Solar Magnetic Tracking. IV. The Death of Magnetic Features

The removal of magnetic flux from the quiet-sun photosphere is important for maintaining the statistical steady-state of the magnetic field there, for determining the magnetic flux budget of the Sun, and for estimating the rate of energy injected into the upper solar atmosphere. Magnetic feature death is a measurable proxy for the removal of detectable flux. We used the SWAMIS feature tracking code to understand how nearly 20000 detected magnetic features die in an hour-long sequence of Hinode/SOT/NFI magnetograms of a region of quiet Sun. Of the feature deaths that remove visible magnetic flux from the photosphere, the vast majority do so by a process that merely disperses the previously-detected flux so that it is too small and too weak to be detected. The behavior of the ensemble average of these dispersals is not consistent with a model of simple planar diffusion, suggesting that the dispersal is constrained by the evolving photospheric velocity field. We introduce the concept of the partial lifetime of magnetic features, and show that the partial lifetime due to Cancellation of magnetic flux, 22 h, is 3 times slower than previous measurements of the flux turnover time. This indicates that prior feature-based estimates of the flux replacement time may be too short, in contrast with the tendency for this quantity to decrease as resolution and instrumentation have improved. This suggests that dispersal of flux to smaller scales is more important for the replacement of magnetic fields in the quiet Sun than observed bipolar cancellation. We conclude that processes on spatial scales smaller than those visible to Hinode dominate the processes of flux emergence and cancellation, and therefore also the quantity of magnetic flux that threads the photosphere.Comment: Accepted by Ap

A Unique Exposure of Quaternary Deposits in Johnson County, Iowa

The Klein Quarry, in Johnson County, Iowa, exposes a unique section of Quaternary deposits. The section extends along the axis of a Late-Sangamon erosion surface. It is mantled by Wisconsinan loess: a 4-5m upper increment of Late-Wisconsinan loess and a thin increment (0.2 to 0.5m) of mixed loess and Wisconsinan-age pedisediment (\u27basal-loess sediments\u27). Some soil development has taken place in the basal-loess sediments (basal-loess paleosol), and this soil merges with the underlying Late-Sangamon Paleosol. The Late-Sangamon erosion surface is developed on Pre-Illinoian age deposits of the Wolf Creek Formation which include (from top to bottom) an upper basal till (the Aurora Till Member), a thin, laminated diamicton, and an underlying stratified fluvial sequence of sand, silt, and gravel. These overlie till of the Alburnett Formation which is locally preserved in low-relief sags on the underlying bedrock surface of Devonian Cedar Valley Limestone. Sedimentary structures, pebble fabrics, and stratigraphic relations suggest that: the stratified fluvial sequence originated as a proglacial fluvial outwash that evolved into a low-energy slackwater environment; the laminated diamicton was derived from glacial sediments which were resedimented and deposited in this slackwater environment; and this was followed by overriding of glacial ice and deposition of the basal till. The Late-Sangamon erosion surface is marked by a stone line and a relatively thin increment of associated pedisediment which overlies the stone line. Various hillslope components are exposed going down the Late-Sangamon paleohillslope. The erosion surface progressively truncates the Aurora Till Member, the laminated diamicton, and most of the stratified sequence of the Wolf Creek Formation. Properties of the stone line and pedisediment vary in a complex, but systematic way. The characteristics of the stone line and lowermost pedisediment vary downslope directly with textural variations in the different deposits underlying the erosion surface. The uppermost pedisediment, however, shows little relationship to the materials underlying the stone line. The upper, younger pedisediment has resulted from reworking older pedisediment and from transport of sediment from farther upslope. The greater transport distance and reworking results in greater sorting and a less direct relationship to local source materials. The Lare-Sangamon Paleosol formed on this paleohillslope, and is developed in the Late-Sangamon pedisediment, stone line, and the underlying Wolf Creek Formation deposits. Sedimentological variations in the pedisediment affect various paleosol properties. Thickness of the paleosol varies (1.8 to 2.3 m) directly with the thickness of pedisediment, becoming thicker down the paleoslope. The increase in paleosol thickness is also directly matched by an increase in B-horizon thickness. The pedologic and sedimentologic features indicate that the Late-Sangamon erosion surface - pedisediment - paleosol evolved slowly and systematically. Pedisediment muse have accumulated in the lower-slope positions at a slow enough rate that B-horizon soil development kept pace with sediment accumulation

wuHMM: a robust algorithm to detect DNA copy number variation using long oligonucleotide microarray data

Copy number variants (CNVs) are currently defined as genomic sequences that are polymorphic in copy number and range in length from 1000 to several million base pairs. Among current array-based CNV detection platforms, long-oligonucleotide arrays promise the highest resolution. However, the performance of currently available analytical tools suffers when applied to these data because of the lower signal:noise ratio inherent in oligonucleotide-based hybridization assays. We have developed wuHMM, an algorithm for mapping CNVs from array comparative genomic hybridization (aCGH) platforms comprised of 385 000 to more than 3 million probes. wuHMM is unique in that it can utilize sequence divergence information to reduce the false positive rate (FPR). We apply wuHMM to 385K-aCGH, 2.1M-aCGH and 3.1M-aCGH experiments comparing the 129X1/SvJ and C57BL/6J inbred mouse genomes. We assess wuHMM's performance on the 385K platform by comparison to the higher resolution platforms and we independently validate 10 CNVs. The method requires no training data and is robust with respect to changes in algorithm parameters. At a FPR of <10%, the algorithm can detect CNVs with five probes on the 385K platform and three on the 2.1M and 3.1M platforms, resulting in effective resolutions of 24 kb, 2–5 kb and 1 kb, respectively

Deep learning cardiac motion analysis for human survival prediction

Motion analysis is used in computer vision to understand the behaviour of moving objects in sequences of images. Optimising the interpretation of dynamic biological systems requires accurate and precise motion tracking as well as efficient representations of high-dimensional motion trajectories so that these can be used for prediction tasks. Here we use image sequences of the heart, acquired using cardiac magnetic resonance imaging, to create time-resolved three-dimensional segmentations using a fully convolutional network trained on anatomical shape priors. This dense motion model formed the input to a supervised denoising autoencoder (4Dsurvival), which is a hybrid network consisting of an autoencoder that learns a task-specific latent code representation trained on observed outcome data, yielding a latent representation optimised for survival prediction. To handle right-censored survival outcomes, our network used a Cox partial likelihood loss function. In a study of 302 patients the predictive accuracy (quantified by Harrell's C-index) was significantly higher (p < .0001) for our model C=0.73 (95$\%$ CI: 0.68 - 0.78) than the human benchmark of C=0.59 (95$\%$ CI: 0.53 - 0.65). This work demonstrates how a complex computer vision task using high-dimensional medical image data can efficiently predict human survival

Neural phase locking predicts BOLD response in human auditory cortex

Natural environments elicit both phase-locked and non-phase-locked neural responses to the stimulus in the brain. The interpretation of the BOLD signal to date has been based on an association of the non-phase-locked power of high-frequency local field potentials (LFPs), or the related spiking activity in single neurons or groups of neurons. Previous studies have not examined the prediction of the BOLD signal by phase-locked responses. We examined the relationship between the BOLD response and LFPs in the same nine human subjects from multiple corresponding points in the auditory cortex, using amplitude modulated pure tone stimuli of a duration to allow an analysis of phase locking of the sustained time period without contamination from the onset response. The results demonstrate that both phase locking at the modulation frequency and its harmonics, and the oscillatory power in gamma/high-gamma bands are required to predict the BOLD response. Biophysical models of BOLD signal generation in auditory cortex therefore require revision and the incorporation of both phase locking to rhythmic sensory stimuli and power changes in the ensemble neural activity

Zn3As2 Nanowires and nanoplatelets: highly efficient infrared emission and photodetection by an earth abundant material

The development of earth abundant materials for optoelectronics and photovoltaics promises improvements in sustainability and scalability. Recent studies have further demonstrated enhanced material efficiency through the superior light management of novel nanoscale geometries such as the nanowire. Here we show that an industry standard epitaxy technique can be used to fabricate high quality II-V nanowires (1D) and nanoplatelets (2D) of the earth abundant semiconductor Zn3As2. We go on to establish the optoelectronic potential of this material by demonstrating efficient photoemission and detection at 1.0 eV, an energy which is significant to the fields of both photovoltaics and optical telecommunications. Through dynamical spectroscopy this superior performance is found to arise from a low rate of surface recombination combined with a high rate of radiative recombination. These results introduce nanostructured Zn3As2 as a high quality optoelectronic material ready for device exploration.T.B., P.C., Y.G., H.H.T., and C.J. acknowledge the Australian Research Council. T.B., P.C., Y.G., H.H.T., and C.J. thank the Australian National Fabrication Facility for access to the growth and microscopy facilities and Centre for Advanced Microscopy and Australian Microscopy and Microanalysis Research Facility for access to microscopy facilities used in this work. Y.W., B.B., H.E.J., and L.M.S. acknowledge the financial support of the National Science Foundation through grants DMR-1105362, 1105121, and ECCS-1100489