Standard Correction Techniques Research Articles

REPUBLIC: A variability-preserving systematic-correction algorithm for PLATO’s multi-camera light curves

Abstract Space-based photometry missions produce exquisite light curves that contain a wealth of stellar variability on a wide range of timescales. Light curves also typically contain significant instrumental systematics – spurious, non-astrophysical trends that are common, in varying degrees, to many light curves. Empirical systematics-correction approaches using the information in the light curves themselves have been very successful, but tend to suppress astrophysical signals, particularly on longer timescales. Unlike its predecessors, the PLATO mission will use multiple cameras to monitor the same stars. We present REPUBLIC, a novel systematics-correction algorithm which exploits this multi-camera configuration to correct systematics that differ between cameras, while preserving the component of each star’s signal that is common to all cameras, regardless of timescale. Through simulations with astrophysical signals (star spots and planetary transits), Kepler-like errors, and white noise, we demonstrate REPUBLIC’s ability to preserve long-term astrophysical signals usually lost in standard correction techniques. We also explore REPUBLIC’s performance with different number of cameras and systematic properties. We conclude that REPUBLIC should be considered a potential complement to existing strategies for systematic correction in multi-camera surveys, with its utility contingent upon further validation and adaptation to the specific characteristics of the PLATO mission data.

Evaluation of Distortion and Residual Stresses in Dissimilar Metal Laser Welds

The distortion and residual stresses in laser weld joints play an important role in performing the intended functions. The objective of this research work is to evaluate distortion and residual stresses induced in dissimilar metal butt weld joints. The 304 L stainless steel and mild steel sheets of 0.98 mm thick are used in automobile industries. The laser welding experiments are conducted on dissimilar metals as per the L9 orthogonal array design matrix and optimal process parameters obtained using Artificial Neural Network. A mathematical model is proposed to estimate the angular distortion and longitudinal residual stresses in dissimilar weld joints. The longitudinal, transverse and twisting type distortions are evaluated using the Coordinate Measuring Machine, whereas residual stresses using an X-ray Diffractometer. The standard correction techniques are applied for background error correction and peak position was obtained using the Gaussian curve fitting technique. The outcome of the research work is useful for the evaluation of distortion and residual stress in dissimilar metal weld joints.

Accuracy in Mooring Motion Temperature Corrections

Abstract Moored temperature sensors, whether fixed or profiling, routinely need to be corrected to remove the signals associated with the vertical motion of the sensors when the moorings “blow over” in strong flow events (for profiling sensors the problems occur only at the upper end of the profiling range). Hydrographic data are used to estimate the accuracy with which moored temperature sensors in the Gulf Stream can be corrected for mooring motion aliasing using standard correction techniques, and the implications for other ocean regions are discussed. Comparison with hydrographic data and coincident inverted echo sounder (IES) data from the Synoptic Ocean Prediction Experiment (SYNOP) shows that the errors inherent in mooring motion corrected temperatures during significant pressure deflections are potentially 2–3 times as large as previous estimates based on a smaller dataset of observations in the Kuroshio at approximately the same latitude in the Pacific. For sensors with a nominal level of 400 dbar and a typical root-mean-square pressure deflection of 150 dbar, accuracy limits of up to 0.7°C on the “corrected” temperatures are applicable. Deeper sensors typically have smaller accuracy bounds. There is a suggestion that the presence of a mode water layer near the nominal depth of the shallowest sensor can result in much higher errors in mooring motion corrected temperature data. The accuracy estimates derived herein should apply not only to moorings deployed in the Gulf Stream but also to all currents that exhibit similar velocity amplitudes and thermal gradients such as the Agulhas or Kuroshio.

Simulation of Laser-Induced Incandescence Measurements in an Anisotropically Scattering Aerosol Through Backward Monte Carlo

Laser-induced incandescence (LII) measurements carried out in aerosols having a large particle volume fraction must be corrected to account for extinction between the energized aerosol particles and the detector, called signal trapping. While standard correction techniques have been developed for signal trapping by absorption, the effect of scattering on LII measurements requires further investigation, particularly the case of highly anisotropic scattering and along a path of relatively large optical thickness. This paper examines this phenomenon in an aerosol containing highly aggregated soot particles by simulating LII signals using a backward Monte Carlo analysis; these signals are then used to recover the soot particle temperature and soot volume fraction. The results show that inscattered radiation is a substantial component of the LII signal under high soot loading conditions, which can strongly influence properties derived from these measurements. Correction techniques based on Bouguer’s law are shown to be effective in mitigating the effect of scatter on the LII signals.

Compound-specific carbon isotope analysis of volatile organic compounds in water using solid-phase microextraction

The compound-specific isotope analysis technique in conjunction with solid-phase microextraction using a carboxen–polydimethylsiloxane fiber was tested and implemented for isotopes analyses of organic compounds aiming for environmental application in contaminated groundwater. δ 13C values of several chlorinated methanes and ethenes, toluene and chlorobenzene were determined using a gas chromatograph coupled to an isotope ratio mass spectrometer through a combustion interface. Direct and headspace solid-phase microextraction (D-SPME, HS-SPME) methods were tested in order to determine the optimum conditions to obtain reproducible δ 13C values at very low concentration (μg/L range) and, to elucidate the carbon isotopic effects associated with the competitive extraction. For D-SPME, higher accuracy and precision of δ 13C results were obtained with no salted aqueous standards. Despite that the δ 13C of those compounds analyzed with both methods showed similar precision (<0.5‰) and accuracy, the highest sensitivity was reached with HS-SPME. Furthermore, the δ 13C values of cis-1,2-dichloroethylene, chorinated methanes and aromatic compounds obtained using HS-SPME showed measurable deviations with respect to the isotopic composition of pure phase compounds, however, these deviations are constant according to the analytical uncertainties, indicating that they are not affected by competitive extraction, and they could be corrected using standard correction technique based on internal calibrated standards.

Applications of neutron activation to microelectronic materials research at the Cornell TRIGA reactor

We present results from our use of neutron activation analysis (NAA) for the measurement and interpretation of the elemental content of materials being researched for applications in microelectronics. Examples include characterization of silicon-germanium and nickel silicide alloys, magnesium silicate crystals and ceramics for packaging of integrated circuits. High resolution delayed X-ray spectroscopy has been successfully employed as a complement to conventional gamma-ray analysis for determination of relative impurity concentrations. Fast neutron induced interferences are removed from gamma-ray spectra via the internal standard correction technique, based on the measurement of fast reaction rates.

A dispersion-free trajectory correction technique for linear colliders

In this paper, we describe a new trajectory correction technique for high energy linear accelerators. Current correction techniques force the beam trajectory to follow misalignments of the beam position monitors (BPMs). Since the particle bunch has a finite energy spread and particles with different energies are deflected differently, this causes “chromatic” dilution of the transverse beam emittance. The algorithm which we describe in this paper reduces the chromatic dilution by minimizing the energy dependence of the trajectory. To test the method we compare the effectiveness of our algorithm with a standard correction technique in simulations of the Stanford Linear Collider (SLC) linear accelerator and a design linac for a Next Linear Collider (NLC). While the simulations do not indicate that chromatic dilutions are a serious problem in the SLC linac, they would be debilitating in a future linear collider because of the very small beam sizes required to achieve the necessary luminosity. For example, in simulations of the NLC we have found that with typical alignment tolerances the beam size increased substantially after correcting the trajectory with a standard correction algorithm. In contrast, after correcting with our technique, the dilution was negligible. We feel that this technique will prove essential for future linear colliders.