RESUMEN
Fog computing has recently emerged as an extension of cloud computing in providing high-performance computing services for delay-sensitive Internet of Things (IoT) applications. By offloading tasks to a geographically proximal fog computing server instead of a remote cloud, the delay performance can be greatly improved. However, some IoT applications may still experience considerable delays, including queuing and computation delays, when huge amounts of tasks instantaneously feed into a resource-limited fog node. Accordingly, the cooperation among geographically close fog nodes and the cloud center is desired in fog computing with the ever-increasing computational demands from IoT applications. This paper investigates a workload allocation scheme in an IoT-fog-cloud cooperation system for reducing task service delay, aiming at satisfying as many as possible delay-sensitive IoT applications' quality of service (QoS) requirements. To this end, we first formulate the workload allocation problem in an IoT-edge-cloud cooperation system, which suggests optimal workload allocation among local fog node, neighboring fog node, and the cloud center to minimize task service delay. Then, the stability of the IoT-fog-cloud queueing system is theoretically analyzed with Lyapunov drift plus penalty theory. Based on the analytical results, we propose a delay-aware online workload allocation and scheduling (DAOWA) algorithm to achieve the goal of reducing long-term average task serve delay. Theoretical analysis and simulations have been conducted to demonstrate the efficiency of the proposal in task serve delay reduction and IoT-fog-cloud queueing system stability.
RESUMEN
Software-defined acoustic modems (SDAMs) for underwater communication and networking have been an important research topic due to their flexibility and programmability. In this paper, we propose a reconfigurable platform for SDAMs based on the TI AM5728 processor, which integrates dual-core ARM Cortex-A15 CPUs and two TI C66x DSP cores. The signal processing and A/D, D/A for physical-layer communication are implemented in the DSP cores. The networking protocols and the application programs are implemented in the ARM cores. The proposed platform has the following characteristics: (1) Due to the high-performance dual-ARM cores, the whole NS3 network simulator can be run in the ARM cores. Network protocols developed in a software simulation platform (e.g., NS3 platform) can be seamlessly migrated to a hardware platform without modification. (2) A new physical-layer module associated with real acoustic channel is developed, such that a data packet generated from the application layer will be transmitted through a real acoustic channel. The results of networking experiments with five nodes are presented to demonstrate the effectiveness of the proposed platform.
RESUMEN
The long propagation delay in underwater acoustic channels has attracted tremendous attentions in designing Medium Access Control (MAC). The low acoustic propagation speed and wide area of the acoustic communication range led to a wide range of variations in the propagation delay. This paper identifies an important characteristic of two-scale delay variations by field test results. We carry out simulations to study the impact of delay variations on MAC, and the results suggest a slot length adaptation scheme for the handshake and slotting based MAC. We further model an absorbing Markov chain to derive the closed-form equation for the throughput of MAC with adaptive slot length. Both the analytical and simulation results show that our proposed slot length adaptation improves significantly the throughput of MAC in underwater acoustic networks. Particularly, the Slotted-FAMA with an adaptive slot length achieves more than double the throughput than the Slotted-FAMA with a fixed slot length in a network with six nodes.
RESUMEN
Underwater acoustic communication network (UACN) has been considered as an essential infrastructure for ocean exploitation. Performance analysis of UACN is important in underwater acoustic network deployment and management. In this paper, we analyze the network throughput of three-dimensional randomly deployed transmitter-receiver pairs. Due to the long delay of acoustic channels, complicated networking protocols with heavy signaling overhead may not be appropriate. In this paper, we consider only one-hop or two-hop transmission, to save the signaling cost. That is, we assume the transmitter sends the data packet to the receiver by one-hop direct transmission, or by two-hop transmission via mobile relays. We derive the closed-form formulation of packet delivery rate with respect to the transmission delay and the number of transmitter-receiver pairs. The correctness of the derivation results are verified by computer simulations. Our analysis indicates how to obtain a precise tradeoff between the delay constraint and the network capacity.
RESUMEN
Liver-targeted drug delivery improves the efficacy of anti-liver cancer agents and reduces systemic toxicity by limiting the bioavailability of these drugs to within tumors. Liver targeting reagents with galactose residues, which selectively combine to asialoglyco protein receptors, have previously been used to improve liposome-encapsulated drug accumulation within liver cells. They lead to a reduction in liver cancer cell growth and have been used to cure certain hepatic diseases. In the present study, curcumol, which is the primary active component of Chinese traditional medicine Rhizoma zedoariae, was encapsulated in galactosylated-liposomes to enhance its anti-liver cancer efficacy. Galactosylated-liposomes and normal liposomes were labeled with propidium iodide. Galactosylated-liposomes with increasing concentrations of galactosylated-stearate (Gal-s) had a notably increased level of uptake in HepG2 cells (hepatoblastoma) compared with SGC-7901 (gastric cancer) and A549 (non-small cell lung cancer) cells. When the percentage of Gal-s reached 20%, liposome uptake plateaued. In the in vitro anti-liver cancer experiment, the anti-liver cancer efficacy of galactosylated-curcumol-liposomes increased significantly more compared with normal curcumol liposomes and free curcumol as indicated by cell survival rate and lactate dehydrogenase release rate. Collectively, these results demonstrate that galactosylated-liposomes are able to enhance the in vitro liver-targeting effect and anti-liver cancer efficacy of curcumol.