IM promptly after thaw were predominantly cleared after 3 days, whereas equivalent cells cultured overnight prior to implantation survived more than 3 months. DiscussionThe IM route supports prolonged cell survival of both neo-natal and adult-derived MSCs, although short-term MSC survival was comparable between all tested routes up to day 3. IM implantation presents a useful alternative to achieve clinical benefits from prolonged MSC dwell time at a homeostatic implant site and is a minimally invasive delivery route suitable for many applications. However, optimized thaw protocols that restore full biological potential of cryo-preserved MSC therapies prior to implantation must be developed.

Modeling and performance analysis for mobile cognitive radio cellular networks

In this paper, teletraffic performance and channel holding time characterization in mobile cognitive radio cellular networks (CRCNs) under fixed-rate traffic with hard-delay constraints are investigated. To this end, a mathematical model to capture the effect of interruption of ongoing calls of secondary users (SUs) due to the arrival of primary users (PUs) is proposed. The proposed model relies on the use of an independent potential interruption time associated with the instant of possible interruption for each ongoing call in every visited cell. Then, a Poisson process is used to approximate the secondary users’ call interruption process due to the arrival of PUs. Based on this model and considering that unencumbered service time (UST) and cell dwell time (CDT) of SUs are independent generally distributed random variables, analytical formulae for both the probability distributions of channel holding times and inter-cell handoff attempts rate are derived. Also, a novel approximated closed-form mathematical expression for call forced termination probability of SUs is derived under the restriction that the UST is exponentially distributed. Additionally, by considering all the involved time variables exponentially distributed and employing fractional channel reservation to prioritize intra- and inter-cell handoff call attempts over new call requests, a queuing analysis to evaluate the call-level performance of CRCNs in terms of the maximum Erlang capacity is developed. The accuracy of our proposed mathematical models is extensively investigated under a variety of different evaluation scenarios for all the considered call-level performance metrics. Numerical results demonstrate that channel holding time statistics are highly sensitive to both interruption probability of ongoing secondary calls and type of probability distribution functions used to model CDT and UST. From the teletraffic perspective, numerical results reveal that the system Erlang capacity largely depends on the relative value of the mean secondary service time to the mean primary service time and the primary channels’ utilization factor. Also, the obtained results show that there exists a critical utilization factor of the primary resources from which it is no longer possible to guarantee the required quality of service of SUs and, therefore, services with hard-delay constraints cannot be even supported in CRCNs.

LFA-1 activates focal adhesion kinases FAK1/PYK2 to generate LAT-GRB2-SKAP1 complexes that terminate T-cell conjugate formation

Lymphocyte function-associated antigen 1 (LFA-1) affinity and avidity changes have been assumed to mediate adhesion to intercellular adhesion molecule-1 for T-cell conjugation to dendritic cells (DC). Although the T-cell receptor (TCR) and LFA-1 can generate intracellular signals, the immune cell adaptor protein linker for the activation of T cells (LAT) couples the TCR to downstream events. Here, we show that LFA-1 can mediate both adhesion and de-adhesion, dependent on receptor clustering. Although increased affinity mediates adhesion, LFA-1 cross-linking induced the association and activation of the protein-tyrosine kinases FAK1/PYK1 that phosphorylated LAT selectively on a single Y-171 site for the binding to adaptor complex GRB-2-SKAP1. LAT-GRB2-SKAP1 complexes were distinct from canonical LAT-GADs-SLP-76 complexes. LFA-1 cross-linking increased the presence of LAT-GRB2-SKAP1 complexes relative to LAT-GADs-SLP-76 complexes. LFA-1-FAK1 decreased T-cell-dendritic cell (DC) dwell times dependent on LAT-Y171, leading to reduced DO11.10 T cell binding to DCs and proliferation to OVA peptide. Overall, our findings outline a new model for LFA-1 in which the integrin can mediate both adhesion and de-adhesion events dependent on receptor cross-linking.

Vehicle Positioning and Speed Estimation Based on Cellular Network Signals for Urban Roads

In recent years, cellular floating vehicle data (CFVD) has been a popular traffic information estimation technique to analyze cellular network data and to provide real-time traffic information with higher coverage and lower cost. Therefore, this study proposes vehicle positioning and speed estimation methods to capture CFVD and to track mobile stations (MS) for intelligent transportation systems (ITS). Three features of CFVD, which include the IDs, sequence, and cell dwell time of connected cells from the signals of MS communication, are extracted and analyzed. The feature of sequence can be used to judge urban road direction, and the feature of cell dwell time can be applied to discriminate proximal urban roads. The experiment results show the accuracy of the proposed vehicle positioning method, which is 100% better than other popular machine learning methods (e.g., naive Bayes classification, decision tree, support vector machine, and back-propagation neural network). Furthermore, the accuracy of the proposed method with all features (i.e., the IDs, sequence, and cell dwell time of connected cells) is 83.81% for speed estimation. Therefore, the proposed methods based on CFVD are suitable for detecting the status of urban road traffic.

Experimental Study of Micro‐Scale Taylor Vortices Within a Co‐Axial Mixed‐Flow Blood Pump

Taylor vortices in a miniature mixed-flow rotodynamic blood pump were investigated using micro-scale particle image velocimetry (μ-PIV) and a tracer particle visualization technique. The pump featured a cylindrical rotor (14.9 mm diameter) within a cylindrical bore, having a radial clearance of 500 μm and operated at rotational speeds varying from 1000 to 12 000 rpm. Corresponding Taylor numbers were 700-101 800, respectively. The critical Taylor number was observed to be highly dependent on the ratio of axial to circumferential velocity, increasing from 1200 to 18 000 corresponding to Rossby numbers from 0 to 0.175. This demonstrated a dramatic stabilizing effect of the axial flow. The size of Taylor vortices was also found to be inversely related to Rossby number. It is concluded that Taylor vortices can enhance the mixing in the annular gap and decrease the dwell time of blood cells in the high-shear-rate region, which has the potential to decrease hemolysis and platelet activation within the blood pump.

Timescales and Frequencies of Reversible and Irreversible Adhesion Events of Single Bacterial Cells.

In the environment, most bacteria form surface-attached cell communities called biofilms. The attachment of single cells to surfaces involves an initial reversible stage typically mediated by surface structures such as flagella and pili, followed by a permanent adhesion stage usually mediated by polysaccharide adhesives. Here, we determine the absolute and relative timescales and frequencies of reversible and irreversible adhesion of single cells of the bacterium Caulobacter crescentus to a glass surface in a microfluidic device. We used fluorescence microscopy of C. crescentus expressing green fluorescent protein to track the swimming behavior of individual cells prior to adhesion, monitor the cell at the surface, and determine whether the cell reversibly or irreversibly adhered to the surface. A fluorescently labeled lectin that binds specifically to polar polysaccharides, termed holdfast, discriminated irreversible adhesion events from reversible adhesion events where no holdfast formed. In wild-type cells, the holdfast production time for irreversible adhesion events initiated by surface contact (23 s) was 30-times faster than the holdfast production time that occurs through developmental regulation (13 min). Irreversible adhesion events in wild-type cells (3.3 events/min) are 15-times more frequent than in pilus-minus mutant cells (0.2 events/min), indicating the pili are critical structures in the transition from reversible to irreversible surface-stimulated adhesion. In reversible adhesion events, the dwell time of cells at the surface before departing was the same for wild-type cells (12 s) and pilus-minus mutant cells (13 s), suggesting the pili do not play a significant role in reversible adhesion. Moreover, reversible adhesion events in wild-type cells (6.8 events/min) occur twice as frequently as irreversible adhesion events (3.3 events/min), demonstrating that most cells contact the surface multiple times before transitioning from reversible to irreversible adhesion.

Effector T Cell Egress via Afferent Lymph Modulates Local Tissue Inflammation.

Memory/effector T cells recirculate through extralymphoid tissues by entering from blood and egressing via afferent lymph. Although T cell entry into effector sites is key to inflammation, the relevance of T cell egress to this process is unknown. In this study, we found that Ag recognition at the effector site reduced the tissue egress of proinflammatory Th1 cells in a mouse model of delayed hypersensitivity. Transgenic expression of "tissue exit receptor" CCR7 enhanced lymphatic egress of Ag-sequestered Th1 cells from the inflamed site and alleviated inflammation. In contrast, lack of CCR7 on Th1 cells diminished their tissue egress while enhancing inflammation. Lymph-borne Th1 and Th17 cells draining the inflamed skin of sheep migrated toward the CCR7 ligand CCL21, suggesting the CCR7-CCL21 axis as a physiological target in regulating inflammation. In conclusion, exit receptors can be targeted to modulate T cell dwell time and inflammation at effector sites, revealing T cell tissue egress as a novel control point of inflammation.

T cell egress via the afferent lymph modulates the course of local tissue inflammation (CAM1P.149)

Abstract T cells recirculate through extralymphoid tissues by entering from the blood and egressing via the afferent lymph. While T cell migration into effector sites is key to inflammation, the influence of T cell egress in this process is not known. In a mouse model, antigen recognition at the effector site reduced the egress of antigen-specific pro-inflammatory Th1 cells. Transgenic expression of ‘tissue exit receptor’ CCR7 enhanced egress of antigen-sequestered Th1 cells from the inflamed site and ameliorated inflammation. In contrast, lack of CCR7 on Th1 cells diminished their tissue egress while enhancing inflammation. Lymph-borne Th1 and Th17 cells draining the inflamed skin of sheep chemotaxed to the CCR7 ligand CCL21, suggesting the CCR7-CCL21 axis as a physiological target in regulating inflammation. In conclusion, exit receptors can be targeted to modulate T cell dwell time and inflammation at effector sites, revealing T cell tissue egress via lymph as a novel parameter of the pathophysiology of inflammation.

Evaluation of Call Performance in Cellular Networks With Generalized Cell Dwell Time and Call-Holding Time Distributions in the Presence of Channel Fading

Call-completion probability, call-dropping probability, and handoff rate are important performance measures of wireless networks. In this paper, we study the joint effect of channel fading and handover failure on these performance measures. For the case of Rayleigh and lognormal fading channels and for generalized distributions of the cell dwell time and the call-holding time, we derive simple closed-form expressions that closely approximate these performance metrics. The results are given in terms of the moment-generating function (MGF) of the distribution for the call-holding time and may be useful in the cross-layer design and the optimization of wireless networks.

A Mobility Model and Performance Analysis in Wireless Cellular Network with General Distribution and Multi-Cell Model

Multi-cell mobility model and performance analysis for wireless cellular networks are presented. The mobility model plays an important role in characterizing different mobility-related parameters such as handoff call arrival rate, blocking or dropping probability, and channel holding time. We present a novel tractable multi-cell mobility model for wireless cellular networks under the general assumptions that the cell dwell times induced by mobiles' mobility and call holding times are modeled by using a general distribution instead of exponential distribution. We propose a novel generalized closed-form matrix formula to support the multi-cell mobility model and call holding time with general distributions. This allows us to develop a fixed point algorithm to compute loss probabilities, and handoff call arrival rate under the given assumptions. In order to reduce computational complexity of the fixed point algorithm, the channel holding time of each cell is down-modeled into an exponentially distributed one for purposes of simplification, since the service time is insensitive in computing loss probabilities of each cell due to Erlang insensitivity. The accuracy of the multi-cell analytic mobility model is supported by the comparison of the simulation results and the analytic ones.

System-Level Analysis of Mobile Cellular Networks Considering Link Unreliability

Traditionally, system-level performance evaluation of mobile wireless communication networks has been addressed by only considering resource insufficiency, whereas the effect of an unreliable wireless channel has largely been ignored because of the complexity that its inclusion entails. To fill this void, a general analytical model for the system-level performance evaluation of mobile wireless networks taking into account both resource insufficiency and link unreliability is proposed in this paper. The effect of link unreliability is captured through the appropriate probabilistic characterization of the ldquounencumbered call-interruption time.rdquo Additionally, useful functional relationships between the call-interruption processes of the proposed analytical model and some system-level parameters that can easily be obtained from statistics collected at base stations (BSs) are derived. For the sake of generality, the involved time variables (i.e., cell dwell time, unencumbered call-interruption time, and channel holding time) are considered generally distributed. Then, general and easily computable mathematical expressions for many useful performance metrics under more realistic considerations are obtained. The analytical model proposed here is able to provide new and important insights into the dependence of system performance on link unreliability. Such understanding of this teletraffic engineering issue is vital for planning, designing, dimensioning, and optimizing mobile cellular networks for present and future wireless communication systems beyond the third generation.

Distribution of random sum cell dwell times in wireless network

The distribution of a random sum of the cell dwell times (CDTs) for a complete call in a wireless network is derived in terms of a weighted sum of Erlang distributions. The weights are found to be functions of the moments of the cell dwell time. To validate the derived results by computer simulation, the gamma, Weibull, Pareto, and lognormal distributions for the CDT are considered.

State-dependent call admission control in hierarchical wireless multiservice networks

State-dependent call admission control (SDCAC) is proposed to make efficient use of scarce wireless resource in a hierarchical wireless network with heterogeneous traffic. With SDCAC, new calls are accepted according to an acceptance probability taking account of not only cell dwell time but also call holding time and system state (i.e., occupied bandwidth). An analytical method is developed to calculate performance measures of interest, e.g., new call blocking probability, forced termination probability, overall weighted blocking probability. Numerical results with not only stationary but nonstationary traffic loads are presented to show the robustness of SDCAC. It is shown that SDCAC performs much better than the other considered schemes under nonstationary traffic load.

Performance analysis of fractional guard channel policies in mobile cellular networks

In this letter, recursive formulas for the new call blocking and handoff failure probabilities for Fractional Guard Channel (FGC) policies in cellular networks are derived. The effect of users' mobility on the maximum system capacity achieved with the Guard Channel (GC), the Limited Fractional Guard Channel (LFGC), and the Uniform Fractional Guard Channel (UFGC) strategies is then evaluated. Results show that maximum system capacity decreases exponentially as the mean cell dwell time decreases and that the relative capacity gain of each scheme depends on the mean cell dwell time. It was also found that LFGC outperforms GC and UFGC under any mobility condition.

Progression of regulatory gene expression states in fetal and adult pro‐T‐cell development

Precursors entering the T-cell developmental pathway traverse a progression of states characterized by distinctive patterns of gene expression. Of particular interest are regulatory genes, which ultimately control the dwell time of cells in each state and establish the mechanisms that propel them forward to subsequent states. Under particular genetic and developmental circumstances, the transitions between these states occur with different timing, and environmental feedbacks may shift the steady-state accumulations of cells in each state. The fetal transit through pro-T-cell stages is faster than in the adult and subject to somewhat different genetic requirements. To explore causes of such variation, this review presents previously unpublished data on differentiation gene activation in pro-T cells of pre-T-cell receptor-deficient mutant mice and a quantitative comparison of the profiles of transcription factor gene expression in pro-T-cell subsets of fetal and adult wildtype mice. Against a background of consistent gene expression, several regulatory genes show marked differences between fetal and adult expression profiles, including those encoding two basic helix-loop-helix antagonist Id factors, the Ets family factor SpiB and the Notch target gene Deltex1. The results also reveal global differences in regulatory alterations triggered by the first T-cell receptor-dependent selection events in fetal and adult thymopoiesis.