Infection rates following initial cerebrospinal fluid shunt placement across pediatric hospitals in the United States

Journal ArticleObject. Reported rates of CSF shunt infection vary widely across studies. The study objective was to determine the CSF shunt infection rates after initial shunt placement at multiple US pediatric hospitals. The authors hypothesized that infection rates between hospitals would vary widely even after adjustment for patient, hospital, and surgeon factors. Methods. This retrospective cohort study included children 0-18 years of age with uncomplicated initial CSF shunt placement performed between January 1, 2001, and December 31, 2005, and recorded in the Pediatric Health Information System (PHIS) longitudinal administrative database from 41 children's hospitals. For each child with 24 months of follow-up, subsequent CSF shunt infections and procedures were determined. Results. The PHIS database included 7071 children with uncomplicated initial CSF shunt placement during this time period. During the 24 months of follow-up, these patients had a total of 825 shunt infections and 4434 subsequent shunt procedures. Overall unadjusted 24-month CSF shunt infection rates were 11.7% per patient and 7.2% per procedure. Unadjusted 24-month cumulative incidence rates for each hospital ranged from 4.1 to 20.5% per patient and 2.5-12.3% per procedure. Factors significantly associated with infection (p 11% of children who underwent uncomplicated initial CSF shunt placements within 24 months. Patient, hospital, and surgeon factors contributed somewhat to the wide variation in CSF shunt infection rates across hospitals. Additional factors may contribute to variation in CSF shunt infection rates between centers, but further study is needed. Benchmarking and future prospective multicenter studies of CSF shunt infection will need to incorporate these and other patient, hospital, and surgeon factors

Experimental investigation of stress rate and grain size on gas seepage characteristics of granular coal

Coal seam gas, held within the inner pores of unmineable coal, is an important energy resource. Gas release largely depends on the gas seepage characteristics and their evolution within granular coal. To monitor this evolution, a series of experiments were conducted to study the effects of applied compressive stress and original grain size distribution (GSD) on the variations in the gas seepage characteristics of granular coal samples. Grain crushing under higher stress rates was observed to be more intense. Isolated fractures in the larger diameter fractions transformed from self–extending to inter-connecting pathways at a critical compressive stress. Grain crushing was mainly caused by compression and high-speed impact. Based on the test results of the original GSD effect, the overall process of porosity and permeability evolution during compression can be divided into three different phases: (1) rapid reduction in the void ratio; (2) continued reduction in the void ratio and large particle crushing; and (3) continued crushing of large particles. Void size reduction and particle crushing were mainly attributed to the porosity and permeability decreases that occurred. The performance of an empirical model, for porosity and permeability evolution, was also investigated. The predictive results indicate that grain crushing caused permeability increases during compression, and that this appeared to be the main cause for the predictive values being lower than those obtained from the experimental tests. The predictive accuracy would be the same for samples under different stress rates and the lowest for the sample with the highest proportion of large grain diameter

Predicting the whispering gallery mode spectra of microresonators

The whispering gallery modes (WGMs) of optical resonators have prompted intensive research efforts due to their usefulness in the field of biological sensing, and their employment in nonlinear optics. While much information is available in the literature on numerical modeling of WGMs in microspheres, it remains a challenging task to be able to predict the emitted spectra of spherical microresonators. Here, we establish a customizable Finite- Difference Time-Domain (FDTD)-based approach to investigate the WGM spectrum of microspheres. The simulations are carried out in the vicinity of a dipole source rather than a typical plane-wave beam excitation, thus providing an effective analogue of the fluorescent dye or nanoparticle coatings used in experiment. The analysis of a single dipole source at different positions on the surface or inside a microsphere, serves to assess the relative efficiency of nearby radiating TE and TM modes, characterizing the profile of the spectrum. By varying the number, positions and alignments of the dipole sources, different excitation scenarios can be compared to analytic models, and to experimental results. The energy flux is collected via a nearby disk-shaped region. The resultant spectral profile shows a dependence on the configuration of the dipole sources. The power outcoupling can then be optimized for specific modes and wavelength regions. The development of such a computational tool can aid the preparation of optical sensors prior to fabrication, by preselecting desired the optical properties of the resonator.Comment: Approved version for SPIE Photonics West, LASE, Laser Resonators, Microresonators and Beam Control XV

Method for predicting whispering gallery mode spectra of spherical microresonators

A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit is developed to simulate the whispering gallery modes of a microsphere in the vicinity of a dipole source. This provides a guide for experiments that rely on efficient coupling to the modes of microspheres. The resultant spectra are compared to those of analytic models used in the field. In contrast to the analytic models, the FDTD method is able to collect flux from a variety of possible collection regions, such as a disk-shaped region. The customizability of the technique allows one to consider a variety of mode excitation scenarios, which are particularly useful for investigating novel properties of optical resonators, and are valuable in assessing the viability of a resonator for biosensing.Comment: Published 10 Apr 2015 in Opt. Express Vol. 23, Issue 8, pp. 9924-9937; The FDTD toolkit supercomputer scripts are hosted at: http://sourceforge.net/projects/npps/files/FDTD_WGM_Simulator

Enhancing thermal properties of asphalt materials for heat storage and transfer applications

The paper considers extending the role of asphalt concrete pavements to become solar heat collectors and storage systems. The majority of the construction cost is already procured for such pavements and only marginal additional costs are likely to be incurred to add the necessary thermal features. Asphalt concrete pavements are, therefore, designed that incorporate aggregates and additives such as limestone, quartzite, lightweight aggregate, copper slag and copper fibre to make them more conductive, or more insulative, or to enable them to store more heat energy. The resulting materials are assessed for both mechanical and thermal properties by laboratory tests and numerical simulations and recommendations are made in regard to the optimum formulations for the purposes considered

Influence of the thermophysical properties of pavement materials on the evolution of temperature depth profiles in different climatic regions

The paper summarizes the relative influence of different pavement thermo-physical properties on the thermal response of pavement cross-sections, and how their relative behaviour changes in different climatic regions. A simplified one-dimensional heat flow modelling tool was developed to achieve this using a finite difference solution method for studying the dynamic temperature profile within pavement constructions. This approach allows for a wide variety and daily varying climatic conditions to be applied, where limited or historic thermo-physical material properties are available, and permits the thermal behaviour of the pavement layers to be accurately modelled and modified. The model was used with available thermal pavement materials properties and with properties determined specifically for the study reported here. The pavement materials included in the study comprised both conventional bituminous and cementicious mixes as well as unconventional mixtures that allowed a wide range of densities, thermal conductivities, specific heat capacities and thermal diffusivities to be investigated. Initially, the model was validated against in-situ pavement data collected in the USA in five widely differing climatic regions. It was found to give results at least as good as others available from more computationally expensive approaches such as 2D and 3D FE commercial packages. Then the model was used to compute the response for the same locations had the thermal properties been changed by using some of the unconventional pavement materials been used. This revealed that reduction of temperature range by several degrees was easily possible (with implications for reduction of rutting, fatigue and the Urban Heat Island effect) and that depth of penetration of peak temperatures was also achievable (with implications for winter freeze-thaw). However, the results showed that there was little opportunity to displace the peak temperatures in time