Amorphous Placement and Informed Diffusion for Timely Monitoring by Autonomous, Resource-Constrained, Mobile Sensors

Personal communication devices are increasingly equipped with sensors for passive monitoring of encounters and surroundings. We envision the emergence of services that enable a community of mobile users carrying such resource-limited devices to query such information at remote locations in the field in which they collectively roam. One approach to implement such a service is directed placement and retrieval (DPR), whereby readings/queries about a specific location are routed to a node responsible for that location. In a mobile, potentially sparse setting, where end-to-end paths are unavailable, DPR is not an attractive solution as it would require the use of delay-tolerant (flooding-based store-carry-forward) routing of both readings and queries, which is inappropriate for applications with data freshness constraints, and which is incompatible with stringent device power/memory constraints. Alternatively, we propose the use of amorphous placement and retrieval (APR), in which routing and field monitoring are integrated through the use of a cache management scheme coupled with an informed exchange of cached samples to diffuse sensory data throughout the network, in such a way that a query answer is likely to be found close to the query origin. We argue that knowledge of the distribution of query targets could be used effectively by an informed cache management policy to maximize the utility of collective storage of all devices. Using a simple analytical model, we show that the use of informed cache management is particularly important when the mobility model results in a non-uniform distribution of users over the field. We present results from extensive simulations which show that in sparsely-connected networks, APR is more cost-effective than DPR, that it provides extra resilience to node failure and packet losses, and that its use of informed cache management yields superior performance

Amorphous Placement and Retrieval of Sensory Data in Sparse Mobile Ad-Hoc Networks

Abstract—Personal communication devices are increasingly being equipped with sensors that are able to passively collect information from their surroundings – information that could be stored in fairly small local caches. We envision a system in which users of such devices use their collective sensing, storage, and communication resources to query the state of (possibly remote) neighborhoods. The goal of such a system is to achieve the highest query success ratio using the least communication overhead (power). We show that the use of Data Centric Storage (DCS), or directed placement, is a viable approach for achieving this goal, but only when the underlying network is well connected. Alternatively, we propose, amorphous placement, in which sensory samples are cached locally and informed exchanges of cached samples is used to diffuse the sensory data throughout the whole network. In handling queries, the local cache is searched first for potential answers. If unsuccessful, the query is forwarded to one or more direct neighbors for answers. This technique leverages node mobility and caching capabilities to avoid the multi-hop communication overhead of directed placement. Using a simplified mobility model, we provide analytical lower and upper bounds on the ability of amorphous placement to achieve uniform field coverage in one and two dimensions. We show that combining informed shuffling of cached samples upon an encounter between two nodes, with the querying of direct neighbors could lead to significant performance improvements. For instance, under realistic mobility models, our simulation experiments show that amorphous placement achieves 10% to 40% better query answering ratio at a 25% to 35% savings in consumed power over directed placement.National Science Foundation (CNS Cybertrust 0524477, CNS NeTS 0520166, CNS ITR 0205294, EIA RI 0202067

Late deflation study : hemodynamic effects of IAB timing in humans

Conventional IABP timing deflates 100% of the balloon volume before the onset of left ventricular ejection and has been well established in the literature as a safe and effective method. Yet, recent studies suggest that deflation of the IAB at or near the onset of systole improve myocardial efficiency (Kern, 1999, 1129). To test whether deflation of the JAB at a later deflation time reduces left ventricular workload and enhances coronary perfusion, four timing methods were evaluated in 20 patients: T1 (100% JAB volume deflated before onset of ejection), T2 (60% IAB volume deflated before and 40% volume during ejection), T3 (25% IAB volume deflated before and 75% volume during ejection) and T4 (100% deflation simultaneous with left ventricular ejection). To identify an optimal timing point for the deflation of the JAB, data was analyzed. Data analysis consisted of three main parts: elimination of files containing noise artifact, normalization of data for ease of analysis, and correction for variations in mean aortic pressure and heart rate which take into account the dynamic state of the heart. Late LAB deflation at 50% of the volume deflated prior to left ventricular ejection produced significantly greater percentage changes in systolic pressure time index (SPTI), diastolic pressure time index (DPTI), the SPTI/DPTI ratio, systemic vascular resistance (SVR) as compared to conventional timing, T1. No significant change in heart rate or cardiac output was established

Nanostructured Mg-ZK50 Sheets Fabricated for Potential Use for Biomedical Applications

Magnesium (Mg) alloys are widely used in biomedical applications thanks to their combination of exceptional mechanical properties, biocompatibility, and biodegradability. Mg-ZK alloy series; for instance, ZK40, ZK60 and ZK61; is an example of the most commonly used Mg bio-alloy. Zirconium (Zr) acts as a grain refiner when added to Mg, which manipulates the material structure by producing a refined internal structure and enhancing its properties. In addition, when Zinc (Zn) is added to a Mg-Zr alloy, strength is improved. Therefore, given the favorable properties of ZK alloys in biomedical applications, the current research aimed for the fabrication and the evaluation of a new ZK alloy with a new composition; ZK50, as a potential biomaterial for biomedical applications. Three stages were implemented in order to achieve the objective of this study. In the first stage, ball milling process was used to synthesize nanostructured Mg-ZK50 alloy from elemental powders (Mg, Zr, and Zn). The produced powders (BM) were studied using SEM, XRD and TEM to determine the internal structure refinement as well as the phase development due to milling. In the second stage, Powder-in-Tube (PIT) rolling process followed by annealing was applied to produce consolidated thin sheets from the BM powders. Accordingly, in the third stage, the effect of annealing on the internal structure, mechanical properties, corrosion behavior and cytotoxicity was evaluated. The mechanical milling of the elemental powders produced a nanostructured alloyed powder after 45 hrs of milling with a crystallite size of 8.83 nm, which is considered the finest internal structure for Mg and Mg based alloys to date. Afterwards, nanostructured thin sheets were successfully produced using PIT at 300 °C with 67% reduction percent. The modulus of the sheets was found matching to that of human bones. It is worthy to note that annealing was found to have a detrimental effect on the corrosion behavior of the alloy. However, a hydroxyapatite layer was formed which indicated that the produced sheets induced osteoinductivity of the bone. Moreover, cytotoxicity of the sheets was not affected by the sheets and all the produced sheets showed an acceptable toxicity level within the cells. In conclusion, the produced Mg-ZK50 nanostructured alloyed sheets are considered a new potential biomaterial for orthopedic implants that induces osteoinductivity and prevent stress shielding

Assessing systems reliability: a Probabilistic Risk Assessment (PRA) approach

Assessing the reliability performance of complex system involves dealing with events whose occurrence cannot be predicted easily. Not only a good descriptive procedure of the system's components is required but the solution requires some means by which the likelihood of the events can be expressed in terms of quantitative methods. This can be done by adopting a probabilistic risk and reliability assessment method to assess system behaviour. This requires enhancing the reliability analysis with a probabilistic risk analysis technique. The procedure of integration suggested in this work is called Probabilistic Risk Analysis [PRA]. It involves: 1) Identification of the potential events of failures and their modes of failures. 2) Estimation of the consequences of these failures on the total system. 3) Estimation of the probability of occurrence of each event of failure. 4) Comparison of the results of the analysis against an acceptability criterion or criteria. The third step is the focus of this paper where the novelty of this work appears. Rather than drawing a deterministic FTD for identifying probability of occurrences of the failure events a probabilistic one is suggested to cater for any risks or uncertainties involved in the system. By allowing probabilistic input of basic events a probabilistic top event is produced giving managers more freedom to check among a range of failure probabilities that the system might fall in rather than one limited deterministic failure value. This gives more practicality to the assessment of the whole system resulting in better actions and higher reliable performance