Prediction of remaining life of power transformers based on left truncated and right censored lifetime data

Prediction of the remaining life of high-voltage power transformers is an important issue for energy companies because of the need for planning maintenance and capital expenditures. Lifetime data for such transformers are complicated because transformer lifetimes can extend over many decades and transformer designs and manufacturing practices have evolved. We were asked to develop statistically-based predictions for the lifetimes of an energy company's fleet of high-voltage transmission and distribution transformers. The company's data records begin in 1980, providing information on installation and failure dates of transformers. Although the dataset contains many units that were installed before 1980, there is no information about units that were installed and failed before 1980. Thus, the data are left truncated and right censored. We use a parametric lifetime model to describe the lifetime distribution of individual transformers. We develop a statistical procedure, based on age-adjusted life distributions, for computing a prediction interval for remaining life for individual transformers now in service. We then extend these ideas to provide predictions and prediction intervals for the cumulative number of failures, over a range of time, for the overall fleet of transformers.Comment: Published in at http://dx.doi.org/10.1214/00-AOAS231 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Is the Use of Intestinal Helminths Safe and Effective in the Treatment of Allergic Rhinitis?

OBJECTIVE: The objective of this EBM review is to determine whether the use of intestinal helminths is safe and effective in the treatment of allergic rhinitis.STUDY DESIGN: Review of three English language, blinded randomized controlled trials from 2009, 2010, and 2010.DATA SOURCE: Randomized, controlled, blinded trials comparing the use of intestinal helminths versus visually matched placebo as a treatment for allergic rhinitis found using PubMed and Ovid databases.OUTCOMES MEASURED: Several different systems were used to evaluate the symptoms or occurrence of AR. Bager et al.2010 uses symptom scores of AR scale of 0 to 3. Feary et al.2009 used the Juniper rhinoconjunctivitis quality of life questionnaire. Flohr et al.2010 used the International Study of Asthma and Allergies in Childhood (ISAAC). Mean symptom score and incidence recorded in daily diaries were used for adverse events.RESULTS: Bager et al.2010 reported a mean difference in symptom scores of AR as 0.0 a t-test produced a p-value of 0.87 with a 95% CI 0.0(-0.5, 0.4). Feary et al.2009 reported no difference between the treatment and control groups (MD 0.33, 95% CI -0.27 to 0.93). No serious adverse events were reported in Bager et al.2010 or Feary et al.2009. There were several gastrointestinal adverse events reported including indigestion, flatus, upper abdominal pain and diarrhea. Flohr et al.2010 reported a mean difference of 1.39 between experimental and control groups 95% CI (0.89-2.15) with a P-value of 0.1. The relative risk increase of AR was 37% after treatment. Absolute risk increase or AR was 1.8%. The number needed to harm (in this case cause AR after elimination of helminthic infection) was 56 patients.CONCLUSIONS: The efficacy of intestinal helminths as a treatment for Allergic rhinitis is inconclusive. The P-values comparing the effect of treatment to placebo were not statistically significant. The controlled administration of helminths can be considered safe since there have been no reports of severe adverse events. Mild Gastrointestinal adverse events have been reported. Flohr et al.2010 demonstrates possible protective actions of helminthes but more research is warranted to obtain more conclusive data

Elucidating the mitochondrial architecture of branched-chain amino acid metabolism enzymes: implications for treatment

Branched chain amino acid (BCAA) metabolism occurs within the mitochondrial matrix and is comprised of 17 enzymes, some shared, organized into three pathways for the catabolism of leucine, isoleucine, and valine (LEU, ILE, and VAL respectively). However, the physical relationships of the various enzymes in the pathways are unknown. Diseases such as isovaleric academia, propionic and methylmalonic acidemias, and maple syrup urine disease are among the disorders caused by genetic deficiencies of BCAA metabolism. I examined the BCAA pathways and their physical interactions in vitro through proteomics analysis and in situ using stimulated emission depletion microscopy. The functional interactions of the pathways were measured by flux analysis with labeled LEU, ILE, and VAL in patient and wild type cell lines, with quantification of the labeled metabolic end-products of each pathway. I examined novel potential treatments for propionic acidemia patient derived cell lines, quantitating protein, ROS production, and mitochondrial mass response to therapeutic agents. My proteomic and imaging studies are consistent with the existence of one or more energetically favorable, metabolite-channeling BCAA super-complex(es). Flux studies demonstrate that the end products of LEU, ILE and VAL metabolism are generated in both wild type and patient derived cells lines, implying cross-talk of BCAA pathways, and a close proximity of shared enzymes. Additionally, I found that the end-product of ILE and VAL, propionyl-CoA, does not readily enter the TCA cycle, as previously thought, while propionyl-CoA from odd chains fats does. Finally, propionyl-CoA carboxylase (PCC) deficient cell lines showed improved mitochondrial function when treated with a cardiolipin binding protein that stabilizes the inner mitochondrial membrane in cell cultures. PCC protein amount was slightly increased in treated patient cells, and ROS and mitochondrial mass was significantly decreased. These results provide novel insight into BCAA metabolism and offer new opportunities for the development of therapeutic agents for their defects. Furthermore, because propionyl-CoA derived from odd-chain fatty acids does, in fact, readily enter the TCA cycle, results from the metabolic flux studies will impact public health by changing potential therapies used to replenish the TCA cycle intermediates for disorders of fatty acid oxidation as well as BCAA metabolism

Visual selective attention and aging

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A study of column equilibration time in hydrophilic interaction chromatography

© 2018 Elsevier B.V. The time taken to achieve full column equilibration for isocratic analysis of acidic, basic, and neutral solutes in hydrophilic interaction liquid chromatography (HILIC) was compared using the mobile phase disturbance method, column efficiency measurements and retention time stability. Full equilibration, which could take up to an hour, was best measured by the last procedure and was found to depend on the nature of the stationary phase, the pre-equilibrium (e.g. storage) solvent and the flow rate. While longer equilibration times are a relatively minor inconvenience in isocratic analysis, they are surprisingly not a barrier to the use of gradient elution in HILIC. A repeatable partial equilibration giving retention time stability equivalent to that in isocratic analysis was demonstrated for an equilibration time of only ∼5 min, using as few as 2 preliminary conditioning runs on a column that had taken the longest time to achieve full equilibration. Due to selectivity changes that occur dependent on the equilibration time, it is necessary to use identical gradient conditions in a series of analyses, which however appears to be facile on a modern HPLC instrument

Understanding and manipulating the separation in hydrophilic interaction liquid chromatography

© 2017 Elsevier B.V. Hydrophilic interaction liquid chromatography (HILIC) has emerged as a valuable complimentary technique to reversed-phase (RP), being especially suited for the analysis of polar and ionised solutes, which are difficult to retain in RP. For solutes amenable to both separation mechanisms, HILIC provides a different selectivity to RP, and also offers possibilities as an orthogonal mechanism for 2-dimensional LC when combined with RP. HILIC has further advantages of lower column back pressures, and increased sensitivity with mobile phase evaporative detectors such as electrospray mass spectrometry. This review covers progress in our understanding of the HILIC technique, principally over the last ten years, including the classification of columns, the factors that control retention and selectivity, and attempts to model the separation process and its kinetics

Practical observations on the performance of bare silica in hydrophilic interaction compared with C18 reversed-phase liquid chromatography

The kinetic performance of a bare silica and C18 phase prepared from the same sub-2. μm and 3.5. μm base materials were compared in the HILIC and RP mode using both charged and neutral solutes. The HILIC column was characterised using the neutral solute 5-hydroxymethyluridine, the weak base cytosine, and the strong base nortriptyline, the latter having sufficient retention also in the RP mode to allow comparison of performance. Naphthalene was also used as a simple neutral substance to evaluate the RP column alone. The retention factors of all substances were adjusted to give similar values (k'. ~. 5.5) at their respective optimum linear velocities. Reduced van Deemter b-coefficients (determined by curve fitting and by the peak parking method, using a novel procedure involving switching to a dummy column) were significantly lower in HILIC for all substances compared with those found under RP conditions. Against expectation, c-coefficients were always lower in RP when compared with HILIC using sub-2. μm particles. While measurement of these coefficients is complicated by retention shifts caused by the influence of high pressure and by frictional heating effects, broadly similar results were obtained on larger particle (3.5. μm) phases. The mechanism of the separations was further investigated by examining the effect of buffer concentration on retention. It was concluded that HILIC can sometimes show somewhat inferior performance to RP for fast analysis at high mobile phase velocity, but clearly shows advantages when high column efficiencies, using longer columns at low flow velocity, are employed. The latter result is attributable to the lower viscosity of the mobile phase in HILIC and the reduced pressure requirement as well as the lower b-coefficients. © 2014 David V. McCalley

Effect of mobile phase additives on solute retention at low aqueous pH in hydrophilic interaction liquid chromatography

© 2016 Elsevier B.V. Trifluoracetic acid (TFA) added to the aqueous acetonitrile mobile phase induces some unexpected changes in the ionic component of retention in hydrophilic interaction separations when using Type B silica and amide-bonded silica columns. TFA use results in anion exchange properties which contrast with the cation exchange typically found with ammonium salt buffers. The significant cation exchange properties of silica hydride columns are also moderated by TFA. Similar behaviour was shown in a metal- free amide column operated on a system washed with a metal complexing agent, suggesting that adsorbed metal cations were not responsible for this anion exchange behaviour. Both suppression of silanol ionisation at low pH and ion pairing of bases with TFA could contribute to this effect. It is also possible that the column surface acquires some positive charges at the low pH of TFA. A surprising reversal of the properties of the columns back to predominately cation exchange behaviour was shown using methanesulfonic acid (MSA), which appears to be a stronger acid than TFA in high concentrations of acetonitrile. MSA maintains sufficient ionic strength in the mobile phase even at low concentrations, giving good peak shape, which could be useful for mass spectrometry detection. Besides giving different selectivity to TFA, MSA also gives different selectivity to that of ammonium salt buffers, suggesting it may be useful in manipulating the selectivity of a separation. Similar changes to the selectivity with TFA could be achieved by adding neutral methylsulfonate salts to the TFA mobile phase. While it is possible that methylsulfonate ions are retained on the stationary phase surface, experiments using ion pair reagents of opposite charge yielded the same results as MSA salts. It therefore seems more likely that the higher ionic strength of these solutions negates the influence of charges that may be formed in TFA solutions. Ion pairing effects with MSA are expected to be limited

Core-Shell, Ultrasmall Particles, Monoliths, and Other Support Materials in High-Performance Liquid Chromatography

A review of the developments that have taken place in the area of supports for high performance liquid chromatography in recent years