PCA based health indicator for remaining useful life prediction of wind turbine gearbox

Fault prognosis of wind turbine gearbox has received considerable attention as it predicts the remaining useful life which further allows the scheduling of maintenance strategies. However, the studies related towards the RUL prediction of wind turbine gearbox are limited, because of the complexity of gearbox, acute changes in the operating conditions and non-linear nature of the acquired vibration signals. In this study, a health indicator is constructed in order to predict the remaining useful life of the wind turbine gearbox. Run to fail experiments are performed on a laboratory scaled wind turbine gearbox of overall gear ratio 1:100. Vibration signals are acquired and decomposed through continuous wavelet transform to obtain the wavelet coefficients. Various statistical features are computed from the wavelet coefficients which return form high-dimensional input feature set. Principal component analysis is performed to reduce the dimensionality and principal components (PCs) are computed from the input feature set. PC1 is considered as the health indicator and subjected to further smoothening by linear rectification technique. Exponential degradation model is fit to the considered health indicator and the model is able to predict the RUL of the gearbox with an error percentage of 2.73 %

Two-step synthesis and hydrolysis of cyclic di-AMP in Mycobacterium tuberculosis.

Cyclic di-AMP is a recently discovered signaling molecule which regulates various aspects of bacterial physiology and virulence. Here we report the characterization of c-di-AMP synthesizing and hydrolyzing proteins from Mycobacterium tuberculosis. Recombinant Rv3586 (MtbDisA) can synthesize c-di-AMP from ATP through the diadenylate cyclase activity. Detailed biochemical characterization of the protein revealed that the diadenylate cyclase (DAC) activity is allosterically regulated by ATP. We have identified the intermediates of the DAC reaction and propose a two-step synthesis of c-di-AMP from ATP/ADP. MtbDisA also possesses ATPase activity which is suppressed in the presence of the DAC activity. Investigations by liquid chromatography -electrospray ionization mass spectrometry have detected multimeric forms of c-di-AMP which have implications for the regulation of c-di-AMP cellular concentration and various pathways regulated by the dinucleotide. We have identified Rv2837c (MtbPDE) to have c-di-AMP specific phosphodiesterase activity. It hydrolyzes c-di-AMP to 5'-AMP in two steps. First, it linearizes c-di-AMP into pApA which is further hydrolyzed to 5'-AMP. MtbPDE is novel compared to c-di-AMP specific phosphodiesterase, YybT (or GdpP) in being a soluble protein and hydrolyzing c-di-AMP to 5'-AMP. Our results suggest that the cellular concentration of c-di-AMP can be regulated by ATP concentration as well as the hydrolysis by MtbPDE

MtbDisA synthesizes c-di-AMP through two intermediates.

<p>DAC assay was done in 10 µl reaction mixtures containing 25 mM Tris-HCl (pH 8.5), 0.6 mM MnCl₂, 300 µM ATP and 2 µM of MtbDisA and incubated at 37°C. The reaction mixture was subjected to reverse phase LC and the products were detected with UV (λ 260 nm). The absorption chromatograms with peaks labeled with the corresponding species have been shown. (A) Peak for only ATP is detected in the control reaction (without enzyme). ATP is converted into c-di-AMP in the presence of MtbDisA as can be seen in (B). Two more peaks are detected in ‘B’ which are the intermediates of the reaction and are labeled ‘I’ and ‘II’. In (B) the DAC reaction was terminated after 5 min whereas in (C) and (D) the reaction was continued for 10 and 60 min respectively. Peak for ADP has been labeled.</p

Hydrolysis of c-di-AMP by MtbPDE.

<p>The reaction mixtures of PDE assay were separated by reverse phase LC and the products were detected by measuring absorbance at 260–4 min have been shown here. The peaks have been labeled with the name of the eluted species. Number on the peak is the retention time of the species. (A) shows the hydrolysis product of c-di-AMP by MtbPDE. Inset shows the control reaction without the enzyme. (B) pApA was hydrolyzed by MtbPDE to AMP. Inset shows the control reaction without MtbPDE. (C) MtbPDE hydrolyzes ApA to AMP and adenosine (D) Hydrolysis of c-di-GMP by MtbPDE to 5′-GMP. Inset shows the control reaction without MtbPDE. (E) Mutant protein D130AH131A does not hydrolyze c-di-AMP.</p

Reaction intermediate ‘I’ was determined to be pppApA.

<p>(A) LC-ESI-MS/MS spectrum of [M+H]⁺ precursor ion m/z 837.05 (reaction intermediate ‘I’). (B) Figure depicting the interpretation of the fragmentation as observed in (A).</p

Detection of the intermediate ‘I’ of the DAC assay.

<p>(A) LC - ESI -MS spectrum showing the peaks corresponding to proton and manganese ion adducts of the intermediate ‘I’ of molecular mass 836 Da. (B) Expansion of the region, m/z 442–452 of the spectrum shown in (A): m/z values and intensity distribution of isotope peaks indicating doubly charged manganese ion adduct of ‘I’.</p

c-di-AMP can exist as multimers.

<p>The DAC reaction mixture was subjected to LC-ESI-MS and the mass spectra of the different multimeric forms have been shown here. (A) The LC-ESI mass spectrum showing signals corresponding to monomer, labeled ‘1′ and other multimeric forms, labeled ‘2′ and ‘3′ (B) Expansion of the region, m/z 648–672 of the spectrum in ‘A’ depicting isotope peaks corresponding to peak 1, which indicate presence of monomer and dimer (C) Expansion of the region, m/z 976–1000 of the spectrum in ‘A’, which shows isotope signals corresponding to peak 2 providing evidence for the presence of trimer of c-di-AMP (D) Expansion of the region, m/z 1306–1330 of the spectrum in ‘A’, indicating the presence of dimeric and tetrameric forms of c-di-AMP.</p