Impulsive Noise Mitigation in Powerline Communications Using Sparse Bayesian Learning

Additive asynchronous and cyclostationary impulsive noise limits communication performance in OFDM powerline communication (PLC) systems. Conventional OFDM receivers assume additive white Gaussian noise and hence experience degradation in communication performance in impulsive noise. Alternate designs assume a parametric statistical model of impulsive noise and use the model parameters in mitigating impulsive noise. These receivers require overhead in training and parameter estimation, and degrade due to model and parameter mismatch, especially in highly dynamic environments. In this paper, we model impulsive noise as a sparse vector in the time domain without any other assumptions, and apply sparse Bayesian learning methods for estimation and mitigation without training. We propose three iterative algorithms with different complexity vs. performance trade-offs: (1) we utilize the noise projection onto null and pilot tones to estimate and subtract the noise impulses; (2) we add the information in the data tones to perform joint noise estimation and OFDM detection; (3) we embed our algorithm into a decision feedback structure to further enhance the performance of coded systems. When compared to conventional OFDM PLC receivers, the proposed receivers achieve SNR gains of up to 9 dB in coded and 10 dB in uncoded systems in the presence of impulsive noise.Comment: To appear in IEEE Journal on Selected Areas of Communication

Use of Focus Groups in Survey Item Development

Focus groups are rapidly gaining popularity as a field research tool. This technique can be particularly effective in survey item development, as illustrated here via development of the Volunteer Work Behaviors Questionnaire. The steps involved in this process, ranging from item generation to finalizing logistics, are outlined. Implications for further research are proposed

Revisiting the analytical solution approach to mixing-limited equilibrium multicomponent reactive transport using mixing ratios: identification of basis, fixing an error, and dealing with multiple minerals

Multicomponent reactive transport involves the solution of a system of nonlinear coupled partial differential equations. A number of methods have been developed to simplify the problem. In the case where all reactions are in instantaneous equilibrium and the mineral assemblage is constant in both space and time, de Simoni et al. (2007) provide an analytical solution that separates transport of aqueous components and minerals using scalar dissipation ofPeer ReviewedPostprint (published version

The photochemistry of carbon monoxide in the stratosphere and mesosphere evaluated from observations by the Microwave Limb Sounder on the Aura satellite

The photochemical production and loss rates for carbon monoxide (CO) in the stratosphere and mesosphere are evaluated using measurements from the Aura Microwave Limb Sounder (MLS) and the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS). The distributions of reactive trace gases involved in the photochemistry of CO, including OH, CH4, O(D-1), Cl, as well as temperatures for calculating reaction rates, are either directly observed or constrained from observations. We map the CO net production and loss as a function of pressure (10-0.02 hPa, about 30-75 km altitude), latitude (approximately +/- 70 degrees), and season. The results indicate that photochemical loss dominates over production for nearly all conditions considered here. A minimum photochemical loss lifetime of about 10 days occurs near the 2 hPa pressure level, and it follows the region of maximum sunlight exposure. At high latitudes during winter, the CO lifetime is generally longer than 30 days. Time scales become much shorter in spring, however, when CO lifetimes can be 15-20 days poleward of 60 degrees latitude in the upper stratosphere. On the basis of these results, CO is a suitable tracer during autumn to spring above the 0.1 hPa pressure level but not in the upper stratosphere near 1 hPa.</p

Additively manufactured heterogeneous substrates for three-dimensional control of local permittivity

The concept of using additive manufacturing as a method to construct heterogeneous substrates from a single building material via stereolithography is introduced. The dynamic variation of air cavities within the bulk material is used to control the effective permittivity of the host medium. The digitally driven layer process enables full three-dimensional variation of the local permittivity. The high resolution of stereolithography enables sub-millimetre control of air inclusion features. Measurements of the effective permittivity with different air fractions have been compared to analytical results

Neurocognitive outcomes in children experiencing seizures during treatment for acute lymphoblastic leukemia

There is a growing literature for cognitive late effects among childhood cancer survivors, yet little empirical information is known regarding specific neurocognitive outcomes of children who experience seizures while treated for acute lymphoblastic leukemia. This study examined prevalence of on-protocol seizures, seizure risk factors, and neurocognitive change in children with therapy-related seizures in comparison to the normative sample and a matched cohort of children without on-protocol seizures. Participants included children enrolled on the St. Jude frontline leukemia treatment protocol, Total Therapy 15 (TOTXV) - the first systematic investigation of intensified chemotherapy agents plus optimal intrathecal therapy without irradiation. Out of 498 children, 19 experienced therapy-related seizures. To increase the statistical power of comparisons, the 19 children were matched on relevant variables to two children without on-protocol seizures. Neuropsychological assessment and magnetic resonance imaging each occurred across three treatment time-points. Results revealed a 3.82% two-year incidence of seizures during TOTXV with over 50 percent of seizures during induction and consolidation phases. No demographic or clinical factors were predictive of seizures; although, a trend for standard/high treatment intensity was observed. When the neuropsychological performance of the seizure group was compared to normative scores, patterns of differences emerged and maintained across time-points for domains of attention, working memory, and processing speed significantly elevated for the seizure group. Similar patterns also emerged across time-points between the seizure group and the non-seizure cohort. At therapy completion, the seizure group performed significantly worse for attention and working memory tasks than the cohort, and these deficits persisted two years later with the addition of processing speed deficits and significantly worse intellectual functioning. Imaging findings indicated that children with therapy-related seizures experienced more significant early neurotoxicity (i.e., leukoencephalopathy) than non-seizure cohorts. Based on these preliminary findings, it appears that children who experience treatment-related seizures are at greater neurocognitive risk when compared to counterparts who do not. Findings point to a relationship between on-therapy seizures, leukoencephalopathy, and deficits in neuropsychological performance, specifically attention, working memory, and processing speed skills, which may lead to overall declines in intellectual functioning. Further research is needed to identify changes in neurocognitive status that indicate risk for long-term CNS effect in the hope of providing greater comprehension on how to earlier treat and prevent cognitive late effects

Massive stars as thermonuclear reactors and their explosions following core collapse

Nuclear reactions transform atomic nuclei inside stars. This is the process of stellar nucleosynthesis. The basic concepts of determining nuclear reaction rates inside stars are reviewed. How stars manage to burn their fuel so slowly most of the time are also considered. Stellar thermonuclear reactions involving protons in hydrostatic burning are discussed first. Then I discuss triple alpha reactions in the helium burning stage. Carbon and oxygen survive in red giant stars because of the nuclear structure of oxygen and neon. Further nuclear burning of carbon, neon, oxygen and silicon in quiescent conditions are discussed next. In the subsequent core-collapse phase, neutronization due to electron capture from the top of the Fermi sea in a degenerate core takes place. The expected signal of neutrinos from a nearby supernova is calculated. The supernova often explodes inside a dense circumstellar medium, which is established due to the progenitor star losing its outermost envelope in a stellar wind or mass transfer in a binary system. The nature of the circumstellar medium and the ejecta of the supernova and their dynamics are revealed by observations in the optical, IR, radio, and X-ray bands, and I discuss some of these observations and their interpretations.Comment: To be published in " Principles and Perspectives in Cosmochemistry" Lecture Notes on Kodai School on Synthesis of Elements in Stars; ed. by Aruna Goswami & Eswar Reddy, Springer Verlag, 2009. Contains 21 figure

Knockout of the BK β2 subunit abolishes inactivation of BK currents in mouse adrenal chromaffin cells and results in slow-wave burst activity

Rat and mouse adrenal medullary chromaffin cells (CCs) express an inactivating BK current. This inactivation is thought to arise from the assembly of up to four β2 auxiliary subunits (encoded by the kcnmb2 gene) with a tetramer of pore-forming Slo1 α subunits. Although the physiological consequences of inactivation remain unclear, differences in depolarization-evoked firing among CCs have been proposed to arise from the ability of β2 subunits to shift the range of BK channel activation. To investigate the role of BK channels containing β2 subunits, we generated mice in which the gene encoding β2 was deleted (β2 knockout [KO]). Comparison of proteins from wild-type (WT) and β2 KO mice allowed unambiguous demonstration of the presence of β2 subunit in various tissues and its coassembly with the Slo1 α subunit. We compared current properties and cell firing properties of WT and β2 KO CCs in slices and found that β2 KO abolished inactivation, slowed action potential (AP) repolarization, and, during constant current injection, decreased AP firing. These results support the idea that the β2-mediated shift of the BK channel activation range affects repetitive firing and AP properties. Unexpectedly, CCs from β2 KO mice show an increased tendency toward spontaneous burst firing, suggesting that the particular properties of BK channels in the absence of β2 subunits may predispose to burst firing

Validation of Aura Microwave Limb Sounder HCl measurements

The Earth Observing System (EOS) Microwave Limb Sounder (MLS) aboard the Aura satellite has provided daily global HCl profiles since August 2004. We provide a characterization of the resolution, random and systematic uncertainties, and known issues for the version 2.2 MLS HCl data. The MLS sampling allows for comparisons with many (similar to 1500 to more than 3000) closely matched profiles from the Halogen Occultation Experiment (HALOE) and Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). These data sets provide HCl latitudinal distributions that are, overall, very similar to those from (coincident) MLS profiles, although there are some discrepancies in the upper stratosphere between the MLS and HALOE gradients. As found in previous work, MLS and ACE HCl profiles agree very well (within similar to 5%, on average), but the MLS HCl abundances are generally larger (by 10-20%) than HALOE HCl. The bias versus HALOE is unlikely to arise mostly from MLS, as a similar systematic bias (of order 15%) is not observed between average MLS and balloon-borne measurements of HCl, obtained over Fort Sumner, New Mexico, in 2004 and 2005. At the largest pressure (147 hPa) for MLS HCl, a high bias (similar to 0.2 ppbv) is apparent in analyses of low to midlatitude data versus in situ aircraft chemical ionization mass spectrometry (CIMS) HCl measurements from the Aura Validation Experiment (AVE) campaigns in 2004, 2005, and 2006; this bias is also observed in comparisons of MLS and aircraft HCl/O-3 correlations. Good agreement between MLS and CIMS HCl is obtained at 100 to 68 hPa. The recommended pressure range for MLS HCl is from 100 to 0.15 hPa.</p