Reconstructing diffusion fields sampled with a network of arbitrarily distributed sensors

Sensor networks are becoming increasingly prevalent for monitoring physical phenomena of interest. For such wireless sensor network applications, knowledge of node location is important. Although a uniform sensor distribution is common in the literature, it is normally difficult to achieve in reality. Thus we propose a robust algorithm for reconstructing two-dimensional diffusion fields, sampled with a network of arbitrarily placed sensors. The two-step method proposed here is based on source parameter estimation: in the first step, by properly combining the field sensed through well-chosen test functions, we show how Prony's method can reveal locations and intensities of the sources inducing the field. The second step then uses a modification of the Cauchy-Schwarz inequality to estimate the activation time in the single source field. We combine these steps to give a multi-source field estimation algorithm and carry out extensive numerical simulations to evaluate its performance

Using World-Wide-Web technology for pathology education

In this article, we describe the development of computer-based learning programs for pathology students at Jefferson Medical College. These programs are authored using HTML (HyperText Markup Language), and are available to students on campus and via the internet. Our computer-based learning resources include scheduling information, course goals and objectives, glossary of key words, self-assessment programs and image-based case studies. These educational programs are popular with the students. We recommend the use of World Wide Web technology to improve teaching and learning in pathology education

Estimating localized sources of diffusion fields using spatiotemporal sensor measurements

We consider diffusion fields induced by a finite number of spatially localized sources and address the problem of estimating these sources using spatiotemporal samples of the field obtained with a sensor network. Within this framework, we consider two different time evolutions: the case where the sources are instantaneous, as well as, the case where the sources decay exponentially in time after activation. We first derive novel exact inversion formulas, for both source distributions, through the use of Green's second theorem and a family of sensing functions to compute generalized field samples. These generalized samples can then be inverted using variations of existing algebraic methods such as Prony's method. Next, we develop a novel and robust reconstruction method for diffusion fields by properly extending these formulas to operate on the spatiotemporal samples of the field. Finally, we present numerical results using both synthetic and real data to verify the algorithms proposed herein

Spatiotemporal Sampling Trade-off for Inverse Diffusion Source Problems

We consider the spatiotemporal sampling of diffusion fields induced by M point sources, and study the associated inverse problem of recovering the initial parameters of the unknown sources. In particular, we focus on characterising qualitatively the error of the obtained source estimates. To achieve this, we obtain an expression with which we can trade the sensor density for performance accuracy. In other words, by evaluating the optimal sampling instant for a given sensor density-and using the corresponding field samples at that instant-we can expect to obtain an improvement in the estimation performance when compared to an arbitrary sampling instant. Finally, several numerical simulations are presented, to support the theoretical results obtained

Impact of Burkholderia Infection on Lung Transplantation in Cystic Fibrosis

Rationale: Lung transplantation offers the only survival option for patients with cystic fibrosis (CF) with end-stage pulmonary disease. Infection with Burkholderia species is typically considered a contraindication to transplantation in CF. However, the risks posed by different Burkholderia species on transplantation outcomes are poorly defined. Objectives: To quantify the risks of infection with Burkholderia species on survival before and after lung transplantation in patients with CF. Methods: Multivariate Cox survival models assessed hazard ratios of infection with Burkholderia species in 1,026 lung transplant candidates and 528 lung transplant recipients. Lung allocation scores, incorporating Burkholderia infection status, were calculated for transplant candidates. Measurements and Main Results: Transplant candidates infected with different Burkholderia species did not have statistically different mortality rates. Among transplant recipients infected with B. cenocepacia, only those infected with nonepidemic strains had significantly greater post-transplant mortality compared with uninfected patients (hazard ratio [HR], 2.52; 95% confidence interval [CI], 1.04–6.12; P 5 0.04). Hazards were similar between uninfected transplant recipients and those infected with B. multivorans (HR, 0.66; 95% CI, 0.27–1.56; P 5 0.34). Transplant recipients infected with B. gladioli had significantly greater post-transplant mortality than uninfected patients (HR, 2.23; 95% CI, 1.05–4.74; P 5 0.04). Oncehazards for species/strainwereincluded,lung allocation scores of B. multivorans–infected transplant candidates were comparable to uninfected candidate scores, whereas those of candidates infected with nonepidemic B. cenocepacia or B. gladioli were lower. Conclusions: Post-transplant mortality among patients with CF infected with Burkholderia varies by infecting species. This variability should be taken into account in evaluating lung transplantation candidates.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91898/1/Murray LiPuma AJRCCM 2008.pd

Stability of hydroxylated minerals on Mars: A study on the effects of exposure to ultraviolet radiation

The density and composition of the Martian atmosphere allow solar ultraviolet photons with wavelengths as short as 190 nm to reach the surface. We investigate the hypothesis that this UV radiation is capable of inducing the release of water from iron oxyhydroxide minerals resulting in the formation of oxide phases. These experiments, which utilize a quadrupole mass spectrometer to monitor the water vapor pressure above mineral samples during cyclic exposure to ultraviolet radiation, offer 5 to 6 orders of magnitude greater sensitivity than previous attempts to establish and quantify this process. We find no evidence that UV photons are capable of liberating OH from the crystal lattice of minerals, and we set a minimum ultraviolet radiation-induced dehydroxylation time of 10^8 years for removal of this structural OH from mineral particles at the Martian surface. The overturning timescales for surface fines are likely to be shorter than this lower limit for exposure time. Thus we conclude that UV-stimulated dehydroxylation is not a significant process at the Martian surface and that iron oxyhydroxides, if formed during an earlier water-rich environment, should still be found on Mars today. The lack of clear evidence for iron oxyhydroxides at the Martian surface further suggests that Mars' surface was never warm and wet for a long enough period of time for Earth-like weathering to have occurred

Crater population and resurfacing of the Martian north polar layered deposits

Present-day accumulation in the north polar layered deposits (NPLD) is thought to occur via deposition on the north polar residual cap. Understanding current mass balance in relation to current climate would provide insight into the climatic record of the NPLD. To constrain processes and rates of NPLD resurfacing, a search for craters was conducted using images from the Mars Reconnaissance Orbiter Context Camera. One hundred thirty craters have been identified on the NPLD, 95 of which are located within a region defined to represent recent accumulation. High Resolution Imaging Science Experiment images of craters in this region reveal a morphological sequence of crater degradation that provides a qualitative understanding of processes involved in crater removal. A classification system for these craters was developed based on the amount of apparent degradation and infilling and where possible depth/diameter ratios were determined. The temporal and spatial distribution of crater degradation is interpreted to be close to uniform. Through comparison of the size-frequency distribution of these craters with the expected production function, the craters are interpreted to be an equilibrium population with a crater of diameter D meters having a lifetime of ~30.75D^(1.14) years. Accumulation rates within these craters are estimated at 7.2D^(−0.14) mm/yr, which corresponds to values of ~3–4 mm/yr and are much higher than rates thought to apply to the surrounding flat terrain. The current crater population is estimated to have accumulated in the last ~20 kyr or less

The North Wyke Farm Platform: Methodologies Used in the Remote Sensing of the Quantity and Quality of Drainage Water

The North Wyke Farm Platform(NWFP) for agri-environmental research in temperate grassland was established in the UK in 2010 (Orr et al. 2011). Here we describe the instrumentation and methodologies used to monitor the quantity and quality of drainage water at a total of 15 H-flumes draining 5 sub-catchments within three farmlets. Each of 15 flume laboratories is supplied with 3 kW of mains power and connected to both fibre optic and UHF (Ultra High Frequency) radio networks for data exchange. The radio data network also provides telemetry for rain gauges and soil temperature/moisture probes located away from the flumes and within the catchment blocks. Water flow is measured using bubbler flow meters and when flow is above a defined threshold level, water is pumped into bespoke 13-litre stainless steel bypass cells on a 15-minute cycle using bi-directional peristaltic pumps. A range of sensors located within the bypass cells measure the following water quality parameters: nitrate, ammonium, dissolved organic carbon, temperature, conductivity, turbidity, pH and dissolved oxygen. Total phosphorus and ortho phosphorus are measured at one flume in each farmlet. Networked auto-samplers are also provided at each flume site for the measurement of other wa-ter quality parameters as required. All data are logged and sent to a dedicated server at a 15 min resolution while a web front end allows advanced visualization capabilities and remote control of the entire system. The system is configured to allow for flexibility and future expansion to a wider range of parameters