642 research outputs found
Baseline correction for NMR spectroscopic metabolomics data analysis.
BackgroundWe propose a statistically principled baseline correction method, derived from a parametric smoothing model. It uses a score function to describe the key features of baseline distortion and constructs an optimal baseline curve to maximize it. The parameters are determined automatically by using LOWESS (locally weighted scatterplot smoothing) regression to estimate the noise variance.ResultsWe tested this method on 1D NMR spectra with different forms of baseline distortions, and demonstrated that it is effective for both regular 1D NMR spectra and metabolomics spectra with over-crowded peaks.ConclusionCompared with the automatic baseline correction function in XWINNMR 3.5, the penalized smoothing method provides more accurate baseline correction for high-signal density metabolomics spectra
On the cumulants of affine equivariant estimators in elliptical families
AbstractGiven a statistical model for data which take values in Rd and have elliptically distributed errors, and affine equivariant estimators μ̂ and μ̂ of a mean vector in Rd⊗Rn and a d × d scatter matrix, expressions are given for the covarances of the estimators in terms of their expectations and some unknown constants that depend on the model and the estimator. Higher order cumulants are also developed. These results place considerable constraints on the possible cumulants of μ̂ and μ̂, as wel as those of estimators of higher order behavior such as multivariate skewness and kurtosis. These expressions are obtained using tensor methods
Photon trains and lasing : The periodically pumped quantum dot
We propose to pump semiconductor quantum dots with surface acoustic waves
which deliver an alternating periodic sequence of electrons and holes. In
combination with a good optical cavity such regular pumping could entail
anti-bunching and sub-Poissonian photon statistics. In the bad-cavity limit a
train of equally spaced photons would arise.Comment: RevTex, 5 pages, 1 figur
Novel method for photovoltaic energy conversion using surface acoustic waves in piezoelectric semiconductors
This paper presents a novel principle for photovoltaic (PV) energy conversion
using surface acoustic waves (SAWs) in piezoelectric semiconductors. A SAW
produces a periodically modulated electric potential, which spatially
segregates photoexcited electrons and holes to the maxima and minima of the SAW
potential. The moving SAW collectively transports the carriers with the speed
of sound to the electrodes made of different materials, which extract electrons
and holes separately and generate dc output. The proposed active design is
expected to have higher efficiency than passive designs of the existing PV
devices and to produce enough energy to sustain the SAW.Comment: v.3 4 pages, 3 figures, submitted to proceedings of ECRYS-2011 to be
published in Physica
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Urine Complement Proteins and the Risk of Kidney Disease Progression and Mortality in Type 2 Diabetes.
ObjectiveWe examined the association of urine complement proteins with progression to end-stage renal disease (ESRD) or death in people with type 2 diabetes and proteinuric diabetic kidney disease (DKD).Research design and methodsUsing targeted mass spectrometry, we quantified urinary abundance of 12 complement proteins in a predominantly Mexican American cohort with type 2 diabetes and proteinuric DKD (n = 141). The association of urine complement proteins with progression to ESRD or death was evaluated using time-to-event analyses.ResultsAt baseline, median estimated glomerular filtration rate (eGFR) was 54 mL/min/1.73 m2 and urine protein-to-creatinine ratio 2.6 g/g. Sixty-seven participants developed ESRD or died, of whom 39 progressed to ESRD over a median of 3.1 years and 40 died over a median 3.6 years. Higher urine CD59, an inhibitor of terminal complement complex formation, was associated with a lower risk of ESRD (hazard ratio [HR] [95% CI per doubling] 0.50 [0.29-0.87]) and death (HR [95% CI] 0.56 [0.34-0.93]), after adjustment for demographic and clinical covariates, including baseline eGFR and proteinuria. Higher urine complement components 4 and 8 were associated with lower risk of death (HR [95% CI] 0.57 [0.41-0.79] and 0.66 [0.44-0.97], respectively); higher urine factor H-related protein 2, a positive regulator of the alternative complement pathway, was associated with greater risk of death (HR [95% CI] 1.61 [1.05-2.48]) in fully adjusted models.ConclusionsIn a largely Mexican American cohort with type 2 diabetes and proteinuric DKD, urine abundance of several complement and complement regulatory proteins was strongly associated with progression to ESRD and death
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