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We investigate a wireless system of multiple cells, each having a downlink shared channel in support of highspeed packet data services. In practice, such a system consists of hierarchically organized entities including a central server, Base Stations (BSs), and Mobile Stations (MSs). Our goal is to improve global resource utilization and reduce regional congestion given asymmetric arrivals and departures of mobile users, a goal requiring load balancing among multiple cells. For this purpose, we propose a scalable cross-layer framework to coordinate packet-level scheduling, call-level cell-site selection and handoff, and system-level cell coverage based on load, throughput, and channel measurements. In this framework, an opportunistic scheduling algorithm-the weighted Alpha-Rule-exploits the gain of multiuser diversity in each cell independently, trading aggregate (mean) downlink throughput for fairness and minimum rate guarantees among MSs. Each MS adapts to its channel dynamics and the load fluctuations in neighboring cells, in accordance with MSs' mobility or their arrival and departure, by initiating load-aware handoff and cell-site selection. The central server adjusts schedulers of all cells to coordinate their coverage by prompting cell breathing or distributed MS handoffs. Across the whole system, BSs and MSs constantly monitor their load, throughput, or channel quality in order to facilitate the overall system coordination.Our specific contributions in such a framework are highlighted by the minimum-rate guaranteed weighted Alpha-Rule scheduling, the load-aware MS handoff/cell-site selection, and the Media Access Control (MAC)-layer cell breathing. Our evaluations show that the proposed framework can improve global resource utilization and load balancing, resulting in a smaller blocking rate of MS arrivals without extra resources while the aggregate throughput remains roughly the same or improved at the hot-spots. Our simulation tests also show that the coordinated system is robust to dynamic load fluctuations and is scalable to both the system dimension and the size of MS population.

Two kinds of dental stem cells (DSCs), dental pulp stem cells (DPSCs) and stem cells from human-exfoliated deciduous teeth (SHED), have been identified as novel populations of mesenchymal stem cells that can be induced to differentiate into osteoblasts, chondrocytes, adipocytes, and neuron-like cells in vitro. As we know, both of them originate from the neural crest, but have distinct characteristics and functions in vitro and in vivo. The regeneration potential of DSCs declines with advanced age; however, the mechanism of the impaired potential in DSCs has not been fully explored. In this study, we investigated whether declined neurogenic differentiation capacity is associated with an altered expression of Wnt signaling-related proteins in vitro. We compared stem cells isolated from human dental pulp in two age groups: the exfoliated deciduous teeth (5-12 years), and the third permanent teeth (45-50 years). We found that the expression levels of neuron markers, such as βIII-tubulin, microtubule-associated protein 2(MAP2), tyrosine hydroxylase (TH), and Nestin were lower in the DPSCs group compared with that in the SHED group; however, in supplementation with human recombinant Wnt1 in the medium, the DPSCs were prone to neural differentiation and expressed higher levels of neurogenic markers. In summary, our study demonstrated that Wnt/β-catenin signaling may play a vital role in the age-dependent neural differentiation of DSCs. Therefore, DSCs may provide an ideal source of stem cells that can further extend their therapeutic application in nerve injury and neurodegenerative diseases.

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