Improved Approximation Algorithms for Connected Sensor Cover

Wireless sensor networks have recently posed many new system building challenges. One of the main problems is energy conservation since most of the sensors are devices with limited battery life and it is infeasible to replenish energy via replacing batteries. An effective approach for energy conservation is scheduling sleep intervals for some sensors, while the remaining sensors stay active providing continuous service. In this paper we consider the problem of selecting a set of active sensors of minimum cardinality that maintains sensing coverage and network connectivity. We study different variations of this problem. The main contribution of this paper is a thorough investigation of algorithms for covering an area with sensors that have fixed locations

Severe traumatic brain injury in children elevates glial fibrillary acidic protein in cerebrospinal fluid and serum

Objectives: 1) To determine the levels and half-life of glial fibrillary acidic protein (GFAP) in both cerebrospinal fluid and serum; 2) to determine whether serum GFAP levels correlate with functional outcome; and 3) to determine whether therapeutic hypothermia, as compared with normothermia, alters serum GFAP levels or half-life in children with severe traumatic brain injury (TBI). Design: Laboratory-based analyses; postrandomized, controlled trial. Setting: Four Canadian pediatric intensive care units and a university-affiliated laboratory. Patients: Twenty-seven children, aged 2-17 yrs, with severe TBI (Glasgow Coma Scale score of <=8). Interventions: Hypothermia therapy (32.5[degrees]C) for 24 hrs with cooling started within 8 hrs of injury and rewarming at a rate of 0.5[degrees]C every 2 hrs or normothermia (37.0[degrees]C). Measurements and Main Results: GFAP was measured in cerebrospinal fluid and serum, using enzyme-linked immunosorbent assay. Levels of GFAP were maximal on day 1 post-TBI, with cerebrospinal fluid GFAP (15.5 +/- 6.1 ng/mL) 25-fold higher than serum GFAP (0.6 +/- 0.2 ng/mL). Cerebrospinal fluid GFAP normalized by day 7, whereas serum GFAP decreased gradually to reach a steady state by day 10. Serum GFAP measured on day 1 correlated with Pediatric Cerebral Performance Category scores determined at 6 months post-TBI ([rho] = 0.527; p = .008) but failed to correlate with the injury scoring on admission, physiologic variables, or indices of injury measured on computerized tomography imaging. The areas under the receiver operating characteristic curves for pediatric intensive care unit day 1 serum GFAP in determining good outcome were 0.80 (pediatric cerebral performance category, 1-2; normal-mild disability) and 0.91 (pediatric cerebral performance category, 1-3; normal-moderate disability). For a serum GFAP cutoff level of 0.6 ng/mL, sensitivity and specificity were 88% to 90% and 43% to 71%, respectively. Serum GFAP levels were similar among children randomized to either therapeutic hypothermia or normothermia. Conclusions: GFAP was markedly elevated in cerebrospinal fluid and serum in children after severe TBI and serum GFAP measured on pediatric intensive care unit day 1 correlated with functional outcome at 6 months. Hypothermia therapy did not alter serum GFAP levels compared with normothermia after severe TBI in children. Serum GFAP concentration, together with other biomarkers, may have prognostic value after TBI in children.Peer reviewed: YesNRC publication: Ye

Microspacecraft Platform with Bipropellant Propulsion System and 3-Axis Stabilization for Missions in Earth Orbit and Beyond LEO

This paper presents a low-cost microspacecraft platform concept for missions which require high D-v capabilities of up to about 1,500 m/s, using auxiliary launch opportunities, e.g., from the Ariane 5 ASAP. The proposed concept is extremely flexible and can be adapted to specific mission requirements, thus permitting low-cost missions to Earth orbit, as well as to the Moon, Mars, and selected asteroids. A particular focus of this paper is on the modularity of the proposed concept, including the bipropellant propulsion system needed to provide the required D-v, the lightweight structural concept, and the 3-axis attitude determination and control system (ADCS), as well as the available P/L masses and the most important spacecraft characteristics and constraints. The proposed microspacecraft platform is derived from the LunarSat concept, which has been developed by a team led by the Technische Universität München, Germany, and Surrey Satellite Technology Ltd., UK. Consequently, the LunarSat spacecraft and mission are presented as an example of the proposed concept