A new variable tap-length LMS algorithm to model an exponential decay impulse response

This letter proposes a new variable tap-length least-mean-square (LMS) algorithm for applications in which the unknown filter impulse response sequence has an exponential decay envelope. The algorithm is designed to minimize the mean-square deviation (MSD) between the optimal and adaptive filter weight vectors at each iteration. Simulation results show the proposed algorithm has a faster convergence rate as compared with the fixed tap-length LMS algorithm and is robust to the initial tap-length choice

Implementing positivity constraints in 4-D resistivity time-lapse inversion

Over the last 25 years 2-D and 3-D resistivity surveys have been used for a wide range of engineering, environmental, hydrological and mineral exploration surveys (Loke et al. 2013). In some surveys, the purpose includes the monitoring of subsurface changes with time (Chambers et al. 2014). The 4-D smoothness-constrained inversion method (Loke et al. 2014) has proved to be a stable and robust method for the inversion of time-lapse data sets. This method inverts the data sets measured at different times simultaneously and it includes a temporal smoothness constraint to ensure that the resistivity changes in a smooth manner with time. In some surveys, such as infiltration experiments (Kuras et al. 2016), it is known that the subsurface resistivity should only decrease (or increase) with time. As the standard 4-D inversion method does not explicitly constrain the direction of the changes with time, this could result in artefacts where an increase in the resistivity is obtained in the inverse model while it is only expected to decrease (or vice versa). In this paper we describe a modification of the 4-D smoothness-constrained inversion method to remove such temporal artefacts

Interpolation of landslide movements to improve the accuracy of 4D geoelectrical monitoring

Measurement sensors permanently installed on landslides will inevitably change their position over time due to mass movements. To interpret and correct the recorded data, these movements have to be determined. This is especially important in the case of geoelectrical monitoring, where incorrect sensor positions produce strong artefacts in the resulting resistivity models. They may obscure real changes, which could indicate triggering mechanisms for landslide failure or reactivation. In this paper we introduce a methodology to interpolate movements from a small set of sparsely distributed reference points to a larger set of electrode locations. Within this methodology we compare three interpolation techniques, i.e., a piecewise planar, bi-linear spline, and a kriging based interpolation scheme. The performance of these techniques is tested on a synthetic and a real-data example, showing a recovery rate of true movements to about 1% and 10% of the electrode spacing, respectively. The significance for applying the proposed methodology is demonstrated by inverse modelling of 4D electrical resistivity tomography data, where it is shown that by correcting for sensor movements corresponding artefacts can virtually be removed and true resistivity changes be imaged

Metallothionein-I/II expression associates with the astrocyte DNA damage response and not Alzheimer-type pathology in the ageing brain

Oxidative stress and oxidative DNA damage are early features of mild cognitive impairment and Alzheimer’s disease (AD), occurring before the formation of classical AD neuropathology, and resulting from an imbalance between pro- and anti-oxidants. Astrocytes play a major neuroprotective role, producing high levels of anti-oxidants including metallothionein-I and –II (MT-I/II). In the present study we characterized the immunoreactive profile of MT-I/II in the temporal cortex of the Cognitive Function and Ageing Study (CFAS) aging population-representative neuropathology cohort, and examined H2O2-modulation of MT transcription by human astrocytes. MT-I/II is primarily expressed by astrocytes in the aging brain, but is also associated with pyramidal neurons in a small proportion of cases. Astrocyte expression of MT-I/II does not correlate with Alzheimer-type pathology (Aβ plaques and neurofibrillary tangles) but does relate to astrocyte oxidative DNA damage (rs= 0.312, p= 0.006) and the astrocyte response to oxidative DNA damage in vivo (rs= 0.238, p= 0.04), and MT gene expression is significantly induced in human astrocytes response to oxidative stress in vitro (p=0.01). In contrast, neuronal MT-I/II does not relate to oxidative DNA damage or the neuronal DNA damage response, but is significantly higher in cases with high levels of local tangle pathology (p=0.007). As MT-I/II is neuroprotective against oxidative stress, modulation of MT-I/II expression is a potential therapeutic target to treat the onset and progression of cognitive impairment

The Time-Domain Spectroscopic Survey: Understanding the Optically Variable Sky with SEQUELS in SDSS-III

The Time-Domain Spectroscopic Survey (TDSS) is an SDSS-IV eBOSS subproject primarily aimed at obtaining identification spectra of ~220,000 optically-variable objects systematically selected from SDSS/Pan-STARRS1 multi-epoch imaging. We present a preview of the science enabled by TDSS, based on TDSS spectra taken over ~320 deg^2 of sky as part of the SEQUELS survey in SDSS-III, which is in part a pilot survey for eBOSS in SDSS-IV. Using the 15,746 TDSS-selected single-epoch spectra of photometrically variable objects in SEQUELS, we determine the demographics of our variability-selected sample, and investigate the unique spectral characteristics inherent in samples selected by variability. We show that variability-based selection of quasars complements color-based selection by selecting additional redder quasars, and mitigates redshift biases to produce a smooth quasar redshift distribution over a wide range of redshifts. The resulting quasar sample contains systematically higher fractions of blazars and broad absorption line quasars than from color-selected samples. Similarly, we show that M-dwarfs in the TDSS-selected stellar sample have systematically higher chromospheric active fractions than the underlying M-dwarf population, based on their H-alpha emission. TDSS also contains a large number of RR Lyrae and eclipsing binary stars with main-sequence colors, including a few composite-spectrum binaries. Finally, our visual inspection of TDSS spectra uncovers a significant number of peculiar spectra, and we highlight a few cases of these interesting objects. With a factor of ~15 more spectra, the main TDSS survey in SDSS-IV will leverage the lessons learned from these early results for a variety of time-domain science applications.Comment: 17 pages, 14 figures, submitted to Ap

Main-Belt Comet P/2012 T1 (PANSTARRS)

We present initial results from observations and numerical analyses aimed at characterizing main-belt comet P/2012 T1 (PANSTARRS). Optical monitoring observations were made between October 2012 and February 2013 using the University of Hawaii 2.2 m telescope, the Keck I telescope, the Baade and Clay Magellan telescopes, Faulkes Telescope South, the Perkins Telescope at Lowell Observatory, and the Southern Astrophysical Research (SOAR) telescope. The object's intrinsic brightness approximately doubles from the time of its discovery in early October until mid-November and then decreases by ~60% between late December and early February, similar to photometric behavior exhibited by several other main-belt comets and unlike that exhibited by disrupted asteroid (596) Scheila. We also used Keck to conduct spectroscopic searches for CN emission as well as absorption at 0.7 microns that could indicate the presence of hydrated minerals, finding an upper limit CN production rate of QCN<1.5x10^23 mol/s, from which we infer a water production rate of QH2O<5x10^25 mol/s, and no evidence of the presence of hydrated minerals. Numerical simulations indicate that P/2012 T1 is largely dynamically stable for >100 Myr and is unlikely to be a recently implanted interloper from the outer solar system, while a search for potential asteroid family associations reveal that it is dynamically linked to the ~155 Myr-old Lixiaohua asteroid family.Comment: 15 pages, 4 figures, accepted for publication in ApJ Letter